Arctic Sea Ice : Forum

Cryosphere => Greenland and Arctic Circle => Topic started by: Espen on June 25, 2013, 01:40:58 PM

Title: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 25, 2013, 01:40:58 PM
Here is to be a animation showing the tongue separation / calving in August - September 2012:

Since I have problems uploading this animation (load-restrictions?) it is 2,3 mb only ::)

You can see it here hopefully! If not please report back ;)

https://docs.google.com/file/d/0B_a0Tecpig0jTkFvbkpUMEI4VGs/edit?usp=sharing
Title: Re: Zachariae Glacier / North East Greenland
Post by: Tor Bejnar on June 25, 2013, 01:43:32 PM
It works just fine.  Thanks!
Title: Re: Zachariae Glacier / North East Greenland
Post by: mspelto on June 27, 2013, 05:03:02 PM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fglacierchange.files.wordpress.com%2F2012%2F08%2Fzis-2013sm.jpg&hash=1e0aaac5ff06ee5b066d95cc4b4a9478)
Zachariae Ice Stream June 17 2013 note all the late 2012 icebergs yellow dots, terminus position which has retreated since July 2012 and the rift that promises to release more icebergs as soon as the ice has cleared.
Title: Re: Zachariae Glacier / North East Greenland
Post by: Espen on June 27, 2013, 05:20:32 PM
Mauri,

It looks like we actually had a calving in July 2012, and I think it can be seen on this animation, where the calved piece is moved forth and back:

https://docs.google.com/file/d/0B_a0Tecpig0jTkFvbkpUMEI4VGs/edit?usp=sharing
Title: Re: Zachariae Glacier / North East Greenland
Post by: Espen on June 28, 2013, 11:19:39 PM
As Mauri noted above there is action to be watched this season, there was a calving event last season on August 20 2012, this is clearly seen on the 3 following image:
Title: Re: Zachariae Glacier / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 24, 2013, 11:24:07 AM
Nioghalvfjerdsfjorden update:

Title: Re: Zachariae Glacier / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 24, 2013, 07:34:52 PM
As advised earlier today the break up of fast ice in North East Greenland is now in progress:

The quality of the image, is due to the fact it is a swath image. :-[

Please click on image to enlarge!
Title: Re: Zachariae Glacier / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 24, 2013, 08:18:59 PM
Just from the oven:

Title: Re: Zachariae Glacier / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 24, 2013, 11:11:53 PM
Here you find some evidence that the melting season in some places is ahead of 2012:

Please click on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 25, 2013, 09:37:17 PM
A composite Landsat Image of the Zachariae Calving 2012:

Please click on image to enlarge, very large size:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 25, 2013, 09:37:23 PM
A composite Landsat Image of the Zachariae Calving 2012:

Please click on image to enlarge, very large size:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: werther on July 25, 2013, 11:41:18 PM
Evening Espen,
From what I saw on r03c03 tonight, I'd say the Zachariae is losing some big calvings. Can you get a similar image on '13?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 25, 2013, 11:53:34 PM
Hi Werther;

Where do you this calving *)? And what do mean with on 13?

*) Are you thinking about the break up of fast ice outside Zachariae?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: mspelto on July 28, 2013, 02:13:45 PM
Lots of calving off the front of ZIS as the large rift noted early this summer has peeled off as of July 23.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FJoekelbugt%2F20130726AQUA.jpg&hash=028388b2c9d0b6bf1e236dfd7083ad92)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 31, 2013, 06:51:22 PM
Places to be observed during the Indian Summer in the NE:

Marked with Green color.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: ghoti on July 31, 2013, 08:27:45 PM
The shattering and rapid eastward flow of the chunks of ice along the north coast towards the head of the Fram has been spectacular in the last few days.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 31, 2013, 08:34:42 PM
Ghoti;

Yes it is a very interesting part of the Arctic, at least IMHO! ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 01, 2013, 01:40:13 PM
Is 79 or Nioghalvfjerdsfjorden on the move a certain crack pattern in front of the glacier may indicate so? Have a look.

Please click on the image to enlarge !
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 02, 2013, 03:38:31 PM
We all know about the famous Petermann and what headlines she is creating when calving, but compared to Zacharia Glacier she a minor in that discipline, estimated loss of Glacier surface / area at Zachariae is somewhere in the region of +/- 1,850 km2 between 1976 and 2013, where as Petermann "only" calved some +/- 400 km2.
Petermann may win the sideline competition when it comes to volume?

Please click on image to enlarge and for much better details!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on August 12, 2013, 05:25:47 PM
Some fresh Zachariae calving:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 12, 2013, 05:37:14 PM
How long can that aborted tongue last with warmer waters able to attack from both sides?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 12, 2013, 07:36:01 PM
Probably quite a few years depending of the thickness?!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 13, 2013, 10:18:12 PM
If melting is a "problem" elsewhere, I am pretty sure we have action in the Jøkelbugt/Zachariae area *). The delta area (between Zachariae Glacier and her aborted daughter "The tongue") there is a lot of motion not seen in the satellite era. Out in the sea we only have a little left of fast ice island,  but remember this fast ice disappearance happened before:

Todays images from Modis are too cloudy :-\

*) As reported by Yuha, one of our movement spotters, see above! ;)

Please click on image to enlarge and for better details!

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 13, 2013, 10:37:35 PM
Notice on the image above from Jøkelbugt 2003, the Delta Area (click on the image to enlarge) is not that developed, and Spaltegletscher north of 79 is reaching much further north, than today.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 20, 2013, 04:59:44 PM
More action from Zachariae, the glacier retreated substantially since 2012, I will make an animation later. Notice how little is left of the fast ice of the coast compared to 2102. I may be the first year in about 10 years Belgica Bank will be without it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 29, 2013, 10:40:00 AM
Further retreat of Zachariae Isstrøm in August seen from this Landsat image animation:

Please click on image to start animation and enlargement.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 29, 2013, 11:37:01 AM
Spaltegletscher part of Nioghalvfjerdsfjorden ( 79 ) Gletscher could soon calve a major part of what is left of that gletscher, a large crack is observed across the glacier (+/- 6 km) and there is only 1.7 km to go before it reach an opposite crack. The images below show the glacier and below that a close up of the crack.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 29, 2013, 04:14:07 PM
More evidence of retreat at Zachariae Glacier, this time the southern part of the glacier:

Please on image to start animation and enlargement.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2013, 01:05:13 PM
Interesting action is seen at Zachariae Glacier, the ice in front of the new established calving front is now being cleared, this has not been seen since satellite image were available, this is where the Red Arrow is located.

Further south at Sanddal (Sand Valley) a heavy flow of silt (sandy alluvium) is clearly seen (Green Arrow).

Opposite most other places in the arctic, big changes are seen in this area.

Please click on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on September 06, 2013, 05:52:52 PM
Would this heavy flow of silt be evidence of a large volume of basal melt water flowing out from under the land ice? What has the melt season looked like in this region of Greenland?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2013, 06:08:20 PM
If someone asked me, whats up in Grenland? My answer would definitely be Zachariae Isstrøm / Glacier. For the first time in satellite and recent history there will be open sea in front of this glacier, last year the main glacier was separated from its original tongue to the ocean.
Why did this happen? My answer would be, I know some will disagree, it is due to lack of surface flow from GIS in this area, none of the glaciers in this relative large area from L. Ibstrup Bræ / Storstrømmen in the south to Kofoed-Hansen, Blæsebræ, Gammel Hellerup Gletscher, Zachariae Isstrøm, Nioghalvfjerdfjorden and Spaltegletscher in the north are showing signs of movements seen from above (landsat), all actions, in my opinion is coming from below, but what is the reason for this? 

In the image below I want you to study the area marked with GREEN until the real sea freeze begins, later this month.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2013, 06:13:24 PM
Would this heavy flow of silt be evidence of a large volume of basal melt water flowing out from under the land ice? What has the melt season looked like in this region of Greenland?

Hope I answered some of your ?s
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2013, 06:32:08 PM
I am sorry to bother you again but I find this is very important (the latest image):
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2013, 07:17:53 PM
Aprox. Zachariae before 1980 green area:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on September 07, 2013, 01:59:46 AM
Would this heavy flow of silt be evidence of a large volume of basal melt water flowing out from under the land ice? What has the melt season looked like in this region of Greenland?

Hope I answered some of your ?s

Actually raised more than you answered but I think my questions should be on the "Stupid Questions" thread.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 17, 2013, 08:35:37 AM
Although the melting seems to be over, action is still taking place in the Arctic Area, at Zachariae Glacier, a new bay " Zachariae Bay" is born in front of the Glacier, as you can see from this animation from September 5 to 16, the debris and ice  (Sep 5) from the glacier is now flushed out, that can be seen under the light clouds on the September 16 image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 17, 2013, 10:35:12 AM
Another Landsat animation showing the action between Aug. 21 2013 and Sept. 9 2013.

Apart from the retreat / calving south of Kap Zachariae, a surge movement at the glacier is also seen:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 17, 2013, 10:52:20 AM
Another closer look around Kap Zachariae:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 19, 2013, 08:10:27 PM
First clear image from Modis in a long time, and the creation of a new bay "Zachariea Bugt" is in progress:

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 21, 2013, 11:32:25 AM
Aug 24 - Sep 9 2013
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 24, 2013, 07:20:46 PM
Zachariae Bay development in progress:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on September 24, 2013, 07:59:12 PM
Is the tongue disintegrating right before our eyes?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on October 02, 2013, 10:43:41 PM
It is not over yet!
Exiting stuff is happening right now, "Zachariae Bay" in front of Zachariae Isstrøm is cleared from ice and other "hard" water debris, this never happened before in modern history, at least not in the satellite age and probably much longer back.
It will be interesting to see if this retreat action will accelerate as I suspect or it will result in a surge which I doubt.
I also expect the X-Zachariae Tongue to get beaten up from both sides in the next few seasons.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 06, 2013, 06:12:15 PM
You thought it was over? No Wipneus came up with some really amazing stuff, now we can retrieve images from Landsat you didn't know existed , and they look like you clicked them from a low flying Cesna, I my self believe these images are game changer when it comes to observe glaciers, GIS etc.
What is your opinion. And on top of the above fact, this image below proof Zachariae is now divided into 2 pieces: The Glacier and its X-tongue:

Look at the details they are just out this world.
Thanks again to Wipneus for this new tool.


Click on image to enlarge, please do it is worth it!!!

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 09, 2013, 01:22:21 PM
New images are coming in from our Lab in the Netherlands:

Kap Zachariae / Lambert Land / North East Greenland

Notice the huge difference between 2000 and 2013, 1600 km2 of Glacier ice disappeared or almost 20 times the size of Manhattan or 8 times what Jakobshavn (the big star) lost and almost 3 times as much as the other darling Petermann lost in the same period.
But Zachariae did that with almost no notice.
Some experts even say it is business as usual?

Please click on images to enlarge.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on November 16, 2013, 03:11:56 PM
These images are great, I think I can see the edge of the ice shelf and the icebergs illuminated by the low sun giving an indication of freebord, or is that an artifact of imageprocessing?
Also interesting is the small ice cap seen, in the light of the Miller at al paper discussed elsewhere on the forum.
Could you comment on what can be seen on more recent IR images, which of course have much lower resolution, but might give an idea how things are changed by less landfast ice. There are plenty of cracks in the ice which is forming in the cold darkness.

http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311160720.NOAA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311160720.NOAA.jpg)
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311100647.NOAA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311100647.NOAA.jpg)
looking for older images for comparison I came acros this: http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200911222149.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200911222149.ASAR.jpg)
I have to admit I don't understand what sensor was used and how to interpret this image, but it looks a lot clearer than AVHRR. Can anybody explain?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: idunno on November 16, 2013, 04:38:58 PM
Judging by the cumulative meltdays map from here...

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)

NE Greenland has been hotter than most of the rest of the island.

2 questions;

1. Am I misreading that map?

2. If not, isn't it both very odd, and potentially very closely related to the events described above in this thread?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on November 17, 2013, 02:30:44 AM

http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311160720.NOAA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311160720.NOAA.jpg)
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311100647.NOAA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201311100647.NOAA.jpg)
looking for older images for comparison I came acros this: http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200911222149.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200911222149.ASAR.jpg)
I have to admit I don't understand what sensor was used and how to interpret this image, but it looks a lot clearer than AVHRR. Can anybody explain?
ASAR was a micro-wave radar sensor system with a resolution of perhaps 150-m;
AVHHR is an infra-red (=thermal) sensor system with spatial resolution of 1000-m at best;
MODIS is an optical/thermal sensor system with a resolution of 250-m at best;
LandSat is an optical/thermal sensor system with a resolution of 15-m at best.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 17, 2013, 10:12:08 AM
And to add to Andreas list:

Sentinel-2 from late 2014:
visible, near infrared and shortwave infrared sensors comprising 13 spectral bands: 4 bands at 10 m, 6 bands at 20 m and 3 bands at 60 m spatial resolution , with a swath width of 290 km.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 17, 2013, 02:16:35 PM
Further firn / glacier retreat.

As can be watched on the animation below, climate and weather changes are not taken its toll only in the sea around Zachariae Isstrøm and Kap Zachariae / Lambert Land *).
A little north of Kap Zachariae a firn (glacier) is found in Misanthropen Fjelde **), the area of this firn has been reduced considerably since 2000, the same happened to several other firns in the area surrounding Zachariae Isstrøm.

*) The name Land van Lambert is found on charts from 1718, and named after ? Lambert, a Dutch whale hunter.

**) Named after the sled dog Misanthropen

Please click on the image to start animation and enlargement!
.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on November 17, 2013, 03:54:59 PM
Thank you Andreas and Espen, I attach below images from 2009 which show the calving front at that time as a step from thick glacier to thinner sea ice and icebergs (the DMI site only goes back to 2009 as far as I can tell)
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20090901AQUA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20090901AQUA.jpg)
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200908301233.ASAR. (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/200908301233.ASAR.)
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20090712TERR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20090712TERR.jpg)
The ASAR image picks that calving front out more clearly as a white line which shows glacier and tongue still hanging together a.f.a.i.c.t. What I find interesting in the radar image is that the image of 30.8. shows the structure of the sea ice which also can be seen in the visible image of 21.7. but not in the visible 1.9.
That, I guess is due to the radar penetrating snow cover, but how much more can it tell about the condition of the ice? I am thinking of the "darker" ice along Lambertland. I know I behave like a kid which follows every answer by a new question ::)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on December 15, 2013, 05:39:49 PM
I may just have overlooked this before but think for anybody wondering why this glacier is worth keeping an eye on, have a look at the bedrock elevation map in http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/ (http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/)
This made clear to me why Espen thinks that here is a major outlet for the Greenland Ice Sheet.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on December 16, 2013, 01:04:32 AM
I do not think  it coincidence that the fastest sea terminating glaciers on Greenland have low elevations of land between the interior sub-sea level Greenland.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 04, 2014, 07:49:28 PM
The guys from the North East is a back in town:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 09, 2014, 08:46:35 PM
First good image this season from Modis showing Zachariae Isstrøm and The 79 Gletscher, looking forward to many hours of studies, since it is the most interesting part of Greenland, in my opinion ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on March 10, 2014, 04:47:17 AM
I used to be quite worried about Nioghalvfjerdsfjorden and NEGIS. But after staring at the Bamber(2013) bed data, i am more worried about Jacobshawn and Petermann because i see channels for seawater to penetrate to the heart from those two.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 10, 2014, 09:13:17 PM
Hi Sid,

I am still looking for visuel bed-data for both the Jøkelbugt Area ( Zachariae and 79th) and Dove Bugt (L. Ibstrup Bræ , Bredebræ and Storstrømmen), I believe we are in for some surprises.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on March 11, 2014, 03:04:22 AM
Profs. Bamber and Howat were kind enough to make the dataset available to me. I can do detail views or perspective, or contours, please see

http://membrane.com (http://membrane.com):/sidd/greenland-2013/

for some i have already done. Let me know what you need. I am travelling over the next 2-3 weeks, but i  will try to help as speedily as I may.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on March 11, 2014, 09:10:06 AM
Espen, does the bedrock map Mauri Pelto shows( link in my earlier post) not sufficient / doubtful?
 
A view of the basal topography from Joughin et al (2001) indicates that the acceleration occurs in the same area as the bed depth drops significantly below sea level 200 km from the ice front. The base of the glacier is 300-700 meters below sea level all the way to the ice front. The thickness at the grounding line is noted as 550-600 meters by Rignot et al (2001). The result is an ice flux at the grounding line of ZIS of some 11 cubic kilometers per year, this is much less than the 40+ cubic kilometers from Jakobshavn Isbrae and similar to the 12 cubic kilometers from Petermann Glacier.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 11, 2014, 03:33:29 PM
I may just have overlooked this before but think for anybody wondering why this glacier is worth keeping an eye on, have a look at the bedrock elevation map in http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/ (http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/)
This made clear to me why Espen thinks that here is a major outlet for the Greenland Ice Sheet.

I have, perhaps, another important reason why we should be concerned about many of the larger sea terminating glaciers in Greenland. We always use the term "bedrock" when describing the topography under these glaciers. I believe this is a potentially highly inaccurate description of the areas where these glaciers are grounded.

We know that the Humboldt Glacier releases large amounts of silt during its episodic upwellings. Bedrock should not, I believe, release so much silt during these periodic releases of melt water.

http://www.flickr.com/photos/greenpeaceusa09/3830848485/# (http://www.flickr.com/photos/greenpeaceusa09/3830848485/#)

I suspect these relatively large yet low areas of elevation under the sea terminating glaciers are more likely to have the characteristics of glacial moraines, material that has been scoured from the interior of Greenland and deposited. The large moraines deposited across North America as the ice sheets retreated at the end of the last ice age are a mix of boulders, gravel, sand and other loose materials. Attached is a map of the major moraines in North America.

As seen on this topography map of Ohio, large ice sheets can deposit moraines with elevations of 1000 feet or more when they retreat. Aren't the ice sheets on Greenland thicker than the ice sheets that covered North America? If so the material scoured and deposited would likewise be larger.

http://www.dnr.state.oh.us/portals/10/pdf/sem_tone.pdf (http://www.dnr.state.oh.us/portals/10/pdf/sem_tone.pdf)

The moraines are very prone to erosion and I think this could very well be the fate of these elevated areas that we call "bedrock". They are nothing of the sort. As melt water continues to find its way to the bottom of these large sea terminating glaciers, these elevated areas will erode and wash into the sea. This altered topography will reveal the true nature of the seas connections to the interior of Greenland, wide and shallow plains terminating in shallow estuaries as the rivers reach the sea.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 11, 2014, 03:45:40 PM
I have a lot of questions regarding current research on Greenland.

Does anyone have a map of the retreat of the Greenland ice sheet from previous warm periods? I seem to recall that the ice sheet retreated to the center of the top half of Greenland. Did the ice sheet edge line up with these elevations under the sea terminating glaciers? If so this would  support the idea these elevations are moraines.

Also, is there research about the nature of the seabed around Greenland? Are the surfaces of the seabed surrounding Greenland different where these sea terminating glaciers exist? It would seem we might be able to find deposits of loose material at these exit points for the major glaciers, boulders, gravel and other materials that washed into the sea as the glaciers retreated.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 11, 2014, 04:24:42 PM
When you consider the possibility that these relatively low elevations under the sea terminating glaciers are not bedrock but, in reality, loose materials deposited by the last major ice sheet retreat on Greenland and revisit the topography map under the Zachariae Isstrom Glacier provided above by Andreas T., the low lying areas nearest the sea begin to resemble a large river delta, evidence of ongoing erosion of the moraine deposits into the sea.

I've attached a landsat image of the Chesapeake Bay river deltas for comparison purposes.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 13, 2014, 08:46:12 PM
It is pretty clear I've either killed or mortally wounded this thread with my wildly speculative and grossly ill informed posts. Given the damage has already been done, I thought I would put one final bullet in the thread by asking a hopelessly naïve question.

Is it foolish to think that the behavior of sea terminating glaciers, rivers of ice, would mirror the behavior of the rivers lying, or would otherwise lie, deep beneath them? In other words, should we be surprised that a river of ice and the river beneath it would move rapidly through a deep gorge or canyon as it races to the sea? Likewise, shouldn't Humboldt Glacier move slowly across a broad plain just as a river might as it winds its way slowly to the sea.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on March 13, 2014, 09:36:59 PM
Having grown up in an area shaped by the debris of the last ice age (just north of the Alps) I often wondered how the ice produced those hills of gravel and sand. The way I would interpret that Zachariae map is that the trough under its lower part is produced by the scouring of the ice which most likely leaves loose sediment on the sea floor in front of it. That shows up as the higher elevation greens beyond the grounding line.
Rivers spread gravel into alluvial fans and may cut into it when they have sufficient gradient, but ice scours on a wide front and builds up deposits in front of it, that is what produced the lakes of southern Germany.
Speed of the ice flow is determined by gradient. The connection with the width of the flow is through availability of upstream material. A faster flowing Humboldt glacier would lower its gradient and slow itself down. I think what is able to change the present flow rates is the change in viscosity of the ice and the friction between ice and bedrock that warming and meltwater brings.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Martin Gisser on March 13, 2014, 10:03:15 PM
Having grown up in an area shaped by the debris of the last ice age (just north of the Alps)
Ha! Me too. I'm currently sitting near the river Alz in Burgkirchen. Where are you from?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 14, 2014, 10:37:51 AM
You cannot have perfect weather everywhere I guess. Still through the clouds I think this first Landsat 8 image of the Zachariae icestream is of interest: the calving front is visible (retreated perhaps?) and very few "calvings".

(according to the meta data the sun elevation is 7.5 degrees)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 14, 2014, 11:04:51 AM
The 79N fjord image is even more difficult to read. Under magnification the calving front can be seen on the right (hint: there are 6 little islands buttressing the glacier there).

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 14, 2014, 04:23:06 PM
Wipneus,

Great images, where did you get those images, I didnt know Landsat 8 (2014) got that far north already?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 14, 2014, 06:22:03 PM
Wipneus,

Great images, where did you get those images, I didn't know Landsat 8 (2014) got that far north already?

I get them here (http://earthexplorer.usgs.gov/) these days. As you see some images are available the next day. The coverage is spotty though, I have no luck yet with finding the pieces of the PII-2012 for instance even if they must be at a much lower latitude.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 14, 2014, 09:59:16 PM
Thanks Wipneus! ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Stephen on March 16, 2014, 11:38:29 PM
http://www.abc.net.au/news/2014-03-17/global-warming-melts-greenland-ice-sheet/5324848 (http://www.abc.net.au/news/2014-03-17/global-warming-melts-greenland-ice-sheet/5324848)

"In a study published in the journal Nature Climate Change, researchers said a surge in temperature from 2003 had eased the brakes on a long "river" of ice that flows to the coast in north-eastern Greenland."

Any comment regarding the source paper for this news item?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 17, 2014, 05:32:34 AM
Zachariae Isstrøm is definitely on the move, not so much 79th Fjords. Zachariae even moved during the last dark season.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on March 17, 2014, 07:44:36 AM
"Zachariae Isstrøm is definitely on the move, not so much 79th Fjords. Zachariae even moved during the last dark season."

Right on. I attach Fig 4d and 4e from Khan(2014) doi:10.1038/NCLIMATE2161
see how ZI is still grounded unstable on retrograde bed but NG is already afloat from deepest point out to calving front.


Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 17, 2014, 06:11:32 PM
http://www.abc.net.au/news/2014-03-17/global-warming-melts-greenland-ice-sheet/5324848 (http://www.abc.net.au/news/2014-03-17/global-warming-melts-greenland-ice-sheet/5324848)

"In a study published in the journal Nature Climate Change, researchers said a surge in temperature from 2003 had eased the brakes on a long "river" of ice that flows to the coast in north-eastern Greenland."

Any comment regarding the source paper for this news item?

Another study of Zachariae Isstrøm etc. is just published in Copenhagen showing more or less the same. I now better understand the "Radio Silence" when I asked into the matter over the last couple of of years here in CPH, they wanted to publish the "secret" first?

But the fact is, the Jøkelbugt Area with Zachariae Isstrøm, 79 Fjord etc. will be one of the most interesting and important places to watch when talking about changes in the Arctic, as I have noted several times before. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 17, 2014, 06:25:12 PM
An article ( in danish) with the new study made by DTU Space, Copenhagen:
http://www.dtu.dk/Nyheder/2014/03/Nu-smelter-den-nordligste-del-af-indlandsisen (http://www.dtu.dk/Nyheder/2014/03/Nu-smelter-den-nordligste-del-af-indlandsisen)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 17, 2014, 07:16:02 PM
And here in English: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2161.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2161.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: icefest on March 18, 2014, 08:16:09 AM
And here in English: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2161.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2161.html)
Thank you for that link Espen, all the others were behind a different paywall than I have access to.

PM me for help if anyone else cannot see it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 23, 2014, 08:57:19 AM
Sun elevation is still low (11 degrees) but far better quality images on the 22nd.

(better resolution if you click those pictures)

Here is the calving front of Zachariae:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 23, 2014, 08:59:46 AM
And here 79N:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 23, 2014, 09:39:14 AM
And here a small animation of ice movements at Zachariae since end of melting season (September 24 2013) up to yesterday March 22 2014.
It is clear Zachariae is moving during the winter.

Please click on image to enlarge and start of animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 23, 2014, 10:08:12 AM
We can expect further calvings and retreat, 3 - 5 km from the calving front south of Kap Zachariae is ready to move.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 23, 2014, 10:31:24 AM
The red line is indicating where we will probably will see more calving or retreats in the near future:

Please click on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on March 23, 2014, 12:54:47 PM
One thing I find interesting about those images is that the dark glacier surface and the exposed rock surfaces surrounding it show very little snowcover. Is that the result of wind blowing it away or does it just not get much precipitation up there?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 23, 2014, 01:00:41 PM
One thing I find interesting about those images is that the dark glacier surface and the exposed rock surfaces surrounding it show very little snowcover. Is that the result of wind blowing it away or does it just not get much precipitation up there?

This time of the year more likely the wind.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: lanevn on March 25, 2014, 11:21:41 AM
'Stable' NE Greenland ice sheet is melting away (http://www.theecologist.org/News/news_analysis/2312123/stable_ne_greenland_ice_sheet_is_melting_away.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 26, 2014, 08:10:30 PM
I always focused on the Jøkelbugt area, because I believe it is the place that will show, something is completely wrong, and I am afraid we will soon find out, so please all interested; keep your eyes focused here and not so much the other trivial places! ;) 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 26, 2014, 08:42:55 PM
"But the increasing contribution from the very cold northeastern part of the ice sheet during the last seven to eight years is new and very surprising."

Not surprised, anyone with little interest could see that happen?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 29, 2014, 06:45:40 PM
Here are some relatively new images from Zachariae Isstrøm (DTU Space 2012) I believe seen from north of Nørreland towards Lambert Land and Kap Zachariae:

More or less the same scenery we see at Jakobshavn.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 29, 2014, 06:51:56 PM
And one more (DTU Space 2012), in the clean Sunday dress ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Jmo on March 30, 2014, 03:08:21 PM
Thanks Espen. Amazing photos.  I assume you've seen Chasing Ice? Hard to know the scale, but that's a (small?) melt pond on the right?  normal for March? Cheers
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 30, 2014, 04:54:46 PM
Here are some relatively new images from Zachariae Isstrøm (DTU Space 2012) I believe seen from north of Nørreland towards Lambert Land and Kap Zachariae:

More or less the same scenery we see at Jakobshavn.

Has the surface of this glacier always been so dark or has surface melt darkened it over time which would cause higher surface albedo and melt?

I also am fascinated by the face of the tabular icebergs. There are black streaks that run deep into the glacier exactly where the surface would suggest a large amount of melt. Is this what I am seeing? Are these vestiges of past moulins or at least evidence of surface melt making its way to the base of the glacier prior to calving??
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 05, 2014, 03:03:18 PM
Here is an image taken on a flight from Norske Øer towards Lambert Land, the previous tongue of Zachariae Isstrøm is seen to the right. Image: DTU Space.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 05, 2014, 03:51:41 PM
Do you know the date of this image Espen?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 05, 2014, 06:15:28 PM
Wipneus,

Yes I do it was taken on September 1 2012, so a bit old :(
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 07, 2014, 07:07:14 PM
Using Wipneus talents in imaging and with the help from Landsat 1.

The image show the big changes at Zachariae Isstrøm since 1976.

The red shaded area marked on the glacier has disappeared since 1976.
it means that at least 200 km2 of the glacier has disappeared and is now open sea at the end of the melt season.

Click on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 07, 2014, 10:43:08 PM
Thanks Espen, that's great. I don't suppose the red lines represent the yearly retreat ?

i am back home, and i shall try post some bedrock and ice elevation detail after i catch my breath.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 08, 2014, 04:58:01 AM
Sidd,

No that is the total retreat since 1976.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 12, 2014, 06:36:14 PM
Here is first cut at ice surface contours for NE GRIS
i will add labels on the contours, but for now, bear in mind they are spaced 100 m apart. Color scheme is horrible, and lines are too thick, will fix. Thought you might like to see some rushes.

will also do bedrock as time allows. Also there is a new ice surface dataset from Viet Helm for both GRIS and AIS, which i have not yet had the time to look at.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 12, 2014, 06:37:29 PM
Didnt attach the image in the last post

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 12, 2014, 06:53:36 PM
Against the odds that is how I see the area too ;), looking forward to some more details. :D

Especially the bedrock details.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 13, 2014, 01:04:47 PM
It is fascinating to watch how a huge glacier like Zachariae Isstrøm is moving, this animation is based on 2 images from March 22 2014 and April 11 2014 or 20 days apart, and it is easy to see the whole glacier moving:

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: icefest on April 13, 2014, 02:17:37 PM
It's incredible that the older icebergs are still frozen in the FYI, while the rest of the glacier pushes the closer ones along.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 14, 2014, 09:29:51 PM
"Just out of the satellite" further movement at Zachariae Isstrøm, and now a "Sea Ice Tsunami"  is clearly seen (2nd frame) in front of the calving front:

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 15, 2014, 06:39:09 AM
Here is a composite of ice surface contour,ice surface velocity, and bedrock. For detail and bedrock contour go to

http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)

and

http://membrane.com/sidd/greenland-2013/convel.html (http://membrane.com/sidd/greenland-2013/convel.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: werther on April 15, 2014, 10:58:04 AM
Morning all,

for everyone that wants to have a close look on this area this summer. Polarstern will be there with Andreas Muenchow on board. Follow his new blog entry here:
http://icyseas.org/2014/04/14/north-greenland-glacier-ice-ocean-interactions-2014/ (http://icyseas.org/2014/04/14/north-greenland-glacier-ice-ocean-interactions-2014/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 15, 2014, 07:52:20 PM
It's a pity, Zachariae Isstrøm is not calving Ice Islands like Petermann, because what is happening with this glacier I find far more important than most of the other glaciers in Greenland.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on April 15, 2014, 11:59:57 PM
Not sure I agree with that sentiment, Espen, but the contrast between the collapsed Zachariae and the apparently stable Niogshalvfjerdsfjorden certainly raises a number of interesting questions that the Greenland ice sheet story is not as simple and straightforward as some political factions want us to believe ;-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 16, 2014, 06:12:22 AM
Now the back pressure is gone, it is natural the ice will flow in the direction where Zachariae is and 79 will probably stay relatively stable and just melt slowly away.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on April 16, 2014, 03:37:56 PM
Fair and descriptive enough; but the question stands on why the back-pressure disappeared at Zachariae but not at Nioghalvfjerdsfjorden?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 16, 2014, 08:31:08 PM
Hi Andreas,

I believe it is sea and current related, the process started in the early 2000s, especially 2003 stands out, the whole sea in front of Zachariae and 79 was literally sea ice free in 2003:
https://forum.arctic-sea-ice.net/index.php/topic,238.msg7988.html#msg7988 (https://forum.arctic-sea-ice.net/index.php/topic,238.msg7988.html#msg7988)
After 2003 Zachariae started to disintegrate from the south and inside Jøkelbugt, in the period before 2003 not much happened to both Zachariae and 79, but between 2003 and 2012 the disintregation of Zachariae continued and reached the southern point of Lambert Land ( Kap Zachariae )  this I disscussed with Mauri Pelto then
http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/ (http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/)
When Jøkelbugt became ice free up to Kap Zachariae, Zachariae Isstrøm woke up, the back-pressure was not there and the whole glacier started to move and at a fairly high speed, and this process has continued during the winter and spring of 2014.
https://forum.arctic-sea-ice.net/index.php/topic,400.msg24181.html#msg24181 (https://forum.arctic-sea-ice.net/index.php/topic,400.msg24181.html#msg24181)

Why did this reaction to changes at sea happen to Zachariae "only".

Several reason I belive.

1. With no back pressure it is more natural for the ice from GIS to go trough the Zachariae Gate than the 79 Gate or the Storstrømmen Gate there are simply fewer topographical obstacles on the Zachariae Gate route.

2. I also think sea temperature and currents changed dramatically after 2003 especially in the bay in front of Zachariae Isstrøm (Jøkelbugt), even huge ice pieces from the glacier seems to melt even before they get out of the bay and into the sea outside.
What was the reason for the sea changes in and around 2003?
I think you have more theories and facts on this matter, but I believe there is a relative high average sea temperature difference between Zachariae Isstrøm and 79?

Please on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 16, 2014, 09:31:22 PM
A new animation March 22 - April 16 2014 from Zachariae Isstrøm:

Please click on image to start animation!

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 16, 2014, 09:41:50 PM
" ... fewer topographical obstacles on the Zachariae Gate route."

That is also what i see in bedrock contours as linked from in

http://membrane.com/greenland-2013/sidd/convel.html (http://membrane.com/greenland-2013/sidd/convel.html)

 I wonder how far back there is sea water penetration into the subglacial hydrology as in Lewis(2009) DOI: 10.1002/hyp.7343

I enclose two images from fig 4, the second is the legend, the first is the NE quadrant of GIS. The Figure caption is the text below:

Figure 4. Meltwater evidence along the ice sheet perimeter (number of confirmed meltwater features within a 50-km vicinity of a modelled outlet) versus meltwater intensity (total annual meltwater volume per unit thawed area, cm) within each hydrologic sub-basin, illustrating that rivers, streams, and proglacial lakes are generally more prevalent near ‘wet’, hig–producing modelled meltwater outlets than ‘dry’, low-producing outlets (as seen in similar size variations in blue and red circles). Modelled hydrologic flow network delineates realized (‘wet’, solid lines) and unrealized (‘dry’, dashed lines) drainage patterns
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 16, 2014, 09:43:55 PM
I should point out that the Lewis paper is based on the 2001 Bamber dataset (the paper predates his 2013 dataset, which is what i am using)

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 17, 2014, 08:55:02 AM
Detail animation of the Zachariae calving front based on Landsat 8 images processed for natural color at 15m resolution. Images form March 13 to April 14 were used.
Watch a new crack opening.
In the last frame an arrow indicates my best estimate of the ice movement: 10pix right and 2pix down, translating to 152 m in 32 days or 4.8 m/day with perhaps an error of +/- 15%.

(click the pic for that animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 17, 2014, 01:17:06 PM
The Nioghalvfjerdsfjorden is moving much slower indeed. Attached sequence shows a channel at the center of the glacier dated 2013 September 6 and 2014 April 2.
The ice moved 14pix right and 1 pix up. Total movement is 210m in 208 days giving an average velocity of 1m/day with an error of about +/- 10%.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 17, 2014, 05:59:53 PM
One more to establish the velocity of the Zachariae. Dates as in the previous post: 2013 September 6 and 2014 April 2.

There is a nice little hexagon shaped feature in the ice that makes is easy to match pixels in the two images. I get 78pix to the right and 6 pix down. That is 1173m in 208 days, a velocity of 5.64 m/day with maybe 3% margin of error.
Picked another feature and got the same number so the velocity is quite uniform in the middle of the ice stream. Both measurements are marked with an arrow.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 17, 2014, 06:20:28 PM
Wipneus it would be interesting to see how the velocity is compared to last year, my gut feeling tells me Zach is accelerating?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 17, 2014, 06:40:42 PM
Wipneus it would be interesting to see how the velocity is compared to last year, my gut feeling tells me Zach is accelerating?

That is exactly what I have in mind in "watching the giants waking up". Unless you find a suitable earlier Landsat 8 image that means going to landsat 7 images that are not as nice and take days to order from the USGS. Of course we will also watch the progress during the coming season.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 17, 2014, 11:35:57 PM
Attached image is closeup of bedrock topo at the mouth of Nioghalvfjerdsfjorden and Zachariae from Bamber-2013. Zachariae is connected through deeper channels to the future inland sea.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 18, 2014, 07:46:29 AM
And not to mention the Delta shaped outlet at Zachariae Isstrøm against the Arrow shaped outlet at 79?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 18, 2014, 08:45:34 AM
Espen pointed to a landsat 8 image taken on 2013 May 25. That gives us an opportunity to estimate the ice velocity of the Zachariae during the last melting season.
This image is taken on the ascending half of the landsat 8 orbit. That is normally the night side, but in the Artic summer that does not matter. The orientation of the image is slightly different though so I had to do some rotation to align images using the nearby rocky islands.

The hexagon-shaped feature is there as well. It moved during 104 days 42pix right and 8pix down. That translates to 641m, or 6.2 m/day. I estimate an error of about +/- 0.4, due to the manual image manipulation that was required.

So no speed-up can be seen this way. I am not sure if the speed of such glaciers is expected to vary much between the seasons?

(click the pic for a rather nice animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 18, 2014, 12:40:27 PM
Added 2012 July 9 to the sequence. I decided that for the purpose of measuring velocity color is not required. With some searching the hexagonal feature can be found.
Distance traveled 2013 Sep 6 is 144 pix to the right 21 pix down. That is 2183 m in 423 days or 5.2 m/day. Not much acceleration to be seen but it depends on the accuracy of the 2013 May 25 data point, if taking the difference with that date I get about 3.9 m/s. I really need more data points.

In the animation look at the glacial lakes, they stay in the same place while the local ice is moving.

(click for that animation on the picture)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 18, 2014, 08:49:08 PM
"ook at the glacial lakes, they stay in the same place while the local ice is moving."

That is quite amazing, how can that happen. I find it hard to believe that the ice somehow flows "around" the lake depression ...

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 18, 2014, 09:06:22 PM
Sidd,

The glacial lakes are located where the ice is more or less stationary (they are not situated in the actual stream) , there is probably a new future Kap below?
I think that can be observed on your bedrock map above?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 18, 2014, 11:05:23 PM
I have asked Prof. Pelto to look. He indicates he may be able to do so this weekend.

i think the answer may be that the lakes reform in the same place year after year. Could the depressions they form in be a feature of the flow like stationary ripples in a stream ?

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 18, 2014, 11:20:41 PM
Added 2012 July 9 to the sequence. I decided that for the purpose of measuring velocity color is not required. With some searching the hexagonal feature can be found.
Distance traveled 2013 Sep 6 is 144 pix to the right 21 pix down. That is 2183 m in 423 days or 5.2 m/day. Not much acceleration to be seen but it depends on the accuracy of the 2013 May 25 data point, if taking the difference with that date I get about 3.9 m/s. I really need more data points.

In the animation look at the glacial lakes, they stay in the same place while the local ice is moving.

(click for that animation on the picture)

That is about ½ the amount / day compared to Jakobshavn (width x velocity) pretty impressive this far north? Or am I wrong?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 19, 2014, 12:09:53 AM
The following image is a close up of the ice surface
along Nioghalvfjerdsfjorden and Zachariae Isstrom.
Note that ice is piling up behind the first, but not the
second. The warming ocean reaches deeper under Zachariae.
Zachariae is a wider and deeper connection to the future inland
sea.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 19, 2014, 05:54:50 AM
I knew i had a more recent ref to basal hydro than Lewis(2009)
Linvingstone(2013) fig 5b) attached, putative subglacial hydro, subglacial lakes, rignot velocity in obe pic
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 19, 2014, 06:02:06 AM
sorry ref for the last is

doi:10.5194/tc-7-1721-2013

open access

also, in light of my supposition that the (supra) glacial lakes reform in the same place because of flow features in the ice surface, see Sergienko(2013)

doi: 10.3189/2013JoG12J040

not open, but i attach fig 2, illustrating effect of bed topo on surface
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 19, 2014, 09:10:29 AM

also, in light of my supposition that the (supra) glacial lakes reform in the same place because of flow features in the ice surface, see Sergienko(2013)

Thanks for digging that up Sidd. I thinks that is what we are seeing.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: mspelto on April 19, 2014, 12:27:38 PM
Nice new images sets from this spring I had looked at the March but not the April Landsat.  The supraglacial lakes form in same geographic location mainly because of the bed of the glacier induces changes in the surface of the glacier.  Depending on the speed of movement and ablation rate, the lake could persists or not.  The lakes form because of the surface features, but do not necessarily disappear as they move beyond that feature. Lampkin (2011) is a paper that best describes the bed-surface relationship and lag. http://onlinelibrary.wiley.com/doi/10.1029/2010JF001725/abstract (http://onlinelibrary.wiley.com/doi/10.1029/2010JF001725/abstract)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 19, 2014, 10:15:45 PM
Thanks for the comment, Prof. Pelto. There is another paper in 2011 by Lampkin and VandeBerg (that is how it is capitalized in the journal) in Hydrological Processes DOI: 10.1002/hyp.8170 that is relevant also. I attach Fig 2
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 19, 2014, 10:19:03 PM
The second name in the last ref i posted should be spelled VanderBerg Sorry.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 19, 2014, 10:21:19 PM
Sidd,

That makes sense, nice digging! ;)

That gives the expression " Sweep under the carpet" a new meaning?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 20, 2014, 09:38:05 AM
Velocity between mids of 2010 and 2012 is about 4.4 m/day, measured at the hexagon feature which moved 3.148 km in those two years.

I postpone an updated animation until I added some more years and can plot distance vs time. Until then not much sign of significant acceleration in the period considered.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 20, 2014, 11:40:40 PM
Comparison of surface contour and bedrock in the subject area
For other such comparisons and some previous work please see

http://membrane.com/sidd/greenland-2013/walkback.html (http://membrane.com/sidd/greenland-2013/walkback.html)

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on April 21, 2014, 05:08:12 PM
Velocity between mids of 2010 and 2012 is about 4.4 m/day, measured at the hexagon feature which moved 3.148 km in those two years.
For context, please note, that Rignot and Kanagaratnam (2006, Science) give a velocity profile across the glacier that peaks at about 1,600 m/y or 4.4 m/day for Zachariae from 2004-05 ;-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 21, 2014, 07:05:08 PM
For context, please note, that Rignot and Kanagaratnam (2006, Science) give a velocity profile across the glacier that peaks at about 1,600 m/y or 4.4 m/day for Zachariae from 2004-05 ;-)

Thank you Andreas, that is nice to know.

Have you any indication how much Summer and Winter might differ from such an  annual average?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 21, 2014, 08:57:08 PM
From the Rignot paper, some historic(2000) seasonality variation:

"We examined the seasonal variability in flow
speed of major glaciers in fall 2000. We found
no velocity change from September to January at
the 1% level over the 24-day averaging period of
Radarsat-1. On the Petermann Glacier (1 in Fig.
1), a continuous set of observations in 2004
reveals an 8% increase in the summer months
compared to winter (Fig. 2A). A similar sea-
sonality is detected on Nioghalvfjerdsbrae and
all southeast Greenland glaciers and has been
observed on Jakobshavn Isbrae (8) and Colum-
bia Glacier, Alaska (9). Winter velocities are
therefore only 2% lower than the annual means,
and flow changes must exceed 8% to be sig-
nificant."

I atttach the figure referred to, y axis is meter/year

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 22, 2014, 10:52:40 AM
Thanks Sidd, 8% is about 0.4 m/day. Small but not entirely negligible.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on May 02, 2014, 11:53:39 PM
I may have an idea as to why Zachariae is breakig up faster than Nioghalvfjerdsfjorden. I attach a pic showing a trough under the former. Some more detailed discussion is at

http://membrane.com/sidd/greenland-2013/Zachtrough/ (http://membrane.com/sidd/greenland-2013/Zachtrough/)

with some graphs of the water temperature, and 150, 200m depths (the latter are relevant in the context of the water temperature variation with depth)

Briefly: The trough allows warmer Atlantic Intermediate water to the base of the ice. Also the bed is deeper under Zachariae, and the deepest area is larger.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 03, 2014, 10:27:44 PM
Very interesting, and it makes sense, but the color scheme confuses me a bit. ???
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on May 04, 2014, 12:31:08 AM
Mr. Espen, apologies for the color scheme. I attach some images with a different scheme.
The first image shows temperature vs depth from Aagard(1968, "The East Greenland Current North of the Denmark Strait:Part 1", Arctic, v21) fig 4. Note that 200m is a good depth to watch.
The second image is temperature vs depth across Fram, eastward from 16W along 79 N. (This is from just east of Norske Oer. Note the lack of Atlantic Intermediate water on the continental shelf.
The third is to show the pathway for warm water from south east. The fourth is a closeup of the
trough and a small ridge from the upper corner of Lambert; the latter provides an additional barrier to Atlantic Intermediate water from the southeast getting under Nioghalvfjerdsfjorden.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on May 04, 2014, 01:07:48 AM
I neglected the reference for the second image, which is Fig 3a) from Fahrbach et al. Polar Research 20(2), pp217-224 in 2001.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 04, 2014, 06:43:11 AM
Nice work Sidd, I wonder what impacts, when the the previous tongue of Zachariae is gone?

And I am surprised of the relative shallow water of the southern part of Jøkelbugt, and the depth of the future "Zachariae Sea" .
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 05, 2014, 04:02:19 PM
Two Zachariae images 2014/4/2  and 2014/5/4 compared. Zachariea keeps moving with an average estimated speed of over 6 m per day.

(click for the animation to start)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 05, 2014, 05:13:24 PM
Wipneus, it is amazing to watch this monster, now that we know how fast the thing is moving, it would be interesting to estimate the size of the retreat, which at this point would be much higher?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 18, 2014, 03:45:46 PM
An interesting video from NASA showing a retreating grounding line works:

The link is below

GroundingLineRetreat 20140507 1280 (http://www.youtube.com/watch?v=dXVWGGmNRiI#ws)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 20, 2014, 09:30:56 PM
May 20 update, I am pretty impressed how this thing is behaving this season:

Please click on image to start the animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 22, 2014, 07:45:11 PM
Zachariae Isstrøm, aka Speedy Gonzachariae, is still on the move, note the new cracks relatively far behind the obvious calving front:

Please click on the image to start the animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 22, 2014, 09:00:11 PM
It is obvious we have a same calving pattern as for instance Petermann, although in smaller scale, the "outcasts" are just floating into the sea, different to Helheim and Jacobshavn where "they" are turned upside down, another proof of thickness and space underneath?   
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 28, 2014, 05:57:30 AM
Zachariae Isstrøm update:

Further strong movement at "Speedy Gonzachariae":

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 28, 2014, 04:07:59 PM
It is obvious we have a same calving pattern as for instance Petermann, although in smaller scale, the "outcasts" are just floating into the sea, different to Helheim and Jacobshavn where "they" are turned upside down, another proof of thickness and space underneath?

I would just like to make certain I understand this.

A calved iceberg would more likely flip if its thickness or depth is more than its breadth. Since they are floating out to sea, without tipping, this would suggest they are not as deep, right?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 28, 2014, 04:13:09 PM
Zachariae Isstrøm update:

Further strong movement at "Speedy Gonzachariae":

Please click on image to start animation!

When I look at the speed of this glacier and evidence of substantial cracking occurring far from the  calving face, it seems this glacier could  become a real monster for ice mass loss.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 28, 2014, 04:14:13 PM
Shared Humanity,

Yes, is what I believe, but I don't have any evidence to support is, just my logical sense? ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 28, 2014, 04:17:37 PM
Zachariae Isstrøm update:

Further strong movement at "Speedy Gonzachariae":

Please click on image to start animation!

When I look at the speed of this glacier and evidence of substantial cracking occurring far from the  calving face, it seems this glacier could  become a real monster for ice mass loss.

Shared Humanity,

Yes I believe this glacier got some more confidence, after the "front wall" went away, and it will be one of the more interesting glaciers to follow in the near future.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 28, 2014, 04:24:20 PM
Espen....

I  have other questions. I am fascinated by the tongue of glacier that has been separated and has open sea on both sides. Are there other Greenland glaciers where this has happened? Would this exposure to sea on both sides cause this tongue to be especially vulnerable? In the Antarctic threads, there is a great deal of research discussing the impact of sea water in moving the grounding line and thinning the shelf of a glacier. Could this be happening on both sides of this tongue? What portion of this glacier is currently grounded? As the portion that is grounded shrinks, could we possibly see a catastrophic failure where the bulk of the glacier calves in a very short space of time. By short, I mean something like that spectacular calving event from "Chasing Ice".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 28, 2014, 04:35:31 PM
S. H.

I think the tongue will remain where it is for years to come, but disintegrate from both the fjord and sea side. The separation of the tongue I believe is unique in this scale.   
The direct sea access to Zachariae Isstrøm will strengthen the calving and retreat rate, seem to be very obvious by now.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 28, 2014, 04:40:59 PM
Thanks, Espen.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on May 28, 2014, 09:21:49 PM
taking the north south extent of the image as 25km I get approx. 500m for the width of the narrowest of the icebergs. Am I getting these figures right Espen?
this is very close to the thickness shown by sidd some while back
"Zachariae Isstrøm is definitely on the move, not so much 79th Fjords. Zachariae even moved during the last dark season."

Right on. I attach Fig 4d and 4e from Khan(2014) doi:10.1038/NCLIMATE2161
see how ZI is still grounded unstable on retrograde bed but NG is already afloat from deepest point out to calving front.
It does not look like these bergs are grounded though so their thickness would be somewhere less than that. It seems to me that the profile shown in that paper explains the breaking up at the calving front by the deformation the ice undergoes (and likely crevassing) as it moves over the ridge about 35km back from the 2011 calving front.
Something noticeable in your animation is that the icebergs furthest from the glacier are not moving (held by landfast ice I guess) and there seems to be ridging were the glacier pushes against that landfast ice.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 28, 2014, 10:52:20 PM
Andreas,

No you are right, the "calves" are not stranded, they are stuck in the fjord ice / sea ice for the time being.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 29, 2014, 09:33:33 AM
Here is the same scene but at higher resolution and in natural colors. I have created a "double exposure" image with one made 64 days before on 2014-3-24. Same path/row gives images from the satellite in the same position and less apparent movement.

My favorite "hexagonal feature" can be seen on the left, a bit above the middle.

The ice moves about 390 meter, which gives an average "speed" of about 6.1 m/day. Most of the calves move at about the same speed except three of them that hardly move at all.

I have marked the ridge that apparently separates the sea ice moving with the glacier and the fast ice with arrows.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 29, 2014, 09:53:35 AM
Here is a curious detail of a developing ridge line a bit to the north in the same set of images. In the first image the line is still rather uniform, two months later it is notched. The width of the notches is comparable with the movement of the glacier ice on the left. I'd think it is where the moving sheet of ice either moves over or below the fast ice sheet.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TerryM on May 29, 2014, 07:16:55 PM
The "double exposure" is very effective. Thanks


Terry
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2014, 10:40:21 AM
Zachariae update:

Please click on image to start animation!

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2014, 11:39:53 AM
Wondering how Zachariae will react after a few months of sun and a sea ice free bay?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 31, 2014, 04:28:55 PM
Zachariae update:

Please click on image to start animation!

Espen....looking at this animation, how many kilometers (meters?) are captured on the horizontal axis? I am interested in how far the pronounced cracks that have formed are from the calving face.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2014, 04:58:39 PM
Shared Humanity,

Wipneus made several images above in this thread with scales?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on May 31, 2014, 05:10:12 PM
Using the scale in Wipneus' image from the 29th I measure the stationary iceberg lowest (most southerly) in Espen's image as about 1.5 km in the horizontal (east - west) extension, you could use that to give an idea of scale.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 31, 2014, 05:16:18 PM
Espens's Landsat 8 images have the standard 30m/pixel resolution. This image is 498pixels wide, or 14.94 km.

My images can be 15m, but sometimes 30m or 60m to reduce the files to workable size. The raw images are about 600MB.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2014, 05:23:37 PM
I will estimate the furthest crack at the moment to be approximately 4,5 km from the calving front.
So to be on that glacier anywhere near the calving front will be risky business.

ps: Petermann is far more reliable!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2014, 09:14:35 PM
There is room for a considerable retreat this season, and hopefully actions will be taken.
There are few other glaciers further north to be observed.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on May 31, 2014, 09:17:39 PM
Thanks, everyone.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on May 31, 2014, 10:28:12 PM
I'm not an expert but I believe the current events at Zachariae provide a rare opportunity to observe one of the most dynamic phenomena in glaciology. A marine terminating glacier with the grounding line and calving front at the same spot on a retrograde bed is a highly unstable configuration. I think we are going to see a lot of papers on Zachariae over the next decade.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 10, 2014, 04:57:25 AM
Speedy Gonzachariae on the move as usual:

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 11, 2014, 06:23:22 PM
What is all the fuss about?

When I realized what was going around Zachariae Isstrøm sometimes in 2012, it became clear to me to keep an eye on this glacier anyway I was always fascinated with the Jøkelbugt Bay area for some strange reason so it was not really a burden.
The tongue of Zachariae was separated from the glacier that year (2012), a very unusual behaviour imho. This event went more or less unoticed, I discussed it with Mauri Spelto and he blogged it, but that is the only place I have seen / heard anything about it, except from what has been discussed in this thread.
Then I tried to scale things.
Petermann vs. Zachariae and Jakobshavn vs. Zachariae and I came to the conclusion;
What is all the fuss about? Am I the only who can see the potential here?
I hope not, it may be because a lot of scientists keep radio silence till when they release all their papers, lets hope so??
We all know the media hype about Petermann and Jakobshavn, you heard about Zachariae? Then try to Google it?
But the fact is Zachariae Isstrøm lost several times the glacier area in just 12 years (from 2002) than Jakobshavn lost in more than hundred years (from 1913), did you know that?
Jakobshavn reminds me of Shania Twain: That don't impress me much!

Please click on image to enlarge!!

Jakobshavn and Zachariae images below (same scale) and both from 2002.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on June 11, 2014, 09:30:02 PM
Isn't Zachariae the glacier with another glacier right next to it (one with a number or something), or am I mixing up my East Greenland glaciers?

