Arctic Sea Ice : Forum

Cryosphere => Greenland and Arctic Circle => Topic started by: Espen on February 23, 2013, 06:15:42 PM

Title: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on February 23, 2013, 06:15:42 PM
Petermann looks suspicious, will it surprise us once more this season (2013)?
Title: Re: Petermann?
Post by: Neven on February 23, 2013, 06:33:00 PM
Hi Espen, how exactly is it looking suspicious? Any new cracks?

One would think Petermann will be quiet for a while now.
Title: Re: Petermann Glacier
Post by: Espen on February 23, 2013, 07:20:50 PM
Hi Neven,

Yes I agree she should be calm for a while, logically , but I have noticed some shades in the images from DMI, that is worth investigating during the season?
Title: Re: Petermann Glacier
Post by: Gray-Wolf on February 25, 2013, 12:34:08 AM
Well at least we're in virgin territory so we need not be bound by looking to the way Petermann used to typically behave? I think we are free to speculate as to why we find ourselves where we are and whether this signals a move towards a different mode of 'working' for this 'drain' glacier?

How close is the ocean water to the 'lip' into the basin beyond? What happens as the 'ice tongue' recedes? does it become thinner? does the ice mass beyond speed up to push it faster forward?

I think we may be about to see how we accelerate ice loss from the G.I.S.?

Title: Re: Petermann Glacier
Post by: Espen on February 25, 2013, 10:34:17 AM
Gray-Wolf,

Yes I am pretty sure we have a new set of standards, when we look at the various glaciers in the northern parts of Greenland.
I don't see records of so many important glacier movements in one season, as seen last season (2012),
we had Petermann: Big calving, Steensby: First ever reported calving, Zachariae: The ice tongue separation, Newman Bugt unnamed glacier: Calving.
Yes 2013 will be an interesting season glacier wise!
Title: Re: Petermann Glacier
Post by: Gray-Wolf on March 04, 2013, 03:56:27 PM
Seeing as we are now beyond 'historic' measure of retreat it is hard to figure whether we should , as Neven points out, expect a period of extension before the next cracks/calving occurs or whether it's retread upslope continues?

If the fjord is below sea level all the way to the basin beyond then what is to stop the warm bottom waters penetrating ever further into the Fjord? If so then we should expect further destabilization of the glacier and further thinning/calving events?

It will be interesting to see how those 'spur' glaciers react once the main glacier has retreated beyond them? Some very big 'splashes as they drop into the Fjord below (and wobbling of the glacier tongue as the waves impact them?).
Title: Re: Petermann Glacier
Post by: Espen on March 06, 2013, 08:10:50 PM
First Modis image of Petermann this season:

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013065.terra.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013065.terra.250m)
Title: Re: Petermann Glacier
Post by: Espen on April 18, 2013, 08:22:25 PM
The Melt is on:

When studying the 250M Modis from Petermann Fjord and Glacier, it is now clear the surface (snow) melt is on, the sea ice structure is clearly seen, both in the fjord and in Kennedy Channel:

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013108.aqua.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013108.aqua.250m)
Title: Re: Petermann Glacier
Post by: CraigsIsland on April 19, 2013, 12:36:02 AM
good eye; bad news  :o
Title: Re: Petermann Glacier
Post by: Jim Hunt on April 20, 2013, 01:17:22 PM
In perhaps not entirely unrelated news, NASA Operation IceBridge have just announced on their Facebook page that:

Quote
IceBridge will fly a 7 hour science mission today over the Humboldt and Petermann Glaciers in northwest Greenland.

https://www.facebook.com/NasaOperationIcebridge (https://www.facebook.com/NasaOperationIcebridge)
Title: Re: Petermann Glacier/North West Greenland
Post by: Hunter on April 21, 2013, 04:59:40 PM
Petermann Yesterday (4-20-13)

Credit to my friend, the Icebridge Navigator



Title: Re: Petermann Glacier/North West Greenland
Post by: Hunter on April 21, 2013, 05:01:20 PM
Petermann Yesterday (4-20-13)

Credit to my friend, the Icebridge Navigator
Title: Re: Petermann Glacier/North West Greenland
Post by: Hunter on April 21, 2013, 05:05:15 PM
Petermann Yesterday (4-20-13)

Credit to my friend, the Icebridge Navigator
Title: Re: Petermann Glacier/North West Greenland
Post by: TerryM on April 21, 2013, 05:36:04 PM
Hunter & Icebridge Navigator


WOW!


Terry
Title: Re: Petermann Glacier/North West Greenland
Post by: anonymous on April 21, 2013, 05:39:59 PM
Hunter & Icebridge Navigator

WOW!

Terry

Exactly. O_O
Title: Re: Petermann Glacier/North West Greenland
Post by: Hunter on April 21, 2013, 05:57:11 PM
Petermann Yesterday (4-20-13)

Credit to my friend, the Icebridge Navigator


(forgot the last 3 pics)
Title: Re: Petermann Glacier/North West Greenland
Post by: Hunter on April 21, 2013, 06:06:04 PM
And im sure someone wants to see the old crashed kee-bird.  You can see some pics of this on google earth and there is a movie about it on youtube, sad story.

http://en.wikipedia.org/wiki/Kee_Bird (http://en.wikipedia.org/wiki/Kee_Bird)
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on April 22, 2013, 06:43:59 AM
Hunter;


Great images thanx!! :)
Title: Re: Petermann Glacier/North West Greenland
Post by: Andreas Muenchow on April 22, 2013, 04:41:53 PM
Awesome pictures of Petermann. Looooove them. I was actually drinking coffee saturday morning watching the P3 flight track in real time, here is my screen-shot that I was planing to turn into a blog post later this week with some of the awesome and very public IceBridge data that the same people and the same plane collected in 2003, 2003, 2007, 2010, and now again in 2013.
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on April 22, 2013, 05:34:06 PM
Hello Andreas;
By checking the above images supplied by Hunter from Petermann, I noticed the first contributory glacier entering from Hall Land (cant find the name) it was just in front of the calving point in July 2012, but now Petermann passed by at some few 100 meters? What is the average speed of Petermann?
Title: Re: Petermann Glacier/North West Greenland
Post by: Andreas Muenchow on April 22, 2013, 08:17:47 PM
@Espen:

The tiny side glacier near the north-western terminus of Petermann Gletscher is not named, I just checked reports by Drs. Coppinger (1876), Koch (1928), and Higgins (1991) who all show this glacier without a name.

Petermann has been advancing historically by about ~1 km/year (Higgins, 1991) which has been increasing to perhaps 1.2 km/year over the last few years. One can see this advance really well from NASA's IceBridge data along identical flight paths that show very distinct topography of the ice and its melt-channels that can be traced from year to year. The attachment shows two slices along the glacier using radar for under-ice and laser altimeter for surface topography from 2010 and 2011. Sliding one into the other for maximum correlation, I get an average speed of 1.26 km/year between these two years.

EDIT: Figure caption contains an error, the glacier is grounded on land near km-0 in the plot. One of my co-authors made me redo all figures for a more pleasing zero reference as the grounding line instead my silly -19 km.
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on April 22, 2013, 08:44:23 PM
Andreas;

Thanx for the answer, so the advance fits my sighting, my current info on grounding from edge is +/- 55 kms.
But I know that glacier got a name (female) as I recall it, but cant find the damn map! Well it is Monday! 
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on June 25, 2013, 09:51:43 PM
Here is an animation of the calving events in 2010 and 2012 plus a fake calving in 2009.
The Petermann Express:
https://docs.google.com/file/d/0B_a0Tecpig0jUTgtU3FhRUIwQ00/edit?usp=sharing
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on June 29, 2013, 04:38:14 PM
Checking out Landsat I stumbled over a fissure I never noticed before, although it is pretty far from the present calving front of Petermann Glestcher (aprox. 65 km). The fissure is located of Kap Bemerton and opposite Porsild Glestcher, and it is about 5 km in length, it may be a thing to watch?

Click on image to enlarge! 
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on June 29, 2013, 06:27:17 PM
I wondered how much the funnel-shaped form of Petermann Fjord has to Petermann Glaciers flow rate. The narrowest point in the fjord is approximately at Edith Glacier at the beginning of the fjord and the widest point is down by Porsild Glacier at the bottom of the fjord. What I find most interesting is that the calving front is now in an area of the fjord which only gets wider and wider, and logically this should affect the glacier's speed and subsequent calvings.
What are your opinions and thoughts about this, below you will find selected width points in the fjord, all points starting from the beginning of the fjord.

Width points at:

Edith Glacier 16,4 km

Unnamed Glacier 18,0 km

Belgrave Glacier 18,8 km (where the calving front is now)

Faith Glacier 19,0 km

Sigurd Berg Glacier 20,6 km

Porsild Glacier 21,4 km
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 16, 2013, 03:26:33 PM
BTW today is the birthday of Pll-2012 :)
Title: Re: Petermann Glacier/North West Greenland
Post by: TerryM on July 16, 2013, 07:30:01 PM
Espen


Weren't you the first to spot it making it's break for freedom? I remember that I wasn't even looking since the fast ice was still in place.
Andreas and his mates managed to get into the Fjord behind PII-2012 while the ice island was still trying to make it into Hall Basin. [size=78%]http://icyseas.org/author/muenchow/ (http://icyseas.org/author/muenchow/)[/size] has some wonderful first hand Arctic exploration accounts of that voyage.


We're a little behind 2012 in Nares Strait this year and this may have an effect on the September Minimum figures. Nares only advects about a tenth of what Fram does, but it's often very thick, MYI that exits there.


I can't imaging a calving event at Petermann this year, but I certainly wasn't expecting one last year either. Every time I think I've figured out something about Arctic ice - it changes.


Terry
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 16, 2013, 07:45:03 PM
No I was "beaten" by Arcticicelost80 but we are talking minutes :)

I don't know when we can expect a new calf, the only fracture worth talking about is of Kap Bemerton well inside the glacier aprox. 65 km from the present calving front. But I expect more action further north Ryder and Ostenfeldt just to mention a few.

Click on image to enlarge!
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 22, 2013, 11:03:38 PM
Just preparing for the season ;):

Please click on image to enlarge!

Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 23, 2013, 12:47:50 PM
With some help from Landsat. This image contains 6 large images and is then reduced to web use, due to "weight" limits on this site.

Please click on image to enlarge!
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 23, 2013, 02:03:21 PM
P2-2012 update:

Please click on image to enlarge!

Title: Re: Petermann Glacier/North West Greenland
Post by: Phil. on July 23, 2013, 07:18:15 PM
Espen


Weren't you the first to spot it making it's break for freedom? I remember that I wasn't even looking since the fast ice was still in place.
Andreas and his mates managed to get into the Fjord behind PII-2012 while the ice island was still trying to make it into Hall Basin. [size=78%]http://icyseas.org/author/muenchow/ (http://icyseas.org/author/muenchow/)[/size] has some wonderful first hand Arctic exploration accounts of that voyage.


We're a little behind 2012 in Nares Strait this year and this may have an effect on the September Minimum figures. Nares only advects about a tenth of what Fram does, but it's often very thick, MYI that exits there.


I can't imaging a calving event at Petermann this year, but I certainly wasn't expecting one last year either. Every time I think I've figured out something about Arctic ice - it changes.


Terry

It looks to me that the 'plug' in the Hall Basin will disintegrate in about a day then I'd expect the fractured ice trapped behind it to head south, also with the back pressure gone I'd expect some fragmentation in the mouth of Petermann.
Title: Re: Petermann Glacier/North West Greenland
Post by: Espen on July 23, 2013, 07:47:48 PM
Phil,

Hall Basin will be cleared in a few days, and the sea ice covered part of Petermann Fjord soon there after.
We may see some mini calvings during August / September but I don't expect a real one, but you never know!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 31, 2013, 02:43:08 PM
Long time no see!

Please click on image to enlarge and for better deatails!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Phil. on July 31, 2013, 02:55:11 PM
Indeed Espen, I was just looking at that same image on MODIS.  It seems to me that there is a slight northern drift in the strait with in situ melting if you compare with the earlier image today.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 31, 2013, 03:53:44 PM
Phil,

Yes; there is a lot of in-situ melting around the clock, Nares, North and North East.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 02, 2013, 11:15:56 AM
Believe it or not, Petermann is preparing a new calf, two new cracks have evolved since June. These 2 new cracks will not result in such large calvings we saw in 2010 and 2012, as they are relatively close to the current calving front, respectively approx. 1 and 2.5 km, but it shows that Petermann Glacier and for that matter the ice sheet is on the move. The landsat image below shows the new fissures.

Please click on the image to enlarge and better details:
Title: Re: Petermann Gletscher / North West Greenland
Post by: no1der on August 02, 2013, 06:26:11 PM
Espen - Could it be that flow from Faith Gl. is causing that part of last year's calving front to flake off?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 02, 2013, 06:30:40 PM
Espen - Could it be that flow from Faith Gl. is causing that part of last year's calving front to flake off?
HI no1der

It may be so, although I have no idea what forces are behind Faith Glacier, but for sure it is a factor in the whole game!

And you are right it will probably be a "flake".
Title: Re: Petermann Gletscher / North West Greenland
Post by: Jmo on August 09, 2013, 01:44:32 AM
Another glimpse through the clouds.
Fairly rapidly approaching the 2012 calving front (though some melt to go yet...).
It is fascinating how dynamic the ice is.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Phil. on August 10, 2013, 05:00:08 PM
Today's MODIS shows melting back to the calving front today.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 11, 2013, 08:03:38 PM
The next calving can be expected anytime soon, that is at least what I can tell from today's Modis image, it will be around 6 km2 and is along the fissure line 1 km from the present calving front I reported above in this thread (August 2 2013).

https://forum.arctic-sea-ice.net/index.php/topic,53.msg11365.html#msg11365 (https://forum.arctic-sea-ice.net/index.php/topic,53.msg11365.html#msg11365)

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013223.aqua.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2013223.aqua.250m)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 12, 2013, 10:43:33 PM
Petermann showed again today:

I believe we had a fringe calving recently?
Look for the arrows.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 14, 2013, 02:13:03 PM
Petermann calving

Seems like we have a little calf? Follow the arrow! Left side of the calving front

Click on image to enlarge!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 17, 2013, 07:11:54 PM
With greetings from Petermann and the rest of Greenland

Canada she is yours now, take good care of her:
Title: Re: Petermann Gletscher / North West Greenland
Post by: weatherintel on August 17, 2013, 07:43:23 PM
Petermann is EXACTLY where it was last year on this date (area wise).  The shape of the terminus and it's position relative to the valleys north and south of it is unchanged. There are no major fractures sen either.  This summer has been the coldest in at least 7 years in NW Greenland as well.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 17, 2013, 08:09:49 PM
weatherintel,


Did you check the name of that iceberg? ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: JMP on August 18, 2013, 01:02:13 AM
This summer has been the coldest  in NW Greenland as well.


One cold summer will hardly put a dent in a glacier's movement. That's just an itty bitty baby wobble  (not even a step) back toward what used to be normal.   The converse - the warmest in at least 7 years - would however have a significant impact being ((dare i say)- another huge step for mankind?) away from what used to be normal.   Peterman calved off a huge amount, 370 km^2  from 2010 to 2012 but that was only maybe 15% of the ice mass lost during that time - the rest being lost to ocean melt. 
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 18, 2013, 10:51:45 PM
Erased wrong dates
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 18, 2013, 11:30:56 PM
Petermann Glacier August 18 2013:

Please click on image/animation to enlarge:
Title: Re: Petermann Gletscher / North West Greenland
Post by: Jmo on August 19, 2013, 06:54:32 AM
Espen - that's interesting.  So those two pieces of ice near the seemingly unchanged terminal face were pushed into the fiord on the wind?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 19, 2013, 07:28:45 AM
Jmo;

When you study the images carefully you will notice something is missing.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Phil. on August 19, 2013, 04:08:43 PM
Nice clear shot on MODIS today.

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013231080500-2013231081000.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013231080500-2013231081000.250m.jpg)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 20, 2013, 12:53:57 PM
Another fringe calving seems to be underway:
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 20, 2013, 02:00:08 PM
Now it is clear a fringe calving happened, and I believe more is coming along those fissures I reported earlier this month

Approx. 5 km2 gone since July

https://forum.arctic-sea-ice.net/index.php/topic,53.msg11365.html#msg11365  :

Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 20, 2013, 02:53:27 PM
A little more info:

Please click on image to enlarge:
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on August 20, 2013, 04:22:20 PM
A little more info:

Please click on image to enlarge:

I have no understanding of the way glaciers behave.

Could this fringe calving which causes this glacier face to recede to match the rest of the glacier front (perhaps this fringe calving would actually cause this area to recede past the bulk of the glacier face) set up Peterman for the next big calving across the center of the glacier?
Title: Re: Petermann Gletscher / North West Greenland
Post by: ghoti on August 20, 2013, 05:58:15 PM
There wouldn't by any chance still be a camera (from "chasing ice") still operating and pointing at the calving front of the glacier would there? That would be too good to be true.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 20, 2013, 07:48:39 PM
Shared Humanity,

I would not be surprised to see another small calving at where the second fissure was, even before this meltseason is over.

Ghoti,

That camera from "chasing ice" I believe was installed at Jakobshavn Glacier.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 20, 2013, 08:25:38 PM
Petermann August 20 2013:

Click on image to start animation.

Title: Re: Petermann Gletscher / North West Greenland
Post by: Phil. on August 22, 2013, 12:21:51 PM
Shared Humanity,

I would not be surprised to see another small calving at where the second fissure was, even before this meltseason is over.


It looks like another small piece broke away yesterday.
Title: Re: Petermann Gletscher / North West Greenland
Post by: jdallen on August 31, 2013, 11:15:08 PM
Greetings all;

New  poster on this thread.  Would anyone care to expound on what implications the mid-Greenland canyon may have on movement of the Petermann Glacier?

Any sense if, with increasing melt, we might actually see sub-glacial flow of melt water out of the channel?

Is it possible some of the changes we are seeing over time might already be driven by meltwater flow?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 31, 2013, 11:55:46 PM
Greetings all;

New  poster on this thread.  Would anyone care to expound on what implications the mid-Greenland canyon may have on movement of the Petermann Glacier?

Any sense if, with increasing melt, we might actually see sub-glacial flow of melt water out of the channel?

Is it possible some of the changes we are seeing over time might already be driven by meltwater flow?

No immediate since it has always been there, but yes, there are melt water channels placed inside Petermann Glacier already, that became a fact a few years ago in a scientific report.

I myself believe the these melt water channels have an important role in the disintegration we see with many glaciers connected to massive ice sheets like eg. GIS.

And I believe these melt water channels were seen  at the recent massive calving at Helheim Glacier on July 24 2013 and onwards, Helheim actually lost about 25% of all glacier ice lost in the period 1972 - 2013 (included), they can be seen here:
 https://forum.arctic-sea-ice.net/index.php/topic,553.msg14149.html#msg14149
please also watch the video in the same thread, the image is captured from that video
Title: Re: Petermann Gletscher / North West Greenland
Post by: Laurent on September 01, 2013, 10:38:26 AM
Petermann will collect the melt water from a very very large area, Jakobshawn collecting area looks small compare to it !
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on September 04, 2013, 04:12:05 PM
Between August 19 and 28 2013 a small piece of ice 0.8 x 1.3 = 1.04 km2 took of from Petermann Glaciers left flank.

Please click on image to enlarge a start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on September 13, 2013, 04:24:39 PM
Nice sunny day at Petermann Fjord, it almost looks like Petermann had some "regrowth" :)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Andreas T on September 14, 2013, 05:17:51 PM
Sorry, this might belong into the stupid questions topic, but where can I find the picture on modis? Is it possible that there is a mistake in the date the picture was taken? With the sun down the glacier the edge is clearly identified, but surely it can't have moved several km since August?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on September 14, 2013, 05:27:14 PM
Sorry, this might belong into the stupid questions topic, but where can I find the picture on modis? Is it possible that there is a mistake in the date the picture was taken? With the sun down the glacier the edge is clearly identified, but surely it can't have moved several km since August?

Here is a Modis link for the same date, showing the "regrowth" ( it is sea ice packed nicely up against the PG calving front)

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2013256190000-2013256190500.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2013256190000-2013256190500.250m.jpg)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Andreas T on September 14, 2013, 05:52:46 PM
Thanks Espen, I shouldn't have doubted you (or have payed more attention to the smiley) :-[  I misread the band of open water for a shadow. The slight difference in colour between the sea ice and the glacier in the high res image shows you are right!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on September 14, 2013, 06:03:16 PM
That is OK Andreas, nice we had this solved before someone jumped on it! ::)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on September 18, 2013, 12:05:48 PM
As reported earlier this season, there is a fissure of Kap Bemerton (Petermann Fjord).
As you can see from this animation below a glacier is a dynamic place, in the period between June 12 and September 10 this year or ~3 months, the glacier moved ~ 300 meters or at a speed about 1.2 km per year.
The size of the fissure did not change much though.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on October 07, 2013, 12:23:06 PM
It is now time to say Good Winter to Petermann Glacier, at least in when it comes to  Modis :-\
Title: Re: Petermann Glacier/North West Greenland
Post by: Andreas T on November 18, 2013, 02:32:23 AM
Checking out Landsat I stumbled over a fissure I never noticed before, although it is pretty far from the present calving front of Petermann Glestcher (aprox. 65 km). The fissure is located of Kap Bemerton and opposite Porsild Glestcher, and it is about 5 km in length, it may be a thing to watch?

Click on image to enlarge!
Trying to learn more about ASAR images, I think that fissure can be seen in April 2012
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/201204010003.ASAR.jpg (http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/201204010003.ASAR.jpg)
sorry if that just makes the wait for the sentinel2 satellite an annoyingly long time :(
My interpretation would be that the radar picks out changes in depth (from satellite) and therefore shows up fissures like the one where the future PII-2012 will seperate 3 months later.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 02, 2014, 07:24:14 PM
First image from Petermann this season, it is an ASAR image from DMI:

Please click on image to enlarge!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 02, 2014, 07:49:42 PM
The New ASAR images from DMI is pretty good calving predicting tool I believe.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 07, 2014, 08:45:35 PM
First image from our friend Petermann courtesy of Modis:

Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 07, 2014, 08:46:54 PM
Now it is spring! ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 08, 2014, 09:00:21 PM
There seems to be loads of snow on top of Petermann this season:
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on March 08, 2014, 10:28:42 PM
There seems to be loads of snow on top of Petermann this season:

Is this net good or bad? Higher albedo may slow this years melt but, if the snow fell early last fall, the increased insulation may have discouraged ice thickening.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 08, 2014, 11:09:57 PM
I don't think more snow cover  makes a difference, it is more important what happening under and in the the glacier, and I don't expect another calving this season, unless it a a very big one!
Title: Re: Petermann Gletscher / North West Greenland
Post by: crandles on March 08, 2014, 11:31:36 PM
I don't think more snow cover  makes a difference, it is more important what happening under and in the the glacier, and I don't expect another calving this season, unless it a a very big one!

I suspect SH is thinking about good or bad for arctic sea ice, as the glacier is obviously above equilibrium thickness so "increased insulation may have discouraged ice thickening" doesn't make sense unless talking about sea ice.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on March 09, 2014, 12:16:58 AM
I don't think more snow cover  makes a difference, it is more important what happening under and in the the glacier, and I don't expect another calving this season, unless it a a very big one!

I suspect SH is thinking about good or bad for arctic sea ice, as the glacier is obviously above equilibrium thickness so "increased insulation may have discouraged ice thickening" doesn't make sense unless talking about sea ice.

Yes, thank you. I meant for sea ice.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 09, 2014, 09:43:04 AM
The only serious fissure to be seen at Petermann Gletscher is at Kap Bemerton, aprox. 30 km from the present calving front, although there are some small fissures at Faith Gletscher.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 14, 2014, 09:36:51 AM
First Landsat 8 image of the season. Cloud free, but the low sun elevation (5 degrees) makes the image somewhat lacking brilliance and detail.

Attached an overview in 30 m resolution. I will add an 15 m cut of the calving front. I am open to suggestions for other details, comparisons with autumn 2013 and details to watch this season.

(you must click the pic for full resolution images)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 14, 2014, 09:40:34 AM
Detail of the previous image but in the highest resolution.

(assuming that you do click the picture)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 18, 2014, 08:17:03 PM
Fantastic images, Wipneus, in 2 months time we will have the Sentinel-1 images too! ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 19, 2014, 06:45:23 AM
Talking about what is  possible with the Sentinel-1 (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Prepping_for_radar_vision) :
Quote
This ‘interferogram’ shows Petermann Glacier grinding towards the sea along the northwestern coast of Greenland. Two Radarsat-2 TOPS images acquired 24 days apart were used to generate it. Radarsat-2 was programmed specially by MDA to work in an experimental imaging mode called Terrain Observation by Progressive Scans (TOPS) in azimuth  to match the way ESA’s Sentinel-1 will image Earth.

Synthetic Aperture Radar Interferometry – or InSAR – is a technique where two or more satellite radar images acquired over the same area are combined to detect large-scale surface changes. Small changes on the ground cause changes in the radar signal phase and lead to rainbow-coloured fringes in the interferogram.

This image shows some stationary and relatively slowly moving features, as well as some large areas of much faster moving ice. The interferometric fringes are widely spaced in the stationary areas and closer together in the centre of the glacier where the ice is moving much faster.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2014%2F03%2Fpetermann_on_the_move%2F14327502-1-eng-GB%2FPetermann_on_the_move_node_full_image.jpg&hash=c79c5fb13bf255d705f5ce8b5334c17c)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Andreas T on March 19, 2014, 08:57:45 AM
Thanks for another great image. At what time of the year was this taken and is there a scale for interference fringes / altitude change?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Laurent on March 19, 2014, 09:58:52 AM
There is something I do not understand, if I read well, they say that the colored parts are the ones that move faster...but how can it be that the interior move and not the exit (Petermann glacier) ?
Title: Re: Petermann Gletscher / North West Greenland
Post by: TerryM on March 19, 2014, 10:49:33 AM
WOW! simply WOW!


Terry
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 19, 2014, 10:54:32 AM
Thanks for another great image. At what time of the year was this taken and is there a scale for interference fringes / altitude change?

I don't know, the image just says released 17/03/2014. But the description indicates it is captured "recently" :

Quote
So that users are fully prepared for the images Sentinel-1A delivers, Canada’s Radarsat-2 was recently programmed by MacDonald, Dettweiler & Associates to scan Earth’s surface using the same novel ‘interferometric’ wide-swath mode technique as Sentinel-1. Consequently, a suite of images was acquired over various sites.

Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 19, 2014, 10:58:17 AM
There is something I do not understand, if I read well, they say that the colored parts are the ones that move faster...but how can it be that the interior move and not the exit (Petermann glacier) ?

My understanding is that large distances between colored bands indicate slower speed. As speed increases the colors come closer and closer together, until they appear no longer separated and blend into the grey. That is why the glacier is grey and the ice covered land has al the colors.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 19, 2014, 10:02:38 PM
It is interesting to see how far inside the flow of ice begins, it is at least the length what we regard as the fjord.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Andreas T on March 20, 2014, 09:05:43 AM
As I understand it the image shows a change in surface elevation. Flow of the ice can of course occur where that surface has a downward gradient but gradient and elevation does not change over time. My question about the timing of the image was therefore about whether this is showing a seasonal change in the ice. Clearly this is only the beginning of some very interesting and useful data. Getting this information over several seasons will show where the ice is getting thinner with amazing detail and coverage.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on March 20, 2014, 04:31:50 PM
OK.....stupid question.

Could the capture of surface changes on the ground be finding both evidence of movement but also melt?
Title: Re: Petermann Gletscher / North West Greenland
Post by: icefest on March 20, 2014, 10:23:33 PM
I'm not sure about whether elevation changes will differentiate movement and melt, but depending of radar wavelength it should be able to detect surface water vs ice.

Please comment if you know if this is false.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Andreas T on March 21, 2014, 01:01:35 AM
I found the answer to one of my questions here https://earth.esa.int/documents/10174/134665/S1-TN-ESA-SY-0452_RSAT_TOPS_InSAR_Scenes_Report  (https://earth.esa.int/documents/10174/134665/S1-TN-ESA-SY-0452_RSAT_TOPS_InSAR_Scenes_Report)
The images on which the interferogram is based were taken on 11.4.2013 and 5.5.2013.
A frequency of 5.4 Gigahertz would mean 2.8cm change in height for each line (my guess, the esa document doesn't seem to give that information)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 21, 2014, 07:11:46 PM
What I meant with the ice flow from deep inside the GIS is better seen within the red line
The same is seen at Jakobshavn, and it is a indicator where  the glacier is heading in the future:
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 23, 2014, 04:45:40 PM
Here is a "new" images compiled of very old Danish aerial images, and long before several calvings:

Please click on image to enlarge.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 23, 2014, 05:29:52 PM
Here is another one of the major glaciers feeding Petermann Gletscher, this time Sigurd Berg Gletscher:

Please click on image to enlarge.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 26, 2014, 12:20:54 PM
Clear weather in abundance in North Greenland it seems.

Here is a medium resolution (60m) overview of a Landsat image of Peterman on March 25. High 15m resolution detail shots will follow, requests will be considered.

Note: I am experimenting with color optimization using ImageMagick, instead of doing it with the Gimp.  This avoids some discretization errors due to the 8 bit limitation of the Gimp, but I am not really happy with the result yet. The "adjust white balance" button in the Gimp works better.

Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 26, 2014, 12:40:42 PM
Hi-res (15m) cut-out of the calving front. It is worthwhile to zoom into the image to see the details.
You can see several cracks that can lead to new calving at some time.

Belgrave Glacier in the upper right, Faith Glacier in the dark lower left corner.

BTW, sun elevation is still a low 10.5 degrees.

(picture needs a click for full res image)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 26, 2014, 01:03:31 PM
Hi -res (15m) cut -out upstream of the calving front. The big crack is above Cape Bemerton, to the right is (I think) Porsild Glacier.

(no fun if you do not click the picture)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 26, 2014, 06:01:00 PM
Wipneus,

What would we we do without your magic? ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: TerryM on March 27, 2014, 05:26:21 PM
Wipneus


Would it be possible to get one of your great images of the MYI piece that's acting as the northern ice dam in Nares Strait? The stability of this formation may have an effect on Arctic sea ice lost this season.


Terry
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 27, 2014, 06:46:48 PM

Would it be possible to get one of your great images of the MYI piece that's acting as the northern ice dam in Nares Strait? The stability of this formation may have an effect on Arctic sea ice lost this season.


Terry,

I am afraid we may not have that luck. The dam is at the limit of Landsat 8 high latitude reach.

In the attached image you see images at path,row: 44,1 and 46,1.  That is the nearest images in the whole Landsat 8 archive (2013 and 2014).

As I see it we need path,row=45,1  to see some part of the dam. There is none in the archive.

Landsat images apparently are very spotty, at the northern latitudes there is a lot of overlapping orbits so I get multiple opportunities at Peterman and Zachariae/N79.

At least the weather is favorable, much better than in 2013 until so far.

Screenshot of USGS Earth explorer: http://earthexplorer.usgs.gov/ (http://earthexplorer.usgs.gov/):
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on March 27, 2014, 07:13:21 PM
Wipneus and Terry,

The images will come later there is an image (LC80372472013137LGN01) from May 17 2013, but they are rare?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 28, 2014, 07:33:26 AM
Espen I forgot the ascending paths. That is normally the night side, but during the arctic summer we  will have to consider those as well.

Unfortunately current images are not extending that far north yet, attached IR image near Scoresby Sound is has a center latitude of about 71 degrees and is about as far north as we can get them now.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Wipneus on March 28, 2014, 07:38:36 AM
Espen, if I search the scene LC80372472013137LGN01 that you found, Earth Explorer reports the row as 882. As the maximum row count is 248, I guess the image is rare indeed.
Title: Re: Petermann Gletscher / North West Greenland
Post by: TerryM on March 28, 2014, 08:30:42 AM
Thanks so much for your efforts. The ice dam will break in it's own time & I was only hoping that an image might indicate how robust it is.
Without the interference of PII-2012 Nares Strait will allow more of the old MYI from Lincoln Sea to drain than was the case in 2013 & I believe that this blockage played some part in the high minimums we experienced last year.
I guiltily confess to hoping that we will have a large enough ice retreat that TPTB will finally take notice, though after the tepid response to 2012 I suppose that's a chimera. Perhaps a vicious el nino and the destruction that will entail will do the trick, but something has to affect the BAU playbook that almost every government now seems intent on following.
Michael Mann's dating of a 2C rise to 2036 should have been a wakeup call for anyone interested in self preservation but the MSM and governments more interested in petro dollars than the next generation seem to have swept it under the rug. I'll feel terrible for all those who are destroyed by whatever cataclysm it is that finally drives the message home but scientific reasoning and logical arguments have fallen on deaf ears.
Sorry for the rant.
Terry
Title: Re: Petermann Gletscher / North West Greenland
Post by: Jim Hunt on March 30, 2014, 07:21:58 PM
Terry - Have you seen the latest DMI RadarSat images?  Go to http://ocean.dmi.dk/arctic/kennedy.uk.php (http://ocean.dmi.dk/arctic/kennedy.uk.php) and search through the ASAR archive. By way of example:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FKennedy%2F20140326rs02.ASAR.jpg&hash=f1107fc52cefd74aa44f4fe06b1225a5)
Title: Re: Petermann Gletscher / North West Greenland
Post by: mspelto on April 19, 2014, 12:44:22 PM
It is evident in spring 2014 that there is no rift that is substantial enough to predict an imminent large calving event. 
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on April 19, 2014, 01:01:56 PM
It is evident in spring 2014 that there is no rift that is substantial enough to predict an imminent large calving event.

I agree, there may be some minor calvings due to 2 fissures at the southern edge. The Kap Bemerton fissure is to far away, though.: Image courtesy of Wipneus / Landsat
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on April 19, 2014, 03:19:22 PM
If you follow those two crevasse that you've pointed out in a gentle curve to the most active calving portion of the glacier face, it looks as if there are cracks/crevasses that align fairly well with these two. Could this entire portion of the calving front be at risk of calving and, if so, is this still a minor calving event?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on April 19, 2014, 03:27:11 PM
If you follow those two crevasse that you've pointed out in a gentle curve to the most active calving portion of the glacier face, it looks as if there are cracks/crevasses that align fairly well with these two. Could this entire portion of the calving front be at risk of calving and, if so, is this still a minor calving event?

Minor? At least compared to the more recent calvings.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on April 19, 2014, 03:31:26 PM
If you follow those two crevasse that you've pointed out in a gentle curve to the most active calving portion of the glacier face, it looks as if there are cracks/crevasses that align fairly well with these two. Could this entire portion of the calving front be at risk of calving and, if so, is this still a minor calving event?

Minor? At least compared to the more recent calvings.

Thanks Espen, so, one more question. Given the landfast portion of the glacier front seems more resistant to calving, if this landfast portion were to calve, would this expose the more active portion of the calving front to more rapid retreat?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on April 19, 2014, 03:39:05 PM
If you follow those two crevasse that you've pointed out in a gentle curve to the most active calving portion of the glacier face, it looks as if there are cracks/crevasses that align fairly well with these two. Could this entire portion of the calving front be at risk of calving and, if so, is this still a minor calving event?

Minor? At least compared to the more recent calvings.



Thanks Espen, so, one more question. Given the landfast portion of the glacier front seems more resistant to calving, if this landfast portion were to calve, would this expose the more active portion of the calving front to more rapid retreat?

If these fissures will result in a calving, it will probably "only" be involving a third of the present calving front (+/- 6 km).
Title: Re: Petermann Gletscher / North West Greenland
Post by: sidd on April 20, 2014, 11:45:11 PM
Comparison of surface and bedrock. Note the kinks where surface contour crosses bedrock canyons. Csatho saw this also, in 2006. For more such comparison and some of Csatho's work, please see

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

sidd
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on April 26, 2014, 12:12:10 PM
There is 1 year between these 2 frames (April 25 2013 and April 25 2014), the scene is the fissure at Kap Bemerton (Petermann Gletscher):

Notice in the second animation from Petermann Front, the 2nd fissure at the left is developing, could be the next calving reason?

Please click on image to start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on April 26, 2014, 02:26:07 PM
New fissures, this image is from April 25 and is also seen in the animation above, I have encircled the newly developed fissures, they follow a same pattern as pre-calvings.

Please click on image to enlarge!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on May 16, 2014, 09:35:02 AM
Fissure update.

The fissures observed at the Northern shore of Petermann between Kap Eisendecher (Hubert Glacier) and Kap Fulford (Sigurd Berg Glacier) seems to develop into something that may lay the foundation for another major calving in the future (encircled #1).
The fissure seen at Kap Bemerton on the opposite shore is all ready known (encircled # 2). 

Please click on image to enlarge!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on May 22, 2014, 06:01:11 PM
Petermann update. Fissures in progress. See the red encircled areas:

Please click on image to start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 01, 2014, 10:20:53 AM
Fissure development, one of the fissures reported above is getting more pronounced now, the fissure is encircled in red in the animation below:

2nd image is May 31 2014 and not May 31 2013.

Please click on the image to start animation! 
Title: Re: Petermann Gletscher / North West Greenland
Post by: icefest on June 01, 2014, 10:51:02 AM
I'm assuming that's meant to say 2014.

Do you have any images from the same time last year so we can compare how much of the increased fissure visibility is due to melting snow and how much due to an increase of the fissure size?
i.e. compare 29-apr-13/31-may-13 to 29-apr-14/31-may-14
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 01, 2014, 11:27:09 AM
I'm assuming that's meant to say 2014.

Do you have any images from the same time last year so we can compare how much of the increased fissure visibility is due to melting snow and how much due to an increase of the fissure size?
i.e. compare 29-apr-13/31-may-13 to 29-apr-14/31-may-14

The aniamtion is based on April 29 2013 and May 31 2014.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on June 01, 2014, 03:17:21 PM
Espen......

I love your animations  of the various  glaciers. I look at them every time you post one. Heck, I look at every non-animated image as well.

As I've scanned these images, it's becoming very clear that you can find repeating patterns of fractures as you move away from the calving face. These fractures often (not always) mimic the shape of the calving face. The images follow this pattern on both of the grounded sides of the glacier. I will often follow the pattern further away from the calving face to see where the next fracture will appear. I may be kidding myself but I can frequently see where these will occur.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 01, 2014, 05:17:51 PM
Shared Humanity,

Yes Landsat 8 is a goldmine when it comes to evidence, just wished I had the same capacity as Wipneus to further dig into it :-[
Title: Re: Petermann Gletscher / North West Greenland
Post by: johnm33 on June 01, 2014, 06:19:17 PM
I always check out, and appreciate these animations too, this one however looks more to do with the sun being first aligned with then at 90deg. ish to the fissures.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 01, 2014, 06:56:05 PM
I always check out, and appreciate these animations too, this one however looks more to do with the sun being first aligned with then at 90deg. ish to the fissures.

Hello Johnm33,

That may be so, but then we need an explanation why the 2 fissures in front, not do the same?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Yuha on June 01, 2014, 07:09:42 PM
Thanks for the images and animations, Espen.
A couple of observations about the latest:

There seems to be a very minor calving happening on the right-hand side.

Those brown stains on the right margin in the May image are probably melt water off the banks.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 10, 2014, 08:51:02 PM
The fissures mentioned above are definitely expanding.

Please click on image to start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on June 28, 2014, 02:04:32 PM
Petermann update:

In the animation below you will find 4 spots of interest.

1. A fissure to crack development, although this crack is a part of the melt water channel system, it is also a crack on its own, and a possible mother crack for a future major calving.

2. This crack, just outside Belgrave and Hubert Glaciers, will probably already this season result in a minor calving.

3. The 2 cracks seen left of Faith Gletscher, will probably soon result in a worth to mention calving.

4. Between May 25 2014 and June 27 2014, Petermann Gletscher moved ~ 120 meters, measured at the major melt water river outlet.

Please click on image to start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 05, 2014, 07:59:18 PM
Reminder of the good old days:

Please click on the image to start animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: crandles on July 05, 2014, 08:07:11 PM
Looks like second image is 2014 not 2006  ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 05, 2014, 08:12:13 PM
Looks like second image is 2014 not 2006  ;)

Corrected thanks! ;)
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 07, 2014, 06:43:55 PM
Further crack expansion near the calving front just outside Hubert Gletscher and Belgrave Gletscher:

Please click on image to start the animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 13, 2014, 09:41:40 PM
Washington Land situated between Petermann Gletscher to the north, Humboldt Gletscher to the south and Nares Strait to the west, and a future large island when the ice is gone.
Over the last 38 years we can watch how the ice fields (iskapper) are getting smaller and smaller:

Please click on the image to start the animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 16, 2014, 07:48:51 AM
The chances of having Petermann calving this season is increasing by the days:

 
Title: Re: Petermann Gletscher / North West Greenland
Post by: Sonia on July 16, 2014, 12:49:34 PM
Those cracks on the southern side look more prominent as well.  Also very interesting in that image is how the melt ponds on the sea ice all all disappeared.  I imagine this is from the ice decompressing following the Nares breakup.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on July 16, 2014, 02:29:18 PM
Those cracks on the southern side look more prominent as well.  Also very interesting in that image is how the melt ponds on the sea ice all all disappeared.  I imagine this is from the ice decompressing following the Nares breakup.

Wouldn't that be pond drainage?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Sonia on July 16, 2014, 02:56:41 PM
Those cracks on the southern side look more prominent as well.  Also very interesting in that image is how the melt ponds on the sea ice all all disappeared.  I imagine this is from the ice decompressing following the Nares breakup.

Wouldn't that be pond drainage?

Right.  I'm thinking that as the ice is allowed to expand down the fjord, the "seals" break on the ponds and they drain.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 21, 2014, 07:03:40 AM
Further crack development:

Please click on image to start animation!

Title: Re: Petermann Gletscher / North West Greenland
Post by: Shared Humanity on July 21, 2014, 12:23:20 PM
Espen..

What is that  trail of visible brown surface that extends along  the eastern length of the glacier? Is it soil debris that  has been picked up, transported and exposed by melt?
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on July 21, 2014, 05:33:30 PM
Espen..

What is that  trail of visible brown surface that extends along  the eastern length of the glacier? Is it soil debris that  has been picked up, transported and exposed by melt?
Yes it is sand/rock debris which originates from a desert like place in Hellerup Land (just behind Kap Agnes) between Sigurd Berg Gletscher and the very large Porsild Gletscher.
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 01, 2014, 09:32:51 PM
On the day of the calving at Ryder Gletscher, a very similar glacier to Petermann Gletscher in most ways, only the size is the difference, as only women know the importance of!
It is time for a fissure / crack update. As you can see from the animation below there is plenty of room for many headlines in the near future (within a few years), so don't worry if the sea ice don't go your way, there is always the glaciers. The potential future calving events are encircled in red:

Please click on image to start the animation!
Title: Re: Petermann Gletscher / North West Greenland
Post by: Espen on August 05, 2014, 03:49:54 PM
Petermann Calving?

This is only a modis image from today, that little piece mentioned above may have calved already?

Will be updated as soon better images are available!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 21, 2014, 05:07:16 PM
The ice peninsula in front of Belgrave Glacier took off:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: solartim27 on September 08, 2014, 11:11:27 PM
The calving face did a big drop off over the last week:

Day 244:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2014244.terra.1km.jpg (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2014244.terra.1km.jpg)

Day 251:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2014251.terra.1km.jpg (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2014251.terra.1km.jpg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: solartim27 on September 08, 2014, 11:16:45 PM
Looking at reply #110 above, it looks like some ice rubble might just have floated away, as opposed to a calving event.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on February 12, 2015, 01:53:04 PM
The first high resolution (10m/pix)  Ground Range Detected ( GRD) data covering the Petermann calving front entered the ESA Sentinel public archive ( aka datahub).

I think it is fantastic (click on the picture for the full image) Sorry that I had to reduce the resolution to 20m/pix for a reasonable image size.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on February 12, 2015, 02:00:43 PM
Nice image, it is easy to see where the next potential calving point is.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: cats on February 13, 2015, 12:17:33 AM
Anreas Muenchow has an interesting new post on Petermann over at his blog - http://icyseas.org/2015/02/08/lab-notes-of-a-physical-oceanographer/ (http://icyseas.org/2015/02/08/lab-notes-of-a-physical-oceanographer/) - he is hoping to install some instruments on Petermann this summer - hoping to crowdfund this project (see https://experiment.com/projects/ocean-warming-under-a-greenland-glacier (https://experiment.com/projects/ocean-warming-under-a-greenland-glacier) )
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on February 27, 2015, 08:00:23 AM
Contours from Morlinghem
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on February 28, 2015, 04:05:47 PM
Nice. It's been a puzzle how the Grand Canyon actually connects up to exit through Petermann, especially how it gets past that 600 m knob. The canyon has left little trace in the glacier outlet proper, that has all been over-written by glacial erosion and differential isostatic depression. Even though the canyon is quite broad with gently sloped walls, the Petermann channel is several times wider and deeper, so clearly cannot be attributed to canyon water erosion.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 01, 2015, 02:04:13 PM
The Morlighem .nc bedrock files only use radar sounding data up through 2013. This provides the opportunity to use the 2014 flight segments in the Petermann area to test the accuracy of bottom topography and its interpolation.

The images below show two radar segments from 2014 that go down the lower region of Petermann Glacier proper, an area below sea level on the contour map above. They would have to be co-registered with the contour map to probe its accuracy.

Note that 2014 is the very first year that Cresis has labelled the vertical axis with WGS-84 geoid elevations, ie zero is zero (sea level). This key reference level can be carried transitively to recalibrate depth from flight segment from other years that a 2014 path intersects, and so on to all earlier years.

The radar squiggles have been interpreted by Muenchow 2014 as bottom crevasses in the Petermann ice sheet. That paper called attention to an area of dramatic crevasses but less striking ones occur across the whole channel (extrapolating from the five along-channel overflights). These may contribute to current melting and future calving.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 03, 2015, 11:59:30 AM
Here is an annotated version of the flexure hinge that marks the start of Petermann's bottom crevasse zone. Click on the first image to see full size. The along-glacier flight is on the west side of the glacier (red track in GooglE, second image); all 8 north-south tracks show the same pattern: the 17 km long crevasse zone extends east-west across the entire glacier.

The hillshaded surface elevation map shows ice has piled up just south of the hinge line, as expected from the abrupt change in surface slope. It is 48 km from the start of the hinge line to the glacier's calving front.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 03, 2015, 03:19:07 PM
Here is the full set of available north-south radargrams through the crevasse zone of Petermann glacier. These thumbnails allow for a quick comparison of this zone to show how it varies from east to west. There are no flight segments directly perpendicular to the glacier channel but the next post will provide several diagonal transects, some of which are nearly orthogonal.

Short of a program specifically targeted to the crevasse zone, this ensemble provides the best possible sense of the structure and variability of the bottom crevasse field (which has no surface manifestations). It may be possible to track individual crevasses through pattern matching -- some may extend from wall to wall -- though the radar resolution may not be enough.

Other than a brief mention in Muenchow 2014, this crevasse zone does not seem to have a literature even though it was clearly documented in 1997 overflights.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 04, 2015, 01:08:58 PM
The images below show 4 transects of the Petermann glacier in the crevasse zone. Vertical lines show where they meet the previously described along-channel slice through the zone. As with the upheaval region to the south, these not-quite orthogonal sections help in reconstructing a three-dimensional view of the crevasse area.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 05, 2015, 12:22:07 PM
Petermann glacier, being so far north, is very favorable for Landsat8, with almost daily coverage. The scene below, from Sep 2014, shows cross-hatched surface features in the crevasse zone. It's not clear what these represent nor whether they have any connection to the crevasse features shown above.

A number of melt lake feature can be seen, these peak much later in the season than say Jakobshavn. The melange in front of the calving front is also much later to melt out.

It is not so easy to place a lat,lon grid on EarthExplorer Landsat images. One method is to use the lat,lon of the four corners that are provided in metadata and interpolate under the assumption of a regular mercator grid. The other is to view the preview image as a 'street map' as more lat,lon grid numbers are visible (instead of being white on white as in satellite view).

Unlike Jakobshaven, the underlying Google Earth map has only a fuzzy worldview image at high zoom levels (even though incredibly clear 15 m Landsat images are in the public domain). The second image below provides a coordinate system for the crevasse system and some key fixed rock features seen in almost all scenes that allows for correlation of visible and ice-penetrating radar imagery.

The final image shows the calving front in mid-August of 2014 quite a distance from the crevasse zone.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 06, 2015, 02:05:59 PM
I consider it 'cheating' to actually look at prior publications on Petermann before analyzing the data first myself. Some of these papers are excellent but others look nutty today (in light of data that became available later). Petermann mostly gets in the news for its mammoth big calving events but not so much for 'awakening' or sea level rise (to which floating ice shelves don't contribute).

There are a couple more things to do here such as put the glacier's grounding line to images above, rescale some to less spikey 1:1, and add more Greenland place names, but more importantly look for possible connections between the floating shelf, hinge line, subglacial melt channels, crevasse zone, termination of the upheaval region, and entrance of the not-so-Grand Canyon to the main glacial channel.

Looking now at two ice penetrating radar images from last summer 20140505_01_036, 20140502_01_010 and their earlier low resolution connector 20030514_01_011, it is clear that a small relic of the upheaval zone continues into the confined region of Petermann glacier.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 08, 2015, 09:24:38 PM
First image from Petermann by Modis:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 09, 2015, 03:37:21 PM
Below, the first image tracks back the only upheaval to enter the glacier outlet proper. This is quite complicated to do because Cresis does not use a consistent depth scale except for 2014 where elevations are finally given sensibly (ie relative to WGS84 geodetic datum). I used the 2014 segments wherever possible. Otherwise the meter scale is arbitrarily offset on every flight segment, of every flight with 0 having no fixed meaning relative to sea level.

It is a real mystery why no one from the glaciological community intervened during the first 21 years of the program. No use has ever been made of these radar images other than bed topography.

