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Author Topic: Zachariae Isstrøm / Nioghalvfjerdsfjorden / NE Greenland  (Read 423618 times)

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #600 on: February 27, 2016, 09:25:15 AM »
Zachariae Isstrøm update:

Please click to enlarge and animate!
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notjonathon

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #601 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.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #602 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. 
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notjonathon

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #603 on: March 02, 2016, 01:17:53 AM »
Thanks. So definitely reacting to the added heat in the arctic.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #604 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #605 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.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #606 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.

Xulonn

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #607 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?

DaveHitz

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #608 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.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #609 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!

Tor Bejnar

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #610 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.
Arctic ice is healthy for children and other living things.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #611 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.


Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #612 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.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #613 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.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #614 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.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #615 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?
 
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #616 on: March 22, 2016, 09:12:59 PM »
Quote
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.
Quote
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?

Quote
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.
« Last Edit: March 22, 2016, 11:27:59 PM by A-Team »

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #617 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.

nukefix

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #618 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/

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #619 on: March 23, 2016, 12:18:29 PM »
Quote
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
« Last Edit: March 23, 2016, 01:45:32 PM by A-Team »

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #620 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.


A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #621 on: March 24, 2016, 01:22:04 PM »
Quote
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-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
« Last Edit: March 24, 2016, 03:16:33 PM by A-Team »

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #622 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!
Have a ice day!

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #623 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


Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #624 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! ;)
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oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #625 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #626 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #627 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. 

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #628 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.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #629 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #630 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #631 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.


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #632 on: April 03, 2016, 10:16:41 PM »
Melt ponds and melting areas are showing up early this season on top of Zachariae Isstrøm:
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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #633 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):


“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #634 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 :-)

AbruptSLR

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #635 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #636 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #637 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.


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #638 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #639 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?

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #640 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 ...

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #641 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.


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #642 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

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #643 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).

Have a ice day!

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #644 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.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #645 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.


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #646 on: April 08, 2016, 02:31:33 PM »
Superb animation. Thanks

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #647 on: April 15, 2016, 12:18:57 PM »
Strange sketch in the snow cover of a melt pool on the Zachariae.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #648 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
Have a ice day!

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #649 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