When starting the ASIB I planned on writing a series about Greenland glaciers, but never got any further than Jakob and Peter, although I vaguely remember Zack being next in line.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 11, 2014, 09:40:36 PM
Neven,

Yes Nioghalvfjerdsfjorden or 79 North is just upstairs ( next door north of Lambert Land, named from a Dutch fisher/hunter btw.), although the name is fascinating there is not much business there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:06:55 PM
Found a new paper.
Northeast Greenland melting ice will accelerate sea-level rise (http://www.futuretimeline.net/blog/2014/03/22.htm)
Abstract found here.http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html (http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 11, 2014, 11:15:44 PM
Found a new paper.
Northeast Greenland melting ice will accelerate sea-level rise (http://www.futuretimeline.net/blog/2014/03/22.htm)
Abstract found here.http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html (http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html)

I wonder where they got the inspiration?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:17:13 PM
Epsen strikes again?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:23:29 PM
BTW Think you do have a point. Based on elevation map. That one has the shortest distance to get into the interior and that largest section of the interior.
Does have a problem though. Location, location , location. Most researches use military to help them into the interior and the military is in the south. Would be very costly to get up north and up untill the last few years held back by ASI. No ASI and presto you have a wide open door to move through.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 11, 2014, 11:32:43 PM
LRC1962,

Scientists are like anyone else, pick the low hanging fruits, pr and funds, and let the nerds do the rest.
It is the same way tourism evolves, backpackers first and then the business starts from there?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:42:52 PM
Guess it took research paper .
http://www.dr.dk/Nyheder/Viden/Miljoe/20140317134002.htm (http://www.dr.dk/Nyheder/Viden/Miljoe/20140317134002.htm) This one has good side-byside speed change comparison.
http://www.theregister.co.uk/Print/2014/03/17/previously_stable_greenland_glaciers_now_rushing_to_the_sea/ (http://www.theregister.co.uk/Print/2014/03/17/previously_stable_greenland_glaciers_now_rushing_to_the_sea/)
Study from ocean influence http://icyseas.org/2013/10/31/ocean-circulation-and-melting-glaciers-off-north-east-greenland/ (http://icyseas.org/2013/10/31/ocean-circulation-and-melting-glaciers-off-north-east-greenland/)
Another paper http://www.the-cryosphere-discuss.net/8/2331/2014/tcd-8-2331-2014-print.pdf (http://www.the-cryosphere-discuss.net/8/2331/2014/tcd-8-2331-2014-print.pdf)
Main other hits is the usual CD doing damage control by trying to trivialize the calving.
Hope this helps.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: CraigsIsland on June 11, 2014, 11:45:30 PM
LRC1962,

Scientists are like anyone else, pick the low hanging fruits, pr and funds, and let the nerds do the rest.
It is the same way tourism evolves, backpackers first and then the business starts from there?

"Opportunity"

And it's saaaaddddd...I can't think of any Shania Twain songs off the top of my head.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:46:27 PM
I cherry pick low hanging fruit on google. Unfortunately neven and ASIB monopolize the best when it comes to the Arctic. ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 11, 2014, 11:51:46 PM
Found Nature publication through another portal. Legal???
Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming
 (http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 12, 2014, 12:00:30 AM
I cherry pick low hanging fruit on google. Unfortunately neven and ASIB monopolize the best when it comes to the Arctic. ;)

Fairly new most of them (2014) and from skimming, some details pretty in-acurate, yes they are in a hurry now!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 12, 2014, 12:12:42 AM
A few nice images http://www.livescience.com/44115-images-northeast-greenland-glaciers.html (http://www.livescience.com/44115-images-northeast-greenland-glaciers.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 12, 2014, 12:25:57 AM
I limited google to 1 year.  Very little as you say previous to that. Media likes a juicy paper then picks out what they think are juicy facts then fill in the rest of the space with 'facts' .  Then leave it up to the scientist to try and get the real facts out.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: cats on June 12, 2014, 07:29:31 AM
I think Andreas Munchow is currently on the Polarstern headed to this area (http://icyseas.org/2014/04/14/north-greenland-glacier-ice-ocean-interactions-2014/ (http://icyseas.org/2014/04/14/north-greenland-glacier-ice-ocean-interactions-2014/) ) so perhaps there will be some more information and studies of this area soon.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on June 12, 2014, 01:28:34 PM
Scientists are like anyone else, pick the low hanging fruits, pr and funds, and let the nerds do the rest.
It is the same way tourism evolves, backpackers first and then the business starts from there?

I think this is a very unfair view of scientists.

First, scientist choose their research topics primarily based on their (or their supervisor's) personal scientific interests and the potential to achieve scientifically significant results. PR potential is rarely the top criterion. Funding is important of course, and that's why scientist spend a lot of effort in trying to convince funding agencies that what they want to research is worth funding.

Second, science takes time. The recent Nature paper mentioned above was published in March 2014 but submitted already in October 2013. The research very likely started months earlier, well before the first post in this thread, and quite likely some of the authors first became interested in the topic some time in 2012 if not earlier. There are likely other research groups currently studying Zachariae but have not reached a publication stage yet. Others are probably watching with interest but do not currently have the resources for a new project or are waiting for more data before starting a project. We just don't hear about these because scientists do not seek publicity for unfinished research.

Third, there are good reasons why scientists "flock" to the same glaciers. If you develop a new glacier model or a new technique for analyzing glacier data, what you want to do is to demonstrate that your new method is in some way better than previous methods, so you apply your method to a heavily studied glacier.

Sorry for this outburst. You may have guessed that I am a scientist myself though not in a field that has anything to do with glaciers or climate.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Steve Bloom on June 12, 2014, 09:34:51 PM
Espen, probably you're aware of this but quite a lot of advance information can be gleaned from scientific conference submissions, i.e. AGU, EGU and relevant specialist events.  Sometimes, there's a lot of detail in the abstracts or even complete posters, other times the juicy stuff requires being there in person (although AGU at least is rapidly expanding its video offerings).  Other times it's just a teaser, as in the last sentence of this EGU one:  http://meetingorganizer.copernicus.org/EGU2014/EGU2014-3872-3.pdf. (http://meetingorganizer.copernicus.org/EGU2014/EGU2014-3872-3.pdf.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 13, 2014, 07:10:55 PM
Scientists are like anyone else, pick the low hanging fruits, pr and funds, and let the nerds do the rest.
It is the same way tourism evolves, backpackers first and then the business starts from there?

Sorry for this outburst. You may have guessed that I am a scientist myself though not in a field that has anything to do with glaciers or climate.

And I am not an scientist ;) maybe a pre medialist?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: LRC1962 on June 14, 2014, 01:51:04 AM
From Wikipedia
A scientist, in a broad sense, is one engaging in a systematic activity to acquire knowledge. In a more restricted sense, a scientist may refer to an individual who uses the scientific method.[1] The person may be an expert in one or more areas of science.[2] Scientists perform research toward a more comprehensive understanding of nature, including physical, mathematical and social realms.
I think that is a good definition. You may not have a degree, but there is no question you fit the definition in my mind. You may not think yourself an expert, but based on what you have produced here you have produced many very high quality university level papers.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 20, 2014, 05:55:21 PM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fmap2.vis.earthdata.nasa.gov%2Fimagegen%2Findex.php%3FTIME%3D2014171%26amp%3Bextent%3D479936%2C-1157008.4460606%2C575936%2C-1021584.4460606%26amp%3Bepsg%3D3413%26amp%3Blayers%3DMODIS_Terra_CorrectedReflectance_TrueColor%2CMODIS_Aqua_CorrectedReflectance_TrueColor%26amp%3Bformat%3Dimage%2Fjpeg%26amp%3Bwidth%3D375%26amp%3Bheight%3D529&hash=18104a46d9918ebd388b41be90408b64)
I'm not quite sure what the line along the east of those islands represents. (it was there yesterday, so I think I can exclude cloudshadow)  My guess is a lead frozen over with thin ice which starts to loose snow cover before thicker ice. Am I correct? Is it of significance? Might it lead to earlier loosening of the landfast ice there?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 20, 2014, 06:27:10 PM
Andreas T,

It is definitely a lead, can be seen on this ASAR image from June 19 2014:

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 20, 2014, 07:00:53 PM
Here is a 15m hi-res detail from May 27 where the lead, if existing, should be visible. At first I thought not, then it shows as some extra smooth ice a bit to the right of this island.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 20, 2014, 07:06:29 PM
Wipneus,

With all respect, what does an image from May 27 2014 show?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 20, 2014, 07:23:31 PM
Frozen lead?

Or nothing perhaps.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 20, 2014, 07:24:14 PM
This seems to be an old lead, I think it can be recognized in this AVHRR image from January
http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201401030645.NOAA.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201401030645.NOAA.jpg)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 21, 2014, 09:58:45 AM
Zachariae update:

More movements and action

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 21, 2014, 02:39:48 PM
Andreas Muenchow has some nice photos of old bits of Zachariae near Isle de France
http://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/ (http://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/)
interesting to see them from a different perspective
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 21, 2014, 02:49:14 PM
Andreas Muenchow has some nice photos of old bits of Zachariae near Isle de France
http://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/ (http://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/)
interesting to see them from a different perspective

Yes those ice cubes really are impressive!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 05, 2014, 03:24:24 PM
Zachariae calving from in 15m res. Lots of melt ponds now, discolorings and all kinds of interesting creases, wrinkles and cracks are appearing

I will make a comparison with a previous date later to check the movement.

You must click the picture if you are ready for a 4M downlod.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 05, 2014, 03:34:55 PM
Zachariae calving from in 15m res. Lots of melt ponds now, discolorings and all kinds of interesting creases, wrinkles and cracks are appearing

I will make a comparison with a previous date later to check the movement.

You must click the picture if you are ready for a 4M downlod.

When I look at this image, (beautiful by the way) I can't help but get the sick feeling that  glaciologists are seriously underestimating the potential sea level rise due to glaciers. Not only this one but every single sea terminating glacier that is grounded below sea level. Just as they were surprised by having the Northeast Coast of Greenland getting unlocked, they will be registering surprise by how quickly these glaciers speed up, melt, calve and retreat.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Laurent on July 05, 2014, 04:15:52 PM
Seeing how many lakes will drain...yes, there will be lubrification...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 05, 2014, 04:38:27 PM
Here is an detail animation created with images on 2014-04-14 and 2014-07-03. Path/Row are the same:9/3 to minimize distortion.
My favorite hexagonal feature can be recognized (about 40% from the left, a bit above the middle) and helped me to measure the movement there: 31 pix to the right and 1 up. That translates to 5.8 m/day.

I am afraid the crack that will destroy my hexagonal feature, is already forming.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 05, 2014, 04:46:39 PM

I am afraid the crack that will destroy my hexagonal feature, is already forming.

Not to worry. Another hexagonal feature will form west of it soon although it will crack later.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 05, 2014, 05:00:13 PM
Thanks Wipneus!

Yes it is a very dramatic scene, and one of the more serious of the kind, I wonder where this will end in September, we are into the "land of retreat" everyday now!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 06, 2014, 10:46:24 AM
And now the last reminder animation for now, and my pet project, is it not impressive?

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 12, 2014, 10:37:53 AM
Zachariae is still on the move:

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 18, 2014, 04:03:00 PM
1 weeks movement at Zachariae Isstrøm:

Please click on image to start animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 20, 2014, 05:07:08 AM
It looks like Zachariae is slowing down a bit, but the calves move on:

Please click on image to start the animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 23, 2014, 06:55:28 PM
Talking about slowing down, Zach woke up to a sudden rush.
In a time span of just 24 hrs a lot of change is seen:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 23, 2014, 08:02:11 PM
the bay in front of Sanddal is quickly loosing its ice and with its entrance stick firmly closed by landfast ice it clearly is melting. Probably has been thin for some time. It always surprises me how this happens from the land side out. Is there enough runoff to warm the sea, is it the air warmed on the ice free surfaces?
http://1.usa.gov/1pd7Hzf (http://1.usa.gov/1pd7Hzf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 23, 2014, 08:15:46 PM
the bay in front of Sanddal is quickly loosing its ice and with its entrance stick firmly closed by landfast ice it clearly is melting. Probably has been thin for some time. It always surprises me how this happens from the land side out. Is there enough runoff to warm the sea, is it the air warmed on the ice free surfaces?
http://1.usa.gov/1pd7Hzf (http://1.usa.gov/1pd7Hzf)

Andreas,

It is very common the sea ice break from inside out, especially in the fjords where melt water from numerous rivers melts the sea ice. The same is the case around Sanddal (Sand Valley) and Kofoed-Hansen Bræ in the bottom of the fjord.

A good example is this shot from Hagen Bræ, where river water melts the sea ice:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 23, 2014, 08:25:39 PM
Or this from the extreme north (Flade Isblink / Marsk Stig Bræ), where the glacier actually function as a giant melt water river, note the nice delta to the right of the glacier (Prinsesse Ingeborg Halvø), probably the northern most delta system in the world:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 23, 2014, 08:59:46 PM
I find this more obvious where river waters have some distance to run and time to get warmed. In Sanddal it seems to be coming straight off the ice
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 25, 2014, 07:15:01 PM
Ice around Ile de France is breaking uphttp://1.usa.gov/1pkzrz3 (http://1.usa.gov/1pkzrz3)
It will be interesting to see how the flow up the east coast affects the still landfast ice.
I would expect higher temperatures near the surface, but how do deeper currents respond to that?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TerryM on July 25, 2014, 08:40:49 PM
Spring Tide today at NE Greenland so fast ice may be pulling out.
Terry
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on July 26, 2014, 02:38:16 AM
Spring Tide today at NE Greenland so fast ice may be pulling out.

Perhaps caused by the tide, there was a big calving:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 26, 2014, 05:41:53 AM
Spring Tide today at NE Greenland so fast ice may be pulling out.

Perhaps caused by the tide, there was a big calving:

No it was more a movement of already calved calves.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 28, 2014, 03:56:20 PM
Zachariae update, just a bit relocation of calves:

Will be interesting to see how the calves and the glacier will react when the sea ice is gone in a few weeks?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 28, 2014, 04:51:57 PM
Espen...

What does the northeastern face of the separated tongue look like?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 28, 2014, 07:25:25 PM
Espen...

What does the northeastern face of the separated tongue look like?

SharedHumanity,

This is an image from august 2013
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 28, 2014, 10:25:52 PM
Thanks Espen....looks like a  lot of  melt ponds on the ice last fall.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 28, 2014, 10:31:51 PM
Thanks Espen....looks like a  lot of  melt ponds on the ice last fall.

The remains will be depending on the sea, meaning in-situ disintegration and melt since it is now a "dead body".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 03, 2014, 10:00:31 AM
Fast ice is now cracking over big way (Aqua-MODIS Aug 2):
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 03, 2014, 11:12:39 AM
Wipneus it is actually not fast ice since it was almost all gone last year, but it is interesting to see that the Belgica Bank is holding on. There is no fast ice left in East Greenland, the only fast ice left around Greenland I can think of is a few spots between Hellefiskfjord and Sands Fjord
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 04, 2014, 06:06:11 AM
Zachariae update, still moving on:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 04, 2014, 08:23:38 PM
Nioghalvfjerdsfjorden / 79 N Glacier update, I wonder if this glacier is still alive, hardly no movements in over 2 months, maybe due to its next door neighbor Zachariae taking over calving business?: 

Please click on the image to start the animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 06, 2014, 03:18:20 PM
Sequence of Zachariae Jul 3 - Aug 4.
Obviously calving has been faster than the glacier itself. My favorite "hexgonal" feature is still visible.
During the 32 days between the images, the feature moved 7.5 m/day, faster than any measurement before. That could be because it is nearing the calving front, more inwards I measure a speed of about 6.7 m/day, that is still among the highest measurements.

(click to view 2.5M animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 06, 2014, 03:44:23 PM
Sequence of Zachariae Jul 3 - Aug 4.
Obviously calving has been faster than the glacier itself. My favorite "hexgonal" feature is still visible.
During the 32 days between the images, the feature moved 7.5 m/day, faster than any measurement before. That could be because it is nearing the calving front, more inwards I measure a speed of about 6.7 m/day, that is still among the highest measurements.

(click to view 2.5M animation)

Wipneus,

It looks like the southern part of calving front / area is moving more than the northern, the southern part is even expanding southward towards the hidden Kap. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 06, 2014, 04:07:59 PM

It looks like the southern part of calving front / area is moving more than the northern, the southern part is even expanding southward towards the hidden Kap.

Yes, in comparison the glacier is moving rather uniformly.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on August 06, 2014, 09:42:34 PM
there is a trough under the southern edge, i suspect warm water is coming in there. i believe i have posted some topo earlier, but i am very pressed for time and cannot verify.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 06, 2014, 09:48:58 PM
there is a trough under the southern edge, i suspect warm water is coming in there. i believe i have posted some topo earlier, but i am very pressed for time and cannot verify.

sidd

Yes Sidd, I know you are busy, yes I suspect a change is happening in the "southern front".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 08, 2014, 06:42:17 PM
Same Landsat image as in post #232, but compared with one taken April 14, 112 days difference.

Here is a detail of the 79N calving front, as Espen noted very little movement about 4 pixels which calculates to 4*15/112=0.54 m/day. Less then a tenth of the speed of Zachariae! Even the calving in progress is not making much progress at all.

(click to animate)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 08, 2014, 06:48:13 PM
Now this is 60km upstream. Here the movement is much faster, about 3.5 m/day.

(must click this one as well)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 08, 2014, 10:13:46 PM
Now this is 60km upstream. Here the movement is much faster, about 3.5 m/day.

(must click this one as well)

So the question is, what is happening in between? ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Hans on August 08, 2014, 10:36:07 PM
Now this is 60km upstream. Here the movement is much faster, about 3.5 m/day.

(must click this one as well)
A remarkable feature in the 2014-08-04 image of the animation above. The meltwater lake in the bottom-right corner has some faint echo imprints down stream. We have seen in other occasions that melt lakes year-on-year form on the same geographic location and don't move with the ice. Are these white spots the remains of the "same" melt lake in previous years?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 08, 2014, 11:25:49 PM
Hans,

It is called a watermark, you see them often in banknotes etc.  ;)

Nice catch by the way!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 09, 2014, 03:39:09 PM
Now this is 60km upstream. Here the movement is much faster, about 3.5 m/day.

(must click this one as well)
A remarkable feature in the 2014-08-04 image of the animation above. The meltwater lake in the bottom-right corner has some faint echo imprints down stream. We have seen in other occasions that melt lakes year-on-year form on the same geographic location and don't move with the ice. Are these white spots the remains of the "same" melt lake in previous years?

The only possible explanation for the melt lakes not moving is that they are related to the underlying topography.

The water marks suggest that Alan Greenspan is somehow involved.   ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 14, 2014, 11:19:35 AM
An evening (ascending part of the orbit) image of Zachariae shows more of the relief on the surface due to the longer shadows.

Enjoy (must click for a download of 3.5 MB image).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 14, 2014, 05:01:56 PM
Zachariae update, notice not a scratch on the former tongue?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 21, 2014, 07:04:08 AM
Here is the new piece from BBC on this region: http://www.bbc.com/news/science-environment-28852980 (http://www.bbc.com/news/science-environment-28852980)

"A new assessment from Europe's CryoSat spacecraft shows Greenland to be losing about 375 cu km of ice each year. Added to the discharges coming from Antarctica, it means Earth's two big ice sheets are now dumping roughly 500 cu km of ice in the oceans annually. "The contribution of both ice sheets together to sea level rise has doubled since 2009," said Angelika Humbert from Germany's Alfred Wegener Institute. "To us, that's an incredible number," she told BBC News.

Significant thinning is seen also in the North East Greenland Ice Stream (NEGIS). "This has three outlet glaciers and one of these, the Zachariae Isstrom, has retreated quite a bit and some volume loss has already been reported. But we see now that this volume loss is really propagating to upper areas, much further into the interior of the ice sheet than has been recorded before," explained Prof Humbert."

I chased down the article and the original graphic (which is much higher resolution but still badly anti-aliased, use http://pdfaid.com/ExtractImages.aspx (http://pdfaid.com/ExtractImages.aspx) for that (page 13, image 18). A lot of the color key was not used at all but for those that were, I worked out their percentages. (Seems like I discussed this article 2-3 week ago on the Jakobshavn forum when it was still being finalized.)

The real research action is not at the calving front but about halfway up to the ridgeline. A large consortium drilled the NEGIS core back in 2012 and those papers have now come out -- really first rate. The rate-of-loss image shows however that the Zachariae Isstrøm, while no longer slumbering, is not yet a major player in sea level rise.

Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2
V. Helm et al
http://static2.egu.eu/media/filer_public/ac/f2/acf2d697-4a67-433b-bfd4-2a1f569cdb86/tc-2014-18.pdf (http://static2.egu.eu/media/filer_public/ac/f2/acf2d697-4a67-433b-bfd4-2a1f569cdb86/tc-2014-18.pdf)

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)
P Vallelonga et al
http://www.the-cryosphere.net/8/1275/2014/ (http://www.the-cryosphere.net/8/1275/2014/)

Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming
SA Khan et al
Nature Climate Change 4, 292–299 (2014) doi:10.1038/nclimate2161
http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf (http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf)
http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf (http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf)

Inferred basal friction and surface mass balance of North-East Greenland Ice Stream using data assimilation of ICESat-1 surface altimetry and ISSM
E Larour et al
http://www.the-cryosphere-discuss.net/8/2331/2014/tcd-8-2331-2014.pdf (http://www.the-cryosphere-discuss.net/8/2331/2014/tcd-8-2331-2014.pdf)

Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream
BA Keisling et al
Annals of Glaciology 55(67) 2014
doi: 10.3189/2014AoG67A090 (paywalled but obtained)

Dilatant till facilitates ice-stream flow in northeast Greenland
K Christianson et al
Earth and Planetary Science Letters 401 (2014) 57–69
doi.org/10.1016/j.epsl.2014.05.060 (paywalled but obtained; also at DeepDyve)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 22, 2014, 03:52:27 AM
Because it doesn't have remarkable calvings or spectacular retreat, we tend not to pay attention to Humboldt Glacier but this area of the ice sheet appears to be losing elevation faster than Peterson or Zacharie.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 22, 2014, 06:29:43 AM
Zachariae update:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 23, 2014, 02:24:53 PM
Zachariae Isstrøm current retreat up date:

As you can see from the image below, Zachariae already retreated ( ~13,5 km2) considerably during the 2014 season, and the season is not over yet:

No changes on the former tongue.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 23, 2014, 06:20:20 PM
Here are the historic elevation changes and calving front positions along with transects up the main channels. It represents a prodigous amount of imagery acquisition and processing as can be seen from the Supplemental Material. Sidd posted parts of this before.

This is a very different system from the other glaciers, originating as it does on the distant central ridgeline above an area of abnormal but steady geothermal heat flux, with sharp shear margins and not much by way of tributaries. I've attached a radar transect that, while not quite the one we want, still shows that summit radar horizons -- and their ice dating -- get all the way to the coast with deformations mostly along shear margins and not so evident bottom freezeups like at Petermann.

Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming
SA Khan et al NATURE CLIMATE CHANGE | VOL 4 | APRIL 2014
http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf (http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf)
http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf (http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 23, 2014, 06:37:25 PM
Here are the historic elevation changes and calving front positions along with transects up the main channels. It represents a prodigous amount of imagery acquisition and processing as can be seen from the Supplemental Material. Sidd posted parts of this before.

This is a very different system from the other glaciers, originating as it does on the distant central ridgeline above an area of abnormal but steady geothermal heat flux, with sharp shear margins and not much by way of tributaries. I've attached a radar transect that, while not quite the one we want, still shows that summit radar horizons -- and their ice dating -- get all the way to the coast with deformations mostly along shear margins and not so evident bottom freezeups like at Petermann.

Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming
SA Khan et al NATURE CLIMATE CHANGE | VOL 4 | APRIL 2014
http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf (http://www.indiaenvironmentportal.org.in/files/file/greenland.pdf)
http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf (http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf)

A-Team,

One thing puzzling me, is if Zachariae is grounded as they describe it, how come those calves float around so freely?

(Maybe this belong to the stupid question thread?) 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on August 23, 2014, 10:27:24 PM
One thing puzzling me, is if Zachariae is grounded as they describe it, how come those calves float around so freely?

My (completely uneducated) guess is that during calving the bottom part of the calve crumbles into small pieces and the resulting calve is not as high as the calving front. The smaller pieces of ice between the big calves could be the remains of the bottom parts.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 23, 2014, 10:53:30 PM
Or maybe the Zachariae calves got a cork+ gene built in? ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 24, 2014, 12:00:44 AM
Espen, various possibilities. I did not enclose the locations of the depicted transects but see below. If you can align bed topography with satellite surface images, you might find the transects are farther inland than the calved pieces. Alternatively, the cartoon might not have attempted to depict the situation accurately ... wouldn't be the first time. Possibly but implausibly, the situation might have changed since that illustration was made.

Otherwise, no: pieces would not be free to move about. There is partial buoyancy and some flexure with tides but that can barely be detected with double interferometric SAR (example of Petermann posted in Jakobshavn forum).

On the technical side, the color errors in the bed DEM below should have been caught during peer review. The original submitted image and especially the depth key are so badly dithered that it is not possible to locate say the -1000 to -900 m regions (if there even are any), even by using H of the HSV decomposition which can sometimes save the day.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 24, 2014, 01:10:43 AM
I pulled out the Cresis file that constitutes the last part of the radar horizon montage in post #249. This area is a ways south of Zachariae though the upper horizons would still be representative in most respects. Einar Mikkelson/Sonaneibraeen might have been a specific target of the flyover.

The region (yellow arrows) where the Cresis picked surface (red) coincides with the picked bedrock (magenta) is presumably exposed bedrock though that doesn't fit with the imagery or the apparent trough.

You just know OIB flew lots of rasters and flowlines on Zachariae; the question is, stored under what file names, for which many years, for which radar configurations, which flight lines include the NEEM/Ngrip ridge, ie finding the optimum for the calving region. This would settle the channel bedrock depth and loose floe issues.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 24, 2014, 09:58:02 AM
Alternatively, the cartoon might not have attempted to depict the situation accurately ... wouldn't be the first time. Possibly but implausibly, the situation might have changed since that illustration was made.

Otherwise, no: pieces would not be free to move about. There is partial buoyancy and some flexure with tides but that can barely be detected with double interferometric SAR (example of Petermann posted in Jakobshavn forum).

On the technical side, the color errors in the bed DEM below should have been caught during peer review. The original submitted image and especially the depth key are so badly dithered that it is not possible to locate say the -1000 to -900 m regions (if there even are any), even by using H of the HSV decomposition which can sometimes save the day.

Yes A-Team I am sometimes very surprised how bad they present their findings, most with "Mickey Mouse" like graphic, but I doubt Zachariae is grounded as they show it?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 24, 2014, 03:08:53 PM
I can't imagine how a grounded glacier could be calving so quickly with tabular icebergs.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 24, 2014, 04:27:57 PM
I can't imagine how a grounded glacier could be calving so quickly with tabular icebergs.

Unless someone had a conveyor system installed for the purpose?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 24, 2014, 06:30:13 PM
Here is the radar data from 2012. It shows the surface and bedrock fairly clearly, maybe not exactly where we wanted.

The first is a funky reconciliation of the Cresis track icon, seemingly in mercator coords over a totally antiquated satellite image, with Cresis kml google earth projection over that poor quality imagery. Both should really stub in Howat et al's careful photomontage of the Greenland coast.http://www.the-cryosphere.net/8/1509/2014/tc-8-1509-2014.pdf] [url]http://www.the-cryosphere.net/8/1509/2014/tc-8-1509-2014.pdf (http://[url)
[/url]

Next I assembled the longer continuous track 20120514_02_007-010. Cresis has not prepared these properly so the overlap has to be manually removed frame by frame (short of scripting lat,lon interpolation). I cut off the rocks and the NW corner of 007. This image is 1289 pixels wide so won't display properly unless you click.

I shrunk the width by 50% while bumping vertical exaggeration to 200% after gaussian sharpening of the image with 'unsharp mask' and colorization. Gimp provides effortless initial tiling up of scenes, Filter --> Combine --> Filmstrip.

The third image looks at four slices going to the terminus. I left my thinking cap at the brewpub last night so could not adjust the offsets given the channel has a slightly skew latitude line and the flight lines, while blessedly parallel to each other are kattywumpus to the channel center line. To interpolate the missing sections out to 3D so as to reconstruct ice relative channel bedrock, I would want to combine Cresis' digitization of 2echo_picks with the Bamber 2013 bedrock DEM.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 24, 2014, 07:14:49 PM
Geat work A-Team, image 14 and 20 are identical?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 25, 2014, 12:51:55 AM
Espen, every time you ask for a fix, a whole litter of puppies goes to the pound.

Yes, that row should not have been duplicated. Also notice that when the plane flies a grid like that (ie boustrophedonically), alternate Cresis images will be laid out in the reverse direction. Two of those needed to be flipped above. (Of course that reverses the lat,lon text so that has to be fixed as well.)

There is also some major mickey-mouse in pixel proportionality to find the point of alignment which here I took as when the flight path was over the center Zachariae flowline. That is taken care of below.

I will look tomorrow to see if they ever had a flight right down the middle (surely). The radar swath is something like 100 m which would still leave a lot unobserved but a line across our sections would very much constrain interpolation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 25, 2014, 05:05:14 AM
A-Team it is amazing the fjord is relatively shallow between Skallingen and Lambert Land, that surprises me?
But then again that explains the reduced speed of the glacier, because of that "back pressure".
And why the ice wants to take the "no hazzle" way via the now free Zachariae highway.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 25, 2014, 07:28:21 AM
Yes, good analysis. Here is an interesting scene of an entire flight path from the summit due east down to the Zachariae area. Looks like one of these bottom-up freeze deformation of basal water.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 25, 2014, 05:08:14 PM
A lot more going on than meets the eye with the Greenland ice sheet. Especially in the north, ice-penetrating radar shows  massive deformations beneath the surface. The images below explore one of these slow melodramas, found on a 2012 radar flight path from the summit ridge en route to Zachariae, https://data.cresis.ku.edu/data/rds/2012_Greenland_P3/images/20120514_02/ (https://data.cresis.ku.edu/data/rds/2012_Greenland_P3/images/20120514_02/).

I've taken to displaying flight paths over a surface velocity map (rather than elevation), with the idea that major deformations would be associated with ice movement. However in this case, there seems to be no correlation with velocity, bedrock holes or bumps (shown as lowest radar horizon), surface elevation, surface slope, or ice stream shear margins of Vallelonga et al http://www.the-cryosphere.net/8/1275/2014/ (http://www.the-cryosphere.net/8/1275/2014/).

That seems to leave bedrock geothermal anomalies. Along the lines of Bell et al 2014, meltwater freezes up on the bottom, over time pushing up an incredible deformation of formerly ~ flat radar horizons. The timescale is not know yet; I presume tens of millenia in the making and ongoing today. The curie point Petrunin et al 2013 bedrock geothermal map does not extend this far north.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 25, 2014, 11:08:43 PM
I was curious about the extent of this deformation so looked at 2013 flight lines. It apparently shows up 71 km to the southwest in a slightly subdued form on Cresis scene 20130426_01_049. If so, this is quite a large sub-glacial feature as it could extend quite a ways to the northeast as well.

I added a depth - distance background grid. This shows the first deformation extends from bedrock at 2250 m up the 500 m from the ice surface. The feature in the second track starts at a similar depth but only extends 700 m up. The radar horizons above are in neatly draped wave and what may be a horizontal fold is seen to its east.

Without a handle on the shape and distribution of these features -- and the rheological properties of the ice in them --  the future behavior of the Greenland icesheet will not really follow from modeling off Glen's law and the assumption of tame horizontal ice layers to depth. These bottom freezeups are having a monumental effect.

Existing tracks may be rather sparse for this particular feature; I'll poke around uphill from Petermann where the density of sections is probably more favorable for accurately 3D structure reconstruction.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 26, 2014, 01:17:02 AM
I found a straight shot down the main channel of 79N (Nioghalvfjerdsbrae) from a 2010 DC-3.

In case you are having problems drilling down to exactly the frames wanted at Cresis, the first slide explains the procedure: start with the kml file for the year in question. That will open as many tracks in Google Earth. Mouse over the track you want and start to rename: this seems the only way to highlight the track's id in the Places column. Go to that folder and open its restricted kml file. Mouse over again to find the id of segments wanted. Then back up at the Cresis site to the image folder, verify with 0maps and then open the radar track with or without surface and bedrock markups.

The second image shows three consecutive segments of the channel flyover. It's a good idea to trust their markups of the bedrock because double and triple echoes beneath it are artifacts. Espen is more familiar with what this profile means for Zachariae so I will leave the interpretation to him.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 26, 2014, 04:45:16 AM
Hi A-Team nice work, as usual, it is the profile of 79Fjord you showing above.
But it shows when the back pressure was released at Zachariae (separation from its former tongue) the ice will naturally go the easiest way, and that is not "Route 79".  The steep bottom-end at 79 explains why the ice wants to go the Zachariae route and not "Route 79".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 26, 2014, 04:02:34 PM
Yes, this side of Greenland may be more exposed to Atlantic warm water which will strongly affect marine terminating glaciers. While that might waken them, it is not the whole story ... why this icestream is here in the first place, why it goes so much farther inland without the pronounced overdeepenings commensurate with its size, and what its discharge response can be without tributaries.

It is quite a different situation from Jakobshavn Isbrae and indeed the two don't seem to be connected.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 27, 2014, 03:11:53 AM
Here are three sections of Zachariae. The down-channel flight path is perpendicular to two subsequent cross-channel sections. I do believe ImageJ, somewhere in its many plugins, has the capacity to display the three sections intersecting in perspective with some degree of transparency and ability to rotate to a nice view. Meanwhile I used gimp as a start.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 27, 2014, 09:28:41 PM
Here I made the bump maps of the individual layers, erased some upper firn and radar echoes, and colorized them differently prior to applying perspective transforms with help from an underlying grid layer and then translucencies, all in gimp, for the 25 down-channel and 27 cross-channel.

If uploaded as a gif, blog visitors could download and turn any combinations of radar transects on or off. Maybe better but still not great.  In some key areas, the plane flew dense grids in both directions! PovRay is better in allowing parallel planes to be defined and textures (the radar sections) to be assigned.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 28, 2014, 04:20:52 PM
It is not possible to make a comprehensive account of the number and extent of freezeups in Greenland because flight tracks are still too sparse. However 3 people did examine all radar scenes (especially those from modern 16-element arrays) from 1995-2012 and map them (first slide below).

This is actually not too arduous because it amounts to just scrolling down composite pdfs provided at Cresis (or scripting a 1map filmstrip in gimp). The spectacular one I described above is called Northeast Greenland South in their 2014 report.

Not all freezeups have been described: see below or what about 20130415_01_015  at 68.600 N 35.484 W, 20130423_01_003 at 76.057 N 35.926 W, 20130423_01_022 at 74.937 N 28.753 W or the spectacular 20130423_01_033 at 73.445 N 47.137 W seen in 2013 flights.

It's not feasible to name freezeups systematically because their full extent cannot be determined without dedicated surveying, perhaps radar dragged behind snowmobiles. Two mega-complexes extending for tens of km are located upstream from Petermann and Zacharaie. No marginal freezeups have been found south of Eqip.

Take away the freezeups and most of the Greenland Ice Sheet interior remains plain vanilla layer cake, yet the freezeups are important because they warm interior ice which facilitates its flow. Jakobshavn is an exception, having neither freezeups nor pre-Holocene layers in its fast-moving overdeepened lower 40 km. Bedrock topography is important too; many scenes show lower radar horizons draped.

The NEEM borehole encountered a doubled over recumbent fold that did not get a mention but presumably is a portion of a basal freezeup, though the original drill team report attributes it to downhill ridge drift. Radar may have difficulty demarcating subtle freezeups at great depth or this feature could be too small. This would be the only core that has drilled through a freezeup feature -- annual layers are largely preserved despite the dramatic deformations.

The freezeups are classified by meltwater source and mechanism. The one at Eqip represents marginal freezeup of surface meterological water from meltlake and moulins as overhead ice pressure drives it up bedrock topography where it is subject to glaciohydraulic supercooling.

Those farther inland have to use water melted at depth by pressure and geothermal gradient that is available down drainages computed from the bedrock DEM. The bottom of NGRIP is -2.5º, the enormous pressure puts that above the melting point. Subsequent freezeups of this water down-drainage (and associated latent heat) have a profound advecting effect on the ice above which is 15-20 degrees cooler, deforming it up to a mile above.

The second slide shows the freezeups do not correlate with the surface velocity field except at Petermann (which is the main pressure meltwater outlet for the interior). The mid-elevation clustering would fit with a need for melt water source but radar attenuation could reduce detection higher up. Freezeups are not notably associated with bedrock topology (third slide) though surely ice movement over large rock projections deforms ice layers too. Only a single freezeup was validated by gravity modelling as not generated by side reflection from rock.

The remaining four slides illustrate freezeups, with special attention to Petermann where peak deformation is associated with peak surface velocity. I replaced postage stamps in the article with enhanced radar sections though these are still not at full resolution.

A lot more could be done to characterize the structure of freezeups that have been densely grid-sampled during bedrock mapping. To date, no one has dated freezeup onset or modeled their evolution over time. I suspect the margins would be very instructive in this regard; being less developed, they may retain information about early stages of formation.

Deformation, warming and softening of Greenland’s ice by refreezing meltwater
RE Bell et al
http://www.nature.com/ngeo/journal/v7/n7/full/ngeo2179.html (http://www.nature.com/ngeo/journal/v7/n7/full/ngeo2179.html) (abstract, paywalled)
http://www.nature.com/ngeo/journal/v7/n7/extref/ngeo2179-s1.pdf (http://www.nature.com/ngeo/journal/v7/n7/extref/ngeo2179-s1.pdf) (free, detailed supplement)

The slides are fairly complex so I set the animation at 10 seconds per frame, click if it doesn't start up.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 29, 2014, 10:30:19 PM
More calving and retreat at Zachariae Isstrøm between Aug. 22 and Aug. 29 2014:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 29, 2014, 10:51:38 PM
Retreat situation at Zachariae Isstrøm:

Please click on image to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 30, 2014, 08:14:07 AM
Here is the updated retreat situation between 2009 and 2014, below you find the Byrd Polar Research Center version prior to 2009:

As you can see, the tongue was completely separated from Zachariae Isstrøm in 2012.

As I was discussed with Mauri Spelto back then: http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/ (http://glacierchange.wordpress.com/2012/08/27/zachariae-isstrom-further-retreat-ne-greenland/)

Please click on images to enlarge!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 30, 2014, 04:02:17 PM
Meanwhile ... in the interior, very detailed studies of a site halfway down reveal what is going on above and below this unique icestream (which wasn't even identified until 1993). Probably will have to click on the 4th image below to get the short slide show running.

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)
P Vallelonga et al
www.the-cryosphere.net/8/1275/2014/ (http://www.the-cryosphere.net/8/1275/2014/)
The Cryosphere, 8, 1275–1287, 2014

K Christianson et al
Dilatant till facilitates ice-stream flow in northeast Greenland
Earth Planet. Sci. Lett., 401, 57–69, doi:10.1016/j.epsl.2014.05.060, 2014.

Basal conditions and ice dy- namics inferred from radar-derived internal stratigraphy of the Northeast Greenland Ice Stream
BA Keisling et al
Ann. Glaciol., 55, 127–137, doi:10.3189/2014AoG67A090, 2014.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 31, 2014, 05:37:13 PM
Certain aspects of Greenland-ology are just breathtaking in their audacity. The sheer laziness in not using all available radar data -- do we really have the luxury of dinking around in view of the coming decades?

Let's just say modern radar arrays are not technically worse than those used 15 years earlier so why would a 2014 paper confine itself to 1999 data? Two months in the field translates to ten months in the cubicle so that cannot be the excuse. Surely nine co-authors can find 20 minutes of research time between them.

I cannot picture myself as peer-reviewer reading very far into a paper where authors gesticulate in the general direction of an immense archive but do not cite year, flight, and frame. When 17 years of tracks are reviewed and ~100 rare internal deformations found but no records are kept or gallery provided, I would remind authors of ample storage opportunities on journal supplemental and institutional web sites.

Greenland radar data, ten$ of million$ of it, has largely sat unanalyzed in its archive from 1993 on. It is just unbelievable to me that the OIB science crew is allowed to step off the aircraft without rescaling, tiling, horizoning, and uploading of data -- why are we providing them with laptops?

Meanwhile, Sept 2014 with the last Cresis flight on 22 May, still no kml tracks or curve-fitted horizons -- batch processing rather than pipelining is so 1950's. And that awful photomontage of Greenland from the dawn of motorized flight: https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_063_0maps.jpg (https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_063_0maps.jpg)

Greenland radar evidently has a custom-and-culture problem relative to Antarctica; with croudsourcing it would be fairly easy to do an end run around some of the paid help.

Below I added the 2013 radar transects of the Zachariae icestream to the never-fully-utilized 1996-2012 sections. Given the lame search interface, it is mildly tedious to pull the 2014 but I have those as well.

The radar sections could be distilled with a classification scheme. Here I would toss the 'continuity index' -- its  Holocene overemphasis rather misses the point, which is the more deformable state below. In Greenland, the default vertical ice profile is unadulterated layer cake (eg everything east of Jakobshavn). The layer cake has never been mapped!

Beyond that, I would say topographic draping, shear margins, icesheet marginal turmoil, and bottom freezeups are the main interpretive classes. It would not take rocket science to provide an html 1.0 click-map or mouse-over popups. Interpolation of sparse tracks would consider flow anisotropy, the direction is known. The stratigraphy, often predictably conformal to bedrock, sometimes ignores it entirely for reasons that are surely informative.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 31, 2014, 09:36:26 PM
Studying the latest images from Landsat, I found some of the calves from Zachariae must be grounded somehow, since they don't  move as the other calves ( marked with red spots), the calf with the * even breaks apart:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 01, 2014, 09:20:37 PM
Awright, after a little learning curve with Google Earth, all the ice-penetrating radar tracks in Greenland, 1993-2013. The lower image will need a click to get it animated.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 01, 2014, 09:28:51 PM
Amazing stuff, it must terribly boring to do those flights across the ice sheet, but then the glaciers and other fringes must be an incredible experience. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 01, 2014, 10:40:24 PM
Yes, I think the flights are long, loud, cold, not without risk but rather boring over hours of layer cake -- really have to applaud the people providing this data.

I look forward to the day that you and I can rent online a radar or camera drone in Illulisat, fly it from wherever we are, to wherever want for the day, then knock off a post. No more scrounging around for journal articles.

I moved the full size animation into storage here: http://tinyurl.com/mppcwe8 (http://tinyurl.com/mppcwe8)

The still montage below shows the existing flight paths around the new NEGIS core site. I've labelled some of them -- that is key to actually drilling into right radar scenes. The bright yellow blotches shows bottom freezeups according to Bell 2014.

The background ice surface velocity map is from Vallelonga 2014 -- that grid of little arrows is more effective than color or contours in some ways. I don't know what software is used to make them -- the length and base of the arrows would be easy in gimp but the directions are another matter, probably involve a vector gis overlay.

Where am I headed with this? Oh, just curious if the freezeup by the N of NEGIS is actually a misinterpreted shear margin. Or vice versa. Something is a little fishy with all that basal melt from the geothermal hotspot on the ridge but the nearby freezeups are not associated at all with flow towards Zachariae/89N.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 02, 2014, 02:15:21 PM
Cresis is what's politely called a legacy database. In hindsight, unfortunate formatting choices were made in the early years (though 1993 was already five years into Photoshop on a Mac Plus) but changing anything now causes backward incompatibility. Actually it is quite easy to reprocess the entire archive.

Several groups are doing just that but it's not clear if anyone will provide a public server (or even share a big zip file). The main issues are optimal resolution enhancement and rescaling, automatic tracing of isochrons and curve-fitting, and serving data per user-defined restrictions (like EarthExplorer, next post).

We realize now that the mushy late Pleistocene ice between bedrock and the Holocene is critical to icesheet movement and history. It will require separate and sensitive contrast reprocessing. This means 'letting go' of what radar reflectors actually mean in electrical engineering or physics terms (propagation of electromagnetic waves through a variable dielectric medium has been under study since Newton).

Surface velocity vectors vis-a-vis flight track bearing are needed within radar images to interpret deformations, as are bedrock peaks and troughs (already provided), temperature column (especially pressure melt zone and basal melt status), presence of recurring melt lakes, and geothermal gradient (largely unknown).

Cresis still has not posted the kml files for April-May 2014. The y axis, for the first time, provides actual elevation (eg sea level WGS84 rather than surface elevations that end-users had to fix from a DEM.

If you should need those kml tracks, simply save any valid path from an earlier year as a text file (template). Then copy out lon,lat coordinates from one of the pdf files for 2014 before that text is rendered as graphic.

Select-all brings misc text (eg axis labels) along for the ride. However a previously prepared a spreadsheet with a number column of 1's and 0's, a sort can pull out the essential lines 1-6 and 17 out from each batch of 51 lines. It is also possible to reprocess lat,lon coordinates for a straight segment into a compass bearing (haversine formula) using lines 1 and 6..

Then, being very careful not to change spacing, replace the list of template coordinates with your own and give the file a new name in a plain text editor while retaining the .kml suffix

This will now display properly as a track in Google Earth which uses the same coordinate convention as Earth Explorer, negative longitudes for Greenland. The -9999 evidently puts your path on the earth's surface. The rest is kml overhead  -- only the coordinate line counts for anything: lon,lat,-9999 space. Kmz is a compressed version of kml, not needed.

In is also possible to add an image link back to Cresis in segmented kml files. Cresis uses very logical file name s so these urls are easily derived from segment name (eg by appending '_1echo.jpg'). Clicking on the segment in Google Earth then brings up the radar scan itself -- very convenient for fast investigation of interesting areas. That is shown in blue in the template below.

In fact multiple images can be added, creating a scrollable stack when viewed in Google Earth. Urls too: the description section below links back to this blog post from Google Earth as well as the master track pdf at Cresis.

In short, the capabilities of Google Earth are exceedingly under-utilized in Cresis kml files but images and urls are easily scripted in across the entire archive and posted to cloud storage. Alternatively the entire set of radar scans could be permanently added to Google Earth via 'post to community forum', just as touristic photos of glacier calvings are.

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document>
   <name>20070910_01.kml</name>
   <Style id="s_frame_highlight">
      <LineStyle>
         <color>ff804000</color>
         <width>3</width>
      </LineStyle>
   </Style>
   <StyleMap id="m_frame">
      <Pair>
         <key>normal</key>
         <styleUrl>#s_frame_normal</styleUrl>
      </Pair>
      <Pair>
         <key>highlight</key>
         <styleUrl>#s_frame_highlight</styleUrl>
      </Pair>
   </StyleMap>
   <Style id="s_frame_normal">
      <LineStyle>
         <color>ff804000</color>
         <width>2</width>
      </LineStyle>
   </Style>
   <Placemark>
      <name>20070910_01</name>
      <Snippet maxLines="0"></Snippet>
      <description><![CDATA[<a href="http://forum.arctic-sea-ice.net/index.php?topic=400.msg35833#msg35833">http://forum.arctic-sea-ice.net/index.php?topic=400.msg35833#msg35833 (http://forum.arctic-sea-ice.net/index.php?topic=400.msg35833#msg35833)</a> ...
<a href="https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140508_01.pdf">https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140508_01.pdf (https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140508_01.pdf)</a><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130402_01/20130402_01_025_1echo.jpg"/><img src=""/><img src=""/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130402_01/20130402_01_025_1echo.jpg"/>]]></description>
      <styleUrl>#m_frame</styleUrl>
      <LineString>
         <coordinates>
            -27.164,75.372,-9999 -60.351,77.213,-9999
         </coordinates>
      </LineString>
   </Placemark>
</Document>
</kml>

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 02, 2014, 05:36:36 PM
Ice-penetrating radar data is to Greenland and Antarctica as a CT scan or MRI is to medicine. No way can slumpage to the sea be predicted just from surface goings on and GRACE mass balance, any more than a medical issue diagnosed from flushed skin and a bathroom scale. Indeed, we see articles now on ice tomography and even Radon transforms (1917) making an appearance.

Gimp has an astonishing feature that makes it very convenient for reprocessing the Cresis ice-penetrating archive: it can not only read whole flight Cresis pdfs into layers but lets you pick any subset from the startup dialog. Each flight segment has 3 parts: overview maps at three scales (only the middle useful), the radar scan itself, and the radar scan marked up for ice surface and bedrock by work-study students.

The last of these is done wrong. A continuous line should have been used rather than dashed magenta, done as a separate transparency layer which sits over the primary radar scan if needed. The magenta should *never* have been dithered in irreversibly. They redeemed themselves somewhat by saving bedrock and surface lines as plotable numeric data (which however were not fitted to anything).

I'm not singling out Cresis for imagery incompetence here even though this was enabled 20 years ago in Photoshop -- I see the "layer error" every day in peer-reviewed climate science articles. I also see a lot of "secondary layer error" in which lots of information is economically encoded in a single layer (fair enough) but that information cannot be unpacked only because of poor palette choice and gratuitous final dithering for print. It's all so unnecessary -- gif layers kicked in back in '87. Have you ever see a piece of software that couldn't open a gif file?

Do maps right by habit and you, as well as the reader, can get on with the science -- and come back to it years later to do something else with it.

There are multiple reasons for wanting flight path segments as a stack of co-registered layers: crop out the borders with one click, remove the black box and scale ticks (which should be outside -- never, ever crush expensive data with internal scale ticks), remove overlaps so consecutive images can be tiled, rescale individual layers to a master scale, and consolidate segment overview into an animated map. This reduces the number of files in the archive 6-fold.

Not to be believed: on a single flight, the data is broken up into segment images of ~ 50 km but these do not partition the data (the images overlap by variable amounts, not provided) nor do they use the same scale (scale not provided). Since features of interest, like an isochron line or freezeup deformation, can run over several consecutive frames, the user faces a nightmare scenario in reversing segmentation on any scale. This may require crowdsourcing to fix but then we have a crowd.

It is easy in gimp to add map overview to segment radar data: after import, chain all the overviews so that they move up as a block (relative to stationary radar data), just high enough so used portion of the lower right corner overview is sticking its head up. Here canvas size has to be enlarged, one layer brought to 'image size' (meaning canvas size) and then all layers brought to canvas size via 'fit canvas to layers' (meaning, in gimpspeak, 'fit layers to canvas').

Cropping then reduces to final minimal size. However, I prefer to first move the lat,lon text block as high as possible in the image. The filmstrip fuses layers as a single horizontal line, so the text block can be moved up to the lowest bedrock level found by the flight path. The reason for doing this not just file size: radar echoes below bedrock are artifacts that would affect the histogram and so affect contrast adjustment.

The flight path segments literally show the flight path as flown, no convention on decreasing lat,lon. That means on a grid, half the images need to be reversed. That reverses text, which is rendered as raster by this point. Text as text is still around in the pdf but it takes a script (or horizontal db sort) to reverse order, and more to put it back under the horizontally flipped image.

High precision digital lat,lon numbers are crazy-making. Stop,start coordinates have to be retained but intermediate values could be taken from where the track met a sensible grid so disparate frames can be intersected. The flight id should be removed from the top and replace the self-evident km,lat,lon abscissa explanation repeated thousands of times. The lat,lon system itself should use the NSIDC/Google Earth/Landsat convention (negative longitudes for Greenland).

I'm not sure whether hairpin turn data has any value -- it might be better to segregate it out and only retain straight line segments. Most flights are indeed straight lines, with the only useful exception those that follow the summit ridge line.

There is a huge issue around scale and composition: are the images provided at the maximal resolution of the original data; if not, has this undercut our ability to enhance lower ice layer contrast?

The image below shows EarthExplorer being tricked into serving up exactly the radar data someone is looking for:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 03, 2014, 01:47:49 PM
Here is pseudo-code that loads the entire Cresis archive, both Greenland and Antarctica, onto Google Earth. The color highlights show two little strings needed for later systemic 'mail merge' insertion.

Clicking on any segment of interest calls up the full resolution radar scan (with or without surface and bedrock annotation) as well as the segment map.

The link back to the Cresis pdf can be replaced one to plain text there, as processed for segment bearing, lat lon start/stop, and properties associated to the segment taken from other databases such as DEM, ice thickness, surface velocity magnitude and bearing. That information could also be placed in the Google Earth 'get info' box.

https://data.cresis.ku.edu/data/rds/
 https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/
   https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/kml/Browse_Data_20130426_01.kml
replace
      <Snippet maxLines="0"></Snippet>
      <styleUrl>#m_frame</styleUrl>
with
      <Snippet maxLines="0"></Snippet>
      <description><![CDATA[<a href="https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20130426_01.pdf">2013_[/color]Greenland_P3/pdf/20130426_01.pdf]https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/pdf/20130426_01.pdf (https://data.cresis.ku.edu/data/rds/[color=purple)</a><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_1echo.jpg"/><img src=""/><img src=""/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_1echo.jpg"/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_0echo.jpg"/><img src=""/><img src=""/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_0echo.jpg"/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_2echo.jpg"/><img src=""/><img src=""/><img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130426_01/20130426_01_026_2echo.jpg"/>]]></description>
      <styleUrl>#m_frame</styleUrl>

    process next file in line 3 folder, repeat until exhausted
   process next file in line 2 folder, repeat until exhausted
 process next file in line 1 folder, repeat until exhausted
post to cloud
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on September 03, 2014, 02:33:58 PM
@ A-Team:

Are your detailed comments about graphics file or the actual data files that contain x, y, f(x,y) with physical units attached?

Which radar data files do you recommend using in scientific inquiries?

I use the .pdf or .jpg files merely as a guide to the actual digital data where x is longitude, y latitude, and f(x,y) anything the radar (or laser altimeter) measures.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 03, 2014, 04:44:08 PM
Andreas, right, there are different ways to go. Cresis is really built around MatLab format as you mention. However I only use open source methods on this blog (not $2300 proprietary software with big learning curve) to encourage broader visitor engagement with data -- someday we may need crowdsourcing help in curating these scans.

Below I finish stripping out the Cresis archive to Google Earth which is freeware widely used by educated laypeople. I also stripped in the main Greenland relational databases Bamber/Howat/Helm/Joaghin to potentially put more blogger boots on the ground.

You raise a very interesting question, whether there is any better resolution in the f(x,y) numeric data than in the default graphics provided. I would say no. Or at least all Greenland journal articles use the latter.

However a couple of people are coloring Greenland scans according to line by line vertical integration of radar attenuation and displaying them Antarctic-style in iView4D (again, proprietary with free viewer). Bump-mapping definitely improves visuals but I have not seen it used yet to implement a scientific parameter. 

C Panton is the only person I have seen publishing anything intelligent wrt horizon enhancement. Obviously Pleistocene ice contrast needs to be sharpened to the max before auto-digitizing stratification. I think it is a mistake to optimize each scan segment separately when there are intersecting flight paths, nearby grid lines, and multiple years of data on NEGIS, Petermann and Jakobshavn.

It is just astonishing to me that no one has reconstructed 3D subglacial deformation structures when fast free and friendly ImageJ is sitting there with all the necessary plugins for analysis and visualization. I would think these would be laterally anisotropic and bilaterally symmetric wrt the direction of ice flow, with the edges less developed and so revelatory of earlier formation history.

It is vastly more efficient for 2-3 people to do the skilled reprocessing so the kazillions can work off an advanced launch platform. We learned that during the human genome project -- far better to have the assembly, gene tracks and browser as a service provided by specialized professionals rather than rebuilt over and over by incompetent mds as it takes time away from their competency in disease research.

Here is pseudo-code that loads all useful text from entire Cresis archive, both Greenland and Antarctica, onto Google Earth, along with surface velocity, bedrock depth and ice thickness at the midpoint of the track segment.