The second image shows 7 consecutive segments of this upheaval feature at 10 km width and 5:1 vertical exaggeration. Click to see it at the (2014's) original resolution. The path spans 126 km but is by no means the end of this upheaval ridge (see earlier Petermann Grid tracebacks in the subglacial topography forum) . By the two southernmost scenes, the ridge has joined the main massive upheaval zone.

The third image shows a 10 km section of the fourth and tallest segment (~700 m) at 1:1 scale. This has the effect of rounding off an impossibly steep upheaval to a rounded hill that represents a section through a long ridge. There is no known explanation for the radar structure; the dark bands bear no relationship to overall ice isochron stratigraphy but may reflect density contrasts or impurities.

The final image shows a continuous down-glacier flight path from 1997 for purposes of providing a uniform depiction of bedrock and surface elevations. It passes slightly to the west of the upheaval at 80.266º. Note once again convergence at the crevasses zone of gradually shoaling bedrock and rapidly plunging ice surface elevation, which would be more subtle using something less than provided 29.9:1 scale.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 12, 2015, 12:57:39 PM
I've been looking at five concepts for the Petermann-Humboldt sector using ice penetrating radar data from 1995-2014:

-- the old ice layer cake stratigraphy continues right up to and even into Petermann proper on its western wall indicting slow movement and unexceptional history for ~125 kyr, applicable to all of Humboldt as well yet only Petermann has the massive upheaval features.

-- Humboldt is the broadest marine outlet glacier in Greenland but this is an accident of geography, not the result of past glacial excavation; Petermann has classical steep fjord walls but no glacial overdeepenings (like Jakobshavn) but instead a bedrock hump indicating it has never been a large volume ice conveyance.

-- the radar data itself, discarding kriging artifacts connecting adjacent basins, does not support the not-so-Grand Canyon making the published big bend westward into the entrance to Petermann Glacier (ie south of Kap Egedesminde) but instead a route north and east of the rock ridge east of Petermann never entering it.

-- the grounding line is where it is because of a paleo debris wedge partly excavated by Porsild glacier entering from the east

Seismic Architecture and Geometry of Glacial Grounding-Zone Wedges from Greenland and North Africa
C Decalf, E Fugelli, J Dowdeswell
AAPG 3P Oct 2013
http://www.searchanddiscovery.com/documents/2013/30310decalf/ndx_decalf.pdf (http://www.searchanddiscovery.com/documents/2013/30310decalf/ndx_decalf.pdf)

Ice-sheet grounding-zone wedges (GZWs) on high-latitude continental margins
CL Batchelor, JA Dowdeswell
Marine Geology 363 65–92 2015
https://www.sciencedirect.com/science/article/pii/S0025322715000304?np=y (https://www.sciencedirect.com/science/article/pii/S0025322715000304?np=y)

Seismic architecture and geometry of grounding-zone wedges formed at the marine margins of past ice sheets
JA Dowdeswell, E Fugelli
GSA Bulletin 124 1750-1761 2012
http://gsabulletin.gsapubs.org/content/early/2012/09/13/B30628.1 (http://gsabulletin.gsapubs.org/content/early/2012/09/13/B30628.1)

-- Petermann, currently moving 3 m/day (a tenth the speed of Jakobshavn), will likewise speed up once the last of its floating ice shelf disintegrates this decade. However the curvature of its smaller basin defined by two summit ridge forks and its narrowing exit funnel geometry (noted earlier here by Espen) requiring flow convergence have major implications for near-term future ice flow given its incompressibility of ice and the need for mass conservation.

None of these considerations seems to explain the association of the upheaval zone and the long ridge described above with Petermann's velocity field, nor the observed similarity with the upheaval zone of Zachariae on the low accumulation side of the summit ridge.

The 2014 radar imagery below, not available at the time of the Bamber 2013 Grand Canyon paper, show the canyon does not now, nor did it ever, drain into the entrance of Petermann fjord. This is established beyond any doubt by placement of 20140505_01_036, 20140502_01_011, 20140505_01_038 etc of Cresis 'good_kml' coordinates on Google Earth.

The topography of the former drainage has been greatly rearranged from what we see today by compression of bedrock by the weight of overlying ice. The gentle swale called the Grand Canyon, 10:1 vertical scale exaggeration below, has little relevance to ice flow in Greenland today.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on March 12, 2015, 04:46:24 PM
-- Petermann, currently moving 3 m/day (a tenth the speed of Jakobshavn), will likewise speed up once the last of its floating ice shelf disintegrates this decade.
Why do you prophesize ice shelf disintegration, is the ocean warming up at a relevant depth? As far as I can remember the grounding line is stable and there's not much thinning or speed-up so I'm wondering why you think the ice-shelf will be gone in an instant?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 12, 2015, 05:01:17 PM
As A-Team mentioned above Petermann is definitely moving, this animation show how much in 6 months: 
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 12, 2015, 06:21:34 PM
-- Petermann, currently moving 3 m/day (a tenth the speed of Jakobshavn), will likewise speed up once the last of its floating ice shelf disintegrates this decade.

That would be a surprise?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 12, 2015, 08:49:37 PM
As A-Team mentioned above Petermann is definitely moving, this animation show how much in 6 months:

It is interesting to watch that the tongue of Belgrave Gletcher *) is withstanding the pressure of Petermann?

*) The glacier at the front to the right of Petermann.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 13, 2015, 12:17:31 AM
Quote
Why prophesize ice shelf disintegration, is the ocean warming up at a relevant depth?  The grounding line is stable and there's not much thinning or speed-up
It doesn't take long when 25% of the ice tongue can be lost in a single year so yes I expect all the post-hinge line ice that you see today will have gone out to sea, as happened at Jakobshavn (attributed there to warming ocean). It's easy to find and follow distinctive fixed markers in the ice in either Landsat or Sentinel; five years out is a testable prediction, unlike climate 200 years out, safely beyond accountability.

However, just as a small tongue at Jakobshavn gets replenished each winter, new thin floating ice will replace calved ice at Petermann indefinitely. The issue with Greenland and Petermann in particular, is whether it will ever be a significant contributor to sea level rise. Pick your favorite flux gate here, it doesn't matter where up-channel of the grounding line. The reality is, if ice flux doesn't change at the Parca gates, we are not even talking a mm of sea level rise from here.

Petermann is a totally one-off situation that is not productively compared to other Greenland or Antarctic glaciers:

Quote
Interannual changes of the floating ice shelf of Petermann Gletscher from 2000 to 2012
A Muenchow et al
Journal of Glaciology, Vol. 60, No. 221, 2014 doi: 10.3189/2014JoG13J13
http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf)

Petermann Gletscher, northwest Greenland, drains 4% of the Greenland ice sheet into Nares Strait. Its floating ice shelf retreated from 81 to 48km in length during two large calving events in 2010 and 2012. We document changes in the three-dimensional ice-shelf structure from 2000 to 2012 using repeated tracks of airborne laser altimetry and ice radio-echo sounding, laser altimetry and visible imagery.

The recent ice-shelf velocity measured by tracking surface features between flights in 2010 and 2011 s 1.25km/yr, 15–30% faster than estimates made before 2010. The steady-state along-flow ice divergence represents 6.3 Gt/yr mass loss through basal melting (5 Gt/yr) and surface melting and sublimation (1.0 Gt/yr).

Airborne laser altimeter data reveal thinning, both along a thin central channel and on the thicker ambient ice shelf. From 2007 to 2010 the ice shelf thinned by 5m/yr, which represents a non-steady mass loss of 4.1 Gt/yr . We suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events.
My sense is far too much attention is being paid to nostalgic topics such as iceberg hazards where the deeper issues with Petermann's future have not so much do with attention-getting calving events (aka loss of buttressing). While the ocean is indeed warming (not as fast as the Zachariae side), there is a surprising amount of melt above and below for 80º N and even visible side melange.

However Petermann has gone through warm millennia before, both in the Holocene and Eemian, and even very rapidly ramped warming. On these, we don't have to opinionate on short-term trends because the past is right there in 125 kyr of ice penetrating radar record, once we get past some rubbish and neglect.

As noted earlier, after mopping up a few more things on the remote sensing record for the Humboldt/Petermann basin, a transition to literature review is definitely in order, probably starting with the 2012 paper below and the 21 that cite it (eg the Muenchow paper above). 

The response of Petermann Glacier to large calving events and its future stability in the context of atmospheric andoceanic warming
FM Nick et al
Journal of Glaciology, Vol. 58, No. 208, 2012 doi: 10.3189/2012JoG11J242
http://ftp.vub.ac.be/~fpattyn/papers/Nick2012_JGLAC.pdf (http://ftp.vub.ac.be/~fpattyn/papers/Nick2012_JGLAC.pdf)

Quote
Despite some publicity to the contrary, neither the observations nor the model results point to a significant effect
from the loss of 25% of the floating ice tongue on the flow of Petermann Glacier. The cause lies in the low level of back-
stress provided by the ice shelf at or near the glacier front.

From our numerical modelling, we conclude that marine outlet glaciers with a long and relatively thin ice shelf are
not sensitive to changes in their terminus region.

From combined velocity observations and model results, we conclude that the seasonal variations in the velocity of Petermann Glacier are mainly controlled by surface melt and consequently enhanced basal lubrication, and to a lesser extent by frontal back pressure caused by ice melange or sea ice.

Our results further show a dominating influence of sub-shelf ocean melt on future glacier stability. This emphasizes
the urgent need for more observations of fjord temperatures and heat circulation.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 13, 2015, 12:44:59 AM
Quote
note the tongue of Belgrave Gletcher, the northeastern-most contributing glacier, is still discharging despite the pressure of Petermann unlike several of the tributatary glaciers to the south

Place names in the interior are hard to come by -- note Espen's nice earlier compilation on this forum. I am still looking for a proper name for 'Arrowhead Island' at the southwest entrance. Pilespids ø?

Here is a brand new compilation of 733 Greenland glacier names. It comes as an excel table with lat,lon but no accompanying map (!!!) with the glacier names attached. The ones for NW Greenland (listed under Qaanaaq) are extracted below. It would be feasible to load these into Google Earth -- surely this was the job of the authors, not the readers

Getting Greenland’s glaciers right – a new dataset of all official Greenlandic glacier names
AA Bjørk et al
http://www.the-cryosphere-discuss.net/9/1593/2015/tcd-9-1593-2015.pdf (http://www.the-cryosphere-discuss.net/9/1593/2015/tcd-9-1593-2015.pdf)

This site has quite a few obscure Kaps like Schoubye and glaciers like Porsild, all slightly misplaced: http://mapcarta.com/19187754 (http://mapcarta.com/19187754)

Espen has also grabbed the very first Landsat-8 of 2015 Petermann. These will soon pile on because of the polar orbit, the azimuth being rather oblique if accustomed to ~180º of Jakobshavn. Long shadows are cast by steep high walls on the upper west end of the channel on much of the Petermann imagery which otherwise can be extraordinarily sharp.

LC80380022015070LGN00
Sun Elevation 5.45403859
Sun Azimuth -154.85800992

Academy Gletsjer   77.2345   -65.3164
Bamse Gletsjer   78.0224   -72.1669
Berlingske Bræ   77.0607   -69.4712
Bowdoin Gletsjer   77.6934   -68.5829
Brother John Gletsjer   78.2834   -72.2654
Bryant Gletsjer   77.5257   -69.3009
Bu Gletsjer   78.0598   -72.2383
Cecil Gletsjer   80.8651   -61.7795
Chamberlin Gletsjer   76.719   -68.4795
Child Gletsjer   78.0717   -72.4301
Clements Markham Gletsjer   77.9475   -71.8501
Cluett Gletsjer   76.1741   -68.3171
Constance Gletsjer   81.0778   -62.4186
Diebitsch Gletsjer   77.9521   -71.5907
Döcker Smith Gletsjer   76.3   -61.7666
Dodge Gletsjer   78.1761   -72.6796
East Branch Gletsjer   77.7336   -68.3524
Edith Gletsjer   81.058   -62.19
Faith Gletsjer   80.9504   -61.8693
Fan Gletsjer   77.5629   -69.6524
Farquhar Gletsjer   77.7   -66.233
Gable Gletsjer   77.6167   -68.1828
Gade Gletsjer   76.3833   -62.7665
Gnom Gletsjer   77.6059   -68.7698
Harald Moltke Bræ   76.5797   -67.626
Hart Gletsjer   77.6991   -67.1759
Heilprin Gletsjer   77.5167   -65.6664
Helland Gletsjer   76.2533   -64.8682
Hermiarrupaluk   77.4312   -70.4834
Hermiarrupaluk   77.5009   -68.7533
Hermiarrurruaq   77.4494   -70.6344
Hermipaluk   75.9394   -66.5167
Hermipaluk   76.0473   -65.5518
Hermipaluk   77.2065   -70.4837
Hiawatha Gletsjer   78.8203   -67.0518
Hubbard Gletsjer   77.6025   -67.7419
Humboldt Gletsjer   79.4462   -63.3957
Hundetunge Gletsjer   76.8413   -67.2557
Hurlbut Gletsjer   77.3618   -67.9872
Illuluarsuit Gletsjer   77.8108   -70.9613
Ivar Berendsen Gletsjer   76.9406   -70.0698
Kiatak Gletsjer   77.3403   -71.6945
Kissel Gletsjer   77.4323   -72.2135
Knud Rasmussen Gletsjer   76.7578   -67.7971
Kong Oscar Gletsjer   75.989   -59.8575
Kumait Hermiat   76.0655   -65.6468
Leidy Gletsjer   77.2562   -65.977
Marie Gletsjer   77.2069   -66.0029
Meehan Gletsjer   77.88   -70.2973
Melville Gletsjer   77.7315   -66.6444
Mirror Gletsjer   77.6777   -68.3207
Mohn Gletsjer   76.2667   -63.7998
Morell Gletsjer   76.3167   -62.4999
Morris Jesup Gletsjer   77.907   -71.0812
Nassersorfik; Naherhorvik   76.0941   -67.7789
Neptune Gletsjer   76.1555   -68.2844
Nordre Tvillinggletsjer   76.7275   -67.0014
Østgletsjer   77.5764   -68.2681
Parish Gletsjer   77.4199   -72.0338
Peary Gletsjer   76.1167   -60.3999
Pituffik GGletsjerletscher   76.2774   -68.5855
Politiken Bræ   77.1602   -69.6024
Qaanaaq Gletsjer   77.4999   -69.1936
Rampen   76.773   -67.0206
Rink Gletsjer   76.2167   -60.9999
Robins Gletsjer   77.4072   -71.8968
Salisbury Gletsjer   76.7229   -68.6739
Savage Gletsjer   77.1858   -69.2548
Savissuaq Gletscher   76.2397   -65.2432
Scarlet Heart Gletsjer   77.6545   -69.4092
Sermipaluk   76.0912   -68.2097
Sharp Gletsjer   77.7167   -66.9496
Siorarsuaq Gletsjer   77.854   -70.6716
Skjulgletsjer   76.85   -66.8329
Søndre Tvillinggletsjer   76.6988   -67.0432
Store Landgletsjer   76.5001   -68.2366
Storm Gletsjer   78.1415   -72.7544
Sun Gletsjer   77.779   -69.4287
Sydgletsjer   77.5602   -68.7785
Tracy Gletsjer   77.6564   -65.9679
Tunnelgletsjer   76.8303   -66.8866
Twin Gletsjer   77.5262   -68.6944
Tyndall Gletsjer   77.1299   -70.7566
Ujarahuhhuarruit Itivtiat   77.3783   -72.2667
Verhoeff Gletsjer   77.8757   -69.8513
Vestgletsjer   77.4072   -72.4525
Witzansky Gletsjer   76.8887   -70.1684
Yngvar Nielsen Gletsjer   76.3334   -64.0831
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on March 13, 2015, 04:02:26 AM
Mr. A-Team remarked: "The gentle swale called the Grand Canyon ... has little relevance to ice flow in Greenland today."

Well, we can see the kink in surface contours above the canyon even in the Bamber data (see my reply 117 on this thread)

I haven't tried this with the Morlinghem data yet

sidd
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 13, 2015, 01:45:17 PM
Quote
Prof. A-Team remarked: "The gentle swale called the Grand Canyon ... has little relevance to ice flow in Greenland today." Well, we can see the kink in surface contours above the canyon even in the Bamber data (see my reply 117 on this thread)I haven't tried this with the Morlinghem data yet
It should not then be a problem to provide notable correlation statistics for people like me who cannot see any particular relationship between surface elevation and swale bedrock topography kinks at the #117 imagery cited. http://membrane.com/sidd/greenland-2013/walkback.html. (http://membrane.com/sidd/greenland-2013/walkback.html.)

Note the swale is filled its entire length with undisturbed stratigraphy right down to Eemian, does not follow the gravitational gradient, nor connect to the sea via Petermann, nor correlate at all with ice upheavals, nor track maximal surface velocity: it has been inactive in transport the last 125 kyr, minimally.

Where are the other channels -- in some cases deeper -- that radar shows are there? The swale is only one feature of  bedrock -- there are many comparable excursions. The same false positive/false negative issues come up in Bell 2014, reading surface elevation tea leaves for upheaval detection.

If surface contours could reveal the swale (considered at 1:1 true scale), why is the Grand Canyon paper dated 2013 when the surface elevation has been known for decades?

Why would the radar bedrock program be funded for 22 years (and counting) if bedrock topographic details could be read off from readily measured surface elevation? There had to have been very broad support for it in both the Greenland and Antarctic research communities: when radar is funded, something else isn't.

Note Morlighem is fill-in refinement, not ab initio bedrock. Models require ice thickness at the outset, severe uniqueness issue arise from just current surface elevation and velocity field. These methods alone have not obtained the bedrock profile, the experimental data from radar was essential.

Looking at low angle shadowed Landsat imagery of the surface, it is surprisingly complicated with many features not yet explained -- large patches of rough surface sitting over large patches of smooth bedrock, and conversely. This shows the level of noise in the surface elevation system relevant to predicting bedrock profile -- which will get a whole lot worse when Howat reaches the Petermann basin with 2 m worldview DEM.

Instead of using heavily kriged interpolation of bedrock (data gaps can be 10,000 km2), it is preferable to directly examine radar transects across the swale looking for consistent dips at the surface. In fact, older stratigraphy does sometimes track bedrock bumps and hollows (after high pass filtering) but this is rapidly damped out during times of epic melt and Holocene ice horizons, themselves overlain by upper layers of unconsolidated firn and drifted snowfall. The problem comes elsewhere -- the surface dips but the bedrock doesn't.

Using the recent Sentinel, the 15 m shadowed Landsat of lower Petermann surface of 11 Mar 15 below and the surface velocity map above, how might I reproduce the bedrock profiles shown in #163 and #162?

I am seeing a vast array of surface features below the Petermann channel proper not readily explained by surface, bedrock nor anything in between -- no surprise because local features cannot account for ice dynamics which needs consideration of the whole basin (as well as temperature profiles and other ice properties and interaction with the atmosphere etc). The surprise come in other marine-terminating glaciers in Greenland that don't exhibit this overt surface complexity.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 13, 2015, 04:21:48 PM
A-Team

What do you mean ?:
"I am still looking for a proper name for 'Arrowhead Island' at the southwest entrance. Pilespids ø?"
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on March 13, 2015, 05:00:01 PM
Quote
Why prophesize ice shelf disintegration, is the ocean warming up at a relevant depth?  The grounding line is stable and there's not much thinning or speed-up
It doesn't take long when 25% of the ice tongue can be lost in a single year so yes I expect all the post-hinge line ice that you see today will have gone out to sea, as happened at Jakobshavn (attributed there to warming ocean). It's easy to find and follow distinctive fixed markers in the ice in either Landsat or Sentinel; five years out is a testable prediction, unlike climate 200 years out, safely beyond accountability.
The loss of a large part of the ice tongue might be completely normal. How much thinning is happening at the grounding line and is there evidence of grounding-line migration? Hopefully S-1 allows for grounding line detection with InSAR once the 2nd satellite is up.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on April 12, 2015, 12:05:26 PM
The Kap Bemerton crack got a sister, which can be seen in the animation below, if you doubt it, you can check Wipneus "very-high" resolution image from 2014 here:

https://forum.arctic-sea-ice.net/index.php/topic,53.msg22935.html#msg22935
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on April 12, 2015, 12:27:00 PM
And maybe we have a mother crack for a future calving here, the location is seen in the image below the animation:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on May 16, 2015, 08:56:39 AM
A potential calving crack is expanding further:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on May 17, 2015, 12:00:45 PM
Petermann Gletscher is preparing for a series of minor calvings at the front of Belgrave Gletscher:

A high resolution image of the area is seen below the animation.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on May 17, 2015, 10:31:09 PM
Maybe better seen in this Sentinel Image:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 02, 2015, 07:22:54 PM
On Petermann (but not lower Jakobshavn or Zachariae), you can zoom way in on Google Earth to see some really extraordinary DigiGlobe WorldView2 imagery. This is a great step forward from 15 m resolution Landsat-8 if you are interesting in locating fracture tips and monitoring their progression, though at this point I don't know of free access to a 2015 time series.

The images below look at the northeastern-most rift of the nine fractures currently operative on Petermann. The digiglobe has several rounds of zoom left but the resolution provided below already makes the calving boundaries clear, if not the timing (fractures can remain dormant for years).

The two cracks are only ~300 m from joining up (bottom image). As explained over at Jakobshavn #654, even the digiglobe benefits from CLAHE contrast enhancement.

Losing this minor piece of the ice shelf would have not have the same significance as fracturing of the two largest active fractures midway south. I’m finding Patrick Lockerby’s old posts here provide much better insight into the physics driving Petermann calving than purely descriptive journal articles. These latter however are very important for this peculiarly asymmetric ice shelf and the dominant operative process here, bottom melting.

Here is a link to a 2010 Lockerby post which links to the rest in the series, including calving prediction. The most interesting parts are naming/describing individual tributary glacier sidestreams and analogizing their interaction with the main ice shelf to mechanical 'chatter'. This amounts to brittle failure rather than ductile response (continuum mechanics being the main tool of glaciology).
 
http://www.science20.com/chatter_box/petermann_ice_island_revisited_0 (http://www.science20.com/chatter_box/petermann_ice_island_revisited_0)

 (http://www.science20.com/chatter_box/petermann_ice_island_revisited_0[/url)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 03, 2015, 09:03:59 PM
Quote
Espen:  I have some difficulties interpreting the Sentinel images from June 1, maybe Wipneus can help?
Wipneus: EW med-res image not entirely useless. Wait for a IW mode. more frequent for Jakobshann than Zachariae (waiting for months now).

The extended EW mode lacking any detail, I placed a box in central Petermann at Sentinel search https://scihub.esa.int/dhus/ and under 'advanced' required sensor mode to be IW, finding 28 images. As far as I can tell, the SLC and RAW categories are fairly worthless from our perspective. That leaves IW_GRDH_1SSH which means 10 m pixels on the ground. There were 9 of these.

The image comes as a 16-bit 865 MB file that opens as black in ImageJ. However, looking at the histogram, there is a very tight peak in the near-black. The best first step is to normalize the histogram -- then crop and try CLAHE or Equalize to improve contrast.

The image arrives upside-down but not oriented to south, which is not indicated either. I flip it vertically but do not rotate to north which would be needed, for starters, to co-register with Landsat-8. Next, a 90º CCW rotation which for Petermann's geometry fits nicely on my monitor which is wider than tall. It is still 60 MB after cropping so certain processing steps are still slow.

The attached image is cropped from S1A_IW_GRDH_1SSH_20150527 at maximal resolution. Not totally thrilled with it; Landsat band 8 at 15 m is a lot clearer. Sentinel is not suited for monitoring rift growth in the Petermann ice shelf.

S1A_IW_GRDH_1SSH_20150204
S1A_IW_GRDH_1SSH_20150205
S1A_IW_GRDH_1SSH_20150208
S1A_IW_GRDH_1SSH_20150216
S1A_IW_GRDH_1SSH_20150217
S1A_IW_GRDH_1SSH_20150220
S1A_IW_GRDH_1SSH_20150523
S1A_IW_GRDH_1SSH_20150523
S1A_IW_GRDH_1SSH_20150527*

S1A_IW_SLC__1SSH_20150123
S1A_IW_SLC__1SSH_20150124
S1A_IW_SLC__1SSH_20150127
S1A_IW_SLC__1SSH_20150204
S1A_IW_SLC__1SSH_20150205
S1A_IW_SLC__1SSH_20150208
S1A_IW_SLC__1SSH_20150216
S1A_IW_SLC__1SSH_20150217
S1A_IW_SLC__1SSH_20150217
S1A_IW_SLC__1SSH_20150220
S1A_IW_SLC__1SSH_20150523
S1A_IW_SLC__1SSH_20150523
S1A_IW_SLC__1SSH_20150527

S1A_IW_RAW__0SSH_20150204
S1A_IW_RAW__0SSH_20150205
S1A_IW_RAW__0SSH_20150208
S1A_IW_RAW__0SSH_20150523
S1A_IW_RAW__0SSH_20150523
S1A_IW_RAW__0SSH_20150527
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 04, 2015, 03:54:17 PM
On these forums, we have used almost exclusively bands 3-5 and 8 of Landsat-8, ie the visible RGB channels and the panchromatic. And it is not just us. I got to wondering whether any of the other bands were worth following, maybe band 10, which measures thermal infra-red ground emission (rather than reflected sunlight), could give us ice surface temperature.

Here we know the emission spectrum is that of a blackbody (or rather graybody); the peak in that would give the temperature via Planck's Law except that the satellite records at the top of the atmosphere so the spectrum needs adjusting for absorption in the intervening atmosphere at the time band 10 is measured. As that is beyond the scope of what we can do, I settled for relative temperature.

Band 10 over the Petermann ice shelf displays as indistinct grays even after enhancement of contrast. However there is a special false color palette developed by Glasbey that is designed exactly for this purpose: maximal separation in color space of adjacent grays. (ImageJ will provide this to 8-bit files via Image --> Lookup Tables --> Glasbey.)

This produces rather suggestive bands on Petermann, with temperatures cooling upstream and a pronounced cold spot anomaly on the west-central grounding line which coincidentally (?) has long caused gaps in SAR velocity measurement (yellow arrow). This effect may need a really cloud-free day to be reproducible.

This temperature gradient may or may not have significance to rifting propensity. There has been an automatic weather stations on the ice shelf since 2002 possibly providing ground calibration but it seems not to be working, try 4th link.

http://fiji.sc/Glasbey (http://fiji.sc/Glasbey)
https://github.com/fiji/fiji/blob/master/luts/glasbey.lut (https://github.com/fiji/fiji/blob/master/luts/glasbey.lut)
http://www.bioss.ac.uk/people/chris/colorpaper.pdf (http://www.bioss.ac.uk/people/chris/colorpaper.pdf)
http://cires1.colorado.edu/science/groups/steffen/gcnet/mapSelect.php (http://cires1.colorado.edu/science/groups/steffen/gcnet/mapSelect.php)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on June 04, 2015, 08:28:34 PM
A-Team, please see my post in Jakobshaven-thread about conversion of S-1 images to log-intensity for human viewing.

Also, SAR-images are not photographs and the top-left pixel of the image is the first sensed pixel, so the images are "flipped" depending on ascending/descending acquisition geometry. S-1 Toolbox can be used to convert from imaging geometry to map coordinates, I could write short instructions in case anyone is interested..
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 05, 2015, 05:03:16 PM
Sentinel is not producing photographs? True, no film or lenses involved but the end product is indistinguishable from one once amplitude and phase are tossed. We have seen many examples of the best that the Danish Meteorological Institute could do with Sentinel. http://ocean.dmi.dk/arctic/kennedy.uk.php. (http://ocean.dmi.dk/arctic/kennedy.uk.php.)

DMI does appears to have fixed one great aggravation with Sentinel, its re-projection to standard Greenland coordinates (if I recall EPSG 3408, NSIDC EASE-Grid, polar stereographic 70º N 45ºE). It is absolutely imperative to bring Sentinel images into layers that co-register with all the other GIS data types, even if it slightly degrades the resolution.

Could you please list the steps in the S-1 Toolbox for re-projecting a IW Sentinel image for Petermann and attach an example of the product image at 10 m?

However the question asked above is how do we best monitor crack propagation at Petermann. The answer is obviously with 0.3 m visible WorldView3 satellite to which we do not seem to have  access, despite the US scientific license. However we do have a superb baseline for August 2014 due to Google Earth having just put up two WorldView2 images covering most of Petermann.

These photos prove that 15m Landsat-8 is incapable of reaching fracture tips and that Sentinel 10 m IW is considerably worse. Both are kms away from imaging the 2014 tips, much less any progression in 2015. This is because they do not have sufficient resolution/contrast. Consequently, we are reduced to monitoring crack width far from the propagation zone. But here too it takes a gross change to give 2-3 pixels of change. And lighting angle and melt condition can complicate width change measurement.

Fracture origins and gross extensions can be dated using glorious 2000-08 NASA imagery which I'll post shortly; some have frozen in with marine ice and are dormant; others, as Espen noted a page back, are much newer and seem to be active.

The first image below shows the fracture tip on the longest rupture on Petermann in the upper right corner, at about 1 m. What has happened here since August 2014? We have no idea.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 13, 2015, 02:50:17 PM
Summer is arriving at Petermann, several melt ponds are showing up on top of the glacier:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 13, 2015, 04:39:58 PM
Yes, suddenly soggy. If leading a trip there, Espen, please don't forget to take the kayaks out of the water *before* reaching the moulin.

http://www.telegraph.co.uk/news/earth/earthpicturegalleries/5851014/Greenpeace-in-Greenland-The-Arctic-Sunrise-surveys-the-Petermann-glacier.html?image=11 (http://www.telegraph.co.uk/news/earth/earthpicturegalleries/5851014/Greenpeace-in-Greenland-The-Arctic-Sunrise-surveys-the-Petermann-glacier.html?image=11)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on June 13, 2015, 05:18:27 PM
WOW!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Shared Humanity on June 13, 2015, 06:28:32 PM
Several as in hundreds?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 13, 2015, 06:57:41 PM
Several as in hundreds?
Why exaggerate?  ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 13, 2015, 09:03:51 PM
Espen, you crack me up. Can we meet halfway? It's 2.4 km from the new tip to the center drain.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 13, 2015, 09:58:37 PM
Not much change the last 3 weeks on the west side. Today's image is displaced a few pixels downward and is halfway transparent, allowing the older image to show through, for purposes of crack propagation comparison.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 14, 2015, 04:14:16 PM
The graphic below shows hours of sunshine at the latitude of the growing tip shown two posts above. This is related to, but not the same, as ground level insolation (energy impingent) adjust for albedo (energy received by the surface).

The nearest weather station may be Hans Island. It is showing 3.17° C currently and above zero air temperatures the last three days. This is not necessarily a good proxy for the central Petermann ice sheet so may not explain the abrupt onset of melting there observed by Espen. http://dalriada.sams.ac.uk/aws_hans/ (http://dalriada.sams.ac.uk/aws_hans/)

The polar orbit of Landsat-8 is such that coverage of Petermann is really extraordinary, with 17 images for the first 14 days of June, many of them clear. Here Zachariae had 10 and Jakobshavn calving front only 4 during this same period.

The downside of Petermann coverage is that these images don't often have the same or even similar path,row. Thus some allowance has to made for different viewing geometries if images are to be aligned. However the bigger issues for fracture comparison are change in illumination angle and melt status.

For example, if two images a few days apart could be perfectly aligned, subtracting the earlier from the more recent would yield the newly melt areas. However the slightest distortion would cause some issues with this. Central Petermann moves ~3 m/day or a pixel every 5 days at 15 m resolution; motion on the side tributaries tapers off to fixed ice.

June path rows for Petermann ice sheet:

LC80 30 248 2015 158 LGN00
LC80 33 248 2015 163 LGN00
LC80 34 248 2015 154 LGN00
LC80 35 248 2015 161 LGN00
LC80 36 002 2015 152 LGN00
LC80 36 247 2015 152 LGN00
LC80 36 248 2015 152 LGN00
LC80 37 002 2015 159 LGN00
LC80 39 001 2015 157 LGN00
LC80 39 002 2015 157 LGN00
LC80 40 001 2015 164 LGN00 today
LC80 41 001 2015 155 LGN00
LC80 42 001 2015 162 LGN00
LC80 43 001 2015 153 LGN00
LC80 44 001 2015 160 LGN00
LC80 46 001 2015 158 LGN00
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 15, 2015, 06:29:29 PM
The animation below shows three years of Landsat-8 images, mid-June of 2013-15, of rifts in the northwest corner of Petermann's floating ice shelf.

It is 'challenging' to properly align these given that the glacier moves NNW about a km per year (67 pixels at 15 m resolution if a year apart) while new rifts open and old ones widen, in addition to compressive deformation and path,row viewing geometry issues.

For the purposes of seeing changes, it does not work so well to align to fixed rock along the channel because the 'same' feature is not in the same place from year to year. However feature pairs often remain in the same relative position as this ice shelf is not dynamically thinning. The animation therefore is in co-moving Lagrangian coordinates rather than Eulerian. This causes Faith Glacier (FG) to 'move' down from year to year.

2015 164 40 001 LC80400012015164LGN00 June 13
2014 168 41 001 LC80410012014168LGN00 June 17
2013 163 43 001 LC80430012013163LGN00 June 12

Click to view animation. Frames are at 800 ms except for 2015 which is 1600 ms. The lower image is a fixed side-by-side at the 700 pixel width allowed.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 15, 2015, 06:45:14 PM
The animation below shows three years of Landsat-8 images, mid-June of 2013-15, of rifts in the northwest corner of Petermann's floating ice shelf.

It is 'challenging' to properly align these given that the glacier moves NNW about a km per year (67 pixels at 15 m resolution if a year apart) while new rifts open and old ones widen, in addition to compressive deformation and path,row viewing geometry issues.

For the purposes of seeing changes, it does not work so well to align to fixed rock along the channel because the 'same' feature is not in the same place from year to year. However feature pairs often remain in the same relative position as this ice shelf is not dynamically thinning. The animation therefore is in co-moving Lagrangian coordinates rather than Eulerian. This causes Faith Glacier (FG) to 'move' down from year to year.

2015 164 40 001 LC80400012015164LGN00 June 13
2014 168 41 001 LC80410012014168LGN00 June 17
2013 163 43 001 LC80430012013163LGN00 June 12

Click to view animation. Frames are at 800 ms except for 2015 which is 1600 ms.

Nice work A-Team, try the same with the cracks around Kap Bemerton?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 15, 2015, 07:22:39 PM
Quote
try the same with the cracks around Kap Bremerton?

Here is what I have so far on the east side, same three June dates and years. The central ice shelf is sliding past an ice stream contributed by a tributary glacier. As it does so, large brittle blocks of the middle tributary ice shear and slowly pivot as they move seaward at a slightly lower velocity. The medial moraine is shown in colors in the animation.

This process began in earnest sometime prior to the year 2000 and may be associated with rift initiation on the NE side of the ice shelf. (The NW side has no significant tributary glaciers and indeed Petermann spills into valleys there, eg above Kap Schoubye.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 16, 2015, 04:55:40 PM
Quote
try the same with the cracks around Kap Bemerton?

The triple rift of today has developed fairly recently. The northernmost member is not visible in 2009 but fairly well developed (but not as extensive) in 2012. It has stalled for the last three years as the strain was taken up by a rift below it that developed in 2013. That rift too stalled as the strain was taken up by a major new rift, again up-glacier, that arose in mid-summer 2014 but has extended in 2015 (though not in recent weeks -- see #189 ).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 16, 2015, 05:34:40 PM
The first image shows an enlargement of the elbow in the oldest rift in the Kap Bemerton area. The rift is 130 m in width (from top to bottom on left edge of image). These rifts go clear through the ice shelf to the sea water underneath (as determined in some cases by CTD casts). Over time, a stagnant rift can fill in with marine ice, captured meltwater, avalanching ice from the sides, and snowfall (though that is minimal according to several years of AWS measurement).

The second image shows a detail of the main rift on the other side of the fjord. The 'intrusive ice dike' is 10 m across and squeezed up (by tributary block brittle fracture and subsequent rotation) about the same amount going by the shadow lengths.

The third image shows the south lateral moraine of Sigurd Berg glacier just to the east of the dike, which becomes a prominent medial moraine as this glacier joins Petermann and undergoes severe shearing as it moves downstream (due to its lesser velocity). Over time, the grit comprising the moraine can be spread by meltwater into channels.

These high resolution Worldview2 images suggest that the 15 m scale of Landsat is not sufficient to resolve the physical forces operating on this ice shelf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: gideonlow on June 17, 2015, 10:03:39 AM
Wait a minute . . . what's that watermark-like facial image doing there in the corner of the last image (Petermann moraine shear.jpg)???  :o
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 17, 2015, 11:06:45 AM
It is not August Petermann?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 17, 2015, 12:47:27 PM
Artistic license? Petermann was a distinguished German cartographer of the 19th century. Never traveled to Greenland, much less this glacier or his 2940 m berg. Similarly, Alexander von Humboldt never visited Humboldt Glacier.

Petermann made some mighty fine maps of Greenland in 1865 and 1869, below. He proposed that warm currents from the Atlantic and Bering Sea could lead to open water in the Central arctic. More details are cross-posted at http://forum.arctic-sea-ice.net/index.php/topic,417.msg54320.html#msg54320 (http://forum.arctic-sea-ice.net/index.php/topic,417.msg54320.html#msg54320)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 17, 2015, 01:30:18 PM
The animation below pushes the limit -- and then some -- on resolution of Landsat-8 band 8. The most active rift at the moment on the Petermann ice shelf has almost reached the midline.

Although comparing June 10th to June 15 seems to show unambiguous change, the widespread melting, growth in the size of melt ponds and water flow in tributaries can be confused with tip propagation in comparing June 13th to June 15th.

The resolution has been bumped up to 5 m. It's debatable whether this helps very much; a week from now the situation will be clearer. Note detecting a linear feature is easier than point features because of spatial correlation.

Unless someone feels up to purchasing WorldView3 imagery, this seems to be the end of the road in terms of tip propagation monitoring -- it  does not help particularly to apply de-speckling, sharpening, or shadow exagerating.

This is a fairly respectable crack, 15 feet, in terms of jumping over. There is no guarantee that it will continue growing, nor that it will lead to a calving rift, this summer or ever.

If it does, I estimate (from google earth pixel counting, assuming a semi-circular route extension) that the area calved off will be ~220 km2, similar to the 2010 event and maybe twice that of 2012. As the ice is already floating, calving would not contribute directly tp sea level rise, nor indirectly via glacier acceleration as modeling suggests very limited importance to buttressing.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 17, 2015, 02:09:22 PM
Below is a 10 m resolution Sentinel radar image from 27 May 15 shown in false color and reduced resolution. At the original size, the image was very speckled; I could not find any way of usefully sharpening ground features (never the design intent). So it sees through clouds which is helpful but is not suitable for up-to-the minute rift tip monitoring.

Nukefix has a better way of processing using Sentinel toolbox software, step-by-step at link below. I've found the software easy to install, stable in operation, and having advanced commands for processing this type of imagery. The most useful thing for us will be interferometric velocity measurements but that entails a much higher level of processing sophistication.

http://forum.arctic-sea-ice.net/index.php/topic,154.msg54200.html#msg54200 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg54200.html#msg54200)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 18, 2015, 04:08:19 PM
 Looking to see if the melt this year is more/less extensive than in the past, there were cloud-free Landsat-8 scenes  for June 15th for 2015 and 2014 and for June 10th of 2013. The path,rows do not match very well, so it did not prove feasible to align perfectly to the walls of the fjord (not to mention the 1.2 km yearly advance of the ice shelf).

Overall, surface melt water (ponds and drainage channels) is very sensitive to date. The peak date can occur mid to late June because the water can later work its way down through crevasses. Here the 2013 hardly shows any melt whereas 2014 and 2015 are quite similar.

The same specific ponds re-occur to a large extent. These are distributed systematically with respect to large scale longitudinal flow-line features, more on that below.

LC80 43 001 2013 163 LGN00
LC80 41 001 2014 168 LGN00
LC80 36 248 2015 168 LGN00
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 18, 2015, 05:17:13 PM
The Petermann ice shelf has a number of fascinating surface features that provide a window to the forces acting on it. In part these are driven by rigid but somewhat deformable ice trying to flow through a narrowing, northerly curving funnel-shaped fjord (as described earlier by Espen).

The images below show the northwest corner by Faith Glacier. The first is just band 8 of the 15 Jun 15 Landsat-8; the second overlays a crude regional feature classification; the third provides some measure of objective support for that via a Canny edge filter.

Here the wall curvature and compressive forces from tributary glaciers across the fjord could give rise to elastic compression resulting in small amplitude longitudinal waves in the ice (to be contrasted with brittle fracture of tributary ice along the opposite fjord wall from Porsild to Belgrave).

These frozen waves hug the walls for a long ways but nearer the calving front fan out towards the center line. The visibility of these features is greatly enhanced by melt water collecting in the wave troughs. In fact ridging is very subtle and not seen in the late afternoon illumination of the 11 August 14 ultra high resolution WorldView image.

The third zone consists of a broad flowline feature defined by oblique shorter wavelength herringbone that extends back beyond the hinge line many km upstream. Note the wave pattern is almost 45º to the flow line but arcs around to perpendicular more towards the center (where it could even be split into a fourth zone of classification).

There are quite a few candidates for the underlying physical process: differential velocity across the shelf (fastest in the center), compensation for channels under the shelf hollowed out by circulating sea water, or a 'frozen rapid' caused by flow over a bedrock sill or bulge far upstream that is not indicative of forces acting locally far downstream.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 19, 2015, 05:59:33 PM
The animation below compares two Landsat-8 images of different years but the same path,row and approximate dates, namely  2015 153 43 001 and 2013 163 43 001 The images are rotated to put the fjord approximately horizontal and aligned along the central drainage (thus fjord walls move as the ice sheet advances).

The very fact that the left part of the images (the northwestern half of the fjord in Landsat view) are almost perfectly alignable after two full years means there is no velocity gradient across the ice shelf -- it is moving as a block other than for rifts and along the compression ridges along the rocks.

This contradicts a recent determination of velocities by a very experienced radar interferometry group (2nd image). This is troubling to say the least because of the number of glaciers where we are trusting the latter type of analysis. http://web.stanford.edu/group/radar/group.html (http://web.stanford.edu/group/radar/group.html)

An earlier synoptic scale measurement of Petermann does not provide sufficient resolution in the channel. I contoured this with the G'mic online tool. (21st-Century Evolution of Greenland Outlet Glacier Velocities, T. Moon et al DOI: 10.1126/science.1219985)

The right part of the animations shows a very significant velocity drop across Sigurd Berg tributary line, along with some block rotation and deformation, in somewhat better agreement though not in details.

Of course, there is nothing quite like some GPS stations drilled into fixed positions in the ice by AP Ahlstrøm et al which cover up to July 2012. Note the ice sheet has to be thickening somewhat for the velocity to decrease between the lower two stations. http://www.earth-syst-sci-data.net/5/277/2013/essd-5-277-2013.pdf (http://www.earth-syst-sci-data.net/5/277/2013/essd-5-277-2013.pdf)

Click to animate. The image has to be rather wide to take in an entire transect block of the fjord near the calving front  at 15 m resolution.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 20, 2015, 04:50:15 PM
The animation below, taken from the one above, shows motions in the Petermann ice shelf relative to the calving front and central drainage channel held fixed. The 2013 image has blue infill of morraine, the 2015 pink. Large displacements correspond to lagging absolute motion. The region with yellow inflow illustrates the gradient of motion -- it keeps up better with the central ice shelf. Note too deformation and rotation of some of the tributary blocks.

What should you look for in the animation:

(1) nothing is happening on the left side, that says even though the images were taken 740 days apart they can still be shifted into pixel-perfect alignment. That is only possible when the geometry of the central ice shelf is moving as a rigid block all the way to the calving front (barely visible dip in center).

(2) towards the center of the animation, to the right of the secondary drainage channel, there is a suggestion of the ice not quite keeping up with the main block which is moving at ~3 m per day. There could be a contribution from satellite viewing geometry to this even though the path,rows match and the nadirs flown differ only slightly. However the slippage is only a pixel or two which at 15 m Landsat resolution amounts to ~30 m out of a possible 3*740 = 2220 m so only a bit more than 1%.

(3) the real interest is nearer the fjord wall. Here the relative motion in the ice flows contributed by the Porsild and Sigurd Berg glaciers upstream shows dramatic slowing and even rotational distortion. These flows were once marked by clean lines of morraine grit but those has been block-faulted and shifted over time, a process that was just barely underway in year 2000 imagery (to be posted later).

(4) Along the fjord wall, especially in small embayments, the ice is stationary. Because the coordinate frame co-moves with the central block, ice that co-moves with the fjord walls (ie rapidly) is actually not moving at all in the fixed Greenland rock reference frame. Confusing? Well, it's even more confusing doing it the other way round.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 21, 2015, 06:27:10 PM
Below I tried to figure out a puzzling feature up-glacier on Petermann. The region is about 21 km southeast of the last rock on northwest channel (unnamed, shaped like an Native American arrowhead). It shows up in all Landsat-8 bands as well as that precious interferometric image of Petermann made in Radarsat2 emulation.

The later image was discussed here a year ago at #86 -#97. However coming upon an important image like this, it is imperative to reverse-search it by all three tools to find the highest available resolution, as explained over on Developers Corner / Re: Getting hi-res Landsat Images. This will also uncover all previous scientific uses of the image. In this case, an image with much better resolution of the fringes, 1484 x 1716 pixels, was available along with other useful goodies.

Note as the glacier passes over a bedrock mound or trough, the velocity field obtains a slight upward component which otherwise follows the glacier surface. This can show up in the insar line-of-sight motion as an area of wider/tigher fringes that could be misinterpreted as slowing/speeding (which would cause havoc with glacier continuum mechanics, not observed).

http://forum.arctic-sea-ice.net/index.php/topic,638.msg54112.html#msg54112 (http://forum.arctic-sea-ice.net/index.php/topic,638.msg54112.html#msg54112)
http://www.esa.int/spaceinimages/Images/2014/03/Petermann_on_the_move (http://www.esa.int/spaceinimages/Images/2014/03/Petermann_on_the_move) click on hi-res link
https://earth.esa.int/documents/10174/134665/S1-TN-ESA-SY-0452_RSAT_TOPS_InSAR_Scenes_Report (https://earth.esa.int/documents/10174/134665/S1-TN-ESA-SY-0452_RSAT_TOPS_InSAR_Scenes_Report) expert technical note
http://rs.tudelft.nl/~rlindenbergh/education/Thesis_Lennert_van_den_Berg.pdf (http://rs.tudelft.nl/~rlindenbergh/education/Thesis_Lennert_van_den_Berg.pdf) U Delft van den Berg MS thesis Chap.4

The feature under investigation has a inexplicable wave pattern to its south and leaves an peculiar ice track for many km downstream of its head. By great good fortune, there was an east-west Cresis radar track right through the middle of it, 20100324_01_036, which shows ice thickness, an upheaval feature, and unusual flares reaching the surface.

This is shown as an overlay along with coordinates and elevation transects provided by Google Earth which establish that the feature is a elevated surface bump within a depression lying at the base of the descending ridge separating Petermann and Humboldt and the overall descending ice sheet. Note two seasonal melt channels curve around the periphery (ie do not descend into it — it is a bump.)

Overall, an oblique airplane photograph would be very beneficial here. Alternatively, the hill-shaded DEMs being made with 0.5 m WorldView imagery are photorealistic but not yet available for northwest Greenland. The inset shows Russell Glacier at just half the available resolution.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on June 21, 2015, 11:58:13 PM
This contradicts a recent determination of velocities by a very experienced radar interferometry group (2nd image). This is troubling to say the least because of the number of glaciers where we are trusting the latter type of analysis. http://web.stanford.edu/group/radar/group.html (http://web.stanford.edu/group/radar/group.html)
Perhaps they used InSAR to derive only the range-component of velocity?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 22, 2015, 03:37:17 PM
Quote
Perhaps they used InSAR to derive only the range-component of velocity?
No, this was quite the fancy study ... of Ryder Glacier to the north. The Petermann image is not in the dissertation and i  not described further on their web site.

Here is a more recent study that seems to better capture the horizontal velocity gradient seen on Landsat today. I've added the 2 km width checkerboard to their distance tape ... as Espen notes, the narrowing and turning of the channel has to have some effect on the ice sheet. The image does not have sufficient resolution to really capture what is going on with tributary blocks.

That paper concluded that the velocity response of Petermann to unbuttressing from large calving events was minimal (free full http://ftp.vub.ac.be/~fpattyn/papers/Nick2012_JGLAC.pdf (http://ftp.vub.ac.be/~fpattyn/papers/Nick2012_JGLAC.pdf)).

I find these muddy colors make for an ineffectual display (and one that cannot be inverted to recover the original x,y data grid). It might be better to contour. Another option is to animate the cross-sectional velocity graph, along the lines of MacGregor's animation of Greenland ice thickness by age (1:36 into https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4249 (https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4249)).

The second image below is from "Unprecedented Retreat in a 50-Year Observational Record for Petermann Glacier, North Greenland"  by OM  Johannessen et al (free full http://159.226.119.58/aosl/CN/article/downloadArticleFile.do?attachType=PDF&id=383 (http://159.226.119.58/aosl/CN/article/downloadArticleFile.do?attachType=PDF&id=383)). It shows retreat history over a highly distorted ERS-1 SAR base map. 

They also determined a velocity history of Petermann, concluding no statistically significant trend exists for 1993-2011. However 2011-2015 are seeing consistent reports on the high end, pushing 1400 m/yr in July (see #203 GPS graphic). It's quite difficult to get consistent (ie 1-15 July) remote sensing imagery over a long time frame.