Not all flight paths are perpendicular (resp aligned) to the direction of ice movement and so those motion component magnitudes need to be provided for interpretation of deformations.

https://data.cresis.ku.edu/data/rds/ (https://data.cresis.ku.edu/data/rds/)
 https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/ (https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/)
  https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140521_02.pdf (https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140521_02.pdf)

#download pdf, open in any pdf viewer, select all, paste into plain text editor to dump images, retain text
#open in any database reader such as excel, import with break at 78 lines per record
#create a derived database:
 line 21 extract string with LEFT(xxx,15) to RIGHT(xxx,45) to extract scene name (result 20140429_01_011)
 line 31 extract string with MID(xxx,9,6),-MID(xxx,18,6) to obtain start lat,lon (result 69.321,-49.965)
 line 36 extract string with MID(xxx,9,6),-MID(xxx,18,6) to obtain end lat,lon (result 68.963,-49.982)
#haversine bearing of flight segment http://mathforum.org/library/drmath/view/55417.html (http://mathforum.org/library/drmath/view/55417.html)
  #convert decimal degrees to radians
    mult 0.017453293 radians/degree
  # bearing angle east of north
      = mod(atan2(sin(lon2-lon1)*cos(lat2),cos(lat1)*sin(lat2)-sin(lat1)*cos(lat2)*cos(lon2-lon1)),2*pi)
#extract direction and magnitude of surface velocity field from Joaghin 2012 using central lat,lon above
#determine ice velocity components Vx,Vy into and along plane of radar section
#extract ice thickness from Bamber 2013 using central lat,lon above
#extract bedrock depth from Bamber 2013 using central lat,lon above
#add 8 fields of derived database to Google Earth descriptor <description>put here</description>

    process next file in line 3 folder, repeat until exhausted
   process next file in line 2 folder, repeat until exhausted
 process next file in line 1 folder, repeat until exhausted
post to cloud

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on September 03, 2014, 05:21:29 PM
Andreas, right, there are different ways to go. Cresis is really built around MatLab format as you mention. However I only use open source methods on this blog (not $2300 proprietary software with big learning curve) to encourage broader visitor engagement with data -- someday we may need crowdsourcing help in curating these scans.
I totally agree with the sentiment and despite being a scientist, I do NOT use MatLab or any other software requiring licensing fees, pay-walls, or black-box-magic. I love coding in shell-scripts and Fortran (not kidding, I am a dinosaur, but one not yet dead  ;D ... have a look at http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf) (open access) as a remote-sensing and glaciology paper using some of the data streams we are discussing here (I was then only interested in Petermann Gletscher).

You raise a very interesting question, whether there is any better resolution in the f(x,y) numeric data than in the default graphics provided. I would say no. Or at least all Greenland journal articles use the latter.

I respectfully disagree. Native digital resolution (information content) is ALWAYS better than ANY graphic files. These files usually include information loss and even when it does not such as with GeoTiff, then the display of such files on a pixelated surface (a computer screen or piece of paper) ALWAYS reduces actual resolution.

All that said ... I agree totally with your sentiment that public data collected at tax-payers expense should be made accessible in both graphical and digital form. Strength in diversity.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 03, 2014, 09:36:28 PM
"Native digital resolution (information content) is ALWAYS better than ANY graphic files."

Mmm, it depends on useable bit depth (aka significant digits base 2). They are entirely equivalent at 8-bit depth. That is, BMP graphics format will take any f(x,y) matrix of numbers normalized and truncated to that bin depth and makes a completely equivalent graphic out of it: run it the other way, the exact same starting matrix will be recovered from the graphic.

Yes, you can use pi computed to 100 million decimal points to figure the area of a circle but no, you won't learn anything from doing it. Insignificant digits are like bad poker hands: anyone can hold them, disciplined players fold them. For a reason.

You can see from histograms of Cresis graphics -- even pure layer cake, below -- there is nothing remotely resembling 16-bit depth in radar significant digits. Notably, the critical Eemian layer is totally blown out, I'm not even seeing 4-bit precision. We're not really trying to do much more here than watch the autosnake follow along on a horizon or measure thinning away from the summit. Just peak and trough position, not values.

In hindsight, probably a total community screw-up in not re-imaging the f(x,y) contrast contextually. We may need to bring in a really bad-ass digital signal processor to squeeze out the last drops of water here. Weak contrast has been beaten to a pulp in software because of medical imaging.

We went round and round on this topic already with Landsat-8 GeoTiff. The panchromatic comes as 12-bit grayscale, advertised as 16 bit. Indeed tight histogram scenes benefit from that extra precision. However once fully exploited by contrast stretching, no utilizable information is lost dropping back down to 8-bit.

ImageJ can do 32- and 64-bit too though it is rarely asked; Gimp can hold 1000 channels of 24-bit RGB color without breaking a sweat. Wavelet decompositions of optical satellite Greenland poop out already at level 5, why do 10. White snow, drab clouds: nobody home.

I've seen quite a few published examples in Greenland science of certifiably preposterous retention of insignificant digits. There is no usable information in presenting the Bølling-Allerød horizon to the nearest micron when the radar reflection appears ten meters thick.

On the other hand, I'm ok with with someone trying to measure a one meter per year slide of upper ice sheet or isostatic post-glacial rebound with every scrap of high precision dual-phase GPS they can get their hands on.

I never had much use for f(x,y) thinking as a math professor. Research mathematics is not actually done that way but rather bootstrapping off a good picture of the first non-trivial example, say a Hopf fibration. That can quickly morph into incomprehensible publications on irreducible representations of exceptional Lie groups breaking on non-abelian gauge theories. Of course those are written up back in f(x,y) by way of obfuscation.

I think f(x,y) thinking is a big mistake here too, same reason. I myself look for something completely mindless in exploring large-dimensional parameter spaces (eg dragging gimp contrast curve ~ the space of differentiable functions, lots of them) -- the human visual system, especially on autopilot, rarely lets a good pattern fly by. Sure, I might write this up as monte carlo convoluting some cost potential function against a numerical f(x,y) array but I certainly wouldn't do it that way. Not when Gimp has real-time preview.

Nice Petermann article ... and thx for sticking to open source! If I may ask, what is your initial reaction to the RE Bell 2014 deformation paper doi:10.1038/ngeo2179 as far as upstream Petermann goes? It is a total zoo over there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on September 04, 2014, 12:09:36 AM
@A-Team:

I suspect that we mean the same thing, but different disciplinary backgrounds make us use words that have different meaning in different communities. A graphic to me is alway a pixelated version generated from measurements that are not necessarily pixelated (= measured on a regular grid). Measurements are expressed as digits (=numbers) that also carry units. In order for the digit to have meaning (be significant), someone else must be able to measure the process and get the same result. We agree on pi and poker.

I do take offence, however, when you judge that f(x,y) thinking is a big mistake, but perhaps I do not know what your words mean as they may originate from a community using language that I do not speak or think. I take f(x,y) as a simple dependent variable f that depends on some other variables (usually space-time). All are measurements that have acceptable ranges, errors, and units.

The number (=digit) with units always suggests a measurement which also suggests a range of what is reasonable and what is not. This measurement error determines the number of significant digits that an f(x,y,z,t) as well as the (x,y,z,t) carries. There is no point to represent a process that only knows 1 and 0 as a 2-bit number when 1 bit will do perfectly. We agree that a process measured accurately (a number with units this also) at the level of a 2-byte number should never, ever be represented as a 1-byte number. This is waste, it throws away useful information. I suspect that this is what you complain about. It is not discretization that matters, it is discretization relative to measurement error in f and x and y and z and t.

Real things in the real world have real units or scales with real units. So, I correct my prior statement that "Native digital resolution (information content) is always better or equal than any graphics files." It is possible that I abused the word resolution which may have different meaning in different communities. In well-designed physical experiments digital resolution should be close to accuracy of the measurement to maximize efficiency.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 05, 2014, 04:12:19 PM
Indeed it just sounds like  differences in specialty languages. Great but the discussion has got me fretting about what the actual vertical resolution in these radar images (hopefully not set by printable page sizes, 1993 and all that).

The scale right now is about 3000 m vertical to 51 000 m horizontal for an aspect ratio 17:1 but could the data have supported say 34:1? No one would be so crazy as to set out on striation markup without maximizing this, yet...

It is a curious situation (now that the bedrock DEM is behind us) in that it would be ok to trade off horizontal for better resolved vertical. There would also be advantages in completely reprocessing the Cresis archive using curvilinear surface/bedrock masking prior to contrast adjustment.

The real gain comes from further partitioning that mask with above/below Bølling-Allerød on flight segments where that is available. However the authors collecting that data islandwide never did anything with it, other than posting a spreadsheet with 495,000,000 cells.

Here is the last bit of pseudo code. Its output is a small Google Earth kml file letting anyone load all 21 years of radar overflight attaching radar horizon imagery to flight path segments. That enables very rapid analysis of all data from all years covering a regional sub-glacial feature, for example a freezeup above Zachariae (see grid overlay below).

Since the radar imagary is not degraded in any way in the Google Earth display and captured cleanly by whole-window screenshot, it is very easy to make trajectories through data from all years. On a Mac, 'command option shift space' puts the image into clipboard, open new window Preview on Mac implements that, horizonal flip fixes grid issues, saving as is as an 'Untitled' document series retains capture-order on disk upon name sort, open as layers gives co-registered images in correct sequence and orientation in Gimp, thus animating the trajectory after intermediate frame interpolation.

This yields perhaps ~20x savings in time needed per feature in getting the data to the human interpreter. The alternative described above for the EarthExplorer web portal is more easily scriptable: the analyst draws a line segment over the flight path display, lat,lon intersections are found based and a gif layer animation created that automatically opens in a new browser tab. Either way, all ~200 regions of putative bottom freeze-ups could be galleried up in a day.

Flight paths are broken into segments of ~50 km. These segments are critical to extracting only the radar imagery wanted for a specific investigation but now are only displayed in Google Earth within the lowest level of the Cresis file hierarchy, not within the second lowest level (flight paths for a given year).

Although Google Earth is capable of displaying the attached imagery for each segment, Cresis did not implement that feature which is just a single kml description line). The pseudo code fixes this, building the appropriate jpg url from the blessedly systematic file storage nomenclature used at Cresis. Only the unannotated 1echo image is attached here; 0maps and 2echo can easily be added or substituted. The image appears instantly upon clicking on a segment; the url itself appears in Google Earth's 'Get Info' box.

The segments themselves are broken into 42 sub-segments, probably to record intermediate surface elevations along the flight track. These sub-segments are not displayed in Google Earth and can only be accessed by opening kml as plain text. Since lat,lon are given to 14 decimal points each (hello?) and the kml files are otherwise rather simple, sub-segments take up over 90% of file size. The pseudo code below captures just the start,stop coordinates of the segment, rounding them to 3 decimal places. (The sub-segment data provided local slope, subsumed already in making the surface and bed elevation maps.)

#replace spaces (%) with tabs (^):
%-
#with:
^-

#replace:
^^<Snippet maxLines="0"></Snippet>
^^<styleUrl>#m_frame</styleUrl>
^^<LineString>
^^<coordinates>
^^^

#with:
^^<Snippet maxLines="0"></Snippet>
^^<description><![CDATA[<img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/[chars7-24 line2]/images/[chars 7-18 line2]/[chars 7-22 line2]_1echo.jpg"/>]]></description>
^^<styleUrl>#m_frame</styleUrl>
^^<LineString>
^^<coordinates>
^^^[round(col4,line7triple,3)],%[round(col46,line7triple,3)]

^<Placemark>
^^<name>20130410_01_050</name>
^^<Snippet maxLines="0"></Snippet>
^^<styleUrl>#m_frame</styleUrl>
^^<LineString>
^^^<coordinates>
^^^^-48.84072,69.91995,1010.15 -48.84833700000001,69.90869000000001,985.39 -48.85561,69.89740399999999,1053.44 -48.862802,69.886115,1008.66 -48.870437,69.87485599999999,1004.84 -48.87799200000001,69.86359400000001,842.1499999999999 -48.88549699999999,69.852327,967.3199999999999 -48.893065,69.841065,890.01 -48.900456,69.82979,904.54 -48.90784699999999,69.818516,1129.6 -48.915329,69.807247,1079.1 -48.922738,69.795974,1049.71 -48.930155,69.784705,1315.3 -48.937808,69.77345099999999,1318.06 -48.94497499999999,69.76215999999999,1056.32 -48.952355,69.750888,948.4900000000001 -48.959784,69.73961799999999,970.55 -48.966967,69.728329,1079.28 -48.974771,69.71709199999999,1058.1 -48.982143,69.70582,1096.82 -48.98886900000001,69.694501,1143.99 -48.996553,69.68325299999999,1157.22 -49.003971,69.67198399999999,1012.28 -49.011848,69.66075499999999,1003.4 -49.019463,69.649501,1023.64 -49.026066,69.63817,1087.93 -49.033758,69.62692699999999,1073.76 -49.041128,69.615661,990.2499999999999 -49.048318,69.60438000000001,1024.19 -49.05747600000001,69.593271,1106 -49.064368,69.58196599999999,1082.09 -49.071746,69.570701,1112.34 -49.07907,69.559427,1046.94 -49.08600200000001,69.548125,971.03 -49.093245,69.536845,951.67 -49.10017,69.525542,911.59 -49.107079,69.514239,974.0700000000001 -49.11463499999999,69.50298600000001,943.26 -49.121832,69.491702,982.51 -49.12898400000001,69.480418,1015.09 -49.13621899999999,69.46914099999999,920.21 -49.13757400000001,69.467044,916.28

^<Placemark>
^^<name>20130410_01_050</name>
^^<Snippet maxLines="0"></Snippet>
^^<description><![CDATA[<img src="https://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130404_02/20130404_02_062_1echo.jpg"/>]></description>
^^<styleUrl>#m_frame</styleUrl>
^^<LineString>
^^^<coordinates>
^^^^-48.841,69.920,1010.150 -49.138,69.467,916.280
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 05, 2014, 08:09:02 PM
Easy to get carried away with extraneous capabilities of Google Earth and forget why you came there. Here I have picked an area of study and started marking up 1993-2013 radar track data (bottom layer) I want to extract with thickening of lines indicating the radar horizon image is loaded and color indicating polarity (east to west, north to south taken as positive).

I'll be happy to get the data into gimp. Google Earth has no undo command whatsoever. It responds irreversibly to mouse-overs even when not the active software. It saves but doesn't say where or under what name. It is somewhat aware of standard interface conventions yet one commonsensical but unfortunate click can send it into a tailspin. However it is a very serviceable interface to the Cresis data and would not take much to automate.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 05, 2014, 08:16:21 PM
A-Team you are unstoppable ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 06, 2014, 01:01:37 AM
I may have gone too far this time, Espen. No idea how to get back and only a couple hours of battery left. Was trying to make the point (inset, upper right) that there are 2-3 irregular tracks from other years angling across the more favorable rectilinear grid. The idea here is make the 3D model from the grid alone, that is, hold back the cross-grid tracks to test model interpolation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 06, 2014, 06:07:24 AM
Easy to get carried away with extraneous capabilities of Google Earth and forget why you came there. Here I have picked an area of study and started marking up 1993-2013 radar track data (bottom layer) I want to extract with thickening of lines indicating the radar horizon image is loaded and color indicating polarity (east to west, north to south taken as positive).

I'll be happy to get the data into gimp. Google Earth has no undo command whatsoever. It responds irreversibly to mouse-overs even when not the active software. It saves but doesn't say where or under what name. It is somewhat aware of standard interface conventions yet one commonsensical but unfortunate click can send it into a tailspin. However it is a very serviceable interface to the Cresis data and would not take much to automate.

A-Team interesting to see there was not much interest in 79 compared to Zachariae.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 06, 2014, 04:13:37 PM
Yes and interest waxed and waned even there. The big grid fly-over was in 2010 by DC-8. That was supplemented by P-3 flights in 4 other years. In some cases, those provided exactly the missing grid lines, though probably with quite different radar arrays.

However these flight lines were archived as ~50 km units that are inconveniently chosen with respect to grid cells. The flights themselves were not quite north-south/east-west but approximately aligned with and against ice movement.

Going off into the weeds, one of 'vertical' lines was not up a meridian, moving from 26.914 to 26.662 or 5.5 km off vertical and the 'horizontal' grid line hopefully 'orthogonal' went from lat 78.494 to 79.515 or 3.0 km off constant latitude, both over ~50 km using http://www.movable-type.co.uk/scripts/latlong.html (http://www.movable-type.co.uk/scripts/latlong.html).

I don't know who requested this coverage nor what became of it in terms of publications. It may just represent a parcel of programmatic coverage of marine outlet glaciers: bedrock troughs and sills, surface thinning and ice shelves.

The image below illustrates some of the technical issues involved in using flights here -- one of the most intensively surveyed areas in Greenland -- to extract 3D structure from bidirectional 2D slices. Just pulling up archived imagery, re-tiling flight segments, and aligning relevant parts along a meridian (or subglacial feature axis) is already quite a chore.

I'm just about there with that but then there is the issue of display manipulation and interpolative software for doing this effortlessly (as a petroleum geologist or xray technician would).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 06, 2014, 11:27:19 PM
Here is how those flown grid lines up from 89N and Zachariae stack up for lat,lon according to the kml overlays as measured Google Earth.

I've also added the direction of icestream flow down from its summit origin (bright red arrows); it is considerably broader than shown. Three earlier flights came directly down the center (considered later). Ordinary icesheet flow, ~50 m/yr, comes from the left. Flow direction is quite oblique to the grid flown.

Measurements show that grid 'squares' are neither square nor even rectangular, even making allowances for spherical earth approximations, deepening the mystery of flight plan intent. The left edge of the grid is 98 km.

I've added an underlay (yellow spray paint) of very approximate positions of bottom freezeups reported by RE Bell 2014. Even though this is one of most intensively areas in Greenland, track density still does not provide adequate sectioning 'resolution'. That is, the freezeup features, though maybe a dozen sq km in extent are too small for detailed 3D reconstrucion. Drone radar -- not yet available for Greenland -- can easily provide the cross sectional coverage required.

It is also quite feasible, as explained a few posts back, to re-process the entire Cresis archive (in the pdf per-flight format) and mark up every intersection of every flight segment with every other segment after WGS84 y=mx+b considerations, noting every angle of intersection (relative bearing).

This would allow auto chaining up of every flight into one giant islandwide grid system. It is custom and culture for the database host to provide or at least serve these large pre-computes. Conceivably it lies in the matlab sector of the archive. It must have been done at some point within Bamber 2013 to arrive at the bedrock net prior to re-gridding. The EarthExplorer server and mid-level GIS software routinely provide intersection data.

However next post shows a quick way of doing this yourself without writing a line of code, purchasing proprietary software, or waiting upon an institution to implement.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 07, 2014, 04:32:08 PM
It is straightforward to build an flight path intersection tool and proximity detector. Begin with the simple flat-file database described above -- all the text, none of the images -- found in the pdf files Cresis provides for each flight.

There are 22 flight groups for Greenland from 1993-2014. These average a dozen or so individual flights, and those flights average a couple dozen flight segments.  For each flight pdf rendered as text extracting cells 61-62, 85 and 120-121 and re-tabbing reduces archive to a manageable 3-column, ~6800 line excel-type database of the form:

Data Frame ID     StartLatCoordN  EndLonCoordW
20140409_01_019   78.798          26.583
20110511_03_001   78.519          23.219
20100413_01_001   78.912          22.885
20030512_01_029   78.313          23.579
19990517_01_014   79.107          26.460


To find all flight segments "in proximity" to a given segment (eg 20100413_01_001), first consider its bounding box (below, dotted box around gold arrow). This consists of its horizontal longitude constraint intersected with its vertical latitude strip, which are determined by the start, end coordinate pairs (lower left, upper right corners of bounding box).

In the example illustrated, the dark blue arrow actually intersects the initial flight segment whereas the green segment is merely in proximity (one foot in bounding box) and could not quite be used to chain out a continuous grid from the initial segment. The purple flight segment arrows might also be considered in proximity depending on how loosely that parameter was set whereas the pink arrow is probably out of bounds in terms of relevance.

Sorting the database first by the latitude column and then by longitude quickly selects all records with a foot within the bounding box (or however conditions are relaxed), in this case the blue and green arrows.  A brief linear algebra consideration (two line equations y=mx+b) gives the common point of intersection of the blue line with the initial gold segment but the point from the green line intersection does not fall on the green arrow.

Note in the case of the flight path of the gold arrow, the previous and subsequent flight segments are known to slightly overlap so both qualify as intersecting segments. Here the points of intersection indicate redundancy and so guide automatic clean fusion (ie tiling) of consecutive flight segments.

Iterating now off the blue arrow, the full grid of intersecting ice penetrating radar sections that include the initial gold segment can be chained out to a specified number of rounds or for a larger bounding box.

This database could be constructed just once and then provided as backend to an search portal, much in the manner of Landsat and Sentinel image servers: the visitor draws a path or a bounding box and receives back a zip file containing the relevant Cresis profiles and metadata describing overlap and intersection that allows their interactive display in a free 3D frame viewer such as used in Antarctica (link given earlier).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 08, 2014, 02:58:47 AM
Here is the best single frame for the bottom freezeup due west of 79N in northeast Greenland. The three slides show as-is at Cresis, enhanced grayscale (mostly unsharp mask plus sinusoidal bump map), and colored tentatively by region. The ultimate idea with interpretation is to identify the physical process at work via their impact.

The flow of ice here is west to east, approximately in the plane of the radar section. Thus the main uplift is on the left and the rest is earlier uplift that has moved downstream. Note the uplift is not manifested as a surface disturbance and cannot be attributed to sharp peaks or valleys in the bedrock -- many more extreme bedrock profiles have relatively undisturbed ice profiles.

Holocene layers have slumped as (river analogy) they rose over the boulder and entered the low pressure eddy behind it. This is mostly a story of late Pleistocene ice with enhanced rheology due to warmer temperatures from adjacency to geothermal source and from latent heat released by bottom water freeze-on.

Fifty cubic km of ice didn't lifted up yesterday; the deformation instead represents a process starting some twenty thousand years ago that continues more rapidly today (though still slowly). It's easier to deform sideways than lift all that ice above, given the disappearance of back pressure at the ocean front -- squeezing a tube of toothpaste under a heavy rock.

Next, fill out the shape using nearest grid neighbors, work out the volume better, and make a heuristic animation showing this feature growing from its earliest beginnings.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 08, 2014, 08:05:57 PM
Bump maps provide 'unreasonably effective' enhancements of radar imagery, at least perceptually. Mostly gimp/PS/imageJ users explore filter tools and settings at random, occasionally finding something with a nice effect, never looking under at the hood at what the tool is doing mathematically.

That works, but below I chase down how bump maps work and whether parameters can be chosen rationally on a per-image basis (perhaps locally) and so optimally enhance the whole ice-penetrating radar archive as a pre-compute This might follow upon, or be integrated with, Panton's initial reprocessing (elliptical unsharp mask) which already removes a lot of noise from radar horizon data.

On a flat grayscale image, bump maps first compute a very fundamental mathematical object, the gradient: a vector at each pixel whose direction points to steepest descent (pixel values on the 0,255 scale decreasing fastest) and whose magnitude measures that. On a familiar contoured hiking map, the gradient describes the initial route and potential acceleration of a fallen raindrop.

This is already good news for radar profiles because the gradient is physically meaningful being naturally orthogonal to radar horizon bands. At gentle deformations, striations are still follow-able but now sloped so the gradient is no longer quite vertical, with that departure described for each reflector by Panton's slope map.

From the image's gradient, bump maps create a shaded relief map according to how lighting is set by parameter choices. For an ordinary digital elevation map, these vary sun azimuth and elevation until the landscape is favorably illuminated, with shadows providing the visual clues for vertical dimension.

That's done by taking the dot product (projection) with respect to a second unit vector at each pixel representing direction to the light source. This amounts to the magnitude of initial gradient vector x the cosine of the included angle. The resulting scalar is then mapped to the 0,255 grayscale, with flatter gradients at lesser projections resulting in darker shades of gray.

This creates a new image with the same dimensions as the old but now realistically shadowed, representing the gradient and a light source. If realism is not wanted, the x,y components of the gradient itself can be captured in any coordinate system by two special cases using zero elevation and orthogonal azimuths, with gray again giving magnitude.

Gimp provides an additional depth control slider that amounts to changing contrast via 'equalize' histogram followed by a specified degee of 'fade'. That command expands the contrast locally in proportion to the pixel population at each level of gray; it can also done 'rationally' within the 'levels' menu.

So far, this is just a description of 'emboss', only the first round in the bump map process. However it already raises issues of the balance between scientific and esthetic image processing, as well as optimal processing of segments containing deformations, adjacent segments in a flight path, neighboring segments taken in different years with different radar configurations and indeed whether the whole archive could or should be reprocessed.

The first animation below holds elevation and depth constant at 45º and 25% while varying azimuth by increments of 30º. The second holds azimuth and depth constant at 245º and 25% while varying elevation by increments of 30º. The third holds elevation and azimuth constant at 120º and 245º while varying depth by increments of 10%. I reduced file size but you may have to click to get animations started.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 09, 2014, 05:12:00 PM
The animation below shows some enhancements that draw out features that might not have been so evident in the original scan, though usually the feature can be recognized once you look back.

The second image shows four consecutive slices north to south on the 79N/Zacharie grid described above. The second frame is the one enhanced separately above at higher resolution. Note the surprising series of little blips to the right that extend more consistently than the any of the large dramatic features. They run some 40 km and are not bedrock induced deformations but possibly incipient bottom freeze-ups induced by sheet water flow.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 10, 2014, 11:29:44 AM
More calving and further retreat at Zachariae Isstrøm:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on September 11, 2014, 02:51:03 AM
Espen..

Looking at the animation, there is the appearance of a very odd dark area that is well back of the calving face. It runs parallel to the calving face, is quite long and is just southeast of where you placed your name. It seems to be showing up where there appears to be significant thinning of the glacier. Is this snow melt? Could this be a fracturing or calving of such a large part of  the glacier?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 11, 2014, 05:19:54 PM
Shared Humanity, I think it is a "watermark" of the bedrock, showing up at the surface?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 11, 2014, 05:29:05 PM
Here are the areas of the various calving front changes assuming 30 m Landsat pixels. Now showing orange and yellow swapped per comment below. Pixel count is divided by 30x30 = 900 m^2 to arrive at areas. Volumes (not shown) require using ice depth from recent radar imagery.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 11, 2014, 06:06:41 PM
A-Team nice work, I think you should swap yellow (aug22) with orange (sep9)?

It is correct, I did not change the resolution (30M)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 11, 2014, 09:05:55 PM
A-Team but is still impressing how much glacier ice was lost in just 5 years, and that is more than 3 times the area of Manhattan (A figure Americans will understand)?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 12, 2014, 03:56:19 PM
I put together the vertical grids for the area described above west of 79N. These intersect with the horizontal grid and so give some idea of the areal extent of bottom freezeup features. The table below shows the separate horizontal and vertical rescaling necessary to join pairs of Cresis radar tracks, even those on the same flight path.

Each round of rescaling degrades the image -- this was a terrible way to store primary experimental data. It would have been far better to have left each flight as a continuous image with visitors provided a  'rectangle select' portal.

It is a complete nuisance to locate and retain intersections of horizontal and vertical grid flight segments because flight segments are oblique with respect to lat, lon lines and no correspondence exists between frame breaks. It is almost easier to align the images after the fact, as indicated in the image below.

While this example shows that it is feasible to get orthogonal sections to a given feature of interest (eg the small coastal cones), the several km scale intrinsic to features is not adequately sampled by the ~ 6 km scale that separates flight grid segments here.

Bottom freezeups are an important new mechanism for heat transfer into the deep interior of the ice sheet (from surface melt lake moulins and geothermal/pressure melt) -- ice deformation is exceedingly sensitive to temperature. Future ice flow would be seriously mis-modeled (on the slow side) by assuming temperature profiles from summit cores like NGRIP that did not happen to pass through a freezeup. However it may prove necessary to drill through one to experimentally determine both temperature and origin of these deformations.

HorVerFrame
100.0100.020100330_07_18
99.3099.4320100330_07_17
96.56100.020100330_07_14
102.8100.020100330_07_13
99.5299.7120100330_07_9
101.0100.020100330_07_10
100.3100.020100330_07_5
103.0100.020100330_07_6
103.7100.620100330_07_1
109.099.4320100330_07_2
107.6100.020100330_06_1
77.0499.1420100330_06_2
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2014, 03:17:11 PM
The first image shows a favorable horizontal radar flight path segment for 3D reconstruction (20110502_01-033) -- it has an interesting bottom freezeup feature and is sliced by four vertical flight path segments that provide cross-sectional information.

The process begins by drawing flight paths in Google Earth, linking Cresis images to the segments, and then assembling thumbnails onto to a screen shot. This assures that the final product will be informative.

Next, equations for each of the five lines are determined in slope-intercept form (neglecting earth curvature, WGS84, ice surface elevation and so forth) along with intersection lat,lon coordinates. This is a mild nuisance to set up in a spreadsheet but once done it provides pseudo code for marking up all flight path intersections (and angles if oblique) for all flights for all years, something Cresis could have done. An extra decimal point is also needed because of subtractions of numbers with little variation.

Transforming the grid pieces into perspective view allows the 3D structure of the freezeup to be visualized, noting that the sections here are ~9 km apart. This quickly gets complicated as one layer blocks the next, so it is necessary to have on-off and transparency controls. That's a bit much so I simply made an animation that steps through the layers.

This is the very first reconstruction of a freezeup as far as I know. The icesheet here is flowing slowly from lower left to upper right.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 14, 2014, 03:55:14 PM
A-Team it is fantastic what you can retrieve from those data, and on top of that you show it in a way not experts can understand it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2014, 04:32:49 PM
Thx, Espen!

I have a hidden agenda though, explain things once by example, get people to realize they could be doing this themselves, then just kick back and just enjoy their results. (So far this hasn't worked real well.)

Some places have a much higher density of flight path grid lines than 79N/Zachariae, such as Eqip/Jakobshavn, Petermann and Camp Century. They can be seriously katywumpus in terms of orientation. I shall leave these as an exercise for our esteemed blog visitors.

Down the road, I expect freezeups will be flown in tight orderly grid by the radar drone (which is capable of 5m turns). However Petermann especially is worth doing at this time since its longer feeder canyon is providing it with water for what may be one gigantic connected freezeup feature.

While freezeups are primarily a northern Greenland story, that is precisely the area that is waking up. Overall i think the Greenland story will be one of more heat working its way into and underneath the icesheet, warming it, and so softening the rheology. This will result in unblocking the margins faster than IPCC envisions, which in turn will remove the main resistive force holding the central ice sheet in place, and so the restraint on sea level rise.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 14, 2014, 05:09:57 PM
A-Team, why all the activities at Camp Century, must have been a sub contract to the Military, wonder if they ever cleared the site for nuclear debris?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 15, 2014, 12:09:49 AM
I suppose they have to start from Thule when flying northern Greenland, that being the only full airport. Not sure they do that much straight instrument flying in bad weather (have to stay very low for radar to minimize side-scatter) so might head up to Camp Century for visual orientation, then head out on the mission from there if conditions are still go.

Seems like they pass over NEEM and NGRIP quite a bit too. Since nothing happens on the summit ridge, if the radar configuration changes in some fashion every year, they have year-on-year interpretive controls as well as the borehole characteristics.

In the 1968 Broken Arrow incident -- a pilot of an always-in-the air B52 stuffed foam cushions over a hot air vent catching the plane on fire -- the crew mostly ejected but the plane flew on with four hydrogen bombs (and their conventional explosive fuses) until it crashed on sea ice in North Star Bay and exploded.

Some of the nuclear contamination was taken back to the US  -- 500,000,000 gallons worth -- but they never could find the 4th secondary.

This should not be confused with separate Camp Century nuclear contamination. During its brief operational life, that reactor (loaded with 20 kg of enriched uranium-235) discharged 47,078 gallons of radioactive liquid waste into an  icecap well. No attempt was ever made to recover it; the site is slumping badly and the waste would have moved with it.

Eventually the US resolved the Thule situation by declaring there never was a fourth bomb with serial number 78252, or maybe 78252's components had been removed with the others, in any case not to worry just because one itty bitty 1.1 megaton hydrogen bomb named 78252 could not be located, see, because there was, like, maybe a typo in the cargo manifest or sumpin and it didn't never exist.

One US document BBC obtained in July 1968 said the futile Star III submarine "search for a missing weapon is confidential NOFORN.” NOFORN means no foreigners can see, especially not Danes or Five Eyes partners, so familiar today from Snowden documents.

However a blackened section of ice was found which had refrozen with shroud lines from a weapon parachute, with a US  document reading: "Speculate something melted through ice such as burning primary or secondary."

The US was concerned back then, but not now, that the Russians would find the missing bomb and learn secrets of  nuclear warhead design. WH Chambers, a former nuclear weapons designer at the Los Alamos nuclear laboratory, told  BBC "there was disappointment in what you might call a failure to return all of the components."

Years later, a definitive 279-page report of the Danish Institute of International Studies (DIIS) resolved the matter once and for all claiming: "There is no bomb, there was no bomb and they were not looking for a bomb [with the risky submarine search].”

Period photos and datasheets for the B28 bomb show a 4.2 m long, 0.5 m diameter object weighing 984 kg containing plutonium, lithium-6 deuteride and tritium, plus fission and high explosive components.

The very same Fogh Rasmussen in charge today of fomenting NATO aggression in countries like Georgia and the Ukraine, blew off Thule workers exposed to plutonium, saying elevated thyroid cancer could surely be attributed to heavy drinking at the remote airbase. Workers were to accept a small one-time payment in exchange for future silence.

A nuclear scientist recently told reporters "we really don’t know what has happened to this bomb. It’s not going to explode but the possibility remains of very large contamination with all of the dangers that involves."

Nobody got around to measuring land contamination until 2007:

"The results show levels of plutonium in soil at Narsaarsuk ranging from background values around 39 Bq m-2 up to levels of 1.7 MBq m^2. Local sub-areas of sizes ranging from a few hundred to a few thousands of square metres show elevated levels above 10 kBq m^2 of plutonium. Based on geostatistical analysis, the total amount of plutonium in soil at Narsaarsuk is estimated at 270 GBq (100 g)."

"Investigations were carried out at  to determine the occurrence of radioactive particles in air. This involved collection of airborne particles with an air sampler, collection of airborne particles on sticky foils, collection of rain samples and collection of particles that could be resuspended by wind from the soil surface to the air. Small amounts of plutonium were found in air and rain samples..."

http://orbit.dtu.dk/en/publications/id%28c3b7244a-5c9d-49a1-84aa-4397903103ec%29.html (http://orbit.dtu.dk/en/publications/id%28c3b7244a-5c9d-49a1-84aa-4397903103ec%29.html)

There's a comprehensive account of the contamination at wikipedia:

https://en.wikipedia.org/wiki/1968_Thule_Air_Base_B-52_crash (https://en.wikipedia.org/wiki/1968_Thule_Air_Base_B-52_crash)

The local people avoided direct exposure because the US had previously relocated them to a canvas tent concentration camp at Qaanaaq:

"The town of Qaanaaq was established in the winter of 1953 when the United States expanded their airbase at Thule and forcibly relocated the population of Pituffik, Dundas, and Uummannaq 31 km to the north within four days during the height of the Cold War. The settlement was subsequently moved another 100 kilometers to the north."
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 15, 2014, 03:45:35 AM
Zachariae Isstrøm update: Massive calving activity ( in just 5 days) along the whole glacier front.

This season seems to be one of the largest retreats at Zachariae in recent times, only the 2011 retreat was larger (until now).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 15, 2014, 04:20:18 PM
Interesting how Zach continues to calve this late in the season. Jakobshavn has been so cloudy lately, no Landsats for weeks and weeks. Just like last Sept-Oct.

This is my last post of the season. I will be traveling offline for the next 5-6 weeks as I move operations down to Tucson for the winter.

Here are a few things I didn't have time to finish. Hopefully someone else will have a chance to work them up:

-1- Develop a surface map of Greenland colored by a classification scheme indicated what is below: layer cake, freeze-up, bedrock deflection, icestream, shear margin and so forth. Tint to show age of oldest identifiable stratum, deploy saturation to show residual thickness of undateable ice, reserve grayscale for surface elevation.

-2- Explain common second rank tensors of continuum mechanics used in Greenland icesheet modeling with pictures and examples, with special attention to invariants and a self-evident proposition called Glen's Flow Law. The idea here is not to do numerical modeling ourselves but get visitors to the point where they can better evaluate model icesheet predictions being published.

-3- Ramifications of the new N15 temperature dates for Greenland ice cores: if Greenland didn't melt during the Eemian as claimed, why aren't there thousands of meters of additional ice below the summit ridge (where little movement towards the coast occurs)? If the Eemian was warmer earlier and longer than O18 indicates, what becomes of model calculations? NEEM drilled through a double fold of recumbent ice -- was this down-ridge slumpage as stated or a small bottom freezeup feature associated with local geothermal warm spot meltwater?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 15, 2014, 08:53:55 PM
A-Team I will be missing you and your great posts.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 16, 2014, 03:24:38 PM
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

I'm not sure what these gentlemen are discussing below, something seismic no doubt. But look at the stratigraphy in the background -- an uncanny resemblance to ice-penetrating radar sections of Greenland. You just know that petroleum geologists have fantastic display and analytic software ... if only we could get them to take an interest in Greenland!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 16, 2014, 05:13:24 PM
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

I'm not sure what these gentlemen are discussing below, something seismic no doubt. But look at the stratigraphy in the background -- an uncanny resemblance to ice-penetrating radar sections of Greenland. You just know that petroleum geologists have fantastic display and analytic software ... if only we could get them to take an interest in Greenland!

A-Team yes I will try to sum up, the glacier situation around Greenland, maybe sometimes in October, I am glad my key interest nowadays is the glaciers in Greenland, far more interesting than the sea ice ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: CraigsIsland on September 16, 2014, 05:27:13 PM
Thank you sirs -I'm assuming of course. It's been eye-opening to watch the posts on Greenland. I'll try to out forth some time dedicated to analysis if I get around to it. Have a nice break A-Team!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on September 16, 2014, 11:36:50 PM
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

A lot of thanks from me too, Espen and A-Team. You have really been doing a great job over here!

I had actually promised Espen to do a blog post on all those animations he did of various glaciers showing changes over time, but never came round to it (sorry, Espen!). I'll very gratefully post any summary you guys come up with, but I'll leave that up to you to decide.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 30, 2014, 10:19:39 PM
And here is my favorite, Zach always impress me, because this is not a "Mickey Mouse" glacier like so many others, and here she come:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Sonia on October 01, 2014, 03:57:43 PM
The calves appear to be moving more freely now.  Compare to animations posted over the summer where many of them appeared grounded.

Looking at some of those prior animations now, it looks like maybe the calves weren't exactly stationary but were staying in formation as they moved with the glacier advance.  So maybe they were being pushed over the ground.  Yet something keeps them separated from each other.  I wonder if it is regolith scoured upstream that becomes a moraine now at the end of glacier.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 02, 2014, 08:34:48 AM
My hexagonal feature - handy to track the movement of the glacier over the years - has now calved.

(click for hi-res image)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on October 02, 2014, 04:12:05 PM
Wipneus,

Nothing last forever! ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 22, 2014, 11:36:19 AM
My first shot at the Sentinel data are  Zachariae and  Nioghalvfjerdsfjorden. This is just half the usual resolution (to keep the image size manageable).

Click the picture for a 3MB image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 22, 2014, 12:32:14 PM
That last image has a resolution of 80m/pix (from the original 40m). There are also images available with 25m resolution such as one on October 20.

With some scaling and rotating I assembled a quick animation of Zachariae. It shows that the calving continues while optical information is missing.

(pic needs a click to animate)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on October 22, 2014, 04:49:46 PM
This really shows there is something serious going on at Zachariae, we are in an unplugged mode?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Sonia on October 22, 2014, 04:54:33 PM
Oh these are nice.  I've been enjoying the Sentinal images on the DMI site recently but the higher resolution here is impressive.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on October 23, 2014, 12:03:32 AM
This really shows there is something serious going on at Zachariae, we are in an unplugged mode?

I was thinking the same thing.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 02, 2014, 12:48:31 PM
Wipneus,

Your animation of Zachariae showing calving continuing late into October makes me wonder how far upstream Sentinel could still measure icestream movement. The two dates you provided are a good start on the three needed for false color RGB interferometric fringe counting (as done so nicely on Petermann).

It would be interesting to compare velocities today to older data in the standard Greenland-wide map (below). That ESA search interface (https://scihub.esa.int/dhus/) is a mediocrity compared to EarthExplorer -- if they can't do it better,  just borrow the code. At this file size, some preview imagery would be helpful.

I attached the best available overall velocity map for NEGIS along with (after struggling with the inept interface) a map showing Sentinel coverage of upper Zachariae. There is better recent data midway in 3  papers from 2014.

The head of Zachariae (about 75ºN -40ºW) is quite remarkable: it seems to sit over an anomaly of the geothermal field. The icestream was not even discovered until 2000 -- the initial paper proposed (most improbably) that melting starts over a caldera.

Fahnestock, M., W. Abdalati, I Joughin, Brozena and P. Gogineni. 2001.
High geothermal heat flow, basal melt, and the origin of rapid ice flow in central Greenland.
Science, 294 (5550), 2338-2342. doi:10.1126/science.1065370.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 08, 2014, 11:23:47 AM
More action is seen at Zachariae Isstrøm:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 10, 2014, 08:45:54 PM
Hopefully some ppts from Session 4806 of the Dec 2014 AGU meeting will become available soon. This sounds like a warming ocean story propagating up-glacier in a delayed reaction, rather than change emanating from more basal lubrication (more melt lakes or increasing geothermal hotspot at the head of the icestream).

J Mouginot et al:  We study the 79north (Nioghalvfjerdsbræ) and Zachariæ Isstrøm sector of the Greenland Ice Sheet using a combination of satellite and Operation IceBridge (OIB) remote sensing data and numerical ocean modeling.

Around 2004, the southern portion of the floating ice tongue of Zachariæ Isstrøm began to break up, presumably due to changes in sea-ice/ocean conditions in the northeast.  Although the floating portion of the glacier started to speed up in response to the reduction in ice shelf buttressing, it was not until 2012 that the velocity of the grounded portion increased significantly.

In 2014, Zachariæ is calving at its grounding line, which retreated 5 km in 1996-2011. The southern ice tongue is gone, and the northern ice tongue is detached from the glacier. We use satellite-derived ice velocity and refined ice thickness based on mass conservation to estimate discharge of these glaciers.

We compare the results with RACMO2.3 surface mass balance and reconstruct the mass balance of this sector for the period 1992-2014 to show that most mass loss picked up after 2012, not in the earlier 2000's as stated in a recent study.

We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates.

The grounding line of 79north also retreated in 1996-2011, but its flow speed has remained constant. We attribute this contrasting evolution of the two glaciers to a difference in sea floor bathymetry, which allows an intrusion of larger amounts of warm subsurface waters for Zachariæ since the early 2000s, but limits access of such currents for 79north.

Nioghalvfjerdsbræ will likely undergo a fast recession [# years?] until its grounding reaches a topographic barrier [sill] about 30 km upstream, where ice retreat will temporarily slow down.

We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 10, 2014, 09:29:39 PM
Hopefully some ppts from Session 4806 of the Dec 2014 AGU meeting will become available soon. This sounds like a warming ocean story propagating up-glacier in a delayed reaction, rather than change emanating from more basal lubrication (more melt lakes or increasing geothermal hotspot at the head of the icestream).

J Mouginot et al:  We study the 79north (Nioghalvfjerdsbræ) and Zachariæ Isstrøm sector of the Greenland Ice Sheet using a combination of satellite and Operation IceBridge (OIB) remote sensing data and numerical ocean modeling.

Around 2004, the southern portion of the floating ice tongue of Zachariæ Isstrøm began to break up, presumably due to changes in sea-ice/ocean conditions in the northeast.  Although the floating portion of the glacier started to speed up in response to the reduction in ice shelf buttressing, it was not until 2012 that the velocity of the grounded portion increased significantly.

In 2014, Zachariæ is calving at its grounding line, which retreated 5 km in 1996-2011. The southern ice tongue is gone, and the northern ice tongue is detached from the glacier. We use satellite-derived ice velocity and refined ice thickness based on mass conservation to estimate discharge of these glaciers.

We compare the results with RACMO2.3 surface mass balance and reconstruct the mass balance of this sector for the period 1992-2014 to show that most mass loss picked up after 2012, not in the earlier 2000's as stated in a recent study.

We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates.

The grounding line of 79north also retreated in 1996-2011, but its flow speed has remained constant. We attribute this contrasting evolution of the two glaciers to a difference in sea floor bathymetry, which allows an intrusion of larger amounts of warm subsurface waters for Zachariæ since the early 2000s, but limits access of such currents for 79north.

Nioghalvfjerdsbræ will likely undergo a fast recession [# years?] until its grounding reaches a topographic barrier [sill] about 30 km upstream, where ice retreat will temporarily slow down.

We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland.

"We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland."

Better late than never ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on November 10, 2014, 11:32:49 PM
"We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates."

I suspected as much. But (and I dont know why) Nioghalvfjerdsfjorden scares me more than Zach.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 11, 2014, 05:04:30 PM
We should get off our butts and process the OIB bathymetry ourselves instead of waiting for journal articles to dribble out. It's readily available and not particularly gnarly in size or column interpretation. ftp://n5eil01u.ecs.nsidc.org/SAN2/ICEBRIDGE/IGBTH4.001/   The lat,lon could be stripped out for a GoogEarth kml path file; for an unknown reason xml format is provided. Not rocket science to inter-convert these in a plain text editor.

#Bathymetry models from the inversion of Operation IceBridge gravity anomalies measured from Sander Geophysics Ltd AIRGrav
# LINE      XX.YYZ XX denotes individual glacier, YY denotes year of flight (20YY), Z greater than zero denotes repeat tracks
# FAG070_mGal   Observed Free air gravity anomaly (mGal)
# FAG_calc_mGAL Calculated gravity anomaly (mGal)
# LON      Longitude on WGS84 ellipsoid
# LAT      Latitude on WGS84 ellipsoid
# X      X co-ordinate in EPSG3413 (polar stereographic, true at 70N, 45W down, WGS84 ellipsoid)
# Y      Y co-ordinate in EPSG3413 (polar stereographic, true at 70N, 45W down, WGS84 ellipsoid)
#BATHY   Modelled bathymetry from gravity inversion. All depths reported in meters with positive downwards and with respect to WGS84 ellipsoid.
#LINE, FAG070_mGal, FAG_calc_mGal, LON, LAT, X, Y, BATHY_m
14.100,49.4,57.4,-49.2,71.54,-147685,-2011087,924
14.100,49.4,57.3,-49.2,71.54,-147685,-2011087,923
14.100,49.4,57.2,-49.2,71.54,-147685,-2011087,922
14.100,49.4,57.1,-49.2,71.54,-147685,-2011087,921
14.100,49.4,57.1,-49.2,71.54,-147685,-2011087,920
...etc etc ...
Bathymetry in fjords of Northwestern Greenland from Operation IceBridge aerogravity.
Kirsty Tinto

Understanding of the influence of water circulation on the melting and dynamics of Greenland glaciers is hampered by a lack of basic information on fjord bathymetry. Here we present results from Operation IceBridge aerogravity surveys along the axes of the fjords of northern Greenland and in a coast-parallel grid across the northwestern fjords in order to provide bathymetric models for this difficult to access region.

Fjord axis profiles reveal the depth and shape of the bed in front of the grounding line for nine glaciers around the northern coast of Greenland. Sills are revealed approximately 20 km offshore of the grounding lines of Petermann, Steensby and Ryder glaciers, with depths similar to those of their grounding lines.

Sills have not been identified in the other northern fjords. In Northwest Greenland, the recently released IBCAO v3 shows deep troughs in the continental shelf but does not resolve the connection between these troughs and the channels of the outlet glaciers that cut the coast. The changes observed in velocity and surface elevation of these glaciers does not follow a simple spatial pattern, and the influence of ocean waters is not fully understood.

The new IceBridge survey provides a bathymetry model of the area between the marine IBCAO data and the grounded glaciers and shows for the first time the linking pathways at depth of individual outlet glaciers to shelf troughs.

Bathymetry and geology of Greenlandic fjords from Operation IceBridge airborne gravimetry
Tinto, KJ et al 2011 AGU

The Greenland Ice Sheet is drained by outlet glaciers that commonly flow into long, deep fjords. Glacier flow is controlled in part by the topography and geology of the glacier bed, and is also affected by the interaction between ice and sea water in the fjords. This interaction depends on the bathymetry of the fjords, and particularly on the presence of bathymetric sills, which can control the influx of warm, saline water towards the grounding zone.

The bathymetry and geology of these fjords provide boundary conditions for models of the behaviour of the glaciers and ice sheet. Greenlandic fjords can be over 100 km long and up to 1000 m deep, with sills a few hundred metres above the bottom of the fjord.

Where bathymetry is not well known, the scale of these features makes them appropriate targets for aerogravity surveys. Where bathymetry is known, aerogravity can provide information on the geology of the fjord, but the sometimes narrow, sinuous fjords present challenges for both data acquisition and interpretation.

In 2010 and 2011 Operation IceBridge flew the Sander Geophysics AIRGrav system along the axes of more than 40 outlet glaciers distributed around the coast of Greenland. The AIRGrav system has high precision, fast recovery from turns and the capacity for draped flights, all of which improve the quality of data acquisition along fjord axes.

Operation IceBridge survey flights are conducted at or lower than 500 m above ground surface, at speeds of ~140 m/s, allowing full amplitude resolution of features larger than ~5 km, and detection of smaller scale features.

Fjord axis data are commonly of lower quality than data from grid-based gravity surveys. Interpretation of these data is improved by combining repeated survey lines from both seasons as well as incorporating other datasets, such as radar, and magnetic data from Operation IceBridge, digital elevation models and geological maps.

While most fjords were surveyed by a single axial track, surveys of Petermann Glacier include parallel flow lines, allowing new constraints on the bathymetry under its floating ice to be more reliably modelled. This work is a preliminary review of the fjord axes surveyed by Operation IceBridge and presents models of representative fjords. The surveys include major features, such as the fjord in front of Kangerdlugssuaq Glacier and under the the floating ice in front of Petermann, 79 N and Zachariae Glaciers and results identify the limits and applications of IceBridge aerogravity in the Greenland fjords.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on November 12, 2014, 05:44:25 AM
there are antarctic tracks in there also
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 12, 2014, 12:12:59 PM
Right, they have gotten remarkable results from Operation IceBridge in Antarctica (first two images below). Oddly, for Greenland, the only previous use of airplane-borne OIB gravity seems to have been the Bell 2014 paper on basal freezeups (3rd image, see also Storstrømmen).

Note that radar can penetrate freshwater ice but not seawater, so in terms of floating iceshelves or mélange-covered outlet fjords only gravity can find the topography of bedrock. Farther to sea, side-looking towed sonar has better resolution.

Note NASA maintains quite a nice bibliography of all journal articles based on Operation IceBridge data from 2014- back to 2010. These are linked to the journal (which may or may not be paywalled). These mostly concern Greenland and Antarctica; 3-4 specifically Northeast Greenland (ie Zachariae). http://icebridge.gsfc.nasa.gov/?page_id=596 (http://icebridge.gsfc.nasa.gov/?page_id=596)

There is only so much that can be done from surface observations (eg Lidar dynamic thinning, Landsat calving, Modis albedo, GPS glacial isostatic adjustment, RadarSat surface velocity). While these remain important, Greenland research is shifting more to measurements of the interior, even though seeing into 3000 meters of solid ice seems at first problematic.

To date, the main observational techniques have been 9 boreholes and 21 years of airborne radar; these are now being supplemented with airborne and satellite gravity, seismic reflection, magnetic susceptibility, rapid mobile coring, refined radar, and mass conservation constraints.

These will improve bedrock topography, map variations in the basal geothermal gradient, determine thickness and location of pressure-melted temperate ice (resp. ice frozen to bed), date and map radar stratigraphy and heat content of deformations, global mass balance measurement, and above all measure the internal temperature profile that largely governs ice flow (4th image, my attempt at color temperature overlay on dated radar deformation).

There is a tremendous amount of ice sheet history carried in the contemporary internal conditions. For example, Zachariae fjord gravity connects sills that today block ocean heat exchange to continental shelf troughs ground out during the height of the ice age.

The past and present are both needed to estimate future sea level rise from Greenland. Modelling will be that informative until internal conditions are better constrained factually.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 23, 2014, 01:26:32 PM
An odd coincidence, I met a member of the Zachariae family the other day, and explained him my interest in the Zachariae Isstrøm, first he was not aware of the glacier named after one of his earlier family members, but was rightly proud afterwards (thanks to smartphones and quick internet searches).

This also shows how little is known about this giant glacier?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 30, 2014, 08:00:33 PM
Zachariae Isstrøm is still breathing, in the dark arctic winter:

(I dont think this was common just a few years ago?)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 11, 2014, 09:27:00 AM
The number of publicly available Sentinel-1 L1 data of the Zachariae/N79 area has been fairly disappointing until now. After the first batch of images acquired in the first half of October, nothing  new appeared for weeks. This week new software was activated on the ESA site that promises an increase of more promptly data, it will take some time for the backlog to be filled in.
One image has come available until now, acquired in December 4. Its is of comparative low resolution (40m) and taken from a different orbital position than the ones I have archived. It has dual polarization ( H and V reflection from a Horizontally polarized beam). I created a false color image (HH-amplitude=Red, HV-amplitude=Green and HH-amplitude+HV-amplitude=Blue) using the Sentinel-1 toolbox and reduced the resolution to 80m for the attached image.

(click to see the 1.9MB image)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 13, 2014, 09:21:14 AM
A sequence of two images from Nov 29 and December 11 (Sentinel is in the same orbital postion every 12 days). Resolution is 40m, not good enough for an accurate estimate of the movement.

(click for the 1.6MB animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on December 13, 2014, 04:52:42 PM
Resolution is 40m, not good enough for an accurate estimate of the movement.

Right. I rotated by -23º to make the movement horizontal, then started subtracting the images holding one fixed and bumping the other until a visual minimum was reached, 2 pixels ± 0.5 too much error.

The issue here is really calculating the velocity field, which cannot be assumed uniform for a glacier terminus. This turns out to be super-easy using Fiji (aka ImageJ2) using the built-in plugin bUnwarpJ under Registration as discussed in #msg41327. I first cropped the two images above, moved out of indexed color into grayscale, evened out the contrast and imported the two images into Fiji, ran the plugin using the defaults, and made a simple animation out of the products in Gimp. Elapsed time, including finding a download for Fiji, about five minutes.

bUnwarpJ finds a lot of match points and determines the deformation (b as in Bezier) of a rectangular grid necessary to bring one image into the other. The vectors simply connect before and after grid points. Software like this has been developed to the nth degree for the needs of biomedical imaging (eg tracking cell migrations, straightening out electrophoretic gel lines).

If we had a year's sequences of 30 Sentinel images, the change in the vector field over time would be easy to animate. It also outputs a very extensive text log of what it did. It would also work out of the box on pairs of Landsat images, say two a year apart for slow moving regions near the headwall of NEGIS.

The analog of an SDS gel is straightening out radar stratigraphy, not so much as flattening isochrons as capturing the deformation that does it -- fitting them with b splines as 2D analytic surfaces, Greenland's internal fonts. There are a lot of advantages in getting out of raster into ordinary calculus as the differential geometry of manifolds is exceedingly well-developed especially when that surface is described by splines.

http://forum.arctic-sea-ice.net/index.php/topic,867.msg41327.html#msg41327 (http://forum.arctic-sea-ice.net/index.php/topic,867.msg41327.html#msg41327)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on December 13, 2014, 07:55:56 PM
ESA is planning a full coverage of Greenland with three consecutive cycles during winter, which should allow for feature-tracking everywhere.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 16, 2014, 08:16:32 AM
The backlog for this area seems to be filled backward, about two days per 24 hours, and is now at November 21.

Unfortunately only medium resolution data.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on December 16, 2014, 11:43:11 AM
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 16, 2014, 03:41:25 PM
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario

Thanks, that explains a lot.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 23, 2014, 09:25:45 AM
Filling the backlog continues slowly (we are at Nov 9th) but new additions for the Zachariae outlet are very rare. Bad luck probably, the neighborhood is much better served.
Any way an image from Dec 22 came in, half sized: the Nioghalvfjerdsfjorden has been cut off. With one acquired on Nov 16, three 12 day cycles ago, this leads to the following animation, 80m resolution to show more of the bigger picture. The glacier is moving fast as ever but calvings seem to get increasingly stuck.

(click to see the 1.8MB animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on December 23, 2014, 04:10:19 PM
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario

Thanks, that explains a lot.
Now the new planning is in, the Greenland campaign will start on cycle 38 and run for three consecutive cycles in IW HH:

https://sentinel.esa.int/documents/247904/1685281/Cycle-38.jpg
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on January 05, 2015, 08:53:43 AM
Zachariae Dec 23-> Jan 4.

(must click)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on January 16, 2015, 09:11:32 AM
Zachariae was under the antenna once again. I created a sequence from the medium resolution EW product. I reduced the resolution even further for an overview and used the HH and HV polarizations (by amplitudo) as Red and Green channels. This seems to be what the quick-look images do.

No major calving has taken place since mid October, the pre-cracks of new ones are visible for a while though. I think the back-pressure of the sea ice is holding it back. The glacier itself  is of course unaffected.

(click to see animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on January 16, 2015, 07:41:13 PM
That is nice. 22 Dec - 15 Jan = ~24 days seems to be a decent interval. What other 2014 dates are available should you wish to make a longer animation?

Would we see something similar at Jakobshavn? See about nothing at Petermann?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: AbruptSLR on January 19, 2015, 11:18:57 PM
The linked reference discusses sustained ice mass loss from the Northeast Greenland ice sheet triggered by regional warming, and which show signs of accelerating:

Shfaqat A. Khan, Kurt H. Kjær, Michael Bevis, Jonathan L. Bamber, John Wahr, Kristian K. Kjeldsen, Anders A. Bjørk, Niels J. Korsgaard, Leigh A. Stearns, Michiel R. van den Broeke, Lin Liu, Nicolaj K. Larsen, & Ioana S. Muresan, (2014), "Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming", Nature Climate Change, Volume: 4, Pages: 292–299, doi:10.1038/nclimate2161

http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html (http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html)


Abstract: "The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr−1 of a total of 3.2 mm yr−1. A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbræ) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future."
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 22, 2015, 08:55:00 PM
With the help of Wipneus, I now received my Petermann and Zachariae images printed on canvas and the result is fantastic, thanks Wipneus!! ;)

The Petermann image is 1,3m x 1,3m
The Zachariae image is 1m x 1,5 m

The Petermann image even got a 3D effect (not intentionally).

The images are seen below (in reduced format).

The resolution is even so good I found new details I was not aware of.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on January 24, 2015, 04:26:16 PM
The first Sentinel 1A IW high resolution (10m/pix) product was placed in the public archive today.
It is brilliant! Even when reducing the resolution to 25m there is just no comparison with best image until now: 2014 Oktober 5, 9 cycles * 12 = 108 days.

(click to download a 2.9MB animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 24, 2015, 04:39:43 PM
Yes Wipneus that is a great image, it really shows what we can expect later in the season.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on January 25, 2015, 09:36:07 AM
Canvas? I have a few Zachariaes left in stock. Supplies won't last though. I make you special price?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 25, 2015, 10:23:24 AM
That is a pretty rough canvas?

I am sure there is a market, they are really decorative, and very special!

The print shop who did the printing were impressed with the resolution.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 09, 2015, 03:56:34 PM
Two 12 day cycles with the hi-res Greenland campaign are nearly over. Every place in Greenland should be imaged and archived at least 4 times, two from an ascending orbital position and two descending.

Not yet for Zachariae, there are two images in the public archive. One ascending and one descending.

The quality of the Ascending image that was added earlier today hast surprised me. I was already very happy with the Jan 21 image, but this is even a class better.

Here are two details, to show what I mean.

(click for higher resolution picture)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 15, 2015, 10:58:03 AM
Part of the problem seems to be loss of information in processing the image. The source data file is/are a 16-bit grey scale TIFF's. When extracted using the "official" Sentinel Toolbox 8-bit RGB images get generated (tried png and tiff as ouputs). You would expects that the 16->8 bit transformation would be done while preserving as much detail as possible.
Trying to do this manually, using 16bit capable ImageMagick tools, I found I could do much better than that. Most of the glare in the Zachariae image form Jan 21 disappears this way exposing much more detail between the calvings and the ridged part of the glacier.

That means a lot more work for preparing these images, but quality will be much better than what I showed before (and what DMI and PolarView show).

At the moment I apply the following ImageMagick option to the raw image files:

-contrast-stretch 0x0.05%

(in short: perform a linear stretch from black to white, discarding at most 0% of the black pixels and 0.05 on the white side of the spectrum)

The resulting images can be processed further as 8-bit grey's in the Gimp.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 15, 2015, 11:10:46 AM
Here is the first animation using all hi-res IW mode Sentinel images at 10m/pixel.
Images processed as described above. Movement between Jan 21 - Feb 14, 24 days or 2 Sentinel cycles, is 14 pix to the right and 7 pixels up. That translates to about 6.5 m/day.
It looks that the floating calving's, frozen together with sea ice, kept the front from several more calving's since the last one in October.

(click to start the big animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 15, 2015, 11:29:54 AM
In the image above between the calving's are some are some that look as dark calving's. I am wondering what they are, they appear to be elevated above the surrounding rubble judging the highlight to their right side ( the satellite's radar beam shines from the right in its descending orbital path). But the sudden appearance of one in the south seems to incline they are just smooth pieces of sea ice.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 15, 2015, 11:46:01 AM
Good question, my unqualified guess is, it is a slice from the "big calf" that turned up side down?
And in the same action pushed the "mother" away.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 15, 2015, 12:04:15 PM
Here is the first animation using all hi-res IW mode Sentinel images at 10m/pixel.
Images processed as described above. Movement between Jan 21 - Feb 14, 24 days or 2 Sentinel cycles, is 14 pix to the right and 7 pixels up. That translates to about 6.5 m/day.
It looks that the floating calving's, frozen together with sea ice, kept the front from several more calving's since the last one in October.

(click to start the big animation)

It seems that Zachariae is preparing for a major calving soon?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on February 15, 2015, 04:19:04 PM
Good question, my unqualified guess is, it is a slice from the "big calf" that turned up side down?
And in the same action pushed the "mother" away.

You eye for detail is amazing. It looks like that slice came from the calving face as there is a  noticeable area that receded just  adjacent to it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 15, 2015, 04:27:22 PM
Good question, my unqualified guess is, it is a slice from the "big calf" that turned up side down?
And in the same action pushed the "mother" away.

You eye for detail is amazing. It looks like that slice came from the calving face as there is a  noticeable area that receded just  adjacent to it.

Thanks SH, if that is true, we can conclude the "ice-cubes" with black tops are sliced baby-calves.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 15, 2015, 05:40:07 PM
Good question, my unqualified guess is, it is a slice from the "big calf" that turned up side down?
And in the same action pushed the "mother" away.
Yes, that's exactly what they are, the undersides of icebergs are so smooth that they do not reflect much microwaves back towards the radar.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 15, 2015, 05:44:21 PM
Part of the problem seems to be loss of information in processing the image. The source data file is/are a 16-bit grey scale TIFF's. When extracted using the "official" Sentinel Toolbox 8-bit RGB images get generated (tried png and tiff as ouputs). You would expects that the 16->8 bit transformation would be done while preserving as much detail as possible.
Hmm cannot you export as "Generic binary" from the S1TBX to save all the bits?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 17, 2015, 09:07:10 AM

Hmm cannot you export as "Generic binary" from the S1TBX to save all the bits?

I am not sure how it would help to convert a specified binary (the SAFE product) to an unspecified binary blob. Disadvantages are that the size is blown up by six(seems to convert 16bits grey to 3*32bits RGB). It does not seem to export views created in the toolbox, just the original product.


Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 18, 2015, 11:39:01 AM

Hmm cannot you export as "Generic binary" from the S1TBX to save all the bits?

I am not sure how it would help to convert a specified binary (the SAFE product) to an unspecified binary blob. Disadvantages are that the size is blown up by six(seems to convert 16bits grey to 3*32bits RGB). It does not seem to export views created in the toolbox, just the original product.
You can crop the original product by selecting "Spatial Subset from View" to generate a new product covering just your area of interest. I guess the image-export from the toolbox does not allow one to select the number of bits to be used in the jpeg/tiff/png?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 18, 2015, 12:47:14 PM

 I guess the image-export from the toolbox does not allow one to select the number of bits to be used in the jpeg/tiff/png?

I have not found it.
8 bits is fine though. But I did not find anything to tune (or stop) the capping of the high intensities, thus loosing the information in highly reflecting areas like glaciers. I would expect the scaling option to do the trick (right click on the band and choose "Scale Data") but nothing seems to change.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 18, 2015, 04:22:40 PM

 I guess the image-export from the toolbox does not allow one to select the number of bits to be used in the jpeg/tiff/png?

I have not found it.
8 bits is fine though. But I did not find anything to tune (or stop) the capping of the high intensities, thus loosing the information in highly reflecting areas like glaciers. I would expect the scaling option to do the trick (right click on the band and choose "Scale Data") but nothing seems to change.
In the menus there is Utilities - Dataset Conversion - Convert Datatype with some parameters related to scaling, perhaps that would work?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 21, 2015, 07:25:40 PM
It is amazing how Sentinel is avoiding Zachariae, I am curious to know why?

http://www.polarview.aq/arctic (http://www.polarview.aq/arctic)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 22, 2015, 08:13:31 AM
It is amazing how Sentinel is avoiding Zachariae, I am curious to know why?

http://www.polarview.aq/arctic (http://www.polarview.aq/arctic)

No, I have noticed the same since the data became available.

Bad news: it is getting worse. In the next two cycles (cycle 41 Feb 21-26 and cycle 42 Feb 26- Mar 10) no IW sensor mode (== hi resolution) data aquisition is planned, except for the Jacobshavn spot.
I don't know why cycle 41 is only 6 days long ( the Sentinel cycle is 12 days) nor why the ESA planners call this ramping up. Hopefully because this is just a bad dream.

They do plan to do the full Antarctic coast though.

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario (https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 22, 2015, 10:46:01 PM
THe dedicatesd campaign seems to be over so EW is the best we'll get for the foreseeable future. It's too bad there is no Copernicus climate service yet that would require frequent IW-coverage of ice sheet margins..
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 23, 2015, 02:34:28 PM
THe dedicatesd campaign seems to be over so EW is the best we'll get for the foreseeable future.

resulting in (only) one pair of same orbital position IW Ground Range Detected products over the Zachariae area. There are additional Single Look Complex (SLC) products, that should be convertible to GRD. The SLC->GRD function in the toolbox requires inputs that are beyond my understandings.
If anyone can help that would be much appreciated.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 23, 2015, 02:48:25 PM
A medium resolution EW image shows that the expected calving has not happened yet.

(click for a bigger picture)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 23, 2015, 03:15:24 PM
resulting in (only) one pair of same orbital position IW Ground Range Detected products over the Zachariae area. There are additional Single Look Complex (SLC) products, that should be convertible to GRD. The SLC->GRD function in the toolbox requires inputs that are beyond my understandings.
If anyone can help that would be much appreciated.
In SLC to GRD conversion you basically can leave all the parameters in the default settings. The only parameter you might want to fiddle with is Multilook with which you can set the desired output pixel size. When you change the number of range-looks it calculates the required azimuth looks for generating square pixels automatically. 4 range and 1 azimuth looks results in 14m pixel size while 6 range and 2 azimuth gives 25 meters.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 23, 2015, 03:36:34 PM
This is how far I come:

1) select the SLC->GRD function
2) in the first tab select a SLC product (the SAFE.zip file);

Now I get the error message when I try to prceed:

  2-Calibration: no output product is selected

Tab2 is called 2-Calibratio2, but there is nothing that I can select or enter in that tab as an output product.
Under Tab5, you can specify an output name, but whatever I enter there does not get me any further.

Something very obvious escapes me, but what is the program trying to say?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 23, 2015, 03:48:44 PM
This is how far I come:

1) select the SLC->GRD function
2) in the first tab select a SLC product (the SAFE.zip file);

Now I get the error message when I try to prceed:

  2-Calibration: no output product is selected

Tab2 is called 2-Calibratio2, but there is nothing that I can select or enter in that tab as an output product.
Under Tab5, you can specify an output name, but whatever I enter there does not get me any further.

Something very obvious escapes me, but what is the program trying to say?
Did you select the channel? I think you need to select it even if there's only one..
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 23, 2015, 04:15:53 PM

Did you select the channel? I think you need to select it even if there's only one..

Very logical idea, tried everything but no way to select a source band (nearest thing to channel that I can find) in the SLC2GRD dialog. I would expect something selectable, or entereable, in the "Source Band" boxes. Should it??

Selecting bands outside the dialog does not do anything.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on February 23, 2015, 04:24:42 PM
I think you are confusing the toolbox by selecting a SAFE-product as the source. Instead you should 1st import the SAFE-product so that it's opened in product view, and then select SLC to GRD from the menus when the imported product is active.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 23, 2015, 06:47:46 PM
I think you are confusing the toolbox by selecting a SAFE-product as the source. Instead you should 1st import the SAFE-product so that it's opened in product view, and then select SLC to GRD from the menus when the imported product is active.

Again very logical, the result is exactly the same.

I found my problem now, and as expected it is very stupid and embarrassing: there is another menu item, one layer deeper, that does "Sentinel SLC to GRD conversion". It is now grinding the raster data.

With your help I can go further now, thanks a lot.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on February 27, 2015, 07:31:36 AM
Heres some Nioghalvfjerdsfjorden and Zach contourage from morlinghem, right way up even, deeper holes in the south inland of Zach, no wonder Nioghalvfjerdsfjorden aint doin much tho the tongue is afloat

holes aint so deep compared to down Jacobshawn way

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 27, 2015, 09:16:32 AM

Bad news: it is getting worse. In the next two cycles (cycle 41 Feb 21-26 and cycle 42 Feb 26- Mar 10) no IW sensor mode (== hi resolution) data aquisition is planned, except for the Jacobshavn spot.
I don't know why cycle 41 is only 6 days long ( the Sentinel cycle is 12 days) nor why the ESA planners call this ramping up. Hopefully because this is just a bad dream.


Perhaps bad dream is the explanation. A few IW slices, acquired on Feb 26 appeared in the public archive. Not the Zachariae area yet.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on February 27, 2015, 03:16:06 PM
sidd, on the Zach contourage, could you possibly include more farther to the south and west, pick up more of the ice stream? It diagonals in from the southwest.

I am seeing -500 m and -600 m but not their contextual continuation or maximal depth. Also, could you prepare a companion image without the number overlay?

Right you are, Jakobshavn hit -1634 m below sea level on Jim's clip. Now that is a serious hole. Over a mile deep (5361'). Plus whatever saturated till sitting above bedrock.

I wonder if Morlighem would be willing to add the experimental velocity map at the same gridding and projection. It might be up there at NSIDC under some different project name. I am curious as to whether the velocities know about these holes.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Jim Hunt on February 27, 2015, 03:22:27 PM
sidd, on the Zach contourage, could you possibly include more farther to the south and west, pick up more of the ice stream? It diagonals in from the southwest.

Right you are, Jakobshavn hit -1634 m below sea level on Jim's clip. Now that is a serious hole. Over a mile deep (5361').

This will all be easy peasy, once the right proj4 settings become apparent!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 01, 2015, 08:56:06 AM
Zachariae seen by Sentinel 1A in IW mode on Feb 14 and 26. A large area  with calvings, sea ice and rubble is moving with the glacier.

Click that picture for a 20m/pix resolution animation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 01, 2015, 09:44:51 AM
Yes Zachy is amazing, I wonder where she will take us this season and she is well up in speed already.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 01, 2015, 02:13:38 PM
Here is some more info:

(It explains some of the surface seen at Zachariae. and we will soon see some "growing" rocks)

The Landsat image is from September 30 2014.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on March 04, 2015, 05:19:06 AM
surface velocity map compared to contouring, green is 0, blue is deeper, 100 m interval .
The velocities are larger over deeper beds, almost can pick out each tail and split
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 05, 2015, 05:28:58 PM
First image of Zachariae Isstrøm by Modis:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on March 06, 2015, 11:37:27 AM
Here is an interesting Palsar interferometric image of mid-Zachariae. No explanation provided but it seems to be showing shear lines in the upper ice stream (Negis). Their interest seems to be in characterizing firn and snow accumulation; I've not seen any actual glaciology papers emerge from this to date.

http://web.stanford.edu/~acchen/AGUFall2009Poster.pdf (http://web.stanford.edu/~acchen/AGUFall2009Poster.pdf)
http://web.stanford.edu/group/radar/people/Albert_thesis_small.pdf (http://web.stanford.edu/group/radar/people/Albert_thesis_small.pdf)
http://scholar.google.com/citations?user=Eq1R1XUAAAAJ&hl=en (http://scholar.google.com/citations?user=Eq1R1XUAAAAJ&hl=en)
http://uavsar.jpl.nasa.gov/science/workshops/presentations2013/UAVSAR_WorkShop2013_Greeland_%28Chen%29.pdf (http://uavsar.jpl.nasa.gov/science/workshops/presentations2013/UAVSAR_WorkShop2013_Greeland_%28Chen%29.pdf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on March 08, 2015, 10:38:49 AM
A plain interferogram shows DEM and ice-movement effects mixed together so it can be difficult to interpret. In the fast-moving ice-stream the "fringes" show differential displacement (in the range-direction of the radar) due to movement. 1 fringe corresponds to half of a wavelength ~= 12cm in the Palsar case.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 13, 2015, 09:23:26 AM
No hi-res Sentinel-1 images over the Zachariae area planned over the next month or so. We will have work with the much lower res EW data that is occasionally obtained.
Here we see that the new calving is basically complete, the frozen mix downstream prevents it separating from the glacier.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 16, 2015, 06:47:59 PM
A sequence of Sentinel images from Jan 15 and March 16. Separation is 60 days or 5 Sentinel orbit cycles. Due to the low (40m/pix) resolution I can not say more than the glacier velocity is still 6m/day. Perhaps a minor calving can be seen on the southern edge.

(must click to start the animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 16, 2015, 07:07:58 PM
There is a lot more calving potential ahead, over the whole front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 17, 2015, 06:46:18 PM
Zach is back on the Landsat-stage, here we see September 30 2014 vs March 16 2015.

At first glance nothing is seen, because the whole lot moved in the meantime, but look carefully, September 30 got 2 rows of main debris where as March 16 2015 got 3 rows in front of the calving area.
One more thing to check is the substantial damage at the south of the calving front, just north of the future Kap Zach / Zach Island *):

It is not every day you can name an Island or a Kap ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 28, 2015, 07:07:22 PM
Zachariae before and after the Arctic winter seen by Landsat 8. The calving front has not changed so much, but two calvings were in between. The glacier has continued to move at a speed of about 6m/day.

(click to see the 2.5MB animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 31, 2015, 04:32:31 PM
Latest low res Sentinel 1 image, shown compared with 36 days ago. The cracks of the next calving getting longer both on the north and the south side.

(click to see the animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 31, 2015, 05:41:02 PM
Wipneus, it is very interesting what happens around Kap Zach or Zach Island in the south, that will make the shape of the calving front much different to what is today.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 03, 2015, 04:08:30 PM
Never a dull moment at Kape Zach.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Laurent on April 03, 2015, 04:49:58 PM
Do not forget to click as usual :)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 10, 2015, 10:18:55 PM
Still on the move: (We can expect a very big one soon)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on April 16, 2015, 03:09:58 AM
Zachariae calving from in 15m res. Lots of melt ponds now, discolorings and all kinds of interesting creases, wrinkles and cracks are appearing

I will make a comparison with a previous date later to check the movement.

You must click the picture if you are ready for a 4M downlod.

When I look at this image, (beautiful by the way) I can't help but get the sick feeling that  glaciologists are seriously underestimating the potential sea level rise due to glaciers. Not only this one but every single sea terminating glacier that is grounded below sea level. Just as they were surprised by having the Northeast Coast of Greenland getting unlocked, they will be registering surprise by how quickly these glaciers speed up, melt, calve and retreat.
When I first saw the movement at Ilulissat (2010) I said it would go fast.  We are on an exponential growth curve in ice flow.  We are not headed to a new stable higher flow rate.  Imho it will keep doubling every 5~10 years until it is gone.  A high side estimate rather than a low side one is 50% loss in 100 years.  Or more.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 16, 2015, 05:57:27 PM
Zachariae Isstrøm is showing its muscle, lots of huge potential calvings ahead for this season:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 19, 2015, 09:44:30 AM
A small interesting detail from the calving front:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 21, 2015, 04:13:36 PM
Small caving at Kap Zach. New break line opens further upstream.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 26, 2015, 09:31:19 PM
Zachariae Isstrøm is preparing for a massive calving:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 27, 2015, 09:08:26 AM
Yes. At the same time the (2014) calving's further away have stopped moving with the continuous glacier movement, which indicates to me more back pressure from there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 01, 2015, 10:49:42 PM
Be prepared for a "big one":
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 01, 2015, 11:18:02 PM
The "big one" could be as much as +/- 15 km2, compared to Petermann (small) but Jakobshavn (big).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 04, 2015, 08:19:52 AM
The calving is progressing faster now.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 09, 2015, 08:37:46 AM
So slow that it is difficult to judge when the calving is complete.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 13, 2015, 08:55:03 AM
Latest Landsat image reveals that the new calving is separating from the glacier front. So a new calving front is establishing.

(click to enjoy)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 16, 2015, 09:19:36 AM
Latest Sentinel medium res image also shows the new calving front is brightening up.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 16, 2015, 08:26:52 PM
Still working on it, labours I guess?:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 16, 2015, 10:17:07 PM
The changes at Zachariae Isstrøm since May 2013, a shame the sensors were so bad before 2013 since the year 2012 was dramatic: (the last image in the animation is May 16 2015 not 2014!!)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 20, 2015, 07:53:35 AM
Detail of the "new" calving front of the glacier (which is advancing at 6.9 m/day).

(don't forget to click)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on May 20, 2015, 10:23:30 AM
I would not call it a new calving front just yet as it's still connected - I'm expecting the new piece to shatter once it breaks off completely...any day now I think :)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Jester Fish on May 20, 2015, 09:07:06 PM
I did some crude on-screen measuring to verify what my eyes are telling me: the glacier movement seems to be in rotation around the bottom of the image i.e. the top is moving faster than the bottom.  Anyone else see that?  Just an observation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on May 20, 2015, 11:31:18 PM
I did some crude on-screen measuring to verify what my eyes are telling me: the glacier movement seems to be in rotation around the bottom of the image i.e. the top is moving faster than the bottom.  Anyone else see that?  Just an observation.

I see that too. I believe Kap Zach the rock at the bottom of the picture is to blame, pinning the right-hand side of the ice flow. But best to get answers from the experts here.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 23, 2015, 09:32:24 PM
The calving process is continuing at Zachariae Isstrøm:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 25, 2015, 08:52:16 PM
This time we have look at Spaltegletscher situated in into Dijmphna Sund and a part of Nioghalvfjerdsfjorden or the 79-glacier, it may soon be the end to Spaltegletscher since a serious crack is now almost crossing the whole glacier seen in the lower part of the animation seen below:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 30, 2015, 09:46:30 PM
There are indications of a large movement at Zachariae, more info when more reliable imagery is available.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 31, 2015, 09:00:35 AM
I see nothing in the Sentinel medium-res images yet (taken hours after the Landsat flew over).

(images aligned on the "new" calving front)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2015, 09:43:58 AM
Wipneus,

From where did you get the May 30 image from, in my polar view there is no image from Zach May 30?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 31, 2015, 11:48:13 AM
Sentinel-1 Scientific Data Hub (https://scihub.esa.int/dhus/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2015, 12:26:11 PM
Sentinel-1 Scientific Data Hub (https://scihub.esa.int/dhus/)

Sorry about that, I thought the polar view site was just as quick?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on May 31, 2015, 04:23:58 PM
There's an image from the 31st as well on scihub now.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on May 31, 2015, 04:26:02 PM
There's an image from the 31st as well on scihub now.

Already checked, thanks!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 02, 2015, 08:07:54 AM
12 day med-res Sentinel animation of the Zachariae calving front(s).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 04, 2015, 09:10:08 AM
But the Landsat optical image shows that  a new minor calving is taking place at the "new" calving front.

(pls click)

[EDIT: circled the feature at A-Teams's request]
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 04, 2015, 04:39:05 PM
Wipneus, any chance you could overlay some arrows or text? I'm not sure above what I should be looking at, quite a few changes to choose from. Thx! (PS: Images below have had local contrast enhancement and are inverted.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 04, 2015, 06:31:01 PM
Wipneus, any chance you could overlay some arrows or text? I'm not sure above what I should be looking at, quite a few changes to choose from. Thx! (PS: Images below have had local contrast enhancement and are inverted.)

A-Team, I modified the post to remove the doubt what I was referring to. I cannot say your "enhancements" bring out my feature very well.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 06, 2015, 06:41:03 AM
Thx for the circled feature above!

I need to know in advance what region is to be enhanced for what purpose. This may or may not be feasible. To make the second frame of the animation below, see http://www.imagemagick.org/discourse-server/viewtopic.php?t=27197 (http://www.imagemagick.org/discourse-server/viewtopic.php?t=27197)

The fringes image (rgb = first, second, second dates as grays) shows the bluish fracture does not have a full length reddish counterpart, so is a new development.

The second animation co-registers fixed features west of the fracture to display geometrical distortion elsewhere, a small clockwise rotation relative to this coordinate frame but also quite bit more fracturing visible at 1.5x magnification. Here I didn't know if the path,row were the same in the two images which would minimize distortion contributed from the satellite. Click to view.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 06, 2015, 09:09:07 AM
Here I didn't know if the path,row were the same in the two images which would minimize distortion contributed from the satellite.

Yes May-1 to June-2 is 32 days, 2 Landsat Cycles. Actually I show very few animations that are not from the same orbital position. I can not remember any Landsat animation that was not.

Thanks for the instructive comments!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 06, 2015, 03:36:51 PM
May-1 to June-2 is 32 days, 2 Landsat Cycles.  my animations are ~always use the same path,row.

Excellent practice. Others, in their search for pairs of cloud-free days, may not realize why this is important in avoiding artifacts, so I chased down the accession numbers (which are unambiguous in the case of Landsat-8 dates) to confirm the path,row business and look at the centers of scene (nadirs directly below satellite) which can wander a bit even with the same path,row.

Here they are both favorably near to the fracture of interest (rather than on the image margins) but displaced southeasterly by 5.4 km. This has a minimal effect compared to unavoidable sun elevation differences (and so shading), here over 7º.

This is what made possible widespread co-registration of upstream glacier features above by simple pixel shifting without the need for non-linear warping. Warping is problematic for Zachariae, Petermann and Jakobshavn because there aren't any fixed points (rocks) in the interior and everything else is in non-uniform motion. This means correcting along the coastal direction only.

I have been wrestling with the same issue of best fixed reference frame on a 15-year time series at Petermann. This is another story of a warm ocean current melting the underside of an ice shelf underside so does not have the dynamic thinning/stretching, calving and grounding line migration issues of Zachariae but instead a tapering of velocities as the main ice stream brushes against the edge of a tributary glacier contribution, which in turn brushes against a later tributary, which in turn brushes against a third tributary, which in turn scrapes along the rock wall.

Here two old fractures have remained the same distance apart and can be taken as the fixed points for alignment and rescaling. It all bears an uncanny resemblance to the Transverse Range in California, rotated as the Pacific Plate grinds past the N American.

Entity ID: LC80110032015153LGN00
Coordinates: 79.11406,-25.93111
Acquisition Date: 02-JUN-15
Path: 11
Row: 3
Sun Elevation 32.227“

Entity ID: LC80110032015121LGN00
Coordinates: 79.1478,-26.11325
Acquisition Date: 01-MAY-15
Path: 11
Row: 3
Sun Elevation 25.123º

Distances, bearings, and google earth kml provided by http://www.movable-type.co.uk/scripts/latlong.html (http://www.movable-type.co.uk/scripts/latlong.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 06, 2015, 03:53:12 PM
North East Greenland: Coldest May measured since 1949

http://www.dmi.dk/nyheder/arkiv/nyheder-2015/06/groenland-lagt-paa-is-i-maj/ (http://www.dmi.dk/nyheder/arkiv/nyheder-2015/06/groenland-lagt-paa-is-i-maj/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 06, 2015, 04:51:29 PM
Espen, did you see where someone linked off-site to some most excellent plots of Greenland temperatures?

I cannot relocate that very recent post but it showed temperatures were a full month behind, almost flat-lining cold. If this keeps up, it will not be a big year for meltwater acceleration of Greenland glaciers (though would we be surprised if this stationary situation flipped to stationary extreme warmth later in the season?).

However cold air temperature will have a minimal effect on bulk ocean temperature and CTD stratification near Greenland. Quite a bit of calving front and ice shelf underside melting is driven by a change to warmer ocean. This is not global ocean warming from climate change per se (real but not responsible) but rather pre-existing warmer currents finding their way farther north under climate change and tidal exchange. At least that is the story being told for Zach, Niog, Jakobshavn and Petermann.

I'm not aware of much in the way of meltwater affecting upper Zach or Petermann. Ice deformation is much greater at depth where it is much warmer due to geothermal flux and sliding friction. This zone has only exceedingly weak couplings to the air temperatures 2-3 kms above.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 06, 2015, 05:17:34 PM
A-Team, it will only have marginal effect on glacier activity, although my feeling is Zachariae etc. are slowing down at the moment.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 06, 2015, 08:24:50 PM
That being said (see above) a new calving row is developing:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 06, 2015, 08:42:27 PM
A-Team, it will only have marginal effect on glacier activity, although my feeling is Zachariae etc. are slowing down at the moment.

From my layman's point of view Zach seems to be calving full steam ahead, despite unfavorable conditions (low temps, frozen sea surface), but it's just a gut feeling. Could you perchance show a comparison to the calving front at this date last year? I wish I had your skills/knowhow of finding and presenting such info. Very much a newbie still.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on June 07, 2015, 02:06:16 AM
From my layman's point of view Zach seems to be calving full steam ahead, despite unfavorable conditions (low temps, frozen sea surface), but it's just a gut feeling. Could you perchance show a comparison to the calving front at this date last year? I wish I had your skills/knowhow of finding and presenting such info. Very much a newbie still.

Last year when the sea ice in front of Zachariae melted in late August there was a lot of calving within a few days as shown by the following posts by Espen:

http://forum.arctic-sea-ice.net/index.php/topic,400.msg35513.html#msg35513 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg35513.html#msg35513)
http://forum.arctic-sea-ice.net/index.php/topic,400.msg36496.html#msg36496 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg36496.html#msg36496)

My guess is that those calvings were triggered by the easing of the back pressure by the sea ice.

A potential longer term effect is that the sea ice melting allows all those icebergs to move away which might ease the flow of warm waters to the calving front. If the summer were so cold that the sea ice in front of Zachariae never melts, that might have a significant negative effect.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 07, 2015, 05:29:24 AM
oren asks for "perchance  a comparison to the calving front at this date last year?"

Espen had the good sense to see the changes coming in Zach and open this forum two years ago on June 25, that is to say 440 posts ago. I suspect that Espen and Wipneus between them have somewhere posted exactly the images you are seeking. If not, the easiest way to get started is with the small preview jpg images supplied by EarthExplorer.

From there it all depends on your computer set-up. I don't think any two people here use the same image processing software. People have made good efforts to describe the exact steps to follow in certain cases, notably Wipneus, sidd, and nukefix. This can be a real time and frustration saver as the satellite hosting sites offer next to nothing by way of practical tutorials.

If you can get past the download to a file that will open into a recognizable image on your monitor, the processing software needed for enhancement, cropping, comparison, and animations will have poorly documented and non-intuitive commands, a bizarre user interface such as no un-do's, and many bugs that never seem to get fixed. Followed by issues getting typepad to actually display your result as intended.

However after getting a few work flows down pat, it is great fun and not that time-consuming to pursue personal research agendas, all made possible by free access to satellite data in near real-time. Often someone here is the very first to notice and correctly interpret a new development.

There is a lot of synergy too with numerous contributors having substantial skills in one specialty or another. So Neven's project overall ends up being a very substantial climate change resource, with bloggers educating not only each other but whoever stops by wanting to take their personal understanding to the next level.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 07, 2015, 07:56:44 AM
oren asks for "perchance  a comparison to the calving front at this date last year?"

Espen had the good sense to see the changes coming in Zach and open this forum two years ago on June 25, that is to say 440 posts ago. I suspect that Espen and Wipneus between them have somewhere posted exactly the images you are seeking. If not, the easiest way to get started is with the small preview jpg images supplied by EarthExplorer.

From there it all depends on your computer set-up. I don't think any two people here use the same image processing software. People have made good efforts to describe the exact steps to follow in certain cases, notably Wipneus, sidd, and nukefix. This can be a real time and frustration saver as the satellite hosting sites offer next to nothing by way of practical tutorials.

If you can get past the download to a file that will open into a recognizable image on your monitor, the processing software needed for enhancement, cropping, comparison, and animations will have poorly documented and non-intuitive commands, a bizarre user interface such as no un-do's, and many bugs that never seem to get fixed. Followed by issues getting typepad to actually display your result as intended.

However after getting a few work flows down pat, it is great fun and not that time-consuming to pursue personal research agendas, all made possible by free access to satellite data in near real-time. Often someone here is the very first to notice and correctly interpret a new development.

There is a lot of synergy too with numerous contributors having substantial skills in one specialty or another. So Neven's project overall ends up being a very substantial climate change resource, with bloggers educating not only each other but whoever stops by wanting to take their personal understanding to the next level.

I am SO stupid... It never occurred to me to check further upstream on this thread  ::)

Eyeballing http://forum.arctic-sea-ice.net/index.php/topic,400.msg28071.html#msg28071 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg28071.html#msg28071) compared to the current situation shows the calving front is now further back than the same time last year.
Still doesn't mean much as I am interested in the retreat speed. Next on my agenda is to subtract June 15 - June 14, comparing to June 14- June 13. And to subtract June 15 from Sep 14, and June 14 from Sep 13. And actually measure distances. I will try to do that and in the process learn some useful stuff. Thanks for the pointers.

btw I find it very interesting that Zach continues to retreat from Sep to June, compared to Jakobshavn that advances over the winter and retreats during summer.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on June 07, 2015, 12:43:37 PM
There is a lot of synergy too with numerous contributors having substantial skills in one specialty or another. So Neven's project overall ends up being a very substantial climate change resource, with bloggers educating not only each other but whoever stops by wanting to take their personal understanding to the next level.

That was the whole idea, and I'm really glad the Forum is being used this way.  :)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 14, 2015, 11:03:49 AM
Calving front update, although Zachariae seems to be slowing down for the time being, the calving zone is still moving inland from 2014 (Click on image to enlarge):
The ground image is from September 2014, will be updated later in the season.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 14, 2015, 11:26:42 AM
Detail from the June 13 image, ta first "tranversal" crack in the new calving is visible in the centre of this image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 14, 2015, 11:34:08 AM
In tradition with place name giving in Greenland, I have taken the privilege to name the island south of Kap Zach "Søhesten" (The Sea Horse) in English:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on June 14, 2015, 02:43:54 PM
That's a great name for that island!

Seeing that the calving front has regressed less (on average) each year since 2010, is this proof that global warming is slowing down?  :P  (You know, one contrary cherry-picked bit of data overrides a world full of actual data.  ;D)

More Seriously, do you have ideas why 2010-11 and 2011-12 might have calved so much more than other years?  (I recall that 2012 was a big melt year for Greenland.  Would this be part of the picture?)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 14, 2015, 03:20:09 PM
That's a great name for that island!

Seeing that the calving front has regressed less (on average) each year since 2010, is this proof that global warming is slowing down?  :P  (You know, one contrary cherry-picked bit of data overrides a world full of actual data.  ;D)

More Seriously, do you have ideas why 2010-11 and 2011-12 might have calved so much more than other years?  (I recall that 2012 was a big melt year for Greenland.  Would this be part of the picture?)

I guess it is a combination of high melt in the area for that year and at the same time the collapse of the arch between the present calving front and the former tongue of the glacier.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 14, 2015, 05:37:58 PM
Calving front update, although Zachariae seems to be slowing down for the time being,

I am not seeing anything of a slow down.

Attached is an animation of day 148 and day 164, rendered at 7.5 m/pix. The images are shifted so that what I think is the main glacier (center of the glacier, about one calving inward) are aligned. I noted the shift (using The Gimp with layers visible in difference mode) which was 15 pixels horizontal, 1 vertical.
Ignoring the vertical, that works out as 15*7.5/16 = 7.0 m/day. Even allowing for 2 pixels error, that is still at minimum 6.1 m/day.
I would be surprised to see a slow down, in fact a speed-up is more likely.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 14, 2015, 06:35:43 PM
Calving front update, although Zachariae seems to be slowing down for the time being,

I am not seeing anything of a slow down.


Everything is relative?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 14, 2015, 11:33:10 PM
That's a great name for that island!

Seeing that the calving front has regressed less (on average) each year since 2010, is this proof that global warming is slowing down?  :P  (You know, one contrary cherry-picked bit of data overrides a world full of actual data.  ;D)

More Seriously, do you have ideas why 2010-11 and 2011-12 might have calved so much more than other years?  (I recall that 2012 was a big melt year for Greenland.  Would this be part of the picture?)

Since a lot of the 2014 retreat happened during August and September when the sea ice cleared away, and since 2015 saw quite a retreat during winter and spring, My expectation is that 2015 will finish above 2014 in terms of retreated area. I am working on some calculations to compare the years, still learning the ropes with all these heavy images.

btw my layman's thinking is that Zacharia is currently at a bottleneck of sorts, where the glacier has to squeeze at the relatively narrow pass between Kap Zacharia and Kap Zach. I believe that once it retreats a little further inland it might lose more buttressing and speed up (and possibly retreat faster).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 15, 2015, 02:41:03 AM
#449  animation  rendered at 7.5 m/pix. The images are shifted so the main glacier is aligned. Even allowing for 2 pixels error, that is still at minimum 6.1 m/day.

I think those were about optimal decisions. To expand a bit on the method for Oren and others following along:


Could the final velocity estimate be improved by enlarging to 3.75 m? By using a different interpolation method? By tweaking contrast more? I have no idea. What we need here really is access to two fixed GPS stations on poles drilled into the ice. Then we would have an accurate velocity calibration standard against which to compare potential improvements in image processing.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 15, 2015, 07:38:56 AM
#449  animation  rendered at 7.5 m/pix. The images are shifted so the main glacier is aligned. Even allowing for 2 pixels error, that is still at minimum 6.1 m/day.

I think those were about optimal decisions. To expand a bit on the method for Oren and others following along:

  • two landsat-8s were downloaded with same path,row to avoid relative distortion
  • the dates had enough temporal separation given the ~ velocity so fixed features will be sufficiently separated by pixel displacement
  • Landsat-8 has 12-bit resolution but is bicubic-interpolated to 16-bit already
  • initial operations are done at 16-bit depth, starting with 'normalization' to full dynamic range
  • the images are blown up from 15 m nominal resolution to 7.5 m, again with bicubic
  • processing can be shifted now to 8-bit tools like gimp with convenient features
  • a sensible stationary reference frame is chosen in a scene where everything but rocks is moving
  • vertical thinning is ignored as probably a negligible contributor error over this time frame and season
  • pixel and angle displacements are determined with the 'measure' tool
  • relative velocity (to a different pair of dates) is easier than absolute velocity as the same processing error cancels

Could the final velocity estimate be improved by enlarging to 3.75 m? By using a different interpolation method? By tweaking contrast more? I have no idea. What we need here really is access to two fixed GPS stations on poles drilled into the ice. Then we would have an accurate velocity calibration standard against which to compare potential improvements in image processing.

A-Team thanks for all the detailed pointers. Are you using ImageMagick for the 16-bit stages?
I am trying to calculate some other stuff in my slow crude way, not the glacier speed as I have no chance on improving anything already calculated.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 17, 2015, 08:37:35 PM
More calving activity at Zachariae:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 18, 2015, 01:53:49 PM
Here is a detail animation (taken from different orbit positions, lights and shadows may differ, some distortion possible).
Visible are: old calving breaks in two, small calving flips and a crack getting longer. Quite active for a 4 day difference.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 18, 2015, 10:20:58 PM
Might add some cracking and albedo changes in the sea ice on the southern part of the image not showing up on the lower Worldview resolution
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 21, 2015, 07:24:51 PM
Zachariae Isstrøm update:

Zachariae is still moving ahead.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 22, 2015, 09:10:36 PM
Latest movement at Zachariae:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 24, 2015, 09:21:42 PM
Ka-pow! Suddenly out of nowhere, the solstice celebrations around Zachariae showed some action:

Just imagine the sound level?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 24, 2015, 10:27:36 PM
Very impressive. Here is the 15 m if someone wants to measure areas ...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 24, 2015, 11:17:33 PM
Wow! Looks like a very strong tide went out or something.
This could ease the local buttressing and possibly lead to more calving.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on June 24, 2015, 11:26:06 PM
Am I seeing what I think I am seeing? Zach usually sends off tabular icebergs but this latest calving seems to have rolled over.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on June 24, 2015, 11:34:44 PM
Hmmm, that could explain how much movement there was.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on June 25, 2015, 12:56:32 AM
I think that particular iceberg was too narrow, having width smaller than height, causing it to roll over.

A-Team can you estimate the thickness of the ice from your image?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 25, 2015, 02:08:24 AM
that could explain how much movement there was.that particular iceberg was too narrow, having width smaller than height, causing it to roll over.
The magenta bergs are about 30 pixels thick or 450 m. Not so easy to measure accurately because of shadowing vs rock accretion on the bottom and angled top maybe still showing. The sun angle was 34.8º at an azimuth of -162.7º on this particular Landsat.

Right, instability of a tall but narrow calving product makes sense given the center of gravity and what we saw so graphically in 'Chasing Ice.' Roll-over then creates a massive wave that pushes away the older, stable tabular bergs.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 25, 2015, 06:26:34 AM
Am I seeing what I think I am seeing? Zach usually sends off tabular icebergs but this latest calving seems to have rolled over.

In the earlier days Jakobshavn produced tabular icebergs too, maybe we will see a shift at Zachariae in the future, the next pre-calving line is also relatively narrow.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: mspelto on June 25, 2015, 01:16:54 PM
It was the rapid rift extension illustrated between 6/6 and 6/17 that set this up.  No surprise.  The rift development behind the front is now poorer than typical it seems to me.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 25, 2015, 04:38:09 PM
Here is 104 km of an ice-penetrating radar transect (red and following blue) taken from the set available (pink inset). The dotted magenta line is Cresis' take on the surface, the dotted red line bedrock resp. ice shelf surface. The depth indicators are relative (ie not set to WGS84 sea level). The scheduled 2015 over-flight had to be cancelled because of weather. https://data.cresis.ku.edu/data/rds/
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on June 25, 2015, 07:50:53 PM
Could a speeding up of Zachariae Isstrom be causing thicker ice to be pushed into deep water? If the glacier is moving slow, it might allow sufficient bottom melt that the glacier will be more prone to tabular calving.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on June 26, 2015, 10:05:37 AM
Could a speeding up of Zachariae Isstrom be causing thicker ice to be pushed into deep water? If the glacier is moving slow, it might allow sufficient bottom melt that the glacier will be more prone to tabular calving.

The height of the calving front is probably growing because the bed is getting deeper and the ice surface higher as the calving front retreats. This can be seen in the following image posted by sidd (http://forum.arctic-sea-ice.net/index.php/topic,400.msg22091.html#msg22091) last year.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D400.0%3Battach%3D5356%3Bimage&hash=ab8b01099315a2ffa2fc225e3aacab2a)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on June 26, 2015, 05:02:25 PM
So we could be seeing a major  shift in the behavior of this glacier with thick bergs calving and rolling over. Could this trigger a much faster retreat of the calving front?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 26, 2015, 06:53:17 PM
So we could be seeing a major  shift in the behavior of this glacier with thick bergs calving and rolling over. Could this trigger a much faster retreat of the calving front?

If so we will see the same behavior as seen at Jakobshavn and Helheim, but that said, Zachariae is relatively speaking on the move anyway, but what happens at Zachariae should make any decision maker worried!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 27, 2015, 03:51:42 PM
Big news ... EGRIP, a new core to bedrock will be drilled in the ice stream leading to Zachariae! The 46 metric ton dome at NEEM and sledges of equipment have already been dragged on skis 465 km to the new site (with a Pistonbully 300).

Before stripping out NEEM, its 2550 m deep antifreeze-filled borehole at NEEM, undisturbed since 2012, was logged for temperature (precision 0.01 °C), inclination, azimuth, borehole diameter and pressure.  The temperature data can help reconstruct past surface temperatures and monitori meltwater at the bed. Diameters tracl pressure balance of the liquid in the borehole and putative changes around the folded zones of the Eemian ice. The inclination and azimuth  monitor the deformation of the borehole. The surface velocity  at NEEM has been ~5 m/yr for five years allowing adequate accuracy.

The strain net around the NEEM drill hole will also be remeasured. The motion of the ice sheet is critical to interpretation of ice layers; curiously neither direction nor speed has been constant (1st image below).

Various science projects were conducted en route to EGRIP such as firn and depth radars, even continuing them to Summit. There is a most excellent 96 page pdf that covers everything from scientific priorities to the bamboo pee pole at camp. The project was funded to the tune of 25 million DKK by a Danish charitable foundation AP Møller with historic ties to Maersk shipping.
 
The biggest ice stream in Greenland passes through the EGRIP site. It is not really possible to anticipate future changes in the marine outlets Zachariae, Nioghalvfjerdsfjorden and Storstrømmen without a good grip on NEGIS itself, which supposedly starts over a geothermal anomaly. That will be checked with seismic studies. The ice reaches velocities over 100 m/yr some 200 km from the ice divide yet still 500 km from the coast.

It proved possible to find a site on the upper ice stream without crevasses. The ice at the chosen site is 2550 m to bedrock and flows at 65 m/yr (see attached images). Previous deep cores have all been along the summit ridge; this one would allow study of ice flow dynamics via rheology and deformation below the surface as well as basal sliding, borehole deformation, and basal water processes.

They totally botched the logarithmic color key on the high resolution velocity map (which seems to overlie a hillshaded DEM) and it is not possible read out velocities at specific points nor contour them. The low resolution velocity map did have sufficient detail to let speed profiles to be put on Cresis radar profiles.

Over 50 kyr of radar stratigraphy at EGRIP has been mapped back to NGRIP which in turn is tied in to all the other cores including Antarctica's. A core here will enable climatic studies of this period and especially the Holocene where high resolution records of greenhouse gasses, water isotopes and impurities are not available for East Greenland.

Drilling is a little tricky as borehole will slant 195 meters downhill (7.6% off-vertical) before the three year project is finished in 2020. The drill cores themselves will be ~13 cm in diameter. They have not yet disclosed the precise lat,lon of the drilling site but the ice stratigraphy appears slightly concave upward rather than flat as advertised.

http://www.isogklima.nbi.ku.dk/nyhedsfolder/danske_nyheder/egrip-2015-feltplan/Renland-EGRIP2015FieldPlan.pdf (http://www.isogklima.nbi.ku.dk/nyhedsfolder/danske_nyheder/egrip-2015-feltplan/Renland-EGRIP2015FieldPlan.pdf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on June 28, 2015, 11:02:06 AM
A new updated retreat version (please note the background image is from September 2014, click for enlargement):
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 28, 2015, 06:44:11 PM
The vertically exaggerated oblique image below of the NEGIS ice stream feeding Zachariae is one of the most peculiar features in Greenland. Shear boundaries are already visible just from the ice surface DEM yet there are no real traces in the bedrock DEM corresponding to these surface features and indeed the ice stream flows uphill in places. I took this oblique image from Nasa visualizations http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet (http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet)

That possibly fits with the putative upstream geothermal anomaly providing lubrication to sliding (rather than glacial grinding). The anomaly is model-based and lacks direct observational support. I'm skeptical because it seems improbable that the only proposed heat anomaly in Greenland should lie right along the summit ridge, too much of a coincidence considering the small percentage area.

Zachariae etc are very important to get right because the huge iceshed -- 16% of Greenland -- could potentially be a big contributor to future sea level rise. Without knowing the interior physics of NEGIS, it is difficult to predict its acceleration in respnse to removal of marine buttressing. (For comparison, Jakobshavn drains 8% and Petermann just ~4%.)

EGrip is drilling fairly high up though below the anomaly. Temperature profiles with depth are very sparse in Greenland so the experimental data here will be of great interest. Recent efforts to get at temperatures using radar and layer dating have made some progress but overall have not produced a stellar outcome. http://www.ig.utexas.edu/people/staff/joemac/pdf/MacGregor_2015_JGR_2.pdf (http://www.ig.utexas.edu/people/staff/joemac/pdf/MacGregor_2015_JGR_2.pdf)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Rubikscube on June 28, 2015, 11:34:12 PM
Zachariae etc are very important to get right because the huge iceshed -- 16% of Greenland -- could potentially be a big contributor to future sea level rise. Without knowing the interior physics of NEGIS, it is difficult to predict its acceleration in respnse to removal of marine buttressing. (For comparison, Jakobshavn drains 8% and Petermann just ~4%.)
Is this an estimate exclusively based on current flow rates, and the respective ice thickness, with little or no regard for the underlying topography? 8% to Jakobshavn seems like a terribly low estimate.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 29, 2015, 02:48:48 AM
Is this an estimate exclusively based on current flow rates, and the respective ice thickness, with little or no regard for the underlying topography? 8% to Jakobshavn seems like a terribly low estimate.
No, it is just an area. Each outlet glacier gets to count a spot of area above it if a snowflake falling there would eventually exit through it (assuming unvarying current conditions), that is to say, flow lines or trace-forwards of trajectories on surface velocity maps.

In other words, it's just like dividing a mountain range into its watershed basins. These areas were all quantitated years ago as part of the PARCA circumferential stake line at 2000 m and revisited more recently by a geography expert group in Wales.

Perpendiculars to elevation contours are quite troublesome to calculate from digital data and some landscapes give rise to vexatious anomalies (eg flowlines crossing or disappearing). It is better here to fit a differentiable surface to the DEM.

B Csatho maintains a most excellent interactive tool for this data at http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_AllGates.html (http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_AllGates.html) which I've posted several times on various forums. Jakobshavn there is given 116,401 km2 above 2000 m. It pinches out at the coast, especially to the south.

The ~1% slope of central Greenland means the difference between using on-the-ground area vs projected area is negligible compared to the error associated with determining iceshed boundaries which are difficult to position because ice is nearly stagnant on dividing ridges and an ambiguous nearly horizontal cylindrical surface on the west slope.

Sub-surface flow need not match surface flow direction but in Greenland it does for most practical purposes. And despite all the hulabaloo about sills and canyons, the elevation of bedrock interior in central and northern Greenland actually has a rather small variance around sea level. So, given symmetry about the central NS surface ridge, bedrock topography has little effect on the volume of ice associated with particular snowshed -- you could get a decent ice volume estimate just integrating over each basin's elevation above sea level (or more crudely as the fraction of total Greenland area x total Greenland ice volume)

None of this gives volumes of ice that will be eventually discharged by each glacier. For one thing, annual snow accumulation varies greatly, as does melt and run-off with latitude. For another, the rapidly thinning glaciers could capture iceshed area from slower moving neighbors. And flow rates of Greenland glaciers are accelerating very unevenly.

In summary, area isn't a great proxy but it suggests the relative importance of basins and the numbers in my previous post are the ones that Greenland glaciologists use (especially if writing up a grant proposal for a remote/expensive region like NE Greenland.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Rubikscube on June 29, 2015, 09:55:28 PM
Really appreciated with such extensive answers. I was foremostly thinking about topography because it tells about the potential for future acceleration in speed and volume discharge, but I recon it will be extremely difficult to make a more precise definition of iceshed (based on volume) especially when the timescale of a GIS collapse in unknown.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on June 29, 2015, 11:11:34 PM
Right, that would get into modelling a whole ice sheet whose basal friction and internal temperature profile -- the determinant of the key rheology parameter in Glen's flow low -- are scarcely constrained by observation. It’s tough to make predictions especially about the future, according to baseball coach Yogi Berra. So people just toss out these areas which at least are in the right ballpark.

The attached image shows a typical basin in NW Greenland -- pinched out at the summit ridge, as are its neighbors. Here Humboldt was assigned 3% of the total area in a 2006 study. While Zachariae jumps out as a big number, Greenland-wide you end up having to sum a lot of small numbers, each of which is a special case on its own in terms of topography etc.

It is easier -- and maybe more accurate -- just to watch GRACE mass loss for trend development.

Rignot E and Kanagaratnam P (2006) Changes in the velocity structure of the Greenland Ice Sheet. Science, 311(5673), 986–990 (doi: 10.1126/science.1121381)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 04, 2015, 04:46:22 PM
A new updated retreat version (please note the background image is from September 2014, click for enlargement):

For the last month I have been trying to assess Zachariae's retreat pattern and whether it is slowing down. So having gone through all the process of downloading, unzipping, converting and processing, following A-Team's and Wipneus' detailed guidelines, I finally have some crude output on the subject.

Using Espen's material as a basis, I compared the calving front movement over the 10 cold months of the year, roughly Sep 1 to Jul 1, in both 2013-2104 and 2014-2015. And the result is that in 2013-2014 the calving front advanced during that period (red to yellow line), while in 2014-2015 the calving front actually retreated even though the sea ice still remains. I find that quite interesting. Perhaps it points to accelerated calving front retreat?

p.s. apologies for the grayscale image for 2014, some stuff is still beyond me.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 11, 2015, 09:01:02 AM
Zachariae update. A new calving line is seen and further developing:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 11, 2015, 10:27:50 AM
To satisfy my curiosity, I went back one more year and dug up Jul 1 2013. As can be seen, 2012 to July 2013 did show a retreat during the cold months, somewhat similar in magnitude to 2014-2015 and opposed to 2013-2014. So this behavior is not new. Perhaps it does however predict a bigger retreat year.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 11, 2015, 03:18:48 PM
Zachariae update. A new calving line is seen and further developing:

It will be interesting to see if this calving rolls over or is tabular as the calvings usually are.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 12, 2015, 08:17:45 PM
The latest calving line at Zachariae is moving in a big way in the northern part of the glacier front, sorry about the weather conditions :(
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on July 19, 2015, 09:01:44 PM
Here a rare calving at Nioghalvfjerdsfjorden (79 Fjord), I haven't seen this for quite some time now:

Sorry about the double s in the animation ;)

Please click for animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 23, 2015, 08:29:08 PM
This clear worldview image from 20rd July seems to show the surface structure produced by the movement shown in the velocity chart. I thought it would be nice to compare.
The blue seems to be freshly uncovered ice, it seems to become whiter later, can someone say more about what we see there?
on the 21st the icebergs in front of Zachariae had a sudden push possibly from wind coming down the glacier.
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=400.0;attach=17537;image)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 24, 2015, 10:16:55 AM
Time for a new natural color animation of the Zachariae, July 4 - 20. I kept it low resolution (45m/pix) to be able to show the overview. The development of melt ponds is striking, also have a look at the old tongue in the NE corner of the image. Most melt ponds can be seen appearing or growing, but there are some (look in the SW corner) that drain between the two snapshots.