Petermann velocity m/yr
1993  1030
1994   960
1995   930
1996  1075
1997  1110
1998  1070
1999  1175
2000   965
2001  1095
2002  1045
2003  1100
2004  1050
2005   985
2006  1250
2007  1000
2008  1040
2009  1050
2010  1100
2011  1175

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 22, 2015, 04:18:27 PM
Below is the 20 Jun 15 sequel to #199, adding five days to 'is the east side fracture tip growing?' While the answer in my view is yes, there is nothing dramatic to see here, move along. The confirmable portion of the tip has perhaps advanced 39 pixels in the 5 m image below or 200 m (or 40 m/day); widening rather than extending per se is what makes rift tips initially perceptable at our resolution.

This fracture is a more likely origin of the next significant tabular iceberg than the other growing tip midway down the NW side. The three reasons for this: the history of fracturing at Petermann, stress distributional relief (the NE fracture has a lower pair but that has frozen up, the NW fracture is but 3rd in a series), and the velocity disparity necessary for rifting is more pronounced on the NE.

Petermann rides too low in the water to have a Jakobshavn-type calving front. According to thickness and assumption of hydrostatic equilibrium, it has ~7 m of freeboard in some average sense but look below as researchers on the Arctic Sunrise step ashore to find an ice bollard for their hawser.

The third image added below, an oblique shot of Belgrave, Hubert and the calving front, is an IceBridge plane shot from March 2010. It is a beauty -- click to open to full size. Note how tributary melange bulges up from the ice sheet -- that is not so apparent from Landsat view.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 23, 2015, 11:11:17 PM
There is another beautiful Petermann panorama, too wide for us here so link below. The location is not documented but I am thinking it shows the northeast side from Hubert Glacier down to Sigurd Berg. This would be a good one to add to Espen's google map online project at tps://www.google.com/maps/d/viewer?mid=zbdKKg4fRHYo.kjkUmepfXc9A

Along those lines, note a duplicative  Petermann forum called "Petermann Fjord / North Greenland" ran for a few months back in 2013. Espen and Andreas Muenchow made a great effort there to nail down a comprehensive set of place names for positions along this glacier (a topic that we return to frequently!). It would be worth stripping that fossil forum for its goodies and appending it here.

I found a really neat oblique Icebridge shot of Petermann spilling into Romer Søer (lakes) at the NW corner of Kap Schoubye -- it was unlabelled as such (deplorable practice) and I cannot relocate it at the moment.

http://forum.arctic-sea-ice.net/index.php?topic=270.0 (http://forum.arctic-sea-ice.net/index.php?topic=270.0)
https://docs.google.com/file/d/0B_a0Tecpig0jRm9GbnlLVGFvZDQ/edit?pli=1 (https://docs.google.com/file/d/0B_a0Tecpig0jRm9GbnlLVGFvZDQ/edit?pli=1) Kap Agnes
http://asapdata.arc.nasa.gov/asf/gallery/icebridge/1000205.petermann_glacier_panorama.jpg (http://asapdata.arc.nasa.gov/asf/gallery/icebridge/1000205.petermann_glacier_panorama.jpg)

Meanwhile, today's fracture extension. If just my imagination, then a prediction for future fracture extension.

I came across some contrasting quotes from three prominent Petermann researchers after the 2012 event: http://www.samoanews.com/node/6907 (http://www.samoanews.com/node/6907)

Quote
"It's dramatic. It's disturbing," said University of Delaware professor Andreas Muenchow, who was one of the first researchers to notice the break. "We have data for 150 years and we see changes that we have not seen before." Glaciers do calve icebergs naturally, but what's happened in the last three years to Petermann is unprecedented, Muenchow and other scientists say.

Quote
"This is not part of natural variations anymore," said NASA glaciologist Eric Rignot, who camped on Petermann 10 years ago.

Quote
Ohio State University ice scientist Ian Howat said there is still a chance it could be normal calving, like losing a fingernail that has grown too long, but any further loss would show it's not natural: "We're still in the phase of scratching our heads and figuring out how big a deal this really is."

Normally in a scientific situation like this, with a bimodal probability distribution (year of calving event, surface area calved off) estimable using data back to the 1876 map and decades necessary for the front to recover from an event filling in for years missing maps/imagery, monte carlo sampling would be employed (see wiki).

That might show that the probability of a distribution as extreme or more than observed in terms of date and extent could arise from natural (random) variability is less than p =0.0000001 or some such. That would be as close to a proof as it gets in science. However that doesn't say when, where, or why the next rifting will occur, my objectives with this series of posts.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 24, 2015, 05:52:45 PM
Petermann has changed quite a bit over the satellite record, not just the much-studied retreat of the ice shelf but also in the interaction of the main with tributary glaciers, which has gotten much more intense possibly because the main glacier is moving relatively faster and beyond the ductile limit of tributary ice.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 24, 2015, 06:08:30 PM
Nice work A-Team, good to have an engaged and dedicated "sailor" on board ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 28, 2015, 03:50:14 AM
Well, watching these rift tips elongate is like watching paint dry. Today's image does show some changes from 10 days ago. Note with widening of the crack coming down from the top and the extension of the one coming in diagonally. It's not clear that the two fractures 'know' about each other and have plans to meet.

Even if this did result in a calving this season, the area involved is minor and it would not destabilize the rest of the ice shelf, much less cause the main glacier to measurably accelerate from so little reduced buttressing.

This ice shelf has a very interesting channelized underside that has been extensively studied, most recently in two papers from Andreas Muenchow and coworkers. The bedrock topography too is quite inexplicable, rather lopsided and not at all the classic U-shaped fjord profile.

http://muenchow.ceoe.udel.edu/papers/Muenchow2014-JGlac.pdf (http://muenchow.ceoe.udel.edu/papers/Muenchow2014-JGlac.pdf)
https://www.researchgate.net/publication/274695487_Bathymetry_in_Petermann_fjord_from_Operation_IceBridge_aerogravity (https://www.researchgate.net/publication/274695487_Bathymetry_in_Petermann_fjord_from_Operation_IceBridge_aerogravity)

It's not clear that ice shelf surface features reflect either of them to any extent, which implies departure from hydrostatic equilibrium, and raises the question how stable that can be over the long term. Petermann has some commonalities with Antarctic ice shelves but I'm skeptical about any lessons in either direction.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 28, 2015, 05:47:36 PM
At the mouth of Petermann Fjord, just behind Offley Ø and between
Kap Mary Cleland and Kap Tyson can you find this beautiful natural wonder lets call it "Offley Deltaet"

It reminds me of Edward Munch?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 28, 2015, 06:03:15 PM
Quote
At the mouth of Petermann Fjord, just behind Offley Ø
Are you at liberty to disclose the source of this image? Interestingly, it is not known to reverse-search at  https://www.imageraider.com/ (https://www.imageraider.com/)

The image below shows an oblique view of Humboldt and Petermann that I took from the updated NASA visualization of Greenland ice layer ages (at ~50x vertical exaggeration of the DEM) 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)

One has to wonder why Petermann was 'needed' to drain the ice sheet -- it seems an afterthought. Humboldt had a broad outlet yet that glacier is still sleeping in terms of output. If Petermann is fairly new, that could perhaps explain the 'immaturity' of its bedrock profile.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 28, 2015, 06:13:00 PM
From Google maps Terra Metrics images.

Or https://www.google.com/maps/d/edit?mid=zbdKKg4fRHYo.kjkUmepfXc9A (https://www.google.com/maps/d/edit?mid=zbdKKg4fRHYo.kjkUmepfXc9A)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 28, 2015, 06:25:13 PM
And I not sure Humboldt discharge less ice than Petermann, Humboldt just dont brag about it the same way Petermann does.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 29, 2015, 03:13:30 AM
Quote
Humboldt just don't brag about it like Petermann does.
.
Hmmm, that might account for some of the difference. Though Petermann doesn't talk much about its dominant ice shelf bottom melt nor enhanced inland velocity and isn't really responsible for those hyperventilated headlines on calving.

This 2015 Humboldt paper is talking trough but pleading pinning points, free full at google scholar but oddly paywalled at the journal itself and not yet on university sites or ResearchGate. They re-determined basal topography to much better resolution ... fig.2 is a great step forward. I'm moving the discussion of it over to the Humboldt forum though.

Quote
Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG’s terminus occupies a large overdeepening.

HG’s retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°Ca–1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG’s northern lateral margin.

Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72 km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century.

JR Carr et al Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland
Journal of Glaciology, Vol. 61, No. 225, 2015 doi: 10.3189/2015JoG14J128
http://www.igsoc.org:8080/journal/61/225/j14j128.pdf (http://www.igsoc.org:8080/journal/61/225/j14j128.pdf)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 29, 2015, 08:11:34 PM
My immediate estimate (just watching for a few years), without any proof or documentation is, both Zachariae and Humboldt are in the same league as Petermann when it comes to ice discharge, but I may be wrong, I am not an expert!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 29, 2015, 08:51:08 PM
Just a reminder of what my thoughts are about the "Majors":

https://forum.arctic-sea-ice.net/index.php/topic,400.msg28208.html#msg28208
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 30, 2015, 04:54:23 PM
The issue for me is not just which marine glacier is discharging how much now -- for that we have the 2014 Enderlin study of 178 glaciers -- but which ones are accelerating today, how mass budgets (discharge + melt - accumulation) are changing, and whether there are any runaway situations in terms of sea level rise contributors in the near or medium term future.

I tend to think you have correctly identified the two hot button issues, Jakobshavn and Zach/79, methods may leave something to be desired?

Of the 178 glaciers studied, 4 accounted for roughly half and the top 15 accounted for 77% of the 739 ± 29 Gt of ice lost due to acceleration since 2000  Helheim Glacier dropped from third to fifth place and newbie SE Greenland glaciers Koge Bugt and Ikertivaq South joined the list.

Note in 2000 Petermann edged out Zach but Humboldt was not too far behind. (I'm skeptical about '79fjorden' discharge.) But with cumulative anomalies to 2012 added in, Zach gets ahead as best I could tell from the sketchy article info. Considering basin sizes really puts the spotlight on Zach/79/NEGIS.

http://dspace.library.uu.nl/bitstream/handle/1874/296062/grl51346.pdf?sequence=1 (http://dspace.library.uu.nl/bitstream/handle/1874/296062/grl51346.pdf?sequence=1)
http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/full (http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/full) for supplemental

"The relative contribution of ice discharge to total loss decreased from 58% before 2005 to 32% between 2009 and 2012. As such, 84% of the increase in mass loss after 2009 was due to increased surface runoff. These observations support recent model projections that surface mass balance, rather than ice dynamics, will dominate the ice sheet's contribution to 21st century sea level rise."
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 05, 2015, 05:48:30 PM
Petermann has been moving at a record pace of 1403 ± 20 m/yr according to a centerline measurement I made between today's cloud-free day and that of a Landsat8 16 days earlier (same orbital path, row necessary for alignable geometry). The error estimate comes from looking at sensitivity to a bump pixel measurement, sub-pixel rock alignment on both sides, scene center time differences, more accurate number of days in year, and so forth.

The velocity of Petermann has been measured numerous times since the 1950's with a variety of methods, notably photogrammetry and GPS devices fixed in the ice (see earlier post). These measurements are not made at an agreed-upon spot (here due west of Sigurd Berg), nor necessarily averaged over the same time span (here 16 days), or date in season.

The previously reported record for a quite similar location was ~1350 m/yr for a brief peak in early July 2013, post #203, suggesting the 04-20 July 2015 average may be higher still. (However any speedup over the last two years would only borderline detectable since methods differ.)

One bit of confusion has arisen from posting as km/yr rather than in meters per year. The former is easy to just brush off as unchanging ~1 km/yr whereas the pronounced acceleration is apparent expressing in m/yr where relative error shows up better. While this speed-up is quite respectable for ~81º N, it is nothing like the ~300% at Jakobshavn, 1050 km to the south.

The first image below gestures at the methods that work best for measurement. The tool in Gimp can be positioned precisely at higher magnification: it figures the pythagorean length on the pixel displacements. Enlargement is better done with bicubic rescaling than by linear bumping of monitor resolution.

None of the fractures have progressed measurably over the last five days; the rift coming from the NE corner is most active right now. Melt on the ice shelf is most notable in the hinge line region off Porsild Glacier; melt on the ice shelf per se does not affect speed via basal lubrication as it is floating. It's not clear what if anything the different shades of blue portend.  The cold anomaly shows up in the same spot again in Landsat band 10 in the glasbey palette but does not appear correlated. Colors in the lower right corner are clouds.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 08, 2015, 02:47:56 AM
Things have warmed on the weather maps but I am yet to see any dramatic changes in terms of ice shelf melt features on Petermann or east of Humboldt ... maybe something will emerge in the next days. It does seem like the west side of north Greenland is experiencing more of this high than the east.

Note too the lower Petermann melange has fractured as the Nares breaks up -- this could release pressure holding rifting back.

The large melt feature below Porsild Glacier forms every year in a low spot (lower right corner). There is very little glacial 'conflict' at the confluence so the origin of this depression may have more to do with compressional forces as the glacier ends its dive off higher elevation at the grounding line here. 

Melt on the ice shelf obviously doesn't contribute to basal sliding lubrication since the shelf is already floating. Freshwater discharge under the ice shelf may however significantly affect basal access and influence of relatively warm ocean water. It's not at all clear how much meltwater is being released below the ice shelf at the grounding line by the glacier itself .

I've looked at various schemes for measuring surface melt area and comparing locations year to year. If some combination of channels should result in a consistent separation of ice and melt in some color space, then the melt could be lifted off by specifying a point and radius in the color picker. Transitional areas make this difficult to do with any accuracy but see ...

Spaceborne derivation and validation of supraglacial lake volume along the western margin of the Greenland Ice Sheet
http://www.the-cryosphere-discuss.net/9/3257/2015/tcd-9-3257-2015.pdf (http://www.the-cryosphere-discuss.net/9/3257/2015/tcd-9-3257-2015.pdf)

Estimating supraglacial lake depth in western Greenland using Landsat 8 and comparison with other multispectral methods
www.the-cryosphere-discuss.net/9/3257/2015/tcd-9-3257-2015.pdf (http://www.the-cryosphere-discuss.net/9/3257/2015/tcd-9-3257-2015.pdf)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: cats on July 08, 2015, 08:11:14 AM
An interesting expedition and research this summer at Petermann - http://polar.se/en/expedition/petermann-2015/ (http://polar.se/en/expedition/petermann-2015/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 09, 2015, 04:40:43 PM
Quote
Petermann Glacier is connected to the inland ice through an ancient (perhaps pre-glacial) channel system, which extends from Petermann Fjord, deep into the inland ice along a pathway near the NEEM and NGRIP ice cores. This implies that the expedition with icebreaker Oden, targeting the longer-term marine history of the Petermann system, is constrained near its inland-ice source by well published deep ice-core data.

I sincerely hope they find someone familiar with the scientific literature on interior Greenland to write up the land portion of expedition (which going by the many publications of the distinguished PIs will really be about moraine sediment cores and foraminifera as Holocene temperature recorders).

Ice from NEEM nor NGRIP does not flow towards Petermann and never has over the last 115 kyr, minimally. Ice does not flow down the "ancient channel system" but instead obliquely across it. Radar stratigraphy establishes beyond any doubt that the ice has not flowed down the channel trough the Last Glacial and has not contributed any ice present in the Petermann fjord at any time during the Holocene.

Now they could have said something like:

Quote
"The stratigraphic ages of all ice cores in Greenland are cross-correlated today, so to the extent these layers extend towards Petermann (see image below), the ice there can be dated despite the immense basal upheavals that dominate the apron of the fjord. Thus the extreme folding of the nearest core, NEEM, does not present issues since stratigraphy from any other drill site can replace problematic layers.

"From this we know that 300 m of ice underlies the 60 kyr triple and reaches Kap Schoubye and that Holocene stratigraphy, at least on the northwest side of the fjord, extends to the grounding line and beyond.

"However the longer-term marine history of the Petermann system is not well-constrained by ice layer chemistry and chronology data alone because ice flow in northern Greenland is extremely complicated even on the barely moving summit ridge and the region just above the fjord has been subject to unknown thermal flow processes on a massive scale resulting in extreme basal upheavals that nearly reach the fjord entrance itself on the northeast."
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on July 10, 2015, 04:58:14 PM
Where to place the 5 drill holes through the floating section of Petermann to observe ocean temperature and salinity for the next few years?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 10, 2015, 09:59:36 PM
That is a very good question for us forumites to opinionate/bloviate over. First though, a round of applause for those out in the field arduously and riskily obtaining important field data that cannot be had from armchair remote sensing!

The significance of ocean waters warming and eroding ice shelf underside is not limited to Petermann as similar processes may be operative at Nioghalvfjerdsfjorden and indeed under Antarctic ice shelves. Petermann, while not a tour destination, is relatively more accessible and could provide early model guidance to the others.

Both aspects of ocean interaction with ice shelf are non-intuitive: it is not a matter of waiting centuries for local water to warm. Oceans have indeed warmed slightly but the issue here is pre-existing warmer currents advancing to new places, already possessing ample heat to melt ice sheet undersides.

Secondly, the induced bottom melting is not uniformly planar but by all accounts quite pronounced just down from the grounding line and elsewhere channelizing the ice underside in a complex fashion driven by daily and seasonal fjord circulation and intertwined temperature, salinity and density profiles.

Five drill holes is a decent but not extravagant number. These could conceivably be guided in their placement or augmented by one-time casts through 'whirlpools' and other direct routes through the ice which we could conceivably locate beforehand. These holes have some interest in that they collect regional melt water and inject it locally on top of the subsurface water column. However one-off casts at random tidal stages and season pale in comparison to steady time series and the effort could be a huge resource waster.

I'm supposing hot water drilling (no ice cores, no gravity sediment) with an instrumented wire frozen in (rather than moorings), periodically reporting from a top package to a satellite, not betting the farm on relocation and one-time retrieval. However placed, these strings will drift down their flow line some 3-4 km over the lifetime of the project. Thus, to the extent the bathymetry is known to resolution, these could be placed over bedrock channels or set instead to drift over troughs and sills.

Thermisters and conductivity give density and perhaps changes in ice depth overhead. I don't have a sense whether currents will be measured or are even disentanglable from positional drift via topside GPS (or more simply, corner radar reflectors).

Given five drill sites, it seems like the first decision is allocation between horizontal versus flowline transects. I would discard both edges as not representative nor safe to drill; these might add up to 7-8% of the width. It wouldn't make sense to drill too close to the calving front either.

The benefits of a staggered hole line escapes me, so that leaves a 3+3 configuration of horizontal plus flowline, either T or +. For now, I would say 3 across fairly near the grounding line and 2 down the flowline from the northeasternmost hole, subject to revisiting the bedrock radar and what is known already about shelf bottom channeling and fjord circuation
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 11, 2015, 06:42:55 PM
The DMI Sentinel scenes of Petermann are only at moderate resolution but very convenient for making a time series. The filmstrip below shows the daily pattern from 25 Jun 15 to 10 Jul 15. Sentinel consistently detects certain features and their development.

The physical significance of these is not clear, other than flowlines, rifts and melt progression. There is an intriguing central feature between Porsild and Kap Schoubye, just below or maybe part of the grounding line, so part of the glacier rather than its floating ice shelf. Note too the melt region between Porsild and Sigurd Berg.

DMI is not the optimal place to monitor rifting or velocity -- that is best done with 15 m Landsat band 8 (or for those with access, WorldView 0.5 m) with full-on Sentinel resolution also useful. There are two active rifts right now, in the NE near the calving front and midway along the NE wall, the upper crack. These have progressed somewhat but not dramatically to date.

I've redone the images several times to get a more effective immediate display. Animation did not work because of too much jitter (Sentinel images have warped geometry), the filmstrip is too wide except for the fanciest monitors, so I ended up breaking up the 16 dates into 4 image of 4 days each. The latest date is on the left, ie July 10th in the left corner the first image, July 7th in right corner (file names are confusing).

To make these, I selected 'Sentinel only' at DMI and the default 16 images. These turned out to be a nice daily series without glitches. After uploading in gimp as 16 layers, cropping and so forth, I used 'filmstrip' in the filters -> combine submenu. This tiles up only the active layers. By adding an alpha channel, selecting and deleting the blank black followed by 'autocrop' cuts the product down cleanly to 4 tiled dates.

I did not enhance contrast or false-color etc because the original grayscale in Sentinel has a physical meaning (but what?).  Part of it is roughness/smoothness of the ice at scales commensurate with the probing radar wavelength.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 11, 2015, 06:47:26 PM
The physical significance of these is not clear.

Watch the cracks on the right?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 11, 2015, 08:11:32 PM
Getting back to developing resources for optimal placement of Andreas M's 5 drill sites later this month, here is a matched set of locally enhanced contrast viewed in the 'glow' false color palette. This sometimes can draw out features and trends that would be visible in grayscale but not necessarily jump out there.

I'll put together a reference Landsat image shorlty where people can place their 5 dot grid as well as something for bedrock topography and ice shelf bottom channeling.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on July 12, 2015, 08:31:13 PM
Thanks for the help and suggestions, everyone; here is what I got so far as one (of several) plans. Please note that this one oceanographer's perspective what good locations are. There are other oceanographer's plans which may even be better, and then there are people interested in sediments to core that have a different set of questions in mind that are as or even more important. There is also bottom topography under the ice-shelf (very poorly known) that will impact both sediment cores and ocean pathways of warm waters. So, there is always a give and take, but it is good fun. [I am also working off LandSat channel-8 imagery as the drilling requires a source of fresh water in the forms of some of the many ponds.]

EDIT: Grounding line is thick black line near km-0; open circles are sensor locations with the underside of the ice from laser altimeter flights shown as blue track lines to the east and west of the central channel of the floating glacier. AWS is a new automated weather station that shall support 5 sensors ocean sensors, all other locations support only 2. Looks like we may also have several very fancy differential GPS to resolve vertical (and horizontal) motion such as tides to within a centimeter or so for the 20-30 days that the ice drilling team works on the floating glacier.

EDIT-2: And yes, I am watching Espen's crack near km-30. All sensors shall be deployed to the south of it so that with another ice-island potentially forming there, our sensors are not drifting away with it.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 12, 2015, 08:44:06 PM
Hi Andreas, good idea to keep the holes behind the newly formed potential calving line.
How long do you expect it takes to drill those holes?

PS: Oden is now heading towards Faeroe Islands.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on July 12, 2015, 10:20:24 PM
If all goes well, then it takes about 5 days to drill each hole. So if only that bloody sea ice would flush out of Nares Strait between now and when Oden will arrives at Thule Air Force Base on July-29 ... [Writing a blog post on that as we speak, give me a few hours to finish it.]
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 13, 2015, 05:21:03 PM
Still digesting above information. Meanwhile I looked to see what Cresis has for EW transects in this region: not too many, most are NS. They need to show another decimal point or two on their radargrams for lat,lon to allow better compatibility with Google Earth which goes to 6 decimal points.

I looked at a 2002 horizontal transect that actually went right up the Porsild Gletcher, meaning it captures the transition zone. There are two pronounced bedrock channels sections on the sides at depths 680 and 891 m; the asymmetry has been noticed previously (east side is 211 m deeper).

These depths need to be adjusted to WGS84 sea level via a track crossing from 2014 where this was first annotated by Cresis. The plane also made at 34º turn from oblique; I 'corrected' that flight segment to horizontal by cosine projection of image width.

These are actual 2 km wide channels, not just dips in one section (potholes) because they have profile-matching counterparts that extend for considerable distances in other sections. It is not clear when or how (ice or water erosion along faults?) these formed nor why they should be so close to the walls (no tributary glaciers on the west side).

The second two sections are from a somewhat oblique flight that doubled back. The eastern channel may be migrating more centrally. I did not try to second-guess Cresis here, just used their magenta and red surface picks. The vertical spacing bars are at 500 m intervals.

The eastern channel is quite close to the wall and may underlie chaotic tributary ice melange downstream. It is not clear if bedrock profile controls erosion of the ice sheet underside to any extent. Note the bedrock profile overall is quite rugged and has no resemblance to a classic U-shaped fjord valley.

Possibly two small glaciers formed the U-shaped  channels and only later was the intervening terrain reamed out during heavier glaciation, a work still in progress. This fits with the regional view of small narrow glaciers and an 'immature' landscape. Petermann flos was blocked by a huge glacier across Kane for a long period.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 13, 2015, 05:55:01 PM
Quote
working off LandSat channel-8 imagery as the drilling requires a source of fresh water in the forms of some of the many ponds.

Might be better off with their 731 product initially than band 8. The 731 can be pansharpened to 15 m with 8 with retention of colors (though this will gain little).  My impression is less meltwater now than two weeks ago (maybe some meltponds drained?) and it is mostly down south near or past the grounding line. And this despite clear weather.

I've attached the 12 July 15 taken at time 19:15:20.1278839Z which didn't cover any further south. Not really seeing ice in the fjord breaking up, indeed Kane ice outside is sort of in a holding pattern. Sometimes Sentinel GRDH imagery is better for ice status, the hv 002.tif image.

The fracture tips have not developed any further on band 8 as of today, but the middle one could very well over thenext 2-3 years.

Vertical GPS to a cm at five sites for three weeks, that could be very instructive. How long does it need to collect signal before making a measurement or is it continuous?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 13, 2015, 06:40:03 PM
The sea ice in the fjord will go soon after The Nares Express begins its journey to the south ;)

Andreas and his team will have no problems entering the fjord later in the month or August, maybe they will watch a minor calving as well, that piece in front of Belgrave Glacier could easily be sent of while they are there?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 13, 2015, 07:10:07 PM
The Belgrade rift tip has been progressing south which is not conducive to joining up with the rift coming down from the south. However removing or even softening of the melange would relieve back pressure on the Belgrade portion so your scenario could come to pass. As the ice shelf moves up now at 3 m per day, it has to push the whole fjord melange ahead which results in its own compression.

However removing that issue does not equate to extensional forces. Those are coming from friction with the slower moving adjacent tributary. This friction is not evenly distributed, causing rear parts of the ice shelf to be held back while forward section moves ahead at the bulk speed, resulting in the shear that gives rise to the rift and its widening and tip extension.

The midway rift was active earlier in the summer but has stagnated, though it would not be a good idea to set up a tent straddling the tip. The nearby melt ponds (which are seen in earlier years) have either frozen over or drained.

In past years, an interior rift developed inside the frozen-in Belgrade rift's NE corner to give an early warning. We might be able to see that even at 15 m width. The Greenpeace ship in 2011 moored more to the west, at the central channel. That does not appear to be flowing this year, much less kayak-able 35 km inland.

I wonder if Andreas or others can use the US license to Worldview3 to get current imagery, which is something like 0.3m.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 14, 2015, 04:34:46 PM
Here is a more northern transect of Petermann, this time from 2014 which is closer to current ice conditions than 2002 (bedrock won't have changed but the ice has moved ~ 17 km since). The transect is oblique, with its northeastern part past the nominal position of the grounding line.

It is 173 m from ice surface to interior bedrock at its highest. The western channel is still evident (and seemingly occupied by an upheaval: orange tinting) but the eastern one is ambiguous but regardless no longer deeper. Central basal topography again is rough, not that of a U-shaped fjord so might have younger sediment under the ice shelf.

The magenta and red lines represent Cresis' interpretation of the radar, which is challenging at places for the bedrock. The  image without markups can be viewed here: https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/images/20140331_01/20140331_01_006_1echo.jpg

The second image is more oblique, intersecting the first on the west side and then angling up to just below Sigurd Berg. No sign of the eastern channel midway up the fjord; that on the west side is present but not a continuation (because it is below the intersection). The bedrock may appear to have a jagged surface but that is due to scale: only 185 pixels per 10 km -- each pixel represents 54 meters. Two layers of echoes, only partly shown below, is sometimes taken as characteristic of radar reaching reflective sea water instead of bedrock, in which case the red line represents a transect through channels on the underside of the ice shelf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on July 14, 2015, 05:14:52 PM
Ohhh ... /me runs off to get the radar (and corresponding laser altimeter) data for this 2014 section across Petermann near the grounding line ...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 14, 2015, 06:57:39 PM
Thank you A-Team for being so helpful on "our" behalf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 14, 2015, 10:03:01 PM
The Cresis radar collection is a fantastic public resource, right in there with Landsat, Sentinel and Modis for importance, intuitive interpretation and ease of use. I would say under-utilized though.

Not everyone archives their radar imagery though. Right now, I'm trying to get a hold of some secretive footage of Humboldt's northern pinning point.

The really smart groups like Renland send their people -- including their Photoshop whiz -- to Kansas for hands-on device building and advance training with custom sled radar data processing. So many cores drilled at the wrong place ... not going to happen at Renland. (Petermann ice shelf has different issues -- not looking for flat isochron stratigraphy because that's last seen 100 km back.)

Somewhere many posts ago I put up quite a few NS flowline radar tracks of which there are many (including near-exact repeats of different years) though none along the melange edges. I have some new processing tricks now so re-did a central 2014 flight line below -- be sure to view at full 1066 pixel width. To tile these tail-to-head, the second image had to be rescaled 82.2%, a bizarre aspect not expected (but the norm) of consecutive Cresis flight segments.

20140512_01_013_2echo_picks.jpg
20140512_01_014_2echo_picks.jpg

The second image shows all Cresis flight segments over Petermann for 1993-2014. These are really easy to load into Google Earth -- the only trick is to notice the big kml that does an entire year is at the bottom, out of initial sight. The way stations are provided at fabulous precision and can be extracted from kml viewed as plaintext. I don't recall any north of Humboldt available for 2015.

This jumble of tracks cannot be resolved at any Google Earth blow-up because they deliberately flew second and third flights in later years right on top of previous years to the best ability of plane GPS. They can be resolved though by just activating one year at a time in GE checkbox column.

The third images show two 2014 flowline tracks that resulted from the plane looping around at the end of the fjord and making another pass down a more westerly flowline (which controls for a number of technical radar issues). It is not so easy to align these (latidude? flowline normals?) but it does seem that the two do have some, but not all, features in common. Here the secondary and tertiary echoes are helpful.

Physically, features that extend horizontally may amount to ocean circulation erosive patterns on the underside of the ice sheet.

These region does not seem to have horizontal transects but those can be reconstructed using all the many verticals and kriging in between (left as exercise). Again, view image in a separate browser tab at full size (native Cresis resolution).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 17, 2015, 04:52:43 PM
Even the moderate resolution Sentinel provided at DMI provides quite an informative quick look. The image from July 16th shows Nares Strait with some open water but lots of large blocks of ice. It appears that an adjacent large block in the Petermann Fjord is becoming detached but currently has no place to exit.

Three pronounced white streaks on the ice shelf correspond to the longitudinal surface drainage channels which for some reason are better radar reflectors than intervening ice. There is also noteworthy reflections from melange along both sides.

The most interesting feature, seen consistently in recent Sentinel imagery, are the three 'plumes' coming in from tributary glaciers on the northeast side, most notably from the southernmost tributary, Porsild and Sigurd Berg.

The problem here is ice coming off these glaciers is immediately and completely deflected at their confluences with the main Petermann glacier, over much shorter distance scales. Only the 'plume' from Sigurd Berg is in the appropriate location. The others may have more to do with the grounding line / hinge line /equilibrium float line region ather than representing discharge, though this association too could be coincidental. These lines can shift over time; they have not been redetermined in recent years but may be visible in radar through some indirect effect.

Contrast has been adaptively enhanced in the image in the right half to bring out features.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 17, 2015, 06:12:56 PM
A-Team, I never thought about the grounding line marks at Petermann just below Sigurd Berg Gletscher, the same can be seen at Hagen Bræ: https://forum.arctic-sea-ice.net/index.php/topic,396.msg56639.html#msg56639

Things are not that complicated when you find the right thread in the ball of yarn ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 17, 2015, 07:14:41 PM
That is a really good idea, Espen. Rather than just staring at Petermann, find support from comparative glaciology. What others do we have where the grounding line is known, in addition to Hagen Dazs? This is where Mauri Pelto's knowledge comes in handy, it would be a lot of work to chase down otherwise. After that, what is the physical basis for visibility on non-visibility on Sentinel radar or 731 Landsat.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 17, 2015, 07:52:10 PM
A-Team actually we dont need all them flights
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 19, 2015, 06:48:50 PM
Thirteen years ago, a comprehensive sample of 7 evenly spaced north-south tracks were flown over Petermann glacier and ice sheet. Three of these were re-flown in 2014. This provides an opportunity to compare lower surfaces of the ice sheet, provided the images can be aligned (since the calving front has retreated and the grounding line may have moved).

Since the ice sheet has moved about 10 km towards the sea over this time frame, it would seem that any fixed features on the lower surface of the ice sheet would be displaced by that distance, unless consistent erosion of the underneath by warm ocean water and refreezing of water onto displaced ice sheet conspire to keep a stationary pattern.

The first image establishes locations at Google Earth and aligns Cresis radar tracks 20020528_01_011 and 20140505_01_017-18 based on up-glacier features. Here the resolution (pixels provided per km of flight line) in 2002 was only half that of 2014 (18.7 pxl/km) which itself is not extravagant relative to plausible crevasse or channel dimensions, not quite 2 pixels per 100 m.

The crevasse region appears 'more developed' in the 2014 frame. At one time, E Rignot -- who camped on Petermann for three field seasons -- suggested that the ice sheet might break off at the hinge line rather than piecewise down the ice sheet. Ice depth here in these image is about 500 m.

Another alignment option is to anchor each north-south track (which follow ice flow lines) to the conveniently orthogonal flight segment from the same year, 20020528_01_019, which even more conveniently corresponds quite well to the grounding line.

These intersections are somewhat a nuisance to determine since every flight segment image uses different horizontal and vertical scales and is inadequately marked up for latitude and longitude. However these can be interpolated fairly easily provided the plane is not flying a curving path; additionally, there can be a good match between features as seen in NS and EW views. Below are the 2002 images not yet with this registration -- click to view at full width.

The 3rd image provides the last of the 2014 tracks (the other two are above). It has been enlarged to the point of diminishing returns in the region downstream of the grounding line. The magenta and red horizons were drawn on at Cresis; there may be a slight advantage to also display the unannotated companion image (1echo).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 21, 2015, 04:32:43 PM
Whoa ... the seasonal ice in front of the Petermann ice shelf is breaking up on an overnight time scale. The movement is attributable to tides and currents, not to glacier push. (I did last 3 days 20-19-18 July 15 side-by-side below because Sentinel images are not regionally alignable due to geometric distortion.)

Stand by ... I am looking for higher resolution imagery for today. There may be some slight calving of the ice sheet itself. Landsat is clouded over for the 20th; Sentinel has not yet posted for today.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 21, 2015, 04:50:12 PM
Wow!
from Polar View 2015-07-20 full resolution:
(edit:  the bluish mask is sure skewed!)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 21, 2015, 05:28:17 PM
I see many (what I think are) cracks - red ovals show where calving fronts may occur (if I'm not 'seeing things').
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 21, 2015, 05:53:33 PM
Might want to look at the GRDH instead of GRDM (H for high, M for medium) at the Sentinel hub https://scihub.esa.int/dhus/  Interesting how in going from Landsat to Sentinel we are merely swapping sun shadows for ascending oblique pushbroom view of walls blocking the radar.

Some of those cracks have been there for 5-7 years without progressing. None of the Sentinel image types are adequate for tracking progression compared to 15 m Landsat (or WorldView which is on-demand plus we don't have access to). But let's see what shows up today, the 21st.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 21, 2015, 06:36:48 PM
Thanks, A-Team
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: solartim27 on July 21, 2015, 07:44:07 PM
So, is this clouds, corrupt data, or did someone detonate a small thermonuclear device?  Looks like the left side went away, with the center portion stable.  Click to animate.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 21, 2015, 09:26:39 PM
Interesting observation.  (Don't forget to crop after co-registration, if you can get down to 700 pixel width, animations will display w/o click.)

Those black bands -- and the disappearance of yesterday's clean rifts -- are a bit mysterious. I suppose the bands could be low, wet, salty spray (elevated dielectric) that then murk up radar penetrance. Smoke wafting across the scene? The calving front does not seem affected insofar as it can be seen at all.

Looking now at HV send-receive polarization, the bands are gone -- but so are the rifts. Are we looking at surface melt or frazil? -- this ice wasn't very thick to begin with. We need to look at other wavelengths. Hmm, Aqua showing banded clouds regionally (standing waves in air pressure). Hard to say what is underneath at Petermann ... looks like water.

s1a-ew-grd-hv-20150721t123227-20150721t123327-006909-00956a-002.tiff
s1a-ew-grd-hh-20150721t123227-20150721t123327-006909-00956a-001.tiff
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 21, 2015, 10:07:12 PM
Just an example from Kimmirut in Canada, watch how quickly the sea ice disappear over the last 7 days:

http://www.lookr.com/lookout/1198520951-Kimmirut#action-play-month (http://www.lookr.com/lookout/1198520951-Kimmirut#action-play-month) 
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 21, 2015, 10:07:34 PM
Here is 'NOAA" at DMI (which may refer to the NOAA-19 weather satellite instrument package). The 19th is there in the lower half to show where Petermann is located (DMI co-registers the images). The second calving of seasonal ice is clearly visible. On the upper image of July 21st, a lot of clouds cover the upper fjord. I've not seen an explanation of what the colors signify in these images.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 23, 2015, 06:47:15 PM
I'm curious to see what Petermann will do now that the backpressure from seasonally frozen melange has been released. It has been cloudy lately but the 22 July 15 Landsat has the immediate calving front. This being the 23rd, the Sentinel is more to the point. No noteworthy response as yet.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 23, 2015, 07:10:11 PM
A-Team, I dont believe the sea ice back pressure in Petermann Fjord play a major role, on the other hand I think melt water do, it is cutting through the glacier ice in many places, like what a Glaser do when he wants to cut a window glass.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: icefest on July 24, 2015, 03:10:51 AM
No matter what the glacier does, that blue and white photo looks magnificent, A-Team.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 27, 2015, 08:50:01 PM
Quote
dont believe the sea ice back pressure in Petermann Fjord play a major role, on the other hand I think melt water do, it is cutting through the glacier ice in many places

It's important here to keep in mind the 7 distinct components of the Petermann system: the glacier proper, its attached floating ice shelf, the ice from the four east side tributaries, ice along the western wall, and floating melange in front of it all.

The glacier is pushing the whole system forward all year long at about 3 m per day (with mild seasonal variations). The ice shelf moves at this speed too as it is rigidly connected and there is little internal dynamics (thinning or thickening by stretching or compression).

The tributary ice is not quite keeping up and an area of rotating blocks (ball bearings) takes up the difference though there is shearing too. At its edge, this ice is essentially frozen to the eastern wall. The western wall has no tributary ice but is deformed (wrinkled longitudinally) by drag between the rock walls and the moving central ice.

The melange goes from nothing most summers to a continuous extension of the floating Nares Strait ice. If that ice is stuck, which it often is, the melange has nowhere to go even as the ice shelf keeps pushing on its rear. This compression should result in ridging and rafting by early spring but we may not have enough resolution to see it.

If you accept Newton's 3rd law, the rigidly frozen melange exerts a force to the south, equal and opposite to the force exerted on it by the ice sheet. The magnitude of this force varies seasonally.

After the irresistible force meets an immovable object business gets sorted out, this melange buttressing force still may effectively resist the opening and widening of rifts (especially those near the calving front) because these represent parts of the ice sheet moving faster than parts somewhat hung up on the tributary sides.

Rift origination in Petermann Glacier has nothing to do with melt pond draining or hydrofracturing of melt water extensional crevasses. Rifts always originate on the sides on flat ice. On the west, that means off the rock walls; on the east, on the tributary ice boundary.

No rift has ever originated in the central 2/3 of the ice sheet, hinge line or anywhere else during the satellite, aerial photographic or explorer-map eras as far as I can tell.

Rift development and tip propagation initially precede obliquely backwards towards the center for the reason given. Exposed sea water in the rift can freeze over without really healing the rift however.

In 2010 and 2012, I recall an overwintering rift developed a rift within the rift that extended through this briny thin ice which eventually came to fail fairly abruptly across the entire width as leveraged motion became prodigious. Landsat did not provide high resolution imagery in these years.

Water from any active meltwater channels or intercepted melt lakes could accrue in the rift bottom but is not material since that ice is already so thin/weak/warm/briny compared to the ~200 m ice that must be broken to extend the rift. The water has little access to the growing rift tip and lacks sufficient volume, depth and time for tip melt or hydrofracture. It will simply find a melt channel through the brine ice and exit to the fjord water below.

Rifts do originate and extend mostly in the summer season, at a time when the upstream glacier is moving at its fastest, meaning the side drag is at its highest. The ice up to the grounding line is at interior ice sheet temperatures but over the ~50 years it spends in the fjord adjust to ocean temperatures from below and solar and air heat inputs from above, as dirichlet boundary conditions of Fourier's heat equation. The issue here is not ductile vs brittle but rather tensile failure.

None of the 2015 rifts developed liquid water this year. I don't recall any liquid water in any of the 0.5 m resolution WorldView rifts for August 2014 either. Rifting is mainly just a carpenter snagging his shirt on a nail.

Now Rignot one time suggested -- because of maximal erosive cavitation just past the grounding line -- that the ice sheet could calve off everything in one giant event due to tidal flexure. That hasn't happened to date but the big news is that Andreas M is setting out to actually measure tides within the fjord, notably under the ice shelf, using differential GPS.

It is possible that large tides and resonances over bedrock sills have some responsibility for rift origination hot spots or tip propagation, in a manner reminiscent of a very slow swell (here seiche or soliton) breaking up pack ice. However that would crack the ice straight across the channel which is not the reverse herringbone pattern of the contemporary rift set.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 27, 2015, 10:08:01 PM
This year had considerable meltwater at some points in mid June to mid July but apparently not as much or as late as in some years. How though do we go about making a quantitative home comparison?

First off, we will be limited to 2013-15 because that is the range of Landsat-8 and there is no hope of a process working across different instruments.

The Landsat preview image has some possibilities: melt water shows up clearly as dark blue on medium blue. If our eye can see it, the gimp color picker can pull it.

When you click on a dark blue pixel, that defines a point (color) in the RGB color cube. However the tool has an adjustable radius in that space, enabling it to pick out every pixel in the image within that little sub-cube defined by the tolerance, either contiguously with it or globally.

Even better, the tool can be set to find a more representative average of whatever radius out from the designated pixel. By filling in a little square in an unused part of the image with this average color, it can be used as a better base color (for non-contiguous picking) even if it never exactly occurred in the original image.

The selection of meltwater pixels can often be improved by the 'grow' and 'border' commands which firm up lake boundaries by picking up off-color pixels that really belong to the melt but cannot be picked initially without making the selection too broad.

So far, so good but the initial image consists of 30 m bands 1,3, and 7 whereas there may be better combinations where meltwater really jumps out. The combinatorics of picking 3 bands out of the 10 available (10*9*8 = 720) already requires a walk-through animation generated by a script to see what was working.

Even fancier, given two representative areas (melt vs nearby ice), the distance between cluster centers in color space could be calculated in advance to eliminate many frames in the animation, or even just filter to the best (which might not be so apparent visually). This is effectively re-inventing support vector machines (see wiki) without much thought to the kernel.

To precede more rationally, it might make sense to de-correlate the Landsat bands with principle component analysis. The first 3 components then serve as RGB, presumably with beneficial effects on meltwater color space isolation. However there is the issue here of whether contrast enhancement should be provided first to the higher bands. See second link below.

Another option -- which is surprisingly effective -- is rapidly scrolling through a large number of color spaces besides RGB (still using bands 137). There is freeware for this (Dstretch) that acts as an ImageJ plugin. It has been primarily used for faint petroglyph visualization; I've discussed ages ago in other forums but don't know if it still works in ImageJ2.

http://forum.arctic-sea-ice.net/index.php/topic,154.msg34636.html#msg34636 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg34636.html#msg34636)
http://forum.arctic-sea-ice.net/index.php/topic,909.msg34293.html#msg34293 (http://forum.arctic-sea-ice.net/index.php/topic,909.msg34293.html#msg34293)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 29, 2015, 11:41:28 PM
There was quite an interesting Sentinel showing at DMI today. Despite low resolution, I am finding not a whole lot gained by downloading the very large high resolution images. In this case, only the HH polarization matched DMI features. I've attached the large version for what it is worth, s1a-ew-grd-hh-20150729t1127226-001.tiff which will need a click to display

There do seem to be things happening but without a Landsat of the same day, these brightening areas on radar reflectance are difficult to interpret. Landsat though has been cloudy. This was a huge issue for about six weeks in 2014.

The fjord ice has cleared. Again. Hopefully it stays that way until Andreas M's ship can get in.

I added July 30th. This just scans through a succession of adaptive contrast adjustments, hopefully drawing out the best of this DMI Sentinel product somewhere along the way. ImageJ animations are really easy, not the overhead of Gimp.

Landsat showed up with something for the 29th, quite a bit of it cloudy. It looks like a very small piece maybe calved off the extreme NW corner. Cracks here have not widened or extended. This has no significance to the future lifespan of this, one of the last remaining ice shelves in the Northern Hemisphere.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 12:41:52 AM
And here is a welcome calving to Andreas at Petermann:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 01:13:56 AM
And more shaky ground will be waiting for Andreas, the crack further down is developing:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 01:44:21 AM
Here is a revised animation showing July 31 vs August 1 2015, note the crack further down the glacier:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2015, 07:20:27 AM
Nice action! This is a good one to study for its mechanistic history -- growth from the vertical rift until it met the more established horizontal rift that had taken an unproductive turn to the south. We should check winds from the Hans Island AWS as well as Petermann's own (if it's still reporting).

However the pivoting that moved the northeast side out and away could just as well be attributable to retreating tidal currents tuggin on the newly unbuttressed calving edge. Note the calved piece cannot rotate because of two pinning points. Although it is still free to translate to the NNE, that may not reflect the forces available to it.

Petermann is much more favorable for time series of rapid events than Jakobshavn because of the almost daily Landsat images of the former compared to weekly for the latter.

The area of the broken off piece is  94977*56.25/1000000 = 5.34 km2, counting the pixels, using the 7.5 m/pxl square and sq m in a sq km (needs a commonsense check, maybe tomorrow). I'm not real sure why we would want to, but compare this to the 59 km2 for Manhattan Island.

The tabular berg will not tip like ones at Jakobshavn as it is ~0.1km thick (ie 100 m below, 10 m freeboard). This means the volume estimate comes in at 0.53 km3, still much larger than the inside of a Walmart SuperStore. As we know, calved ice shelves do not contribute to sea level rise as they are already floating (though this one isn't fully).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2015, 07:36:04 AM
The middle rift has not extended in the 01 Aug 15 image -- it is indistinguishable from the 31 Jul 15 in Landsat band 8 15 m. It often appears to change in the Landsat preview image, probably because of illumination or melt issues. However the tip has notably extended since mid-August 2014.

The history of any Petermann ice sheet fracture can be tracked back to the year 2000 using the previously posted image series assembled by NASA. Most have a multi-year history of initiating and extending, followed by pausing if not end-stage stagnation. Rifts never quite heal over as new ice is briny whereas ice coming off the Summit is completely fresh.

The second image was provided, as a lab notebook sketch, by Andrew Muenchow on his very informative outreach blog. It looks like they decided on a 1 1 (1+1) 1 array for their steam-drilling, tidal GPS, sediment sampling and CTD casts. This is quite a ways south, 10 km maybe, of the fracture tip area. Not that it wouldn't be hair-raising to be camped there as this broke off.
http://icyseas.org/2015/07/20/petermann-glacier-tidal-heaving/ (http://icyseas.org/2015/07/20/petermann-glacier-tidal-heaving/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on August 02, 2015, 09:38:35 AM
It seems that the calving took place along with clearing of the sea ice.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 10:09:01 AM
It seems that the calving took place along with clearing of the sea ice.

It was a Blue Moon action?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 11:31:52 AM
This image "screen dump from Google Earth" before the latest calving show a large brown area, looks like rocks but probably mud, any ideas?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 02:28:36 PM
Just received a mail from the Captain on Oden, they are fighting the ice in Nares Strait  but through the worst and now entering Washington Strait.
Andreas is informed that a "parcel" is waiting around the corner.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2015, 02:42:35 PM
Those wonderful high resolution Worldview images in zoomed Google Earth were taken in July/August 2014 (discussed already in posts many moons ago) show lines of glacial till from tributary glaciers, notably Sigurd Berg and Porsild. Initially lateral moraines, these become medial moraines as tributaries merge. Not so common in central or northern Greenland glaciers but you can see lots of them by googling images of more erosive 'Alaska glaciers'.

At first this till looks like solid rock but that is because it is draped as a thin layer conforming to forms in the ice. The rift is not cutting through solid rock but merely through dirty ice. In some regions, the glacial flour has been redistributed by meltwater flow but mostly it is frozen solid (mud is liquid).

The till provides excellent markers for the slow-motion (decadal) shearing at the ice sheet/tributary ice boundary as shown before in earlier animations. There is no till on the northwest side because the minor tributary glaciers are not coming down off a highland and so have little erosive capability.

There is no scientific interest in the till per se as the parent rocks would provide better geological sampling. However since some members of the Muenchow expedition plan to sample Holocene moraines under the Petermann ice sheet, the question comes up, especially for the northernmost sampling site, as to whether sediment would be confused by the contribution of tributaries rather than Petermann itself.

In terms of tides, a blue moon has no significance beyond the large spring tides of any full moon syzygy. Andreas M has posted diurnal data on neap tides in the Nares Strait, including from a station just opposite Petermann.

Nothing is currently known about tidal circulation within Petermann fjord as that falls between the cracks for global tide modeling projects. We do know however from the work of E Rignot that the hinge line below Porsild can be detected by SAR fringes, that is, the boundary between grounded glacier and floating ice sheet as only the latter rises and falls with the tides.

The team will be studying tidally driven vertical motion of the floating ice sheet using differential GPS at four of their study stations, as well as the 3 m/day horizontal creep.

The range of outcomes are discussed at the iceseas link above: one extreme is the sea cave scenario in which the ice shelf is too rigid to rise with an incoming tide (meaning hydrostatic pressure rises instead), another where the ice shelf itself is rigid but flexes at the hinge line, and a third where the ice shelf can bend throughout its length to accommodate an incoming tide (ie a wave front passing through successive GPS units). Warmish ice might be flexible enough over the time scale of tides to accommodate them without crevassing.