For measuring the average speed I used the Gimp image editor with both images stacked and displaying their difference:
- boost the resolution to 5m/pix.
- align the images using the various rocks.
- align the images near the centre of the glacier front, about one calving away from the latest developing calve;

The latter alignment required a shift of (x,y)=(26,2) pixels, that works out to 8.1 m/day for speed. Assuming a 2 pixel uncertainty in the procedure that would be a range of 7.5-8.7 m/day.

That is high compared with previous measurements (upto until now about 6-7 m/day). Until confirmed with newer images I'd suggest a possible speed-up.

(can't escape the click)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on July 24, 2015, 01:45:47 PM
Whitish light blue ice next to the July 4 melt ponds are generally covered by melt pond water on the 20th.  I suspect these were melt ponds last year that froze, and are now covered by new melt water.  (I have no expertise in this, however.  My air photography class [remember pocket stereoscopes?] 40 years ago did not include any images with ice.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 25, 2015, 10:50:55 AM
An alternative explanation for the whitish areas Tor has spotted would be this: I have noticed in photos by Jason Box (dark snow project) that the darkened surfaces of the ice can be cleared of the accumulated dust, soot and algae which make it so dark by meltwater flowing over it. even more so by a draining meltpond. If the whitish area was a meltlake last year it is likely that draining of that lake flushed the "dirt" away.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 25, 2015, 04:31:39 PM
I have to admit, I am drawn to the Greenland glaciers threads every day, mainly for the beautiful images that Espen posts and now, more frequently, by the personally challenging explanations provided by A Team. I would like to thank both of you.

I really got interested when I stumbled across this research which develops a much more detailed map of the underlying topography.......

http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf (http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf)

As always, I am challenged to explain their approach.

I have always been fascinated by Jacobshavn (visit that thread often) and Espen always expresses that he is more concerned about Zachariae. I decided to go back and look at the detailed topography maps that have been developed, using the  mass conservation technique. (See below)

I now understand the concern. This glacier is a monster. There is an enormous section of the ice  sheet, well inland from the calving face, which is grounded many hundreds of meters below sea level.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 25, 2015, 04:42:39 PM
This clear worldview image from 20rd July seems to show the surface structure produced by the movement shown in the velocity chart. I thought it would be nice to compare.
The blue seems to be freshly uncovered ice, it seems to become whiter later, can someone say more about what we see there?
on the 21st the icebergs in front of Zachariae had a sudden push possibly from wind coming down the glacier.
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=400.0;attach=17537;image)

When you look at obvious surface melt occurring here and align this melt with the detailed topography map I have just posted, it seems the location of the melt is concentrated over where the ice sheet is grounded well below sea level. As this melt water drains, it would seem to have to pool here.

I don't believe surface winds can move glaciers so quickly. Could we be seeing the effects of sub glacial melt water pulses?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 25, 2015, 08:59:14 PM
sorry if I have not been very clear, its the icebergs in the sea in front of the glacier which moved. They do rise quite high above the water possibly enough to be moved by wind a few hundred meters in a day. But increased flow of meltwater is also something one can expect, its just the suddenness comparing 14th - 20th with 20th - 21st. which caught my eye.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: P-maker on July 25, 2015, 11:21:42 PM
Andreas T,

“The blue seems to be freshly uncovered ice, it seems to become whiter later, can someone say more about what we see there?”

Let me have a go at interpreting your image:

Starting in the left hand side, the first ¼ is a white melting snow surface gently sloping towards the sea. Near the foot of this slope you see the light bluish zone, which is most likely slush ice near the base of the slope. Please observe the clear blue drainage channels on the eastern side of this zone draining water from the slush ice. Once the water has drained off, the snow turns white again. The large homogenous white areas in the centre of the image  is most likely superimposed ice formed during initial melt this year or during earlier melting seasons. The easternmost 1/3 of the image consist of greyish bare ice with plenty of melt lakes. The glacier tongue itself is clear of melt lakes, since they have all drained through cracks in the ice.

Sorry to say Andreas, but in my view the front of the glacier and all the newly produced icebergs in front of it are moving eastwards at roughly the same speed between 4th and 20th July. The mélange between the icebergs seems to be rather compact, so the suggested movement by winds is highly unlikely.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 29, 2015, 01:37:08 PM
A Sentinel 1A hi-res pair of images that can be compared with the Landsat pair I posted a few days ago. Differences:

- radar vs optical
- 10m vs 15 m resolution
- 12 days cycle vs 16 days.

A hi-res S1A image seems now to become available every 12 days. Due to the speckle noise in the radar images the method that I use is much harder to employ and even useless at longer intervals than 12 days (at the current surface conditions).

Using the same method as in the Landsat case,  I measure the speed at the center of the calving front of 8.3 m/day (range 7.4 - 9.2). A little larger error, but confirmation that this is definitely beyond the 6-7 m/day measured during the past year.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on July 29, 2015, 04:38:31 PM
I measure the speed at the center of the calving front of 8.3 m/day  but definitely beyond the 6-7 m/day measured during the past year.

That’s of great interest if it is a non-seasonal increase, ie matching late July dates with 2013 ~ 2014 and 2015 a jump. The % increase looks to be very large, 30%? I’m not sure what the best way of estimating error in this percentage increase; the usual way of combining independent gaussian errors during division may not be applicable here.

I’m thinking Landsat-8 would have 3 full years of July/Augest data whereas Sentinel started posting this October or so. (It would be very problematic anyway to combine a Sentinel with a Landsat for a velocity measurement.) However cloudy days can frustrate plans to get closely matched Landsat date pairs at peak summer velocities. In theory Earth Explorer allows filtration by cloud content but that last 5% can still sit exactly where you don’t want it.

It might work better to script a download of just the blue preview and Band 10 cirrus. Someone has mirrored Landsat-8; this may allow an escape from whole package downloads at EExp. Though really since the time window is fairly small and the returns so far apart, it might be faster just to do this visually on the preview to the preview.

Sentinel is too speckled.

I have looked at many procedures for cleaning up Sentinel images, none of which notably improve ice feature resolution. I could try a few more things with hv modulating vv  in gimp ‘modes’ or in ImageJ ‘math’ on stack but this is one where a physics-based rational procedure could be more effective than monkey at the keyboard.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 29, 2015, 10:50:24 PM
Up-thread I can find measurements by Wipneus of (m/day):
6.1 in April-May 2014
7.5 (6.7 further from the front) in August 2014
6 during the 2014-2015 winter (Oct-Mar?)
7.5 in early June 2015.
8.3 in late July 2015.
To compare to a more distant past, Rignot 2006 shows Zacharia's speed as 1600 m/y (4.4 m/day) in 2005, and about 1400 m/y (3.8 m/day) in both 2000 and 1996.

I believe this is an acceleration in top speed of about 10-20% year over year, and 50-70% in 10 years, up from 0% acceleration in the preceding period.
Of course, comparison of matching dates over both winter and summer will give a better estimate.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on July 30, 2015, 12:11:18 AM
Nice work, chasing this history down. Goes to show measuring velocity is one thing, measuring changes in velocity (subtracting similar numbers from each other) takes it to a whole new level of error issues.

At 10% increase in velocity per year, it would take Zach 14 years to catch up to Jakobshavn's 28 m/d in late July 2015; 10 years at 15%; and 8 years at 20%. Assuming JI itself is no longer accelerating as fast as it has been. Petermann, the only other ice stream with noteworthy velocity roots in the interior, is a ways back at 3 m/day with no drama on the horizon.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on July 30, 2015, 04:15:32 PM
I have looked at many procedures for cleaning up Sentinel images, none of which notably improve ice feature resolution. I could try a few more things with hv modulating vv  in gimp ‘modes’ or in ImageJ ‘math’ on stack but this is one where a physics-based rational procedure could be more effective than monkey at the keyboard.
Speckle-noise is multiplicative and cannot be cleaned out with a *loss* of resolution. I  think the resolution of the EW-mode of S-1 is simply too coarse for detailed mapping - better to wait for IW-data that should be more available in the future. In any case velocity-mapping by cross-correlation is preferable to manually picking features to track..
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on July 30, 2015, 11:27:01 PM
IW velocity-mapping by cross-correlation is preferable to manually picking features to track

Good point. Getting at the velocity vector field manually over any kind of area would drive a person to distraction. Repeating over many image dates would finish them off. However there is some value in identifying hotspots, anticipating what magnitudes to expect and determining whether acceleration is plausibly within reach of IW Sentinel within what sort of time frame and what level of error.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 01, 2015, 11:58:00 PM
2nd calving this season at Nioghalvfjerdsfjorden this time larger than the previous:

Please click on image for animation!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 03, 2015, 02:31:07 PM
Detail sequence of Landsat 8 images from 17th July and 2nd Aug (one cycle = 16 days apart).

I used the panchromatic (band 8) 15m/pix data, over-sampled at 5m/pix and aligned the images just above the new calving line. From the displacement needed for the alignment the speed of the glacier can be calculated. This time it is 25x1 pixels, which gives 7.8 m/day, range 7.2 - 8.4 assuming uncertainty of two pixels.

See the shadow in the last frame (RH side, above the middle), something seems to be sticking its nose far above the surrounding bergs.

(click to start the animation)


Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 03, 2015, 02:56:16 PM
My first impression was this was a patch of water that had opened up without melange. Then I realized that must be a shadow, similar to the one being cast just a little bit south but this shadow is much longer. It has to be an iceberg, no?????
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 03, 2015, 03:43:03 PM
Now you say it, it has the look of a patch of open water as well.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 04, 2015, 02:25:39 AM
It sometimes helps to 'invert' these Landsats ...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: andy_t_roo on August 04, 2015, 05:52:39 AM
IW velocity-mapping by cross-correlation is preferable to manually picking features to track

Good point. Getting at the velocity vector field manually over any kind of area would drive a person to distraction. Repeating over many image dates would finish them off. However there is some value in identifying hotspots, anticipating what magnitudes to expect and determining whether acceleration is plausibly within reach of IW Sentinel within what sort of time frame and what level of error.

In the presence of contrast changes, normalised mutual information is a much better alignment measure that cross-correlation
Correlation matches absolute brightness values, where as mi roughy corresponds to comparing histograms.

The extreme example is 'match a white square on a black background with a black square on a white background' any corr. Based measure will return ' don't overlap the squares at all' any mi based measure will return 'overlap the squares as much as possible'.
Mi is also relatively insensitive to multiplicative noise, as long as the underlying 'texture'is still there.

Another alternative approach is to preprocess the data with x, and y gradient operators, and match vs offset is based on  abs (corr x) + abs(corr y)

You should be able to co register Landsat and sentinel data that way, given that edges in one field are also edges in the other, and we know the precise scaling factor between the 2 data sets.

(I have done post research looking at how to compare and align medical images)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 06, 2015, 06:29:18 PM
2nd calving this season at Nioghalvfjerdsfjorden this time larger than the previous:

Please click on image for animation!

Any one else note the lack of melt water on the surface in the later pix rather than the first one?

Did it all go to bed rock?  The ones that got smaller all look to be interconnected.  The ones that got bigger don't look to be interconnected.

That is a lot of water to go somewhere.  Could it start moving soon?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 08, 2015, 05:11:30 PM
In this sequence a few of the calving's break and/or topple over. Among them is the piece of ice - in the orange circle - that has my "hexagonal" feature, that I have used to track the glacier movement for years. It is now finally gone (under).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 08, 2015, 06:59:29 PM
Seems like there are 3-4 others flipping over. With a careful study of before and after surface areas, it seems like those that are completely rolling over (to expose the underside of the glacier) could be distinguished from those just flipping on their sides. The former might reveal meltwater channels or ocean water erosion.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 08, 2015, 07:48:54 PM
I can count 7 places?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 09, 2015, 07:03:07 AM
Interesting ... seems like a lot. Note the orangish color around the very freshest turned ice. That would be bluish in the original (just subtract the %s provided from 100%) which I believe Wipneus made as fairly close to natural color. It is moderately difficult to exaggerate the orange (to isolate it) while leaving the rest undisturbed; what worked best is channel remixing. Probably principle components would work better.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: P-maker on August 09, 2015, 08:12:41 AM
Gents,

please observe that those bergs, which flip over, all cast a longer shadow after their flip. This may indicate that they either had a keel before they flipped, or that they were more porous than surrounding icebergs.

Cheers P
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 13, 2015, 06:59:33 AM
Gents,

please observe that those bergs, which flip over, all cast a longer shadow after their flip. This may indicate that they either had a keel before they flipped, or that they were more porous than surrounding icebergs.

Cheers P
A simpler explanation lies in the shape of the bergs. The tabular bergs have an even height above water and an even depth below. The volume giving it its buoyancy is area x average depth which in this case is the depth at any point, The same applies to  the height. After breaking into an irregular shape and turning it can have greater height and greater depth in some places despite the same ratio of volume above and below water.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on August 13, 2015, 11:02:21 AM
A simpler explanation lies in the shape of the bergs. The tabular bergs have an even height above water and an even depth below.
Not sure about the even depth as that should depend on the shape of the fjord-bottom. At Jakobshavn it seemed like the center of the trunk was thinker in the middle of the flow.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 13, 2015, 05:47:23 PM
A simpler explanation lies in the shape of the bergs. The tabular bergs have an even height above water and an even depth below.
Not sure about the even depth as that should depend on the shape of the fjord-bottom. At Jakobshavn it seemed like the center of the trunk was thinker in the middle of the flow.
The free floating ice that has been that way for a bit would be more than less flat bottomed.  Give or take a bit.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 13, 2015, 10:54:52 PM
the row of bergs which turned sideways at calving a few weeks ago show flat bottoms and a constant thickness at least in that middle part of the glacier
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 14, 2015, 07:19:39 PM
Detail sequence of Landsat 8 images from 17th July and 2nd Aug (one cycle = 16 days apart).

I used the panchromatic (band 8) 15m/pix data, over-sampled at 5m/pix and aligned the images just above the new calving line. From the displacement needed for the alignment the speed of the glacier can be calculated. This time it is 25x1 pixels, which gives 7.8 m/day, range 7.2 - 8.4 assuming uncertainty of two pixels.

See the shadow in the last frame (RH side, above the middle), something seems to be sticking its nose far above the surrounding bergs.

(click to start the animation)
It looks to me to be something pushed up out of the water.  It is at the approximate point of contact between the advancing calving event and the prior events left overs.  Is the new one starting to role over?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Sonia on August 15, 2015, 12:27:31 AM
Today's Terra image shows some cracks in the Northeast Water Polynya.  The breakup is happening a little later than in the last two years.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 16, 2015, 10:05:51 AM
Follow up of the sequence presented on 8th August. Since these Landsat images are not from the same orbital position they cannot be perfectly aligned, I aligned -best effort- just above calving front.
More calvings do break or topple or flip over (the non-exclusive "or" is meant). The dark shadow identified some weeks ago is gone leaving a somewhat darkened patch of ice melange.

(click on the picture)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 16, 2015, 12:28:53 PM
Somehow it feels that the rate of calvings has slowed down (gut feeling, not verified).
I'm anxiously waiting for the clearing of the sea ice, which could bring about a significant retreat. It's running late this year.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on August 16, 2015, 03:33:56 PM
Below is a close-up of a berg breaking in half, with one half rotating 45º or so about a horizontal axis exposing a cleavage plane. The other smaller berg has only a small eastward piece rotating, not clear why it is so white (= dark in original).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 18, 2015, 06:43:05 PM
Below is a close-up of a berg breaking in half, with one half rotating 45º or so about a horizontal axis exposing a cleavage plane. The other smaller berg has only a small eastward piece rotating, not clear why it is so white (= dark in original).
looks like shadows to me.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 18, 2015, 06:50:05 PM
That is rotten ice and is just disintegrating.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 22, 2015, 09:15:19 AM
Detail of the sequence 14-20 August. The images are from different orbital positions, so some distortions and shadowing are from that. A thin sliver off the "new" expanding calving front shows it is unstable and collapses.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 22, 2015, 06:10:14 PM
It is barely visible in the animation above, but rendering the image to 5m/pixel shows the beginning of a future calving front a bit clearer. Added an arrow, just to be sure.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 22, 2015, 10:16:08 PM
It is barely visible in the animation above, but rendering the image to 5m/pixel shows the beginning of a future calving front a bit clearer. Added an arrow, just to be sure.

Genius observation.
I'd never have noticed it myself, but now that you pointed it out it's very clearly shown in the animation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 25, 2015, 06:06:05 PM
On today's hi-res (IW) sentinel 1 image that developing future calving front is easy visible.
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 28, 2015, 06:53:04 PM
Animation of the two 2015 calvings of Nioghalvfjerdsfjorden in natural color (45m/pixel).

(click to start)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 27, 2015, 12:07:41 AM
Zachariae is still moving:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 27, 2015, 04:07:56 PM
Yearly review, not much change in calving front position, but the amount of ice debris in front of Zachariae Isstrøm is substantially larger:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on September 29, 2015, 12:07:05 AM
Yearly review, not much change in calving front position, but the amount of ice debris in front of Zachariae Isstrøm is substantially larger:

I think the main difference this year is that the sea ice in front of ZI never went away, which prevented the big flushing and retreat that happened last year in August.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 20, 2015, 09:35:17 AM
Animation from Sentinel 1A 23rd Sept-17th Oct, 24 days or 2 S1A cycles. Estimated speed measured at the calving front #3 (#1 is the front that has fully calved) is 6.2-7.2 [m/day], a bit slower than in the beginning of this summer. Measuring using the visually alignment method using the Gimp is far more difficult anyway: less tiny details are visible on the glacier surface.

About calving fronts: 4 more features are visible that could be future fronts 4-7.

(click to start animation)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 20, 2015, 09:38:04 AM
Detail of the same sequence: one of the upside down icebergs (the one with my hexagonal feature down now) breaks up again.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on October 20, 2015, 12:45:09 PM
What is causing the even spacing of future bands 4-7?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 04, 2015, 10:06:05 PM
Zachariae Isstrøm still alive https://www.youtube.com/watch?v=qM0zINtulhM (https://www.youtube.com/watch?v=qM0zINtulhM)

Here is a youtube of the animation: https://youtu.be/aV9qHDB8X4w (https://youtu.be/aV9qHDB8X4w)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on November 09, 2015, 12:37:49 PM
S-1 IW HH 5.11.2015 in UTM zone 27 at 15 pixel-size:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 09, 2015, 05:25:56 PM
Awesome image.

Might as well be grayscale? It is coming up as RGB, that would cut file size down from 49 MB to 12 MB. With two dates and grayscale, we can make a movement RGB in ImageJ.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: AbruptSLR on November 12, 2015, 09:41:03 PM
The linked reference (and associated articles) discuss how the grounding line of Zachariæ Isstrøm became detached from a submarine sill and has been losing ice mass at an accelerating rate since 2012:

J. Mouginot, E. Rignot, B. Scheuchl, I. Fenty, A. Khazendar, M. Morlighem, A. Buzzi and J. Paden (12 Nov 2015), "Fast retreat of Zachariæ Isstrøm, northeast Greenland", Science DOI: 10.1126/science.aac7111


http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract (http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract)


Abstract: "After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come."

See also:
http://news.uci.edu/research/massive-northeast-greenland-glacier-is-rapidly-melting-uci-led-team-finds/ (http://news.uci.edu/research/massive-northeast-greenland-glacier-is-rapidly-melting-uci-led-team-finds/)

Extract: "A glacier in northeast Greenland that holds enough water to raise global sea levels by more than 18 inches has come unmoored from a stabilizing sill and is crumbling into the North Atlantic Ocean. Losing mass at a rate of 5 billion tons per year, glacier Zachariae Isstrom entered a phase of accelerated retreat in 2012, according to findings published in the current issue of Science."


http://www.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html?_r=0 (http://www.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html?_r=0)

Also see:


Carolyn Gramling (2015) "How warming oceans unleashed an ice stream", Science

http://www.sciencemag.org/content/350/6262/728.summary (http://www.sciencemag.org/content/350/6262/728.summary)

Summary: "Beneath the calm, white surface of Greenland, rivers of ice are flowing into the ocean—and some are moving very fast indeed. The speedy glaciers on the island's warmer west coast, shedding kilometers of ice into the sea each year as warm ocean waters undermine them, have raised the most alarm about potential sea level rise. But now, a vulnerable glacier on the other side of the island, part of a massive flow of ice known as the Northeast Greenland Ice Stream, shows that yet another region of Greenland is feeling the effects of warming oceans. And a new study suggests it's likely to continue its rush to the sea for decades to come."

Edit: See also:
http://climate.nasa.gov/news/2366/ (http://climate.nasa.gov/news/2366/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on November 12, 2015, 10:43:41 PM
The Guardian has an article (http://www.theguardian.com/environment/2015/nov/12/collapsing-greenland-glacier-could-raise-sea-levels-by-half-a-metre-say-scientists):

Collapsing Greenland glacier could raise sea levels by half a metre, say scientists

Huge Zachariae Isstrom glacier has begun to break up, starting a rapid retreat that could continue to raise sea levels for decades to come

(https://i.guim.co.uk/img/media/4a95a3bbee852fe5fa3a814693e5bdc9986c4902/0_432_920_552/master/920.jpg?w=620&q=85&auto=format&sharp=10&s=4b5c6e786188e8a3f83e80794e14aec7)

A major glacier in Greenland that holds enough water to raise global sea levels by half a metre has begun to crumble into the North Atlantic Ocean, scientists say.

The huge Zachariae Isstrom glacier in northeast Greenland started to melt rapidly in 2012 and is now breaking up into large icebergs where the glacier meets the sea, monitoring has revealed.

The calving of the glacier into chunks of floating ice will set in train a rise in sea levels that will continue for decades to come, the US team warns.

“Even if we have some really cool years ahead, we think the glacier is now unstable,” said Jeremie Mouginot at the University of California, Irvine. “Now this has started, it will continue until it retreats to a ridge about 30km back which could stabilise it and perhaps slow that retreat down.”

Mouginot and his colleagues drew on 40 years of satellite data and aerial surveys to show that the enormous Zachariae Isstrom glacier began to recede three times faster from 2012, with its retreat speeding up by 125 metres per year every year until the most recent measurements in 2015.

The same records revealed that from 2002 to 2014 the area of the glacier’s floating shelf shrank by a massive 95%, according to a report in the journal Science. The glacier has now become detached from a stabilising sill and is losing ice at a rate of 4.5bn tonnes a year.

Eric Rignot, professor of Earth system science at the University of California, Irvine, said that the glacier was “being hit from above and below”, with rising air temperatures driving melting at the top of the glacier, and its underside being eroded away by ocean currents that are warmer now than in the past.

“The glacier is now breaking into bits and pieces and retreating into deeper ground,” he said. The rapid retreat is expected to continue for 20 to 30 more years, until the glacier reaches another natural ledge that slows it down.

The scientists recreated the history of the glacier from aerial radar, gravitational measurements and laser profiles, and from radar and optical images taken from space. The combined data reveal the changing shape, size and position of Greenland glaciers over the past four decades.

To the north of Zachariae Isstrom, the scientists studied a second large glacier called Nioghalvfjerdsfjorden. Together, the two glaciers drain a region of nearly 200,000 sq km, amounting to 12% of the Greenland ice sheet. Were both to melt, they would contribute a full metre to global sea levels.

The monitoring showed that Nioghalvfjerdsfjorden glacier was also melting rapidly, but retreating more slowly than Zachariae Isstrom along uphill terrain. If the thinning continues at today’s pace, the scientists believe the ice shelf will become vulnerable to break up in the near future.

The bleak assessment of the glaciers’ retreat comes only months after Nasa launched an urgent six year project called Oceans Melting Greenland, aptly contracted to OMG, to understand the processes that drive the loss of Greenland ice.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 13, 2015, 12:53:44 AM
This is an absolutely stunning article, both from the sea level rise perspective and as satellite imagery tour de force. It is free full text with fabulous displays in the supplemental.

Looking at the carefully constructed flowlines though, I have to wonder whether Storstrømmen to the south shouldn't be a bigger part of the mix. And the bottom upheavals have to brought in as well. See #262 on the 6th page of this forum.

http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.full (http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.full)
http://www.sciencemag.org/cgi/content/full/science.aac7111/DC1 (http://www.sciencemag.org/cgi/content/full/science.aac7111/DC1)

Eric Rignot, a principal co-author, was also featured today in a very decent NY Times interview on Jakobshavn, balanced off by more cautious quotes from Joughin. (I snuck an http:// link to our forum in the comment section to see if it would draw traffic.) The WaPo obtained an interesting assessment of the new paper by J Box and astonishingly sourced the  accession number of the Landsat (if only we could get the journals to do this!).

http://www.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html (http://www.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html)
https://www.washingtonpost.com/news/energy-environment/wp/2015/11/12/scientists-say-greenland-just-opened-up-a-major-new-floodgate-of-ice-into-the-ocean/ (https://www.washingtonpost.com/news/energy-environment/wp/2015/11/12/scientists-say-greenland-just-opened-up-a-major-new-floodgate-of-ice-into-the-ocean/)

A round of applause to Espen for seeing the significance of Zachariae so far back? We have a very respectable forum on this already and this article is supplying a much improved baseline on sills and speeds for our future coverage.

On ZI, we find that the grounding line in year 1996 (5) was positioned 450-m below sea level (bsl), on a previously unknown sill that crosses the entire glacier width. Seaward of the sill, the seafloor drops to 800-m bsl (Fig. 1D). Inland of the sill, the glacier bed remains between 400 and 700-m bsl for 30 km. The bed then rises to reach a ridge at sea level. The ridge is cut across by a 300-m deep channel that connects with interior regions where the bed remains 300-m bsl for another 150 km.

On NG, the 1996 grounding line was 600-m bsl. We find no sill and the bed is sloping upward until 45 km inland. Seismic data collected in the 1990s (6) indicate that the ice shelf floats on a 900-m bsl cavity. The seafloor rises to 200-m bsl to the east where the ice front is anchored by islands and ice rises and 600-m bsl to the north into Dijmphna Sund.

We map the glacier grounding lines from 1992 to 2015 (Fig. 1C and figs. S2 and S3) using differential satellite radar interferometry (DInSAR). The grounding line of ZI retreated by 3.5 km at its center between 1996 and 2010, and 3.5 km in 2011-2015 (Fig. 1C). The mean rate of grounding line retreat therefore quadrupled from 230 m/yr to 875 m/yr before and after 2011. On NG, the grounding line retreated 1 km between 1992 and 2011, and has remained stable since. The DInSAR observations reveal a downward tilting of the ice front surface of ZI by 75 cm between Dec. 16-20 and Dec. 20-24, 2014 in a section 1-km wide by 7-km long (Fig. 1C). We attribute this deformation to a buoyancy-driven rotation of the terminus depressed below floatation and facilitated by the propagation of basal crevasses to the water line (8).

We project that ZI may continue retreating rapidly for another 20-30 yr. Its ice front will progressively widen from 19 km at present to 50 km about 30 km upstream, thereby increasing ice discharge. The height of the calving cliff will increase from its current 75 m to enhance the risk of ice fracture (11). With the formation of a calving cliff, the ocean-induced melt rates will increase significantly because buoyant melt water plumes rise faster along a vertical face than along a near-horizontal ice shelf bottom (5, 12). Beyond 30 km, the retreat will be slowed down by a rising bed topography but submarine channels will maintain the contact with the ocean into the deep interior.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on November 13, 2015, 01:01:30 AM
A round of applause to Espen for seeing the significance of ZI so far back?

Absolutely! Espen should be thrilled, because he's been saying for a long time that Zachariae doesn't get the attention it deserves.

Well done, Espen!  :-*
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 13, 2015, 03:00:20 AM
Espen's been saying for a long time that Zachariae doesn't get the attention it deserves.
Indeed his first post along those lines was on June 25, 2013 though Peak Indignation was not attained until a year later (post #175) as Jakobshavn and Petermann continued to hog all the attention. Please note that wipneus, sidd, nukefix and others have made important contributions to this forum in the areas of panchromatic sharpening, netCDF presentations, sentinel radar reprojection and IceBridge ice penetrating radar.

Flipping through the older posts, I'd say this has been a very respectable forum scientifically, considering it's done in real time. The Rignot group has introduced a few new techniques like mass conservation, difSAR and airgrav inversions that raise the bar for remote sensing bloggers but it's possible we can add them to our bag of tricks.

The prospects for new data on Zachariae in 2016 are excellent. The NEEM dome has been dragged over to middle NEGIS for a deep ice core and the critical near-shore bathymetry and physical oceanography may also get done. This is a very curious ice stream overall but one that we are getting a predictive grip on, once rheology temperatures and ocean circulation are in hand.

If the current trend continues, the northeast corner will become a significant contributor, or perhaps the largest contributor, in the near future -- Shfaqat Khan

http://www.scientificamerican.com/article/once-stable-greenland-glaciers-face-rapid-melt/ (http://www.scientificamerican.com/article/once-stable-greenland-glaciers-face-rapid-melt/)
http://www.climatecentral.org/news/new-greenland-ice-melt-fuels-sea-level-rise-concerns-17187 (http://www.climatecentral.org/news/new-greenland-ice-melt-fuels-sea-level-rise-concerns-17187)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on November 13, 2015, 04:57:03 PM
What is causing the even spacing of future bands 4-7?
Good question, I think the bands must be snow-covered surface depressions on the radar image. Are they also visible on this radar echogram or what is causing the banding upwards from the GL?

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on November 13, 2015, 05:58:42 PM
Right now there's massive discharge of fresh water at Z.I. http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif (http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 13, 2015, 06:55:30 PM
on this radar echogram what is causing the banding upwards from the grounding line?

The scale on these radargrams is 10 pxls/km horizontally vs 200 vertically, ie there's a 20:1 compression of the horizontal. This results in exaggeration of banding. Basically as the radar passes over bedrock with steep topography, there is attenuation of backscatter by the steep walls. The Cresis radars typically collect from about 100 m x 100 m so data is not point-like.

I'm of the opinion banding artifacts can be removed by masking prior to local contrast adjustment. In ImageJ this amounts to turning down the CLAHE filter action proportionally to overly bright or dark regions (which is an allowed operation). Typically people blast a copy of the original image with gaussian blur to create the companion image mask.

There's been hesitation about doing this systemically because the dB of attenuation has a physical meaning which is then lost (or warped beyond recognition). It's similar to tweaking Sentinel images for purposes other than for which it was designed eg surface roughness. However if the interest is in cleaning up the radargrams so that layering can be traced across the ice sheet, it makes sense. (It's not as if the originals get destroyed in the process.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: AbruptSLR on November 13, 2015, 07:47:19 PM
Right now there's massive discharge of fresh water at Z.I. http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif (http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif)

This is a re-post from another thread, but I provide it here to emphasize the importance of water drainage from coastal glaciers throughout Greenland, including for Z.I.:

Shuanggen Jin and Fang Zou (2015), "Re-estimation of glacier mass loss in Greenland from GRACE with correction of land-ocean leakage effects", Global and Planetary Change, doi: 10.1016j.gloplacha.2015.11.002


http://www.sciencedirect.com/science/article/pii/S0921818115301168 (http://www.sciencedirect.com/science/article/pii/S0921818115301168)

Abstract
The Gravity Recovery and Climate Experiment (GRACE) satellites can estimate the high-precision time-varying gravity field and the changes of Earth's surface mass, which have been widely used in water cycle and glacier mass balance. However, one of larger errors in GRACE measurements, land-ocean leakage effects, restricts high precision retrieval of ocean mass and terrestrial water storage variations along the coasts, particularly estimation of mass loss in Greenland. The land-ocean leakage effect along the coasts in Greenland will contaminate the mass loss signals with significant signal attenuation. In this paper, the precise glacier mass loss in Greenland from GRACE is re-estimated with correction of land-ocean leakage effects using the forward gravity modeling. The loss of Greenland ice-sheets is − 100.56 ± 8.86Gt/a without removing leakage effect, but − 171.56 ± 19.24Gt/a after removing the leakage effect from September 2003 to March 2008, which has a good agreement with ICESat results of − 184.8 ± 28.2 Gt/a. From January 2003 to December 2013, the total Greenland ice-sheets is losing at − 254.10 ± 6.90Gt/a from GRACE measurements with removing the leakage effect by 43.15%, while two-thirds of total glacier melting in Greenland is occurred in southern Greenland for the past 11 years. The secular leakage effects on glacier melting estimate mainly locate in the coastal areas, where larger glacier signals are significantly attenuated due to leaking out into the ocean. Furthermore, the leakage signals also have remarkable effects on seasonal and acceleration variations of glacier mass loss in Greenland. More significantly accelerated loss of glacier mass in Greenland is found by − 12.11 Gt/a2 after correcting leakage effects.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on November 13, 2015, 08:41:19 PM
on this radar echogram what is causing the banding upwards from the grounding line?

The scale on these radargrams is 10 pxls/km horizontally vs 200 vertically, ie there's a 20:1 compression of the horizontal. This results in exaggeration of banding. Basically as the radar passes over bedrock with steep topography, there is attenuation of backscatter by the steep walls. The Cresis radars typically collect from about 100 m x 100 m so data is not point-like.
So you're saying that if the fjord-bottom is very slanted the radar-return is smaller? In any case the previous two flights didn't show the same banding (the image is from the very recent Zacharias-paper).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 13, 2015, 08:56:38 PM
Better late than never ;)
I remember when Zachariae Isstrøm was more less Google unknown and that is only a few years ago.

My best moment wíth this glacier was when I informed a grand something son of Georg Hugh Robert Zachariae [1850-1937] a Danish naval officer, that a very important and huge glacier had his family name, this happened 2 - 3 years ago.

Thanks guys!

(there a several more "unknown" glaciers out there)

Lets drop the filters that prohibit viewers to watch what we are doing!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 13, 2015, 10:35:33 PM
the previous two flights didn't show the same banding
Probably didn't follow exactly the same flight path, so not over the same steep bedrock terrain. They seldom do, by intent, since the objective is to cover the ground with a grid. I didn't notice any accession numbers accompanying these images.  There is a case however over at Petermann where they did deliberately re-fly three lines over the ice shelf.

However the radar design changes each season, sometimes drastically. The height above the ice can also make a big difference, ie sled vs 1500 m vs way up in the sky. To my knowledge, the Cresis ice penetrating radar never shows any surface features beyond various horizontal echoing artefacts. Firn radar is something else again.

The image below shows the only repeated track at Zachariae.  Blow up the scale and the tracks will diverge. So it depends on this divergence vs the size of the sloped bedrock feature as to whether it is actually a repeat. I have no idea if these are the ones used in the paper.

My best moment wíth this glacier was when I informed a Danish naval officer
You dress up in a uniform like that while writing your forum posts?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: P-maker on November 13, 2015, 11:39:04 PM
Hi Johnm33 & ASLR

Good to know that one of my observations on the ASIB ( see http://neven1.typepad.com/blog/2012/12/piomas-december-2012.html?cid=6a0133f03a1e37970b017c34bfc063970b#comment-6a0133f03a1e37970b017c34bfc063970b (http://neven1.typepad.com/blog/2012/12/piomas-december-2012.html?cid=6a0133f03a1e37970b017c34bfc063970b#comment-6a0133f03a1e37970b017c34bfc063970b) ) turned out be really important.

A 12 GT/year  increase in volume loss from Greenland is also worth a note.

From time to time I see a clear line of thinking: Ideas brought to market on this site do indeed have a chance to survive immediate peer criticism. Soon, some enthusiastic researchers go off on their own in order to document ideas proposed here. Within a year or two, they come back with solid science, robust estimates and enhanced credibility. This is the way it should work. I now only hope, that the turn-over time from ideas to solid science can be reduced quite a bit. We do not have all the time in  the world to get every little detail in the cryosphere confirmed by trial and error.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 14, 2015, 10:03:47 AM
Zachariae Isstrøm, still moving and new future calving cracks are made in the process:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on November 14, 2015, 10:57:13 AM
The linked reference (and associated articles) discuss how the grounding line of Zachariæ Isstrøm became detached from a submarine sill and has been losing ice mass at an accelerating rate since 2012:

J. Mouginot, E. Rignot, B. Scheuchl, I. Fenty, A. Khazendar, M. Morlighem, A. Buzzi and J. Paden (12 Nov 2015), "Fast retreat of Zachariæ Isstrøm, northeast Greenland", Science DOI: 10.1126/science.aac7111


http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract (http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract)


Abstract: "After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come."

This is one of the most important research papers I've seen on this forum relating to Greenland. Finally ZI is getting the attention it deserves, along with some very detailed data showing the acceleration and retreat quantitatively, and providing detailed bathymetry and grounding line location.

Personally, I keep wondering whether at some point ZI will accelerate enough that it will divert ice currently discharging through NG, as both are fed from NEGIS if I understand correctly, and ZI has lost its heavy buttressing while NG is buttressed by the islands at its calving front. I'm not sure how much "cross-talk" between the drainage sub-basins is actually possible. A good way of trying to assess that is a multi-year Landsat animation of the area behind both calving fronts, showing the various flow directions on the ice-sheet and where the drainage divide actually is (which unfortunately I'm unable to produce with my limited computer resources).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 14, 2015, 11:10:00 AM
The linked reference (and associated articles) discuss how the grounding line of Zachariæ Isstrøm became detached from a submarine sill and has been losing ice mass at an accelerating rate since 2012:

J. Mouginot, E. Rignot, B. Scheuchl, I. Fenty, A. Khazendar, M. Morlighem, A. Buzzi and J. Paden (12 Nov 2015), "Fast retreat of Zachariæ Isstrøm, northeast Greenland", Science DOI: 10.1126/science.aac7111


http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract (http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract)


Abstract: "After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come."

This is one of the most important research papers I've seen on this forum relating to Greenland. Finally ZI is getting the attention it deserves, along with some very detailed data showing the acceleration and retreat quantitatively, and providing detailed bathymetry and grounding line location.

Personally, I keep wondering whether at some point ZI will accelerate enough that it will divert ice currently discharging through NG, as both are fed from NEGIS if I understand correctly, and ZI has lost its heavy buttressing while NG is buttressed by the islands at its calving front. I'm not sure how much "cross-talk" between the drainage sub-basins is actually possible. A good way of trying to assess that is a multi-year Landsat animation of the area behind both calving fronts, showing the various flow directions on the ice-sheet and where the drainage divide actually is (which unfortunately I'm unable to produce with my limited computer resources).

I don't see any new hard facts in these papers besides what we already knew?

This blog should be the collector of those funds they are looking for!

http://forum.arctic-sea-ice.net/index.php/topic,13.msg66022.html#msg66022 (http://forum.arctic-sea-ice.net/index.php/topic,13.msg66022.html#msg66022)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 14, 2015, 01:02:48 PM
don't see any new hard facts in these papers besides what we already knew?
The paper is very mainstream, no reason not to be. Its main purpose is to document, quantitate and explain  accelerating change at Zachariae by consolidating history over the satellite era and improving on many of the fine details of bedrock and surface flow. And the point is made, developments at Z are a bit alarming especially for its latitude.

While we knew all this here in some vague sense, it's quite a bit different pulling it together for a Science article (the review process alone took them from June into mid-October). Ask yourself, how far would we have gotten just telling peer reviewers come to this forum.

The devil is in the details. It's one thing to say Z is heating up and another to say by how much. We gesticulate at a kriged bedrock map and say 'it's retrograde, the future is bleak' but another to actually get it right. Here we learned the retrograde slope does not end at a sill 30 km from the calving front because there is a 300 m deep passageway and more retrograde slope beyond.

Where do I find this on the forum? Where did we comprehensively measure flowline velocities and acceleration? Where did we revise the ice volume discharge estimated by S Khan 2015? We copy and paste so much that it is easy to forget we observe a lot but don't actually derive too many results, mostly recycle them.

whether ZI will accelerate divert ice currently discharging through NG how much "cross-talk" between the drainage sub-basins is actually possible multi-year Landsat animation of the area behind both calving fronts flow directions on the ice-sheet and where the drainage divide actually is

Right. As the calving front (aka ocean) moves so far inland, it seems like it would melt into NG and utterly change its buttressing forces. I have not really seen any predictions about the extent of 'ice piracy' (called watershed capture on land). If this was extensive during the Eemian, Z should have excavated a far deeper channel offshore than NG -- but here we await better bathymetry.

A Landsat animation at the two flow divergences and iceshed boundaries (NG/Z and NEGIS/Stors) would be quite instructive. The slow steps there involve the download, cropping, co-registration, and consistent contrast repair of large files. Then there would be the issue of km scale and whether the motion could even be displayed at the resolution necessary. NEGIS itself is very narrow upstream with sharp shear boundaries.

It is trending right now to blame warm ocean currents for everything coming loose on Greenland glaciers. This is the tail wagging the dog. The ocean has nothing whatsoever to do with the whole anomaly of upstream NEGIS. We have to wonder if that is really attributable to a geothermal excursion and how stable that is.

Finally, note that the distribution of bottom upheavals doesn't really correlate well with any property of NG or Z described in this paper. Their significance to future flow scenarios needs to be considered.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on November 14, 2015, 09:57:08 PM
The linked reference (and associated articles) discuss how the grounding line of Zachariæ Isstrøm became detached from a submarine sill and has been losing ice mass at an accelerating rate since 2012:

J. Mouginot, E. Rignot, B. Scheuchl, I. Fenty, A. Khazendar, M. Morlighem, A. Buzzi and J. Paden (12 Nov 2015), "Fast retreat of Zachariæ Isstrøm, northeast Greenland", Science DOI: 10.1126/science.aac7111


http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract (http://www.sciencemag.org/content/early/2015/11/11/science.aac7111.abstract)


Abstract: "After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. Its equal-ice-volume neighbor, Nioghalvfjerdsfjorden, is also melting rapidly but retreating slowly along an upward-sloping bed. The destabilization of this marine-based sector will increase sea-level rise from the Greenland Ice Sheet for decades to come."

This is one of the most important research papers I've seen on this forum relating to Greenland. Finally ZI is getting the attention it deserves, along with some very detailed data showing the acceleration and retreat quantitatively, and providing detailed bathymetry and grounding line location.

Personally, I keep wondering whether at some point ZI will accelerate enough that it will divert ice currently discharging through NG, as both are fed from NEGIS if I understand correctly, and ZI has lost its heavy buttressing while NG is buttressed by the islands at its calving front. I'm not sure how much "cross-talk" between the drainage sub-basins is actually possible. A good way of trying to assess that is a multi-year Landsat animation of the area behind both calving fronts, showing the various flow directions on the ice-sheet and where the drainage divide actually is (which unfortunately I'm unable to produce with my limited computer resources).

I don't see any new hard facts in these papers besides what we already knew?

This blog should be the collector of those funds they are looking for!

http://forum.arctic-sea-ice.net/index.php/topic,13.msg66022.html#msg66022 (http://forum.arctic-sea-ice.net/index.php/topic,13.msg66022.html#msg66022)

Well the fact that it's all concentrated in one article. Plus, at least for me: the detailed bathymetry map, the flow vectors, the division of basins between ZI and NG, the grounding line location, the measurement of acceleration, all things that I have been wondering about. I am a layman in these subjects, and not much time on my hands, so possibly it all already existed somewhere - but I couldn't find or didn't know to look for it.
In addition, I believe (thanks to your work here) that ZI is extremely important, and much overlooked, so this kind of high-profile paper is surely a step in the right direction.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on November 16, 2015, 08:40:43 PM
on this radar echogram what is causing the banding upwards from the grounding line?
The scale on these radargrams is 10 pxls/km horizontally vs 200 vertically, ie there's a 20:1 compression of the horizontal. This results in exaggeration of banding. Basically as the radar passes over bedrock with steep topography, there is attenuation of backscatter by the steep walls. The Cresis radars typically collect from about 100 m x 100 m so data is not point-like.
So you're saying that if the fjord-bottom is very slanted the radar-return is smaller? In any case the previous two flights didn't show the same banding (the image is from the very recent Zacharias-paper).
Hold on folks, the LiDAR shows them as surface-depressions so they are visible both in LiDAR and Cresis. I'll postulate that these are the quasi-periodic crevasses seen also with optical sensors and SAR.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on November 17, 2015, 10:15:23 AM
Medium resolution (40m/pix) Sentinel 1A animation shows a calving at calving front #2. The new iceberg seems to lie on its side.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on November 17, 2015, 05:12:10 PM
Same as above, but instead of just using the HH polarization I create RGB images with the HV polarization for red and HH for green, blue is unused.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 18, 2015, 02:33:52 PM
I looked at the annual velocity maps in the supplement to Mouginot 2015 to see if Zachariae might be doing a bit of ice piracy from its slower moving neighbor Nioghalvfjerdsfjorden to the north. There are six years between 2001 and 2014 for which data coverage is available for the region of potential interest.

This would totally change future discharge scenarios should Zacharia start draining the conjoined watersheds. However if this is happening, its onset is very slow. A better analysis would require the underlying data grayscales for the respective years to undo the logarithmic tinting of the Modis grayscale mosaic. The article does not indicate if or where those are available.

The third image takes the original slides for 2014 and 2001 (extreme time difference available), decomposes to HSV to capture the tint as grayscale, exponentiates those and renormalizes to [0,255] in ImageJ , then makes an RGB with blue taken as a neutral gray. Most of the relative change is near the calving fronts and again with only meagre support for upper iceshed capture.

It would also be feasible to take a pair of 2015 Landsats to see if ice flow still corresponds to their map of flowlines in the critical region.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on November 19, 2015, 12:37:24 PM
Scihub is down but Polarview has another EW-scene from yesterday.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 19, 2015, 04:13:41 PM
S
Scihub is down but Polarview has another EW-scene from yesterday.

Yes it is usually more down than up?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 19, 2015, 04:47:36 PM
Yes it is usually more down than up?
Yes it is usually more down than up.

Totally incompetent interface. Not even high school level programming in the US. They seem content just having the satellite go round and round. Getting the data to the user community seems to be their lowest priority ... yet it is the highest.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 20, 2015, 02:59:10 PM
Here is a very decent composite of 1200 Sentinel wide-mode velocity determinations that shows what the instrument is capable of:

This map of Greenland ice sheet velocity was created using data from Sentinel-1A in January–March 2015 and complemented by the routine 12-day repeat acquisitions of the margins since June 2015. About 1200 radar scenes from the satellite’s wide-swath mode were used to produce the map, which clearly shows dynamic glacier outlets around the Greenland coast. In particular, the Zachariae Isstrom glacier in the northeast is changing rapidly, and recently reported as having become unmoored from a stabilising sill and now crumbling into the North Atlantic Ocean. (Colour scale in metres per day).

http://www.esa.int/spaceinimages/Images/2015/11/Ice_sheet_in_motion (http://www.esa.int/spaceinimages/Images/2015/11/Ice_sheet_in_motion)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 20, 2015, 07:57:25 PM
Yes it is usually more down than up?
Yes it is usually more down than up.

Totally incompetent interface. Not even high school level programming in the US. They seem content just having the satellite go round and round. Getting the data to the user community seems to be their lowest priority ... yet it is the highest.

And it continues for now 3 days:

The Sentinels Scientific Data Hub will be back soon!

Sorry for the inconvenience,
we're "performing" some maintenance at the moment.
We'll be back online shortly!


No bad feelings here (because ESA pinched the Jakobshavn event!!)

http://www.bbc.com/news/science-environment-34041531 (http://www.bbc.com/news/science-environment-34041531)

We all know it happened between Aug. 14 and 16, but ESA can only prove it happened between Aug. 13 and 19, and that is not newsworthy especially not with BBC?

https://forum.arctic-sea-ice.net/index.php/topic,154.msg60933.html#msg60933 (https://forum.arctic-sea-ice.net/index.php/topic,154.msg60933.html#msg60933)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on November 23, 2015, 05:04:04 PM
ESA's data hub was back on line for a short while. Enough for a hi-res (10m/pix) detail animation of the event mentioned in %556 and #557. The calving from front #2 is seen broken in 4 parts at least.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on November 24, 2015, 03:27:56 PM
Looking at the void below Nioghalvfjerdsfjorden's ice shelf it's no wonder that coastal currents and tides make no impact, its like a vast auditorium .5km high x by 75m long, plus it has a baffle on the sea bed by the entrance.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FlmtQR%2F0379acd0aa.jpg&hash=e43f8443ff198d3bc2cb8d26c125a73e)
To the north of it however lies a long fjord with little ice cover which is prone to tidal movement and shows signs of attacking the ice shelf from the side. Here's a detail
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Flwo0K%2Ff1da4c9bb9.jpg&hash=594edb3d0e7822fa7662154456d86a3b)
and for orientation
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FllJX6%2F141a95abc0.jpg&hash=c37f2be629fad61382e2bd5c7c2dc3b6)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on November 24, 2015, 03:42:56 PM
ESA's data hub was back on line for a short while. Enough for a hi-res (10m/pix) detail animation of the event mentioned in %556 and #557. The calving from front #2 is seen broken in 4 parts at least.

There also appears to be a small calving on the ice face that has occurred where the bergs have rolled over. Could this calving have triggered this break up?

If you look closely at the animation, you can see a dark rectangular patch appear that looks just like the calving that rolled over earlier in the season.

(Edit....Oooops...just read comment 556...already noted.)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on November 26, 2015, 04:27:01 PM
It's off-topic, but I thought this might be interesting to A-Team, Espen, Wipneus, nukefix et al:

Revealing glacier flow and surge dynamics from animated satellite image sequences: examples from the Karakoram

F. Paul
Department of Geography, University of Zurich, Zurich, Switzerland

Abstract. Although animated images are very popular on the internet, they have so far found only limited use for glaciological applications. With long time series of satellite images becoming increasingly available and glaciers being well recognized for their rapid changes and variable flow dynamics, animated sequences of multiple satellite images reveal glacier dynamics in a time-lapse mode, making the otherwise slow changes of glacier movement visible and understandable to the wider public. For this study, animated image sequences were created for four regions in the central Karakoram mountain range over a 25-year time period (1990–2015) from freely available image quick-looks of orthorectified Landsat scenes. The animations play automatically in a web browser and reveal highly complex patterns of glacier flow and surge dynamics that are difficult to obtain by other methods. In contrast to other regions, surging glaciers in the Karakoram are often small (10 km2 or less), steep, debris-free, and advance for several years to decades at relatively low annual rates (about 100 m a−1). These characteristics overlap with those of non-surge-type glaciers, making a clear identification difficult. However, as in other regions, the surging glaciers in the central Karakoram also show sudden increases of flow velocity and mass waves travelling down glacier. The surges of individual glaciers are generally out of phase, indicating a limited climatic control on their dynamics. On the other hand, nearly all other glaciers in the region are either stable or slightly advancing, indicating balanced or even positive mass budgets over the past few decades.
The Cryosphere (http://www.the-cryosphere.net/9/2201/2015/tc-9-2201-2015.html)

And EGU press release here (http://www.egu.eu/news/210/revealing-glacier-flow-with-animated-satellite-images/) (where the animations can be viewed).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 26, 2015, 05:30:03 PM
It's off-topic, but I thought this might be interesting to A-Team, Espen, Wipneus, nukefix et al:

Revealing glacier flow and surge dynamics from animated satellite image sequences: examples from the Karakoram

F. Paul
Department of Geography, University of Zurich, Zurich, Switzerland

Abstract. Although animated images are very popular on the internet, they have so far found only limited use for glaciological applications. With long time series of satellite images becoming increasingly available and glaciers being well recognized for their rapid changes and variable flow dynamics, animated sequences of multiple satellite images reveal glacier dynamics in a time-lapse mode, making the otherwise slow changes of glacier movement visible and understandable to the wider public. For this study, animated image sequences were created for four regions in the central Karakoram mountain range over a 25-year time period (1990–2015) from freely available image quick-looks of orthorectified Landsat scenes. The animations play automatically in a web browser and reveal highly complex patterns of glacier flow and surge dynamics that are difficult to obtain by other methods. In contrast to other regions, surging glaciers in the Karakoram are often small (10 km2 or less), steep, debris-free, and advance for several years to decades at relatively low annual rates (about 100 m a−1). These characteristics overlap with those of non-surge-type glaciers, making a clear identification difficult. However, as in other regions, the surging glaciers in the central Karakoram also show sudden increases of flow velocity and mass waves travelling down glacier. The surges of individual glaciers are generally out of phase, indicating a limited climatic control on their dynamics. On the other hand, nearly all other glaciers in the region are either stable or slightly advancing, indicating balanced or even positive mass budgets over the past few decades.
The Cryosphere (http://www.the-cryosphere.net/9/2201/2015/tc-9-2201-2015.html)

And EGU press release here (http://www.egu.eu/news/210/revealing-glacier-flow-with-animated-satellite-images/) (where the animations can be viewed).

Seems to be a reinvention of the wheel? ;) Although it has been done for years now?

In other words:  Scientific Dishonesty
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on November 26, 2015, 07:10:04 PM
reinvention of the wheel  been done for years now   Scientific Dishonesty
Neven, thanks for bringing this to our attention. I'm afraid I don't share Espen's enthusiasm for this effort. First I double-checked the date 26 November 2015 as it is easy to mistakenly come across an old piece on the internet and think it is new, say 26 November 1995 but no, they somehow thought this was new and cutting edge, not noticing apparently that the gif89 animation spec utilized dates back, as the name itself states, to 1989.

The authors and EGU seem extremely naive -- compare this to the knock-your-socks off photorealistic effort posted today on Antarctica ocean bottom waters. http://forum.arctic-sea-ice.net/index.php/topic,622.msg66462.html#msg66462 (http://forum.arctic-sea-ice.net/index.php/topic,622.msg66462.html#msg66462)

The journal and press release don't actually offer the animations. That is a separate 64 MB zip download and unpack. The format is nice and large, 1736 × 1231, but there are a only a meagre number of frames (7) from unspecified years of the much much longer Landsat record looping at 100 ms (which makes no scientific sense as last year is not particularly relevant to the first).

The co-registration looks good but the colors are awful (given Landsat has long offered an online tutorial on natural color.) The resolution isn't specified but looks way off -- Landsat is much better than this and the project purpose really required full resolution. They should have tiled it down to 15 m and probably just stuck with band 8 grayscale. However there doesn't seem to be anything of scientific interest in the scene I looked at.

I clipped a forum-sized piece out of it, retaining original resolution, below. In the US at least, this would not be a satisfactory submission to a high school (ages 12-16) science fair project.

This is likely not a case of scientific dishonestly. Picture instead a distinguished elderly professor enjoying a three pint lunch with a old friend now a journal editor, office desks piled high with scientific reprints, shelves sagging from the weight of books and conference procedings, no need here for that internet thingamjigie, that's best left to the grandkids but hey look at what one of them showed me the other day on her portable telephone, a picture that moves, we could maybe use that in glaciology?

I've proposed elsewhere a massive pre-compute to animate the entire Landsat and Sentinel catalogs, all years, storing it at Amazon AWS, and serving whatever region visitor selected at the portal. This would have to be done by professionals because of contrast and cloud issues, not to mention significant but not insurrmountable CPU time. The end user just makes the final selection of frames and tweaks the defaulted animation speed.

This is what they do in the rest of science. Climate change is too important; we don't have time any more for people clowning around pretending to do research. They're hogging a university chair that should go to a productive young scientist. 