The tides themselves are not large here, going by the nearest site with data, Discovery Bay in Canada, but it takes work to lift the many megatonnes of ice sheet even the slightest. Tides themselves cannot be equated to oceanic circulation under the ice shelf because of meltwater flows and other issues that could be more important in disrupting temperature and density stratification.

The issue really is that a stagnant layer of water under the ice sheet would exchange heat very slowly with the bottom ice, whereas the current paradigm both here and in Antarctica calls for more dynamic circulation patterns and rapid channelized melt of the underside, resulting in a shorter shelf life.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2015, 03:53:24 PM
Quote
It seems that the calving took place along with clearing of the sea ice. It was a Blue Moon action?
We have a great opportunity here to observe surface currents not only in the Nares Strait (been done) but also in the inlet to Petermann Fjord. My impression is that clearing/re-packing of the sea ice against the calving front has taken place repeatedly in the last week on an overnight time scale.

Now we have a chance to follow the journey of this particular tabular iceberg within the inlet. It has a distinct shape and a sizable area many times the size of a football field Walmart parking lot. This is of interest in determining tidal and wind driven circulation which have implications for sea water circulation under the ice shelf proper (and so its stability).

Here we are going to need coverage provided by all the open source satellites to get enough snapshots to measure velocity between them. Note for this we need timestamps. As discussed above, it is best practice to attach these to images or file names so they cannot get separated.

I see now that DMI does provide the UTC timestamp for NOAA images in the upper right corner (2015-08-02  07:27 UTC for the 02 Aug 15 below) though not for Modis Terra, Aqua or Sentinel. However the NOAA-19 imagery is really marginal for tracking our berg. We might however get images 4 times a day between Landsat, Sentinel, Aqua and Terra (depending on the A-train ordering of polar orbit satellites).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 03:55:03 PM
There is nothing special about the Blue Moon, that is simply only a 2nd full moon in a calendar month, but that said I believe full moon and the accompanying "tidal" movements have an impact on floating glaciers in particular, that was seen at 79 Fjord around July 31 2015  http://forum.arctic-sea-ice.net/index.php/topic,400.msg59045.html#msg59045 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg59045.html#msg59045)

and to my best recollection at the 2 latest and only recorded calvings at Steensby Gletscher.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 02, 2015, 06:04:02 PM
The calf is preparing its trip to the south image from 12:50 UTC August 2 2015:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2015, 07:04:18 PM
Definitely broken away from its mooring points. Not clear if something more has happened.

Whoa ... where did all the ice go in Nares overnight?

Sentinel is perhaps showing a crack already in the cleaved piece.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 02, 2015, 07:55:04 PM
I don't enough about that image to interpret what it shows, but this http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_367.A2015214154500-2015214155000.1km.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_367.A2015214154500-2015214155000.1km.jpg) shows ice in Nares at 15:45 UTC
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 02, 2015, 08:41:29 PM
aqua has the better view http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2015214143000-2015214143500.500m.jpg (http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2015214143000-2015214143500.500m.jpg)

the ice is moving south faster below Peterman fjord, than above (north of it)where it moves not very much, which opens up an easy route for Oden which is (was?) moving at 7.7 knots http://oden.geo.su.se/map/ (http://oden.geo.su.se/map/)
The ice map is misaligned on that chart (same thing happened at the start of last years cruise)
or is that just my explorer playing up?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on August 03, 2015, 12:48:18 AM
There is nothing special about the Blue Moon, that is simply only a 2nd full moon in a calendar month, but that said I believe full moon and the accompanying "tidal" movements have an impact on floating glaciers in particular, that was seen at 79 Fjord around July 31 2015  http://forum.arctic-sea-ice.net/index.php/topic,400.msg59045.html#msg59045 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg59045.html#msg59045)

and to my best recollection at the 2 latest and only recorded calvings at Steensby Gletscher.


When watching for changes in fast ice formations I've found that a few days after a spring tide is often the most likely time to see some action. My assumption has been that the extreme tide fractures the ice & then it takes a day or so for wind or current to move the freed portion.


Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 03, 2015, 04:51:49 AM
Quote
I've found that a few days after a spring tide is often the most likely time to see some action.
Attribution not easy between big tide, peak melt season, melange buttressing removal, or all of the above. if this keeps up, where does it end?

I would not care to be out in a kayak right about now in front of the Belgrade Glacier chaos -- the lower rifts just shattered with the release of blocking pressure. In turn, what up-glacier is contingent on them?

Note the surface till from Sigurd Berg/Porsild being taken for a ride down the fjord, to confuse the next generation of sedimentary geologists. The calved piece is riding down a conventional flowline, no sign of cross-currents.

Viewing this same region in 2013 and 2014, it is apparent that this calving event was over two years in the making.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 03, 2015, 10:32:58 AM
Just received an email from Andreas:

Espen:

Thank you for the e-mail that reached me today. It was delivered by the Captain in person to me during a science meeting, so it was shared with a few people aboard. We did indeed see the small 2-5 km^2 calving on the north-eastern side of Petermann where we will arrive tommorrow morning. There are people from 10 different countries aboard including the ice-drilling team from the British Antarctic Service that will try to drill through the ice-shelf to deploy ocean sensors below the ice cavity. I am struggling with the instrumentation for the central hole which incudes an automated weather station as well as 5 discretly sampling ocean sensors. All data will be transmitted, if I can work the eletronics and Iridium, thrugh the web, so you (and everyone else) should have almost real time access to what is happenening both above and below Petermann's ice-shelf.

Andreas
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 03, 2015, 12:52:22 PM
Andreas M does a fantastic job of communicating climate research ... this is really a sea change from the past where people worked secretly, fretting endlessly over data theft and being scooped by ruthless competitors [based on what happened to Rosalind Franklin].

To get a sense what may be going on at Petermann, I looked up two PI's on the Oden grant to get a grip on their research interests (last ten papers): quite impressive. To root around in the articles, enter the names into Google Scholar, then go to Profiles (to remove hits to similar names) and then reverse-sort chronology to most recent for active links (or just paste complete titles below into regular Google search).

Alan C Mix is a professor of oceanography at Oregon State active in paleoceanography, paleoclimatology, micropaleontology and geochemistry who directs the OSU Stable Isotope lab http://stable-isotope.coas.oregonstate.edu/ (http://stable-isotope.coas.oregonstate.edu/)

Links between atmospheric carbon dioxide, the land carbon reservoir and climate over the past millennium
TK Bauska, F Joos, AC Mix, R Roth, J Ahn, EJ Brook
Nature Geoscience

Climate change decouples oceanic primary and export productivity and organic carbon burial
C Lopes, M Kucera, AC Mix
Proceedings of the National Academy of Sciences 112 (2), 332-335

Tracing Bering Sea Circulation With Benthic Foraminiferal Stable Isotopes During the Pleistocene
MS Cook, AC Ravelo, AC Mix, IM Nesbitt, N Miller
AGU Fall Meeting Abstracts 1, 08

Seismic stratigraphy of the Bering Trough, Gulf of Alaska: Late Quaternary history of Bering Glacier dynamics
A Montelli, SPS Gulick, LL Worthington, AC Mix, S Zellers, JM Jaeger
AGU Fall Meeting Abstracts 1, 1287

Synchronization of North Pacific and Greenland climates preceded abrupt deglacial warming.
SK Praetorius, AC Mix,
Science, 345(6195), 444-448.

Oxygen isotope stratigraphy in the Gulf of Alaska (IODP Exp. 341)
H Asahi, AC Mix, I Suto, CL Belanger, A Fukumura, S Gupta, S Konno, ...
AGU Fall Meeting Abstracts 1, 1286

Long-term perspective underscores need for stronger near-term policies on climate change
SA Marcott, JD Shakun, PU Clark, AC Mix, R Pierrehumbert, AP Goldner
AGU Fall Meeting Abstracts 1, 4044

Timing of Cordilleran Ice Rafting, Freshwater Discharge, and Implications for Subsurface Ventilation in the Northeast Pacific During the Last Deglaciation
S Praetorius, AC Mix, FG Prahl, MD Wolhowe, MH Davies
AGU Fall Meeting Abstracts 1, 06

A High-resolution Detrital and Oxygen Isotope Record from Flemish Pass, Labrador Sea
E deJesus, JS Hoffman, PU Clark, AC Mix
AGU Fall Meeting Abstracts 1, 1420

Advection of Sea-Ice Meltwater and Halocline Water Along the Siberian Continental Margin
D Bauch, S Torres-Valdes, I Polyakov, E Chernyavskaya, A Novikhin, ...
AGU Fall Meeting Abstracts 1, 1006

Martin Jakobsson is a professor of maringeologi och geofysik at Stockholm U

A New Digital Bathymetric Model of the World's Oceans
P Weatherall, KM Marks, M Jakobsson, T Schmitt, S Tani, JE Arndt, ...
Earth and Space Science

Mapping the Surficial Geology of the Arctic Ocean: A Layer for the IBCAO
DC Mosher, RC Courtney, M Jakobsson, C Gebhardt, L Mayer
OTC Arctic Technology Conference

Grain Size Variability and Sea Ice in Middle to Late Quaternary Sediments along the Lomonosov Ridge, Arctic Ocean
R Gyllencreutz, M O'Regan, LA Lowemark, M Jakobsson
AGU Fall Meeting Abstracts 1, 1294

An Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient
M Jakobsson, JA Dowdeswell, M Canals, BJ Todd, EK Dowdeswell, ...
AGU Fall Meeting Abstracts 1, 0971

High-resolution Mapping of Offshore and Onshore Glaciogenic Features in Melville Bay, Northwestern Greenland
F Freire, R Gyllencreutz, S Greenwood, LA Mayer, M Jakobsson
AGU Fall Meeting Abstracts 1, 0973

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
MJ Bentley, CÓ Cofaigh, JB Anderson, H Conway, B Davies, ...
Quaternary Science Reviews 100, 1-9

Reconstruction of changes in the Amundsen Sea and Bellingshausen sea sector of the West Antarctic ice sheet since the last glacial maximum
RD Larter, JB Anderson, AGC Graham, K Gohl, CD Hillenbrand, ...
Quaternary Science Reviews 100, 55-86

Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM
JB Anderson, H Conway, PJ Bart, AE Witus, SL Greenwood, RM McKay, ...
Quaternary Science Reviews 100, 31-54

Acoustic evidence of a submarine slide in the deepest part of the Arctic, the Molloy Hole
F Freire, R Gyllencreutz, RU Jafri, M Jakobsson
Geo-Marine Letters 34 (4), 315-325

Middle to late Quaternary grain size variations and sea-ice rafting on the Lomonosov Ridge
M O'regan, E Sellén, M Jakobsson
Polar Research 33
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 03, 2015, 01:31:54 PM
Just the Aqua and somewhat later Terra snapshots of yesterday's calving event. They did capture some intermediate states. I have not located timestamps for them. Changes in the NW corner are shadowing artifacts though this region could also go. There may be other satellite coverage but we don't have access to it.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on August 03, 2015, 04:32:53 PM
It looks like the Oden placed a weather buoy at the mouth of the Petermann fjord. I now see temperature pressure and dew point data for there on Wundermap.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 03, 2015, 06:37:11 PM
13:35 UTC:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 03, 2015, 10:33:11 PM
Quote
It looks like the Oden placed a weather buoy at the mouth of the Petermann fjord. I now see temperature pressure and dew point data for there on Wundermap.
Hmmm, is there some trick to getting it to display or is the satellite out of position to receive? I am not seeing an active station on Petermann at http://www.wunderground.com/wundermap/. (http://www.wunderground.com/wundermap/.) There has been an AWS there for years as part of the overall Greenland network but it has not been actively reporting for the last couple of years.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 03, 2015, 10:53:52 PM
could wundermap be using weatherdata from Oden itself?
http://oden.geo.su.se/map/ (http://oden.geo.su.se/map/) shows air pressure and temperature and relative humidity.
Also water temperature, wind speed and direction. It is at the entrance of Peterman fjord at low speed. The data points from earlier today show speeds of 8knots without making much progress on the map, I wonder whether that is an indication of it ramming through ice where short bursts of speed are to be expected. Comparison with worldview shows it should have entered the ice.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 03, 2015, 11:23:10 PM
Makes sense. Though I've not heard of wundermap accepting mobil base stations. And it has not updated in quite a whileThey have not yet reached the edge of the icesheet and would not have set up on their first drill station. As part of differential GPS, they are placing a triangulation unit quite high on rock wall. But that wouldn't be suitable for ice shelf conditions. So ship meteorology. Unless they are just using Hans Island.

I interpret 12:50:00 GMT-700 (PDT) as local time in Corvallis, Oregon (home of PI Mix) or Pacific Daylight Time and 7 hours off Greenwich Mean Time which is UTC for our purposes. However it was 14:29 there when I retrieved the weather report.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on August 03, 2015, 11:42:37 PM
I don't see it anymore on Wundermap so I don't know what to think. It was labeled as Buoy and 4 letters which I of course  didn't record and don't remember :(

When I clicked on it for more details it had no history graph which I interpreted as normal for a station that has just started up. Oh well not important really since the Oden provides the same data.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Subjectivist on August 04, 2015, 12:57:59 AM
Do the tabular bergs that break off of Petermann get names like the ones that form in Antarctica from the ice shelves there?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 04, 2015, 01:30:22 AM
If you go back to the start of this thread two years ago  you'll find people talking about PII2012 and about its fragments later in the Nares strait thread.
Also have a look at http://icyseas.org/2012/07/17/petermann-glacier-and-2010-and-2012-ice-islands/ (http://icyseas.org/2012/07/17/petermann-glacier-and-2010-and-2012-ice-islands/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 04, 2015, 10:08:48 PM
At 18:50 GMT+1 Oden was back in Peterman fjord reporting 11.4m/s wind from 187 deg (i.e. south?) 5.8 deg C air temp and -1.2 deg water temp. http://oden.geo.su.se/map/ (http://oden.geo.su.se/map/)
The sea ice overlay is still way out but can be switched off
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 05, 2015, 03:37:53 PM
The calved pieces continue to move north along the side of the fjord with little evidence for any rotational eddies but a slight drift to the center. The area of tabular iceberg calculated above could almost be doubled given the secondary pieces, still not quite half of annual forward movement of 1.25 km * 14 width = 18 km2.

Note both polarizations show two distinct regions on the calved piece. Possibly the southern portion (right half) got sloshed with sea water during the calving process.

There appears to be additional wasting along the northwestern wall. It is hard to see in there as the tall steep walls can shadow both Landsat (sun angle) and Sentinel (forward scanning).

This Sentinel image hh hv RGB has a lot of other interesting features back on the mainland, no idea what they are or why just showing up now (end-season ablation? improved processing?)

The Oden looks to be moored at the calving front, hooray let the online science begin!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: cats on August 05, 2015, 11:08:46 PM
Here is a link to a nice blog post by Céline Heuzé - http://polarfever.com/2015/08/05/sea-ice-vs-glacier/ (http://polarfever.com/2015/08/05/sea-ice-vs-glacier/) . She is on board the Oden.  There are some great pictures of the sea ice they have encountered as well as a picture of the face of Petermann
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on August 05, 2015, 11:29:50 PM
I noticed today that the Oden is moving around and that the water temperatures are above 0C.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 05, 2015, 11:44:52 PM
Nothing like being there. Sometimes looking straight down from 7,080 km is hard to interpret relative to an oblique image (say off the bridge of the Oden).

The first image follows up on the apparent debris stream along the west wall seen in Sentinel above. I managed to mostly lift off the shadows but it is still not clear whether fjord water has been able to work its way down along the rocks or the ice sheet continues over to the rocks but just with smoother ice. The ice sheet moves at a meter per day so is not frozen on.

Over at the rifted area on the east wall, it looks to be a clean break with no further rifting induce by loss of the buttressing from the first rifted ice. Note the break is right at the incoming Belgrade Glacier ice -- it will be vying for fjord space with the oncoming ice sheet. Further down, the major future rift remains dormant.

The third image shows the rather dingy-looking face of Petermann from Céline Heuzé's blog linked above (as contrast adjusted). I like to get these things on the record here because external links have a way of disappearing. It does not quite show the area we need. I presume that is Faith Glacier but photos can also get horizontally flipped.

She has an early blog post too about shipboard safety http://polarfever.com/2015/08/03/helicopter-safety-and-ctd-yoga/ (http://polarfever.com/2015/08/03/helicopter-safety-and-ctd-yoga/) and a twitter feed with more pictures. https://twitter.com/clnhz (https://twitter.com/clnhz)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 06, 2015, 09:08:30 AM
Here is a link to a nice blog post by Céline Heuzé - http://polarfever.com/2015/08/05/sea-ice-vs-glacier/ (http://polarfever.com/2015/08/05/sea-ice-vs-glacier/) . She is on board the Oden.  There are some great pictures of the sea ice they have encountered as well as a picture of the face of Petermann
a link from that site leads to more photos at
 https://petermannsglacialhistory.wordpress.com/2015/06/18/hello-world/ (https://petermannsglacialhistory.wordpress.com/2015/06/18/hello-world/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 06, 2015, 06:00:34 PM
That and the twitter site are billed as the official account for the Petermann Glacier expedition on I/B Oden - August 2015. No team member name is associated with it; possibly multiple individuals contribute. Or it is done back on campus somewhere by an outreach PR person?

It is really sketchy on photo locations for an expedition carrying all these high precision GPS units. Ordinary cell phone cameras can sometimes stamp position (don't know if the ship carries a tower emulator). It would be better to 'attach' photos to a Google Earth view (ironically as Andreas M and Espen have done so extensively here).

For example, where in the world are these people "looking for clues in rock, sediment, shells, & bone along Petermann Fjord to decipher past sea level changes" whereas Petermann fjord itself is shown on the undated Landsat drape over 30 m DEM (which wasn't effective) as far too steep and mountainous to have the flat ice-free terrain shown in the image.

Quote
Land teams have all been deployed – boulder, ice shelf, & ecology teams are on site and ready to go!

Current oceanographic data are sparse, providing only a “snapshot” of conditions  and almost nothing is known about how the oceanography of the fjord varies over time – does warm water permanently circulate beneath the floating tongue? Does turbulence in the fjord help melt the ice?
I attached today's Sentinel. The calved pieces have moved to the central part of the fjord. It is not easy to disentangle tides, currents, and wind pushing on them. However movement is 'trending' towards exit out into the Nares current.

https://twitter.com/@Petermann_ice/
https://petermannsglacialhistory.wordpress.com/2015/06/18/hello-world/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: cats on August 07, 2015, 08:33:43 AM
From this blog post - http://polar.se/blogg/mammal-observations-hall-land/ (http://polar.se/blogg/mammal-observations-hall-land/) it is possible that some of the photos of the land might be Hall Land - I don't know where exactly that is, but other Greenland experts on the forum can perhaps locate it.  My understanding is that the land teams were delivered to their research locations via helicopter, so perhaps they are "in the vicinity" of Petermann
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Sleepy on August 07, 2015, 09:20:48 AM
A bit more info from the Swedish Polar Research Sectreteriat regarding Petermann 2015.
http://polar.se/en/expedition/petermann-2015/ (http://polar.se/en/expedition/petermann-2015/)

Quote
The expedition will examine the relatively unexplored outlet end of this large system, by documenting changes in the grounded Petermann Glacier, its buttressing ice shelf, and ocean conditions since the end of the last glacial period. Primary scientific questions include:
1.How sensitive is Petermann ice shelf extent to documented climate changes within the Holocene?
2.Is ice-shelf response independent of, or linked to, variations in the grounded Petermann Glacier, ocean thermal conditions, or relative sea level (i.e., sill depth)?
3.What are the rates of change and variability of these systems in response to early Holocene warming, Neoglacial cooling, and post-Neoglacial (late 19th century to present) warming?

Chief scientists: Alan Mix, Oregon State University, USA and Martin Jakobsson, Stockholm University
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 07, 2015, 07:22:32 PM
Am I the only one who got problems downloading Landsat data?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 07, 2015, 07:55:01 PM
Odd situation.

Search works. The small 731 preview image works and enlarges.

The large 731 preview image gives this error message: Not Found The requested URL /browse/full/landsat_8/LC80342482015218LGN00 was not found on this server.

The big package download started but then stalled, now it is going again, now it is stalled again.

This is Friday noon in America, not to mention lunchtime at Chicago server center. Your expectations are too high? Check back with us mid-morning Monday. At least it is a clear enough day!

Hmm, now I am seeing everything works fine going back four images to 03 August. I recall them having announcing some service downtime on Wednesday or so. Probably messed things up rather than fixing. So they have one bad pointer to the big preview but why 3% or so of the big file downloads ok is harder to understand.

Ok ... now they are back from lunch and looking into it. New message: "Service Temporarily Unavailable. The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later."

It is working again. Is this a great country or what!?! Not the 'Natural Color' though, just the big package (from which you can make your own 'Natural Color' by stacking bands 731 in ImageJ and going to Color -> RGB.
We should be able to see the Oden at 15 m resolution
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 07, 2015, 08:00:30 PM
OK, I thought I was banned for bashing a certain middle east "allied" of the US ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 07, 2015, 08:54:35 PM
Allies? http://www.wrmea.org/2006-may-june/uss-liberty-and-the-nsa-one-deceit-too-many.html (http://www.wrmea.org/2006-may-june/uss-liberty-and-the-nsa-one-deceit-too-many.html)

Meanwhile, no sign of the ship along the calving front. Do we have lat,lon for them today? -- that Oden tracker is lame at higher resolution. The calved piece is in the upper left of the second image. Too bad they didn't arrive in time to put an AWS/GPS on it ... I am assuming its motion is more due to wind than to current.

Nothing happening at the Big Rift.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 07, 2015, 09:01:56 PM
And my grandfather was "prisoned" or rather "K-Zded" because of them, waist of life!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 07, 2015, 09:04:47 PM
This http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/ (http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/) has a  picture of a warmwaterdrilling site next to a meltwaterchannel on Petermann. Maybe a Swedish speaker can translate?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 07, 2015, 09:18:04 PM
This http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/ (http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/) has a  picture of a warmwaterdrilling site next to a meltwaterchannel on Petermann. Maybe a Swedish speaker can translate?

Often I am proud to be 100% Scandinavian, and together we do pretty well, socially in the top (despite the high taxes)  but one of the reasons we are there, and because we have the trust in other people, that really makes the difference, and believe me I have to more visited mote than 70 countries.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 07, 2015, 09:29:48 PM
säker, inga problem min svenska är grov men

2015-08-07
Expedition: Petermann 2015
A trip in history to predict the future

Latitude: 81 ° 4'N
Longitude: 61 ° 28'W
Speed: 4 knots
Temperature: 5 ° C

It is now a week since we left Thule,  and after a polar bear visit, amazing views and more than 40 seals, we reached Petermann Glacier in northwestern Greenland on Tuesday.

In recent days, researchers from participating countries flew in. The first group to reach solid ground, the Swedish project, explored two Arctic areas near Petermann Glacier - Hall Land and Ellesmere Island both of which really belong to Denmark (just like Hans Island) which in turn we think of as a Swedish colony and so it's all Swedish property. ;)

On Monday they were flown in and pitched their first field camp in Hall Land where they will collect plants, insects and bones and drill permafrost cores to look for ancient DNA. By looking at these ancient DNA samples, researchers want to reconstruct how the ancient ecosystem structures looked and use that to predict how the Arctic ecosystem will be affected by future climate change.

The second field group packed two full helicopters on Tuesday and flew out to the Washington Land to investigate how the ice has retreated in history. They will be using a hammer and chisel to collect stones so that with Be10 and  Cl36 dating, they can determine when stones were last exposed to cosmic rays -- the stones thus can reveal how the ice and sea levels have changed over the last 15,000 years.

The last group consists of four scientists from the British Antarctic Survey (BAS) and the University of Delaware. They were flown in yesterday a couple of kilometers up on the glacier. Using a hot water drill, they will bore through the ice shelf, then use a CTD to find out how the circulation of water looks under the ice over time. By studying water circulation researchers get some clues about what links there are between the ocean and the large melt water channels running under the glacier.

[The lat,lon are not provided to much precision; they should really be given as kml files in Google Earth. I am not seeing the big orange tent on Landsat. The northernmost location provided a few posts back in Andreas M's lab sketch is more than a few km in from the calving front.]
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on August 07, 2015, 09:43:18 PM
Thank you for the (not too literal ;)) translation
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Sleepy on August 08, 2015, 06:13:27 AM
A-team, översättningen var väl ok, förutom ett stycke. Är även du från våra kolonier?

Here's a bit more about cosmogenic exposure dating from the 2004 expedition.
http://polarforskningsportalen.se/en/arktis/forskarrapport/cosmogenic-approach-glacial-history-greenland/ (http://polarforskningsportalen.se/en/arktis/forskarrapport/cosmogenic-approach-glacial-history-greenland/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on August 08, 2015, 04:27:05 PM
More photos and description of activities by the Oden expedition on twitter...

https://twitter.com/Petermann_Ice (https://twitter.com/Petermann_Ice)

and Instagram

https://instagram.com/petermann_ice/ (https://instagram.com/petermann_ice/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Jim Hunt on August 08, 2015, 04:31:12 PM
Not to mention on YouTube:

http://youtu.be/nqfJ6HdoloQ (http://youtu.be/nqfJ6HdoloQ)

via https://twitter.com/polarforskning (https://twitter.com/polarforskning)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 09, 2015, 07:25:40 AM
Real-time information quite a difference from the old explorer days where they would go off the radar for years at a time, frozen into the ice.

It appears that a really small additional piece has calved off. I traced it back to its origin...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 09, 2015, 02:37:50 PM
It looks like the 2 cracks below Belgrave and Hubert Glacier are expanding:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 09, 2015, 07:49:50 PM
Melt and sun angle can affect images at different dates (which do not have the same path,rows and so cannot be accurately aligned). Note especially the lower right hand corner where the drainage is changing markedly in appearance. It may be better to just watch for rift tip growth on the B8 15 m band -- the main rift cannot really pivot about a fixed tip because it is too weak to resist such a torquing (and so propagates instead). That has indeed happened this year but not recently.

That would be cool if the Petermann expedition could hang a grad student out the helicopter window to take a high resolution picture of the rift tip.

* To what extent do secondary (and here, tertiary) parallel up-glacier rifting distribute shear forces away from the initial rift and so delay eventual calving?

* Will one of these become the eventual rift assuming the primary freezes in to stagnancy?

* Is this process influenced by absolute position relative to the fixed rock wall frame, ie as the ice shelf moves towards the sea, the shearing point may stay fixed favoring lower rifts?

The second image takes 3 different dates (days 140, 188, 220) with the same Landsat path,row to see if an 80-day interval resolved the widening issue of the second rift. These Landsats annoyingly had different pixel sizes meaning they could not be precisely co-registered within ImageJ for cropping to the ice sheet.

It may be that the tributary ice streams from Porsild and Sigurd Berg are falling back unevenly due to friction at their interface with the moving ice shelf and the immovable rigid walls. This does not apply a torque to the portion of ice sheet that has already passed by but does enlarge the lower edge of the rift (but does not lengthen its tip). Thus this secondary feature may now have taken up the response to rifting forces. Between days 140-220 the upper rift tip has noticeably lengthened by a few hundred meters (shown in earlier posts).

I added 2013 and 2014 Landsats almost exactly a year earlier ... very instructive. Tearing of the ice shelf makes global alignment infeasible in addition to the path,row geometric mismatch problems. However large patches in the central shelf are rigid enough to align. This ice shelf is changing much faster than 'glacial speed' but still over a moderate annual scale (until it abruptly fractures without warning).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on August 10, 2015, 10:03:48 AM
Oden nicely visible just outside the calving front (S-1 IW 7.8.2015)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 10, 2015, 07:24:15 PM
Just received some images from our friend Andreas in the far north:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 10, 2015, 08:30:23 PM
Ship has moved over to other side. I'm thinking that metal decks make it a very strong radar reflector. Chopper a big improvement over schlepping gear across rough ice like in the olden days. Does Andreas M have enough web to see the forum or is he just attaching photos to email?

Hmm, is that a crack and incipient rifting (arrow)? Logical place for it. Landsat is cloudy today.,
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 10, 2015, 08:33:51 PM
Espen:

I have not forgotten about you and the wonderful Arctic Sea Ice community with regard to news and reports from Oden, but I get barely by on 3 hours of sleep per night. Nevertheless, there are a few pictures that you wanted and I sent you. This one is of the Petermann terminus with a view towards the southwest. Faith Gletscher is hidden by the perspective, but you see the indentation in the coastline of Washington Land where it should.

Please feel free to share this with anyone in any form on the Sea Ice Forum, including any snipes from e-mails that you think may be of interest.

Andreas

P.S.: Please recall that I do NOT have any access to the internet, only e-mail with attachments <100 kBytes.
________________________________________
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on August 10, 2015, 11:08:04 PM
Just received some images from our friend Andreas in the far north:

Beautiful!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: cats on August 10, 2015, 11:24:37 PM
Those images are wonderful and nice to hear from Andreas, especially since he is obviously super busy.
While poking around the Petermann expedition site, I came across this set of updates (https://petermannsglacialhistory.wordpress.com/updates-from-co-chief-scientist-alan-mix/ ) from the Co-Chief scientist and found them very interesting.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on August 10, 2015, 11:59:09 PM
Thanks, Espen! And Andreas!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on August 11, 2015, 07:32:30 AM
Those images are wonderful and nice to hear from Andreas, especially since he is obviously super busy.
While poking around the Petermann expedition site, I came across this set of updates (https://petermannsglacialhistory.wordpress.com/updates-from-co-chief-scientist-alan-mix/ ) from the Co-Chief scientist and found them very interesting.

Very interesting, he explains the scientific missions in quite a lot of detail.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 11, 2015, 04:55:04 PM
Decent enough Landsat today. It seems like a lot of ice has blown in. The calved piece is still holding together and can be seen at the top. The lower image shows the imaginary band 8 rift I also imagined seeing in Sentinel the other day, qite plausibly just meltwater drainage features. The large piece that calved had a typical piecewise linear fracture coming in from the east that was met by a curvaceous rift coming down from the north so not all fractures are straight lines.

The third image is taken from a zoom provided by Digiglobe to Google Earth. Since this is much higher resolution that Landsat 15m, it is suitable for accurate measurement of rift width, using relocatable points spanning the rifts (rather than rift widths themselves because their boundaries are not reproducibly measured).

The idea is to measure the same distance in 2015 Landsat images to get an idea both of absolute rift width and the average rate of widening. I suspect the team out on the ice, using two of their high precision GPS units straddling the rifts, could actually measure the widening velocity over a 24 hr period even if that were just a cm or two. Not a scientific priority obviously compared to drilling, nor a safety issue (compared to low elevation helicoptering over open water) given they are well up-glacier from these rifts.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 12, 2015, 04:57:45 PM
From Sentinel 1A, there appears to be something going on in the NW corner of the calving front, possibly a prelude to a few sq km of calving. The brightening in radar does not correspond to anything yet in Aqua/Terra; indeed nothing dramatic in yesterday's higher resolution Sentinel. Image shows 11, 10, 09 of August. The Landsat 731 is deeply shadowed in the ROI.

The 30-day widening is shown in the 3rd image, perhaps one 15 m pixel farther across. The tips have not extended at all. That means the torque is growing that could lead to sudden brittle fracture, predictably a SW extension of affected tip (more likely the 3rd than 2nd or 1st.)

Today's Landsat is not showing any calving action in the NW corner, though the ice margin has melted out to the rock wall. The remaining ice is properly called an ice tongue, a specialized part of an ice shelf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Gonzo on August 12, 2015, 06:41:47 PM

"NASA launches operation ‘OMG’"
http://www.msnbc.com/msnbc/nasa-launches-climate-operation-omg (http://www.msnbc.com/msnbc/nasa-launches-climate-operation-omg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 12, 2015, 09:59:15 PM
Here's the year to year comparison of the NW corner. Changes, but not dramatic for a whole year.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 13, 2015, 08:22:45 PM
Andreas reporting from Petermann:

Hi all:

I am ecstatic to report that our weather station on Petermann Gletscher is alive collecting and reporting data. The earlier shut-down 8-hours after deployment on Aug.-10 was caused by Iridium satellite transmissions, not the set-up of hard- or software of the weather station itself. I attach a plot of the data collected so far that is being used by  the ship's operators to prepare and plan for flight operations over the glacier. There will be a massive increase in helicopter flying, because on saturday the CBS 60-Minute team will arrive via helicopter from Qaanaaq, Greenland about 250 miles to the south.

The five ocean sensors are NOT yet plugged into the UDel observing system, because ice drilling operations at that site will not start until monday or tuesday. Our graduate student Peter Washam is on the glacier right now. The so-called Ice-Shelf team just completed a second drill hole near the grounding line of Petermann Gletscher where the ice is about 365 m deep with another 300 m of water below the ice. The picture shows Peter at that (second) drill site shortly after the camp there was established there monday. The weather station was set-up about 13 km seaward  at what will become the third drill site. Hopefully he did not forget to re-program the ocean sensors to move bits and bytes along the 600 m long serial cable (4800 baud) at a slower rate than we used them in an calibration test lowering them from the ship to the 600 m deep bottom of the ocean near Petermann Fjord.

The 2 1/2 day long time series shows air temperature about 0.5 and 2.0 m above the ice as well as wind speed and direction as well as atmospheric pressure. A GPS unit shows that the station is drifting about 3 m per day towards the ocean as is expected for this fast moving glacier moving about 1.2 km per year.

My spirits are high after several days of anxious anticipation and waiting for a call from the weather station. Wish us luck.

Andreas (aboard I/B Oden at 81 32.28' N 062 04.0' W on 09:49 UTC)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on August 13, 2015, 10:11:16 PM
Good luck, Andreas!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 13, 2015, 10:59:42 PM
Wow, this is a dicey business -- one mistake or one equipment going south and years of preparation go down the drain.

Did he include any location information on the second drill hole? I will guess that it is sitting right on one of the 2014 radar flight lines. Since it is drifting along each day, it would probably be more useful to locate it on a Landsat relative to identifiable stable features, rather than having one-time lat,lon. That is, lagrangian coordinate work better here (until a widening rift is encountered.

I'm thinking  that they may have drilled deliberately into one of the underside channels (or crevasses) past the grounding line. The 350 m depth of the ice is an important clue as to where they are relative to underside features. I'm recalling the ice actually getting thicker down icesheet for a ways.

Alternatively, they may have drilled through the center of a longitudinal flowline; some reports envision these as hydrostatic equilibrium adjustments of the surface to freshwater melt channels carved in the underside. I am not aware of any previous quantitation of Petermann meltwater, much less buoyant plumes entraining ocean water.

No sonar studies have looked at emergent meltwater cavities at the grounding line -- here the drill hole is too small in diameter and refreezes too fast to lower a sonar device down.

On the PI's blog, he notes they "deployed a seismic profiler and air gun to investigate the sediments and deeper geology of the seafloor. This equipment uses compressed air to produce waves that penetrate deep into the layers of sediment and underlying rock that make up the seabed; this allows us to understand how this important region of Greenland was formed. We’re currently mapping these deeper layers throughout Petermann Fjord and into Nares Strait."

You can see what type of data this type of study produces at the open source article:
Late quaternary ice flow in a West Greenland fjord and cross-shelf trough system: submarine landforms from Rink Isbræ
JA Dowdeswell et al 2014
Quat. Sci. Rev., 92, 292–309.

They were able to get three sediment cores from beneath the ice shelf -- the first ever taken through an ice shelf in Greenland. This was at the first camp, not the grounding line one. I was fascinated by the first step in core logging, which is gamma density scanning with the core still in its tube which is usually done with a heavily shielded Cs137 source. How in the world do they get this thing through natl and internatl airport security and how much does it weigh?

The link below explains the first steps in finding out (non-destructively) what's in the core. Obviously most of this technology was developed for commercial logging, with the climate change research community a side benefit.

http://www.geotek.co.uk/products/sensors (http://www.geotek.co.uk/products/sensors)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 14, 2015, 04:50:36 PM
The 2015 Petermann expedition posted high resolution images of the 28 July 2010 and 06 Aug 2012 mega-calving events and links to the NASA hourly time series. There are a couple of interesting things in those images that have not been commented on before which are relevant to the next big event (which I don't foresee happening in 2015).

First, the 2010 event came very close to calving off not only its 251 km2 but also the 119 km2 of the event that only happened 24 months later. That is, the rift tip of the 2012 event was already well across the central flowline in 2012 and a massive shear zone cutting across the tributary glacier ice had already developed. This would have been 379 km2, a very substantial proportion of the whole ice shelf.

The second thing to notice is that tributary ice, along with its glacial till covering, remained frozen on to the main Petermann ice shelf piece for some days. I don't believe this would be possible today because the relative motion observable over short time scales shows tributary ice is not moving as a block with the ice sheet itself and could not remain attached after calving, as indeed we've seen this year in miniature. This suggests the ice at the interface is warmer than before.

The additional cut-outs below illustrate these points but it is really best to look at the original imagery (which is too large for the forum at 4896 x 3672 pixels). The third image shows a minor rift that is still stagnant today (blue arrow) and on that has become a major development by 2015 (magenta)

The expedition had a meeting on the future of Petermann, with the PI saying "idle speculation" on the ice shelf future should be avoided (until they finish collecting and processing data?).

https://petermannsglacialhistory.wordpress.com/background/
https://petermannsglacialhistory.files.wordpress.com/2015/06/petermann_ali_2010228_lrg.jpg
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 15, 2015, 03:46:57 PM
Here is the first round of data, 2.5 hours worth, from the AWS from http://icyseas.org/. (http://icyseas.org/.) With the sub-centimeter precision of the GPS units they got at the last minute, lurches in glacier movement should be clearly resolved. However issues with variable ionospheric delay and inaccuracy in satellite orbital and
clock information can degrade precision.

There is definitely some noise over short intervals, ie the glacier in reality is only moving forward, not retreating as some successive data points would suggest. The 1200 m/yr is in line with expectations but does not look like a least squares fit yet. This would make more sense with after a week or month of data is at hand.

From blowing up the graph to recover the underlying cvs, it looks like the AWS is sampling displacement 12 times per half hour (576 times per day). The successive readings I looked at below had a 4 m difference, suggesting the noise level is ±2 m. If the ice sheet moves 3.3 meters per day, that would be 0.0057 m (5.7 mm) between sample points.

Convolution smoothing (rolling weighted average) might make some sense here though optimal processing could depend on understanding sources of systematic error (if any). Conceivably, fourier transform would reveal a tidal effect, motion being faster at high tide if the grounding zone is lifted somewhat instead of the ice shelf merely hinging.

Temperatures are well above freezing. The channel shown drains into the small lake that they are using for the steam drill (tower shown). It would be a challenge to locate the drill site on Landsat from the data provided so far.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 15, 2015, 05:27:34 PM
Very nice Landsat today, suitable for locating drill sites, GPS, and weather station. LC80420012015226LGN00 at EarthExplorer taken at 2015:226:18:20:01. These have to be located relative to ice sheet features as their lat,lon coordinates drift. I looked for the yellow tent, helicopter, stream drill near the grounding site on the 731 preview -- rather small and hard to say when the Landsat was taken relative to their short time on site. There are a fair number of drainages and melt lakes in the region and they may have adjusted the site location relative to the earlier sketch Andreas M posted.

I've repeated below GPS velocities from 2011-12 that we considered in #203 on June 19, 2015.
http://forum.arctic-sea-ice.net/index.php/topic,53.msg54449.html#msg54449 (http://forum.arctic-sea-ice.net/index.php/topic,53.msg54449.html#msg54449)
http://www.earth-syst-sci-data.net/5/277/2013/essd-5-277-2013.pdf (http://www.earth-syst-sci-data.net/5/277/2013/essd-5-277-2013.pdf)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 15, 2015, 09:37:53 PM
We're seeing some changes in the NW corner of the calving front; the animation below shows the progression of various rifts from 2013 and 2014 to today. As usual, a progression of rifts develops further upglacier over time and come to adsorb most of the shearing stress. The wall shadows cannot fully be removed and of course vary according to day of year; note too moving lagrangian coordinates providing the alignment give an apparent motion Faith Glacier and fixed rocks as an artifact. With interesting exceptions, many features are remarkably stable over time. If I had to pick a characteristic time scale for time series developments on this ice sheet, it would be a few weeks rather than daily or decadal.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 15, 2015, 09:51:28 PM
A-Team an interesting observation, nice work! ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 17, 2015, 06:07:24 PM
Looking at a long Landsat series of this northwest corner of Petermann, the slow-moving story of the aftermath of the the he slow-moving 2010/2012 collapse comes down to gradual ocean penetration of the region between the ice sheet and its vertical wall, with the loss of ropy ice there not so far from Faith Glacier.

Some glaciologists differentiate between ice sheets and ice tongues. The former are buttressed on their sides by fjord ice or other glaciers with only the calving front facing the ocean; the latter are peninsulas surrounded by ocean water on three sides. Here we have something in between.

The effect here on Petermann is first an insignificant loss of buttressing retarding ice sheet advance, there being no longer resistance on the upper NW side. Second, as the ocean works its way further south (a process measured in years, not decades or seasons), the ice sheet becomes more susceptible to rifting from CCW torques (which would otherwise force the ice sheet against rock). This would favor rift development on the northeast junction of the ice sheet with its tributary glaciers.

The land boundary is not so easy to see because it is almost always in shadows. Below in the 2015-13 comparison, it is tinted green.

It is possible but unproven that the recent calving event was thus facilitated. However forcing from Belgrade glacier may having been a more significant contributor.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 19, 2015, 08:28:22 PM
A new development on the NE corner of the calving front. Looks more like a melt surge than a calving, most pronounced in hv polarization. No Landsat at this time. The enlargement, using both polarizations, does not immediately clarify the interpretation.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 21, 2015, 03:26:58 PM
We've sort of lost track of the Petermann 2015 expedition, what with all the excitement down at Jakobshavn. However some very interesting material is being posted from the Oden which we should capture and consolidate here.

The image below shows a very suggestive bathymetry of the upper fjord (no depth scale provide but maybe 500 meters max), key sills, old lateral moraines, and data collection sites. Some of the tributary glaciers are currently contributing a fair amount of sediment in plumes.

The map also provides a useful history of the calving front right up the minor loss this August. Note some of the sediment cores are at sites that have been covered by the ice sheet, probably for 4,000 years or more. Petermann is already freezing up so further fracturing is unlikely this season.

http://www.geo.su.se/index.php/expedition-logs/1276-petermann-glacier-2015 (http://www.geo.su.se/index.php/expedition-logs/1276-petermann-glacier-2015)

The Delaware researches discovered warm water (0.323ºC) some 800 meters down a hole drilled 100 m through Petermann Gletscher ice. This warm water did not originate in the fjord but arose in the Atlantic and entered the Arctic Ocean near Spitsbergen. Prior to northern Greenland, the water had circulated along Siberia, Alaska and the coast of northern Canada. This data was obtained from the first of five holes drilled through the ice shelf by the British Antarctic Survey crew.

The water temperature is high enough at all depths to melt the underbelly of the ice shelf all the way up to the grounding zone. However the rate will depend strongly on circulation of the contacting water. Tides, up-glacier meltwater exiting at the grounding zone and incoming tributary meltwater would all contribute to this mixing.

There are five ocean sensors packages deployed down each cable. A weather station designed by David Huntley of the University of Delaware provides the command and control between ocean sensors, battery and solar panels. The system calls home every three hours with stored data through the flaky Iridium satellite phone. The battery system is quite challenging to keep alive during the long dark cold winter, but automated data collection represents a huge step forward over systems requiring someone on site or periodically revisiting a very remote area to retrieve data.

http://icyseas.org/2015/08/20/ocean-observing-station-reporting-from-below-petermann-gletscher-greenland/ (http://icyseas.org/2015/08/20/ocean-observing-station-reporting-from-below-petermann-gletscher-greenland/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 22, 2015, 12:34:37 AM
Don't recall if we've seen this very large scale map before ... maybe a few new place names and elevations on it.
http://maps.pgc.umn.edu/arctic/nga/03/preview/Petermanns%20Gletscher.jpg (http://maps.pgc.umn.edu/arctic/nga/03/preview/Petermanns%20Gletscher.jpg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: icefest on August 24, 2015, 10:01:40 AM
Repost from : http://icyseas.org/2015/08/23/taking-the-pulse-of-petermann-gletscher/ (http://icyseas.org/2015/08/23/taking-the-pulse-of-petermann-gletscher/)
Quote from: http://icyseas.org/2015/08/23/taking-the-pulse-of-petermann-gletscher/
Posted by Pat Ryan for Andreas Muenchow

23-August-2015 at 80:57.3 N 061:27.1 W

(note correction below)

I just may have made a discovery that I cannot share with anyone on the ship right now. The giant mass of ice that is Petermann Gletscher just slowed down moving only 1 meter per day for the last 3 days rather than the 3 meters per day that it usually does and that has been reported in the scientific literature. This measurement comes from the newly deployed University of Delaware weather station that also contains a not-so-fancy $300 Garmin GPS as well as 5 ocean sensors that measure temperature and salinity about 95-m, 115-m, 300-m, 400-m, and 810-m below the surface of the floating and moving ice.

Time Series of Glacier Drift
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwA8%2F82f2c7f61b.jpg&hash=c2a57e5ab6a6c1243cdddb04e27b497b)
Time Series of Glacier Drift (correction appears below)
As the glacier puts on the breaks, I also see a rather dramatic increase in ocean temperature from -0.6 to -0.35 degrees Celsius within about 10-m of the ice-ocean interface. The saltiness of the ocean also increased from below 34.1 to above 34.2 practical salinity units that you can think of as grams of salt per kilogram of water, roughly. Only 20 m below in the water column, the opposite is happening: The water there cools a little bit and becomes fresher. This suggests some mixing as the salinity differences become smaller and heat from the lower layer moves up towards the ice. Some force must be applied to the fluid to do this. Recall that a force is mass times acceleration. The force of a mosquito splashing on the wind shield of your car is small, because the mass of the mosquito is small even though its acceleration (from zero to the speed of your car) is large. Now imaging this glacier: Its mass is enormous, so you only need to change its velocity a tiny amount, from 3 to 1 meter per day, say, to generate a massive amount of force.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwCb%2F2ddff1a82c.jpg&hash=f9d7ced7e8aca67fc0f395da7f3110fb)
As I look outside my cabin window right now, I see the terminus of Petermann sitting there innocently not appearing to do much, but it is literally changing the face of the earth as it moves fast, slows down, moves some more, and over 1000s of years cut a very deep fjord and perhaps canyon deep into the mountains and even deeper into the sea floor. The helicopters are whizzing overhead right now returning all the gear that was needed to drill through 100s of meters of hard glacier ice to provide access holes to both ocean and sediments that has been in total darkness for many 100s of years.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwDc%2Ff6f744ea91.jpg&hash=4cc18e791842e9e77311004fd12453c8)
Still, there is life down there, lots of it Anne Jennings, who closely looks at the sediment cores, tells me. We speculate that the life is supported by vigorous ocean flow that connects the open fjord with the glacier covered deep ocean. Food stuff like plankton may move some distance under the floating glacier to support a population of other critters that I know nothing about. No narwhals this year so far, though.

So why I am writing this up here rather than share it with people on the ship? Well, this is Sunday morning and there was much to celebrate last night when the ice drilling team returned after 2 weeks camping on the ice and collecting data from their three drill holes. Furthermore, the the ocean weather station reported for the first time in over 2 days uploading all the data I show above. This happened well past midnight and several of us discussed the data and future plans in the cafeteria until 1:30 am. So the people not working right now are all sleeping (10:30 am here) as we probably will work through the night to map the Atlantic waters flowing into the fjord at its sill towards Nares Strait …  which we have not yet done over the 3 weeks we have been in the area. I probably also should help with unloading the helicopters or getting the Chief Scientist Alan the data files he needs to catalogue the water samples we collected last night. Work on Oden never stops … as there is so much to do as we are barely scratching the surface or bottom of the ocean here. [Incoming helicopter, 4th one since I wrote these lines too fast, perhaps.]

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwEa%2F09b77dcc7d.jpg&hash=d3d689e0b9a8503730bdcee6ec4125f7)
Correction:

Petermann Gletscher did slow down the last few days by about 10% as measured by the GPS at the UDel ocean-weather station. The suggested slow-down to 300 meters per year, however, is false, because I did not properly take into account how the station was moved by 30 meters to the south-west. The correct and updated estimate is the figure below. Please discard the the above figure erroneous.

Sorry for the confusion … more data coming from this station will place the short term change in glacier speeds into a larger context. Furthermore, the present “cheap” GPS system will need to be verified by a set of three “fancy” differential UNAVCO GPS that were recovered today, but we have not yet decoded the data contained on those units.

Back to CTD profiling the water properties across the sill at the entrance to Petermann Fjord that we will have to complete by 3 am or in about 6 hours.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwEX%2Faef6036d7b.jpg&hash=90ec389db56d52f5ed694006e201312e)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Hunter on October 05, 2015, 04:54:52 PM
Quick Petermann update from this morning :)


"Petermann Glacier's remnant floating ice shelf, from an altitude of 34,000'. This photograph was shot at roughly 0845 Thule local time. Note the very low illumination angle of the sun on the terrain. These low sun angles create challenges for DMS photography, especially for our sea flights, which lie far to the north, and thus farthest from the sun in early autumn in the high Arctic. Note also the thick haze on the horizon, an indication of high atmospheric moisture content and increased likelihood of cloudiness (NASA/Operation ICEBridge/John Sonntag)."
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on October 05, 2015, 05:37:25 PM
Beautiful photo ... oblique images are very helpful in visualizing terrain and steepness of tributary glaciers. Note how the NE corner -- the region that broke off this summer, seems to be filling up with ice again (dotted line on Sentinel). The ice shelf only gains a km from a year of forward motion so never really catches up on the larger calving events (as these amount to decades of glacier motion).