I am getting really fed up with glaciology on the data sharing and informatics side. We don't have time for mickey mouse any more. This means intervention on the peer review side: learn it, fix it, or forget it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 26, 2015, 08:21:43 PM
reinvention of the wheel  been done for years now   Scientific Dishonesty
Neven, thanks for bringing this to our attention. I'm afraid I don't share Espen's enthusiasm for this effort. First I double-checked the date 26 November 2015 as it is easy to mistakenly come across an old piece on the internet and think it is new, say 26 November 1995 but no, they somehow thought this was new and cutting edge, not noticing apparently that the gif89 animation spec utilized dates back, as the name itself states, to 1989.

The authors and EGU seem extremely naive -- compare this to the knock-your-socks off photorealistic effort posted today on Antarctica ocean bottom waters. http://forum.arctic-sea-ice.net/index.php/topic,622.msg66462.html#msg66462 (http://forum.arctic-sea-ice.net/index.php/topic,622.msg66462.html#msg66462)

The journal and press release don't actually offer the animations. That is a separate 64 MB zip download and unpack. The format is nice and large, 1736 × 1231, but there are a only a meagre number of frames (7) from unspecified years of the much much longer Landsat record looping at 100 ms (which makes no scientific sense as last year is not particularly relevant to the first).

The co-registration looks good but the colors are awful (given Landsat has long offered an online tutorial on natural color.) The resolution isn't specified but looks way off -- Landsat is much better than this and the project purpose really required full resolution. They should have tiled it down to 15 m and probably just stuck with band 8 grayscale. However there doesn't seem to be anything of scientific interest in the scene I looked at.

I clipped a forum-sized piece out of it, retaining original resolution, below. In the US at least, this would not be a satisfactory submission to a high school (ages 12-16) science fair project.

This is likely not a case of scientific dishonestly. Picture instead a distinguished elderly professor enjoying a three pint lunch with a old friend now a journal editor, office desks piled high with scientific reprints, shelves sagging from the weight of books and conference procedings, no need here for that internet thingamjigie, that's best left to the grandkids but hey look at what one of them showed me the other day on her portable telephone, a picture that moves, we could maybe use that in glaciology?

I've proposed elsewhere a massive pre-compute to animate the entire Landsat and Sentinel catalogs, all years, storing it at Amazon AWS, and serving whatever region visitor selected at the portal. This would have to be done by professionals because of contrast and cloud issues, not to mention significant but not insurrmountable CPU time. The end user just makes the final selection of frames and tweaks the defaulted animation speed.

This is what they do in the rest of science. Climate change is too important; we don't have time any more for people clowning around pretending to do research. They're hogging a university chair that should go to a productive young scientist. 

I am getting really fed up with glaciology on the data sharing and informatics side. We don't have time for mickey mouse any more. This means intervention on the peer review side: learn it, fix it, or forget it.

I am happy I am not a Peer!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on November 26, 2015, 08:23:44 PM
If this makes it into The Cryosphere, it should be possible to do something similar with the Jakobshavn/Zachariae images produced by you wonderful lot.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on November 26, 2015, 08:34:23 PM
I would prefer The Sun or Daily Mail. larger audience?

And a wider peer review result?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Neven on November 26, 2015, 11:30:25 PM
Well, if you want to get into the Sun or Daily Mail, you'll have to make an animation of a glacier that is growing. If you want, I can give you David Rose's mail address. Or just send it to the GWPF and they'll forward it to their operative. ;-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 01, 2015, 10:24:01 AM
Latest IW image from sentinel 1a. No "sudden" changes in the last 12 day sentinel 1 cycle. Cracks at new calving fronts #3-5 can be seen slightly extending/developing. General speed (measured at fron #5) is about 7.5 m/day.
The animation is scaled at 40m/pix and needs a click to start.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 04, 2015, 08:39:44 AM
NASA's Earth Observatory Image of the d (http://earthobservatory.nasa.gov/IOTD/view.php?id=87086)ay is dedicated to Zachariae today.

They have a nice ]comparison of 1999 with 2015.

And a You-Tube movie of the 2015 season as seen by Landsat 8:
https://youtu.be/-BXWTSu8KkQ (https://youtu.be/-BXWTSu8KkQ)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on December 04, 2015, 11:26:36 AM
a nice comparison of 1999 with 2015
It is. The constancy of melt lake positions is amazing given how far forward the glacier has advanced over 15 years. There is a fair amount of inconsistency across matching lakes as to which year had the greater melt.

It is not so easy to auto-compare surface areas of liquid water between the two years because of the many shades of blue and submerged ice showing through. Depth is not doable for individual ponds without calibration. Thus a comparison of volumes of standing liquid water could only be roughly estimated. However there are methods for doing this from Landsat that have been carried out on West Greenland in recent publications.

The first animation provides an overall comparison of melt lakes. It is rotated 90º CW for purposes of better fitting forum space. The Nasa slider comparison is more effective but it doesn't seem like we can replicate it here (<div class="compare-container" id="compare-container">).

The second animation compares 3 specific melt lakes at 15 m resolution (which requires doubling down on the 1999 Landsat-7). The two scenes were aligned on fixed rocks above and below before cropping as lakes alone cannot be reliably enough aligned.

The third animation looks at details of one melt lake. Here the 1999 was contrast-adjusted and unsharp-masked to minimize distractions in comparing with 2015.

The fourth animation compares what Nasa terms the ice shelf remnant. Some features appear retained but shifted; earlier and  intermediate years are needed to get a handle on the origin and evolution of this region. Here 2015 has dramatically more melt -- possibly this area is more affected now by warming ocean. The animations all run at 400 ms.

It is a pity too see so much work (co-registering and pan-sharpening 26 Landsat-8 scenes from 2015) disappear down the rat hole of youtube -- better that Earth Observatory had archived the frames or at least listed the scene accessions needed for bulk download. It is a real nuisance to recover individual days: capturing a time series for the lakes above requires many frame grabs from the HD version, which does not include the date of the scene nor explain the relationship to the underlying 15 m resolution. And then there are the issues of mpeg codecs, intermediate fudged frames and the stupid upper drop shadow degrading the scientific value every frame.

Here we would just like to crop out a region of interest from the full screen HD display. This may be possible from http://www.youtube.com/editor (http://www.youtube.com/editor) if you wish to enroll and stay within the google ecosystem. This was a slide show from the beginning, not a video.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on December 04, 2015, 09:32:44 PM
a nice comparison of 1999 with 2015
It is. The constancy of melt lake positions is amazing given how far forward the glacier has advanced over 15 years. There is a fair amount of inconsistency across matching lakes as to which year had the greater melt.

It is not so easy to auto-compare surface areas of liquid water between the two years because of the many shades of blue and submerged ice showing through. Depth is not doable for individual ponds without calibration. Thus a comparison of volumes of standing liquid water could only be roughly estimated. However there are methods for doing this from Landsat that have been carried out on West Greenland in recent publications.

The first animation provides an overall comparison of melt lakes. It is rotated 90º CW for purposes of better fitting forum space. The Nasa slider comparison is more effective but it doesn't seem like we can replicate it here (<div class="compare-container" id="compare-container">).

The second animation compares 3 specific melt lakes at 15 m resolution (which requires doubling down on the 1999 Landsat-7). The two scenes were aligned on fixed rocks above and below before cropping as lakes alone cannot be reliably enough aligned.

The third animation looks at details of one melt lake. Here the 1999 was contrast-adjusted and unsharp-masked to minimize distractions in comparing with 2015.

The fourth animation compares what Nasa terms the ice shelf remnant. Some features appear retained but shifted; earlier and  intermediate years are needed to get a handle on the origin and evolution of this region. Here 2015 has dramatically more melt -- possibly this area is more affected now by warming ocean. The animations all run at 400 ms.

It is a pity too see so much work (co-registering and pan-sharpening 26 Landsat-8 scenes from 2015) disappear down the rat hole of youtube -- better that Earth Observatory had archived the frames or at least listed the scene accessions needed for bulk download. It is a real nuisance to recover individual days: capturing a time series for the lakes above requires many frame grabs from the HD version, which does not include the date of the scene nor explain the relationship to the underlying 15 m resolution. And then there are the issues of mpeg codecs, intermediate fudged frames and the stupid upper drop shadow degrading the scientific value every frame.

Here we would just like to crop out a region of interest from the full screen HD display. This may be possible from http://www.youtube.com/editor (http://www.youtube.com/editor) if you wish to enroll and stay within the google ecosystem. This was a slide show from the beginning, not a video.

I have noticed this before at several location like at Humboldt Gletscher:

https://forum.arctic-sea-ice.net/index.php/topic,800.msg30731.html#msg30731 (https://forum.arctic-sea-ice.net/index.php/topic,800.msg30731.html#msg30731)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on December 06, 2015, 01:33:44 PM
I have noticed this before at several location like at Humboldt Gletscher:

https://forum.arctic-sea-ice.net/index.php/topic,800.msg30731.html#msg30731 (https://forum.arctic-sea-ice.net/index.php/topic,800.msg30731.html#msg30731)

I remember that post. A real eye-opener.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 09, 2015, 06:54:24 PM
Also a late appearance of a Sentinel 1A IW (hi-res at 10m/px) from 4th December.
Here is a detail showing, exactly in the image center, a small opening at the position of calving front #4 (center right in this image is #1) since 22nd Nov.  The image in post #564 suggest of such an opening at calving front #5.

If last year can be taken as a guidance, these small opening may open fully during 2016.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 19, 2015, 03:25:42 PM
Added a new frame for 16 December to the animation above. The crack mentioned above, and a few more in the area are opening and getting longer.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 22, 2015, 09:33:13 AM
Also more north, the future calving fronts (up to #5) can be seen developing as this hi-res (10m/pix) Sentinel 1A sequence shows.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on December 22, 2015, 07:58:46 PM
Yes Wipneus, this Monster is really amazing, the question is what will happen when the "pool" between the previous tongue and the calving front is filled with calving debris?
It is hard to get true that "Pinball" location!

https://www.youtube.com/watch?v=4AKbUm8GrbM (https://www.youtube.com/watch?v=4AKbUm8GrbM)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on December 23, 2015, 07:03:32 AM
In August 2014 the sea ice cleared and the whole debris was washed away, along with major calving. This year the sea ice remained throughout August and the debris keeps piling up. I wonder what 2016 will bring.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 23, 2015, 09:59:21 AM
Yes Wipneus, this Monster is really amazing, the question is what will happen when the "pool" between the previous tongue and the calving front is filled with calving debris?


Espen, all this activity of the future calving fronts indicates to me that there is little back-pressure from the the pool yet. The latest calving, a few weeks ago, managed to push quite a lot of bergs in front of it,  forwards.  Just by toppling over.

In the mean time, Sentinel 1A has increased the frequency of Zachariae images noticeably.  I could produce an image every day if I had the time (most lower resolution than the ones above)

Here is today's sequence. The (40m/pix) image is good enough to show the calving activity as well.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 14, 2016, 07:06:29 PM
Zachariae Isstrøm update, still moving impressively:

Click on image to enlarge and animate!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on January 14, 2016, 09:40:38 PM
Animation not working for me. Maybe it's too large?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 14, 2016, 10:01:16 PM
Animation not working for me. Maybe it's too large?

Here is a smaller version:

Click on image to animate!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on January 15, 2016, 08:17:48 AM
Thanks Espen. Monster on the move.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on January 16, 2016, 05:51:44 PM
Yes Wipneus, this Monster is really amazing, the question is what will happen when the "pool" between the previous tongue and the calving front is filled with calving debris?


Espen, all this activity of the future calving fronts indicates to me that there is little back-pressure from the the pool yet. The latest calving, a few weeks ago, managed to push quite a lot of bergs in front of it,  forwards.  Just by toppling over.

In the mean time, Sentinel 1A has increased the frequency of Zachariae images noticeably.  I could produce an image every day if I had the time (most lower resolution than the ones above)

Here is today's sequence. The (40m/pix) image is good enough to show the calving activity as well.

Great animation!

If you look at the bergy bits that are close to the tongue of ice that separated from the main glacier, (well documented by Espen) the movement of the glacier front is pushing them towards the face of the tongue. You would think the back pressure from the stationary tongue and sea ice formation would have locked these in place by now.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on January 18, 2016, 08:29:06 AM
Zachariae still moving on with speeds 6-7 m/day at the calving fronts. In this animation of medium resolution (EW, 40m/pix) Sentinel 1A images, the boundary ( right side, middle) between sea ice/ice melange that is moving with the glacier and the more stationary sea ice "brightens" up. Ridging I presume.

 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on January 18, 2016, 10:12:20 AM
I came across a very nice javascript treatment of Zachariae that switches the view seamlessly upon mouse-over between separate co-registered layers for surface and bed elevations, ice thickness, surface velocity (linear or log), and satellite image.

This is a very slick container for data. Note a layer need not be static, it could be a gif animation. Also, layers can be 24-bit color png or jpg, or for that matter 16-bit tifs like Landsat.

Go to the first link below to see it in action. (The controller below won't work because of limitations in forum software.)

At the second link, I cleaned up the code into so that it displays properly at 700 pixel width with an easily modified controller so it can display our data. It is an alternative to animated gifs which gives the end-user better viewing options.

http://nholschuh.com/glaciers.html (http://nholschuh.com/glaciers.html)
http://forum.arctic-sea-ice.net/index.php/topic,1259.msg68520.html#msg68520 (http://forum.arctic-sea-ice.net/index.php/topic,1259.msg68520.html#msg68520)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on January 20, 2016, 04:14:56 AM


I am happy I am not a Peer!
I would like to review that.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on January 28, 2016, 09:01:26 PM
Zachariae Isstrøm movement January 16 to January 28 2016:

Note that Kap Zach is becoming more visible.

Please click on image to animate!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 10, 2016, 04:42:51 PM
A detail shows a cracking area where nearly every day new cracks appear, or existing cracks getting wider and longer. Resolution 10 m/pix, images 24 days (2 sentinel cycles) apart.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on February 12, 2016, 10:54:13 AM
Possible big crack on 79N so far back it could be above the grounding line, or of little significance, we'll see.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fn52jC%2F668cdf6488.jpg&hash=5948f921212b2d1caf6711b281ff9eea)
taken from the high res version of http://www.polarview.aq/images/106_S1jpgsmall/201602/S1A_EW_GRDM_1SDH_20160211T180446_B34D_N_1.jpg (http://www.polarview.aq/images/106_S1jpgsmall/201602/S1A_EW_GRDM_1SDH_20160211T180446_B34D_N_1.jpg)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 12, 2016, 12:16:55 PM
John, here is a landsat image from August 2014 (different projection). I think most of the cracks are already there.

(click for the 30 m/pix image)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on February 12, 2016, 01:10:00 PM
Wipneus "John, here is a landsat image from August 2014 (different projection). I think most of the cracks are already there."
Thanks, it looks like it's moved a little downstream since then but nothing out of the ordinary. I look forward to seeing it in daylight.
[added] Looks like it was an artifact of some sort it's there on the 11th http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20160211s01a.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20160211s01a.ASAR.jpg)  but gone on the 12th http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20160212s01a.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/20160212s01a.ASAR.jpg)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on February 22, 2016, 11:33:11 AM
Detail from center of 79N from Polar View http://www.polarview.aq/images/106_S1jpgsmall/201602/S1A_IW_GRDH_1SSH_20160221T083440_247C_N_1.jpg (http://www.polarview.aq/images/106_S1jpgsmall/201602/S1A_IW_GRDH_1SSH_20160221T083440_247C_N_1.jpg)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fnh9Zi%2F9af6f84943.jpg&hash=34e32770425fe5c6ab2959bddd84209e)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on February 24, 2016, 10:33:51 AM
Images across the calving front of 79N guesstimate 35km wide
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fnjunu%2Fa8f5e410b8.jpg&hash=e12c89c65f4b76dc3466ba185af1562f)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fnjurs%2F116d636930.jpg&hash=002b998f5b09c237f4bd9af315a402b2)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FnjutD%2F289ab085bb.jpg&hash=5ad127b07c38358331f6cafbd12533b3)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 27, 2016, 09:25:15 AM
Zachariae Isstrøm update:

Please click to enlarge and animate!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: notjonathon on March 01, 2016, 02:58:19 AM
Espen:

Does this continual calving of Zachariae date back to pre-1900 (or pre-1950--although glaciers seem to have been retreating since the beginning of the last century), or is it a more recent feature of glacial speedup? It is truly amazing to see new cracks continually forming up-glacier as the face calves.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 01, 2016, 05:16:33 PM
Espen:

Does this continual calving of Zachariae date back to pre-1900 (or pre-1950--although glaciers seem to have been retreating since the beginning of the last century), or is it a more recent feature of glacial speedup? It is truly amazing to see new cracks continually forming up-glacier as the face calves.

notjonathon,

The recent acceleration and retreat of the glacier started back in 2001-2003, at the same time when the sea ice of Jøkelbugt disappeared completely for a couple of melting seasons, whether there is a correlation is not yet proven. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: notjonathon on March 02, 2016, 01:17:53 AM
Thanks. So definitely reacting to the added heat in the arctic.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 09, 2016, 03:51:16 PM
First usable Landsat 8 image from 2016. Here is a pan-sharpened large image at 15 m/pix resolution. Click to see that image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 10, 2016, 12:22:18 PM
Here is a detailed animated sequence with the last Landsat 8 image taken from the same orbital position 14th of September. The current image has been shifted 76x5 pixels to the left and down making the region just upstream of the crack just opening in September. That was calving front #3 in my counting, fronts #4-#6 have become visible during the winter.

76x5 pixels at 15m/pixel and a time difference of 176 days gives an average speed of 6.5 +/- 0.1 m/day.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 22, 2016, 04:51:53 PM
Here is my first Sentinel 2A image from the Zachariae. For the overview I rendered it at 20m/pix, I think at the native resolution of 10m the image would be far too big to post.

Processing in the SNAP tool box: open the product, open an RGB window (menu Windows) and export as png (menu File->export->other->view as image) (takes 30 minutes to save the file).
Cut, scale and annotate in the Gimp.

Click to see the full image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Xulonn on March 22, 2016, 05:18:52 PM
Excellent image, Wipneus, but it is an optical illusion for me.

When I first looked at it, my brain interpreted the icebergs as depressions, and not the raised objects that they really are - and that illusion was persistent. 

Assuming the the bright side of each iceberg is the southern "hillside" which is illuminated by the high-latitude, low-angle sunlight, I know intellectually how the icebergs should appear. 

Like classic optical illusion illustrations, when I stared at it long enough, I finally saw the icebergs as raised objects.   Does anyone else suffer from the same visual misinterpretations?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: DaveHitz on March 22, 2016, 05:27:30 PM
Excellent image, Wipneus, but it is an optical illusion for me.

When I first looked at it, my brain interpreted the icebergs as depressions, and not the raised objects that they really are - and that illusion was persistent. 

Assuming the the bright side of each iceberg is the southern "hillside" which is illuminated by the high-latitude, low-angle sunlight, I know intellectually how the icebergs should appear. 

Like classic optical illusion illustrations, when I stared at it long enough, I finally saw the icebergs as raised objects.   Does anyone else suffer from the same visual misinterpretations?

Imagining that I am holding a flashlight aiming "up" at the picture helps flip my brain. I can move the flashlight around in my mind's eye and the mountains pop. But yes, I get exactly the same illusion.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 22, 2016, 05:29:45 PM
I certainly experience what you mean, sometimes. With printed pictures you can turn the page upside down to get your eyes see the proper depth. I don't see myself doing that on a computer screen!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on March 22, 2016, 05:34:04 PM
LOL
I have turned a computer screen sideways (but more often just my head) to see things 'right'.  I've certainly turned books upside-down - for pictures of pesky craters.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 22, 2016, 05:34:53 PM
Here is a detail in full resolution (10m/pix), the Kap Zach. From the Landsat images we have learned that blueish taints indicate recent cracks/calvings. Here it is exactly the same, those area have recently shown activity in the Sentinel 1A SAR images.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 22, 2016, 05:52:17 PM
And a detail at the center of the "Isstrøm". Several past, present and/or future calving fronts can be recognied (#6 is the most left one). The cracks themselves don't show any bluish color, they are existing during most of pas winter.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on March 22, 2016, 05:53:47 PM
Excellent image, Wipneus, but it is an optical illusion for me.

When I first looked at it, my brain interpreted the icebergs as depressions, and not the raised objects that they really are - and that illusion was persistent. 

Assuming the the bright side of each iceberg is the southern "hillside" which is illuminated by the high-latitude, low-angle sunlight, I know intellectually how the icebergs should appear. 

Like classic optical illusion illustrations, when I stared at it long enough, I finally saw the icebergs as raised objects.   Does anyone else suffer from the same visual misinterpretations?

Imagining that I am holding a flashlight aiming "up" at the picture helps flip my brain. I can move the flashlight around in my mind's eye and the mountains pop. But yes, I get exactly the same illusion.

The illusion is strong but as long as I think of the light coming from the south it is fixed.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 22, 2016, 06:01:56 PM
And a detail in the north. The left most thin crack (about one quarter of the width of the image from the left) has been seen developing in Sentinel 1 SAR images in the past 1-2 months. There is some very faint blue coloring there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 22, 2016, 07:45:29 PM
Great stuff Wipneus!
Do you not have problems downloading from the ESA-site?
I have to "massage" my downloads from the the much lighter Sentinel 1 data?
Could you ship me a 10M Sentinel 2 image?
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on March 22, 2016, 09:12:59 PM
When I first looked at it, my brain interpreted the icebergs as depressions, and not the raised objects that they really are - and that illusion was persistent.
Just take the image and invert it , x --> 255-x. Every image software has a handy command for this. It's sometimes useful to be looking at both.
Great stuff Wipneus! Do you not have problems downloading from the ESA-site?
Yes, congratulations on our first Greenland Sentinel 2A! Do we have a 15 m Landsat of similar date to which we could compare the levels of detail?

The left most thin crack (about one quarter of the width of the image from the left) -- There is some very faint blue coloring there.
I could not confirm this despite splitting the RGB image into three grayscales and looking for excess at 700/4 = 175 pixels in from the left in the blue channel by subtracting, differencing, grain extracting, grain merging, dividing, or multiplying channels in gimp.

Note the blue and green channels are about identical except at the dark end whereas the red is even more extended there (see attached distribution tail and animation). The red (band 4) has the best contrast as noted earlier over on the 2A developer forum.

bin   R   G   B
 0    0   0   0
 1    0   0   0
 2    0   1   0
 3    0   0   0
 4    3   0   0
 5    1   0   0
 6    3   0   0
 7    8   0   0
 8   10   0   0
 9   17   3   0
10   18   1   0
11   23   3   2
12   37   7   0
13   45   7   0
14   41   9   1
15   87   11   1
16   112   12   4
17   192   15   1
18   240   21   1
19   395   22   5
20   461   32   1
21   550   44   8
22   622   54   6
23   748   46   13
24   775   73   7
25   772   81   13


I looked today for Jakobshavn but they are not quite there yet at ESA; the USGS portal is not remotely keeping up.

I also looked at Petermann today. There is 2A coverage but some craziness in the tiling prevlews makes it very unclear which granule should be downloaded. These file packages are just huge, 10x the size of Landsat, but there is no way to simply download the desire 2,3,4 bands and rectangle of interest.

Unbelievable, that they are just now thinking about how to portal the data. It should have all been worked out with proxy data prior to launch.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 23, 2016, 10:52:59 AM
Great stuff Wipneus!
Do you not have problems downloading from the ESA-site?
I have to "massage" my downloads from the the much lighter Sentinel 1 data?
Could you ship me a 10M Sentinel 2 image?

Of course ESA has lots of trouble with their "datahub's". Lots of connections that are broken, and restarts of downloads results in guaranteed corrupted files.
Yesterday the download went smooth, today a S2 file from Peterman (12GB!), dos not get further than 100-200MB  :(

How does an Espen massage work? I can only retry at another time and hope it works this time.

I'l see how best to share bigger processed files.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on March 23, 2016, 11:03:33 AM
Does the Amazon-service for S-2 data work better i wonder...:

http://sentinel-pds.s3-website.eu-central-1.amazonaws.com/ (http://sentinel-pds.s3-website.eu-central-1.amazonaws.com/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on March 23, 2016, 12:18:29 PM
Does the Amazon-service for S-2 data work better i wonder.+
The potential for a bypass of the ESA portal is there. Right now it is in alpha.

There is still no way to just get the main RGB bands which will account for 99.999% of public interest. Still no usable preview to see if your select rectangle is clouded over. An hour and 37 minute download of 8.3 GB followed by immediate deletion of 8.0 GB followed by cropping to 0.003 GB followed by web viewable forum post max of 0.0003.

It's worth a visit just to wonder about how an interface team could be so gloriously incompetent. Where did ESA find these people, did they not ask for previous programming experience? I mean, they can't even get the days of the month to present in order. The map search is separately incompetent.

Normally there is QA baked into every programming process but here it is abundantly clear no one looked at the product prior to release. Did they not watch what happened when a few average users tried to use it? Talking about a few hours at most to at least kill the worst bugs. This is so clueless, it has to be a partnership with a big military-industrial corporate-- a small legitimate shop could not survive at this skill level.

And all this just to reinvent the EarthExplorer wheel! Which is open source, free for the taking!

Here are a couple of March 2016 Petermanns. For some reason, they don't use the last part of the file name, eg T20XNQ
.  I have no idea if these scenes will be useful or not. Meanwhile, the download time has slipped to an hour and 39 minutes remaining, after downloading for 20 minutes!!!

S2A_OPER_PRD_MSIL1C_PDMC_20160322T061228_R041_V20160321T180021_20160321T180021_T20XNQ

S2A_OPER_PRD_MSIL1C_PDMC_20160322T061228_R041_V20160321T180021_20160321T180021_T21XVK


Meanwhile Landsat is posting almost daily Petermann scenes with incredible clarity. Why then bother with Sentinel 2A? Because at Petermann 10 m vs 15 m resolution matters: we are looking at tip widening on ice shelf cracks to get a handle on the next big cleavage event. That extra resolution will be a big help here. And the color too for melt water channels.

LC80370022016082LGN00 22-MAR-16
LC80302482016081LGN00 21-MAR-16
LC80460012016081LGN00 21-MAR-16
LC80390012016080LGN00 20-MAR-16
LC80390022016080LGN00 20-MAR-16
LC80322482016079LGN00 19-MAR-16
LC80410012016078LGN00 18-MAR-16
LC80380022016073LGN00 13-MAR-16
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 24, 2016, 12:33:16 PM
The Amazon S2 service works here much better than de official ESA "hubs", thanks nukefix.

A second Sentinel 2A image of Zachariae appeared, taken 25 hours after the first. Not much movement of the glacier (less than one pixel), but in an animation the one hour-of-the-day  difference makes a big difference in the shadows cast by the low sun.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on March 24, 2016, 01:22:04 PM
The Amazon S2 service works here much better than de official ESA "hubs", thanks nukefix.
I believe they have this for Landsat-8 too. After searching the map and chasing the box around until the file names can be copied, then searching the entire file name at the 'public bucket' for an exact match, I am finding that -- unlike ESA -- the server does not drop me multiple times and the download proceeds at the limit of my connection.

Yesterday I had some issues actually locating what I wanted among the many image tiles. It seems that ESA does not offer a workable preview map. Needless to say, it would be better to offer checkboxes so only the desired tiles are downloaded. Overall I have not found any value yet in the many metadata files.

There is a long undocumented folder chase, eg 'sentinel-s2-l1c>tiles>23>E>LK>2016>2>15>0' that leads to 180 kB previews of the individual bands; the one I tried (in the visible) was all black.

However sentinel-s2-l1c>tiles>22>W>EB>2016>3>23>0 works! And you can just download the bands you want, one at a time!! And, for mac users, the jpeg2000 opens in Preview from which it can be copied to ImageJ and composited into RGB!!!

This one had a very tight histogram that did not utilize more than a tenth of the potential bit depth. After a simple squeeze of the contrast range, the histogram was extremely quantized. So this does not quite solve the 16-bit jpeg2000 problem.

It looks like you can manufacture the download links out of the file name and so skip all the folder surfing. As in:

http://sentinel-s2-l1c.s3.amazonaws.com/tiles/22/W/EB/2016/3/23/0/B04.jp2 (http://sentinel-s2-l1c.s3.amazonaws.com/tiles/22/W/EB/2016/3/23/0/B04.jp2)

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#zips/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#zips/)

This one appears to be the first Jakobshavn. Is it cloudy? That would be nice to know ahead of starting this massive download. Percents don't work. At EarthExplorer, the preview is quite satisfactory. Unfortunately they don't keep up with image ingestion as well as this Amazon site.

S2A_OPER_PRD_MSIL1C_PDMC_20160323T234457_R068_V20160323T151927_20160323T151927
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 24, 2016, 01:40:10 PM
Great stuff Wipneus!
Do you not have problems downloading from the ESA-site?
I have to "massage" my downloads from the the much lighter Sentinel 1 data?
Could you ship me a 10M Sentinel 2 image?

How does an Espen massage work? I can only retry at another time and hope it works this time.


I use the F5 button (Windows) that usually helps!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 24, 2016, 05:56:36 PM
For Espen , I have uploaded a large (800Mb) png file at 10 m/pix, 48bits RGB of the 21 March Zachariae image. Two tiles from the original ESA product. Thumbnail attached.

https://drive.google.com/file/d/0B8NUHa4P2gmlRW5RZExiX0hHeTg/view?usp=sharing

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on March 24, 2016, 07:03:50 PM
For Espen , I have uploaded a large (800Mb) png file at 10 m/pix, 48bits RGB of the 21 March Zachariae image. Two tiles from the original ESA product. Thumbnail attached.

https://drive.google.com/file/d/0B8NUHa4P2gmlRW5RZExiX0hHeTg/view?usp=sharing

Thank you very much Wipneus, really impressive quality! ;)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on March 24, 2016, 11:48:02 PM
The Amazon S2 service works here much better than de official ESA "hubs", thanks nukefix.

A second Sentinel 2A image of Zachariae appeared, taken 25 hours after the first. Not much movement of the glacier (less than one pixel), but in an animation the one hour-of-the-day  difference makes a big difference in the shadows cast by the low sun.

Great animation, though took me a while to get my visual orientation right.
It shows how some of the broken icebergs that have capsized are much taller than the tabular ones that kept their original form. For example see a bit to the left and above the center of the image.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 31, 2016, 03:28:10 PM
With a six day separation and a  time of day difference of only 20 minutes, the ice movement is clearly visible.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Xulonn on March 31, 2016, 04:57:59 PM
That is the best glacier/calving front animation I've seen here yet, Wipneus.

I really appreciate your efforts and continuously improving skills. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on March 31, 2016, 11:21:48 PM
I echo Xulonn; and am looking forward to the final breakup of sea ice hereabouts which seems to have stalled.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on April 01, 2016, 11:56:35 AM
Last year saw the sea ice remaining in place throughout the summer at the mouth of ZI, which slowed down calving front retreat compared to the previous year.
This year there is very significant weakness of sea ice throughout the Atlantic sector. I believe this greatly increases the chances of the sea ice clearing in front of ZI in August, which could lead to washout of all the icebergs, and fast calving and clearing of the fronts developing behind the front. All those lines of tabular icebergs waiting to be separated. Should this indeed happen, it's going to be a very interesting ZI season.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 01, 2016, 12:45:00 PM
The quality of the source (that is the Sentinel 2A) makes this possible. From the same pair of images as above, here is a detail where breaks in two icebergs can be seen. Here the "camera" moves with the advancing ice melange.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 02, 2016, 03:27:55 PM
The pair of images from 21st and 31st of March are the first from identical orbital position and time of day. First thing to notice is that the images align perfectly, no shifting is needed to fix the stationary features (rocks). Very convenient compared with S1A and Landsat.

After re-sampling at 5 m/pix I shifted the images by 14x2 pixels to align the two images at the center of the glacier front. That translates to a velocity of 7.1 m/day, with an uncertainty of +/- 0.5 m/day assuming a 1 (5m) uncertainty.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 03, 2016, 10:16:41 PM
Melt ponds and melting areas are showing up early this season on top of Zachariae Isstrøm:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: AbruptSLR on April 04, 2016, 10:19:43 PM
The attached image comes from Eric Rignot's Dec 2015 AGU presentation & shows that the calving from for Zachariae reached to bottom of a negative bed slope by the end of 2015.  I wonder whether this indicates that the rate of retreat of the calving front will slow for a while.

Eric Rignot (AGU Dec 2015):

https://www.youtube.com/watch?v=3p9uRxX95f4 (https://www.youtube.com/watch?v=3p9uRxX95f4)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on April 05, 2016, 12:24:59 AM
looking at the image i'd say increase instead, less resistance, let's see, i'm always curious how common sense (logics) compares to specific scientific know-how :-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: AbruptSLR on April 05, 2016, 01:02:22 AM
looking at the image i'd say increase instead, less resistance, let's see, i'm always curious how common sense (logics) compares to specific scientific know-how :-)

Maybe you are correct, as I forgot that Zachariae is subject to cliff failures now.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on April 05, 2016, 07:06:00 AM
The way Zach is calving, my gut feeling is that it has not finished retreating and that the next few years could be dramatic. However, much depends on the sea ice and its buttressing effect. Should the sea ice clear regularly every summer, things would be speeding up.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Yuha on April 05, 2016, 07:13:03 AM
I wonder whether this indicates that the rate of retreat of the calving front will slow for a while.

My guess (and just a guess) is that Zachariae will remain in a cliff failure mode and continue to retreat until the calving front/grounding line reaches the end of the deep bedrock plateau.

Then at some point when the ice thins enough and loses touch with the deep plateau, the calving front starts to move forward while the grounding line stays in place. In other words, Zachariae grows a floating ice shelf. I suspect that top and bottom melting will keep the ice shelf from growing very long.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on April 05, 2016, 10:50:25 AM
My guess is it depends on how warm the seawater is at the base, if it's warm enough a fairly rapid retreat to the next ridge, and if that happens quickly a slump beyond that.
Take a look at Nioghalvfjerdsfjorden and see what you think will happen when open water extends beyond the trough below it's front.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FlmtQR%2F0379acd0aa.jpg&hash=e43f8443ff198d3bc2cb8d26c125a73e)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on April 06, 2016, 04:16:12 AM
looking at the image i'd say increase instead, less resistance, let's see, i'm always curious how common sense (logics) compares to specific scientific know-how :-)

Maybe you are correct, as I forgot that Zachariae is subject to cliff failures now.
If we were talking aerodynamics instead of ice dynamics I'd say the fractures ahead of the calving face are the transition from laminar to turbulent flow.  Is there a recognized mechanism that is the perallel to that transition in ice dynamics?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on April 06, 2016, 05:39:12 AM
" ... the fractures ahead of the calving face are the transition from laminar to turbulent flow.  Is there a recognized mechanism that is the perallel to that transition in ice dynamics?"

the proximity of phase change vastly complicates, but i look at it as a transition to granular flow. The granules are kilometers in size ...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 06, 2016, 11:34:57 AM
Melt ponds and melting areas are showing up early this season on top of Zachariae Isstrøm:

I have been noticing the blue and brown colors in the Sentinel 2A images as well and wondering how to interpret them. Are the blue's true signs of melting or lack of snow exposing blue ice? Here are a few animations of the first decade of available images.

First is the brown colors seeping of rock outcrop. Melting helped by the darker color, but not much difference in 10 days.

In the second animation of a patch noted in Espen's graph, the images have been so shifted and rotated to make the ice stationary. As can be seen the blue patch is not growing much, but is mostly shifting upwards relative to the ice.

This brings me to the observation, discussed before in this thread, that a lot of melting ponds are stationary while the ice moves. The explanation is  the ponds are over depressions in the underground while the glacier glides over them.

The third animation is of a bit larger melt pond nearby upstream. Also here there is not much more melting visible in the 10 day. Here only the upper part of the melt pond is blue colored.
That brings me to the fourth animation where the same melt pond is compared with the end of summer last year. Here can be seen that the lake is roughly at the same position, but ice has traveled a considerable distance.  The scale here is 5m/pixel wheer the previous was blown up to 2.5 m/pix.

This, and other melt ponds that show exactly the same behavior, makes me think that here the blue color has to do not only with melt water but also with water from within the melt pond itself. The water becomes exposed as the glacier surface dives downward below the water level in the pond.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on April 06, 2016, 03:53:04 PM
Good bit of detective work.

Jakobshavn has similarly puzzling stationary features to the east of the calving front along the north side of the south branch. In watching stream water flow around a submerged or half-submerged boulder, there will be a standing wave or eddy in back. The water level can be significantly lower there, quite noticeable in a kayak. Flowing ice, even though it is in the solid state, has similiar properties to a fluid. So it seems that nearby meltwater around should accumulate in the depression of the eddy just from gravitational flow from high to low, rather from locally enhanced frictional heat, pressure decompression, or some such there.

https://en.wikipedia.org/wiki/Eddy_%28fluid_dynamics%29
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 06, 2016, 08:08:23 PM
Great work Wipneus!
It seems the ice-lakes (melt ponds) stay put during the winter and "wake" up when the time is right, as A-Team suggest ice even behave like fluid or plastic (so do steel).

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on April 06, 2016, 11:14:38 PM
I've seen "after-images" of lakes in SAR images so clearly the empty melt-ponds move with the flow even if the liquid lake always forms in the same spot every summer.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 08, 2016, 09:15:37 AM
Excellent S2A images keep coming in, also thanks to the favorable weather  conditions.
Here is a detail concentrating on the central glacier where as we know several future (I expect all 2016) calving fronts are developing. From right to left, calving fronts #3-6 are visible.
The two frames of the animation are aligned on the left side. As can be seen on the right the ice moves away, indicating the cracks are widening. I can see visible activity on fronts #4 and #6.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on April 08, 2016, 02:31:33 PM
Superb animation. Thanks
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 15, 2016, 12:18:57 PM
Strange sketch in the snow cover of a melt pool on the Zachariae.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on April 15, 2016, 04:16:17 PM
Strange sketch in the snow cover of a melt pool on the Zachariae.

"Picasso was here" : Naked woman sitting on a bed
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on April 15, 2016, 06:51:11 PM
Strange sketch in the snow cover of a melt pool on the Zachariae.

"Picasso was here" : Naked woman sitting on a bed

hehe... nice observation while the naked part is probably more of an imagination LOL
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 18, 2016, 08:24:37 AM
Zachariae update. In the first animation the ice can be seen grinding around Kap Zach. On the right side of the images one of the larger icebergs can be seen to split in two.
In the second image the 16 April image was shifted 52x6 pixels to align the images on the left. That translates to a daily movement of 6.54 m. All four visible future calving fronts can be seen expanding.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on April 18, 2016, 04:39:19 PM
Wow, nice imagery. The extra umph of Sentinel 2A resolution really makes a difference. And your color pipeline is paying good dividends with these. An interesting technical question, how much better is this than two 30 m Landsat-8 color channels pansharpened to 15 m with band 8. I suppose the comparison to true colors would be to OMG color imagery taken at 13 000 m; however I could not find where they are archiving their gallery of the whole coastline.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 01, 2016, 10:47:09 AM
(R)evolution: images by Landsat-8 (normal 30m/pixel), Landsat-8 pan-sharpened to 15m/pixels end the Sentinel with a normal 10 m/pixel resolution. Everything scaled to 5m/pix.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on May 01, 2016, 04:03:48 PM
The Sentinel is soooo much better. The resolution doesn't tell all.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on May 01, 2016, 10:14:12 PM
(R)evolution: images by Landsat-8 (normal 30m/pixel), Landsat-8 pan-sharpened to 15m/pixels end the Sentinel with a normal 10 m/pixel resolution. Everything scaled to 5m/pix.

Nice product. I am curious what such a triple would look like for the Petermann crack tips that we have been monitoring. The S2A may still be fairly decent at 2.5m. I'm still mulling over whether more could be done to use up the three 10m channels to make an even sharper one channel. Seems like there should be some statistical process while still in 16-bit that could reduce noise, maybe just average or the median pixel value of the three.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: iwantatr8 on May 10, 2016, 06:49:55 PM
A couple of good images from icebridge...

https://twitter.com/NASA_ICE/status/730039454103154688/photo/1?ref_src=twsrc%5Etfw
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 10, 2016, 07:06:26 PM
Among the icebergs, one decides to split.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: DoomInTheUK on May 11, 2016, 12:17:15 AM
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on May 11, 2016, 12:26:46 AM
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.

that's the momentum from separation, everything the brakes separates to a certain amount, see it as a braking not just as a simple separation, there was energy that transferred into kinetic energy, has nothing to do with the surroundings.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: plinius on May 11, 2016, 12:36:51 AM
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.

>> that's the momentum from separation, everything the brakes separates to a certain amount, see it as a braking not just as a simple separation, there was energy that transferred into kinetic energy, has nothing to do with the surroundings.



To be more precise probably a tilt in the two pieces against each other along the old long axis. Acts a bit like a lever.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: DoomInTheUK on May 11, 2016, 10:40:03 AM
On closer inspection it would appear that the lower section has dropped after separation, so I assume the break was caused by the thinner lower part being held up by the top part, and finally snapped off.

Just as Plinius described.  ;)

I still can't lose the Pacman image though.  ::)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 11, 2016, 03:44:51 PM
The Zachariae glacier keeps advancing with an undiminished speed of 6-7 m/day. However there are only few and only small events to report. Yet on the long run new cracks can be seen developing.

In the first animation a 40 day difference shows the forming of a new branch in a sort of "Y"-shape (center of the image, Kap Zach is at the bottom-right). The forming of this new branch is easy visible from S1A radar images as well.

This is a gradual process with multiple little steps. One such step can be seen in the second animation with the images less than 24 hours apart. Some part of the top layer collapses, exposing the open crack.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on May 31, 2016, 12:54:39 PM
The R025 series (images taken when the Sentinel 2A is in relative orbit #025) has until now delivered only images with few or no clouds. That enables series of two months (6 images 10 days apart).

Here is one of the active southern half (near Kap Zach).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on May 31, 2016, 02:38:15 PM
Very nice series. They seem to be using a zero in RO25 rather than the letter oh so make that 'relative zorbit' maybe?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 10, 2016, 06:36:41 PM
Something is broken in the S2A data.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 10, 2016, 08:25:35 PM
"Something is broken in the S2A data."
Let's hope for a quick fix the fast ice thereabouts is shrinking daily.
added
certainly looks like something is happening to N79
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FpoJCp%2Fe66fb4edc4.jpg&hash=40847cd4237cb2ece6ba83b17101290f)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 11, 2016, 01:52:38 PM
what always surprises me in these animations (see wipneus' post #662) is how uniformly th melange moves with the icebergs. What is the driving mechanism there? The whole lot is moving towards sea ice which has not budged for a couple of years now if I recall correctly. I know there is a circulation of buoyant meltwater from beneath the glacier tongue but I would expect this to be stronger or weaker in places across the width of the glacier.
How much is known about this?
Thanks, Wipneus, for providing these animations.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on June 11, 2016, 02:18:22 PM
sea ice which has not budged for a couple of years now
To be accurate, the last time the sea ice cleared was in August 2014, which brought with it a huge retreat and clearing of the icebergs. So this melange definitely plays a role in stabilizing the glacier.
This year I expect the sea ice to clear again due to the warm Atlantic and the low Greenland Sea extent, but we'll see.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 11, 2016, 05:19:53 PM
thanks oren, that helped me find a suitable reference point, looking over longer periods there is relative movement and distances between icebergs change. I don't know whether the allignment of those two Landsat images is the same but using these rocks as markers I hope I'm fairly consistent
first image from 14.9.2014
And here is my favorite, Zach always impress me, because this is not a "Mickey Mouse" glacier like so many others, and here she come:
second from 8.3.2016
First usable Landsat 8 image from 2016. Here is a pan-sharpened large image at 15 m/pix resolution. ...
I have marked recognizable bergs , spotting the changes with breaking and turning bergs is quite fun
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 18, 2016, 06:24:32 PM
Looking to the north of Nioghaivfjerdsfjorden [N79] this from the 15th shows a darker area adjacent to the coast which I suspect is reinforced with freshwater melt from the glacier, and a larger lighter more clearly 'marbled' area of ice further out.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FNEW%2F20160615s01a.ASAR.jpg&hash=fc4e6186786b8bd82886acc27869c8bb)
[ http://ocean.dmi.dk/arctic/images/MODIS/NEW/20160615s01a.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/NEW/20160615s01a.ASAR.jpg) ]
and this shows the lighter area detatched and possibly the purple [ish] ice in the fjord just to the north indicates the beggining of warm water penetration beneath the ice which may lead to the loss of the thicker landfast ice.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FNEW%2F201606181317.jpg&hash=40e2b1fe7904c67b595cbc296b5ae95a)
[ http://ocean.dmi.dk/arctic/images/MODIS/NEW/201606181317.jpg (http://ocean.dmi.dk/arctic/images/MODIS/NEW/201606181317.jpg) ]
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 18, 2016, 06:32:08 PM
Possibly some melt occuring just south of Zachariae too
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FJoekelbugt%2F201606181317.jpg&hash=b10f7da8f2a02da35fc1907e43ee6883)
[ http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201606181317.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201606181317.jpg) ]
added:- I thought I'd take a closer look at the glaciers so this is a detail from https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2016170.aqua.250m.jpg (https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2016170.aqua.250m.jpg)  I can almost persuade myself that warm water is penetrating as far as the north shore of the fjord containing N79, if that's the case some movement will happen soon.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FpxjNp%2F475851c9ea.jpg&hash=d033d5c3902629fd7982d27e956b3296)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on June 19, 2016, 12:27:33 AM
The appearance of the "marbeled ice" is explained by looking back at last autumn when there was some breaking and movement just before darkness returned to that area.
TERRA 1.10.2015
http://go.nasa.gov/26a2Pj7 (http://go.nasa.gov/26a2Pj7)
IR image when light was too low for visible images:
http://go.nasa.gov/1YyNSEF (http://go.nasa.gov/1YyNSEF)
worldview makes it much easier than the DMI site to look through other dates and click from visible to near IR (band 7-2-1) and long IR (band31) but of course doesn't have the SAR images.
The very light shades in the open water area in the SAR image are waves as far as I know

The images which show some ice coloured in purple look like the 7-2-1 images but with purple instead of the darker blue indicating water on the ice surface. Can you point to information on these images?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 19, 2016, 04:11:39 PM
I tweaked this with Gimp to enhance the purple
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FpybSy%2F256077323c.jpg&hash=8463a4d09abd76b0a1d18ba9aafafefd)
I've just realised that the fjord north of N79 [with the triangular island] is actually open to the fjord further north still and that the whole complex is about to become distinct islands, which will leave it very vulnerable to erosion from waters pouring out of the arctic. That'll change the whole dynamic for Nioghalfjersfjorden, if it isn't already.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 20, 2016, 05:57:29 PM
The glacial ice of the Zachariae has become much darker in the last week or so. That is the top of it, where calvings have toppled the ice stays much brighter and the ice melange in between has a color in between.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 20, 2016, 11:06:17 PM
Take a look at the northern side of N79 http://go.nasa.gov/28Ktr5Z (http://go.nasa.gov/28Ktr5Z) then go back to the 12th, http://go.nasa.gov/28Kw2wT (http://go.nasa.gov/28Kw2wT)  is it possible that the glacier is going to begin calving/discharging into the north channel?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 23, 2016, 12:47:06 PM
The "darkening" goes up-glacier and with it the number of melt ponds explodes.
(S2A image scaled to 50m/pix for size).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 23, 2016, 02:19:48 PM
Take a look at the northern side of N79 http://go.nasa.gov/28Ktr5Z (http://go.nasa.gov/28Ktr5Z) then go back to the 12th, http://go.nasa.gov/28Kw2wT (http://go.nasa.gov/28Kw2wT)  is it possible that the glacier is going to begin calving/discharging into the north channel?

This is the "north channel" on June 12 and 22, scaled to 20 m/pix. Nothing beyond a very slow forward movement can be seen. The explosion of melt ponds happened here as well though.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on June 26, 2016, 10:00:59 PM
Thanks Wipneus
Looking through the cloud it seems the Greenland sea ice break-up has reached N79
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FpGX71%2Fb2eb063d66.jpg&hash=1be6e232b9b7c3cb1b9adfb199fb1d94)
http://go.nasa.gov/296EhBV (http://go.nasa.gov/296EhBV)
It won't be long before these sleeping giants wake
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FpIMQV%2F634f58f061.jpg&hash=336c7cef8a351d7b6ac79f1b27c40c29)
http://go.nasa.gov/29aSwpu (http://go.nasa.gov/29aSwpu)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 29, 2016, 02:19:10 PM
The Zachariae glacier is rather smoothly continuing its advancing glacier fronts, opening cracks, melting further and further inland.

So the most interesting I have here is two calvings splitting in one image.  One calving (the darker one) still upright, the other toppled over. There is a crack developing in the ice melange as well. These events are probably not directly related, the crack in the toppled ice berg happened 4 days before the one in the upright calving and the crack in the melange is still older.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on June 29, 2016, 06:13:02 PM
Seems interesting they are all so close to each other. Suggests there is some common root cause. Could it be warm surface water entering the fjord, being drawn in by cold basal melt exiting?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 30, 2016, 10:58:43 AM
Seems interesting they are all so close to each other. Suggests there is some common root cause. Could it be warm surface water entering the fjord, being drawn in by cold basal melt exiting?

It is at the edge where the ice melange that is moving with the glacier front is rubbing the ice melange that is fasted to bedrock. My impression is that this is only a smaller contribution to the forces that  make these ice bergs break.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 30, 2016, 11:00:35 AM
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 03, 2016, 08:41:20 AM
Small calving near "Kap Zach".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 03, 2016, 03:26:14 PM
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 03, 2016, 03:49:54 PM
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?

I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on July 03, 2016, 07:01:44 PM
not sure about melt ponds but it's proven fact that under the ice "embedded" are entire lakes that survive winters. i could imagine that once, relatively warm melt water fills a deep enough reservoir and that will over freeze relatively quickly in autumn, that once that frozen cover is thick enough it would insulate the underlying water, especially if there's a layer of air ( airpockets above water pockets so to say ) that would further insulate the water from the really cold surface due to it's relatively poor conductive capabilities. again i'm sure that those with the background can word this better and/or shed more light, while the existence of embedded lakes i'm 100% positive that they exist because they've been found and in parts explored.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on July 03, 2016, 08:30:53 PM
...
Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?

I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.

I thought I would agree, but did a spot of internet research.  From Wintertime storage of water in buried supraglacial lakes across the Greenland Ice Sheet (http://www.the-cryosphere.net/9/1333/2015/tc-9-1333-2015.pdf), L. S. Koenig, et.al. 2015:
Abstract.
Increased  surface  melt  over  the  Greenland  Ice
Sheet (GrIS) is now estimated to account for half or more of
the ice sheet’s total mass loss. Here, we show that some melt-
water is stored, over winter, in buried supraglacial lakes. We
use airborne radar from Operation IceBridge between 2009
and  2012  to  detect  buried  supraglacial  lakes,  and  we  find
that they were distributed extensively around the GrIS mar-
gin through that period. Buried supraglacial lakes can persist
through multiple winters and are, on average,
below the surface. Most buried supraglacial lakes exist with
no surface expression of their occurrence in visible imagery.
The  few  buried  supraglacial  lakes  that  do  exhibit  surface
expression  have  a  unique  visible  signature  associated  with
a darker blue color where subsurface water is located. The
volume of retained water in the buried supraglacial lakes is
likely insignificant compared to the total mass loss from the
GrIS, but the water may have important implications locally
for the development of the englacial hydrologic system and
ice temperatures. Buried supraglacial lakes represent a small
but year-round source of meltwater in the GrIS hydrologic
system.

From the introduction:
This paper presents an initial study and mapping of over-
winter  surface-melt  retention  in  buried  supraglacial  lakes
(Fig.  1)  within  the  GrIS.  We  define  a  “buried  supraglacial
lake”, hereafter for brevity a “buried lake”, as water retained
through a winter season at shallow depths within the ice sheet
that originally formed, during a previous melt season, as a
(subaerial) supraglacial lake.

I learn something every other day!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on July 03, 2016, 10:24:33 PM
thanks for providing the many more details and sources :-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on July 03, 2016, 11:35:28 PM
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?


I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.
depth.  If they are deep enough then they wont freeze to the bottom. How thick does the sea ice get? 3 meters? 6 meters?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on July 04, 2016, 12:20:31 AM
Looks like 2 melt ponds drain, with effects propagating down to the coast.  Perhaps Wipneus will provide a better image?
Edit:  Circled the 2 areas that I see changes downstream.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: bbr2314 on July 04, 2016, 01:42:31 AM
That is a great animation!

It also begs the question and would seem to suggest that melt ponds allow more warm air to pass *through* Greenland, supercooling in the process and being deposited the opposite site of whichever it enters.

That would explain why 2012's catastrophic melt was followed by mild seasons in both 2013 and 2014.

If Greenland acts as an enormous air conditioner for the Northern Hemisphere/Arctic, its "normal" capacity without melt would certainly be substantial. But with a season like 2012 on the books, it would fracture/split in many more locations versus a typical year in the 20th Century (which would have featured very little such activity). And then as you head into fall and solar radiation begins declining, you still have all the nooks and crannies for the air to pour through as it traverses the Greenland Ice Sheet... "activating" it as a much stronger cold source in the process, as the volume of air that can cool through the ice sheet increases dramatically (in addition to heat removed during nighttime/etc).

....of course then it would certainly follow that through the following fall/winter/several seasons, Greenland's cooling power would be enhanced until the nooks & crannies are filled with ice once more.

But perhaps like we've seen in the Arctic, the "new" ice in these locations is much easier to melt vs. the old stuff, which means that the cycle continues repeating & worsening until there is no rebound year and glaciation begins across the NHEM (specifically NE Canada, then spreading from there) once more.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 07, 2016, 01:13:24 PM
Ice berg breaking, again near Kap Zach.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on July 07, 2016, 05:20:10 PM
I think there was something more than an iceberg breaking?  Aqua images.  Yesterday's Polar View sentinel 1 image border goes right down the center of the glacier, I won't be trying to stitch that together. 

Edit:  New cracks appear to be directly downstream from the disappearing melt ponds from Jul 4th gif.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on July 07, 2016, 09:48:54 PM
Went back for another look on Terra, glad I did because the clouds on the glacier cleared out.  Looks like the cracks have gone a little further than the earlier Aqua gif.  Here is a gif from 7/2 to 7/7, remarkable how many ponds disappear.  Could some have been snowed over?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 08, 2016, 12:27:42 AM
Went back for another look on Terra, glad I did because the clouds on the glacier cleared out.  Looks like the cracks have gone a little further than the earlier Aqua gif.  Here is a gif from 7/2 to 7/7, remarkable how many ponds disappear.  Could some have been snowed over?

Looks like some nice calving there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 08, 2016, 08:33:28 AM

Looks like some nice calving there.

You can say that. First major calving of this year.

Click on the picture to start the animation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 08, 2016, 11:34:29 PM
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: magnamentis on July 08, 2016, 11:57:45 PM
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?

about the melt through i dunno but if you look for a landmark (not ice) and compare the two images once can see that the entire glacier made a big move downstream and whether or not that is a melt through, it could be that the floes gave in to "Massenträgheit" (inertia?)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on July 09, 2016, 06:56:56 AM
I would guess the motion is wind related, and is one of the same changes I had noticed in the earlier post around the 4th.  I asked Wipneus about the melt ponds vanishing, and he said they were probably not related to the calving.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TerryM on July 09, 2016, 12:53:44 PM
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?
Could a sudden change in elevation at the face concurrent with the calving event explain what may be a "sloshing" in the melt pond? The katabatic winds wouldn't reverse & this is the only other force that I can think of that would move the ice floating in the melt pond to head back away from the front.
Terry
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 16, 2016, 09:08:46 AM
Several calvings have broken, toppled over.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 23, 2016, 12:01:59 PM
Just upstream from Z. any ideas what the waves/stripes are about
(https://puu.sh/qbv81/3ff8e65bd8.jpg)
visible on http://go.nasa.gov/2ahxHdB (http://go.nasa.gov/2ahxHdB) too
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 23, 2016, 12:23:09 PM
These features are also seen in 2015 and 2014, less in 2013 when there was less melt exposing the ice. That means they are in the ice or firn layer and seem to be parallel to the direction of ice flow. Some melt ponds are alligned with them
http://go.nasa.gov/2a4YbvA (http://go.nasa.gov/2a4YbvA)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 24, 2016, 12:38:52 AM
Looking at http://nholschuh.com/glaciers.html (http://nholschuh.com/glaciers.html) this image area is 20-30w and 78-80n
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fqc3sw%2F1311d33df1.jpg&hash=9fb88b773cbbbd3d3c098ce9cf8e144e)
and this from polar view is between 78-9 n
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fqc2Ow%2F3184455392.jpg&hash=86a0616f76f4384ab70d379d85ed01aa)
so I'm thinking that perhaps this is the result of some sort of infrasonic resonance propagating back from the calving front in a softened semi liquid basal layer.
IF [bigif] that's right this monster is lubricated and ready to go.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: iwantatr8 on July 24, 2016, 07:13:32 AM
...is the result of some sort of infrasonic resonance propagating back from the calving front in a softened semi liquid basal layer.
...

Er, No.

What you are looking at are the resultant flow features generated from the internal stresses associated with the changing velocity profile of a distinctly non-Newtonian fluid.

Look here http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=0&image_date=160414_160508#output (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=0&image_date=160414_160508#output)
for details of how rapidly the flow velocity changes both across and along the direction of flow.

Then try a couple of free access papers on glacier flow.

https://www.researchgate.net/profile/Gudmundur_Gudmundsson/publication/252424512_Basal_flow_characteristics_of_a_non-linear_flow_sliding_frictionless_over_strongly_undulating_bedrock/links/00463537a060cd6757000000.pdf (https://www.researchgate.net/profile/Gudmundur_Gudmundsson/publication/252424512_Basal_flow_characteristics_of_a_non-linear_flow_sliding_frictionless_over_strongly_undulating_bedrock/links/00463537a060cd6757000000.pdf)

http://www.cpom.org/research/jad-ag.pdf (http://www.cpom.org/research/jad-ag.pdf)
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 26, 2016, 01:10:18 PM
"Er No" Well as interesting as those links were none of them suggested any mechanism for the formation of parallel corrugations aligned with flow. So I thought maybe I'd try to find a similar glacier, none exist so far as I can see, this is defined as a Piedmont in Wiki. but really it's not emerging from any mountains, and it's not gravity driven except in the sense that the pressure is caused by gravity. Then I came across this http://www.nature.com/ngeo/journal/v7/n6/fig_tab/ngeo2167_F1.html (http://www.nature.com/ngeo/journal/v7/n6/fig_tab/ngeo2167_F1.html) which shows that underlying the area which I think bears the imprint of some sort of resonant effect there is a large basin, more or less perfectly situated, I couldn't enhance it sufficiently to be confident and then by chance or design Andreas T put this link up on the season page. http://membrane.com/sidd/greenland-2013/Zachtrough/ (http://membrane.com/sidd/greenland-2013/Zachtrough/)
Looking at that it seems at least possible that some seawater penetration happens,[ bearing in mind the tidal lake in N79] and if not then a reservoir of meltwater may have formed, such that when a calving event occurs sound/pressure waves propogate through the deep channel and resonate below the ice.
 It also helps to make sense of the arched bulge that shows up on the sentinel images.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 26, 2016, 06:48:53 PM
No Sentinel 2 image yet, but Sentinel 1A records a rather large calving event, now more at the center and to the north of the calving front.
Image scaled from 10 to 20m/pix for size.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 27, 2016, 03:45:55 PM
Landsat sequence day 205 in 2015 and day 208 in 2016. Pink line is the calving front in July 2015. The position of the front is similar except in the north where front was more retreated in 2015.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 27, 2016, 05:29:45 PM
"Er No" Well as interesting as those links were none of them suggested any mechanism for the formation of parallel corrugations aligned with flow. So I thought maybe I'd try to find a similar glacier, none exist so far as I can see, this is defined as a Piedmont in Wiki. but really it's not emerging from any mountains, and it's not gravity driven except in the sense that the pressure is caused by gravity. Then I came across this http://www.nature.com/ngeo/journal/v7/n6/fig_tab/ngeo2167_F1.html (http://www.nature.com/ngeo/journal/v7/n6/fig_tab/ngeo2167_F1.html) which shows that underlying the area which I think bears the imprint of some sort of resonant effect there is a large basin, more or less perfectly situated, I couldn't enhance it sufficiently to be confident and then by chance or design Andreas T put this link up on the season page. http://membrane.com/sidd/greenland-2013/Zachtrough/ (http://membrane.com/sidd/greenland-2013/Zachtrough/)
Looking at that it seems at least possible that some seawater penetration happens,[ bearing in mind the tidal lake in N79] and if not then a reservoir of meltwater may have formed, such that when a calving event occurs sound/pressure waves propogate through the deep channel and resonate below the ice.
 It also helps to make sense of the arched bulge that shows up on the sentinel images.
You have not addressed the fact that I showed these parallel lines which you are attributing to a recent event present in previous years. Wipneus' animation shows that the undulations are found in the same place after a year, more clearly than the worldview images.
You seem to be too fond of exotic explanations to look at boring facts. What exactly would your infrasonic resonance do to the ice? it is very thick there and your hypothetical "semiliquid state" would make it flow into the sea very quickly.
Looking at some other S1A images of Greenland glaciers I think there are similar lines although not as clearly at regular spacing as those you show above. But then the geography of width and inclination of the glacier are fairly unique. Secondary flow patterns near the surface of the glacier responding and mutually reinforced by patterns in meltwater runoff and firn accumulation seem a perfectly plausible and sufficient explanation to me but I do not claim to have any in depth knowledge of glaciology.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 27, 2016, 10:29:19 PM
If I implied it was due to a recent event, that was a mistake, it's just that although I've always followed this thread and had probably noticed these lines before I presume I thought these were just the same sort of lines normally seen in a flowing glacier. It's only seeing how similar they are, for the first time, that made me stop and think. Looking back to the first page of this topic[recommended] for clues about dates to look at the oldest sign so far is here http://www.arctic.io/explorer/6oN7g/2013-08-06/9-N78.62644-W23.28894 (http://www.arctic.io/explorer/6oN7g/2013-08-06/9-N78.62644-W23.28894) but they begin to develop more noticibly after the 20th.  Looking at this image there's a bottleneck beneath the bulging arch[on sentinel images] that stops it all sliding to the sea.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fqgz5T%2F8f4fa4e1bd.png&hash=45d8f8c0742060a19f6e05b4cb162e87)
from http://membrane.com/sidd/greenland-2013/Zachtrough/ (http://membrane.com/sidd/greenland-2013/Zachtrough/)
" What exactly would your infrasonic resonance do to the ice?" One thing I would expect is for these corrugations to move across the flow line, but on what time scale?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 28, 2016, 08:09:07 PM
The sea ice over the trough north of Ile de France has been loosened and broken when the movement was northward now the movement of ice further east has resumed its usual southward directionan and it will be interesting to see how the ice inside belgica bank will react, in previous years it didn't move south quickly but that usually happened later in the year.
The other thing I am going to watch out for is whether loss of this ice will make the ice inside the islands melt. The openings between the islands are quite narrow and in previous years like 2013 when there was open water at the calving front of Zachariae, this happened by melting ice not by drifting away.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 29, 2016, 03:48:55 PM
Whatever this is it's extending north and south
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FqiCY5%2Fde6b8c6b8b.jpg&hash=836cd1be44215118eed8520359308b82)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FqiD0Y%2Fc7be37b6bf.jpg&hash=045b02cd534ea41524d245da9c03c6c8)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on August 03, 2016, 10:41:45 PM
Looks like a little bit more than wind motion here.  Aqua band.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 04, 2016, 09:38:15 PM
break up in the iceberg filled sea ice south of Zachariae just a few days later than in 2013. This can get interesting.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on August 05, 2016, 01:21:28 PM
The German research icebreaker R/V Polarstern is working in this area right now, e.g.,

http://www.meereisportal.de/en/seaiceexpedition/where-is-polarstern.html (http://www.meereisportal.de/en/seaiceexpedition/where-is-polarstern.html)

The focus is on glacier-ocean interactions both from a modern (physical oceanography) and ancient (geology, paleo-oceanography) perspective with groups from Germany, England, and the US all working together. Wish them luck to recover those moored sensors computers placed in shallow waters where ice bergs may wipe them off the bottom of the ocean. A Canadian technician I work with is aboard to help, but I have not heart from him for 2-weeks; even simple text-only e-mails can be hard to get off the ship at times ...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 05, 2016, 03:16:23 PM
Water temperatures reported at http://www.sailwx.info/shiptrack/shipposition.phtml?call=dblk (http://www.sailwx.info/shiptrack/shipposition.phtml?call=dblk)  are as high as 2.6oC
is that typical for the North East Water polynya?
With the recent movement and possible opening of sea ice there my curiosity has been drawn to the sediment plumes south of Zachariae. With the work you have done in the area, Andreas, can you point us to information on where that comes from? is it carried from under the ice sheet or is it local sediment from coastal deposits?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 06, 2016, 03:21:52 PM
Looks like a little bit more than wind motion here.  Aqua band.

Indeed. Sentinel 2 images are not coming in when you need them but here is a pair of Landsat 8 images 30 hours apart. The calving is now concentrated in the northern half. There are some indications that this one is initiated not from the glacier but from breakup of the debris field in the south noted by Andreas.

Full resolution (15m/pix, but you must click to see that.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Dave55 on August 08, 2016, 08:29:43 AM
break up in the iceberg filled sea ice south of Zachariae just a few days later than in 2013. This can get interesting.

I don't have the time or tech skills to post imagery but just doing a scroll through MODIS imagery there is massive movement since August 1 and what looks like a big calving in the north. Looks like the the sea ice was acting as a big dam that has now been released.

I'm generally just a lurker here and enjoying reading the discussion and learning a lot but felt this little observation was worth noting.  Back to lurking again!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 08, 2016, 09:26:44 PM
break up in the iceberg filled sea ice south of Zachariae just a few days later than in 2013. This can get interesting.

I don't have the time or tech skills to post imagery but just doing a scroll through MODIS imagery there is massive movement since August 1 and what looks like a big calving in the north. Looks like the the sea ice was acting as a big dam that has now been released.

I'm generally just a lurker here and enjoying reading the discussion and learning a lot but felt this little observation was worth noting.  Back to lurking again!
http://go.nasa.gov/2b1uwXZ (http://go.nasa.gov/2b1uwXZ)
http://go.nasa.gov/2aPGlgD (http://go.nasa.gov/2aPGlgD)

just those two days was impressive.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 09, 2016, 05:16:40 PM
A Sentinel 2A image appeared of the 6th of August, bit cloudy. It shows that the calvings in the northern half have continued since.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on August 09, 2016, 11:53:05 PM
Looks like a big calving in the northern part or the strong northwest winds caused several floating ice islands to turn over. The debris field looks much brighter now. We have to wait for cloud free high-res images to get a better understanding.

Attached is a worldview gif from 4 and 9 August.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 10, 2016, 09:08:35 AM
Not sure about turning over, but the calving did continue there and some icebergs are displaced considerably.
Through the mists or clouds:
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 10, 2016, 07:31:24 PM
I found two clear Landsat images and see what is going on! The whole iceberg field in front of the glacier has been seriously thinned out. The bergs moved, some a considerable distance, to the south.

Images scaled to 30m/pix for size. You must click to start the animation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 10, 2016, 07:47:16 PM
I have been expecting this since forever. The same happened in August 2014, once the sea ice cleared all hell broke loose. And this year the Atlantic side and the Greenland Sea in particular had very low ice.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TenneyNaumer on August 17, 2016, 05:38:02 AM
79N and Zachariae are endlessly fascinating.  I remember seeing Ian Joughlin's ice velocity map back in 2007 or so, and when I saw that the northeast ice stream went southwest hundreds of miles and the inclination was pretty steep, it really grabbed my attention. That map is here:  http://static.skepticalscience.com/pics/Figure6.jpg (http://static.skepticalscience.com/pics/Figure6.jpg)

Do we know if the velocity has increased since 2006 and by how much?

I also have to admit I like the shapes of the calving fronts. 

The other thing is that there used to be an enormous land-fast ice shelf right there that buttressed these glaciers.  I remember it breaking up pretty dramatically in July 2007.  I suppose it probably did that in earlier years, but I was not paying any attention before the winter of 2006-07.  Remember when the sea ice would flow out all down the eastern coast of Greenland? 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on August 17, 2016, 11:24:18 AM
"northeast ice stream went southwest hundreds of miles "
I was looking at this just yesterday
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.polarview.aq%2Fimages%2F106_S1jpgsmall%2F201608%2FS1A_EW_GRDM_1SDH_20160815T185343_2075_N_1.jpg&hash=4d01650eb04f20d99f3d0bfdfe8b094f)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on August 17, 2016, 03:34:18 PM
S-1A 12.8.2015, preparing to calve more (the crack visible on 8.7 has propagated further)

ps. sorry for the jpeg-artefacts I was a bit aggressive with the settings..

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 17, 2016, 06:20:36 PM
http://go.nasa.gov/2bnyU3D (http://go.nasa.gov/2bnyU3D)

In the floating ice that was once part of Zachariae is that a crack in it or some other kind of artifact?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on August 18, 2016, 12:03:45 PM
http://go.nasa.gov/2bnyU3D (http://go.nasa.gov/2bnyU3D)

In the floating ice that was once part of Zachariae is that a crack in it or some other kind of artifact?

To me it looks like a network of melt pond rivers where two bigger ones form parallel lines.

Click on the image for full resolution
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on August 18, 2016, 03:28:45 PM
It is clearly melt ponds and these spell doom for this section of ice that has separated from the glacier. The behavior of this ice shelf will be more like Larsen C in Antarctica. Melt ponds formed across the entire ice shelf, resulting in a catastrophic collapse that occurred in days. I would not be surprised if this entire shelf disintegrated in a single day in the near future, likely not this year as the melt season is coming to a close but soon. Once this area is seasonal sea ice, I think the ice in front of the main glacier will clear out much more quickly each melt season due to surface currents flowing south. This will remove the buttressing effect and speed up the glacier considerably.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on August 19, 2016, 04:38:19 PM
S-1A 19.8.2016, the said crack is propagating further. BTW, this image is a downloaded GeoTIFF from PolarView and appears to have 20m resolution (I have some problems interpreting the metadata). Looks great in SNAP!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 19, 2016, 07:04:36 PM
The calvings away from the glacier front are in movement, much more than the glacier itself. Here is a detail where an iceberg looses a relative small chip, that topples over.
Note that this chip stays more or less in the same position, while the mother iceberg is thrown back quite a distance. Apparently(!) in violation of Newton's Third Law (the action=-reaction thing).
The two images are aligned to one particular iceberg on the left, all movements are relative to this iceberg.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TenneyNaumer on August 20, 2016, 06:37:52 AM
Thanks for posting that photo, johnm33 -- perturbing. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: longwalks1 on August 21, 2016, 03:38:40 PM
perurbation     :  a disturbance of motion, course, arrangement, or state of equilibrium; especially :  a disturbance of the regular and usually elliptical course of motion of a celestial body that is produced by some force additional to that which causes its regular motion

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 21, 2016, 05:40:15 PM
Some small calvings near the top of the calving front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 23, 2016, 12:05:29 AM
Polarstern provides a good illustration how out of date the Greenland coastline is on Sailwx. It would be nice to see some images from the 79North glaciers calving front. Getting that close to Zachariae would probably be pretty dangerous with those 300m bergs turning.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on August 23, 2016, 05:55:10 PM
I believe I found the Polarstern on a Sentinel 2A image. Close to the coordinates reported on Sailwx is a line of broken ice (marked with red arrows). It ends in a polyna where a few pixel are slighly different coloured than typical ice. That should be the ship. Width and length correlate with the ships dimensions

Note: The Polarstern is just 25m wide and 117m long. At native 10m resolution thats slighly less than 2.5*11.7 pixel.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on August 25, 2016, 01:50:23 AM
http://go.nasa.gov/2bHcQRA (http://go.nasa.gov/2bHcQRA)

The ice in the channel over from the Zachariae's outlet is taking a beating.  Toggle back through the past few days to see what is what.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 25, 2016, 11:53:31 AM
Meanwhile, the fast ice has broken away from the 79N glacier. Some larger calvings have gone too.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 26, 2016, 11:58:01 PM
The German research icebreaker R/V Polarstern is working in this area right now, e.g.,

http://www.meereisportal.de/en/seaiceexpedition/where-is-polarstern.html (http://www.meereisportal.de/en/seaiceexpedition/where-is-polarstern.html)

The focus is on glacier-ocean interactions both from a modern (physical oceanography) and ancient (geology, paleo-oceanography) perspective with groups from Germany, England, and the US all working together. Wish them luck to recover those moored sensors computers placed in shallow waters where ice bergs may wipe them off the bottom of the ocean. A Canadian technician I work with is aboard to help, but I have not heart from him for 2-weeks; even simple text-only e-mails can be hard to get off the ship at times ...
according to the weekly report https://www.awi.de/nc/en/about-us/service/press/press-release/unterwegs-im-norske-trog.html (https://www.awi.de/nc/en/about-us/service/press/press-release/unterwegs-im-norske-trog.html) (in English) from the 21st this has been sucessful
In addition, we were able to recover all of the seven moorings deployed on the mid-shelf in 2014. They had been equipped with sensors in order to measure the circulation of Atlantic water in the trough. In turn, an array of four moorings was subsequently deployed with a similar sensor arrangement, which shall be recovered during a R/V Polarstern expedition next summer. We further resumed the helicopter-based operations for the recovery and redeployment of several geodetic and one seismological station on the mainland of Greenland. Fortunately the weather conditions allowed us to conduct at least two operations per day.
The report is worth reading and says 
Over the next week we hope to explore along the edge of the 79N ice shelf itself ...... happy days.

we have seen the subsequent track doing exactly that.
Bruce has reported on the bouy thread that data from some deployed buoys can be seen at the Woods Hole site http://www.whoi.edu/page.do?pid=154416 (http://www.whoi.edu/page.do?pid=154416)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Bruce Steele on August 28, 2016, 11:03:34 PM
My guess is it depends on how warm the seawater is at the base, if it's warm enough a fairly rapid retreat to the next ridge, and if that happens quickly a slump beyond that.
Take a look at Nioghalvfjerdsfjorden and see what you think will happen when open water extends beyond the trough below it's front.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FlmtQR%2F0379acd0aa.jpg&hash=e43f8443ff198d3bc2cb8d26c125a73e)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Bruce Steele on August 28, 2016, 11:26:42 PM
   http://www.whoi.edu/page.do?pid=154416 (http://www.whoi.edu/page.do?pid=154416)

So at 500 meters the water temperature is 1.15C Both the bottom of the floating ice tongue and the grounding point of Nioghalufjerdsfjorden are exposed to melt conditions. So too Zacharriae?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: TerryM on August 29, 2016, 09:58:19 AM
According to Dr. Muenchow at


https://icyseas.org/2013/10/31/ocean-circulation-and-melting-glaciers-off-north-east-greenland/


there are no locations between Belgica bank and the mainland that have anywhere near the depths that the new Woods Hole sensors appear to be showing.


Might we be misinterpreting the data somehow?


I think I remember reading that the water in the Belgica Gyre took a number of years to move up the coast. (no link), If this slow spin is present at depth, and if my memory is correct, the warm Atlantic waters being recorded could have entered the gyre back in 2012 or 13.


My own novice thought has been that the speed of the gyre would be dependent on the speed of the southerly flow of Fram, very similar to the way a rapid flow in a river produces a rapid eddy current.
Terry
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 29, 2016, 11:22:55 AM
repeating what I said in the bouys thread, what is shown in yellow in the  Icy Seas post by Dr Muenchow is the ice surface of the glaciers and the now partly defunct ice shelf off Zachariae.
This means it plots the surface elevation, not the sea floor depth below the ice in those locations. There is a sill (moraine?) in front of the glaciers which leave a much deeper trough behind the sill as they retreat from their (ice age?) maximum extent.
The ITM5 sits on the 79N glacier surface and its probes in the deep water below it.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on August 29, 2016, 01:18:39 PM
We're approaching max/min tides meaning an increased exchange of waters, the 'lake' on the north west shore of the shelf is tidal. I think the tidal surges come from the south up the deep channel, but not knowing the times of the daily snapshot makes that's just a guess. http://go.nasa.gov/2c2KM98 (http://go.nasa.gov/2c2KM98) this link is from the beggining of the last max/min and it's worth clicking through the following days. I'm thinking we'll see some serious action on both glaciers in the next month, but who knows?
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FqSsda%2Fb3302895e9.jpg&hash=7e413d59c82b789c7d2a2a71eecaa9ae)
from Terry's link
(https://puu.sh/qgz5T/8f4fa4e1bd.png)
This is from upthread ht Sidd, I'm assuming the old calving front just n/e of Zacharie is sitting on a morraine and it's looking very vulnerable.
http://www.dmi.dk/fileadmin/user_upload/vandstand_txt_pdf/2016/Danmarkshavn2016.pdf (http://www.dmi.dk/fileadmin/user_upload/vandstand_txt_pdf/2016/Danmarkshavn2016.pdf) Nearest tide prediction I could find, 740N
Not to be missed http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Bruce Steele on August 29, 2016, 05:00:45 PM
At the bottom of the itm5 page it says " ITM5 was deployed on a 1.35 m thick ice flow at the mouth of the 79 North Glacier in Greenland on August 23 , 2016 at 41.0 N, 20.9 W during the ARK-XXX/2 (PS1000) cruise on the German Icebreaker Polarstern."
 So I am afraid we have a mystery as to the depth of the sensors in the array. We also I believe have some inconsistancy in the charted depths of the 79N glacial fjord . Johnm33 just posted a 200 meter
contour that shows a 200 meter contour line in the general vicinity of the sensor array but in the earlier posting from John33  dated  April 5 that I  reported below you can see much deeper depths within the fjord.
 Because the array is a d-bar measure and only the pressure /weight of seawater can make the sensors give the readings they are producing and three of them are producing measurements that exceed
200d-bar/ meters I think we can exclude sensor failure. So on the weight of the evidence I believe the depth of the fjord exceeds 500 meters . And because the quote from the ITM5 page says it was deployed on 1.35 meters of ice  that presumably someone had to drill a hole though to place the buoy in the first place I think we should accept the depth as the depth of the water it sits over.
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on September 01, 2016, 07:04:14 PM
The little bay that was so full of Zachariae calvings earlier this year that some wondered what will happen when it is full has been nearly flushed in days. It too cloudy for S2A images, so back to Sentinel 1.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 01, 2016, 08:00:34 PM
The little bay that was so full of Zachariae calvings earlier this year that some wondered what will happen when it is full has been nearly flushed in days. It too cloudy for S2A images, so back to Sentinel 1.

There is now direct connection to the ocean, and that pulls the debris.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 02, 2016, 10:10:02 PM
there is a new entry on the Polarsterns blog. https://blogs.helmholtz.de/polarstern/en/2016/09/1527/ (https://blogs.helmholtz.de/polarstern/en/2016/09/1527/)
It seems they have been very busy to make the most of the opportunity to get into an area which often isn't accessible.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Cate on September 03, 2016, 03:32:04 AM
That huge floe that's been sitting right out in the road off Zachariae Isstrom---that's got a big crack right running north-south now. Compare Aug 21 and Sept 1.

http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698 (http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 03, 2016, 06:47:58 AM
That huge floe that's been sitting right out in the road off Zachariae Isstrom---that's got a big crack right running north-south now. Compare Aug 21 and Sept 1.

http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698 (http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698)

I could be wrong, but I think its parallel with the 79 degree north latitude glacier. One glacier north of ZI. I've been watching this area with interest for quite some time. I'm wondering whether that last piece of fast ice will break apart before the end of the melt season. Speaking for myself, I've never seen it this fragmented.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 03, 2016, 12:42:42 PM
on worldview it is very easy to scroll back to previous years (back to 2013) for comparison
http://go.nasa.gov/2c9hic8 (http://go.nasa.gov/2c9hic8)
There was just a small piece which stayed fixed on the shallow bank and a small island, Tobias Oer which Espen told us about back then
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Cate on September 03, 2016, 01:01:39 PM
That huge floe that's been sitting right out in the road off Zachariae Isstrom---that's got a big crack right running north-south now. Compare Aug 21 and Sept 1.

http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698 (http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698)

I could be wrong, but I think its parallel with the 79 degree north latitude glacier. One glacier north of ZI. I've been watching this area with interest for quite some time. I'm wondering whether that last piece of fast ice will break apart before the end of the melt season. Speaking for myself, I've never seen it this fragmented.

budmantis, yes, thank you for the clarification. It's the glacier/area Andreas T and Wipneus were discussing just a few posts up.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on September 05, 2016, 02:56:09 AM
The sun is finally low and I'm able to measure the height of icebergs.

On 3rd September Sentinel 2A captured Zachariae Isstrøm with a solar zenith angle of 72.77 degrees. (17.22 degrees above the horizon) The shadow length of icebergs varies between 100m and 180m giving a height of 31-55m above sea level. The 55m should be seen as the maximum of distinguisable peaks. On average the highest icebergs are more in the 40m range. Assuming a tabular berg and 90% of the mass underwater the total height is 310-550m

See attached image for some measurements.

For the iceberg with the green arrow I calculated the following:
Height: 330m
Area: 1.7795 km2
Volume: 0.587 km3
Mass   : 0.528 Gt
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 05, 2016, 06:10:37 AM
Tealight:

What do you think is the margin of error, if any in your calculations?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on September 05, 2016, 12:11:05 PM
Tealight:

What do you think is the margin of error, if any in your calculations?

I rate my shadow length measurement accuracy at around 90%. The area measurement should be over 98% accurate. The polygon drawing tool in SNAP is very precise.

The resolution is 10m and if I'm off by one pixel at 100-180m long shadows the error is 10-5.5%
I also selected edges perpendicular to the incoming solar radiation to keep my angular deviation small. The biggest uncertainty is the surface topography of icebergs, which is hard to estimate with a top down view. The restriction to only being able to measure one edge makes it even harder.

One iceberg had its ripples(perpendicular to the glacier flow direction) alligned with the solar azimuth angle and created a distinct shadow. Its the best example to show the surface height uncertainty. (pictured)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on September 05, 2016, 11:15:02 PM
Seems like somethings worth a closer look than I can manage.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fr1ahH%2Ffbed5f70bb.jpg&hash=e1b34cb9d710d8a2c7005c7ca408f22f)
http://www.polarview.aq/images/106_S1jpgsmall/201609/S1A_EW_GRDM_1SDH_20160905T084314_66B2_N_1.jpg (http://www.polarview.aq/images/106_S1jpgsmall/201609/S1A_EW_GRDM_1SDH_20160905T084314_66B2_N_1.jpg)
http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698# (http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698#)
http://earthexplorer.usgs.gov/browse/landsat_8/2016/006/003/LC80060032016249LGN00.jpg (http://earthexplorer.usgs.gov/browse/landsat_8/2016/006/003/LC80060032016249LGN00.jpg)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Cate on September 07, 2016, 11:57:15 AM
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart. 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Jim Hunt on September 07, 2016, 07:39:13 PM
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart.

Thanks for the heads up Cate. A nice clear day today!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on September 07, 2016, 11:17:26 PM
Seems like somethings worth a closer look than I can manage.

I'm not sure what you were referring to with this Sep 5 image, but here's an animation between Sep 3 and Sep 5. Only thing I can see is the sea ice breaking again and some rotational movement of the bay, with a few clouds at the top of the image.
I know it's not so smooth and only b&w, but hey at least I managed to make a crude animation after a long while.
(must click)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 08, 2016, 01:34:32 AM
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart.

What remains of the main floe must be anchored to a small island and/or very shallow water. Looking over the images of the last three days, it doesn't appear to be moving. Seems likely there will be more pieces breaking off in the next few days.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Cate on September 08, 2016, 04:12:31 AM
budmantis, yes, Andreas T mentions this in post #751 above. It does look grounded there, and everything else around it on the move.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 08, 2016, 06:01:42 AM
budmantis, yes, Andreas T mentions this in post #751 above. It does look grounded there, and everything else around it on the move.

Thanks for reminding me, I had forgotten about that post. Andreas's graphic from 2013 shows that area as being more fragmented than it is this year. What is left of most of that fast ice is still in the vicinity and will likely congeal as the re-freeze takes hold. In a way that is good, we'll be able to talk about it next year!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on September 08, 2016, 12:00:55 PM
Thanks Oren you put it centre stage, I thought the cracks appeared to be extending across a much wider front than usual, there normally being several calving streams. In close up it appears just chance that the various streams cracks are aligned.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: dingojoe on September 13, 2016, 12:24:51 AM
Longtime watcher, rare time poster

Would love a clear shot of this area before the season ends as it looks like there was a mass implosion of the ice in this area.  You get used to watching the breakup of ice along here into big white blocks of ice that dance around and eventually break into smaller blocks or even implode into what looks like, from our satellite view, as powdery ice which will then swirl around in Vincent Van Gogh Starry Nights fashion before melting out. 

It seems that a storm brought strong easterly winds and ultimately snow to the area, but it also looks like virtually all of the blocky white ice (except maybe a core of the fast ice that lives well offshore)  imploded en masse in the past week.   Granted it's only been a few years that we have the kind of technology to view this, but I've never seen an event that quite rivals this.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Cate on September 13, 2016, 02:56:48 AM
dingojoe, great comparison, ice swirling like Starry Nights. Perfect. I am new to watching the ice and it's hard to know what's normal and what's anomalous, so I do appreciate the context you bring from previous seasons--thank you.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Iceismylife on September 13, 2016, 04:00:38 AM
It broke up in 2013.

http://go.nasa.gov/2cSOMcP (http://go.nasa.gov/2cSOMcP)

But it is not normal.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 13, 2016, 08:36:07 PM
Several Danish newspaper are spreading a "canard" involving Jason Box, claiming Spaltgletscher calved, which did not happen, as usual papers gets all the facts wrong:

http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord (http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord)

http://jyllands-posten.dk/indland/trafik/ECE8999622/gigantisk-groenlandsk-isflage-har-revet-sig-loes-efter-varmerekord/ (http://jyllands-posten.dk/indland/trafik/ECE8999622/gigantisk-groenlandsk-isflage-har-revet-sig-loes-efter-varmerekord/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 13, 2016, 10:27:34 PM
#759
The images were not correctly aligned to fixed rock, distorting motion. On these too-dark images, simply hit the 'auto' button within contrast correction -- it makes a huge difference.

They released a Sep 13, 2016 youtube showing 4 Landsat-8 stills, not worth watching.
https://www.youtube.com/watch?v=QzKTIgRW-j8 (https://www.youtube.com/watch?v=QzKTIgRW-j8)

Master's student Karina Hansen alerted glaciology Prof. Jason Box of GEUS, "something looks strange" at Spalte (Split) Glacier.

The ~9 km wide Spalte Glacier is a tributary of the 79 Glacier which today has the Arctic's largest ice shelf. The ice shelf forms the end of the North East Greenland Ice Stream, the only Greenland ice stream clearly reaching the highest elevations.

We observed that between 14 Aug 2015 and 3 Sept 2016 a marine-terminating tributary of the 79 fjord glacier, the Spalte Glacier flowing into Dijmphna Sound has detached and area (more than 95 km2) roughly the area of Manhattan.

The detachment of the ice shelf fragment appears to be nearly 100% complete. But the fragment has not floated away yet.

September 13, 2016 A gigantic piece of ice the size of Manhattan has broken away from a glacier in northeast Greenland. Summer Heat in September occur frequently A gigantic block of ice of more than 95 square kilometers - equivalent to an area the size of Manhattan - has broken away from a glacier in Northeast Greenland. Measurements from 14 weather stations in Greenland are reporting temperatures in 2016 are much higher than they used to be, figures from the Danish Meteorological Institute (DMI).

Floe that has come loose, is one of the consequences of this year's heat record. So says Jason Box, research professor at the Geological Survey of Denmark and Greenland. The hot temperatures is one of the reasons that the floe has broken loose from the glacier, he said. When the ice melts on a glacier, water seeps into cracks in the surface. It has the strength to tear the ice sheet from each other, he explains and points out that other factors also play a role. My guess is that there is melted more ice on Greenland this year than there has been for the past three years, says the professor.

Floe has broken loose from fjordgletsjeren gap that lies outside of the weather station Denmark Port in northeast Greenland. Here arises the monitoring stations also heat record this year.

According to the professor, the high temperatures on the island have major consequences. I think we will see more glaciers will crack on Greenland in the future as a consequence of these drastic temperature increases. The heat is going to affect the ice will continue to melt, but it can go faster now, says the professor.

Floe has not yet moved away from the glacier, but according to Jason Box will glacier float away later in the year if it is not already. Recent satellite images we have received is from September 3, so it will be interesting to see how it looks, the next time they come, he says. Floe seems to be broken into more than a piece already

http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord (http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord)
.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on September 13, 2016, 11:32:30 PM
#759
The images were not correctly aligned to fixed rock, distorting motion.
I know, I kind-of-aligned them manually on a slow laptop which was quite difficult.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on September 14, 2016, 12:46:06 AM
We observed that between 14 Aug 2015 and 3 Sept 2016 a marine-terminating tributary of the 79 fjord glacier, the Spalte Glacier flowing into Dijmphna Sound has detached and area (more than 95 km2) roughly the area of Manhattan.

There is virtually no calving progress between these days. What kind of satellite images have they looked at?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 14, 2016, 05:20:38 AM
I wonder how Jason Box got involved in that "story"?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: binntho on September 14, 2016, 07:33:37 AM
I wonder how Jason Box got involved in that "story"?
In one of the articles (http://"http://www.bt.dk/danmark/gigantisk-isflage-har-revet-sig-loes-i-groenland") in the press today Jason Box is reported as saying that the big chunk hasn't floated away from the glacier yet, but that it will eventually do so.

According to the same report, the latest satellite images they have are from 3rd September, showing the chunk had still not moved away from the glacier. Apparently there is a DMI weather station in the vicinity, but it isn't clear from the article whether they have any direct measurements, possibly a fly-over?

The record temperatures in Greenland this spring and summer are reported in the danish press today, perhaps that has caused some focus on this (potential?) calving, resulting in a bit of premature reporting?

But Jason Cox is quoted directly, saying "The warm temperatures are one of the reasons the icefloe has broken free from the glacier" and "The latest satellite images we have are from the 3rd of September so it will be exciting to see what it looks like the next time".
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2016, 12:08:00 PM
Looking now at two 10 m Sentinel 2A of matched geometry (27XWJ UTM zone 27N) dated July 24th (day 206) and Sept 7th (day 251), some widening is indeed seen over the 46 day interval. The images are aligned to fixed rocks on the fjord walls so the later date reflects some glacier advancement as well as fracture widening.

The full resolution gif will require opening separately to animate. Using the known scale there, the crack has bowed out (widened more centrally, cracking and displacing the wedge above) from 149 m to 323 m over the 46 days for an average rate of 3.8 m per day, in addition to an overall bulk displacement (green) of 113 m to the NE.
 
Glaciologist M Pelto wrote about this situation back in June 2013:

The second set of images indicates the change in terminus position at the northeastern terminus from 2000 to 2011, purple dots, often referred to as Spaltegletscher. The yellow arrow indicates a longitudinal rift that has developed since 2000 that is nearly connected to another rift near the margin of 79 Glacier. Espen Olsen at the Arctic Sea Ice Forum has suggested that this is what will lead to this area breaking off.

The orange arrow indicates the same location marking the terminus of the glacier at its northwest corner. The last image is from June 16, 2013 this MODIS image indicates the two rifts red and yellow arrow at the start of the Spaltegletscher terminus. Followed by Landsat image from June 17, 2013 indicating the new terminus position more clearly and the same rifts. Another iceberg has peeled off since 2011, and the total ice loss since 2001 is 70-80 square kilometers.

Jason Box, Ohio State had noted a loss of about 50 square kilometers from 2000 to 2010. Also apparent is an area of active calving and icebergs in front of Zachariae, check out the new icebergs in the June 17, 2013 Landsat at Zachariae Ice Stream

http://blogs.agu.org/fromaglaciersperspective/2013/06/18/nioghalvfjerdsbrae-79-glacier-northeast-greenland/ (http://blogs.agu.org/fromaglaciersperspective/2013/06/18/nioghalvfjerdsbrae-79-glacier-northeast-greenland/)
http://forum.arctic-sea-ice.net/index.php/topic,238.msg4473.html#msg4473 (http://forum.arctic-sea-ice.net/index.php/topic,238.msg4473.html#msg4473) Espen
http://forum.arctic-sea-ice.net/index.php/topic,238.msg7988.html#msg7988 (http://forum.arctic-sea-ice.net/index.php/topic,238.msg7988.html#msg7988) Espen

Lambert Land separates the Inland Ice outlet glaciers of Nioghalvfjerdsbræ and Zachariae Isstrøm just as Hovgaard Ø splits Nioghalvfjerdsbræ into a main stream that flows into Nioghalvfjerdsfjorden and a northern outlet glacier, Spaltegletscher, that flows into Dijmphna Sund. Spaltegletscher is reported to have had a retreat of 18 km between 1907 and the 1950’s and. in spite of the errors in determining the old frontal positions, a major recession of the outlet glaciers must have taken place during the first half of the 20th century [Satellite Image Atlas of Glaciers of the World, 3rd image]
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2016, 12:13:40 PM
The full size animation (needs click) mentioned above has been moved here as it interferes with forum display of other images. This is at 10 m per pixel scale should be used to make measurements of displacements. Overall motion is fairly complex, comprised of glacier advance, coupled displacements of rigid blocks and their rotations about pivot points.We've seen all this before -- but with fewer blocks -- at Petermann Glacier on the other side of Greenland.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on September 14, 2016, 12:46:06 PM
Superb animation. It definitely looks like an almost-calved situation. I guess SG (Spaltegletscher) is soon to be history. It seems (wild layman guess) that as Zachariae is flowing more easily in the last few years since its separation from its old tongue (and since the sea ice started clearing in August), and perhaps NG (79 Glacier) does the same, there is not enough pressure/flow to feed SG in a significant manner.
If it does disappear completely, this should speed up NG, at least until SG grows back.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2016, 01:23:11 PM
Not so clear what will happen when. The train is leaving the station but winter is setting in, perhaps stopping it in its tracks. Old sutures can be seen in several places. The upper part of SG is also breaking apart as existing fractures widen (not shown).

Below is a close-up of relative motion. The images were compensated for glacier advance, meaning   aligned so as to fix features in the upper left hand corner.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 14, 2016, 04:55:59 PM
But still I am a bit puzzled why this is dramatized? When nothing really happened to Spaltegletscher over the last couple of years??
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 14, 2016, 09:19:51 PM
just something that caught my eye after the recent snowfall are these patches at the edge of the glacier where the snow presumably melted on water / wet ground?
The area marked with W is clearly water but the more earth colored patches (arrows) are very shallow if the are water surfaces

http://go.nasa.gov/2cFrcTi (http://go.nasa.gov/2cFrcTi)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 14, 2016, 09:24:35 PM
sorry should have checked this first: 7-2-1 band shows this to be water on the 7.9.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 14, 2016, 09:25:35 PM
That is Blåsø (Blue Lake) and a unnamed lake.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 14, 2016, 10:11:19 PM
nothing really happened
And attributing it to warmer air temperatures in a very cold region in a rather cold year (at least for same-latitude Petermann) ?

If something were to happen -- and it might -- some people would be inclined to attribute it to warmer ocean water circulating under the ice shelf, rather than air or upstream melt (and subsequent glacial acceleration), though that would be secondary discharge circulation of Atlantic Water from Nioghalvfjerdsbræ itself because of a sill, first image below.

Spaltegletscher is quite interesting in how much structural history it exhibits, for example the three splinters on the right side forced by splitting against the protruding rock peninsula and subsequent pivoting about the circular rock island. Right now SG consists of 6-7 rigid bodies. However to decisively unravel the history and forces acting to create and fragment these, it would take a decade or more of satellite record, not just a single season or couple of years.

http://polardispatches.org/measuring-the-flow-of-water-at-nioghalvfjerdsfjorden/ (http://polardispatches.org/measuring-the-flow-of-water-at-nioghalvfjerdsfjorden/)

Given that the floating ice tongue of Nioghalvfjerdsfjorden Glacier is one of the very few places in the Arctic where ice and ocean interact at an ice shelf base that covers more than just a very small area, this is a region of particular scientific interest.

We therefore decided to enhance the ice thickness data in this area by using recently obtained airborne radar data as well as 5 seismic soundings and airborne data from 1998.

We used spherical triangulation to interpolated the ice thickness data in the area of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm to our regular grid. The resulting ice thickness map was smoothed along the flow lines to avoid interpolation artefacts. Compared to M-2014, the main benefit of our grid is that it also covers the thickness of floating ice in Dijmphna Sund (Figs. 5c and 5d below).

http://www.earth-syst-sci-data-discuss.net/essd-2016-3/essd-2016-3.pdf (http://www.earth-syst-sci-data-discuss.net/essd-2016-3/essd-2016-3.pdf) 2016 free full

The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW).

A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion.

Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

 http://onlinelibrary.wiley.com/doi/10.1002/2015GL064944/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064944/abstract)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on September 14, 2016, 10:21:57 PM
I read somewhere Lake Blaso is tidal, I checked Wiki, wasn't there.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 14, 2016, 10:30:17 PM
Incredible detail and graphics A-Team. Thanks!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: skanky on September 14, 2016, 11:00:43 PM
Here it is from the horse's mouth, as it were:

http://jasonbox.net/news/ (http://jasonbox.net/news/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: dingojoe on September 15, 2016, 06:08:51 PM
Same area as #758 on 9-15

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fgibs.earthdata.nasa.gov%2Fimage-download%3FTIME%3D2016259%26amp%3Bextent%3D484608%2C-1112832%2C680704%2C-926720%26amp%3Bepsg%3D3413%26amp%3Blayers%3DMODIS_Aqua_CorrectedReflectance_TrueColor%2CCoastlines%26amp%3Bopacities%3D1%2C1%26amp%3Bworldfile%3Dfalse%26amp%3Bformat%3Dimage%2Fjpeg%26amp%3Bwidth%3D383%26amp%3Bheight%3D364&hash=3bd66868b801db275abc0c9c6b15f3b6)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 15, 2016, 08:19:22 PM
That is something different from 2013. Toggling from terra to aqua on worldview everything which isn't land is moving . And all the ice has disintegrated, there are no large floes, which I think is a sign of thinning.

http://go.nasa.gov/2cIyhCm (http://go.nasa.gov/2cIyhCm)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 15, 2016, 10:32:40 PM
Despite the fact Spaltegletcher did not calve yet, danish media (national tv tonite) continue to report about this non event, this is "black powder" for people like Anthony Watts, Christopher Monckton and Fred Singer, I dont get it??

Proof of no calving at Spaltegletscher September 15 2016:

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 16, 2016, 01:27:52 AM
But still I am a bit puzzled why this is dramatized? When nothing really was analyzed? The original post is here -- it could be deleted or re-written though the press releases cannot:  http://jasonbox.net/news/ (http://jasonbox.net/news/)
Not his high water mark, indeed troubling.

Four Landsat-8 images were 'prepared' by undescribed methods for the dates bouncing around on images on that web page (first animation below). Having 'prepared' thousands of those myself, that already raised a big red flag because accession numbers, Landsat band, zoom, 
UTM zone, sun angle etc etc were not provided though dates of different years differed by as much as a month and a half.

It emerged that 2013 is way out of alignment, 2015 had too much snow cover, 30 m resolution was used in place of 15 m band 8, and pan-sharpening and color were not done. It seems that 2013 and 2014 nadirs lie just across the border in UTM 26X instead of 27X (see Jakobshavn for problems that ensue from that).

Reverse-engineering their dates at EarthExplorer for accessions provides essential metadata,  enables color re-processing at higher resolution, and permits a wider view of up-glacier conditons  -- more reasons why it's considered non-optional to omit accessions even in a popularized scientific context.

     date     accession              path,row, time of day   sunº   azimuth   snow?
2016 Sep 03   LC80080032016247LGN00    8,3   2016:247:14:51   12.2   -150.5   no
2015 Aug 14   LC80100022015226LGN00   10,2   2015:226:15:02   23.2   -151.9   bad
2014 Jul 22   LC80140022014203LGN00   14,2   2014:203:15:27   29.1   -151.7   no
2013 Aug 20   LC80140022013232LGN00   14,2   2013:232:15:29   21.1   -151.2   some

The discussion itself is way off-base: hydrofracturing is off the table, inapplicable to a floating ice shelf whose grounding line (see above map) is ~100 km to the west, as are air temperatures given the lack of surface drainage features on SG. Continuum mechanics (stress, strain etc) is, as its very name suggests, not relevant to fissuring ice, no reason to bring it up. The lack of a rudimentary google search on sub-surface ice cavities, tides and water circulations, bathymetry, and ice thickness (see above cites) is also problematic.

Moving beyond petty ineptitude, the animation makes clear that Spaltegletscher's past, present and future are all about the relative motion of its uncoupling parts.  Like Espen, I too am greatly puzzled but by the absence of co-moving (Lagrangian) coordinates. That's how motion on top of glacial advance, blocks of rotating ice, diffraction by submerged pinning points, warping by Hovgaard Island  is supposed to be dissected.

It's very instructive (and easy) to work out the relative motions of the block. For example, Nioghalvfjerdsfjorden and much of western SG are surprisingly moving in synch despite the suture zones and fractured melange zone along the coast.

The third animation uses 10 m Sentinel 2A 'processed' by contrast adjustment, absolute layer differencing, histogram equalization and white balancing -- all run as auto commands (in all-platform freeware gimp) to allow anyone to reproduce the outcome on these and subsequent S2A images. The forum version had to be posted at 20 m due to dimensional constraints here.

This shows western SG has moved 71.7 m northeasterly while 79N has gone 41.2 m more ENE betwee  July 24th (day 206) and Sept 7th (day 251)  Thus there's an excellent choice here for a  Lagrangian frame of reference (final frame of 4th animation) to simplify relative motions (relative to mere glacier advance) and determine say whether a fracture widens by the top pulling away or the bottom retreating.

There are some very curious changes in compression wavelengths over the broader scene. These are better explored in the large format 10 m version provided in the next post.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 16, 2016, 01:31:17 AM
There are some very curious changes in compression wavelengths over the scene. These are better explored in 10 m version provided ithis post, it requires a click to animate. (If the forum software will cooperate and load more than the first frame ... may have to load them as singles.)
Spaltegletscher is really an interesting ice sheet. The full resolution images are really worth a look. Because the imagery at 10 m is too large for forum animation software, I've expanded the description of processing so that anyone can download the S2A imagery from AWS and re-create the results on a more robust desktop.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on September 16, 2016, 07:25:11 AM
I don't understand why SG is considered a glacier unto itself when it looks to me at least to be a distributary of the 79 North glacier.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 16, 2016, 01:21:23 PM
SG is a distributary of the 79 North glacier
Right, just a distributary of the 79N ice shelf, but one with an active present and different future. The animation, at 5m, shows crack propagation over the last 46 days. The static image pair is marked up for changes.

The green asterisk shows a bend in a weak westward-draining melt channel used to remove bulk glacier advance from the comparison.

The yellow asterisk suggests the main crack has slowed and turned north, and will not propagate to the western shore freeing (cslving) the SG ice sheet to move out to the Sound.

The red asterisk shows a new more southerly crack propagating rapidly westward. However it may not join up with an existing crack at the suture zone because the orange asterisk indicates it has taken a turn to the north and then east, possibly leading to a small block being created.

This system too shows no sign of propagating to the western rock shore. Some of the blocks at the far north (off-image) may come loose first. These would create medium size tabular icebergs rather than one giant one if the cracks shown here continued westward.

However the lesson from the 2013-2016 series is that events proceed here 'at a glacial pace'. The open water and melange will freeze solid this fall, even as SG continues its bulk motion north. By next melt season, the relationship to pinning points will have changed and new cracks to the south may arise.

Overall though, SG is heading towards disappearance. Like the Petermann ice shelf, pieces will be breaking off much faster than renewed by glacial advance.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: crandles on September 16, 2016, 03:09:24 PM

The yellow asterisk suggests the main crack has slowed and turned north, and will not propagate to the western shore freeing (cslving) the SG ice sheet to move out to the Sound.


After yellow asterisk, there seems to me to be a suggestion of a turn to WNW then N then WNW again. Is that a developing crack, or just a drainage channel, or something else or nothing at all eg image artefact or random image noise?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 16, 2016, 04:08:04 PM
Is that a developing crack, or just a drainage channel, or something else or nothing at all
Not grasping what you mean by 'after' the yellow asterisk, to its immediate right? There are very small drainage channels throughout that follow troughs of compression folds. S2A images have almost no artifacts or background noise as can be seen by cross-correlating separately 3-4x enlarged channels from their posted 10 m resolution.

The animation below shows the rotating ball bearing (weak blue) that is causing the upper right body to pivot to the left (ccw to NW).

The 'force diagram' below shows some progress closing in on what is going on here. It needs a click to see at sufficient resolution. Earlier years are needed still as well as coverage of 79N further west. Another S2A is due tomorrow too.

The most peculiar feature of this ice sheet is the suture zone, the internal fold and the NW shoreline rubble. These must have formed up-glacier (but where and why?) because they are co-moving with the overall ice sheet in the 2013-16 series.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 16, 2016, 06:54:09 PM
Not his high water mark, indeed troubling.

Must be cucumber time?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 17, 2016, 02:24:00 PM
Must be cucumber time (silly season)?
Maybe Denmark had an internet outage first week of Sept, so they couldn't access EarthExplorer, Google Earth or prior scientific papers?

There's a very interesting story going on with Spaltegletscher but not the one being told. It really has to do with Antarctica where the floating ice shelves are being undermined by warmer ocean waters, not Greenland and warmer air temperatures.

The rapidity with which Spaltegletscher is disintegrating is quite remarkable. To see that, it's a good idea to look at the last 10-15 years of Landsat-7/8 imagery which is available with 10-15 minutes of effort at EarthExplorer.

While the 10 meter Sentinel 2A imagery is a great improvement over Landsat, recall that WorldView satellites have truly fabulous resolution, sub-meter. While proprietary, there's a scientific license and even better, free and immediate availability of back dates at Google Earth if you just click on the clock icon in GE Pro.

The first image below shows ice shelf drainage details in front of the splitting island, the second the fracture tip on 27 July 2013, and the third a fully propagated crack that had not resulted in calving three years later.

The second and fourth image show extensive blue water in what could be termed the central melt channel collector instead of suture zone (as above), though this only raises new questions as to why the ice shelf is lower here, where the water drains, what accounts for the extreme meandering, and why it is not central as at Petermann. The elevated fold, which casts shadows at this high resolution, remains an unexplained oddity as does the point of compression wave refraction.

Here is a 12 year series, to be discussed in a subsequent post. Basically Spaltegletscher is undergoing a rapid and recent collapse, even if it hasn't yet calved. Landsat-7 developed a scan line problem after 2003; EarthExplorer is seriously underwater right now with a ten day delay even for current imagery.

S2A 27XWJ 2016 251 Sept 12 see above posts
LC8008003 2016 247 LGN00 see above posts
S2A 27XWJ 2016 206 July 24 see above posts
LC8010002 2015 226 LGN00 see above posts
LC8014002 2014 203 LGN00 see above posts
WV2......... 2013 208 July 27 see Google Earth       
LC8014002 2013 232 LGN00 see above posts
LE7008003 2012 212 ASN00 band 8 being processed
LE7009002 2011 200 EDC00 band 8 being processed
LE7013002 2010 209 ASN00 band 8 being processed
LE7013002 2009 206 EDC00 preview only
LE7011002 2008 206 ASN00 preview only
LE7007003 2007 223 EDC00 preview only
LE7010002 2006 209 ASN01 preview only
LE7007003 2005 201 EDC00 preview only
LE7006003 2007 248 EDC00 preview only
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: prokaryotes on September 17, 2016, 03:56:37 PM
... this only raises new questions as to why the ice shelf is lower here, where the water drains, what accounts for the extreme meandering, and why it is not central as at Petermann. The elevated fold, which casts shadows at this high resolution, remains an unexplained oddity as does the point of compression wave refraction.

Just googled and seems like it is related to fracturing

2009 study

Englacial drainage systems formed by hydrologically driven crevasse propagation
Recent work has shown that surface-to-bed drainage systems re-form annually on parts of the Greenland ice sheet and some High Arctic glaciers, leading to speed-up events soon after the onset of summer melt. Surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation (herein referred to as ‘hydrofracturing’), although little is known about their characteristics. Using speleological techniques, we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in Svalbard, Nepal and Alaska.

In Hansbreen, Svalbard, vertical shafts were followed through 60 m of cold ice and 10 m of temperate basal ice to a subglacial conduit. Deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence. The englacial drainage systems in Khumbu Glacier, Nepal, and Matanuska Glacier, Alaska, USA, formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down-glacier at angles of 558 or less.

The occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process, and that surface-to-bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses.

Theoretical considerations indicate that hydrologically driven propagation of surface fractures will occur where a combination of tensile stresses and water pressure is large enough to overcome the fracture toughness of the ice (Ro¨thlisberger and Lang, 1987; Van der Veen, 1998, 2007; Alley and others, 2005).

Surface fractures can penetrate all the way to the glacier bed if water supply is great enough to fill the expanding fracture and offset freezing onto the walls. It has been argued that supraglacial ponds play a crucial role in this process, by providing an elevated head of water at the ice surface (Hagen and others, 1991; Boon and Sharp, 2003; Alley and others, 2005).

Once established, fractures provide high hydraulic conductivity pathways through the glacier, which may then be enlarged into moulins by flowing water. If the fracture or moulin does not completely close during the winter months, it may be reactivated in the following melt season.

https://www.igsoc.org/journal/55/191/j08j038.pdf (https://www.igsoc.org/journal/55/191/j08j038.pdf)

2008
Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid (<2 hours) drainage of a large supraglacial lake down 980 meters through to the bed of the Greenland Ice Sheet initiated by water-driven fracture propagation evolving into moulin flow.

Drainage coincided with increased seismicity, transient acceleration, ice-sheet uplift, and horizontal displacement. Subsidence and deceleration occurred over the subsequent 24 hours. The short-lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially. The integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup.
http://science.sciencemag.org/content/320/5877/778.full (http://science.sciencemag.org/content/320/5877/778.full)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: crandles on September 17, 2016, 08:04:41 PM
Is that a developing crack, or just a drainage channel, or something else or nothing at all
Not grasping what you mean by 'after' the yellow asterisk, to its immediate right?

no left and slightly above. Above lines drawn in below. Hope that is clear now.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 18, 2016, 11:54:43 PM
The animation below, which needs a click, adds three more years to the original series. The 2011 is a beauty -- and largely free of the malfunctioning scan lines of Landsat-7. The other two have a different viewing geometry; I have not yet traced down the origin of that.