Andreas Muenchow has a couple of very informative posts about the research they did on Petermann this August from the Oden. The differential GPS units needed to measure tidal heaving of the ice sheet were in place for 12 days. It is quite a job to unravel the information in this kind of data. The graphic below shows where instrumentation was moored through drill holes below the ice sheet. They have CTD sensors strung at five different depths (to 800 m).

Quote
The 25 Sep 15 Iridium call was the first in two weeks, but it provided a complete data download without ANY gaps in the hourly time series of weather in the atmosphere (wind, temperature, humidity) and weather in the ocean (temperature, salinity, pressure). The ocean data show that about every 2 weeks with the spring-neap cycles, we see very large excursions of colder and fresher water appear at 2 sensors within about 30 meters of the underside of the ice shelf...
http://icyseas.org/ (http://icyseas.org/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on October 08, 2015, 03:05:55 PM
Petermann is situated at a far more favorable location than Jakobshavn in terms of both Landsat and Sentinel coverage frequency. For example some 32 high resolution 'IW' class images are available from Sentinel between February and October of this year. This enable time series with a given instrument.

While we shouldn't expect too much rifting drama during the winter months, Sentinel will be our only observational tool as Landsat has already gone dark.

Note it is not currently possible to define a polygon covering Petermann (unlike at EarthExplorer) and the ridiculous Sentinel search tool provides a 'match' even if only a tiny corner of the search rectangle is hit.

The horrible user interface at ESA is currently undergoing a long-overdue overhaul -- desperately needed with Sentinel-2 already launched in June (but so far not producing any West Greenland images). There are so many things broken with the site now that there hardly space to list them all. Common web features such as pull-down menu options would greatly help in restricting searches but these seem unknown to the inept interface contractor.

The search tool currently seems to return only Sentinel-1A images unless the user has learned from an unlinked page to type in one of four restricting terms (were we supposed to guess S2MSI1C?):

•   collection:S2samples
•   S2A*
•   platformname:Sentinel-2
•   S2MSI1C
•   producttype:S2MSI1C

The most amusing bug is the long-running typo in the page title: 'Sentinels Scientific Data Hub'. I don't expect this to be fixed -- there is no reporting mechanism for users.

Here is the incoherent update posted today.  Some performance degradation? The interface has been in a state of near-total collapse for months, unable even to put up error messages!

Quote
In view of Sentinel-2 In-Orbit Commissioning Review (IOCR) that is planned for next week we are currently configuring the system in preparation for the routine operations of Sentinel-2. At the same time we are experiencing some performance degradation that will be resolved by the new installation of the Data Hub Software that is currently being deployed.The new software will also introduce a new and improved User Web Interface that will be announced in the coming days. We apologise for any inconvenience caused. 08 Oct 2015 - 10:53
S1A_IW_GRDH   2.10.2015
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S1A_IW_GRDH   20.9.2015
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S1A_IW_GRDH   07.8.2015
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S1A_IW_GRDH   27.8.2015
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S1A_IW_GRDH   10.7.2015
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S1A_IW_GRDH   16.6.2015
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S1A_IW_GRDH   04.6.2015
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S1A_IW_GRDH   23.5.2015
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S1A_IW_GRDH   27.5.2015
S1A_IW_GRDH   17.2.2015
S1A_IW_GRDH   04.2.2015
S1A_IW_GRDH   05.2.2015
S1A_IW_GRDH   20.2.2015
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on November 11, 2015, 02:47:27 PM
Petermann Glacier ... 2015 the year in review

This year saw some interesting developments on the floating ice shelf, precious experimental data being collected beneath it, and new explanations proposed for upstream upheavals so characteristic of north-central Greenland and a few regions in Antarctica.

The event getting the most attention was cleavage of a minor tabular ice in the northeast corner. Events in this region are driven by intrusion of Belgrave glacier almost orthogonally into the advancing ice shelf. Partial pinning then causes rifting as the adjacent region of ice shelf is held back. We can expect a similar repeat event from the same mechanism in 2016.

The northwestern corner above Faith Glacier is undergoing a curious melt-out along the rock wall that, though paused for the winter, may resume this spring. Here the ice shelf is ~100 m thick but winter saltwater ice will only reform to ~2 m and not bond well to older ice. This melt-out may propagate further upglacier in 2016, reducing friction between the ice shelf and the confining fjord walls, resulting in a very slight increase in discharge velocity. However recent papers make a case for the totality of Petermann buttressing being inconsequential (for future sea level rise).

The fractures midway up the ice shelf on the eastern side above Kap Agnes lengthened and widened during early and mid-summer but paused in August. These fractures form in succession as the ice shelf bends around a curve in its fjord and responds to pinning from side glaciers, whose ice continues to slowly revolve as a band of ball bearings mediating transverse differences in flow velocities.

In 2016, the upper fractures will take up the strain as the first rift passes by the source and approaches dormancy, possibly extending to mid-channel or even cleaving off a major berg. Much of the real action is taken place underneath where circulating warm ocean water is eating away the bottom of the ice sheet, predisposing it to rifting that otherwise might not have happened.

The fourth area of interest, extensional crack induced by the west side bend in the fjord walls near Kap Bremerton, showed limited change. Again the glacier moves on during the winter but the crack mechanism does not, so we can expect the action in 2016 to either expand one of the more recent cracks or initiate a new one to the south. This region historically has not been the source of full width rifting (calving).

Petermann Glacier ... new observational data in 2015

Due to its extreme northern latitude and the nature of near-polar satellite orbits, Petermann receives almost daily coverage by Landsat-8 and Sentinel. However due to darkness, Landsat wrapped up its season almost six weeks earlier than at west-central Greenland glaciers like Jakobshavn. However Sentinel embarked on five months of high resolution IW coverage that will allow, in conjunction with differential GPS measurements in August, very high resolution determination of seasonal velocity slowing.

We discussed 18 months ago a very fine interferometric image taken by Radarsat-2 operating in Sentinel mode (#86 to #97). I've since located a much higher resolution version of that image that will reactivate this discussion. However the associated metadata still leaves a lot to be desired (such as the coordinate projection used).

It's imperative to get this image co-located with Landsat and Sentinel in mercator UTM21 as well as IceBridge Cresis radar grids (which come with kml track files). However it is not easy to warp an unknown projection onto the upper ice sheet because Kap Schoubye and Kap Egedesminde across the fjord entrance are the last available ground control points. We'd like to know how the islands of slower motion shown in the SAR correlate with radar upheavals co-locating along flow lines.

Petermann Glacier ... new academic publications in 2014-15

These are somewhat tricky to locate comprehensively as dissertations are not indexed at Google Scholar, papers solely about Petermann don't always indicate that in title or abstract, articles of broader scope may have important sections dedicated to Petermann, and quite a few are indeterminate being buried behind expensive firewalls.

An investigation into the feasibility of applying 3D geological modeling techniques to polar ice sheets
F Mundel
https://epic.awi.de/38445/1/BachelorThesis_FelicitasMundel.pdf (https://epic.awi.de/38445/1/BachelorThesis_FelicitasMundel.pdf)

Radiostratigraphy and age structure of the Greenland Ice Sheet
JA MacGregor
http://tinyurl.com/owjb4al (http://tinyurl.com/owjb4al)

Warming and deformation of the Greenland Ice Sheet by refreezing meltwater
RE Bell 2014
http://tinyurl.com/os5lzru (http://tinyurl.com/os5lzru)

Traveling slippery patches produce thickness-scale folds in ice sheets
M Wolovick
http://tinyurl.com/nt35lfp (http://tinyurl.com/nt35lfp)

Widespread Persistent Thickening of the East Antarctic Ice Sheet by Freezing from the Base
RE Bell
http://www.sciencemag.org/content/331/6024/1592 (http://www.sciencemag.org/content/331/6024/1592)

Ice Shelf Melt Rates and 3D Imaging
C Lewis
https://tornado.rsl.ku.edu/sites/default/files/biblio/TechRpt162.pdf (https://tornado.rsl.ku.edu/sites/default/files/biblio/TechRpt162.pdf)

Airborne fine-resolution UHF radar: englacial reflections, firn compaction and ice attenuation rates
C Lewis, S Gogineni, F Rodriguez-Morales
http://www.igsoc.org:8080/journal/61/225/j14j089.pdf (http://www.igsoc.org:8080/journal/61/225/j14j089.pdf)

Ocean observations from below Petermann Gletscher
A Muenchow
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/62148 (https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/62148)
http://ows.udel.edu/ (http://ows.udel.edu/)
http://icyseas.org/ (http://icyseas.org/)
https://petermannsglacialhistory.wordpress.com (https://petermannsglacialhistory.wordpress.com)

Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland from 2000 to 2012. J. Glac., 60, doi:10.3189/2014JoG13J135, 2014. .pdf
A Münchow, L Padman, and HA Fricker
http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf)

Bathymetry in Petermann fjord from Operation IceBridge aerogravity
KJ Tinto, RE Bell, JR Cochran, A Münchow
http://muenchow.cms.udel.edu/papers/Tinto20 (http://muenchow.cms.udel.edu/papers/Tinto20)

Resolving bathymetry from airborne gravity along Greenland Fjords
A Boghosian
http://onlinelibrary.wiley.com/doi/10.1002/2015JB012129/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015JB012129/abstract)

Unprecedented retreat in a 50-year observational record for Petermann Glacier
OM Johannessen
http://159.226.119.58/aosl/CN/article/downloadArticleFile.do?attachType=PDF&id=383 (http://159.226.119.58/aosl/CN/article/downloadArticleFile.do?attachType=PDF&id=383)

C51B-0712: Over-wintering of Supraglacial Lakes on the Greenland Ice Sheet from Sentinel-1 and Landsat-8 Data
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/85347 (https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/85347)
C Benedek

The response of Petermann Glacier, Greenland, to large calving events, and its future stability in the context of atmospheric and oceanic warming
FM Nick
http://tinyurl.com/qdo6s8g (http://tinyurl.com/qdo6s8g)

Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland
JR Carr, A Vieli, CR Stokes, SSR Jamieson
http://www.igsoc.org:8080/journal/61/225/j14j128.pdf (http://www.igsoc.org:8080/journal/61/225/j14j128.pdf)

A comprehensive interpretation of the NEEM basal ice build-up using a multi parametric approach
T Goossens
www.the-cryosphere-discuss.net/9/5555/2015/ (http://www.the-cryosphere-discuss.net/9/5555/2015/)

Small-scale disturbances in the stratigraphy of the NEEM ice core: observations and numerical model simulations
D Jansen
www.the-cryosphere-discuss.net/9/5817/2015/ (http://www.the-cryosphere-discuss.net/9/5817/2015/)

Petermann place names located on Google Earth
https://www.google.com/maps/d/viewer?mid=zbdKKg4fRHYo.kjkUmepfXc9A (https://www.google.com/maps/d/viewer?mid=zbdKKg4fRHYo.kjkUmepfXc9A)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on November 20, 2015, 03:11:32 PM
Attached is the new Sentinel velocity map for Petermann and Hammond glaciers. The coastal regions have better coverage than the interior (which so far does not represent an improvement). They badly damaged the data with a clumsy jpg overlay of a lat,lon grid. The original all-Greenland map is at the link below. It appears to be in polar stereographic projection though this is not stated.

Quote
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: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on November 29, 2015, 10:58:24 AM
Andreas Muenchow:

The First 100 Days

http://icyseas.org/2015/11/28/below-petermann-glacier-the-first-100-days/ (http://icyseas.org/2015/11/28/below-petermann-glacier-the-first-100-days/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on December 16, 2015, 02:24:48 PM
Quote
Andreas Muenchow: The First 100 Days
First rate job in providing open source, real time accessibility to work in progress.

It's worth noting that the much awaited high precision GPS data (1-2 cm) needed to determine tidal flexure of the ice shelf has not been analyzed yet. Processing that dual-frequency UNAVCO GPS is a whole subspecialty ... the temptation is just to post the raw data online with the hope that a collaborator surfaces (it costs nothing to add another name to a paper).

The comment section notes that K Nicholls of the British Antarctic Service installed radars at two of the three sites that will measure ice thickness directly to give daily melt rates (next season or just Aug 2015?) but that data has not been processed or released (which would make no sense without lots of accompanying experimental context).

The data itself is being updated over at http://ows.udel.edu/ (http://ows.udel.edu/) rather than on the blog section. The Iridium communication satellite, in my view, is very flaky:

2015-12-14: No Iridium Connectivity for 14 days (14 failed calls)
2015-11-19: Air temperature/humidity sensor #1 gives wrong values
2015-11-05: Conductivity sensor at 810-m reporting low, clogged?
2015-10-17: Software upload to reduce data transmissions to 1/day during polar night
2015-10-13: Wind-Sensor reporting 0 until Oct.-15
2015-09-13: No Iridium Connectivity for 12 days (36 failed calls)

The forward velocity of the ice sheet is running just below 1.2 km per year with no indication of a winter slowdown or year-on-year acceleration in the manner of Jakobshavn. The graph of "ocean properties under Petermann ice shelf" is providing the real highlights from the expedition though it takes a background in physical oceanography to draw any conclusions about any warm water circulating under the ice shelf.

The graph is unusual in that the data is displayed over an alpha transparency channel. This makes it convenient to change the background color or drop in a picture. Below, the CTD data at the five different depths along the sensor string are overlaid on a light blue gradient suggesting the increasing depth top to bottom.

It is also easy to lay in grid lines for the temperature, salinity and date that lie underneath (do not interfere with) the data display. As shown, the salinity over-rides temperature. Slightly better practice here would be to use a non-animated gif (or multi-layer tif) so that visitors can download the file and tease apart the data layers.

Tinting grayscales could also embed the data into an arithmetically interactive graphic. Ultimately though, to do any analysis, it's more convenient to just have numerical data in a spreadsheet or statistical package for say, interpolating between the depths sampled to search for stratification.

This data -- which was expensive, risky to acquire, and not experimentally reproducible (time has moved on)  -- should be archived somewhere at the time of publication so that analyses can be checked (or done under alternative assumptions or with additional data years); however that's hardly ever done in glaciology. The notion of emailing authors to get data was seriously undercut by two deaths last year in the same small research group.

Note that the units are 'potential temperature' rather than nominal. The reason for that is explained at:
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_05.htm (http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_05.htm)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on December 16, 2015, 05:31:31 PM
In view of yet another conflicting interpretation of basal ice upheavals in northern Greenland (see first ref in #342), especially in the Petermann and Zachariae areas, I'm looking to revisit the whole issue during the slack season. A separate forum for this and related phenomenon would require moving many dozens of earlier posts and graphics.

While fascinating and unexpected, these basal structures tell us something important about melt conditions at the end Eemian. The response of the ice sheet at that time to warming is our most important paleo clue to Greenland's response to present-day anthropogenic warming and the contribution of melting ice to global sea level rise and Atlantic meridional current disruption.

The merits of explanatory proposals can be compared using the checklist below:

What's the theory predict?
If competing theories can't be distinguished by experimental outcomes, then the relative validity of proposed mechanisms can't be assessed. Conversely if proponents cannot agree to observational outcomes that would invalidate their hypotheses, they have departed planet science for la-la land.

Here we don't get to nuances -- none of the competing upheaval papers explicitly commit to concrete predictions. It's not clear what these theories expect from drilling down to bedrock even through an extreme upheaval. Some will modify their proposal after the fact to fit whatever temperature, ice fabric, impurity, meltwater, conductivity, meteoric vs accreted ice, isotopic profiles emerge. A theory that flexible isn't in the science realm, it's merely curve-fitting.

Experimental ice core data from an upheaval is not in view. The only ongoing drilling to bedrock is at NEGIS. While site coordinates have only been disclosed in vague terms, we can be sure that extensive sled and air radar have shown regular stratification to bedrock -- there won't be tilted layers much less an upheaval at the drill site. That was certainly the choice made at the Renland ice cap.

Steam cores are quite feasible at accessible locations at the relevant depths. While these don't preserve the full ice archive, wire logging devices can capture many properties of the ice. Logged boreholes of Luethi at Swiss Camp and Hubbard at Store Glacier illustrate modern opportunities. It is really on these measurables that theories need to take a stand.

Sled or drone radar surveys are easier still. Radar to date has prioritized bedrock elevation and ice thickness; grid cells appropriate to that are too coarse relative to the intrinsic scale of upheavals and coherent systems of them. It is very difficult to reconstruct a 3D object from a couple of intersecting transects randomly oriented relative to key structural attributes and skew to the local ice velocity field. What's needed are radial grids in polar coordinates centered on individual features and grids of flowlines and isotachs.

Only one paper to date has attempted to reconstruct the overall regional 3D structure of an integrated upheaval system and that only for Petermann. Some papers envision recumbent and overturned folds where others see sheath folds; better radar grids can distinguish these (as can held-back or post-paper radar transects not used in model building).

Eqip is the most convenient site logistically, though it is not clear whether it (or any other upheaval) is 'representative' of all. The extensive upheaval there is 94 km from the Illulisat airport with a ship dock at the calving front hotel. Swiss Camp and Store research sites are close by. Crevasse and snow bridge risk is minimal inland within the nearly flat and slow moving Eqip ablation zone. Sled radars have used nearby, as have steam drills.

Occam's Razor: does it still cut it?
This 14th century principle asserts a simplest most boring explanation is most often right. This translates here to every upheaval in all of Greenland and Antarctica having the same underlying physical mechanism. Such parsimony is perhaps unattractive given very different bedrock, geothermal gradient, basal stress, temperature, viscosity, ice thickness, ice sheet histories, and surface velocity fields where upheavals are observed. So perhaps two physical mechanisms are operative but certainly no more than three. If so, a classification scheme is needed and predictions subordinated to it. Multiple contributing mechanisms at individual features is incompatible with Occam's principle and should be considered only as a last resort.

Absence of upheavals is just as informative as presence.
What accounts for the distribution of upheavals on the Greenland ice sheet? They are overwhelmingly concentrated today north of Eqip with many but not all in regions of moderate thickness and higher surface velocity. Yet for every upheaval, the same radar flight line can show many 'unoccupied' but seemingly indistinguishable sites. Any mechanistic explanation must give equal weight to predicting absence.

Are upheaval radar reflectors distorted isochrons?
In Greenland, upheavals are always bounded from above by the ubiquitous 'three sister" isochrons, accurately dated at NEEM to the middle of the last ice age. The nearly as ubiquitous 'older brothers' dating to 91 kyr sometimes bound the upheaval but more often are caught up in its contortions. Below that there are few consistent markers. Numerous mechanisms attenuating radar returns arise from something other than these presumptive massive volcanic depositions.

Upheaval areas in radargrams can be delimited from above by dark lines but these are often blurrier than any isochron ever observed in calmer regions, There may also be large dark blocks that have no counterpart in isochrons. These dark areas can have elaborate substructure that also require explanation. In these regions, processing radargrams at native resolution to optimally enhanced contrast is imperative, lest important clues be discarded. It's very poor practice to theorize without considering experimentally revealed complexity. The first image below compares a figure from a peer-reviewed geophysics at author-submitted resolution to actual upheaval data.

In their comprehensive mapping study of Greenland stratifications, MacGregor 2015 take a cautious perspective:

Quote
In numerous locations within Greenland’s interior, the deepest radiostratigraphy does not drape smoothly over the observed along-track bed topography. Instead, it is deflected upward across horizontal scales of several kilometers or more, distorting the depth-age relationship of the ice column by up to several hundred meters. These features are most prominent in the onset region of Petermann Glacier in northwestern Greenland (Animation S2).

Bell 2014 mapped the larger instances of these features. The precise cause of this disruption/deflection is unknown, but it is unlikely to be due to flow over undetected highs in the bed topography as previously hypothesized in Legarsky 1998, because extensive radar surveying of the GrIS fails to reveal these postulated highs.

This disruption may be due to buckling associated with spatially or temporally varying basal friction [Hindmarsh 2006 Wolovick 2014], basal freeze-on as inferred for East Antarctica [Bell 2011], or rheological variability within the basal shear layer [NEEM 2013].

Given the variability in magnitude of these radiostratigraphic disruptions, a combination of the above phenomena is also possible, or another as-of-yet unknown process. At least for Petermann Glacier, a plausible scenario is that recently described by Bell 2014 and modeled by Wolovick 2014: basal freeze-on uplifts and overturns the overlying strata, generating complex units that include both accreted and distorted meteoric ice.

These features can contain unusually bright, indistinct, or overturned reflections that do not resemble the monotonous radiostratigraphy of the overlying ice sheet. Unusually bright reflections may be due to a large fabric contrast between meteoric and accreted ice, as hypothesized to occur over Lake Vostok in MacGregor 2009a.

It is possible that some of these coherent reflections and diffuse reflectivity are not isochronal, although they likely remain useful indicators of past flow [NEEM 2013].

Are upheavals oriented along flow lines?
That's not so easily determined because flight lines rarely followed surface flow lines. The few orthogonal grids take a skew angle with respect to flow and, at Petermann, the rare flight lines that did follow flow were unfortunately from years with unsatisfactory radars. The grids are not tight enough to pick up intervening upheavals; at best 2-3 cross sections are available for a body of unknown shape and dimensions, eg there's no reason to suppose the peak height happened to be transected.

Many of those most dramatic upheavals occur in regions of deep and essentially stagnant ice. It simply isn't credible to draw a causal association with flow (or associated frictional basal heat) at meter-per-year sites as there's hardly been any movement since the Eemian, not to mention that a few km over with slightly faster flow there are no upheavals. This leads to the equally unpalatable choices of either disregarding Occam's Razor or the extended upheavals that seem coherently oriented with flow for hundreds of km.

Is the inventory of upheavals comprehensive?
No thresholding criteria were provided in the original mapping article [Bell 2014], no database of relevant Cresis accessions was begun, no kml path file exists. It appears that only the larger dramatic features were mapped based on subjective criteria. And not all of these were found because radar tracks are fairly sparse.

All the work on the Cresis image portfolio thus has to be repeated from scratch. This means the actual distribution of upheavals, perhaps stratified by upward magnitude and horizontal extent, has not been determined. This seriously undermines all manner of correlations with other basic attributes of the Greenland ice sheet.

Most troubling is the NEEM drill hole itself: overturned stratigraphy was carefully documented in the core but nothing resembling an upheaval can be seen in radar despite very intense surveys over the borehole and vicinity. This suggests the ability of radar to detect upheavals at depth is not adequate to locate them, not just at NEEM but by implication over much of north-central Greenland.

Is this an exercise in structural geology?
Yes and no. Stress-strain physics of stratigraphic deformation and flow of sedimentary deposits have been studied for centuries and have clear counterparts in ice sheets. Salt beds and lava flows have temperature/viscosity relationships reminiscent of ice. There are counterparts as well to till hydration state, melt phase change, and crystallization in plate tectonics but with diminishing relevance to glaciers, melt lakes, moulins and basal drainage channels.

Quote
“When I use a word,” Humpty Dumpty said in rather a scornful tone, “it means just what I choose it to mean — neither more nor less.”
“The question is,” said Alice, “whether you can make words mean so many different things.” (Through the Looking Glass, Chapter 6)
Anticline and syncline are terms for compressional folds borrowed from structural geology often inappropriately applied to Greenland ice upheavals. It's impossible to recognize these from a single radar flight lines because the requirement for a longitudinal fold axial plane is inherently two dimensional. If this axis has not been observed, the fold type cannot be distinguished from a dome or basin (technical terms for folds with non-axial symmetries).

An upward deformation of stratigraphic isochrons might be an anticline but such an inference is premature without supporting evidence from multiple flight lines -- these are so sparse that it can't be determined when one feature stops and another has started. It's really a stretch to apply these terms to basal freeze-up deformations: mechanistically more related to salt diapirs, this concept is only dimly related to compressional waves of alternating synclines and anticlines.

In structural geology, overturned and recumbent folds are distinguished from sheath folds. That can sometimes be done from a single transect should it happen to pass through the signature concentric 'eye' of a sheath fold. The second image shows that the folds labelled 'overturns' in the figure above are part of a sheath fold. The subject of folds is very complex overall and highly developed within structural geology.

Are these fossil features or still active processes?
In one scenario, upheaval processes began shortly after the Eemian ended, continued for a few tens of thousands of years, then ceased as an active process, no longer initiating new features nor building out older ones, which however persisted to the present day.

An alternative scenario posits that forces responsible for upheavals are fundamental basal processes not specifically tied to one-off historic ice warming during the Eemian that continue to the present. Processes mentioned here include freeze-on of meltwater at the ice/bedrock interface, slip-stick motion of the glacier and associated heat from friction, hotspots in the geothermal gradient, basal strain from ice sheet motion, temperate ice at the pressure melting point and associated lower viscosities, and so on.

North-central Greenland did not fully melt out during the Eemian (as mapped by MacGregor 2015 via a stratigraphic  age-depth function) but what didn't melt came close. In particular, the upheaval areas of Petermann and Zachariae are not underlain with Eemian ice today even a hundred km and more inland from the grounding line.

In the first scenario, this created a persistent body of temperate ice, perhaps with pockets of meltwater or hydrated till underneath, that was subsequently buried under thousands of meters of subsequent ice age snowfall. Slow equilibration with cold from above meant the temperature and buoyancy anomalies played out slowly, perhaps along the lines of 'thermal-viscous collapse' considered in Colgan 2015 (http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full (http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full)).

The second scenario predicts ongoing development of upheaval features and perhaps observable effects from the Holocene, its Thermal Optimum, or even contemporary anthropogenic warming. However the time scale needed for an observable effect isn't clear:

Even if the earliest radar flight line of 1993 had been fortuitously re-flown in the latest 2015, it isn't plausible than any upheaval change could be seen over 12 years, first because glacier processes generally precede at glacial paces, second the radars would be of very different design and third because a 100 m mismatch in flight lines would invalidate the comparison.

Eqip has favorable repeat radar coverage in different years but the east-west flight lines are displaced to 61 m and north-south to 29 m (3rd image). Note the bedrock drainage map resolution is delusional because kriging guesswork has filled in the blanks left by sparse radar coverage in active topography -- there is no other data other than what is seen along radar tracks (airGrav has been deployed in fjords, ice shelves and ice streams).

Is ice predictably deformed over an upheaval?
It's fair to say that stratigraphic layers above basal upheavals are conformally uplifted with that effect tapering off in Holocene ice, sometimes to the point of imperceptibility. This requires reconciliation with the near-incompressibility of ice, its viscosity, depth and status of firn, and conservation of mass because the ice surface is not notably deformed.

There is no known method by which the presence of upheavals can be systemically detected by any combination of measurable surface properties (such as ultra high resolution DEMs, surface velocity, and surface slope). We only wish there were because then the upheavals could be comprehensively mapped from continuous 2D data, with sparse radar tracks only employed as a cross-check and for details.

At Petermann, the case can be made that the upheavals themselves are anisotropically distributed with respect to surface velocity flowlines (though it's not so clear how to make that point objectively). This has implications for anisotropy of younger layer deformation which so far have not been pursued.

At the Eqip upheaval on a south-to-north track of 2008, isochrons do not notably conform with either bedrock profile nor the upheaval (4th image). This suggests (if not a unique situation) a basis for upheaval categorization.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on December 17, 2015, 02:27:55 AM
@ A-Team:

1. The "lightly" processed, calibrated, and unpublished data are from 5 ocean sensors are posted as ASCII files at

http://ows.udel.edu/data/sbe.all (http://ows.udel.edu/data/sbe.all)

Edit: Formats of (all) data file(s) are explained at

http://ows.udel.edu/data/read.me (http://ows.udel.edu/data/read.me)

2. Iridium dial-up via a 9522B modem is indeed frustratingly intermittent. It may relate to a design flaw that expects the modem to initiate calls in order to stay "registered." I do not know what this means precisely, but neither does the generally respectable company that sells these products. Since I call the Greenland modem from my home (rather than the modem in Greenland calling me at home), the Greenland modem apparently disconnects itself from the network. This makes zero sense to me, this is not documented, actually, the manufacturer discovered this itself. The fix is simple, two lines of code at most, but without a connection there is not way to send this new code to the station. I connected with other people at the Fall AGU who have exactly the same type of problem with the same product in British Columbia and Ellesmere Island. The best case scenario that I am hoping for is that military operations in the area take away bandwidth for a limited time. Data are recorded and stored locally even when Iridium does not connect, but this project was supposed to be real-time with a 2400 baud dial-up serial connection (1980ies style modems).

3. The survey-grade GPS data are about 1 GB per day per station as we accidentally collected data at 1 second intervals rather than the more standard 10 s or 30 s. Furthermore, I currently have zero funds to do this work, but a proposal to do so (as well as maintain the site beyond Aug.-2016) is pending with NSF.

4. The radar data at two sites are collected right now, but data volume is too high for the low-bandwidth we got; so the data will have to wait until we get there next year to pick it up

In summary, this is tiny project done on a shoe-string at multiple institutions in multiple countries by people who genuinely like each other and do what they think is both fun and, we feel, important. Communication with platforms, sensors, and ships north of 78 N latitude is still very much a non-trivial challenge ... at least for me, but Sen. McCain got also rudely disconnected by Iridium when he called the ship in Petermann Fjord last summer.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mati on December 18, 2015, 01:44:18 AM
i did some work on the original Iridium system, and the trouble arises when switching between satellites.  I wonder as well if the northern lattitudes and solar activity contribute to the problem.

oh, and here is a neat thing:
https://en.wikipedia.org/wiki/Satellite_flare#Iridium_flares (https://en.wikipedia.org/wiki/Satellite_flare#Iridium_flares)
http://spaceweather.com/submissions/large_image_popup.php?image_name=J.-Dana-Hrubes-iridium-4-28-08-3-b2-slo_1209376592.jpg (http://spaceweather.com/submissions/large_image_popup.php?image_name=J.-Dana-Hrubes-iridium-4-28-08-3-b2-slo_1209376592.jpg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on December 18, 2015, 05:41:07 AM
Great data, thanx a million Prof. Muenchow. Actually seeing meltwater pulses at 10-30 day periods in depthwise temp and salinity puts mass and heat flux mechanisms in a new light for me.

I am sorry for your bad experience with communications. It has paid me in the past to always have the site with flaky comm (in your case, Iridium) initiate connection attempts. On the other end i need to have two static sites (with large UPS and guarded by ferocious leopards) always listening for connect attempts.

Why two ? Therein lies a tale or five ...

sidd
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on December 18, 2015, 03:57:43 PM
Very helpful posts! Amazing story of the unending adventures that underlies the dry scientific prose of eventual publications.

Given you were teaching a signal processing class this fall, could not a lot of work have gone out the door as a homework assignment?

Did you ever post the locations of the ice radar and drill sites over a 15 m 2015 Landsat? (Since the ice shelf is moving, it may be better to locate them relative to surface features rather than initial GPS.)

At one time there was talk of locating them on a repeated radar flight line. If we can trust the cresis kml waypoints on these, the navigational error on these was less than a meter. One of them continues over the terminal extension of the main basal upheaval feature which does not quite reach the grounding zone but could have oceanographic consequences if it is a major source of meltwater(1st and 2nd images). These features are not associated with surface meltlakes and streams though they could be at Eqip (3rd image).

I'm wondering too about surface AWS and radar measurement of snowfall on the Petermann ice shelf. Rignot, who spent portions of three summers camped NE of the grounding zone, reported winters of little or no net snowfall. Yet it's often said not to be reliably measurable because of wind drift and other factors.

Is firn compactification an issue out on the ice shelf or has it already happened?  I'm not recalling a neutron source on the logging wire that might have measured density going through the ice. Ditto ultrasonic probe of ice fabric (again may not be of interest on a shelf). The radar profiles make the ice look rather reworked.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on December 21, 2015, 03:49:09 PM
The question with using repeat flights, say for progression of underside crevasses near Petermann's grounding zone, is their reproducibility: each of the 22 years used a different radar design and some years different planes and flight elevations.

Previously, track crossings within a single day's flight (cases where the plane later doubled back and crossed an earlier part of its route) have been examined to establish error bounds (~10 m) needed for the bedrock map.

Here the animations below look at the reproducibility across different years of an upheaval zone at Eqip which has a near-perfect route overlap of a north-south track from 2012 (20120421_01_052) and one from 2014 (20140414_02_021), both flown on a P3 out of Illulisat.

If the upheaval has moved or otherwise evolved over those two years, it shouldn't be expected to give the same radar profile. However the bedrock hasn't moved (elastic rebound being negligible) and should line up exactly across the whole image.

The first issue is only in 2008, 2014 and a few others did Cresis use a vertical depth scale tied to the WGS84 ellipsoid (the basis for everything in Greenland glaciology). The vertical scale ticks in other years are correctly spaced at 500 m intervals but the absolute depth numbers are meaningless because the offsets aren't provided -- the 0 is set as the mean surface over that flight frame. Here I used the true scale from the 2014 (which establishes the Eqip upheaval is slightly above sea level).

Second, Cresis crams everything into a fixed template (rather than providing images at intrinsic resolution). Since every flight has different length and depth scales, no two images will have the same vertical or horizontal scale. To compare two images, one must be rescaled by the appropriate scale factors, sometimes radically. While there exists 'smart' rescaling algorithms for 2x, 4x etc here the factors were 87.790% hor and 100.958 ver so some potential exists for introducing artifacts and degrading the image.

Third, it has been belatedly recognized that some sort of mission creep occurred in some flights in some years (they mostly fly at 500 m above the ice surface which slopes at ~1% in west-central Greenland). You can see this in the animation as a residual rotation of 1.26º left after alignment of the matched-scale images.

This could have major ramifications for the bedrock DEM, ice thickness, and modeled movement if this systematic error wasn't removed from applicable flights. It has definitely affected the Petermann area, as first noticed by F Mundel in #342 (who report tilts of 1.35° to the north and 0.98° to the west in Fig.10) and Macgregor 2015.

Cresis (resp. Bamber 2013) at this point have not corrected their archive (resp. DEM).

Overall the correspondence between the two years is fantastic at every level, much better than i had anticipated, so three cheers for Cresis and Operation Icebridge. Some slight differences can be seen in the middle region of the upheaval at 3x (yellow and green bars).

Radar tracks take in reflections over a 100 m wide swath or so, they are not line data in the sense of laser altimeters. Here the two tracks are less than 10 m apart if the plane navigational coordinates are to be believed. It's conceivable reflective properties do indeed vary over a few meters in which case the differences here do not represent time evolution. This is best determined by intensive sled radar grids; Eqip is by far the most convenient site for this.

It can be verified that these differences are perceptible in the originals and did not arise from processing (2nd image). The excellent correspondence overall but differences within the upheaval suggests (one case doesn't prove) certain details of radar reflectivity may be evolving over time within these features. The six east-west flights over this upheaval are offset by 40-200 m so are transecting slightly different sections. I'll look at the variation in these east-west tracks when I get back online; there are quite a few steps in doing this optimally.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: P-maker on December 21, 2015, 04:06:29 PM
A-Team,

thanks for digging this out of the archives. My respect for your way of working keeps increasing year by year, as do the clear ice domes under the GrIS.

Cheers P
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on December 21, 2015, 05:57:47 PM
Quote
Thx for digging thru the archive!
You're welcome! I'm always on the lookout for places where we can move beyond just reporting news and add value. That takes a mix of under-exploited but accessible data in a non-proprietary format, not too technical a topic, and the research community busying itself elsewhere.

Espen has been doing this successfully on the calving fronts, the twist there is real-time incoming data that he is the first to look at and see its significance. However there are quite a few people on quite a few forums doing other things quite impressively. We are head and shoulders above anything going on at scientist twitter sites in terms of creating a useful and comprehensive resource.

I heard the science preprint server ArXiv.org will be starting up a geo/cryo section in 2016 That would be a good place for people wanting to pull together a doi-citable article on a topic (like El Nino) that is currently scattered across many hundreds of posts. ASLR earlier pioneered the use of the comment section on discussion journals as a way of creating a permanent record. It's really a valuable exercise to properly pull together what you know about a topic.

I would recommend these initially over trying a direct submission to a journal which is really expensive and problematic even on merit without listing conventional academic co-authors. But you can sometimes pick these up off a preprint. (I'm at a respectable 5061 citations from articles in other fields but am falling ever farther behind people like Eric Rignot already at 10145 with 2-3 blockbuster articles this year yet to kick out cites.)

Holiday travel looming, I'm going offline (reluctantly).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on December 21, 2015, 06:49:10 PM
If you're reluctant to go off-line, it's usually good to go off-line for a while.   ;)

Thanks for all the great work.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on January 01, 2016, 02:02:15 AM
New post up at http://icyseas.org/ (http://icyseas.org/) with the latest data from under the glacier. The temperature and salinity fluctuations are intriguing!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 01, 2016, 04:25:43 PM
Quote
New post up at http://icyseas.org/ (http://icyseas.org/) with the latest data from under the floating ice shelf ... salinity fluctuations at 95 and 115 m depths are intriguing
2016 ... only one instrumented ice shelf in the northern hemisphere?

Quote
it's usually good to go off-line for a while.
Oh, I'm usually offline for the day by 8:30 am. It works better for me to bite off a small post each morning rather than take long holidays followed by hours of picking up where I left off.

Hmmm, where did I leave off anyway … some oddity in Greenland last time it got warm, beyond just meltwater raising sea level and disrupting planetary heat re-distribution. The last ice age did not wipe the slate clean: the Eemian is not pure paleo. Its legacy, in the form of basal folds and thermal upheavals, is still a driving force today. Thus it is quite wrong to compare Eemian to Holocene; the future of the latter has to build on what the former left behind.

Ice sheets have exceedingly long memories. Because of its proximity to Icelandic volcanoes, that of Greenland has been retained in exquisite detail, not only in the annual climate layers of cores but also in deep stratigraphy visible along ice penetrating radar tracks. That record, a byproduct of bedrock topography determination, handed glaciologists a book in the mid-’90’s that they didn’t want to read.

So here we are, 20 years after the first basal upheavals were observed, forced to read that book anyway — we know southern Greenland is toast, it’s basal conditions of the northern ice that matters.

That’s what I’m writing about: denial.  We cannot afford it any more within the scientific community — it’s high time to get a radar sled over Eqip and a steam drill too.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on January 01, 2016, 04:30:04 PM
Thanks, ghoti, it is very interesting, in deed!
New post up at http://icyseas.org/ (http://icyseas.org/) with the latest data from under the glacier. The temperature and salinity fluctuations are intriguing!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 01, 2016, 05:59:15 PM
The Petermann catchment upheavals are considered from a fresh perspective in the F Mundel paper linked to in #342. This is a German bachelor's thesis (~ US masters?) rather than a journal article, but one overseen by AWI geoscientists with extensive experience on Larsen C and NEEM core layer deformations (see http://www.the-cryosphere-discuss.net/9/5817/2015/tcd-9-5817-2015.html (http://www.the-cryosphere-discuss.net/9/5817/2015/tcd-9-5817-2015.html)).

From a structural geology standpoint, ice folds and flows like a salt bed or rock near its melting point, leading here to a regional interpretation of Petermann cylindrical folds as arising from 3 effects: cross-flow compression from a funnel-shaped catchment, along-flow tensile stress from increasing terminal ice velocity, shear stress from a vertical velocity gradient giving sheath folds.

None of this was developed beyond the cartoon level but a conceptual framework is probably preferable to the overly intricate model in which the core proposition is lost. The author cites the previous upheaval papers but does not compare alternative mechanisms. Very few of the scientific desiderata outlined in #346 are met here.

The main idea here is to move the ice penetrating radar grid sectioning of Petermann into commercial geology software called MOVE 2013.1 which is capable of developing 3D models of internal isochronal surfaces and integrating them with bedrock and surface DEMs as well as surface velocity.

This didn't work very well for a variety of reasons: the academic license version was hamstrung, half the grid utilized the crummy radar design on the 2010 DC8 overflights, the grid was too coarse at 8-9 km relative to feature size, no physical basis existed for interpolating between 2011 grid lines, the horizontal was badly tilted in either the radargrams or the bedrock DEM, too much data had to be discarded as not straight or parallel enough, ill-advised co-mingling of manual traces of isochrons and upheaval boundaries, use of an outdated velocity magnitude map lacking flowlines, and the highly improbable assumption that ice velocity decreases exponentially to zero on a frozen bed as claimed in a 1966 paper.

It is a little troubling to see MacGregor 2015 cited early on but its vastly more sophisticated and comprehensive isochron tracings never utilized. We've seen in earlier posts here that the only isochrons worth tracing in the Petermann area are the 14.5 kyr Holocene beginning, the three sisters at 46.5 kyrs and the two brothers at 91.5 kyr. The author here came to a similar conclusion, tracing only the Holocene and middle-sister (called a highway).

MacGregor 2015 did all this and more, earlier. That data was interpolated by a better method, gridded to the Greenland standard, and stored as a public netCDF archive, with the Holocene and end-Eemian presented as smooth rendered surfaces in a much viewed NASA video. However that effort could not provide the same microscopic evaluation to an individual grid and custom contrast rescue of problematic radar tracks. MacGregor 2015 also sidestepped the issue of upheavals for the reasons discussed in #346 -- they’ve not been proven to be distorted or diffused regional isochrons or indeed any kind of isochron.

The author considered flight intersections but mostly had to toss the poor quality DC8 north-south sections and curved paths which MOVE bizarrely cannot accommodate. There was a serious misunderstanding about lat,lon numbers provided by Cresis, or to put it more fairly, Cresis did something very dumb that later confused everyone: not to subdivide the image frames with the actual high precision GPS waystations.

The graphics below show some worthwhile products from the Mundel paper. The first shows layer tracking, the second the ‘cardboard wine carton’ display of sectional assembly (developed here earlier as a take-apart animation),  the third a perspective view of the grid, applicable shears and final surface (rendered in so-so fashion by MOVE).

As we've seen earlier in #161, the center of this fold belt actually extends all the way up to Kap Schoubye but not quite to the grounding zone. Here the author discarded the DC8 vertical transects (upper blue in flight grid, 3rd image), nearly half the available data. It is very dangerous to interpolate with software because that cannot help but produce smooth folds in every situation.

The fourth image shows regions of high velocity appear strongly correlated with the cylindrical fold belt. However according to Radarsat interferometry in #86and later Sentinel 1A, the outdated velocity map used here is grieviously in error centrally. The distribution of Greenland basal upheavals overall has no association whatsoever with high surface ice velocity. There is no supporting data for the putative inland funnel. However the structural geology approach used here may still have merit.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 03, 2016, 03:58:33 PM
Last March, Wipneus located a striking image taken by Radarsat operating in Sentinel mode (post #86) and observed in #91 that the ice in the fjord proper was moving too fast for the 24 day scene interval to resolve. Andreas T found the ESA's meagre background report and noted a full fringe cycle amounts to 5.55 cm given Radarsat's 5.4 ghz wavelength in #96, while Espen noted how far inland the high velocity region extended in #97.

It is really critical to use reverse image search of the internet (imageraider) and a pdf image extractor (ImageJ) to find the highest resolution version of the image. Almost everything you see on the Internet is badly compressed. I managed to locate the original image and have posted it below (the blog software will only show a thumbnail without a click). Separate coherence and intensity grayscales are also available.

Petermann, being at latitude 81ºN, would be frozen solid on these dates (11 Apr 13 to 05 May 13) per Landsat-8 so loss of height from melt or sublimation are not plausibly contributing to line-of-sight motion seen by the satellite. This region of Greenland has very little annual snowfall so wind ablation is not a factor either.

Fringe separation thus largely represents horizontal motion of the ice sheet --  bare rocks being fixed, marine terminal velocities are fast, the dividing ridge between Hammond and Glacier falls off into the respective catchments, the upper ice sheet is hardly moving toward the interior, in excellent agreement with separately determined speed maps of Rignot and Joughin (1st animation) and more recently Sentinel.

It's easy to independently calibrate velocities using a time series of Landsat-8s at least in the vicinity of the last ground control point (Kap Schoubye, the island resembling an arrowhead).

The 3rd image shows a 2x enlargement of the curious region Espen noted earlier. The center of this corresponds to Mundel's cylindrical fold belt (4th image of previous post). The colored fringes, when broken down to separate grayscale R,G,B channels run as frames of the 2nd animation, suggest surface ice motion.

Note the fast upstream region actually forms two fingers flanking a slow island that widens down-glacier. It is this slow island -- or perhaps its velocity contrast -- that best corresponds to the main structural geology fold proposed by Mundel. Funnel compression and tensile stretching of that model way are too simplistic and would have to be re-elaborated as tensor fields that fit the data.

One could also envision support here for the traveling slip-stick zones proposed by Wolovik 2015, though there's no real experimental information about basal thermal conditions or velocity with depth. Indeed it's hard to see how the bland slope and bedrock topography could produce such a nuanced surface velocity field satisfying mass conservation without noteworthy crevassing of the brittle ice. 

The bedrock lacks anything overtly corresponding to the slow island and fast fingers but does have a broad rise between the below sea level interior and fjord. This creates a curious convergence (noted earlier in discussing longitudinal flightlines) of ice rising basally over bedrock but plunging surficially as it nears the coast.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on January 03, 2016, 11:44:07 PM
The "glitches" are actually features of the data. The jumps are at SAR burst-boundaries where the observation-angle (in azimuth) changes slightly. In other words, the phase-jump is physical.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 04, 2016, 02:13:45 PM
Quote
jumps are at SAR burst-boundaries where the observation-angle (in azimuth) changes slightly.
At the end of the day, the product needs to be a smooth velocity map over the entire scene -- there aren't any glitches on the ground.

The amazing thing to me is how little impact Radarsat has had on Greenland glaciology -- here it appears capable of resolving internal detail of the Petermann velocity field that the last 20 years of interferometry have missed. One has to wonder what other fine structure has been missed elsewhere in north-central Greenland.

Petermann only got picked up as part of a casual survey that included Mt. Etna volcanic bulging and Mexico City ground subsidence. And this was 2013, a great many orbits ago. The scene is huge -- a few dozen would have sufficed for all of coastal Greenland. The casual write-up does not provide the corner lat,lon points nor any gdal guidance on how the image should be re-projected to UTM, GE or PS. Possibly the Sentinel toolbox could do something with it.

I marked up the overtly visible burst boundaries below, For some reason they are most noticeable in the lower part of the scene. This is not strictly due to larger fringe cycle (slower ice sheet motion) because the northeast corner is also slow but doesn't have the fringe displacement.

I looked at fixing things by cutting out the offending boxes and shifting/rescaling but that did not go anywhere. The intensity map (which loses phase information) was only released at reduced size; it has pronounced vertical contrast banding that went uncorrected at ESA but may just need a simple multiplicative rescaling.

Note in post #359, the data is interpreted as an anomalous slow blob occupying in the middle of a typical western Greenland velocity field (widening catchment of uniformly slowing velocity). Someone else might see two incipient ice streams, features isolated by sharp shear boundaries, with a slow island between them, in effect an early stage of NEGIS/Zachariae. The ice stream there is marked by a distinct surface trough which has no counterpart in the ultra-high resolution DEM of Petermann.

I looked at quantitating velocities, which amounts to measuring relative fringe width. These ratios could be converted later to absolute velocities using Landsat calibration (since we aren't real sure what Radarsat is doing). We do know how fast Petermann's ice shelf is moving (~3 m per day) but that internal calibration got wiped out by too much movement over the 24 days.

The 4th image shows some of the options, such as enlarging the scale, desaturation modalities, or color-picking say blue to reduce clutter. While it looks quite feasible, giving 3-4 x higher velocities in the shear zone (pink averages over ten cycles), before going too far down this road I would want to see confirmation of the slow island from a pair of Sentinel 1A images -- the 12 day interval would give better resolution in the critical zone.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 05, 2016, 01:58:52 PM
The first image below compares the April 2013 Radarsat interogram with a 2007 made with a different satellite (ALOS PALSAR ) at a different time of year (summer), as discussed last June in #205. The region available for comparison is fairly small but the patterns are amazingly similar.

The second image focuse on three neighboring glaciers (Newman, Steensby and western Ryder). Here too the fringe pattern of the Radarsat interferogram makes sense in terms of the line-of-sight motion being primarily attributable to horizontal motion of the glacier (rather than vertical melt or thinning).

ALOS-1 PALSAR Global Radar Imagery, 2006-2011, is now open access. I have not done much with it to date but see 3rd image — finally, a decent preview. Note the anomalous velocity region is likely evident in the intensity view of all Palsar imagery, raising again the question of why it hasn’t been noticed earlier. Perhaps poor palette color discrimination combined with low resolution and a logarithmic velocity scale have masked it.

The 4th image shows the Parca stake line velocities along the ~2000 m contour, along with the available radar transects and the region modelled in Mundel 2013 (pale orange box) and the extended upheaval feature tracked here earlier using NS tracks in addition to EW (thick black line). Note the Parca flow lines are unremarkable except for F120 (magenta) which shows signs of converging to the faster F121 flow line. The bedrock under F120 is 96 m above sea level whereas F121 is 7 m below.

The bearings differ by 322.5 - 299.1 = 23.4º over the 42 km separating the stakes; that might not seeem like much yet the ice is incompressible so has to accommodate convergence. the velocities (and so physical displacement) by 34.49 - 28.28 = 6.2 m per year. Even though the F120 velocity has slowed by 22% relative to F121 which would introduce significant strain in the ice, that would not show up in a color palette has to range from 1-1400 m/yr.