There has been quite a bit of twitter action in the last few days, with L Dyke posting an animation of lots of 2016 Landsat previews. It isn't in copyable format. https://twitter.com/laurencedyke?lang=fr

DMI posted a S1A radar image of Sept 13th. That picks up the shallow drainage channel -- which is neither a cleft or incipient fracture through the ice shelf -- in the same whitish color as the actual new crack -- but we don't find that misleading because of nukefix has explained that effect several times over at Jakobshavn forum.

LE7008003 2012 212 ASN00 band 8
LE7009002 2011 200 EDC00 band 8 low snow, excellent contrast
LE7013002 2010 209 ASN00 band 8

left of asterisk: crack extension?
No. Not according to the Sept 12th S2A viewed at 2m with strong enhancement (third image). Even if it did, this would not take it anywhere near the shoreline. The crack next door is not a crack but a shallow drainage channel and reaching it would not liberate an iceberg. There should be a return orbit within the next five days; none is posted yet and could be cloudy (like the Sept 17th Landsat LC80100022016261LGN00) or just not taken.

The Landsat-8 for Sept 15th, LC80120022016259LGN00, has some cloud issues ... it is a slow download because of the jam-up at EarthExplorer, only preview below.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on September 19, 2016, 08:33:46 AM
Probably the last 2016 big calving of Zachariae that we can witness in visible light.

Animation needs a click to start, too big for the 700x700 forum limit.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 19, 2016, 02:37:42 PM
last 2016 big calving of Zachariae that we can witness in visible light.
Closing down for sure, depending on the satellite's offset from local noon. Colors will fade too just like they do for our eyes at twilight. It will still be possible to resuscitate 16-bit images for a while using extreme methods on contrast.

It looks to me like Spaltegletscher is shutting down for the year based on the 15 Sept 16 Landsat-8 LC80120022016259LGN00.

While a noteworthy fracture this summer, this ice sheet makes one almost annually in recent years. Due to glacier advance of 79N during the long cold winter, this opening will have advanced past the pivoting leverage by next summer and may become dormant like the preceding three. It could still be several years away from separating from its base and more years away from tabular icebergs in the East Greenland Current.

Issuing false alarms is not a good idea even if they get good press, any more than crying wolf worked out for that apocryphal shepherd boy in ancient Greece.

Another example would be promoting open water at the north pole -- people here know that the pole is not emblematic of the Arctic Ocean ice pack and open water there is not a meaningful indicator of climate change progression, even though this plays with the public.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on September 20, 2016, 03:17:48 AM
People on R/V Polarstern visited the area last month and placed a self-reporting mooring of ocean temperature, salinity, and currents on <1.5 m thick sea ice between the loose segments of Spaltengletscher. Data for the mooring is reported in real time at

http://www.whoi.edu/page.do?pid=20781 (http://www.whoi.edu/page.do?pid=20781)
(pick ITM5 after scrolling to bottom of page)

located at the red dot over LC80060032016233LGN00_B8.TIF lightly re-processed using open source gdal, GMT, and good-ol' Fortran
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Bruce Steele on September 20, 2016, 10:36:01 AM
Dear Dr. Muenchow, please excuse my status as a rank amateur but could you chart the location of the sill that separates the Nioghalufjerdsfjorden from the Norske Trough. Microcat 4 on the ITM 5 is located in 503.4168 dbar of depth.
There was some discussion of this depth up thread when the WHOI page first started sending data from ITM 5. Some charts show much shallower depths.
                                                          note to Terry:
I have resolved my confusion about the location of ITM5 and you were correct , some locations are in
Degrees / minutes . It shouldn't have confused me and I should be able to read a nautical chart.

The location has not moved much,  79.6841N 20.3483 W when first launched and on Sept. 16
79.6844N 20.3474W
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on September 20, 2016, 04:35:50 PM
Bruce: I do not know that anyone "knows" what the exact sill depths at 79N Glacier are, however, the most recent peer-reviewed publication on this topic is Wilson and Straneo, 2015: Water exchange between the continental shelf and the cavity beneath Nioghalvfjerdsbrae, Geophysical Research Letter ...

You can find a pre-print at http://ironicmtn.com/research/79ng_hydrog.html (http://ironicmtn.com/research/79ng_hydrog.html) which is the web-site of the author and PhD student (Nat Wilson) who placed the mooring with lots of help by others. Have fun.

P.S.: No excuses, we are all amateurs when it comes to nature and the way that different disciplines have to come together to blindly poke this elephant ;-)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 20, 2016, 05:45:55 PM
ITM5 was deployed on a 1.35 m thick ice floe at the mouth of the 79 North Glacier in Greenland on August 23, 2016 at 79° 41.0 N, 20° 20.9 W during the ARK-XXX/2 (PS100) cruise on the German Icebreaker Polarstern
Nice find. This is getting interesting -- an inspired spot to hang an instrumented line through the ice. At first the refrozen gap seems surprisingly thin at 1.35 m for ice that's 3-4 years old but maybe it makes sense for end of melt season.

Landsat-8 posts its imagery in mercator coordinates according to the UTM zone of center coordinate; those posted at the Woods Hole site are given below. Using these and the corner coordinates provided in Landsat metadata, the drill site could be located, which Andreas M already did for the 20 Aug 16 image, LC80382432016233LGN00.

The animation below places the instrument string on the 24 Jul 16 - 07 Sep 16 Sentinel pair of the earlier post #774 in which band 4 is bumped up to 5 m resolution. The drift of 52.7 m between day 236 (Aug 24th) and day 262 (Sep 19th) is 10.5 pixels on the 5 m S2A, shown as the path from the red dot to small yellow dot on the third frame.

The motion of the large block of ice immediately to the NW of the instrument string also appears in this third frame as echoed feature. This ice has moved 1.69 m/d (0.617 km/yr) at very close to a 45º trajectory NE between the two Sentinel images. This compares very favorable to the 1.99 m/day motion of the instrument string at a similar angle. Niogshalvsfjerdfjorden itself is moving more slowly and more easterly as can also be measured off this frame.

79° 41.0 N, 20° 20.9 W
79° 41' 00" N, 20° 20' 54" W
79.6833, -20.34833
513028.57 easting, 8846314 northing in UTM 27X in WGS84 (supported as a preference in Google Earth)

The .dat files provided open in any text editor; it seems the position has changed by 52.5 m over the 26.39563 days between first and last entry which amounts to drifting off to the NE at 59.2º according to GE's display (which regrettably uses a 31 Jul 2013 background image).

%year day longitude(E+) latitude(N+) GF NSAT HDOP
2016  236.58424   -20.3487  79.6840  76   9 1.1
2016  262.97987   -20.3473  79.6844  59  11 0.8

start 513020.30, 8846388.54
stop 513047.79, 8846433.49

HDOP stands for 'horizontal dilution of precision' and serves as a measure of the geometric quality of a GPS satellite configuration, helping to determine relative accuracy of a horizontal position, the smaller the better the geometry. NSAt is probably the Norsat satellite company of Vancouver BC. GF, just a wild guess, has to do with ongoing GPS recallibration of a GF-8048 unit, a commercial GPS disciplined oscillator.

To dump the whole table into a velocity plot, paste the haversine formula into excel, where I've chased down the WGS84 earth radius for this latitude in km for the final constant:
 
=ACOS(COS(RADIANS(90-Lat1)) *COS(RADIANS(90-Lat2)) +SIN(RADIANS(90-Lat1)) *SIN(RADIANS(90-Lat2)) *COS(RADIANS(Long1-Long2))) *6357.444

For updated Sentinel imagery (no further cleavage as of Sep 17th), use this link:
http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/27/X/WJ/2016/9/15/0/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/27/X/WJ/2016/9/15/0/)

The attached .txt file, when renamed .kml, allows easy addition of way stations as the instrument drifts along with the ice it is frozen into.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 20, 2016, 07:34:20 PM
Here is what the data looks like for the other items in the zipped data package. It is spreadsheet friendly.

The 'microcat' seems to be a Sea-Bird MicroCAT conductivity-temperature-depth profiler (CTD) with some conversion of water pressure to water depth needed, which will depend on both the temperature and salinity profile above as modeled from the four microcat data points. None of these sit on the sea floor; the depth was probably determined but is not overtly provided.

%ITM 5, microcat 8575 at 600 dbar, sample interval = 900 seconds
%year day temperature(C) salinity pressure(dbar)
2016  236.62501    1.1457   34.7581 503.310
2016  236.63543    1.1483   34.7576 503.310
2016  236.64584    1.1614   34.7546 503.310
2016  236.65626    1.1571   34.7648 503.310
2016  236.66668    1.1490   34.7622 503.310
...

The 'aquadopp' would be a Nortek doppler acoustic current profiler able to measure current magnitude and direction, reporting as cartesian xyz (ENup) components in m/s (though only to one significant digit). System electronics integrate doppler velocity with temperature, pressure, tilt and compass direction. 

Some 2,520 data lines have been collected so far. There is very little scatter in velocity magnitude, with east ranging from -50 to +50 mm/s, north -60 to +80 mm/s, and up from -50 to +30 mm/s. Here 50 mm/s pencils out to 0.18 km/hr, 0.097 knots, or 4.3 km/day which is about a half EW width of Spaltegletscher.

This could flush the whole underbelly in a couple of weeks if the current moved north as depicted in an earlier post (from Nat Wilson article graphic). However it doesn't very often. Only 1005 days have a northward velocity greater than zero and these average 21.5 mm/sec.  The 1117 days of southbound current average -21.3 mm/sec.

So overall the net current at aquadopp 4 has been -2.17 mm/sec which as sampled 2520 times at 900 sec intervals works out (a lot more care needed here) to -4.9 km displacement to the south which is the opposite of the under ice shelf current anticipated. Here the depth and the other three aquadopp need analysis as well.

5.58 -2.21 -34.8  sum of east, north, up components
0.0022 -0.00088 -0.01 average of east, north, up components

Incidentally, the spelling Spalte Gletscher (two words) is unacceptable. Since day one, it has been just one word, with Spaltegletsjer now being pushed, though not used to date in english language articles, Spaltegletscher preferred at Geus and M Pelto's site. Two words does not work in google search because they are two common german terms. And we don't need any Niog Halv Fjerds Fjorden fjord either.

http://www.the-cryosphere.net/9/2215/2015/tc-9-2215-2015.pdf (http://www.the-cryosphere.net/9/2215/2015/tc-9-2215-2015.pdf)
https://figshare.com/articles/GreenlandGlacierNames_GGNv01/1449148 (https://figshare.com/articles/GreenlandGlacierNames_GGNv01/1449148)

%ITM 5, aquadopp 4
%year day pressure(dbar) temperature(C) east north up (m/s)
2016  236.83333 504.08   1.08   0.00  -0.03  -0.02
2016  236.84375 504.09   1.09   0.02  -0.02  -0.03
2016  236.85417 504.08   1.09   0.01  -0.03  -0.00
2016  236.86458 504.07   1.08  -0.01  -0.03  -0.02
2016  236.87500 504.09   1.08   0.01  -0.03  -0.03
...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 20, 2016, 08:20:51 PM
It is actually Spaltegletscher (Crevice Glacier in English) and no N or J in it.

Named by Elmar Drastrup's 1938-39 expedition for the numerous wide crevasses. Gustav Thostrup and Alfred Wegener were delayed by the crevasses when making the first traverse of the glacier in 1907. GEUS
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 21, 2016, 01:52:29 PM
Geus: named for the numerous wide crevasses.
I believe they are mistaken in that. Spaltegletscher was an ice sheet then and now, never a grounded glacier in the Holocene. It shares a grounding zone with 79N over a hundred km to the west. Crevasses are slow motion ice falls over topography. They do not form on the flats. SG extended all the way to the sea then.

'Spalte' in german translates to split or cleaved. For crevasse, they use the noun
Gletscherspalte. Or depending on context, Kluft, Schrunde or maybe Bergschrund.

Looking at the satellite photo, Hovgaard Island splits off this ice sheet from Nioghalvfjerdsfjorden much in the way a blade at the sawmill peels a sheet of veneer off a log. This would have been evident to Thostrup and Wagener on the ground.

As noted earlier, this is a distributory -- and an unusual one going off almost at a right angle. So it caught their attention and warranted recognition in the name. It's much more common to see the opposite, the confluence of ice streams as in Alaskan glaciers.

There's an alternative, namely a downstream island in the middle of the Spaltegletscher channel where the ice sheet had to flow around both sides (back in the day). However flow around obstacles is common to almost all ice flows.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: P-maker on September 21, 2016, 07:22:31 PM
A-Team,

you are rambling again.

"Spalte" in Danish means "spreading out" and cleavage is the result of this physical process. If there was a rise below sealevel further away from the current ice front, this could have been called "Kløve Gletscher", and they deliberately decided to call it "Spalte Gletscher".

Cheers P
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 21, 2016, 09:11:34 PM
I believe it could have been translated from several meanings, since Gustav Thostrup ( A Dane) and Alfred Wegener (a German) both could use the the word Spalte, but in German most probably Spalten?
Remember none of them were glaciologist so why use fancy words or terms?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 22, 2016, 12:28:13 AM
Good progress, though never quite got to Drastrup actual report and dog sled route, the first page of which should be online [Danish Dog-Sledge Expedition 1938-39] but is not due to a bungled/paywalled Polar Record web site by Cambridge Univ Press, see below.

Hmmm, the 1968 map of Spaltegletscher front looks very much like today's (ie is not suggestive of imminent calving). We've seen this before on West Greenland glaciers like Epiq, no retreat since WWII. However the USGS world glacier satellite atlas says:

In figure 43 the islands of Hovgaard Ø, Lambert Land, and Schnauder 0 can be seen in the central parts of the Landsat image. Lambert Land separates the Inland Ice outlet glaciers of Nioghalvfjerdsbræ and Zachariae Isstrøm just as Hovgaard Ø splits Nioghalvfjerdsbræ into a main stream that flows into Nioghalvfjerdsfjorden and a northern outlet glacier, Spaltegletscher, that flows into Dijmphna Sund.

Spaltegletscher is reported to have had a retreat of 18 km between 1907 and the 1950’s (Davies and Krinsley, 1962),and, in spite of the errors in determining the old frontal positions, a major recession of the outlet glaciers must have taken place during the first half of the 20th century in this part of Greenland.

Davies, W.E., and Krinsley, D.B., 1962, The recent regimen of the ice
cap margin in North Greenland, in Symposium of Obergurgl, Austria (10-18 September 1962): International Association of Scientific Hydrology, Publication No. 58, p. 119-130.
http://hydrologie.org/redbooks/a058/05813.pdf (http://hydrologie.org/redbooks/a058/05813.pdf) free full text!!!

"Named by Elmar Drastrup’s 1938–39 expedition for the numerous wide crevasses. Gustav Thostrup and Alfred Wegener were delayed by the crevasses when making the first traverse of the glacier in 1907."

That quote comes from Anthony K. Higgins:

GEOLOGICAL SURVEY OF DENMARK AND GREENLAND BULLETIN 21 · 2010
Exploration history and place names of northern East Greenland
http://www.geus.dk/publications/bull/nr21/nr21_p001-368.pdf (http://www.geus.dk/publications/bull/nr21/nr21_p001-368.pdf)

"Two Danish [fur seal] hunters, Elmer [sic] Drastrup and Finn Christoffersen ..."

Drastrup, E. 1932: Blandt danske og norske Fangstmænd i Nordøst -
grønland, 132 pp. København: Gyldendalske Boghandel, Nor -
disk Forlag. [Among Danish and Norwegian Catch Men in Northeast Greenland]

Drastrup, E. 1945: Contributions to the geography of Ingolfs Fjord
and the interior of Kronprins Christians Land. Meddelelser om
Grønland 142(1), 28 pp.

Elmar Drastrup, 1909-1981, dansk polarrejsende og forfatter. Elmar Drastrup var fangstmand for Østgrønlandsk Fangstkompagni Nanok på Sandodden fangststation 1931-32, hvor han på en slædetur ved juletid fik voldsomme forfrysninger og måtte returnere til Danmark i sommeren 1932. I vinteren 1933-34 arbejdede han for Lauge Koch på stationen Eskimonæs. Sammen med fangstmanden Finn Kristoffersen foretog han Den Danske Hundeslædeekspedition 1938-39, der havde til opgave at finde en bedre slæderute til Peary Land. Ekspeditionen var finansieret af Scoresbysund Komiteen. Da den nåede Romer Sø på 81ºN, måtte den imidlertid vende om på grund af åbent vand samt unormalt stort snefald. Efter en rejse på 2350 km nåede de to mænd tilbage til udgangspunktet Sandodden i Young Sund (det nuværende Daneborg).

I 1944 var hans bopæl i Nyhavn, men i 1960'erne flyttede han til Mallorca, hvor han antagelig ligger begravet. Han var gift flere gange.

Hans forfatterskab omfatter: Blandt danske og norske Fangstmænd i Nordøstgrønland (1932), tysk udgave Grönlandjäger (1933), Fordi de udfører så store Bedrifter, (1935, omhandler de arktiske slædehunde), Nunatame – Nyt land – en grønlandsk Robinsonade (1943), Grønlandsfærd (1944, med 17 træsnit af Gitz-Johansen), Contributions to the Geography of Ingolfs Fjord and the Interior of Kronprins Christian Land (1945, Bind 142-1 i Medd. om Grønland), Med Pulk og Ski til Lapland (1945), Pelsjægerne (1946), Nanuaraq (1953, børnebog på grønlandsk), Nalagag (1946, børnebog), Polarnattens farer (1956), Med vind i sejlene (1960, om en tur over Atlanten i sejlbåd), Lille Nanok (1975, børnebog).

Elmar Drastrup, 1909-1981, Danish polar traveler and writer. Elmar Drastrup was trapper for East Greenland Fishing Company Nanok on Sandodden hunting station 1931-32, where he was on a sleigh ride at Christmas got violent frostbite and had to return to Denmark in the summer of 1932. In the winter of 1933-34, he worked for Lauge Koch at the station Eskimonæs. Along with catching the man Finn Kristoffersen, he conducted the Danish Dogsled Expedition 1938-39, which had the task of finding a better sled route to Peary Land. The expedition was funded by Scoresby Committee. When it reached the Roman Lake at 81ºN, may however turn back because of open water and abnormally high snowfall. After a journey of 2350 km, the two men back to square Sandodden in Young Sund (the current Daneborg).

In 1944 his home in Nyhavn, but in 1960 he moved to Mallorca, where he presumably is buried. He was married several times.

There had been a previous expedition to NE Greenland led by Johan Peter Koch in 1913 —and in which Alfred Wegener had been a member— that had been named "Mørkefjord Expedition".

Recent Polar Literature  Cambridge University Press
journals.cambridge.org/article_S0032247400042716
[Danish Dog-Sledge Expedition 1938-39 to north-east Greenland; includes a survey of a new route to Peary Land.]  This google search result does not lead to the indicated quote!

Map of Northeastern Greenland by Defense Mapping Agency Aerospace Center, a derivative work of txu-pclmaps-oclc-8322829_b_9.jpg, from the map collection of the Perry-Castañeda Library (PCL) of the University of Texas at Austin.  1:1,000,000 scale Operational Navigation Chart, Sheet B-9, 1st edition. Covers Greenland (Denmark). Lambert Conformal Conic Projection. Standard Parallels 73 20N and 78 40N. Central longitude 32 45W. Operational Navigation Chart B-9, 1st edition.jpg Created: 29 February 1968
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 22, 2016, 01:53:39 AM
There is a 109 year record of hand-drawn maps, aerial photos, Landsat-2 imagery, and more recently interferometric studies of the Spaltegletscher region, usually as a byproduct of a study of 79N or Zachariae. Neither the early Koch + Wegener study nor the Drastrup map seem to be online though the later is available cheaply in booklet form in the UK.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 22, 2016, 08:59:49 PM
fairly clear sky yesterday and today allows to spot Tobias Oer as a fixed speck of white among the drifting ice. (left arrow at 79° 20.3' N 15° 48.2' W)
flip betweem 21. and 22.9. on
http://go.nasa.gov/2dkHJd3 (http://go.nasa.gov/2dkHJd3)
see also http://www.nature.com/nature/journal/v416/n6876/fig_tab/416035a_F1.html (http://www.nature.com/nature/journal/v416/n6876/fig_tab/416035a_F1.html)

the second arrow points to another area where there seems to be no movement but the location is different from the new islands mentioned in the nature article.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: A-Team on September 23, 2016, 01:10:46 AM
These high elevation sites like Petermann and Spaltegletscher have fabulous satellite return coverage -- practically daily for the Sept 2016 Sentinel 2A #tiles/27/X/WJ/2016/9/. This would for allow really neat time lapse photography if skies were clear and something was actually happening on the ice.

The preview mode at the AWS site allows fairly quick screening of cloud conditions at SG itself which does not follow from overall scene cloud percentage. This saves on downloads though these are fairly small and could be co-registered in the stack that can be co-cropped with useless dates (layers) discarded. However the downloads lose all metadata (ie date) except for band!

I located a fair number of older images, the nicest of which is a Landsat-7 from 26 Jun 2001, L71012002_00220010626 (3rd image below, not enhanced). These seem to confirm Spaltegletscher hasn't changed much in recent decades. Will this time be different?

The parent glacier 79N -- the driving force coming down off the summit ridge -- has only moderately accelerated and retreated so the issue is primarily enhanced undercutting of the floating ice shelves by adjacent ocean waters as 2016 was a mediocre year for surface melt in this area.

01 opaque
02 clear
03 clear
04 light clouds
05 clear where needed
06 clear tip only
07 clear #774
10 cloudy
11 cloudy
12 clear
13 opaque
14 so-so
15 clear, see above
16 clear low
17 too cloudy
20 too cloudy

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/27/X/WJ/2016/9/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/27/X/WJ/2016/9/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on September 25, 2016, 08:57:44 AM
It seems it is not over yet. Minor calving in the north, but big cracks open for a future bigger calving. In the mean time one of the week old calvings gives in to the stress and breaks. All in 700x700 pixels.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on October 04, 2016, 09:23:35 PM
Shooting star over Kap Zach Sep 24 - Oct 3 2016?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 06, 2016, 11:30:29 AM
Entering the dark winter period with not one but two radar imaging Sentinels, as S1B has entered full service. That means repeat cycles are reduced from 12 days to 6 days.
Here is an animation (30 m/pix) of such a mixed S1A/B pair. Activity can be seen in about all cracks, so another calving looks possible.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on October 07, 2016, 10:37:24 AM
S-1A&B will be imaging the entire (almost) Greenland coast every six days...incredible! So many new things to be discovered in that data..

Year-round velocity monitoring of every outlet glacier with calving front locations suddenly possible. Optical will never be able to do this...
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on October 08, 2016, 05:49:24 PM
And it is not finished yet, another big calving event. Images in medium resolution EW (extra width 40m/pix) Sentinel mode.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on November 03, 2016, 10:34:33 AM
Even more calvings!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on November 03, 2016, 03:14:59 PM
A very big calving, Zach is always on the move. I keep wondering about the position of the calving front compared with last year, I have a feeling it did not rertreat this year. Didn't succeed yet in making a gif though.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on November 03, 2016, 04:04:09 PM
A very big calving, Zach is always on the move. I keep wondering about the position of the calving front compared with last year, I have a feeling it did not rertreat this year. Didn't succeed yet in making a gif though.

Sometime near the end of summer I thought the same, but after that the calving continued and now the retreat is substantial.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on November 03, 2016, 05:07:57 PM
Wow. That's significant. Thank you Wipneus.
I was expecting a retreat once the sea ice cleared, as it clears the bay and reduces buttressing for the almost-calvings, but didn't notice it actually happened. Guess eyeballing works only some of the time.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on November 04, 2016, 12:48:08 AM
Tides peaked on 1st/2nd, there was melt hereabouts and further north about 4 days ago, and fresh water showing up on hy-com cice. I don't know if thats outflow of surface meltwater or the north flowing coastal current causing melt, but looking at the first animation it looks like the current flowed in along the north shore and undermined the front, there's just a little more movement on the north side. Given the state of things generally I'm really starting to speculate about when the tidal forces open the floodgates here, there's going to be a lot more ice coming out of here than current estimates admit to. There's nothing to stop the bulk of the ice sheet using this exit, and for whatever reason this north-eastern corner seems to be melting fast.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fnsidc.org%2Fgreenland-today%2Fimages%2Fgreenland_melt_days.png&hash=a049be50134b7296ea7bb19e0814b808)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tigertown on November 04, 2016, 01:48:23 AM
Looking on HYCOM SSS model, the fresh water flow appears to have started in mid-June and increased since. How does the land lay on the NE corner;as in which way does it slope? Probably a dumb question, as this flow is most likely from one or more inlets or fjords.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on November 04, 2016, 11:05:56 AM
The island separating the glaciers is about 40k e-w, iirc the arrow indicates the warm current.
(https://puu.sh/qgz5T/8f4fa4e1bd.png)
from upthread posted by sidd  http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 06, 2016, 04:24:36 PM
Some calving activity in that dark (=smooth) glacier ice on the very top of Zachariae.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 07, 2017, 09:33:11 PM
Spaltegletscher a part of 79 Glacier made big headlines back in September 2016:

http://nyheder.tv2.dk/samfund/2016-09-13-enorm-isflage-river-sig-los-efter-gronlandsk-varmerekord (http://nyheder.tv2.dk/samfund/2016-09-13-enorm-isflage-river-sig-los-efter-gronlandsk-varmerekord)

http://jasonbox.net/separation-manhattan-sized-ice-shelf-pieces-79-glacier-far-northwestern-greenland/ (http://jasonbox.net/separation-manhattan-sized-ice-shelf-pieces-79-glacier-far-northwestern-greenland/)

but nothing really happened and I suspect the calf (iceberg) is partly grounded:

Click on image to animate!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on February 15, 2017, 03:34:01 PM
Animation of three and a half month ice streaming made from 9 hi-res (IW) S1B images, 12 days apart. For size the images are scaled at 40m/pixel (from 10).
Apart of the advancing glacier, the development of cracks I notice the melt ponds that one by one lighten up.

Click to load and view the 5Meg animation.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: DrTskoul on February 15, 2017, 04:37:48 PM
Neat!!!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on February 15, 2017, 08:43:44 PM
Very enlightening animation. ZI never sleeps, although calving seems to be on hold (for the moment).

I know there is no consensus on this, but I could swear the animation shows how the immobile sea ice in the enclosed bay slows down the glacier somewhat (and perhaps stabilizes the front a little bit as well). The debris and icebergs can be seen to be pushed before the advancing glacier, and over time the movement propagates further into the bay.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on February 15, 2017, 08:55:56 PM
Very enlightening animation. ZI never sleeps, although calving seems to be on hold (for the moment).

I know there is no consensus on this, but I could swear the animation shows how the immobile sea ice in the enclosed bay slows down the glacier somewhat (and perhaps stabilizes the front a little bit as well). The debris and icebergs can be seen to be pushed before the advancing glacier, and over time the movement propagates further into the bay.

I am one of them, the sea ice , icebergs, and debris etc. in the bay is just piece of cake, considering the forces coming from behind the glacier!
There must be other reasons for the break in calvings at Zachariae?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tealight on February 16, 2017, 12:28:46 AM
Very enlightening animation. ZI never sleeps, although calving seems to be on hold (for the moment).

I know there is no consensus on this, but I could swear the animation shows how the immobile sea ice in the enclosed bay slows down the glacier somewhat (and perhaps stabilizes the front a little bit as well). The debris and icebergs can be seen to be pushed before the advancing glacier, and over time the movement propagates further into the bay.

I am one of them, the sea ice , icebergs, and debris etc. in the bay is just piece of cake, considering the forces coming from behind the glacier!
There must be other reasons for the break in calvings at Zachariae?

As far as I understand glaciers, there are two main forces at play.

The first are the millions of tons of ice pushing the front forwards. This pushing force is very strong but also slow. It can't create calvings because it only pushes the ice. However it can move sea ice out of the way.

The second force are winds/currents attacking the ice from below and above. They a lot weaker than the pusing force of ice, but also quicker and can transport loosely connected ice away from the glacier. It's what we call calving. I think sea ice can be strong enough in winter to withstand this second force.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on February 16, 2017, 11:24:38 AM
My 2c take a look at the bottom image on this, http://membrane.com/sidd/greenland-2013/Zachtrough/ (http://membrane.com/sidd/greenland-2013/Zachtrough/) posted by Sidd way back. The calving ice comes  off in big peices so very inert, they'll hug the coast as they move south, the melting current comes in causing ongoing if varying melt, more on the northern side, that melt water percolates through the bergs and being easy to refreeze consolidates them in the shallows behind the island barrage to the south. To get a massive breakout either that southern ice mass needs to have melted or a torrent of meltwater needs to surge out, I doubt that will happen because there's probably meltwater below the ice seeping out consistently, consolidating the ice to the south.
Now take a pinch of salt.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on March 05, 2017, 01:26:59 AM
https://icyseas.files.wordpress.com/2014/06/p2833.jpg?w=650[/img]](https://icyseas.files.wordpress.com/2014/06/p2833.jpg?w=650) (http://[img width=580 height=435)

This is one of the images in a post on Andreas Muenchow's blog.
https://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/#more-2510 (https://icyseas.org/2014/06/20/icebergs-islands-and-instruments-off-isle-de-france-north-east-greenland/#more-2510)
These were taken some distance away but I believe they are icebergs from Zachariae. I vaguely remember someone measuring the height of icebergs at the calving front from topled bergs as 300m?
The point I am trying to make is that these bergs have pretty high wind resistance, and I can imagine when wind blows down from the inland ice, the lined up bergs would collectively be able to shove the sea ice which is "just" a couple of meters thick into an overlapping ridge.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: budmantis on March 05, 2017, 06:49:35 AM
This looks like it belongs in the Antarctic, not the Arctic. That berg is massive!
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on March 06, 2017, 03:24:11 PM
Isn't that what we are seeing in the picture? It looks like the sea ice is piling up all around that berg.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas Muenchow on March 06, 2017, 04:06:34 PM
Yes; the tabular iceberg is grounded while the multi-year sea-ice around it moves to the south.

The photo was taken during the deployment of ocean current moorings placed on the sea bed in June of 2014. More than 2 years later in August 2016 this specific mooring (as well as all other 6 along the section) were recovered with full 2-year records of ocean currents from the bottom to the surface. So no icebergs plowed across the mooring site(s) and destroyed them. For all I know this iceberg may still be sitting where it was back in 2014.

Below are time series at the edge of a 80 km wide Trough or Canyon that snakes from the Fram Strait to the coastal glaciers such as 79N and Zachariae. The vertical panels show selected depth with surface currents at the top and bottom currents near the bottom. Oceanography is physics in action on the rotating "plane" that we call earth.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 08, 2017, 10:22:50 AM
The sun is back over the Zachariae calving front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on March 08, 2017, 10:13:46 PM
Interestingly, the calving front barely advanced over the winter, although the glacier kept on going.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on March 19, 2017, 07:41:10 AM
Sentinel 2A is back as well. Here is a detail of the northern tip of the calving front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on April 02, 2017, 09:04:04 AM
Two Sentinel 2 images, 27th March one year apart. The two images have been shifted to make the ice at the center (where the most upper crack is visible in the 2017 frame) appear stationary.

The shift (216x6pixels) works out at a glacier speed of about 5.92 m/day (+/- 0.1 m/day).

Compared to my previous estimates in the past there is no increase in speed. The measurement is certainly more up-stream where the speeds where lower anyway.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: ghoti on April 04, 2017, 01:03:28 AM
Photos today from low level flight over the calving front by IceBridge

https://www.facebook.com/NasaOperationIcebridge/photos/pcb.1287064188037265/1287063524703998/?type=3&theater (https://www.facebook.com/NasaOperationIcebridge/photos/pcb.1287064188037265/1287063524703998/?type=3&theater)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on April 30, 2017, 01:19:19 PM
hat tip to Cate: More of these photos can be seen (also by non facebook users) here
https://jeremyharbeck.smugmug.com/Field-WorkExpeditions/Operation-IceBridge-2017-Arctic (https://jeremyharbeck.smugmug.com/Field-WorkExpeditions/Operation-IceBridge-2017-Arctic)
this closer view from a plane overflying the glaciers and icebergs helps to get a better view of what we see in the satellite images.
Especially recomended: finger rafting (as happens where the calving front at Zachariae pushes sea ice into such overlapping layers)
 https://jeremyharbeck.smugmug.com/Field-WorkExpeditions/OIB-Arctic-2017-Daily-Galleries/April-3rd-2017-Zachariae79N-Fram-Strait/n-RmXGWN/i-qnVxs2F (https://jeremyharbeck.smugmug.com/Field-WorkExpeditions/OIB-Arctic-2017-Daily-Galleries/April-3rd-2017-Zachariae79N-Fram-Strait/n-RmXGWN/i-qnVxs2F)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on April 30, 2017, 02:11:56 PM
Thanks Andreas and Cate for the link. Great pictures.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 25, 2017, 09:38:00 AM
Some activity at last (apart from the continuing advancing of the glacier front). Calving toppled over, with others breaking.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on June 28, 2017, 05:43:09 PM
Melt ponds generally increase in numbers and grow in size (but a few do not) in this animation fro two images three days apart.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: zxy on July 06, 2017, 06:12:25 PM
There seems to be a calving in the past 24 hours.

Updated terra image.

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 07, 2017, 07:11:54 PM
Multiple calvings actually. Sentinel 2 images scaled to 30 m/pix for size.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on July 07, 2017, 08:26:17 PM
The one-day growth of the smaller melt pond (lower left corner) is impressive!

Interesting that the mélange on the right remains frozen.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 08, 2017, 02:30:48 AM
the northern end is interesting too, the bergs formed there are narrower than elsewhere along the front where ice which is lee wide than high topples as soon as it separates from the glacier. I assume that means the ice is thinner there. Which would not be surprising with the slower movement it would be exposed to melting from below for longer.
The piece which wipneus focussed on back in March spalled off a southfacing remnant due to sideways pressure. The remnant itself has no forward movement since it is almost separate from the moving glacier.
Sentinel 2A is back as well. Here is a detail of the northern tip of the calving front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 08, 2017, 09:12:41 AM
The one-day growth of the smaller melt pond (lower left corner) is impressive!

Interesting that the mélange on the right remains frozen.
This animatiion and others similar to it are what led me to the unconventional conclusion that in ZI the sea ice has a slight buttressing effect (being enclosed by rocks further east), as it forces the glacier to push all the calved bergs, and crush/ridge the sea ice, in order to advance.
This is why I expect more calving activity when the sea ice clears, typically in August, and the delicately balanced front loses support.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: iwantatr8 on July 12, 2017, 03:21:55 PM
It seems to be a day for lumps falling off icesheets...

http://apps.sentinel-hub.com/sentinel-playground/?lat=79.42821432626154&lng=-19.82860565185547&zoom=12&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.4&gamma=1&time=2015-01-01|2017-07-11&cloudCorrection=none&atmFilter=&showDates=true&evalscript=&showImage (http://apps.sentinel-hub.com/sentinel-playground/?lat=79.42821432626154&lng=-19.82860565185547&zoom=12&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.4&gamma=1&time=2015-01-01|2017-07-11&cloudCorrection=none&atmFilter=&showDates=true&evalscript=&showImage)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 12, 2017, 06:48:53 PM
One of Zachariae's old calvings decides to do something dramatic.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on July 12, 2017, 10:39:16 PM
Paper on the Cryosphere discuss about 79N, (and Peterman and Ryder). 79N is thinning

"At Nioghalvfjerdsbræ the total melt flux (14.2±1.6 km^3/yr water-equivalent) exceeds the inflow of ice
(10.2±0.59 km^3/yr water-equivalent) indicating present thinning of the ice tongue"

I attach part of fig 1 and fig 2. Nice paper,read the whole thing.

http://www.the-cryosphere-discuss.net/tc-2017-99/ (http://www.the-cryosphere-discuss.net/tc-2017-99/)

Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 14, 2017, 12:39:36 PM
A relatively narrow calving is unstable: the calvings topple over.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Tor Bejnar on July 14, 2017, 02:45:04 PM
Although small, they do a good job at pushing previously calved icebergs away from the front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 15, 2017, 10:31:09 AM
I know this has been done before but I find this so impressive I think it is worth repeating. Images are largely self explanatory I hope, icebergs tip over when they are taller than wide. These bergs are 300m tall!  Quite a splash even with ice that is already afloat (not grounded).
In physics terms the work done to move a lot of bergs a few hundred meters sideways is not easily quantified as energy required (from lowering center of mass of the berg). I expect the upwelling of meltwater below the glacier front will add to the push on the floating bergs towards the sea ice which still covers the bay.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 15, 2017, 07:30:18 PM
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on July 15, 2017, 09:09:46 PM
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.
Thanks, amazing resolution. The draining pond's length is ~1-1.5 km assuming each pixel is 10m. Must have been quite a waterfall.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on July 15, 2017, 11:09:27 PM
reading back through the thread I was reminded of the microcat sensors of itm5 which were placed at 79N last August. What I don't understand is the change in pressure, they all seem to be at lower pressure, 10 dbar less than a year ago. This might be that somehow they are sitting less deep in the water or does anyone have a better explanation? Temperatures have risen at all 4 sensors which isn't explained by a change in depth (if that is what happened) because temperature is higher at greater depth.
http://www.whoi.edu/page.do?pid=154416 (http://www.whoi.edu/page.do?pid=154416)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 16, 2017, 12:27:20 AM
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.

That is so cool.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 26, 2017, 04:38:07 PM
Calving to the north of the calving front.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on July 26, 2017, 04:42:07 PM
and one more to the south (Kap Zach)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 26, 2017, 09:31:29 PM
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Hyperion on July 27, 2017, 10:41:38 AM
reading back through the thread I was reminded of the microcat sensors of itm5 which were placed at 79N last August. What I don't understand is the change in pressure, they all seem to be at lower pressure, 10 dbar less than a year ago. This might be that somehow they are sitting less deep in the water or does anyone have a better explanation? Temperatures have risen at all 4 sensors which isn't explained by a change in depth (if that is what happened) because temperature is higher at greater depth.
http://www.whoi.edu/page.do?pid=154416 (http://www.whoi.edu/page.do?pid=154416)

that is very odd looking. every single one of them looks like its risen more than 10m in the water by the pressure change and all at the same rate. Maybe the cables got all twisted up and tied itself in knots near the surface, giggle. Or someone mistook it for a fishing line and tried to pull it up to see if anything was hooked on it. Or had ideas about recovering some copper for the scrap metal dealer. ;D
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on July 27, 2017, 11:05:49 AM
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.
I think that's rather standard with a calving, it looks like the new calved iceberg pushes everything away and ice-melange & sea-ice transfer that impulse quite far.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on July 27, 2017, 11:53:07 AM
Andreas T 'reading back'
 I think Dijmphna sound is a little deeper than the fjord below N79, is it possible bottom melt caused the north end of the 'footprint' to sink raising the ice the sensors are connected to, and redirecting the currents?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: iwantatr8 on July 27, 2017, 12:56:20 PM
Another calving from the front of N79

http://apps.sentinel-hub.com/sentinel-playground/?lat=79.56726268124912&lng=-19.536781311035156&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.5&gamma=1&time=2015-01-01|2017-07-26&cloudCorrection=none&atmFilter=&showDates=true&evalscript=&showImage (http://apps.sentinel-hub.com/sentinel-playground/?lat=79.56726268124912&lng=-19.536781311035156&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.5&gamma=1&time=2015-01-01|2017-07-26&cloudCorrection=none&atmFilter=&showDates=true&evalscript=&showImage)

And given the melt water ponding and draining that we are seeing in the area I wonder how long before the shelf disintegrates.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on July 27, 2017, 03:21:07 PM
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.
I think that's rather standard with a calving, it looks like the new calved iceberg pushes everything away and ice-melange & sea-ice transfer that impulse quite far.

Satellite images of calvings are deceiving. These are high energy, violent events.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: solartim27 on August 04, 2017, 04:04:54 PM
Good article here, lots of pictures and video
Approximately 12 percent of Greenland's ice takes this path - and, as scientists have proven in recent years, the velocity of these flows is increasing. "The ice stream seems to be on the brink of a change," says Dorthe Dahl-Jensen of the University of Copenhagen.
Wrapped in a thick blue, down jacket with a fur collar, the silver-haired glaciologist has just stepped off a special plane. She's leading a field camp where scientists are about to research precisely this change. The project is called EastGRIP. In the name of science, a hole will be drilled through Greenland's 2.5-kilometer-thick (1.5 mile) ice shield. To execute the work, around 20 people are currently living right on the ice, at the 75th parallel north.
http://www.spiegel.de/international/world/a-river-of-ice-scientists-study-greenland-s-role-in-sea-level-rises-a-1161220.html (http://www.spiegel.de/international/world/a-river-of-ice-scientists-study-greenland-s-role-in-sea-level-rises-a-1161220.html)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 04, 2017, 08:37:07 PM
Good article here, lots of pictures and video
Thanks solartim. I found this overview image to be very useful.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.spiegel.de%2Fimages%2Fimage-1146183-galleryV9-ssyc.jpg&hash=cebaed0992b24a5cf7e8365089237579)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 11, 2017, 07:16:44 AM
The sea ice around Zachariae has started breaking and moving in the last few days, which could lead to a quick flushing of the calved icebergs and ice melange, and possibly some extra calving activity of parts of the front currently hanging by a thread.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 12, 2017, 11:21:09 AM
the bergs near the calving front seem to have moved without a calving, but I would want to see a clear Sentinel image to be certain. The sea ice in the bay between the Zachariae glacier and the islands, (Jokelbught I guess?) is mobile but not getting away very far, the exits between the islands are narrow and in the south blocked by remnants of the ice shelf which broke up in 2002 (thats a bit bof a guess, I have not traced them back to that year) image attached
http://apps.sentinel-hub.com/sentinel-playground/?lat=78.09716267271118&lng=-19.786376953125&zoom=9&preset=1_NATURAL_COL0R&layers=B8A,B03,B02&maxcc=99&gain=0.3&gamma=0.7&time=2015-01-01|2017-08-07&cloudCorrection=none&atmFilter=&showDates=false (http://apps.sentinel-hub.com/sentinel-playground/?lat=78.09716267271118&lng=-19.786376953125&zoom=9&preset=1_NATURAL_COL0R&layers=B8A,B03,B02&maxcc=99&gain=0.3&gamma=0.7&time=2015-01-01|2017-08-07&cloudCorrection=none&atmFilter=&showDates=false)
The largest and clearest exit does not have much transport through it because drift is slow and mostly north along side it it seems from looking at movement in 2016 and 2013.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 12, 2017, 12:30:45 PM
looking around on Sentinel I have been intrigued by this meltlake not far from the calving front. As has been commented on elsewhere, these features are located on the glacier surface relative to features of the ground below it. I.e.. as the glacier ice moves along the meltlake stays in a surface depression which probably sits upstream of a bump in the rock surface below the glacier.
I have picked cloud free images from Aug 16 and 17 and the earliest available Mar 17 for an indication of surface contours in low sun angle illumination.
This meltlake does not seem to be very old, I could not see it in the MODIS images before 2014. Therefore it gives an opportunity to follow its development as its effect on the ice moves downstream (of the glacier). Possibly the meltlake has appeared in this location due to thinning of the glacier as the calving front has retreated towards it.
The March image shows a narower part of the lake which seems to have frozen over in the previous winter and I think can be seen again as a darker, deeper area this August. I am looking forward to finding out what happens as this moves towards the rise which stops the lake from draining down towards the sea.
Probably not a profoundly important feature but fun to watch.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 12, 2017, 06:56:02 PM
Interesting, I guess the lack of melt water makes the pond much smaller to spot in previous years.

Here are a couple of Aster images 2001-2016 stacked together of the same spot.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on August 12, 2017, 08:55:12 PM
Thanks, Wipneus, seeing those previous years shows how much variation there is around this spot. I also find it instructive how little trace these earlier, smaller meltpools have left on the present day glacier. I still think that changes in contours and drainage determines size of the pools and that this year's pool looks deeper to me. Further developments (over a year or two will tell more).

I have looked a bit more at ice berg movements at the exits of Jokelbught. I coloured in some of them at what looks to me like the larges gap in the islands south east of Schnauder oer.  The images of July 2016 and 2017 show that these have not taken the exit despite being very close to it when the sea ice broke up and allowed movement last year. There is mevement, i.e. no signs of grounding, there just seems to be little water movement across that gap, maybe it was different in other years.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 13, 2017, 10:12:40 PM
I apologize for the terrible resolution, but in my opinion better than nothing, showing the movement of sea ice in the bay, quite limited but after many months of total immobility.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on August 13, 2017, 11:24:33 PM
I apologize for the terrible resolution, but in my opinion better than nothing, showing the movement of sea ice in the bay, quite limited but after many months of total immobility.

The flow of debris from Zachariae Isstrøm will probably increase during next 3 - 4 weeks, and 2017 could be one of the rare years when all the fast sea ice at Belgica Bank will leave the area as it did in the beginning of this century and what I believe started the extreme activity at Zachariae Isstrøm during the last 15 years.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on August 14, 2017, 07:33:57 AM
A crude Sentinel animation of the bay showing some of the bergs moving away, as well as a minor calving. Interesting that the bergs at the bottom of the image are moving "backwards". The dates are Aug 3rd, 8th and 12th. Click.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on August 17, 2017, 10:06:59 AM
Nice clear day yesterday at N79., shows things opening up for tidal action.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fservices.sentinel-hub.com%2Fv1%2Fwms%2Fb7b5e3ef-5a40-4e2a-9fd3-75ca2b81cb32%3FSERVICE%3DWMS%26amp%3BREQUEST%3DGetMap%26amp%3BMAXCC%3D80%26amp%3BLAYERS%3DB8A%2CB03%2CB02%26amp%3BGAIN%3D0.4%26amp%3BGAMMA%3D1.0%26amp%3BCLOUDCORRECTION%3Dnone%26amp%3BEVALSOURCE%3DS2%26amp%3BWIDTH%3D1286%26amp%3BHEIGHT%3D535%26amp%3BATMFILTER%3DATMCOR%26amp%3BFORMAT%3Dimage%2Fjpeg%26amp%3BBGCOLOR%3D00000000%26amp%3BTRANSPARENT%3D1%26amp%3BNICENAME%3DSentinel%2Bimage%2Bon%2B2017-08-16.jpg%26amp%3BTIME%3D2015-01-01%2F2017-08-16%26amp%3BBBOX%3D-2564004%2C15124747%2C-1789850%2C15451898%26amp%3BPREVIEW%3D3&hash=d37b71efd91be5bbb6dca3bed973fdfa)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 17, 2017, 10:57:46 AM
Some recent events: old calvings break, new calving events and developing crack indicating future calvings. Add to that considerable brightening from recent snow fall.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 17, 2017, 11:03:25 AM
The melt pond discussed by Andreas T has mostly gone.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on August 18, 2017, 11:46:46 PM
I'm wondering how strong the fast ice is, it's certainly looking vulnerable, nothing much changed through the last tidal cycle, except it's 'defences' were swept away. Now with the new moon on monday, and three big tidal cycles up to the equinox things could get very interesting hereabouts.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fservices.sentinel-hub.com%2Fv1%2Fwms%2Fb7b5e3ef-5a40-4e2a-9fd3-75ca2b81cb32%3FSERVICE%3DWMS%26amp%3BREQUEST%3DGetMap%26amp%3BMAXCC%3D4%26amp%3BLAYERS%3DB8A%2CB03%2CB02%26amp%3BGAIN%3D0.4%26amp%3BGAMMA%3D1.0%26amp%3BCLOUDCORRECTION%3Dnone%26amp%3BEVALSOURCE%3DS2%26amp%3BWIDTH%3D1286%26amp%3BHEIGHT%3D535%26amp%3BATMFILTER%3DATMCOR%26amp%3BFORMAT%3Dimage%2Fjpeg%26amp%3BBGCOLOR%3D00000000%26amp%3BTRANSPARENT%3D1%26amp%3BNICENAME%3DSentinel%2Bimage%2Bon%2B2017-08-07.jpg%26amp%3BTIME%3D2015-01-01%2F2017-08-07%26amp%3BBBOX%3D-2427029%2C14837650%2C-2039952%2C15001225%26amp%3BPREVIEW%3D3&hash=a502ef2e3a436a89e3aba5e2f1ba08e2)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fservices.sentinel-hub.com%2Fv1%2Fwms%2Fb7b5e3ef-5a40-4e2a-9fd3-75ca2b81cb32%3FSERVICE%3DWMS%26amp%3BREQUEST%3DGetMap%26amp%3BMAXCC%3D100%26amp%3BLAYERS%3DB8A%2CB03%2CB02%26amp%3BGAIN%3D0.4%26amp%3BGAMMA%3D1.0%26amp%3BCLOUDCORRECTION%3Dnone%26amp%3BEVALSOURCE%3DS2%26amp%3BWIDTH%3D1286%26amp%3BHEIGHT%3D535%26amp%3BATMFILTER%3DATMCOR%26amp%3BFORMAT%3Dimage%2Fjpeg%26amp%3BBGCOLOR%3D00000000%26amp%3BTRANSPARENT%3D1%26amp%3BNICENAME%3DSentinel%2Bimage%2Bon%2B2017-08-18.jpg%26amp%3BTIME%3D2015-01-01%2F2017-08-18%26amp%3BBBOX%3D-2427029%2C14837650%2C-2039952%2C15001225%26amp%3BPREVIEW%3D3&hash=1e9a1d67d5cd85a38bac2c7414c775f0)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D382.0%3Battach%3D50505%3Bimage&hash=de16a75e68a674cd22266db0953fc860)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on August 20, 2017, 06:46:42 PM
Another thin slice is calving.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: oren on September 02, 2017, 10:40:16 AM
So I've been wondering for a while about the old tongue of Zachariae, that got fully separated from the glacier in 2012. I speculate that when it goes, calving activity might pick up due to increased circulation at the front.
It turns out the tongue has been gradually losing bits and pieces, although it's a slow process not expected to finish anytime soon. CLICK to animate Aug 2016 vs. Aug 2017. Note the northeastern corner, the southeastern bulge, and the southernmost bit. For reference, Espen's excellent overview image from up-forum of calving front retreat.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Espen on September 02, 2017, 09:59:51 PM
Updated retreatline 2009 - 2017: Click on image to enlarge
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on September 03, 2017, 12:19:09 PM
Before i saw these pools, center stage, i'd assumed the north side more or less followed the gradient of the glacier slope, does anyone know if they're tidal?
(https://services.sentinel-hub.com/v1/wms/b7b5e3ef-5a40-4e2a-9fd3-75ca2b81cb32?SERVICE=WMS&REQUEST=GetMap&MAXCC=11&LAYERS=B8A,B03,B02&GAIN=0.4&GAMMA=1.2&CLOUDCORRECTION=none&EVALSOURCE=S2&WIDTH=1286&HEIGHT=535&ATMFILTER=ATMCOR&FORMAT=image/jpeg&BGCOLOR=00000000&TRANSPARENT=1&NICENAME=Sentinel+image+on+2017-08-30.jpg&TIME=2015-01-01/2017-08-30&BBOX=-2577763,14914392,-2190686,15077968&PREVIEW=3)
Looking south (http://apps.sentinel-hub.com/sentinel-playground/?lat=78.38098360750396&lng=-20.8685302734375&zoom=8&preset=CUSTOM&layers=B8A,B03,B02&maxcc=11&gain=0.4&gamma=1.2&time=2015-01-01|2017-08-30&cloudCorrection=none&atmFilter=ATMCOR&showDates=false&evalscript=&showImage) there are 5  pieces of the old tongue which eyeballing their debris seem about 200+m thick and look like they're going nowhere, but plenty of the debris looks vulnerable to still warm Atlantic waters and the vagaries of wind and tides, and if it melts or moves away could leave a lot of space for Zachariae to fill.
 
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: nukefix on September 12, 2017, 05:37:40 PM
I think there has been meltwater exiting Zach that has been melting sea-ice close to the calving front. The feature 1st appears on the 26.8. S-2 image:

http://apps.sentinel-hub.com/sentinel-playground/?lat=78.98372644988251&lng=-20.759353637695312&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.3&gamma=1.0&time=2015-01-01 (http://apps.sentinel-hub.com/sentinel-playground/?lat=78.98372644988251&lng=-20.759353637695312&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.3&gamma=1.0&time=2015-01-01)|2017-08-26&cloudCorrection=none&atmFilter=ATMCOR&showDates=true&evalscript=
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: johnm33 on September 12, 2017, 06:46:53 PM
I was thinking it was displacing the bergs seawards, surprised there's not more calving. Better link (http://apps.sentinel-hub.com/sentinel-playground/?lat=79.02164701371296&lng=-20.917625427246094&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.3&gamma=1.0&time=2015-01-01|2017-09-11&cloudCorrection=none&atmFilter=&showDates=false&evalscript=)
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Andreas T on September 12, 2017, 09:58:22 PM
The melt pond discussed by Andreas T has mostly gone.
on the 1. Sept it looked completely gone, drained and frozen till the next season I thought but on the 10. there is more water which seems to have floated the ice cover on the southern lake.
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on September 17, 2017, 08:06:50 PM
It looks partly drained, and frozen over again (as most other melt ponds are now).
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on November 04, 2017, 06:15:08 AM
Discussion paper on the cryo discuss: Simple minded hydrology improves ISSM for 79/Zach/Storstrommen. One way coupled (hydrology to ice) single layer Darcy flow for hydrology, SSA with no thermomechanics and Glen's law for ice, data from the Morlinghem(2014)

Still not so good, but better. Need to put the hydrology in, so I like it.

Open access, read all about it. I attach Fig 10.

https://www.the-cryosphere-discuss.net/tc-2017-221/

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Shared Humanity on November 04, 2017, 04:12:02 PM
Would that firn be ancient ice, dating back to the last ice age?
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on November 04, 2017, 08:51:45 PM
Firn only on the top. NEGIS core should tell us about ice age when the results come out.

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: sidd on November 06, 2017, 04:35:07 AM
And here is a nice model from Choi and the usual suspects (but with no hydrology.) They project that 79N is not going to do tricks, but Zach is going to retreat until it hits a stabilizing ridge 30 km. upstream.

"Our model suggests that 79North will retreat slowly over the next century, whereas ZI will lose its floating ice tongue completely and retreat rapidly for 70 years. After 70 years, ZI will stabilize 30 km upstream of its current position on a topographic ridge. Frontal melt rates need to reach 6 m/day in the summer to dislodge the glacier from this ridge. ZI will then continue a fast and unstoppable retreat, contributing more than 16.2 mm to global sea level rise by 2100."

"ZI will continue to retreat 30 km upstream, and become a grounded tidewater glacier, until it reaches a stabilizing ~200-m step in bed topography. Our simulations show that ZI is in a state of unstoppable retreat that does not depend significantly on ocean forcing, but is due to its current internal dynamics, which is mainly controlled by the bed topography. This retreat will stop once the ice front reaches this stabilizing ridge in the bed topography. An increase in the frontal melt-rate up to 6 m/day in the summer would be necessary in order to trigger a further retreat inland, and this amount of oceanic forcing, while significant, remains within the range of possible scenarios."

doi: 10.1002/2017GL075174

I attach figs 2a and 3. 2a is the control (unperturbed ocean melt)

sidd
Title: Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
Post by: Wipneus on December 13, 2017, 10:40:21 AM
Advance, cracking and calving on the Zachariae front 19th Oktober - 6th December.