The Parca stakes are a bit upglacier from where we need them but measure velocity and bearing (tangent to flowline) much more accurately than could ever be obtained by satellite interferometery or speckle tracking. Over the 3 years of 15m resolution Landsat-8, F121 will move 6.9 pixels and F120 only 1.2 pixels less. That’s quite problematic given the nearest ground control points are 175 km to the north. Landsat-7 would bring more years into the mix but further raise issues in precision alignment.

https://www.asf.alaska.edu/sar-data/palsar/ (https://www.asf.alaska.edu/sar-data/palsar/)
https://vertex.daac.asf.alaska.edu/ (https://vertex.daac.asf.alaska.edu/) nuisance registration but nice interface to many radar satellites

http://forum.arctic-sea-ice.net/index.php/topic,388.0.html (http://forum.arctic-sea-ice.net/index.php/topic,388.0.html) Espen et al on Steensby
http://forum.arctic-sea-ice.net/index.php/topic,886.0.html (http://forum.arctic-sea-ice.net/index.php/topic,886.0.html) Espen et al on Ryder

https://glacierchange.wordpress.com/2012/08/25/steensby-glacier-calving-event-and-retreat-northern-greenland/ (https://glacierchange.wordpress.com/2012/08/25/steensby-glacier-calving-event-and-retreat-northern-greenland/)  M Pelto on Steensby
https://glacierchange.wordpress.com/2010/10/26/ryder-glacier-northern-greenland-transient-snowline-rise/ (https://glacierchange.wordpress.com/2010/10/26/ryder-glacier-northern-greenland-transient-snowline-rise/)  MPelto on Ryder

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 06, 2016, 04:46:18 PM
Upper Petermann receives very regular coverage by Landsat though it's rare to get a cloud-free day of the entire upheaval area. I'm looking here for visual surface counterparts to the massive foldings underneath, hoping to independently validate the anomalous surface velocity zone seen by Radarsat, ie slip motion of consistently identifiable features in consistently registered 2013, 2014 and 2015 scenes.

WorldView3 has 30 times the resolution of Landsat-8 and so can see pixel motion over 1/30 the time interval but access is expensive. Ice motion is slow high in the ice sheet; for shear zones (differential motion) we need to distinguish slow vs slower, not interior slow vs calving front fast.

The upheaval area at Petermann involves an area of roughly 180 km x 110 km which in terms of 15 m Landsat resolution , which works out at maximal blog size of 10 km x 10 km to nearly 200 images or 40 posts at the 4 attachments max, not happening. (This is why Eqip is a better choice: much smaller and denser transects.)

The 19 July 2015 LC80360022015200LGN00 covers it all fairly well (avoiding tiling) and downloads in UTM zone 21 projection as 18,000 x 18,000 pixels. The relevant half can be cut out after rectangularization by a 33º CW rotation.

Overlaying the upheaval flight lines grid and Mundel's fold belt (polar stereographic like bedrock DEM and ice thickness) onto this Landsat raises some issues. The Cresis kml waypoints file provide lat,lon not UTM21; there are online tools for that. Google Earth displays the tracks nicely but in its own projection while also providing UTM22 coordinates. The Landsat metadata file provides the corners in lat,lon (and UTM21) which in theory might allow the Landsat to be uploaded correctly reprojected.

Since a Landsat time series is needed to detect motion and the number of distinctive surface features are far and few between this far up the ice sheet, I did not want to further degrade Landsat image quality as it has gone through many processing steps already to arrive at the UTM21 download, all that is served at EarthExplorer.

The radar stratigraphic rasters too have had a lot of processing and need a lot more. These are specified as chords to the actual curvilinear flight lines; as line segments rather than area, they are not in a projection system but simply WGS84 lat,lon,z.

The set-up is shown in the first image below. I decided to locate a central flight segment through the anomalous surface velocity region in the fold belt on the Landsat by approximate methods, as shown. This was instructive because nothing on the Landsat had the slightest promise for correlating with Radarsat or IceBridge, second image.

Further, the Landsat was lumpy but otherwise so featureless that detection of slow differential motions just wouldn't work. That's too bad because the four vertical sides of a radar grid cell would fit nicely within a blog-sized Landsat at full resolution and we could tile up from there.

However without ground control points, positioning error after all the mickey mouse couldn't be independently assessed. The low budget route, entering the grid corners as EarthExplorer search corners, solves the coordinate conversion issues but not that accurately and only overlays tracks on the greenish low resolution preview image in Google Earth projection.

Here EarthExplorer allows upload of kml and shape files to drive image selection but these are limited to 30 points (radar tracks have 40 or more waystations). Unfortunately, after selecting an image for download, the kml file is tossed rather than being reprojected to an accompanying transparent overlay of the UTM.

Here again the Eqip upheaval is more favorable since it has numerous persistent melt lakes, streams and fixed rocks being near the coast and is so close to Jakobshavn that it resides in the very same Landsats. Access is 100x easier than to the Petermann grid area and many thoroughly studied sites are in the vicinity including Store Glacier and Swiss Camp.

The latter has a very peculiar thermal gradient between two nearly adjacent drill holes, one of which in view of Eqip, may have bored through a radar-unobservable basal deformation. Viewing these as buoyancy imbalances, there won't be radar reflectors if the process is essentially a moving thermal front (called zone refinement in metullurgy) with few impurities to bring out.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 07, 2016, 07:03:05 PM
Ice penetrating radar is so critical to every aspect of Greenland glaciology that it is worth re-processing the entire Cresis archive. There's been considerable progress on some angles of that, see below.

In addition to correcting and uniformatizing the vertical and horizontal scales, fixing the unspeakable tilt error, improving contrast adaptively, I'm looking how best to add compass direction of the flight, direction and magnitude of ice flow across the flight line, replacing horizontal scale with precision GPS waystations, and utilizing curvilinear and haphazard flight segments as held-backs to assess true bedrock, ice thickness and fold model interpolation error. Note surface and bedrock slope are already baked into the images; aircraft bearing is inferable but ice surface velocity is not.

It’s tempting too to plot a track along an overall bedrock DEM 3D visualization but the fact is, no locally relevant data whatsover exists for bedrock other than the track at hand and its intersections.

Petermann is one of the most intensely surveyed regions in Greenland yet a typical 50 km track segment will only have 5 intersecting tracks. A whole lot can happen in topography over 10 km, for example a whole 3000 m mountain range in Nevada could come and go without being detected. However based on flights subsequent to Bamber 2013 it appears more likely that Greenland's bedrock is mostly unremarkable.

I'll also be looking at another mystery: where does the ice go as it is displaced from below by an upheaval? Higher layers are displaced upwards to a certain extent but that effect is soon damped out, not typically resulting in a surface bulge nor accounting for the area of the upheaval as seen in cross section.

Newer ice layers also thin above basal upheavals, possibly anisotropically with respect to prevailing speed and slope, as can be seen from a decreasing inter-sister distance over a hump or as mid-sister to Holocene cross-sectional area. This effect is related to but distinct from draping (or not) of stratigraphy over bedrock topography.

The issue here is recovering internal ice viscosity (temperature); the mystery is how 20 years x 500 glaciolgists can pass by without that being determined.

That has taken a new twist this year as NEEM researchers have started looking more closely at what produced micro-layering of ice crystals in the core. Glen's flow law, used in all modern ice sheet models, is partly derived from short-term experiments on lab ice utilizing enormous external stresses.

However the strain response of grain boundaries etc to low stresses over long glacial time frames is altogether different. This means folds in the NEEM core -- and thus the history and  future of the Greenland ice sheet -- cannot be accurately reproduced using Glen's law.

http://www.the-cryosphere-discuss.net/9/5555/2015/ (http://www.the-cryosphere-discuss.net/9/5555/2015/) T Goossens 2015
http://www.the-cryosphere-discuss.net/9/5817/2015/ (http://www.the-cryosphere-discuss.net/9/5817/2015/) D Jansen 2015
http://www.the-cryosphere.net/8/1129/2014/tc-8-1129-2014.pdf (http://www.the-cryosphere.net/8/1129/2014/tc-8-1129-2014.pdf) M Montagnat ‎2014
http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015JD023290/full (http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015JD023290/full) I Oyabu 2015
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/83886 (https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/83886) K Keegan 2015
https://agu.confex.com/agu/fm15/mediafile/Handout/Paper78793/GPT_Jose_AGU_CReSIS.pdf (https://agu.confex.com/agu/fm15/mediafile/Handout/Paper78793/GPT_Jose_AGU_CReSIS.pdf) G Tsoflias 2015
https://epic.awi.de/33070/1/Eichler2013.pdf (https://epic.awi.de/33070/1/Eichler2013.pdf) J Eichler 2013

I just noticed that the Radarsat velocity anomaly above is visible to a certain extent in Fig.4e of the original Bell 2014 paper, shown below with and without the overlay. The source of the velocity map seems to be Joughin 2010 which represents InSAR data from 4-5 years earlier. It is consistent with our Radarsat but lacks its fine structure resolution.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on January 07, 2016, 08:18:09 PM
"I'll also be looking at another mystery: where does the ice go as it is displaced from below by an upheaval? Higher layers are displaced upwards to a certain extent but that effect is soon damped out, not typically resulting in a surface bulge nor accounting for the area of the upheaval as seen in cross section."

I see no mystery, because the way I look at it, the glacier ice behaves very much like water in a stream  or a river, where the shape of the bottom is not shown on the surface?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: P-maker on January 07, 2016, 11:26:30 PM
Espen,

I do agree with you that overlying layers of ice simply will flow to the sides, as the upheavals rise from the bottom.

A-Team,

Thanks again for your great efforts and extensive attempts at documenting everything in 3D. At times however, I would prefer to see all your ramblings on this issue written up in a neat paper.

I did not check all your references but based on the stuff I did read, I think a number of facts emerge, which I have tried to nail her:

1)   Units of Disrupted Radiostratigrahy (UDRs) mainly occurs under the northern half of GrIS, where ice is cold and bottom freezing is most likely to occur
2)   Most UDRs appear near the heads of ice streams requiring some speed (and surface slope) to produce isolated patches of meltwater through pressure melting near the bottom (or drainage channels from the surface)
3)   A number of elongated (cigar-shaped) UDRs have now been identified and they all seem to follow flow lines near the bottom of ice streams
4)   At least two papers have now identified UDRs under the upper reaches of the Jakobshavn ice stream
5)   It is no wonder that there is a “pervasive tilt error” along these ice streams, in particular not if you consider that they are rapidly disintegrating and thinning near the front and at the same time UDRs are growing from the bottom near their valley heads.
6)   If these UDR upheavals are actually taking place more rapidly over the past 20 years, it must be tricky to figure out the isostatic recovery patterns under these circumstances
7)   It is well known that freezing water breaks even the strongest rocks, thus if you can get the freezing process going near the bottom, it should be a simple matter to lift the entire ice sheet from the bottom and let the overlying layers flow to the sides, thus disrupting the original stratigraphy.

If it is refrozen surface water, you will eventually end up with the youngest ice near the bottom.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on January 08, 2016, 05:11:27 AM
"If these UDR upheavals are actually taking place more rapidly over the past 20 years, ... "

how strong is the evidence for this ?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: P-maker on January 08, 2016, 10:22:38 AM
Sidd,

I agree. This statement should not have been put under the headline "facts". I was simply referring to the observation made by A-Team that these features were not known before the 1990ies. It remains to be seen whether some clever guy can actually document the rise of an UDR over the last couple of decades. This may have a number of implications for moderne glaciology, if this is the case.

Cheers P
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 08, 2016, 02:59:16 PM
Quote
the glacier ice behaves very much like water in a stream  or a river, where the shape of the bottom is not shown on the surface?  overlying layers of ice simply will flow to the sides, as the upheavals rise from the bottom.
Whoa there. Bottom upheavals raise the ice above them, sometimes many cubic km of ice forced thousands of meters overhead. The nearly flat isochronal surfaces in that 95,000 years of upper ice are bent smoothly upwards well into the Holocene and sometimes into firn.

Indeed the Panton paper uses slope departure from horizontal as a proxy for automatic identification of basal upheavals (which have poor contrast in most radar designs). The angle of bending tapers off smoothly in younger ice. That is what's being measured in Fig.1B.

Bottom upheaval pressure also cause the ice above to flow slightly to the sides, manifested as isochronal lines becoming slightly closer over the bump than before. This got caught to a certain extent in the MacGregor 2015 dataset which did not consider deformations (#346 #358). However the radar archive is so vast they could not consider specific cases at high resolution in their Greenland-wide study.

Ice being incompressible, any new volume injected or forced by folding into the bottom has to be accommodated between these two mechanisms, thinning and uplift. This fractional allocation, maybe 15% thin plus 85% uplift, has never actually been measured in a specific case.

For starters, no one has ever tabulated the volumes of ice displaced. That would require much more focused radar tomography than present-day surveys (as called for in the Panton paper). Many uplifted regions have only a single cross section not aligned with flow nor positioned representatively with respect to the global deformation structure. Think of a  low budget CAT scan -- the doctor wants to see if your liver is enlarged but is only given a random abdominal plane.

I would do this by working solely with the two brothers (91 kyr), three sisters (46.5 kyr) and Holocene start *14.5 kyr) -- they're ubiquitous and an adequate proxy for the hundreds of minor isochrons. It's not difficult to pick the layers with the bezier tool of gimp, measure the intervening area, and plot the separation between them.

It's probably better to precede inductively from case studies of experimentally accessible, limited-extent, isolated low-flow deformations like Eqip having many radar cross sections than to initially take on the remote, massive, inadequately gridded Zachariae and Petermann. No one has a clue yet what is going on -- that is why Panton terms them UDRs and why MacGregor sidesteps the whole subject.

A single flight line often provides internal calibration via long uneventful stretches preceding the deformation in which a constant separation defines the unperturbed normal. A few isochrons thus suffice to estimate how thinning thins out with vertical height. Panton gives three reasons to expect linearity -- can't go wrong with that as everything is linear to first order, all that we could aspire to here.

Basal deformations are not always easy to detect, delineate or differentiate from draping over basal topography. Panton's automated method discards sloping isochrons when there is significant bedrock slope but still comes up with  6-7% Greenland affected. However steep bedrock prominences may actually be conducive to deformation initiation in view of ice sheet flow.

Contrast in radargrams is a complex issue. The remedies have some similarities to those for Landsat and Sentinel in that optimal corrections must differ regionally to respect patchiness. Isochron striations bring in linear anisotropy as do crevasse fields that must be exploited by the filters. There are also very pronounced flow anisotropy effects in Petermann fold belt radar as noticed by Mundel.

Image intensity in satellite and ice radar data actually have physical meanings. Those becomes altered, perverted, or even lost in enhancement processes. Some people choke on the whole idea. However it's ultimately about having to optimize information extraction from very expensive data according to the purpose at hand. The original doesn't cut it.

Panton 2014 introduced elliptical band pass filtering empirically adapted to sloped and even curved isochrons. That had a wonderous effect on inter-band noise (and so tracing isochrons) but was ill-adapted to diffuse deformations, even making them worse. Panton 2015 sought to apply these to the voluminous Cresis archive with minimal human intervention.

Image segmentation followed by say ImageJ adaptive contrast applied to deeper ice does much better in pulling out faint upheaval regions. That can be problematic depending on the existence of reflectors and their diffusivity. Tracking isochrons through flares is yet another special situation in radargram enhancement important to isochron continuity In Photoshop or Gimp terms, this is masking the image appropriately before each effect is applied and then reassembling from the parts.

The creative part comes with making an effective mask without tedious manual tracing of boundaries on thousands of individuals radargrams that have built up over 22 years of idleness. Masks can often be defined by semi-automated methods but it's hard to envision these working for more than one year's radar design.

The alternative is optimizing the radar design so that it does a better job on the deformation layer from the get-go. That may be feasible for sled radar at selected sites (eg Eqip or the 2015 Renland ice cap).

The inconvenient truth is a very substantial part of north-central Greenland has significant basal issues, much more than we are acknowledging today. It is complete folly to keep applying the same old classical ice sheet models to the GrIS without first getting to the bottom of these deformations.

Below I relocated some text and links that were previously above. Panton's work was previously covered on these forums at the links below.

http://forum.arctic-sea-ice.net/index.php/topic,400.msg36170.html#msg36170 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg36170.html#msg36170) Zachariae
http://forum.arctic-sea-ice.net/index.php/topic,154.msg34112.html#msg34112 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg34112.html#msg34112) Jakobshavn
http://forum.arctic-sea-ice.net/index.php/topic,909.msg36465.html#msg36465 (http://forum.arctic-sea-ice.net/index.php/topic,909.msg36465.html#msg36465) radon transform

Quote
Automated mapping of near bed radio-echo layer disruptions in the Greenland Ice Sheet
C Panton NB Karlsson
http://www.sciencedirect.com/science/article/pii/S0012821X15006597 (http://www.sciencedirect.com/science/article/pii/S0012821X15006597)

One of the key processes for modulating ice flow is the interaction between the ice and the bed, but direct observations of the subglacial environment are sparse and difficult to obtain. In this study we use information from an extensive radio-echo sounding dataset to identify areas of the Greenland Ice Sheet where internal layers have been influenced by near-bed processes. Based on an automatic algorithm for calculating the slope of the internal radio-echo layers, we identify areas with disrupted layer stratigraphy. We find that large parts of the northern portion of the ice sheet are influenced by locally confined mechanisms that produce up-warping or folds in the layer stratigraphy inconsistent with the surface and bed topography. This is particularly evident at the onset of ice streams, although less dynamic areas close to the ice divide also contain imprints of layer disturbances. Our results show that the disturbances are found in many different flow and thermal regimes, and underscore the need to understand the mechanisms responsible for creating them.

Quote
Tracing Internal Radar Layers in the Greenland Ice Sheet
Christian Panton PhD thesis U Copenhagen 108 pages
http://www.nbi.ku.dk/english/research/phd_theses/phd_theses_2015/christian_panton/Christian_Panton.pdf (http://www.nbi.ku.dk/english/research/phd_theses/phd_theses_2015/christian_panton/Christian_Panton.pdf)

Internal layers in radio-echograms from the sounding of ice sheets have long been a valuable resource in glaciology, but their usefulness have been limited by availability of traced (digitized) layers. To speed up this process, we have developed an algorithm for semi-automatic tracing the internal layers and a fully automated algorithm for mapping the layer slope.

The layer slope is inferred by the intensity response to a slanted Gaussian filter, from which layers can be traced using an active contour model. With these techniques we show that it possible to trace internal layers over distances of hundreds kilometers with minimal operator intervention, and the methods have been successfully validated between two Greenland deep ice cores with internal match points.

In order to remove any operator assistance, we show how the layer slope can be used to detect disturbances in the deep radio-stratigraphy of the Greenland Ice Sheet. We find that the disturbances are scattered over the northern part of the ice sheet, with the highest density upstream from the Petermann glacier. The disturbances do not seem to be correlated with surface velocities and can be found on, and close, to the ice divide. These results highlight the need for high resolution mapping of the interior ice sheet to understand the dynamical nature of the basal environment.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 09, 2016, 01:38:14 PM
Quote
If these UDR upheavals are actually taking place more rapidly over the past 20 years,  tricky to figure out the isostatic recovery patterns
The animation below shows how to filter the Cresis ice penetrating archive for repeated flight tracks with the greatest separation in time (3rd frame) that intersect a known upheaval (4th frame). 

Camp Century, summit ridge drill sites and certain glacier outlets were favorite waystations, so some tracks from the mid-90’s were indeed re-flown in 2011-14 (3rd frame). Early radar designs were already quite decent but center frequencies, bandwidth and power were quite different from post-2010 radar, as was processing. Power is important at depth.

We looked at a 2 year Eqip pair in #351; for an example of a 15 year pair, segments 19990514_01_004 to 008 can be compared to 20140514_01_048 to 063 (magenta line in 3d frame). This gives about 800 km of common track that has upheavals much of the way, compounded by bedrock-driven draping in the southeast. Google search has just discovered Cresis kml so today those search terms and a click can magically display those track segments in Google Earth as well as their pdf booklets.

https://data.cresis.ku.edu/data/rds/1999_Greenland_P3/pdf/19990524_01.pdf
https://data.cresis.ku.edu/data/rds/2014_Greenland_P3/pdf/20140514_01.pdf

The second animation compares the upheavals in a specific instance over a 15 year interval (19990514_01_008 vs 20140514_01_51). The flight lines were 84 m apart in this region according to onboard GPS. There are issues with vertical and horizontal rescaling, as well as radar resolving power and correctable contrast. However looking closely at this pair, the upheavals look very similar despite some wagging at the upheaval top. Certainly the 2014 upheaval is not new.

Keep in mind radargrams are terribly misleading as they stand. The vertical exaggeration is typically 10-20x but can be much higher. This tends to overly dramatize their appearance, squashing the upheaval into a very small horizontal extent. Somewhere way back, I posted the same scene from 1:1 to 50:1 exaggerations, that was an eye-opener -- these are very drawn out features, not the Grand Tetons.

Overall, there isn't any information currently about the temporal origin, initial geographic distribution, initiation mechanisms or subsequent evolution of upheaval systems. Cold ice is quite brittle but here it evidently has had ample time to deform smoothly upwards and flow slowly to the sides. The parameter range allowing that and the very size of some features provides a time constraint (slow development).

It might be worth developing 2-3 scenarios at the extremes and asking what could distinguish between them using either the radar we've got or by targeted experiment. My sense is that warmth of the end-Eemian set the stage for the upheavals as opposed say to awakening volcanism, geothermal excursions, the Holocene Thermal Maximum, or meteoric moulin meltwater.

In this scenario, they began to develop as the ice age had laid down a thick layer of ice of contrasting temperature and continue to growing to this very day, influenced of course by bedrock and slope, depth, temperature and velocity of ice overhead. The evolution is likely slow, steady and incremental rather than sudden and disruptive.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on January 12, 2016, 10:17:12 PM
Quote
C Panton and NB Karlsson
Highlights (http://www.sciencedirect.com/science/article/pii/S0012821X15006597 (http://www.sciencedirect.com/science/article/pii/S0012821X15006597))

• Large parts of the ice sheet are influenced by near-bed processes.
• No correlation between the size of the features, frequency and surface velocity.
• Folds and up-warping can occur in absence of basal melt.
The first point is strongly confirmed by advanced contrast enhancement methods that unambiguously bring out lesser deformations in many older tracks. It seems that Bell 2014 only pulled fairly extreme deformations and those only in selected years. It’s instructive just to look at post-Bell flight data (eg 2014) as this reveals many new deformations per km of novel flight track as well as increasing the documented size of previously known complexes.

The second point goes up against a deeply entrenched misconception that ice flow is somehow responsible for these upheavals. However many deformations occur in essentially stagnant ice. Panton 2015 performed formal correlation statistics, finding R = 0.03 in supplemental.

The third point cannot be fully evaluated until basal melt is better mapped. However it’s fair to say basal deformations are so extensive from Jakobshavn north that naive models (frozen vs unfrozen bed, deviatoric strain) have little applicability to the future of Greenland’s ice. That’s because these deformations introduce a whole new unexplored dimension to ice rheology, temperature and crystal fabric.

Panton 2015 suggests a persistent localized source near NEEM, what might be called an emitter. Over time, steadily formed upheaval would be entrained by ambient ice sheet flow and so move downstream from its fixed point of origin, giving rise eventually to an elongated cylindrical structure aligned along flow. In this situation, neither ice flow per se nor structural geological folding have anything to do with creation of deformation structures.

According to the intersection of the upheaval inventory with long-term repeated flight trackss (4th frame of animation above), examples of repeat flight tracks might exist within the fast-moving region of the Petermann grid (though not at less-flown Zachariae. We’ve only look so far at short time intervals between repeat flights in  fairly slowly moving coastal ice (Eqip) and the stagnant interior (posts #370 and #351).

For grid ice moving at 1 km/day (a third of calving front speed), with 15 years possible between upheaval snapshots, the surface ice will have moved 4 km. That’s easily detectable on radargrams as it corresponds to a 74 pixel displacement. Ice moves slower between surface and bottom but prospects are still good for detecting structural changes in deformations over time. A longitudinal track is more favorable than a cross-flow transect here. Unfortunately the older longitudinals at Petermann have either poor horizontal resolution (eg 1997) or poor radar design (2010).

Back at Eqip, the deformation is smaller and the track crossings more numerous. The first image below shows a new container (template) to uniformatize deformation data from over-flights in many different years and radar designs. The image below shows a complicated but unfortunately common situation where the flight sections are curved. We can’t just throw all the curved data away because much of Greenland is never going to be visited again by ice penetrating radar.

I added a compass that shows flight bearing at each track waystation and surface ice velocity at that point, a bounding box for the deformation and the area it occupies there, the google earth kml thumbnail of the relevant over-flight, and a 1:1 scale in addition to bringing data to a standard 10:1 vertical exaggeration.

Someone at Cresis had the very poor idea of labelling intermediate lat,lon points across the chord instead of along the track (however that can remedied via kml nitty-gritty). The track over the disturbance was further broken here into two independently rescaled segments that have to be tiled up again, with the parameters for that having been discarded. This is on top of mis-placed tick marks for ice depth markers, tick-marks obscuring experimental data, non-use of WGS84 calibration, and non-correction for flight incline (tilt).

Some of the Eqip flights probably followed what the crew perceived as flowlines. We have recent high quality products on velocity magnitude but not direction or trajectory. It’s not so easy to superimpose projections of the flight lines (kml files displaying in non-proprietary Google Earth), Sentinel 1A surface radar, Landsat and Cresis mercator, and various polar stereographic resources such as bedrock DEM.

This is critical though to determining whether the Eqip deformation is attributable (or at least correlated with) bedrock topography, age stratigraphy, flow orientation, or surface features. Note the very poor quality base photo from 25 Aug 2012 used by Google Earth shows, after substantial color tweaking, many small meltwater rivulets running directly over the deformation though no apparent moulins (2nd image).

The two-frame animation shows the relevent tracks within the deformation’s surface bounding box over the quaint 1990’s photomontage of Greenland that Cresis uses as locator map and a 10 Jan 16 Sentinel 1A. It’s quite difficult to register modern satellite imagery as the melt features and extent of ablation change so frequently. I have Landsat frame registered too and will add to this animation in a bit.

Fortunately satellite imagery for Jakobshavn almost always extends up to Eqip and Store. Since I have all the good ones for JI already, it won’t take long to make a high resolution velocity map for surface ice over the upheaval area, the expectation being that Eqip ice is under considerable tensile stress from ice piracy from these larger glaciers to both north and south.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on February 08, 2016, 05:58:56 PM
Images from the Sentinel 1A in EW (extra wide) mode are normally in what they call medium resolution (GRDM), bu over the Petermann they are delivered in high resolution (GRDH) as well. AFAICR that is 40 m/pix and 25 m/pix.
They can be in dual polarization as well. Here is a sequence of images from 20151220 and 20160206, 48 days apart. Color is derived from the polarization, Red=H, Green=V.

On the south bank a crack brightens and gets longer. I don't look at the Petermann images often enough to know whether it is significant.

Click for the animation to start.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on February 08, 2016, 06:53:30 PM
When similar cracks in 2010 and 2012 reached the central channel separating the eastern from the western section of the glacier, a large break-up occurred. So yeah, I think this is important.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on February 08, 2016, 10:30:45 PM

On the south bank a crack brightens and gets longer. I don't look at the Petermann images often enough to know whether it is significant.

Petermann showed the same behavior during the freezing season 2014-2015, when the crack(s) expanded, and then slowed down again during the melt season in 2015. Why? I am not sure, only having some theories involving plasticity.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on February 08, 2016, 11:18:24 PM
The main crack on the southeast bank on the re-oriented image has not yet elongated though I expect it will this summer if the secondary crack below doesn't take over.

There are some changes though on the upper west bank. Basically the ice shelf is moving a little faster centrally than on this edge against the wall, with the effect of slightly straightening the cracks.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on February 09, 2016, 03:19:19 PM
Ice sheets have long memories and those past conditions may remain partially determinative today and in the future. Looking at a Petermann region snippet in MacGregor 2016 got me wondering if the long-standing confluence of ice sheets  across the Nares could somehow explain today's anomalously fast velocity of Petermann well into the interior, as well as its extensive field of basal deformations.

There has been minimal coverage of the Innuitian Ice Sheet chronology on these forums despite very extensive research on the Ellesmere Island side. I located un-paywalled locations for the key articles:

http://forum.arctic-sea-ice.net/index.php/topic,176.msg43315.html#msg43315 (http://forum.arctic-sea-ice.net/index.php/topic,176.msg43315.html#msg43315)
https://www.researchgate.net/publication/223443510_The_Innuitian_Ice_Sheet_Configuration_dynamics_and_chronology (https://www.researchgate.net/publication/223443510_The_Innuitian_Ice_Sheet_Configuration_dynamics_and_chronology) J. England
ftp://soest.hawaii.edu/coastal/Climate%20Articles/Greenland%20thinning%20Holocene%202009.pdf (http://ftp://soest.hawaii.edu/coastal/Climate%20Articles/Greenland%20thinning%20Holocene%202009.pdf) B Vinther
http://www-udc.ig.utexas.edu/external/joemac/pdf/MacGregor_2016_Science.pdf (http://www-udc.ig.utexas.edu/external/joemac/pdf/MacGregor_2016_Science.pdf) MacGregor 2016

MacGregor 2016 write:
Quote
the northwestern sector of the GrIS was connected to the Innuitian Ice Sheet across Nares Strait. After the last deglaciation, the GrIS thinned rapidly at Camp Century. This thinning was attributed to the collapse of the Nares Strait ice bridge ~10 ka, and residual thinning may be ongoing.

The Holocene-averaged flow of this sector of the ice sheet was significantly faster than at present, and its subsequent dynamic deceleration is at least an order of magnitude greater than can be attributed to the LGP-Holocene viscosity contrast. This sector’s Holocene-averaged accumulation rate was significantly lower than at present, which also suggests that substantial dynamic thinning occurred there.

Together, these patterns indicate that faster ice flow in northwestern Greenland during the Holocene included a dynamic response to ice-bridge collapse.
The first image shows flow from the two opposing ice sheets meeting in a saddle across from present-day Hammond Glacier, with flow then diverging to the south and north (Petermann). The Ellesmere Ice Divide was not too far inland, meaning the bulk of Innuitian ice was to its west.

The long bay west of Judge Daly Promontory (opposite Petermann) is apparently where it reached Nares Strait. The whole thing started to collapsed around 10 kyr or some 1700 years into the Holocene, removing an immense buttressing effect from Petermann between 9.0 and 8.5 ky ago. This was followed by post-glacial rebound (3rd image).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on February 13, 2016, 02:00:01 PM
Petermann Glacier jumps out on every display of ice sheet velocities on the Greenland Ice Sheet though the explanation does not (unlike for NEGIS ice stream for which a geothermal hot spot is invoked). The rapid loss of buttressing from the Innuitian Ice Sheet across the Nares Strait in Canada may have played a role in creating the enhanced velocities we see today. However post-glacial uplift of 140 m at fjord mouth of Petermann, by reducing slope, would have the opposite effect.

Mostly I have been puzzling over the treatment of NW Greenland in MacGregor 2016 (see post #376), specifically why the authoritative account of the IIS in England 2006 (and its 91 subsequent citations) is relied on but seeming misquoted. This is not a trivial matter since the 9 kyr isochron plays a central role relative to the quoted 10 kyr collapse of the Nares Strait buttressing bridge versus the 8 kyr date actually provided in England 2006.

Quote
Granite erratics on northeast Ellesmere Island record the onshore flow of Greenland ice that extended p15km inland, overriding local summits (up to 840m above sea level (asl)) and contacting local glaciers that flowed east off the Hazen Plateau...

The absence of Greenland erratics farther inland indicates blockage by Innuitian ice that occupied tributary valleys west of Nares Strait. Farther south, at the north end of Kane Basin, the uppermost erratics (840 masl) are of Ellesmere Island provenance, indicating that the confluence between Greenland and Innuitian ice lay offshore.

Judge Daly Promontory glaciomarine sediments that mark Holocene marine limit (120 masl [date] the progressive entry of the sea from both the north and south ends of Nares Strait starting 9.0 ka BP. Deglaciation progressed to the centre of the strait by 7.5 ka BP, reconnecting the Arctic Ocean with Baffin Bay.

Buttressing by the Greenland Ice Sheet would have reduced the outflow of Ellesmere trunk glaciers into Nares Strait, allowing them to fill their fiords and result in the eastward migration of the Ellesmere Ice Divide.

At the south end of Nares Strait, convergent Innuitian and Greenland ice formed the Smith Sound Ice Steam that eroded large streamlined bedforms on land and possibly on the sea floor in northern Baffin Bay.

After 8 ka BP, the most persistent margin of the IIS occupied Nares Strait, where it remained in contact with the Greenland Ice Sheet until 7.5 ka BP.
Part of this may be due to respective uses of calendar years (from ice core layers or better, tree ring counts) versus C14 dates. Because C14 is not evenly produced in the upper atmosphere, it is necessary to use a calibration curve to relate the two. Because of its half-life, C14 is only useful for about 50 kyr; over that time frame, its dates are about 8% too low (inset, first image).

However it's not that simple because C14 levels are ambiguous especially for the key early Holocene -- a given proportion of C14 can equally well correspond to multiple calendar dates, up to six as shown in the second image. For the 2 kyr span shown, nearly 30% of C14 dating is ambiguous to a couple hundred years. Although that's only to a few percent, it matters greatly relative to the timing of dramatic calendar year events of the end-glacial and early Holocene.

Using the online calibration tool CalPal 2007 at http://www.calpal-online.de/ (http://www.calpal-online.de/)  a C14 date of 8500 years prior to 1950 in England 2006 corresponds to a calendar age of 9521 BP which is in the right direction for MacGregor 2016. If the uncertainty was initially 250 years, the calendar uncertainty would be ±342.

However England 2006 does not date wood but rather marine clam shells in deglacialted deposits. These raise two additional issues, a lag in marine carbon dioxide equilibration with upper atmosphere C14 formation variously estimated as 300-800 years and whether carbonate deposit feeding (Portlandia arctica) or suspension-feeding clams (eg Mya truncata) were utilized, the former giving dates older by 300 years and more.

The interplay of issues here -- fluctuating sea levels, glacial advances, convergences and retreats, isostatic and elastic rebound from deweighting (2nd image), divergence of the jet stream by the 4800 m high Laurentide ice sheet south of the IIS -- is so complex that accurate reconstruction of events has proven elusive. Even ice cores have had problems from the brittle nature of Holocene ice, core locations remote or unrepresentative of the Petermann area, and technical issues with analysis, proxies and shifting interpretations.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Jim Hunt on February 27, 2016, 05:53:25 PM
I wondered why on Earth a CBS producer would want to follow me on Twitter. Then I discovered this:

https://vimeo.com/153941574

Quote
FLYING OVER THE PETERMANN GLACIER IN GREENLAND, AUGUST 2015
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on February 28, 2016, 12:32:52 AM
Except that wasn't Petermann Glacier.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on March 24, 2016, 12:49:30 PM
No S2 image of the calving front yet. Here is a detail of the two upstream rifts discussed some months ago.

Click for the big image.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on March 24, 2016, 05:30:54 PM
Downloaded as a tile from the Amazone S2 site, here is an overview of Petermann at 50 m/pixel. Compared with the previous image, I let the bright peaks saturate somewhat to show more detail in the glacier

Click for the large image.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on March 24, 2016, 05:34:44 PM
And in high res, 10 m/pix, the calving front.

This one requires a click as well.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 24, 2016, 05:45:23 PM
Neat!  Do you have a 10 m piece handy for the critical area of the growing tip? Thx!

The ice shelf frontage looks very much like when we last saw it in Oct 2015. The image clarity is fabulous.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on March 24, 2016, 06:05:06 PM
Sure.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 24, 2016, 06:37:48 PM
Any chance you could resample the tip down to 5 m with bicubic while still in 16-bit? Just one band would do, say band 4 red.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on March 25, 2016, 09:03:42 AM
Of course, although "bicubic" is a bit too much for me to understand atm. Reading the ImageMagick documentation (googling) gives me the impression that bicubic is not a single but a family of options.

So I just use the default, which when specifying -set option:filter:verbose 1 says:

Quote
# Resampling Filter (for graphing)
#
# filter = Cubic
# window = Box
# support = 2
# window-support = 2
# scale-blur = 1
# practical-support = 2
# B,C = 0.333333,0.333333

I attach 16 bits png files of the region with and without scaling. Hope that the 16 bits will survive the forum software.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on March 25, 2016, 11:35:18 AM
Why bi-cubic instead of the more standard bi-linear? Bi-cubic just smooths the end-result more...

https://blog.codinghorror.com/the-myth-of-infinite-detail-bilinear-vs-bicubic/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on March 25, 2016, 03:34:16 PM
Wonderful discussions and imagery. Here is what the LandSat Pan-chromatic Band-8 looks like at 15-m resolution of the same crack that, I am certain, will form the next ice island within a year or two.

I re-gridded and re-projected the LandSat data for ease of quantitative analyses with 'old-fashioned' codes and scripts that, god forbid, even includes Fortran ;-)

EDIT: Spelling. Downloading and processing the original 1 GByte data of a single scene (all 11 Bands) takes less than 5 minutes using nothing more than a MacBook Pro laptop with open-source software only.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 25, 2016, 03:43:56 PM
Quote
So I just use the default
tl;dr:
-- use cubic
-- do early operations in 16-bit
-- share 16-bits on cloud as 1-band tifs like Landsat

Bicubic splines (called 'cubic' in command menus) are what the Landsat-8 and Sentinel 2A have already used getting us to where we are. Sinc (Lanczos3), which has a more information-theoretic basis, was likely considered but not chosen. One is maybe better for downsampling, the other for upsampling. (We've had this discussion before.)

One thing's for sure: ESA would not post at 10 m if they could have had bragging rights for 5 m. They would not have collected at 12-bit if they could have collected 16-bit within error. So we need to be careful not to push too hard on any form of further interpolation since we have no true 5 m or same-day ground measurements to test outcomes against.

However there may be a slightly better option when upsampling to exact 2x multiples. It is not commonly implemented being too restricted (eg not applicable to making 10 m Landsat from 15 m). We commonly shoot for 700 pixel forum width which involves arbitrary multiples in either direction but can attach the original resolution or point to it as necessary.

Nearest-neighbor and bilinear are noticeably sub-optimal (as 0th and 1st order fits to the immediate neighborhood of a given pixel) and rarely used enlarging satellite ground imagery, continuous artwork or photography. They were used in times of limited desktop CPUs (pre-1995) and sometimes even today for quickie monitor blowups and special situations.

You will find no end of silliness online about enlarging abrupt-contrast pixelated cartoon icons, like the fellow above who pleads for vector enlargement, unaware the whole point of bicubic splines is a vector fit capable of arbitrary enlargement, in other words fonts for photos.

It all comes down to how abruptly contrast varies on the ground, what wavelength is under discussion, how the sensor and software decide what goes into a pixel, and what all contributes to spillover and other errors there. On an ice sheet, there actually is information about your favorite 10 m square from its neighboring squares, but with rapidly diminishing returns beyond a two pixel radius.

We are not terribly interested in the literal top-of-atmosphere numerical reflectances from the ice. Some people are. In fact the cryosphere forums are seldom concerned with single-pixel attributes (which species of tree is that?). More commonly we are looking at multi-pixel correlated attributes such as lines (crevasse propagation) or blobs (velocity measurement).

Those are a whole different topic in enhancement because a line or blob can survive enlargement much better (remain perceptually recognizable) than a single pixel because of retained correlation. And lines are anisotropic (have an inherent directionality) which can and should be exploited.

For example, photo can be rotated so lineations are east-west, allowing simple convolutions (bump maps in gimp) to be run north-south. This is a huge deal on radargrams which have many horizontal isochrons that are initially indistinct. Even better is an adaptation to local slope. Etc for surface crevasse fields.

In summary, limited bicubic enlargement beyond the posted resolution has no physical rationale for single pixels (0D) but can be justified for lines (1D) and blobs (2D) which have an additional non-local statistical coherency.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 25, 2016, 04:12:47 PM
Quote
cracks, I am certain, will form the next ice island within a year or two
I am of the same opinion but am betting on strain transfer shifting to the lower crack as the ice shelf slowly moves relative to a fixed feature on the eastern shoreline that marks, but does not cause per se, crack initiation. Moving up the shelf on both sides, quite a few cracks are no longer propagating.

Assuming these cracks extend to full depth and re-freeze in winter from sea water (rather than freshwater melt), that would make for a weak briny bond, implying the strain on them has diminished or they wouldn't become inactive.

Overall the geometry of Petermann is extremely rigid except for the sides (which are very different from each other) and pivoting around a few widening cracks. By displacing Landsats down the channel, precise overlays spanning years of Landsats can be made.

If only we could get someone to install a horizontal interferometer! Then we could watch cracks widen in real time, sort of like watching Nevada stretch with real-time GPS grid tectonics as North American plate motion is opposed obliquely by that of the larger Pacific plate.

One point of confusion we've had on the forum: yes, new shelf is continuously being created off the pinning zone (~1100 meters per year of it); no, that is not remotely keeping up with averaged-out recent rate of loss of ice islands: a single calving event can undo many years of extension.

Petermann glacier is not accelerating appreciably though its velocity is noteworthy well back into the interior, which I proposed elsewhere is a continuing response to Innuitian unbuttressing. (Not so long ago, the Greenland ice sheet  extended 15 km inland on the other side of Nares Strait.)

Thus ice shelf creation will remain slow but steady, being no match for the effect of new warm ocean water circulation under the floating ice shelf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on March 25, 2016, 04:28:04 PM
Agreed on all points.

If only we could get someone to install a horizontal interferometer! Then we could watch cracks widen in real time, sort of like watching Nevada stretch with real-time GPS grid tectonics as North American plate motion is opposed obliquely by that of the larger Pacific plate.

I am working on getting up to Petermann this summer via helicopter from Qaanaaq to service the three ocean-glacier observing sites that we placed in the summer of 2015 from I/B Oden. I still got 3 UNAVCO fancy GPS receivers that allow sub-centimeter vertical and horizontal displacement. The 3 units could be placed in a triangle around the crack. If you know someone who has such an interferometer, please let me know (via e-mail, perhaps).

The attached plot shows the results from a 2 week deployment last summer at the grounding line of Petermann (black lines) as well as 26 km downstream on the freely floating ice shelf (red lines) and 15 km upstream where the glacier sits on bed rock (blue lines).

EDIT: On the horizontal displacement, I removed the 2-week mean displacement at each site (~700 m/year upstream and ~1250 m/year downstream), so only "anomalies" from this mean motion are shown. The vertical displacement is actual raw measured displacement estimated from 30 second samples (but I also got 1 second samples), because this is what UNAVCO reference stations on bed rock at Kap Morton and Kap Schoubye sample at.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on March 25, 2016, 04:44:46 PM
Very interesting.

I have some serious background chaos (visiting relatives) for the next few days. Briefly, we do have ultra-high precision historic worldview satellite data at google earth. Even with Sentinel, the cracks are not that many pixels wide, so one pixel of widening will not be satisfactorily detectable. However Sentinel is not too bad at crack lengthening, which can be leveraged to widening. I looked at all the distraction on Landsat blowups around the tip, the two little melt lakes make a great frame of reference but change seasonally in appearance.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: CraigsIsland on April 13, 2016, 08:58:21 PM
Interesting eco-tourism happening on the glacier: http://the-blue-river.squarespace.com/ (http://the-blue-river.squarespace.com/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: magnamentis on April 13, 2016, 10:31:48 PM
are they aware that this water can be sucked into precipices at any time and them with it?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: CraigsIsland on April 14, 2016, 12:36:09 AM
are they aware that this water can be sucked into precipice at any time and them with it?

lol. I have no idea. Was looking at this from a web design perspective. While "cool" in that you can have the unique blue waters, it's not a good sign for things to come.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on April 14, 2016, 04:26:15 PM
I’ve noted a dozen or so abstract titles from the April 2016 EGU meeting on the What’s New forum and am expanding a bit on them on the appropriate forums. These two Petermann meltwater abstracts are sketchy but we can expect additional information shortly from co-author A Muenchow’s excellent web site https://icyseas.org/ as well as an open access version of whatever journal papers are in preparation.

Quote
Pathways of Petermann Glacier’s Meltwaters, Greenland
Céline Heuzé
23 Feb 2016 AGU New Orleans

Radar and satellite observations suggest that the floating ice shelf of Petermann glacier, north Greenland, loses up to 80% of its mass through basal melting, caused by the intrusion of warm Atlantic water into the fjord and under the ice shelf. Although Greenland meltwaters are key to sea level rise projections and can potentially disrupt the whole ocean circulation, the fate of Petermann’s glacial meltwater is still largely unknown. It is investigated here, using hydrographic observations collected during a research cruise onboard in August 2015.

Two layers are found: one at 200 m (ice shelf terminus depth) mostly on the eastern side of the fjord where a calving event occurred this summer, and one around 500 m (grounding line depth) on the western side.

At the sill at the end of the fjord, approximately 3 mSv* of freshwater leave the fjord around 150 m depth on the eastern side. On the western side, a more complex circulation occurs as waters intrude in. Outside of the fjord in Hall Basin, only one layer is found, around 300 m, but its oxygen content and temperature-salinity properties suggests it is a mixture between Petermann’s meltwater, meltwater from the neighbouring glaciers, surface run-off and sea ice. As Atlantic water warms up, it is key to monitor Greenland melting glaciers to properly assess sea level rise.

Quote
Pathways of Petermann Glacier meltwater, Greenland
Céline Heuzé, Anna Wåhlin, Helen Johnson and Andreas Münchow
EGU General Assembly 15 Apr 2016

… Two methods are used to detect the meltwater from Petermann: a mathematical one that provides the concentration of ice shelf meltwater, and a geometrical one to distinguish the meltwater from Petermann and the meltwater from other ice shelves. The meltwater from Petermann mostly circulates on the north side of the fjord. At the sill, 0.5 mSv of meltwater leave the fjord, mostly on the northeastern side between 100 and 350 m depth, but also in the central channel at lesser concentration.

Meltwater from Petermann is found in all the casts in Hall Basin, notably north of the sill by Greenland coast. The geometrical method reveals that the casts closest to the Canadian side mostly contain meltwater from other unidentified glaciers. As Atlantic Water warms up, it is key to monitor Greenland melting glaciers and track their meltwater to properly assess their impact on the ocean circulation and sea level rise.

*The sverdrup is an rogue honorific unit used strictly within oceanography. Not approvable within SI, its symbol sv had already been allocated to sievert, a measure of radioactivity. One sverdrup represents to an enormous current of water, one cubic kilometer of water per second crossing a flux gate (whose cross-sectional area is unspecified and possibly very broad). All the world’s rivers carry 1.2 sverdrups (making the Petermann flux 0.25% of this); the Gulf Stream varies from 30-150 sv; the Antarctic Circumpolar Current at 125 sverdrups is the largest ocean current. Petermann’s 3 milli-sverdrups represents 3,000 cubic m/s of meltwater exiting the fjord.

Sverdrups are not used in the US, river flow is measured in cfs (cubic feet per second). One sverdrup amounts to an inconvenient 35,314,667 cfs; Petermann works out to 105 944 cfs, about five times that of the Colorado River but only a fifth of the average discharge of the Mississippi River. https://en.wikipedia.org/wiki/List_of_U.S._rivers_by_discharge

These numbers seem impossibly high for Petermann but probably represent an August peak rather than a year-round average, and one that assumes zero mixing with ambient seawater. However since sverdrops are not normalized to cross-sectional area of the flux gate, a slow current across a wide and deep cross-section can yield a large number of sverdrups, extrapolation out from a small number of casts. However in terms of oceanograpphic considerations such bulk heat transport and freshwater density effects, sverdrops work well as defined.

It’s not entirely clear where this freshwater is coming from. Landsat scenes in 2015 showed very little flow in the central channel, little water puddling in the usual northeast side depressions and only briefly filled up-glacier meltlakes. Meltwater formed up-glacier exiting at the base of the grounding zone has been measured by sonar sweeps for a handful of west Greenland glaciers but not yet reported for Petermann.

Petermann is pushing 600 m thick ice across the grounding zone yet this thins to 200 m by the calving terminus. Since dynamic thinning is minimal on a floating ice shelf, the missing ice has presumably been melted by contact with circulating ocean water (which continues even in winter) and hydrostatically adjustment after surface melt. Petermann is at 80ºN so the seasonality of sunlight induced melt is strongly windowed.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: wili on April 14, 2016, 07:29:18 PM
"Sverdrups are not used in the US"

Interesting, since Sverdrup himself lived and worked most of his adult life in the US.

There are a number of Sverdrup's in my area (Minneapolis). A building in the local college (Augsburg) bears the name, and the major interstate highway bridge (35W) that collapsed a few years ago was designed by a Sverdrup, iirc.

(Sorry for the OT comments. Back to science!)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Iceismylife on April 14, 2016, 10:56:41 PM
 in standard units one inch of water loss per day of exposed ice per degree c difference between sea water temp and the local ice melting point.

so 100,000 cfs needs 309 square miles of ice exposed to sea water 1 c above the local melting point.  Is this reasonable for the size of the ice tong?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on April 15, 2016, 11:17:25 PM
A freshwater flux is

sum of (velocity * (1 - Ssalinity/Sref) times area_of_section

where Ssalinity is the measured salinity that varies with depth and across the fjord and Sref is some constant reference salinity that I take as the warm and salty Atlantic water that does the melting of the ice shelf from below. So the units are meters/second * meters * meters to give meters^3/s. A Sv (Sverdrup) is one million of those m^3/s. My favorite Delaware River discharges about 500 m^3/s on average (the Thames River near London is about half of that).

In both a prior publication, e.g., Johnson et al, 2011 (.pdf available at http://muenchow.cms.udel.edu/html/publications.html (http://muenchow.cms.udel.edu/html/publications.html) ) and a new one that uses 2015 data, we find that that indeed about 2000-3000 m^3/s of freshwater exits Petermann Fjord. Dr. Heuze reports this as 2-3 mSv, but this value includes ALL sources of freshwater such sea ice melt, run-off from land, as well as the portion glacier melted by the ocean and by air. In the new publication (not finished yet), we try to distinguish between the ocean's glacier meltwater fraction from all others and it comes out as perhaps 10-20 % of the total freshwater flux across two 2015 sections of independent estimates. These 300 m^3/s originate from the the part of Petermann Gletscher that is melted by and mixing with the warm Atlantic waters.

Just for comparison, the freshwater flux numbers for Nares Strait are about 50,000 m^3/s and that of the Amazon River are about 100,000 m^3/s. So the Arctic Ocean discharges about half an Amazon River of freshwater via Nares Strait into the North Atlantic. Petermann Fjord's contribution at 2,000 or 3000 m^3/s is a small addition that will get lost in the noise of an uncertainty estimate. More details in Muenchow (2016) which is on the above web-site as a .pdf as well (open access this one).

There are devils and details; for example, we do not measure velocity directly (proposal to do so was declined twice many years ago) and thus have to make assumptions that (a) the flow is the result of a specific and simple balance of forces (pressure gradient and Coriolis balance, so-called thermal wind balance from meteorology) and (b) that the total flux of total water is zero to a first approximation. The sum of velocity times salinity anomaly is really an integral across the section (depth across fjord) of the velocity normal to the section with velocity weighted by their salinity. So, velocities where salinity is low (fresher water close to surface) is counted more than velocity where the salinity is high (salty Atlantic waters close to bottom).

ADDENDUM: Velocity section across Petermann Fjord at the sill to Nares Strait. View is from glacier out towards Nares Strait. Red colors are flow out of the fjord, blue colors are flow into the fjord from Nares Strait. Left panel is ocean density from which I subtracted 1000 kg/m^3. Sloping lines of density correspond to velocity (differences in vertical). Stations where the ship stopped and took an ocean profile of temperature, salinity with depth are black triangles at top and thin white lines with depth.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on April 16, 2016, 05:10:05 AM
Thanx for the detailed explanation on Petermann and Nares fluxes, that helped me.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on April 18, 2016, 08:11:29 PM
We might now see a picture of what will be giving birth to a new giant ice berg from Petermann Gletscher, the Starboard crack seems to be resting for a while, but the Port crack is developing a bit (see the animation), the 2 cracks will probably meet sometimes in the near future and result in another "Breaking News" calving :
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on April 18, 2016, 11:41:13 PM
Worth keeping an eye starting in mid-June? It's too cold there for water to melt or cracks to propagate. There have been clear Landsats almost daily ... nothing is happening that I can see except that the ice tongue is slowly marching seaward.

The calculation in the 4th image shows the 'sverdrups' of new ice flowing into ice tongue, more conveniently thought of as cubic meters per second crossing the grounding zone flux gate. The bottom 400 m of this 600 m thick ice will have melted by the time it reaches the front line in ~30 years. Under the old rules.

Petermann did speed up slightly after the last massive calvings (from 1.1 km/yr to 1.2), attributed to loss of buttressing back-pressure. However resistance at the sides is fairly minimal and even if the whole floating ice shelf is lost, Petermann won't speed up dramatically, even with warmish water swirling around the vertical ice front at the grounding zone. According to published theory.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on April 19, 2016, 04:41:30 PM
@ A-Team:

The 450 m^3/s is the volume of ice moving across the grounding zone. About 2/3 of this melts as the 600 m ice at the grounding line appears 30 years later at the terminus with a ice thickness ~200 m. This gives 450*2/3=300 m^3/s. Density of ice is about 90% of water, so if all the melt goes into the ocean as freshwater, we expect 300*0.9=270 m^3/s of glacier meltwater to enter Petermann Fjord as freshwater. This is about half a Delaware River or a Thames River.

We get almost the same number (280 and 340 m^3/s) via a very different method from ocean-only measurements of salinity and temperature with depth and across a Petermann Fjord section along with a arguments on the physics of ocean circulation and mixing. We get two values because we got two sections.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on April 20, 2016, 12:08:01 AM
Quote
we expect 300*0.9=270 m^3/s of glacier meltwater to enter Petermann Fjord as freshwater. This is about half a Delaware River or a Thames River.

That is absolutely amazing to have a river of this magnitude flowing out from under a frozen glacier whose surface features have stable for decades, giving no indication of the melt turmoil underneath. And where is all this fresh water going (to the south) and to what effect?

I would guess there is only minor seasonality to the flow since circulating ocean water deep below has vast thermal inertia and lacks effective contact with the freezing winter or warmer summer air above.

However within ocean circulation per se, in addition to tides, there could be both seasonal effects associated with Nares Strait as well as longer term trends attributable to climate change induced rearrangements in large scale circulation. It is great to have some actual data to put bounds on speculation and put model theory to the experimental test.

Down the road, after total disappearance of the ice shelf, the melt would come from the newly exposed vertical face as the bottom sits on bedrock and is not exposed to sea water. This presents far less surface area (12 km2 than the horizontal under-shelf (~800 km2). It's not clear to me how much of the current oceanic circulatory pattern would carry over to the shelf-free situation, perhaps quite a bit.

Petermann might retreat fairly slowly under oceanic facial melt up its prograde slope until a broad sill is reached several dozen km upglacier so is not a proxy in this sense for the more worrisome retrograde West Antarctic ice shelves.

In terms of temperature-with-depth of ice within the floating ice shelf, this situation presents interesting but manageable boundary conditions for Fourier's heat equation which would have an exact solution here (after certain idealizations) on a trapezoidal slab. Still, it's good to have the thermister strings.

It might be feasible to get at the temperature profile a ways upglacier from the grounding line, though it is problematic that this would shed light on the basal upheaval anomalies which barely extend to Schoubye. Logistically, it would make far more sense to drill basal features at Eqip than here.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on April 29, 2016, 10:52:15 PM
nice ice folding around petermann

 DOI: 10.1038/ncomms11427

open access
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on May 01, 2016, 10:26:55 PM
sidd, nice spotting.

We got an earlier taste of this article from the 3nd author's dissertation, F Mundel. It is a very interesting approach -- forget that it's ice, just model it along the lines of any geological formation distorted by flow.

The graphics are nicely done and provided at a very generous scale (as extracted from the pdf version of the article with ImageJ).

It will be interesting to see the response from the glaciologists who previously put out rather different explanations for it. What sort of additional experimental data could distinguish between them? I am offline traveling the rest of this month and hope to pursue this farther in June.

http://forum.arctic-sea-ice.net/index.php/board,12.0.html (http://forum.arctic-sea-ice.net/index.php/board,12.0.html)
http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364)

Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet
PD Bons et al
http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364)

http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s1.pdf (http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s1.pdf) supplementa

http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s2.mov (http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s2.mov) fly-thru of sheath fold
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on May 18, 2016, 07:04:51 PM
I am quite sure this shows that the upper (and shorter) of the two cracks is widening.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on June 19, 2016, 04:13:01 PM
Also on the Petermann Gletscher melt ponds are forming. Here is a reasonable cloud free image scaled to 30m/pix.

Click for the big picture.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Wipneus on June 19, 2016, 04:18:50 PM
And a detailed animation in 10m/pix of the discussed cracks.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: CraigsIsland on June 19, 2016, 06:23:05 PM
Wipneus- I really like that orange contextual information overlaid on your images/animations. Really helpful!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 19, 2016, 10:02:27 PM
The re-processed image below 'triangulates' the three east side cracks of Petermann. Unless one of the cracks lengthens or widens, we expect the triangle to move downstream with fixed geometry (in R028 S2A images) as the central Petermann ice sheet moves as a rigid block.

The longest crack has extended its tip about 560 (or it least its visibility has improved) from what I recall from following it last fall into November. However this extension is upstream, nearly perpendicular to the direction it 'needs' to go if the ice shelf is to fracture across its entire width.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 27, 2016, 03:33:07 AM
Adam Ash posted a GIF of Nares Strait that included The Petermann Glacier fjord (reposted below).  I find it interesting how much the Petermann Glacier has advanced since 'they' last set the calving front mask in the Worldview images Adam posted.  As Perermann G. is about 20 km wide, the glacier has advanced about 5 km since when(?), last autumn?

(Edit: per Andreas Muenchow's following post, the mask must have been drawn a few years ago.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on June 27, 2016, 04:57:28 PM
Petermann Gletscher speeds vary both in space and time. The advance of the terminus is about 1.25 km per year. This figure summarizes glacier speeds from both remote sensing and GPS tracking. It is part of a manuscript currently under review, but a pre-print is at

http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on June 27, 2016, 10:31:35 PM
Petermann Gletscher speeds vary both in space and time. The advance of the terminus is about 1.25 km per year. This figure summarizes glacier speeds from both remote sensing and GPS tracking. It is part of a manuscript currently under review.

Very interesting and well written (only had time to read a quarter for the time being).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on June 27, 2016, 11:34:35 PM
Wonderful!!


Questions and comments.


Line 62 - I was aware of the "surface undulations" on the former large ice shelves off Ellesmere & Greenland but was not aware of their presence on the Peterman shelf. Are they still present? Do they run with the flow or at right angles to it? Do we know their cause?


Line 192 - I had no idea that the sill would be so far out in the Lincoln Sea. Are most sills so far removed from the straits or fjords they guard?


Line 228 - Any idea why these warm, salty waters would have entered the fjord between 2012 to 2015? Will this drive more rapid melting, or does it indicate less melt water mixing in 2015?


Line 261 - Should "but" be replaced with "and" for clarity?


Line 276 - Any speculation on how, when, or why this very warm, salty core could have been forced over the sill? Am I correct in assuming that this will cause unprecedented melting when it starts rubbing against our glacier, or is it 0nly a small incursion that won't noticeably change things?


Line 322 - I don't understand bothand. Possible typo? Sentence is still difficult for me.


Line 354 - Has this "heat flux" increased since the destruction of almost all of Ellesmere Island's formerly extensive ice shelves?


Line 381 - That's a LOT OF ICE. How does it compare to PII2010 & PII2012?


Line 393 - Are these 10 day eddies only present when ice is flowing, or are they present but hidden through the year?


Fig. 1 - Did PII2012 follow roughly the same path as PII2010?
What do the yellow areas indicate?


Fig. 2 - Koch's map seems to me to be indicating a greater thickness, particularly near Sigurd & Porsild. Is this my imagination, their mistake, or a thinning of the shelf over time.


Fig. 3 - The speed graph seems to indicate highest speed near the grounding line, then a slow down further along. How is that possible? Does the glacier thicken or widen enough to absorb this?


Fig. 4 - Will ice temperature affect how much flex the ice can take before fracturing, or is this too small an amount to be concerned with?


Fig. 5 - For lack of a better place for my question. Is it the Hall Basin Gyre that is driving AW into Petermann Fjord? I had assumed that the coriolis effect would have kept the currents to the right and that the northerly current would have been feeding in.


Please don't feel any obligation to reply. These were just questions and observations that came to me as I read your paper.


Another wonderful example of publishing in a timely manner.


I don't know if you are aware of it, but your dust-up with our former government got a fair amount of publicity on this side of the border, and had some effect on our last election where we "threw the bums out". Canada owes you a huge debt of gratitude.


As Do I
Terry

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on June 28, 2016, 04:11:59 AM
Whow ... this is a full-blown, most constructive review, Terry. I will not address your questions and comments here, but will do so in the revised version of the manuscript. Thank you so much for the detailed feed-back.

I will try to clarify one questions you raised:

The largest glacier speed is indeed at the grounding line with much smaller speeds landward and somewhat smaller speeds seaward. The conservation of mass states that this must be balanced by both melting and/or a change over time in the thickness h of the glacier. More specifically, the time rate of change of ice thickness [d(h)/d(t)] equals the convergence/divergence of the ice thickness [u*d(h)/d(x)] plus the melting. Traditionally people assume a steady state [d(h)/d(t)=0] in which case mass is conserved by a balance between melting=u*d(h)/dx, however, there are two ways that the convergence/divergence term can balance melting: First, the glacier speed u varies along the glacier, that is u=u(x) and second, the rate of change of ice thickness along the glacier can change with distance as well, as it indeed does as the cavity is curved.

For the last 10 years or so, however, Petermann Gletscher is NOT in steady-state because the climate is changing and so does Petermann. This adds another term, d(h)/d(t) to the mass balance which makes matters a tad more complex. This last non-steady term accounts for about half the melting and thinning (5 m per yer) of Petermann. More details on all of this you find in the (peer-reviewed and published) open access Muenchow et al. (2014) at

http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf)

Have fun ... and thank you again for your wonderful questions and comments ... to be addressed in the revised manuscript ;-)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on June 28, 2016, 11:44:26 PM
After reading the full article, I must say it is very interesting and highly informative. Andreas - thank you for sharing the preview.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 29, 2016, 02:28:45 AM
Quote
very interesting and highly informative. Andreas - thank you for sharing the preview.
Indeed this sets the gold standard for timely public dissemination of ongoing research results!

I am wondering though if the situation is not somewhat more heterogenous in horizontal cross-section than a GPS flowline can reveal, especially at the grounding zone and nearer to the walls.

 A German group has been posting interferometric pairs of consecutive S1A IW-grade Petermann imagery (see earlier on this forum). We also have a high resolution fluke of a 2015 Radarsat pair run in S1A emulation.

Additionally, between them, S2A and Landsat-8 cover Petermann almost daily. At 10m resolution over a year, a surface feature would be displaced ~125 pixels, so even a month would do for differential optical interferometry (ie mask the rock, bump the later date back ~12 pixels so the feature is motionless at say the grounding zone, make an RGB using neutral shade for B).

This imagery sees only a plan view of the surface so it knows very little about tidal or buoyant vertical displacements and nothing per se about melt cavities. There may be be swath-reprocessed lidar available though for a very few recent dates.

With a mass conservation law in force, it seems like it should be possible to produce synthetic interferograms of both types from the data. The extent to which these differed from observation is then a measure of this putative horizontal cross-section heterogeneity, or put another way, see what it takes to bring the rest of the flowlines into compliance.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: magnamentis on June 30, 2016, 06:53:34 PM
@Bill Fothergill

thank you for the detailed and comprehensive elaboration in the  IJIS thread :-)

always good to get the greater picture as to at least main and/or all factors that contribute to events or non-events :-)

i thought i post this here to put an end to further OT over there as per your suggestion.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 11, 2016, 12:34:04 PM
Looking now at matched pairs of Sentinel 2A ie 10n days apart, for 'starboard' (northeast wall) crack widening just using band 4 at 8-bit of a 20XNQ of 09 Jul 16, nothing dramatic seems to be happening on the floating ice shelf.

This is a fabulously clear image however so it would make an excellent baseline for developments 10, 20, 30 days out. The slow animation below is a gallery of scenes at resolution along the ice shelf and lower glacier, not a time series.

Melt ponds are numerous right now just below the grounding zone but are not unusually abundant. The twin lakes near the longest starboard crack do not have water in them at this point; nor does the central kayakable channel. There is an unusual feature, possibly sastrugi. south and east of the grounding zone. The melange by the calving front area is complex and would benefit from a color image.

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/7/9/1/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/7/9/1/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Cate on July 18, 2016, 11:39:28 PM
Permalink: http://www.arctic.io/explorer/4Xa5A/2016-07-18/9-N81.3175-W60.81283 (http://www.arctic.io/explorer/4Xa5A/2016-07-18/9-N81.3175-W60.81283)

Crack opens up in Petermann fjord.

Toggle from 17 July to 18 July 2016 to see the big crack appear---looks like a fairly wide stretch of open water right across the channel of Petermann, about midway between the calving front and the mouth of the fjord.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 19, 2016, 12:12:52 AM
Screen shot from today's LANCE MODIS (https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2016200.terra.250m)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 31, 2016, 05:58:50 PM
We mustn't get distracted by Ryder Glacier and miss the big event here at Petermann. The last 4 years have seen some slow development on the starboard cracks but nothing dramatic (1st animation, pinned to twin lake blue dot).

The pattern here has been for new cracks to develop to the south as the glacier moves past some fixed point on shore. There has been a substantial extension of a new crack in 2016 and this may be "the one to watch".  Indeed Sentinel of July 25th does not show the middle of this new crack as well as the later Landsat despite being of higher resolution (5m shown).

The dates on these match fairly well but the Landsat-8 path, row geometries differ because of unavailability of sufficient clear days.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on July 31, 2016, 09:41:28 PM
A-Team
If Petermann should calve either late this season or early in 2017, PII-2016 or PII-2017 might plug up Nares Strait for few years, putting a wrench into any plans for a huge melt-out in that time frame. That said, none of the cracks seem to be racing towards the center channel which Dr. Muenchow seems to regard as a precursor to a calving event.
Relieving Lincoln Sea's buildup of MYI by advection through Nares Strait, and opening the pack in this critical area seems necessary if we are to best 2012's record ice loss.
If Petermann should calf, the resulting ice island might be so deep that it gets stranded within Petermann Fjord and therefor presents no problems to Nares ice advection.
Exciting times.
Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 31, 2016, 10:44:15 PM
What A-Team is mentioning is very important when predicting a future calving, but to become a "Good barn party" you will need a partner (most of the times, and luckily she is from the other side of the valley ).
We have 2 important shear  points at this time in the lifespan of Petermann Gletscher they are Belgrave Gletcher (marked 1.) and Faith Gletscher (marked 2.), and as you see in the animation below   she is getting closer (Port side):
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 31, 2016, 10:58:04 PM
Quote
plug up Nares Strait for few years
Terry, very good point. That's probably the main effect.

Loss of another big piece of the ice shelf will not result in acceleration of Petermann Glacier per se because there is not much buttressing with the rock walls to begin with.

Thus even total loss would not result in sea level rise acceleration attributable to Petermann, even though its inland velocities are remarkable in the overall north-central Greenland context, following Jakobshavn and Zachariae.

The analogy to loss of floating ice shelves in Antarctica at first seems flawed (lack of confining rock walls), as does unstoppable retreat (Petermann has an upstream sill rather than retrograde slope). However the melt underneath by warming ocean waters is spot-on, given Petermann is some years ahead of the Antarctic curve.

Major ice shelf loss at Petermann will trigger another day-after-tomorrow manhatten-sized media circus. While we're best positioned here to provide them dramatic imagery, that should always be accompanied with the fine print about what it does and does not portend.

The new crack is circled below to make clear where the new cross-shelf break might occur. It is the most active feature so far in 2016 though it could end up a dud like the three above it.

And Espen's point is also valid -- port side initiation cannot not be ruled out just because the last two full breaks came from starboard. Actually looking at that history closely, the second event was just a continuation of the first. One event is really meagre statistically, almost as bad as the PDO.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 31, 2016, 11:09:01 PM
I dont think the plug up is a real issue , the berg is too "small" for that to happen, it might have problems exiting but I believe the current is strong enough to be beat it out?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on August 02, 2016, 05:18:11 PM
If Petermann calves this year at the big crack than the calving front would be around 7km further inland than in 2012. Taking the 4.8km advance into account than the ice island would be 11-12km long or wide. Hard to say how the geometry will turn out.

I made the comparison to practice annotations with layers for gifs. The colours of the arrows should be bright red and bright orange, but for some reason GIMP makes them very dull. Does anyone know why? They look correct in the colour selection tool and appear correct in a new blank image.

Click image to animate
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2016, 08:34:30 PM
Quote
for some reason GIMP makes them very dull. Does anyone know why?
Yes. You have the transparency set too high in either the drawing layer, the mode, tool options, or the brush choice. I find sometimes just mousing over the mode sends it somewhere I never intended to go. Gimp comes defaulted to rather arty settings so it takes a while to get it into a scientific configuration.

While you are on a roll, can you pull the depth profile for the putative next ice island from A Muenchow's latest? It might need vertical exaggeration which you can do in gimp by scale change with height uncoupled from width.

This, along with km of width, would give an estimate of ice volume (neglecting all the bottom channelling erosion). I am recalling thickness ramping from 600 m at the grounding zone to 200 m at the front. This could be overlaid on Nares bathymetry (IBCAO) to see where the hangups are out in the channel. I'm thinking that because of the depth ramping, the island won't sit level (freeboard) once it is cut loose though the angle would be meagre. And how many events of this size would it take, allowing for glacial advance, to cut all the way back to the grounding zone?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on August 02, 2016, 09:26:25 PM
A-Team
Exactly!
It's the depth of a future ice island that could pose a problem. PII-2012 grounded in mid channel and spent a freezing season there. A thicker island might slow or halt advection of Lincoln Sea ice for much longer.
PII-2010 had problems exiting Petermann Fjord IIRC, but PI-2012 found a better channel. A new, thicker island might get hung up before entering Nares, or it might not calve until bottom melt has eaten away at the keel.
An island that calves within the next couple of years, while the ice is still very thick, could push back the date for new record melt. I wonder if ice of this depth could damage any sill features and allow more WAW to attack Petermann Glacier.
Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on August 02, 2016, 11:51:00 PM
Quote
wonder if ice of this depth could damage any sill features and allow more WAW
Interesting proposal. These sills are often just terminal moraines (glacial till left from previous highstands, as at Illulisat). So what's not to like about a strong outgoing tide, supporting katabatic wind off the ice sheet, and a broad keel reaming a gap in soft deposits? Drag marks from the Last Glacial Maximum are often seen in high resolution sonar, even on the Arctic Ocean floor itself.

It's too late for ice-penetrating radar once the shelf has become ungrounded. The major sill up-glacier from Kap Schoubye looks more like bedrock than saturated till, though there's meagre seismic data however.

The first August S2A image is in. The jp2 will open in gimp (eventually) but only as 8-bit. For people too busy to dink with Sverdrup and Ryder, a snippet from that is shown below at 10 m, click to see full size. Some possible crack extensions since the Landsat above but more likey just the better resolution. Still, this image makes a great baseline for monitoring developments this month.

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/8/1/0/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/8/1/0/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on August 04, 2016, 01:21:09 AM
While you are on a roll, can you pull the depth profile for the putative next ice island from A Muenchow's latest? It might need vertical exaggeration which you can do in gimp by scale change with height uncoupled from width.
Did you mean from this paper?
http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf (http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf)

He mentions that the ice tongue is about 200m thick and his depth figures show at least 380m deep water at the end of Petermann fjord. If true the ice island shouldn't get stuck at the exit.

I also checked data from NSIDC Bedmachine, but there isn't any bedrock elevation available for most of Petermann Fjord. The surface and thickness values corresond to around year 2000 levels and are useless now.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on August 05, 2016, 01:15:28 PM
The ice shelf is somewhat level at ~200 m below sea level as the above profile (from laser altimeter) shows, so I do not thin plugging up of Nares Strait will be an issue, however, I am concerned about this crack that A-Team documents so well as it is spreading and extending fast, albeit not in a linear fashion towards the central channel.

The cited paper is not yet published, but we got good peer reviews with lots of constructive criticism (as well as a review here by Terry, thank you again) that will make this paper much better than it currently is.

Perhaps related, it looks as if I will be able to get to Petermann via Greenland Air helicopter in 2-3 weeks in order to recover data and repair some of the stations we placed on the ice shelf in 2015 that stopped transmitting data via satellite phone in February. I am both excited and very nervous about the high stakes and price tag of such work ... helicopter rentals are >$70 per minute for 8-10 hours of flying over 2 days and this is AFTER we placed two fuel caches last year along the way from Qaanaaq so that one reach this remote location. Without those caches, the flying time would be 2-4 times as high burning fuel while placing fuel for the grand last leap to Petermann.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on September 06, 2016, 08:56:42 PM
Petermann's ocean weather station is back online after some repairs and replacement of faulty components. It was a very rough night working 33+ hours without sleep, but, amazingly, 800+ meter cables still connect ocean sensors just above the seabed through the 100-m thick ice to the surface and via Iridium (lets hope it works better now with a swapped unit and swapped dataloggers) back to us all.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on September 06, 2016, 11:58:29 PM
Petermann's ocean weather station is back online after some repairs and replacement of faulty components. It was a very rough night working 33+ hours without sleep, but, amazingly, 800+ meter cables still connect ocean sensors just above the seabed through the 100-m thick ice to the surface and via Iridium (lets hope it works better now with a swapped unit and swapped dataloggers) back to us all.
That's great. Thank you for the updates (and the project itself!)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: logicmanPatrick on November 30, 2016, 02:45:36 PM
My 1st post here - I feel like the new kid on the block.  :-)

I've been looking at the Petermann glacier again after a break of some years.  I expect at least one major calving within 3 years.  I base this on what happens with a material which is pushed through a restriction: the sudden strain release can initiate discontinuities in flow - i.e. cracks.

My best guess - and it is a guess at this stage - is a calving about 6 km forward of the large crack shown in all the images above.

Regards to all friends old and new,
Patrick.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on November 30, 2016, 03:50:09 PM
Welcome to the Forum, Patrick! I've released your account, so you should be able to post freely now.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on December 01, 2016, 10:39:09 PM
Hi Patrick

Petermann glacier is almost guranteed to calve within the next 3 years. In fact next year is very likely. Today  I looked at Sentinel 1 images and found that the big crack split near end. The new part moved directly towards the center. I believe in the vicinity another crack is developing directly from the center towards the other shore. If those two combine the calving is 60-70% complete.

Click on image for full resolution
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: logicmanPatrick on December 02, 2016, 02:00:04 AM
Petermann glacier is almost guranteed to calve within the next 3 years. In fact next year is very likely.

I think we are both talking about major, or even spectacular calving as agaisnt run-of-the-mill calving which a given.

During my absence from blogging due to other commitments I have looked at satellite images from time to time, but didn't copy any to my computer or keep notes of dates etc.  Relying entirely on memory - and I know I shouldn't - I recall hints of cracks which appear and disappear from time to time.  It is as if the glacier pressure/flow  is opening and closing some cracks.

With all eyes on the big one, these tiny ones pass by un-noticed.

It may happen that the big crack and others combine to make a 'loose tooth' which rotates slightly and acts as a kind of ratchet.  In that case, a large calving event forward of the big crack becomes more probable.

I reiterate that this is guesswork and memory- no substitute whatsoever for boots on the ground.

Image not showing in preview -  I'm learning the new-to-me interface here - I hope the image shows.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Jim Hunt on December 30, 2016, 08:25:50 PM
A feature on Andreas Muenchow and Petermann in the Washington Post:

http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/ (http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: CraigsIsland on December 30, 2016, 08:59:35 PM

I reiterate that this is guesswork and memory- no substitute whatsoever for boots on the ground.

100% agree. Over multiple disciplines/workplaces etc. - there is nothing like "raw" observations.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Martin Gisser on December 30, 2016, 10:35:37 PM
A feature on Andreas Muenchow and Petermann in the Washington Post:

http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/ (http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/)

Wow! Truely great science journalism. Spread the news, the U.S. MSM is not yet brain-dead.

Quote
A sensor in 3,000-foot-deep waters had found that in the warm, salty Atlantic layer, temperatures were even warmer than just a year earlier, in 2015. Those waters are likely flowing toward Petermann glacier’s grounding line and helping to melt the shelf from below.

“The temperatures at the bottom end of the array continue to increase,” said Muenchow. “It’s getting warmer.”
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on January 01, 2017, 12:36:00 AM
Great article.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Cate on February 15, 2017, 10:39:31 PM
https://www.eurekalert.org/pub_releases/2017-02/uod-usr021517.php (https://www.eurekalert.org/pub_releases/2017-02/uod-usr021517.php)

UD scientists report ocean data from under Greenland's Petermann Glacier

Andreas Muenchow and colleagues---report includes video:

"The researchers recently reported in the journal Oceanography that sensor data from August 2015 to February 2016 confirms that that the floating ice shelf is strongly coupled, or tied, to the ocean below and to Nares Strait, and temperatures vary with the tides and seasons.

Specifically, the paper found that the same water that has been measured in the fjord is under the glacier, lending credence to the idea that the continuity of the glacier depends on the conditions outside the glacier in the fjord....

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on March 14, 2017, 03:04:09 PM
Looks like a calving is underway in the right-hand corner of the tongue!!  PolarView image from yesterday: (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201703/S1A_IW_GRDH_1SSH_20170313T113530_E0B4_N_1.8bit.jp2)  [edit: the 'hand' doesn't point to anything; it's just a relic.]
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on March 14, 2017, 04:05:39 PM
I can see most of this crack in Tealight's posting (http://forum.arctic-sea-ice.net/index.php/topic,53.msg85238.html#msg85238) (above) on August 2, 2016 and in A-Team's July 11, 2016 posting (http://forum.arctic-sea-ice.net/index.php/topic,53.msg83060.html#msg83060).  Some calving happens more slowly than others, I guess.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: prokaryotes on April 14, 2017, 03:23:55 PM
Scientists just found a strange and worrying crack in one of Greenland’s biggest glaciers https://www.washingtonpost.com/news/energy-environment/wp/2017/04/14/scientists-just-found-a-strange-and-worrying-crack-in-one-of-greenlands-biggest-glaciers (https://www.washingtonpost.com/news/energy-environment/wp/2017/04/14/scientists-just-found-a-strange-and-worrying-crack-in-one-of-greenlands-biggest-glaciers)

(https://img.washingtonpost.com/wp-apps/imrs.php?src=https://img.washingtonpost.com/news/energy-environment/wp-content/uploads/sites/43/2017/04/Petermann-crack.jpg&w=1484)

(https://img.washingtonpost.com/wp-apps/imrs.php?src=https://img.washingtonpost.com/news/energy-environment/wp-content/uploads/sites/43/2017/04/S2_Petermann_2017-04-05-1-1.jpg&w=1484)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: DrTskoul on April 14, 2017, 03:42:22 PM
Hydrofracturing???
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: prokaryotes on April 14, 2017, 03:45:13 PM
Hydrofracturing???

Quote
Eric Rignot, a NASA and University of California-Irvine scientist who has studied Petermann up close, commented:

The ice shelf is slowly but surely falling apart. It has been stable from 1901 till the 2000s, then started to break up, especially in 2010-2012. We have seen the glacier speed up for the first time around 2014-2015. Whether this new crack is significant or not is hard to tell as of now. It is unusual to see cracks forming from the center, they usually start from the sides. This could indicate that the ice shelf has gotten too thin in the middle.

Since a meltwater river runs in the middle, hydrofracturing might cause the thinning?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Hunter on April 14, 2017, 05:55:09 PM
Might have a pic for you later on, flew over Petermann about 2 hours ago.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Hunter on April 14, 2017, 09:51:06 PM
Credit NASA
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Hunter on April 14, 2017, 09:53:13 PM
Credit NASA

preliminary data plot not for scientific use.

Last pic is the Kee Bird as it sits today.
https://en.wikipedia.org/wiki/Kee_Bird
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on April 14, 2017, 10:13:45 PM
Scientists just found a strange and worrying crack in one of Greenland’s biggest glaciers https://www.washingtonpost.com/news/energy-environment/wp/2017/04/14/scientists-just-found-a-strange-and-worrying-crack-in-one-of-greenlands-biggest-glaciers (https://www.washingtonpost.com/news/energy-environment/wp/2017/04/14/scientists-just-found-a-strange-and-worrying-crack-in-one-of-greenlands-biggest-glaciers)

This crack was already known in December last year. I posted an image of it in Reply #438 on: December 01, 2016, 09:39:09 PM »
S1B_20161201_Petermann.jpg (1840.12 kB, 2260x1624 - viewed 79 times.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on April 14, 2017, 10:59:53 PM
Hunter, thanks for the amazing images.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on April 14, 2017, 11:10:48 PM
This crack was already known in December last year. I posted an image of it in Reply #438 on: December 01, 2016, 09:39:09 PM »
S1B_20161201_Petermann.jpg (1840.12 kB, 2260x1624 - viewed 79 times.)

I remember that, and I believe Andreas Muenchow has also mentioned it, if memory serves me well.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Cate on April 15, 2017, 12:23:07 AM
Hunter, thanks for the amazing photos and the link re the Kee Bird---very informative. :)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Adam Ash on April 15, 2017, 05:52:51 AM
'A sensor in 3,000-foot-deep waters had found that in the warm, salty Atlantic layer, temperatures were even warmer than just a year earlier, in 2015. Those waters are likely flowing toward Petermann glacier’s grounding line and helping to melt the shelf from below.'

http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/?utm_term=.62144c2fdb37 (http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/?utm_term=.62144c2fdb37)

Great views of the Petermann and Jakobshavn canyons in the video on this page too
The canyon feeding Petermann gives a direct connect to all of inland Greenland.  Huge, and its already melting into a groove...
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4097 (https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4097)
Video at:  'The Earth layer alone with transparency at gamma 1.0.'
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: AndrewB on April 16, 2017, 04:45:18 AM
WaPo: NASA just snapped the first photos of a mysterious crack in one of Greenland’s largest glaciers

https://www.washingtonpost.com/news/energy-environment/wp/2017/04/15/nasa-just-snapped-the-first-photos-of-a-new-crack-in-one-of-greenlands-largest-glaciers/?utm_term=.e72ad91835e0 (https://www.washingtonpost.com/news/energy-environment/wp/2017/04/15/nasa-just-snapped-the-first-photos-of-a-new-crack-in-one-of-greenlands-largest-glaciers/?utm_term=.e72ad91835e0)

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Xela on April 17, 2017, 12:08:27 PM
This crack was already known in December last year. I posted an image of it in Reply #438 on: December 01, 2016, 09:39:09 PM »
S1B_20161201_Petermann.jpg (1840.12 kB, 2260x1624 - viewed 79 times.)

I remember that, and I believe Andreas Muenchow has also mentioned it, if memory serves me well.
According to Andreas Muenchow https://twitter.com/AndreasMuenchow/status/852491527796523008 and Stef Lhermitte https://twitter.com/StefLhermitte/status/852873863427969024 it seems like it's a new crack.

More here: https://twitter.com/Petermann_Ice
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Cate on April 26, 2017, 05:03:00 PM
NASA blog today on the new crack in Petermann.

https://earthobservatory.nasa.gov/blogs/earthmatters/2017/04/24/petermann-glaciers-new-crack/

More details here:

https://earthobservatory.nasa.gov/IOTD/view.php?id=90043
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on April 30, 2017, 06:32:20 AM
I've been thinking about that new crevasse (rift, crack) that appears to 'start' at the longitudinal trough (river bed, "feature") that runs down the middle of Petermann Glacier. (screen shot from the 2nd link above) 
Quote
... Brunt points out that the rift currently appears to end at a feature running down the center of the glacier. “That’s pretty typical,” she said, citing similar occurrences on ice shelves in Antarctica. ...
I'm surprised this is "typical"! Why would ice shelves have a mid-glacial river bed at which rifts start or end? (I'm confused, unless she's referring to chevron cracks that form semi-parallel relatively short cracks when a somewhat brittle material [like a glacier or ice shelf or cheese or clay] is stretched.) 

I wonder if there might be a longitudinal weakness (crack) that runs under the mid-glacier river bed, with the left side of the glacier moving slightly faster than the right side, providing a triple-point.  (Pure speculation!)


I will want to watch this new rift, and see if it connects with other known cracks or the sides of the glacier.

I'm of course also watching what appears to be a completed rift around the right end of the glacier (see my previously post (March 14, 2017), above).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on May 01, 2017, 12:33:33 AM
For a change here are some non-cracking news.

The terminus of Petermann Glacier is mostly blown snow free and left behind blue ice. It looks like several melt lakes survived the winter and appear in a deeper blue. I would really like to know how deep they are and how thick the ice cover is.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: DrTskoul on May 01, 2017, 04:33:16 AM
Neat!!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on May 01, 2017, 06:16:23 AM
Very nice pictures.  Are they draining off the edge as in the Bell paper ? doi:10.1038/nature22048

I commented on that paper here :

https://forum.arctic-sea-ice.net/index.php/topic,622.msg111095.html#msg111095

Ifso that is a stabilizer.

sidd
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on May 01, 2017, 11:13:44 AM
Very nice pictures.  Are they draining off the edge as in the Bell paper ? doi:10.1038/nature22048
...

Most of the lakes are on the part that is about to calve and probably don't have and any effect on stability.


I've been thinking about that new crevasse (rift, crack) that appears to 'start' at the longitudinal trough (river bed, "feature") that runs down the middle of Petermann Glacier. (screen shot from the 2nd link above) 
Quote
... Brunt points out that the rift currently appears to end at a feature running down the center of the glacier. “That’s pretty typical,” she said, citing similar occurrences on ice shelves in Antarctica. ...
I'm surprised this is "typical"! Why would ice shelves have a mid-glacial river bed at which rifts start or end? (I'm confused, unless she's referring to chevron cracks that form semi-parallel relatively short cracks when a somewhat brittle material [like a glacier or ice shelf or cheese or clay] is stretched.) 

I'm not sure there is something as typical rifts/cracks. If something is typical then a glacier flows fasted in the middle, where the ocean is deepest and the lowest friction occurs. Because of the higher speed, the centre of the glacier detaches (cracks) from the main glacier before the sides do. But Petermann Gletscher is squeezed through a small fjord and the edges constantly grind along the rock. If the ice gets struck then cracks develop from the sides.

By the way the centre crack already cut through the main drainage channel. Not good for any rafting fan.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 03, 2017, 02:51:34 AM
Tor
You might want to explore
https://icyseas.org/




I thing you will find many of your questions about the underside of Petermann answered.


Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 03:56:33 PM
Any thoughts on the state of the Petermann Glacier right now, May 27, in relation to open Nares and Lincoln Sea, and warmer SSTs ? And likely near future?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 04:07:13 PM
http://glacierhub.org/2017/05/18/dont-step-on-the-crack-at-petermann-glacier/ (http://glacierhub.org/2017/05/18/dont-step-on-the-crack-at-petermann-glacier/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on May 27, 2017, 05:18:33 PM
Any thoughts on the state of the Petermann Glacier right now, May 27, in relation to open Nares and Lincoln Sea, and warmer SSTs ? And likely near future?
I'm not sure if Petermann is affected by the opening of Nares or not. But in any case it will be interesting to note when the sea ice clears from inside the fjord, and compare it to previous years.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 06:24:26 PM
What's interesting in the long-term, is that the Petermann valley appears to be an almost totally sub-sea-level valley, and maybe the only one that goes all the way to the ancient inland sea of Greenland !
https://arstechnica.com/science/2014/05/greenland-may-lose-more-ice-than-expected/

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on May 27, 2017, 06:38:04 PM
We're in a period of peak tides, with a couple of days to go, the break up in Lincoln can only let in more N Atlantic water which flows far into the fjord. I don't expect anything major in the next few days, but we'll see,
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 27, 2017, 07:40:13 PM
We're in a period of peak tides, with a couple of days to go, the break up in Lincoln can only let in more N Atlantic water which flows far into the fjord. I don't expect anything major in the next few days, but we'll see,
I don't see the connection between the break up of Lincoln Sea ice & more water flow into Petermann Fjord. What am I missing?
Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 08:22:11 PM
Accumulated (melting - mass loss or gain) Anomaly since Sept. 1 2016:
http://polarportal.dk/en/groenlands-indlandsis/nbsp/isens-overflade/ (http://polarportal.dk/en/groenlands-indlandsis/nbsp/isens-overflade/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 08:25:53 PM
We're in a period of peak tides, with a couple of days to go, the break up in Lincoln can only let in more N Atlantic water which flows far into the fjord. I don't expect anything major in the next few days, but we'll see,
I don't see the connection between the break up of Lincoln Sea ice & more water flow into Petermann Fjord. What am I missing?
Terry
Maybe the almost consistent warmer air and SST anomalies going for months now, in the Nares, links then all? And this has led to the early Lincoln break-up, which will probably just accelerate now, and expand. And the SSTAs will infiltrate the bay, and, by summer, the glacier terminus, as air temp. anomalies settle over the glacier itself.

The reason I went looking for glaciers in the area was because of what was happening in the Nares and Lincoln right now. I thought a while back, I wonder if the event goes beyond just the channel and the 'sea'? Turns out there is probably a correlation.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 27, 2017, 10:01:59 PM
We're in a period of peak tides, with a couple of days to go, the break up in Lincoln can only let in more N Atlantic water which flows far into the fjord. I don't expect anything major in the next few days, but we'll see,
I don't see the connection between the break up of Lincoln Sea ice & more water flow into Petermann Fjord. What am I missing?
Terry
Maybe the almost consistent warmer air and SST anomalies going for months now, in the Nares, links then all? And this has led to the early Lincoln break-up, which will probably just accelerate now, and expand. And the SSTAs will infiltrate the bay, and, by summer, the glacier terminus, as air temp. anomalies settle over the glacier itself.

The reason I went looking for glaciers in the area was because of what was happening in the Nares and Lincoln right now. I thought a while back, I wonder if the event goes beyond just the channel and the 'sea'? Turns out there is probably a correlation.
Petermann's sill is located in the Lincoln Sea, but ice cover there has no effect because of stratification. I have noticed large MYI bergs caught in the Hall Basin Gyre that bumped hard against solid FYI in the fjord which may have put sudden pressure on the glacial tongue, but these didn't result in calving.
As far as warming the air over the glacier you have to remember that cold air follows a glacier down hill and blows any SST warmed air away from the glacier.


http://muenchow.cms.udel.edu/papers/29-4_munchow.pdf (http://muenchow.cms.udel.edu/papers/29-4_munchow.pdf)


Fig. 1 shows the location of the sill.


As far as I know neither SST nor ice cover has any connection to calving of marine terminating glaciers. The deeper, warmer waters undercutting the tongue eventually lead to calving. 


Terry

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 27, 2017, 10:33:09 PM


The reason I went looking for glaciers in the area was because of what was happening in the Nares and Lincoln right now. I thought a while back, I wonder if the event goes beyond just the channel and the 'sea'? Turns out there is probably a correlation.
Petermann's sill is located in the Lincoln Sea...
As far as warming the air over the glacier you have to remember that cold air follows a glacier down hill and blows any SST warmed air away from the glacier.

As far as I know neither SST nor ice cover has any connection to calving of marine terminating glaciers. The deeper, warmer waters undercutting the tongue eventually lead to calving. 
Terry

I see. Thanks.
I'm not sure what the relationship of the 'sill', deep in the Lincoln Sea to Petermann's can be? That seems to refer to ancient geology? Where the ancient geological terminus of a much bigger multi-glacier complex may have been?
That warmer SSTs could flow into the fjord seems plausible. Or just getting warmed on the spot by the regional effect of lowered albedo (ever since the sun hit this spot in mid-March), causing warmer air temps than usual. The regional effects of such a huge area of dark water seem probable.

It does seem to me that the air would be in a constant flow down the valley, day and night, unlike a valley outside the Arctic circle (where it alternates wind direction, day and night, due to difference in warming and cooling rates of land and sea-surface, but I'm not sure how that would work on a glacier.) It seems that the wind would be constantly flowing down the valley, day and night, as you suggested?

As in the above image of accumulated melting anomalies (presumably meaning surface air temp. anomalies as well - by correlation), it seems that the glacier has warmer than usual air temps., and that must be because of a regional effect, most likely connected to the low albedo in the Nares, and now the Lincoln. Just guessing. Maybe not?

I think the top image here could have a melting effect on the Fjord sea-ice, compared to the lower one from (roughly) the same date in 2016 for example ? The earlier in the season the sea-ice in the fjord melts (which I think it will - it is more than a month ahead in the Nares right now), surely that will have an effect on the terminus of the glacier itself? Maybe my understanding of glaciers and fjords is too limited.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 28, 2017, 12:23:15 AM
TomB


Interesting discussion, but I'm off to a monthly dinner. If you ever stand at the foot of a glacier you'll face a very chilling wind (breeze is too soft a word) coming from the ice. There are two names for this wind, both which escape me for the moment. (one is specific to Greenland)


The sill is the lowest obstruction that water has to clear before it can get to the calving front. Because of stratification the depth of the sill regulates the temperature of the water that attacks the calving front. Lower sill, warmer water. Afraid this may not even be clear - but I really have to run.


Give my link above a read - its up to date and the author drops by here!


Have Fun
Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on May 28, 2017, 12:50:44 AM
TB, there is a sill between the fjord and Nares Strait. The fjord is actually deeper.
As for effects of early Nares clearing on local glaciers, I would first look at Humboldt glacier, draining into Kane Basin, as it is far wider and its calving front much closer to the area of action. http://forum.arctic-sea-ice.net/index.php/topic,800.0.html (http://forum.arctic-sea-ice.net/index.php/topic,800.0.html)
Petermann is much more stable than other Greenland glaciers, despite several massive calvings in the last few years.
In general I agree with the statement posted up-thread that marine-terminating glaciers are not affected by sea ice cover nearby, and are mostly affected by deeper water temps and currents. I personally believe Zachariae Isstrom is a rare exception, where the calving area is covered by sea ice year-round except some years in August, and the sea ice and iceberg melange is compressed against rocks further ahead, potentially slowing the glacier somewhat. Not albedo, but a small buttressing effect. Even this is just my personal layman opinion, with lots of caveats and unsupported by science. Other potential effects might be more waves and storms when sea ice is absent, but this requires a larger body of water, not a narrow fjord.
Note in the Nares albedo plays a much smaller role than usual as there is an almost-constant southbound current, carrying any accumulated heat out of the Arctic proper. Perhaps if the sea ice were to clear inside the Petermann fjord itself much earlier than usual, then accumulated heat might have some small effect on the glacier. But remember that the thickness of the floating part of the glacier is around 200 meters, and the calving is usually along cracks developing behind the front. Hard to affect by sea surface temps.
Hope this mess is somewhat helpful...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 28, 2017, 03:03:17 AM
Hi Terry and Oren.
Thanks, that makes sense.
The warmer Atlantic water is percolating in over the sill and all the way into the grounding line of Petermann's with water that is at or above 0C.
So I could see how that is more constant temp., and not affected by the surface water, as you pointed out.
---> http://www.pressherald.com/2016/12/30/greenlands-thaw-melts-a-climate-change-skeptic/ (http://www.pressherald.com/2016/12/30/greenlands-thaw-melts-a-climate-change-skeptic/)

“Flow of Atlantic waters into Nares Strait and into Petermann Fjord thus originates from the Lincoln Sea in the north where deep ocean temperatures at sill depth frequently exceed 0.3°C (de Steur et al., 2013). This water is warm relative to the −2.2°C pressure-dependent in situ freezing point at the base of the ice shelf …This observed heat flux is three times larger than the 1.1 × 1011 J s–1 required to melt the ~12 Gt yr–1 of ice that crosses the grounding line: for the ice shelf at its historical minimum extent of ~70 km long and 15 km wide, this is equivalent to an aerial average melt rate of 9.7 m yr–1”
http://muenchow.cms.udel.edu/papers/29-4_munchow.pdf (http://muenchow.cms.udel.edu/papers/29-4_munchow.pdf)

I guess my question to Andreas Münchow would be, has this Atlantic water flowing into the Petermann fjord become warmer because of global warming (of N. Atlantic), or has it always just eaten away at the grounding line, with enough new ice being created above, on the surface of the glacier to more than make up for the loss, increase/sustain overall mass (eg, pre-1970)?
In other words, is the main degrading of these glaciers from recently increased warmth in Atlantic waters (which seems to be suggested in the paper, but I'm not clear on it), or is potential glacier weakening coming from there being less new ice being created above? Or both equally bad?

However, I think, if the SSTs are warmer than usual in the region, the air temps will be warmer than usual, and the melting anomaly (since Aug. 2016) I posted above (Polar Portal), in the Petersonn valley, must be related to this SST anomaly? How else could a valley be warmer (melting more) than usual? Where could that warm air come from?

Can meltwater cut into a glacier causing rifts, sinkholes, and cracks? So if a weakness shows at, or near, the grounding line (or elsewhere), could that crack not be hugely exacerbated by increased meltwater on the surface of the glacier? (I think the warmer SSTs - and even lower albedo - on the Nares and Lincoln could cause the air to be warmer than usual. Can that air rise into the valley? (and the Nares has been open all winter).
I can't think what explains the extra melt anomaly in that valley, especially since it seems to face NW. Perhaps, during the day, with warmer, open water, the sun's heat is captured by the dark surface, but the albedo on the glacier would warm the air above the glacier during the day. That could cause warm, sea-level air, to rise up the valley because warm air above glacier has to rise, leaving a vacuum that must be filled (similar effects occur in valleys outside of Arctic circle, and reverse at night - wind direction changes).

If that melting anomaly goes away (it seems more at Petermann's than Humbolt right now), then that is different. (I agree you would expect to see the same in Humbolt. Humbolt may not show as much melt anomaly because it is a much wider valley? So gets a decent melt most of the time?) But as long as there is more melting than usual in Petermann's, how is that happening, other than warmer air, and is there more of a chance of cracks opening due to warmer air?

It could be that Petermann's is faster moving than Humbolt, and could pile down faster if something loosens, and it has a bigger surface melt anomaly over 10 months now.
Speed --> http://tinyurl.com/yd5cacay (http://tinyurl.com/yd5cacay)
(from : http://climatechangepsychology.blogspot.com/2010/11/nyt-restless-ice-greenlands-glaciers.html (http://climatechangepsychology.blogspot.com/2010/11/nyt-restless-ice-greenlands-glaciers.html))

With all the cracks showing, you guys were talking about, and the melt anomaly in Petersonn's, and the warmer SSTs, and months of winter open water, perhaps something is different this year for this glacier. Worth watching the melt-anomaly this summer maybe.

Anyway, glad to hear the thickness of the glacier could be so thick, and the melt season shorter in that valley, that maybe it will not be too affected.

Thanks for all the info.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on May 28, 2017, 02:37:53 PM
Terry "I don't see the connection" It's easier to know what you think than how you arrived there so I had to think again.
 I was surprised that atlantic waters were making their way through to Nares, and how it was tidally driven, curiously enough in the paper you linked to above.
(https://puu.sh/w3t8I/214b317778.png)
 The tidal surge of atlantic waters arrives in the north atlantic rather like a wave on a beach, that is there's actual movement of water, from there it follows the path of least resistance. If there's solid ice north of Greenland all the way to Nares even though the atlantic waters are moving at depth, perhaps because, the tidal surge, which is quite small, is supressed and pushed further north, either way it has to displace the water present and force it's way through it. The atlantic water is energetically inclined to continue moving east and from 600N has been directly approaching the axis of rotation, thus prone to generate powerful vortices which will rotate more freely in more open water. In fact it's easier to imagine that it's the pull of high tide in Kane basin that draws the atlantic water into Lincoln/ Nares, where even though it comes from the north it hugs the left coast, indicating it's still turbulent. Once the current punches through, and it's just a little easier to punch through with no solid ice cover,  a residual current becomes established and thus the current builds through the new/full moon tidal peaks.   
Tidal flow, Baffin/Kane need work, gives some indication of times either side of Greenland though.
(https://www.uwgb.edu/dutchs/Graphics-Geol/Animations/TideNodes0.gif)
M2 arctic tides, shows atlantic waters eastward impetus, against the 'natural' E-W movement.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esr.org%2FAOTIM%2FM2.jpg&hash=fad65d24e7b3d39330c9ed0d980eddfc)
john
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 28, 2017, 11:11:11 PM
Katabatic winds was of course the name that escaped me last evening, and piteraq winds in Greenland. - Getting old does have it's disadvantages, I can still get there, it just requires more time.


John22
Don't understand your "hugs the left coast", Coriolis effect forces arctic currents to the right, therefor hugging the right coast. In Nares Strait the southerly current flows by Ellesmere while the northerly current hugs Greenland. (except when gyres mess things up.)


TomB
Does knowing that the keel of PII2012 was as deep as the Cheops Pyramid was tall help?


Oren
The sill near the end of Petermann fjord is indeed deeper than the sill out in the Lincoln Sea, so it's the Lincoln Sea sill that determines the temperature and salinity of the water chewing away at Petermann Glacier. I agree that buttressing may slow glacial flow, but don't believe it has a measurable effect on Petermann.


Can I again do a quick plug for:


https://icyseas.org/


This is Andreas Muenchow's blog. He posts here from time to time, is passionate about sharing his extensive knowledge, and has risked much by insisting that the public has the right to know what their tax dollars have helped discover. The blog covers Petermann, Nares Strait & so much more. If I've messed up on this thread it's because I didn't understand what Andreas was saying & if his explanation differs from mine you can rest assured that his is correct.


Terry

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on May 29, 2017, 12:39:21 AM
The sill near the end of Petermann fjord is indeed deeper than the sill out in the Lincoln Sea, so it's the Lincoln Sea sill that determines the temperature and salinity of the water chewing away at Petermann Glacier. I agree that buttressing may slow glacial flow, but don't believe it has a measurable effect on Petermann.

Can I again do a quick plug for:
https://icyseas.org/
Terry you're correct on all fronts, also thanks for reminding me of the admirable Andreas M's blog
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on May 29, 2017, 10:35:21 AM
"hugs the left coast" Petermann remains entrenched on the left, and the atlantic waters penetrate to it's grounding line. That implies that the atlantic waters remain 'energetic'.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on May 29, 2017, 04:39:02 PM

TomB
Does knowing that the keel of PII2012 was as deep as the Cheops Pyramid was tall help?

Interesting.
The problem with that graphic from the news article on Meunchow that I posted above is that it is squished.
The real cross-section would probably look more like this below (or much longer).
So it all depends if those cracks at the grounding line are actually that evident, or if it is just a symbol for much smaller cracks. If the former, then it's bad, especially if anomalous heat in the valley, and melt-fissures are exacerbated.
The floating ice seems vulnerable since it probably does float on the warmer waters.
So now you have warm Atlantic water eating at the grounding line, and presumably rising under the glacier, but added to that, anomalously warm Nares surface water seeping in much more than usual. So the floating ice is more vulnerable this year, and if it recedes, opens up more dark surface water, and I think, warmer air in the valley. Compounding.
It would nice to get a real cross-section, I guess the grounding line does not look as vulnerable as being suggested by some media? Unless there is a lot of seeping surface melt-water at that point.

(PS. I have camped on a glacier, just not one this big)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 29, 2017, 06:13:09 PM
"hugs the left coast" Petermann remains entrenched on the left, and the atlantic waters penetrate to it's grounding line. That implies that the atlantic waters remain 'energetic'.
I'm afraid I don't understand what you are saying.


If it's that Petermann Glacier is west of the predominant southerly flow in Nares and is therefore "entrenched on the left" that is of course correct. Petermann Fjord meets Nares Strait at the Hall Basin Gyre and a portion of the WAW (Warm Atlantic Water) that has crossed the sill in the Lincoln Sea crosses the deaper sill near the end of Petermann Fjord, then erodes the base of Petermann Glacier.


When you say 'energetic', are you referring to temperature, mobility or?


The fresh, cold water exiting from beneath Petermann Glacier is ~ 1/2 the flow of the Thames River. In general it exits the fjord flowing above and to the north side of the fjord - again hugging it's right side.


TomB
Going upthread to #403, page 9 and reading forward may help. Over a ~30 period the glacier is thinned from ~600M to ~200M, it's WAW that is responsible & that water is far beneath, and not mixed with surface water. The ice tongue is for the most part floating on fresh, cold water that has exited beneath the glacier mixed with WAW that has been chilled and freshened by it's contact with glacial ice.


Terry

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on May 29, 2017, 08:36:17 PM
Terry, can you point me to a sea floor map of Nares Strait? You say the sill which determines the inflow of denser but warmer Arctic Intermediate Water is in Lincoln Sea?
A brief search brought up this https://books.google.co.uk/books?id=X0PDBca_EqEC&pg=PA137&lpg=PA137&dq=nares+strait+bathymetry&source=bl&ots=o76j8_33Q0&sig=4EQi56TjLDGnFWRtV_TcViR3Kh4&hl=en&sa=X&ved=0ahUKEwjjruTj2pXUAhWrKsAKHUZTAZMQ6AEIOzAC#v=onepage&q=nares%20strait%20bathymetry&f=false (https://books.google.co.uk/books?id=X0PDBca_EqEC&pg=PA137&lpg=PA137&dq=nares+strait+bathymetry&source=bl&ots=o76j8_33Q0&sig=4EQi56TjLDGnFWRtV_TcViR3Kh4&hl=en&sa=X&ved=0ahUKEwjjruTj2pXUAhWrKsAKHUZTAZMQ6AEIOzAC#v=onepage&q=nares%20strait%20bathymetry&f=false)
is there a clearer source?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on May 29, 2017, 09:12:36 PM
Terry, as you pointed out water coming from the north should keep right, and deep water from the arctic does, penetrating and clearing the fjords on Ellesmere, the atlantic water behaves differently.
 The last graphic by Thomas Barlow makes me think that even the 2ft. tides hereabouts are going to displace vast quantities of water from beneath the glacier, when low, and when the tide turns the glacier itself acts as a huge vacuum pump, sucking in atlantic waters. IIRC this didn't happen years ago when the ice north of Greenland was thick. If the water was more or less neutral it would not penetrate so deeply, I suspect there would just be just a turnover of waters near to Nares which it seems is what happens with arctic waters. Because it gets to the grounding line implies it has plenty of kinetic energy, it 'wants' to be further east, or at least move eastward, and i suspect it 'wants' to be further from the axis of rotation, thus in it's forced journey around northern Greenland and beneath the glacier it will generate powerful vortices, it may even have had a hand in the breakup of ice by the coast today.   To put it another way if this water was in the vicinity of say the Faroes it would be more stable, far enough away from the axis of rotation and moving east at a comfortable speed. I hope that makes sense.
I was looking at full/new moon times for 2015 to compare to fig.7 above it seems there's a 5-7 day delay to temp./salinity peaks.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on May 29, 2017, 09:40:10 PM
Andreas, search google for Nares Strait bathymetry. There a paywalled paper from 1986, and there's also this paper by Andreas Muenchow which has a hard-to-read bathymetric map http://muenchow.cms.udel.edu/papers/Nares2011Warming.pdf (http://muenchow.cms.udel.edu/papers/Nares2011Warming.pdf)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: TerryM on May 29, 2017, 09:52:12 PM
Terry, can you point me to a sea floor map of Nares Strait? You say the sill which determines the inflow of denser but warmer Arctic Intermediate Water is in Lincoln Sea?
A brief search brought up this https://books.google.co.uk/books?id=X0PDBca_EqEC&pg=PA137&lpg=PA137&dq=nares+strait+bathymetry&source=bl&ots=o76j8_33Q0&sig=4EQi56TjLDGnFWRtV_TcViR3Kh4&hl=en&sa=X&ved=0ahUKEwjjruTj2pXUAhWrKsAKHUZTAZMQ6AEIOzAC#v=onepage&q=nares%20strait%20bathymetry&f=false (https://books.google.co.uk/books?id=X0PDBca_EqEC&pg=PA137&lpg=PA137&dq=nares+strait+bathymetry&source=bl&ots=o76j8_33Q0&sig=4EQi56TjLDGnFWRtV_TcViR3Kh4&hl=en&sa=X&ved=0ahUKEwjjruTj2pXUAhWrKsAKHUZTAZMQ6AEIOzAC#v=onepage&q=nares%20strait%20bathymetry&f=false)
is there a clearer source?


This isn't the best I've seen, but may be adequate for your needs.


https://icyseas.org/2012/09/02/petermann-ice-island-2012-breaking-up/


Terry
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on May 31, 2017, 08:38:45 AM
I find this 7,2,1 bands image intriguing, usually darker blues indicate water present on the surface. I find it hard to believe that melt onset is earlier on Petermann than anywhere around. Could it be that this is ice swept bare of snow by katabatic wind? My other option would be föhn but why would that be so much stronger at Petermann?
note that the calving front shows up clearly: bluer on the glacier, lighter on the sea ice.

PS  the same feature can be seen last year but there seems to have been more snow generally at the time.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: bairgon on May 31, 2017, 09:50:05 AM
I had noticed that the brown colour in the valley to the west of the glacier had increased recently. Perhaps the winds are coming from the Strait and blowing south on that valley as well as the glacier, and melting the snow/ice.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: P-maker on May 31, 2017, 10:41:29 AM
Andreas & bairgon

Katabatic wind is a good candidate for the agent shaping the observed patterns. Perhaps enhanced by a weak Föhn effect. I suggest that bare ice at those latitudes this time of the year is a result of sublimation and NOT melt.

It is often the case in Greenland, that the strongest Katabatic winds occur less than 10 km from the ice edge. You will see some snow accumulation on the sea ice just in front of the glacier snout, and then a wind scoured ice surface further out to the north of the glacier and on the lower part of the glacier itself.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on May 31, 2017, 03:35:51 PM
If the current of atlantic water is powerful enough, and it still has a couple of days to run, it may just break in to the fjords north of Petermann, and generate some upwelling there too.
http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)
https://go.nasa.gov/2smqvT3 (https://go.nasa.gov/2smqvT3)
and if not now almost certainly after the next tidal max.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 01, 2017, 01:24:26 AM
Remember that no Nares Strait ice bridge formed during the 2006-7 winter, so as unusual as this year's ice-bridge-free winter/spring is, it it not unprecedented.  (No, it is not a 10-year cycle.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on June 16, 2017, 10:38:57 PM
There's a new IcySeas blog post up about temperatures rising under the Petermann Glacier.

https://icyseas.org/2017/06/16/is-petermann-gletscher-breaking-apart-this-summer/

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on June 18, 2017, 12:07:30 AM
Petermann "wakes up" in July, at least in the past two years. Image source: Enveo Cryoportal
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 19, 2017, 07:26:37 PM
I hope some of this is just cloud. I think that is a crack on the left?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: bairgon on June 19, 2017, 08:25:57 PM
Yep, that does look like a crack on the left?

Yes, looks like it has been developing over the last few days. Animation from 16th June below - it was cloudy before then.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 19, 2017, 08:57:05 PM
What you are seing is probably a string of melt ponds:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 19, 2017, 09:31:43 PM
Oh, ok, Thanks!
Glad that's all it is.
Where you getting that image from?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 19, 2017, 09:37:37 PM
Here's today's DMI Sentinel - shows same curved lineation.  My guess was "a river".  The "air photograph" (I presume) certainly shows the melt ponds!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on June 20, 2017, 03:56:50 PM
The Petermann ice expedition tweeted and animated GIF which shows the progression of the melt ponding.

https://twitter.com/StefLhermitte/status/876836364855259136
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: VeliAlbertKallio on June 23, 2017, 03:31:35 PM
Andreas Muenchow's report suggests me hydrofracturing occurring on a newly-forming crack that is propagating inversely from the centre towards the Petermann glacier's shear zone at the edge. I would see this as evidence of meltwater river induced hydrofracturing in progress which may also be supported that the pressurised water filling the crevasse when it escapes stirs the basal sea water to increase temperature variance of turbulent water. As the meltwater filling crack and the river supply are both getting bigger and bigger, water will exponentially widen and fill this crevasse that acts as a conduit of meltwater discharge as the holding base also gets thinner. It happens just this way, inversely, because the hydrofracturing has not reached yet glacier's base on its bottom and the water builds up presumably on the crevasse.

There's a new IcySeas blog post up about temperatures rising under the Petermann Glacier.

https://icyseas.org/2017/06/16/is-petermann-gletscher-breaking-apart-this-summer/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 23, 2017, 05:51:34 PM
The June 21 Polar View image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1A_IW_GRDH_1SDH_20170621T205011_7884_N_1.8bit.jp2) shows a crack crossing the mid-glacial stream (about 1 red bar's width distance above the red bar) and the string of melt ponds that (on less distinct imagery) looked like a massive crack (or something). (Screen print has the brightness adjusted.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on June 23, 2017, 06:58:59 PM
in colour http://apps.sentinel-hub.com/sentinel-playground/?lat=80.86781552849567&lng=-61.17462158203125&zoom=9&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01 (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.86781552849567&lng=-61.17462158203125&zoom=9&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01)|2017-06-23&cloudCorrection=none&atmFilter=ATMCOR&showDates=true&evalscript=&showImage
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 23, 2017, 08:27:48 PM
Thank you johnm33!  Scrolling up on your image, I see more clearly than ever before what I believe will be the next calving event (right [east] side of the glacier's tongue).  (just above my added red line).  (Ignore the eyes on what appears to be someone from the land of Point.)  At least from this view, there appears to be a 30 or 40 m gap between the hook on the left (west) crack and the straighter (south) crack, and because the two cracks are approaching parallel at the hook's end, there can't be much strength in this 'bridge'.  I'll guess the fast ice in the fjord is holding this would-be (2 x 4 km) ice island in place. (Slight enlargement doesn't have added red marks.) (Edit: image is actually June 22, not 15)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 23, 2017, 08:38:16 PM
Fast ice at the end of Petermann Fjord is beginning to crack. (Sentinel Playground image 2017-06-22 (http://apps.sentinel-hub.com/sentinel-playground/?lat=81.19406437795409&lng=-62.91046142578125&zoom=9&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-06-22&cloudCorrection=none&atmFilter=&showDates=false&evalscript=))
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on June 23, 2017, 11:42:21 PM
Fast ice at the end of Petermann Fjord is beginning to crack.
Small wonder, with so much meltwater on the ice, and air temps reaching 5-8oC in the vicinity.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 29, 2017, 05:00:27 PM
Petermann is having an exceptional meltwater year and calving events, large and small, would come as no surprise. However it's been incorrectluy stated up-forum and elsewhere that the new central crack is an unprecedented crevasse and likely to lead to a massive tabular iceberg.

Actually there is no stress on the ice shelf here, either horizontally or from local buoyancy forces; the alignment angle cuts across meltwater drainages, and there's been no distortion of features on either side. It appeared last year in early July but has largely been stable since (2nd image, 01 Jun 17). This has nothing in common with the physics of hydro-fracturing of Antarctic glaciers at their grounded calving fronts.

The Petermann ice shelf has all sorts of deeply channeled bottom topography as seen by ice-penetrating radar; one of these has merely been eroded up to the surface and re-frozen at the waterline (~30m below ice shelf surface). There's another much older example of this below the eastern calving front that's been dormant for a decade or more.

The animation looks at TorB's terminal pair of cracks over the last 12 months. The first two frames are co-registered to sidewall rocks, ie as provided straight off the Sentinel-1AB site (best by whole-window screenshots). The third frame has the June 2016 ice advanced ~1200m so fixed features west (left) of the drainage channel co-register with the June 2017.

The fourth frame shows by differencing that that the left-central half of the ice sheet indeed moves as a rigid block. Geometric changes on the west side, largely induced by the ongoing collision with the incoming tributary glacier, are then effectively displayed relative to this moving lagrangian reference frame.

What happens next? Last year, after the annual ice in the upper fjord went away, a small piece in the NW corner broke off. There is a similar piece developing this year right at the junction of main ice shelf with tributary ice from much further south (2nd frame); that crack extends into the annual ice.

Alternatively, the much larger piece that Tor has highlighted could come apart, though the lower crack seems to have over-shot the vertical one instead of joining it.

At least 3 other 'traditional' cracks have developed over the last 12 months as the ice shelf has moved past stress-inducing shore features (that induce bends in the channel). These relieve stress on older fractures. Thus a big tabular event may happen at one of these, rather than rapid propagation at a now-dormant feature. The 2nd animation shows changes mid-sheet; note the much slower moving tributary ice along the shore.

While the main fracture is still growing, the direction of propagation is up-glacier rather than than across-glacier. Yet this can literally change overnight.

Whatever, big tabular bergs from floating ice shelves do not raise sea level and, unlike in Antarctica, will not significantly un-buttress Petermann nor speed up discharge of grounded glacier ice from the mainland.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on June 29, 2017, 05:15:01 PM
"Hear Hear"!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on June 30, 2017, 10:36:16 PM
There have been some issues up-forum and elsewhere distinguishing features on the ice surface from intervening clouds, contrails, fog, changing light, melt status and satellite viewing angle.

To be safe, look at more than one date and more than one wavelength. This is best done in the initial post. It just takes a click at either LandViewer or WorldView.

Clouds come and go, ice moves very slowly (up about 3 pixels a week at Petermann at Sentinel-1AB resolution). Ice features are persistent and go with the flow. Compare the visual channel (RGB) with infrared admixtures.

The 3rd frame of the upper animation shows how to make transparency mask for cloud cover: split the 367 into its RGB grayscales, take the B. Then use the mask to preferentially strip off clouds via localized proportionate contrast adjustment.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 01, 2017, 11:49:15 AM
But adding up to what we have seen until now, I do not expect a calving at Petermann this year, maybe a small piece will leave the glacier up front at starboard side.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: A-Team on July 01, 2017, 04:35:33 PM
Maybe we'll get another clear day?

While this appears to be a fairly good surface melt year, that's not really what drives Petermann calving -- the real story is going on underneath the floating ice shelf as warm water swirls underneath. Buttressing annual ice in the upper fjord has not yet melted out.

I looked to see if A Hubbard and J Box ever did anything with the radar data from the 2009 kayak adventure. It seems not. In particular, I could not find the lat,lon of that scary moulin in the central drainage channel. It may have calved off in the last big event, mooting the value of their down-shelf ice thickness soundings.

Quote
"Ocean warming currents are circulating around the fjord and eroding the underbelly of Petermann glacier at an incredible rate," says Hubbard. Melting at the surface of the ice forms huge whirlpools of relatively warm fresh water that bore holes into the floating sheet.

The scientists believe this process is accelerating the ice's demise. In places, the meltwater bores holes through the ice right down to the bottom of the ice tongue. Surfacing seals are proof that some of the holes called moulins pierce to bottom of the ice."


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D53.0%3Battach%3D17085%3Bimage&hash=76ca23e2a680a7ad2dd37b8fe55f21bd)

If similar features exist today, could we identify them with Sentinel-1AB imagery? Possibly, by scanning pairs of dates and looking for disappearance of melt water. That could be done synoptically from loss of blue meltwater color. So it might be worth doing later in season.

Another thing we could do is follow up on previous high-resolution triangulation to map geometric distortion (indicative of strain). It appears to me that the Sentinel-1AB in Land Viewer have pixel-perfect registration on rock features on both sides yet east-central ice features are changing in relative position (on a monthly scale). Ice, even of several hundred meters thickness, is still deformable, especially if it has warmed a bit.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on July 12, 2017, 10:25:37 PM
Does anything think there could be a relationship (conjoining) of these 3 features in the future?
This is from July 8. That seems to be a crack cutting partly across the main central drainage channel, not just another stream flowing into the drain.
(maybe get a better view next time the clouds clear)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 14, 2017, 04:12:04 PM
I'm curious about the crack in Petermann Glacier that appears to have caused a crack in the abutting fast ice (red arrows) (July 13 Sentinel Playground (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.96559216278827&lng=-60.91747283935547&zoom=12&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-07-13&cloudCorrection=none&atmFilter=&showDates=false&evalscript=)).  I wonder if the crack (purple arrow) that is collinear with the dirty streak suggests an unseen crack in Petermann.  And of course, I regularly look for crack growth (or connection) within the red circled area.  Finally, interesting crack propogation in the purple circle area (with enlargement).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 24, 2017, 08:34:13 PM
Here is a GIF showing Sentinel Playground (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.94794615264044&lng=-61.008453369140625&zoom=12&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-07-19&cloudCorrection=none&atmFilter=&showDates=false&evalscript=) images of June 16, June 30 and July 19.  Is it changing light or is the crack widening?  The glacier is certainly progressing!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 24, 2017, 09:50:01 PM
I believe there will be no substantiel calving this calender year.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 24, 2017, 10:59:03 PM
Espen: I curious what you mean.
If "my" piece calves, would you consider that to be a "substantial calf"?  How about a quarter or third of it?  (These are possibilities due to other growing cracks.)  Or do you mean a fjord-wide calving event for which there are also growing cracks? (Such a large calving event is not expected by me this summer.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 24, 2017, 11:08:35 PM
But adding up to what we have seen until now, I do not expect a calving at Petermann this year, maybe a small piece will leave the glacier up front at starboard side.

I think I answered that a while ago.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 26, 2017, 01:35:46 PM
The little piece (about 6 km2) at the front of Petermann Glacier that I have been watching has broken off, as of yesterday, and is all but staying in place (or it just broke before the image was captured).  I won't be surprised if it breaks into three icebergs by the time it reaches Hall Basin (the part of Nares Strait beyond the mouth of Petermann Fjord). (Sentinel Playground (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.9755064136504&lng=-60.876617431640625&zoom=10&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-07-25&cloudCorrection=none&atmFilter=&showDates=false&evalscript=) image)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Shared Humanity on July 26, 2017, 03:38:58 PM
I think I have asked this question before but ......what are the dark brown streaks on the ice that appear on the small calved piece but continue along the glacier? Is this till, dirt and rocks that have been ground from the surface of Greenland?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: MrVisible on July 26, 2017, 04:14:35 PM
I think I have asked this question before but ......what are the dark brown streaks on the ice that appear on the small calved piece but continue along the glacier? Is this till, dirt and rocks that have been ground from the surface of Greenland?

Could be algae. (http://www.bbc.com/news/science-environment-40686984)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 26, 2017, 07:27:39 PM
A bunch of purple arrows point to rock debris that collects on (and within) a glacier.  It is a mixture of ground rock (huge boulders down to clay sized particles) that gets dragged (given it is frozen to the ice) and pulverized along the sides (left, right and bottom) of glaciers or as loose rock on top of them.  Especially as glaciers merge (e.g., tributary glaciers meeting), this debris can be found 'anywhere' along a glacier's cross section.   Some debris (locally extensive - can cover the entire width of a small glacier-see attached from here (http://blogs.ei.columbia.edu/2016/07/02/massive-landslide-detected-in-glacier-bays-fragile-mountains/)) falls onto glaciers from rock-falls or avalanches.  Some of the less 'black' dark areas in this image may be scattered debris. (Up close it may include large boulders.)  Certainly, algae has its part, too (but I don't know much about this).

Mostly (but not entirely) not relevant here, when glaciers flow beyond (below) their accumulation zone (net surface melt), a glacier's surface can become covered with rock debris as any ice above the load melts.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Shared Humanity on July 26, 2017, 10:31:19 PM
Thank you.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 27, 2017, 02:33:08 PM
As Tor reported yesterday- we here see the result of the minor (relative to Petermann) calving that happened on July 25 2017:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 27, 2017, 02:39:33 PM
I suspect tiny-ish pieces of the glacier, given a degree of freedom, flipped on their sides 'pushing' the new iceberg's end out into the fjord.

I don't see any widening of cracks between July 24 and 26 that didn't 'totally open up'. (two Sentinel Playground (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.95814938697019&lng=-60.8477783203125&zoom=13&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-07-24&cloudCorrection=none&atmFilter=&showDates=false&evalscript=) gifs)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 27, 2017, 02:54:39 PM
Belgrave Gletscher to the rigth of the calf is the main culprit to these calvings at the Strarboard side of the Petermann Gletscher, they happen almost every year, so we are not talking abour climate changes this time around.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 27, 2017, 03:11:18 PM
Yes, that tributary glacier would be the 'long term' culprit!  Without (probably) climate change induced major calving of the Petermann Glacier, however, the Belgrave Glacier wouldn't have been able to pull this "non climate change" stunt off.

Now, with the Petermann Glacier no longer plugging its exit [well, only half plugging it for now], I wonder if (or, actually, how soon) we'll be able to discern its flow rate increasing.

And now on to Hubert Glacier (https://www.google.com/maps/d/view?mid=1S6EY5SUuQ7oaaf_ZJiuUOndIGDU&ll=80.9873462473936%2C-60.765380859375&z=9)...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on July 29, 2017, 10:19:17 PM
The iceberg has broken into two main pieces and leaves towards Nares Straight.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 31, 2017, 04:56:28 PM
The smaller iceberg is eager to get away! Polar View image from July 30 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1B_EW_GRDM_1SDH_20170730T121516_4703_N_1.8bit.jp2). (red dots on the two larger icebergs)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 31, 2017, 05:52:26 PM
I've attempted to show the curious crack near mid-glacier growing (widening), with Sentinel Playground  (http://apps.sentinel-hub.com/sentinel-playground/?lat=80.82833511648452&lng=-61.09668731689453&zoom=12&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-07-31&cloudCorrection=none&atmFilter=&showDates=false&evalscript=)images from June 30, July 13 and July 31 (labeled "30" [woops!]), with the mid-glacier stream made, approximately, to not move.  The black side lines show the drift of the glacier between the three images.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas T on July 31, 2017, 07:45:10 PM
this reply to a comment in the Nares thread belongs here I think.
This is from the 24th to me it suggests a surge of warm water coming out of the arctic at depth, into Petermann fjord, and there being forced to the surface melting and forcing out the seasonal fast ice.
...(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%3D40%26amp%3BLAYERS%3DB04%2CB03%2CB02%26amp%3BGAIN%3D0.5%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%2B2017-07-24.jpg%26amp%3BTIME%3D2015-01-01%2F2017-07-24%26amp%3BBBOX%3D-7909093%2C16005302%2C-6360784%2C16659603%26amp%3BPREVIEW%3D3%26amp%3BEVALSCRIPT%3DcmV0dXJuIFtCMDQqMi41LEIwMyoyLjUsQjAyKjIuNV0%253D&hash=adeb971c0bdb2149097488b872a46b3d)
Take a closer look  (http://apps.sentinel-hub.com/sentinel-playground/?lat=81.5981071957334&lng=-61.6552734375&zoom=7&preset=CUSTOM&layers=B04,B03,B02&maxcc=40&gain=0.5&gamma=1.0&time=2015-01-01|2017-07-24&cloudCorrection=none&atmFilter=ATMCOR&showDates=false)
To put it into the terms of physics, what we are seeing with the help of information provided by Dr Muenchow and his colleagues, is that warmer intermediate water  entering the fjord is rising at the glacier front. This is driven by buoyancy as this water mixes with salt free meltwater from below the glacier tongue and surface melt which has entered the glacier through moulins and cracks. This low density water source drives the surface flow out of the fjord while a flow of denser water is drawn in below it. It is a classic imbalance of water columns of different density profiles.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: logicmanPatrick on August 02, 2017, 01:51:25 PM
I had hoped to write an article on the Petermann but have been too busy with my work on the Voynich manuscript.

In brief: the fjord is somewhat sinuous.  Any material flowing through a sinuos conduit will be subjected to forces tending to cause the material to compress on the inside of a bend and to expand on the outside edge or surface.

In the case of a river this is revealed in meanders and ox-bow lakes.  In the case of a stream of ice, the forces tend to open lateral cracks on the outer bends and close them on the inner bends.

The Petermann glacier meanders towards its outlet and flows relatively rapidly.  This account, imo, for the regularity with which new cracks appear at the same point in any bend once the flow has taken the previous crack downstream.

Sediment below a stream of water, or below a stream of ice if there is contact, can affect the dynamics of the flow.

More info on meander dynamics -  for 'floodplain' read 'icecap' - ignore vegetation:
Meandering Rivers Feedbacks ... (http://www.academia.edu/3699199/Meandering_rivers_-_feedbacks_between_channel_dynamics_floodplain_and_vegetation)

hth.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Often Distant on August 06, 2017, 10:23:05 AM
Detached segments melting fast in the warm waters of the fjord.
(https://preview.ibb.co/hqsGma/Sentinel_image_on_2017_08_06.jpg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Juan C. García on August 10, 2017, 01:01:39 PM
Forget That Big Iceberg--A Smaller One in the Arctic Is More Troubling

Quote
The iceberg itself is not particularly notable, according to Dyke. But it could lead to an expansion of major cracks upstream in the ice shelf, causing it to break up more quickly. Most troubling to researchers is a crack at the center of the shelf. It's an unusual place for cracks to form, and it could connect to separate cracks forming at the sides.

https://www.scientificamerican.com/article/forget-that-big-iceberg-a-smaller-one-in-the-arctic-is-more-troubling/ (https://www.scientificamerican.com/article/forget-that-big-iceberg-a-smaller-one-in-the-arctic-is-more-troubling/)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 11, 2017, 11:15:18 PM
Forget That Big Iceberg--A Smaller One in the Arctic Is More Troubling

Quote
The iceberg itself is not particularly notable, according to Dyke. But it could lead to an expansion of major cracks upstream in the ice shelf, causing it to break up more quickly. Most troubling to researchers is a crack at the center of the shelf. It's an unusual place for cracks to form, and it could connect to separate cracks forming at the sides.

I dont understand the fuss about the crack in the center of the glacier, that was seen as early as 1987 and nothing special happened until 2010?
But I agree with Andreas M. what happens underneath the glacier is worrying.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: logicmanPatrick on August 12, 2017, 02:36:32 AM
Despite being busy with my analysis of the Voynich manuscript I have managed to keep an eye on the Petermann glacier.  Please see my post above about the effects of meanders.

My attention has been on the downstream left hand side of the glacier.  (Left with Nares at the top).

Cracks have appeared intermittently in Sentinel images.  I don't think they are artifacts because they appear recur in the same place in images under different illumination.

It looks to me as if a calving of about 3 times the size of the recent one is imminent.  But what do I know. ;-)

Check the images below and see if you Arctic watchers agree.  I have used light green to indicate the cracks.  The crack on the right is the one that the proverbial "everybody" is watching.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.science20.com%2Fsites%2Fall%2Fmodules%2Fauthor_gallery%2Fuploads%2F431944957-peterman_1.jpg&hash=6834d5fcc1cb2d14a6cf2cb80d4fb7be)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.science20.com%2Fsites%2Fall%2Fmodules%2Fauthor_gallery%2Fuploads%2F1884547226-peterman_2.jpg&hash=2dbff08e43e7b34cc3dbc6c538db4952)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.science20.com%2Fsites%2Fall%2Fmodules%2Fauthor_gallery%2Fuploads%2F63556918-peterman_3.gif&hash=68216db46f3f7dfd566d347d29b23b09)
supposed to be an animated gif.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.science20.com%2Fsites%2Fall%2Fmodules%2Fauthor_gallery%2Fuploads%2F1091164372-polarview_12_aug_2017.jpg&hash=2c1064662f12cb775c8e93235f36861b)
polarview 12 Aug. 2017






Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 23, 2017, 06:58:04 PM
Widening gaps.

31 Aug 2016 and 21 Aug 2017.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on December 26, 2017, 09:17:12 PM
Yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201712/S1B_EW_GRDM_1SDH_20171225T195226_3809_N_1.8bit.jp2) (which I haven't viewed for a couple of months) shows a curving lineation on the western half of the glacier that I don't recall seeing before.  Given Thomas' gif from August, I wonder if the lineations I see (there might be quasi-parallel segments toward the west side of the red rectangle) represent the crack extending all the way across the glacier.  If it calves, it is huge, even yuge!

Post Script:  some of this lineation is identified by Thomas in his July 12 post (https://forum.arctic-sea-ice.net/index.php/topic,53.msg120534.html#msg120534) above.  I can see some of my outlined lineation in Thomas' image extending beyond the lower red rectangle (my purple rectangle below, copied from Thomas' post).  Some of it looks like drainage topography in Thomas' image.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on January 11, 2018, 07:01:14 PM
Today, I'm curious about the suggested lineation within the red shape.  It shows on earlier images of Petermann Glacier, but is moderately pronounced in yesterday's Polar View image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1B_EW_GRDM_1SDH_20180110T191942_AD7E_N_1.8bit.jp2).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on March 30, 2018, 08:23:37 PM
This glacier was mentioned on this thread a few years ago.  Here is an AGU's 'From a Glacier's Perspective (https://blogs.agu.org/fromaglaciersperspective/)' article: 
Heilprin Glacier, NW Greenland Pinning Point Decline 1987-2017 (https://blogs.agu.org/fromaglaciersperspective/2018/03/22/heilprin-glacier-nw-greenland-pinning-point-decline-1987-2017/)

Quote
They  observed that retreat began in ~2000 which coincided with a regional rise in summer mean air temperature.
[See link for full image!]

https://blogs.agu.org/fromaglaciersperspective/files/2018/03/heilpring-compare.jpg (https://blogs.agu.org/fromaglaciersperspective/files/2018/03/heilpring-compare.jpg)
I find it interesting that the ice front on the south side of the island identified as "B" hasn't changed.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Shared Humanity on March 30, 2018, 11:40:28 PM
This glacier was mentioned on this thread a few years ago.  Here is an AGU's 'From a Glacier's Perspective (https://blogs.agu.org/fromaglaciersperspective/)' article: 
Heilprin Glacier, NW Greenland Pinning Point Decline 1987-2017 (https://blogs.agu.org/fromaglaciersperspective/2018/03/22/heilprin-glacier-nw-greenland-pinning-point-decline-1987-2017/)

Quote
They  observed that retreat began in ~2000 which coincided with a regional rise in summer mean air temperature.
[See link for full image!]

https://blogs.agu.org/fromaglaciersperspective/files/2018/03/heilpring-compare.jpg (https://blogs.agu.org/fromaglaciersperspective/files/2018/03/heilpring-compare.jpg)
I find it interesting that the ice front on the south side of the island identified as "B" hasn't changed.

Could the two islands be supporting it so, even as it thins, it doesn't fracture?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on March 31, 2018, 10:58:32 AM
Thanks for the interesting article. I think that pretty soon (a few years) the glacier will retreat entirely from both islands A and B, similar to what happened to Espen's new island at Kjer glacier.
If and when thatbhappens, the retreat could accelerate very significantly.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on April 06, 2018, 04:31:37 AM
I think at least a copy belongs here! (Awesome, but I wish I knew exactly where!)
New photos of the new rift in Petermann Glacier

https://twitter.com/NASA_ICE/status/981979361854283777


https://twitter.com/NASA_ICE/status/981979218497196032
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on April 06, 2018, 03:32:57 PM
I think at least a copy belongs here! (Awesome, but I wish I knew exactly where!)
New photos of the new rift in Petermann Glacier

https://twitter.com/NASA_ICE/status/981979361854283777


https://twitter.com/NASA_ICE/status/981979218497196032
I think the link in the tweets points to last year's article about the new rift forming.
https://earthobservatory.nasa.gov/IOTD/view.php?id=90043
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Jim Hunt on April 10, 2018, 02:03:14 PM
I think at least a copy belongs here!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 17, 2018, 03:45:03 AM
Meltponds today
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: sidd on June 17, 2018, 05:38:27 AM
There is a paper by Dow in the latest Nature, arguing that basal channelized belt plays a role: I have posted about this in a different thread

https://forum.arctic-sea-ice.net/index.php/topic,622.msg159198.html#msg159198

They have Things to Say about Petermann, in the light of their theory:

"We observe a similar basal channel–induced fracturing pattern on other ice shelves. A 2-km-wide transverse fracture appeared in 2016 on the ice shelf of Petermann Glacier, Greenland. Petermann Ice Shelf underwent two large calving events in 2010 and 2012 that originated from rifts propagating from the edge of the ice shelf (23). The 2016 fracture, however, was located in the center of the shelf directly overlying a basal channel, and was confined to the regions of the thinnest ice in the channel (Fig. 1C). This fracture intersected a surface river colocated with the basal channel, similar to the Nansen Ice Shelf. The Petermann Ice Shelf basal channel has high melt rates (24) and, combined with the potential for hydrofracture by the surface river, also demonstrates weakening of the shelf as illustrated by the latest fracture event."

I attach a section of Fig 1. The parts of caption pertaining to the Petermann sections is

"transverse fractures are shown in black, basal channels are shown in blue, and black arrows indicate general ice-flow direction ... Landsat image of Petermann Glacier Ice Shelf from 30 April 2017, with the fracture that appeared in 2016. The fracture is intersected by a surface river (pink) and is located directly above a basal channel, with the extent shown in blue, estimated from digital elevation model (DEM) calculations."

sidd
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 21, 2018, 03:38:05 PM
I find it interesting looking at two Sentinel-hup Playground  (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.87053960958786&lng=-61.48944854736328&zoom=11&preset=92_NDWI&layers=B01,B02,B03&maxcc=75&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-06-18&atmFilter=&showDates=false)images from the same place and date, specifically the  "Natural Color" and "NDWI" 'calculated' images.  I presume the NC version shows the melt ponds while the NDWI shows 'saturated snow' as well.  Anybody know enough to correct my interpretation?  The location of these June 18 images includes the mid-glacier stream and the (mid-glacier) transverse crevasse (June 18, 2018).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 22, 2018, 03:56:09 PM
Tracy and Heilprin Glaciers (see recent post (https://forum.arctic-sea-ice.net/index.php/topic,53.msg147947.html#msg147947) - with map)
OMG, the water's warm! NASA study solves glacier puzzle (https://phys.org/news/2018-06-omg-nasa-glacier-puzzle.html#jCp)
in Psy.Org (https://phys.org/) - June 22, 2018 by Alan Buis, Jet Propulsion Laboratory
Quote
A new NASA study explains why the Tracy and Heilprin glaciers, which flow side by side into Inglefield Gulf in northwest Greenland, are melting at radically different rates.

Using ocean data from NASA's Oceans Melting Greenland (OMG) campaign, the study documents a plume of warm water flowing up Tracy's underwater face, and a much colder plume in front of Heilprin. Scientists have assumed plumes like these exist for glaciers all around Greenland, but this is the first time their effects have been measured.
...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 18, 2018, 04:21:51 PM
Petermann Glacier's mid-glacier transverse crevasse is 'full' of water.  Sentinel-hub Playground images from July 16 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.84305762090635&lng=-61.12415313720703&zoom=13&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=51&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-07-16&atmFilter=&showDates=false).  By comparing the colors in the mid-glacier stream with the crevasse water, it appears to me that deeper water is darker blue.  Clearly, the crevasse is not draining at this time (which rather surprises me).  (image has a '100 m' scale showing) 

Edits: A year ago (2017-8-29 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.82637171192728&lng=-61.08724594116211&zoom=14&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=100&gain=1.0&gamma=1.0&time=2015-01-01%7C2017-08-29&atmFilter=&showDates=false)) shows a different distribution of water, including, it seems, water in the middle of the crevasse instead of the up-steam edge.  Crevasse is wider now.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 19, 2018, 09:28:15 PM
What a difference a day can make (July 17 and July 18 - dates at top of gif): check out the higher resolution Sentinel-hub images (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.83867886194986&lng=-61.1039400100708&zoom=14&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=97&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-07-18&atmFilter=&showDates=false).
Looks like the drain was pulled.  Or did something else happen? (e.g., big wet blotches disappeared, too.  Sun angle? Deep freeze?  [No clouds nearby])

That was "Natural Color".
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 23, 2018, 09:38:31 PM
In yesterday (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201807/S1A_IW_GRDH_1SDH_20180722T205019_03CE_N_1.8bit.jp2)'s PolarView (https://www.polarview.aq/arctic), I see lineations on Petermann Glacier again (still): this time a fairly straight one within the long oval going from edge to mid-glacier crevasse.  (Second image has suggestive dots.  There are alternate routes.)  There is a parallel lineation segment just below the dashed like.  (I don't see anything on Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.8619287625714&lng=-61.343536376953125&zoom=10&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=92&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-07-18&atmFilter=&showDates=false) to support there being a crack here.)

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Phil. on July 25, 2018, 10:59:53 PM
As of the 23rd a large floe has broken loose and has started moving.

http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/20180724AQUA.jpg
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on July 27, 2018, 04:09:19 AM
What do you think?
Any chance of these breaking off later this year?
On the south side.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Phil. on July 30, 2018, 06:10:17 PM
As of the 23rd a large floe has broken loose and has started moving.

http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/20180724AQUA.jpg

Still on the move:

http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/20180729AQUA.jpg
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on July 30, 2018, 08:27:13 PM
Darn it, too busy. How big is this one compared to the previous two?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 30, 2018, 09:05:03 PM
Neven, it is just sea ice that has broken off the front of the glacier.  There is no new iceberg.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on July 31, 2018, 12:15:34 AM
Thanks, Tor! I thought it looked too blue to be true.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 01, 2018, 04:02:15 AM
Yea, not  the sea-ice. The other bits look precarious on that south side is what I was looking at, but I'm realizing they are much more stable than they look.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 12, 2018, 04:46:35 PM
It looks like we had a tiny calving at Petermann, no risk for shipping or sea level rise, the small inserted image from today August 12 2018 07:45 UTC Aqua / MODIS, the calving is in the middle of glacier front above the pink arrow.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 12, 2018, 11:20:34 PM
False alarm

Here is the a link to the image from where I got the wrong information, sorry:

https://lance.modaps.eosdis.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2018224074500-2018224075000.2km.jpg
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on August 31, 2018, 09:56:32 PM
A minor starboard calving has happened at Petermann Gletscher:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Alistair on September 07, 2018, 04:27:01 PM
A significant calving? (Worldview from 5/9, can't see anything for clouds on 6/9)  Or is this just worldview drawing a previous line?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Alistair on September 07, 2018, 04:33:41 PM
Ignore previous post - looks like it is a feature of Worldview I hadn't noticed before.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on September 11, 2018, 04:06:59 PM
New ice in Petermann Fjord. (Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.97744489599049&lng=-61.51176452636719&zoom=10&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-09-10&atmFilter=ATMCOR&showDates=false))
P.S. The ~700 m wide rhombus (diamond) shaped iceberg near the left shore short broke off of Petermann Glacier between September 5 and 7.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Phil. on September 11, 2018, 06:47:20 PM
New ice in Petermann Fjord. (Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.97744489599049&lng=-61.51176452636719&zoom=10&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-09-10&atmFilter=ATMCOR&showDates=false))
P.S. The ~700 m wide rhombus (diamond) shaped iceberg near the left short broke off of Petermann Glacier between September 5 and 7.

Looks like there could be a couple more fragments in the near future too.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on September 13, 2018, 10:15:03 AM
Great image from yesterday, looks nice with gain 0.5 and gamma 1.5:

https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.85647469870105&lng=-61.36241912841797&zoom=11&preset=1_NATURAL_COL0R&layers=B01,B02,B03&maxcc=71&gain=0.5&gamma=1.5&time=2015-01-01%7C2018-09-12&atmFilter=ATMCOR&showDates=true
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on October 10, 2018, 11:16:52 PM
It looks like the big side crack made a turn and started growing towards the centre crack. When they connect the next big calving is 3/4 complete.

http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201810/S1A_IW_GRDH_1SDH_20181010T113546_FB8F_N_1.8bit.jp2
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on October 11, 2018, 10:00:30 PM
It looks like the big side crack made a turn and started growing towards the centre crack. When they connect the next big calving is 3/4 complete.

http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201810/S1A_IW_GRDH_1SDH_20181010T113546_FB8F_N_1.8bit.jp2

Tealight nice spotting, we may have a very large calving next summer?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on October 19, 2018, 08:30:46 PM
I repeatedly see 'lineations' that run from the mid-glacier crevasse to the 'left' (west) edge of the glacial tongue on PolarView images (e.g., January (https://forum.arctic-sea-ice.net/index.php/topic,53.msg138537.html#msg138537) and July (https://forum.arctic-sea-ice.net/index.php/topic,53.msg164224.html#msg164224)), as well as from the lateral crevasse to the well developed cracks on the eastern side (as does Tealight).  However, I have not seen supportive imagery using Sentinel Hub (https://www.polarview.aq/arctic). [PolarView (https://www.polarview.aq/arctic) image from yesterday (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201810/S1B_EW_GRDM_1SDH_20181018T192748_6244_N_1.8bit.jp2).  SentinelHub image from Sept. 11 of yellow circle area.]
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on November 14, 2018, 08:48:03 PM
Hiawatha Glacier was mentioned in this thread once, so I post this here.

Impact crater 19 miles wide found beneath Greenland glacier (https://www.theguardian.com/science/2018/nov/14/impact-crater-19-miles-wide-found-beneath-greenland-glacier)
The Guardian  -  November 14, 2018
Quote
A mile-wide iron asteroid hit the Hiawatha glacier perhaps as recently as 12,000 years ago. The resulting impact crater 19.3 miles wide has remained hidden under a half-mile-thick ice sheet until now
Much better article in Science Magazine (https://www.sciencemag.org/news/2018/11/massive-crater-under-greenland-s-ice-points-climate-altering-impact-time-humans).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on December 17, 2018, 06:46:35 PM
Once again I'll show an image suggesting a connection between the mid-glacier crevasse and down-fjord side crevasses  I wonder how many of you think I'm "seeing things" (that aren't there) ...

Dec. 16 image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201812/S1B_EW_GRDM_1SDH_20181216T202508_0266_N_1.8bit.jp2) from PolarView (https://www.polarview.aq/arctic).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: gerontocrat on December 17, 2018, 07:28:40 PM
Once again I'll show an image suggesting a connection between the mid-glacier crevasse and down-fjord side crevasses  I wonder how many of you think I'm "seeing things" (that aren't there) ...
My eyes say yes to the connection but they cannot be relied upon.
Title: Re: Petermann Gletscher / North West Greenland
Post by: nukefix on December 20, 2018, 12:35:31 PM
Petermann is EXACTLY where it was last year on this date (area wise).  The shape of the terminus and it's position relative to the valleys north and south of it is unchanged. There are no major fractures sen either.  This summer has been the coldest in at least 7 years in NW Greenland as well.
It is still flowing 3+ m/day and the past summer looks "normal" to me. The graph is from Enveo Cryoportal.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on December 20, 2018, 04:12:15 PM
Petermann not moving?
Title: Re: Petermann Gletscher / North West Greenland
Post by: crandles on December 20, 2018, 04:17:08 PM
Petermann is EXACTLY where it was last year on this date (area wise).  The shape of the terminus and it's position relative to the valleys north and south of it is unchanged. There are no major fractures sen either.  This summer has been the coldest in at least 7 years in NW Greenland as well.

Note this post is dated 2013!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tealight on January 27, 2019, 12:55:47 PM
Slow and steady growth of the side crack continued, now growing directly towards the centre crack and about halfway there. I'd bet they connect by the start of summer.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: uniquorn on January 27, 2019, 02:15:40 PM
Once again I'll show an image suggesting a connection between the mid-glacier crevasse and down-fjord side crevasses  I wonder how many of you think I'm "seeing things" (that aren't there) ...

Tried to be non destructive/creative with the enhancements. Polarview, yesterday.
edit: Same treatment on jpg2000, never looked at those before. No default as it's practically all black.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on January 27, 2019, 02:56:00 PM
Or year to year:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: uniquorn on January 27, 2019, 04:54:50 PM
Much lower resolution but worldview brightness temperature might add some background info.
https://go.nasa.gov/2FQMJqT
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Neven on February 07, 2019, 10:17:34 AM
New paper our, stating that Petermann velocity has increased by 10% after the 2012 mega-calving, and that new one is coming. From AWI (https://www.awi.de/ueber-uns/service/presse-detailansicht/presse/risse-kuendigen-abbruch-eines-grossen-eisberges-am-petermann-gletscher-an.html):

Quote
Risse kündigen Abbruch eines großen Eisberges am Petermann-Gletscher an

AWI-Forscher messen höheres Fließtempo des Gletschers und sagen eine weitere Beschleunigung im Falle eines Abbruchs voraus

[06. Februar 2019]
Risse in der schwimmenden Eiszunge des Petermann-Gletschers im äußersten Nordwesten Grönlands deuten auf einen weiteren Abbruch eines großen Eisberges hin. Wie Glaziologen des Alfred-Wegener-Institutes, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) in einer neuen Studie berichten, hat sich seit einem Eisberg-Abbruch im Jahr 2012 das Fließtempo des Gletschers um durchschnittlich 10 Prozent erhöht, sodass in der Folgezeit neue Risse entstanden sind – ein durchaus natürlicher Vorgang. Modellsimulationen der Forscher zeigen jedoch: Sollten auch diese Eismassen abbrechen, wird sich der Petermann-Gletscher vermutlich weiter beschleunigen und mehr Eis ins Meer transportieren, mit entsprechenden Folgen für den globalen Meeresspiegel. Die Studie ist im „Journal of Geophysical Research: Earth Surface“ erschienen und frei erhältlich.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on February 07, 2019, 04:05:38 PM
New paper our, stating that Petermann velocity has increased by 10% after the 2012 mega-calving, and that new one is coming. From AWI (https://www.awi.de/ueber-uns/service/presse-detailansicht/presse/risse-kuendigen-abbruch-eines-grossen-eisberges-am-petermann-gletscher-an.html):

Quote
Risse kündigen Abbruch eines großen Eisberges am Petermann-Gletscher an

AWI-Forscher messen höheres Fließtempo des Gletschers und sagen eine weitere Beschleunigung im Falle eines Abbruchs voraus



[06. Februar 2019]
Risse in der schwimmenden Eiszunge des Petermann-Gletschers im äußersten Nordwesten Grönlands deuten auf einen weiteren Abbruch eines großen Eisberges hin. Wie Glaziologen des Alfred-Wegener-Institutes, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) in einer neuen Studie berichten, hat sich seit einem Eisberg-Abbruch im Jahr 2012 das Fließtempo des Gletschers um durchschnittlich 10 Prozent erhöht, sodass in der Folgezeit neue Risse entstanden sind – ein durchaus natürlicher Vorgang. Modellsimulationen der Forscher zeigen jedoch: Sollten auch diese Eismassen abbrechen, wird sich der Petermann-Gletscher vermutlich weiter beschleunigen und mehr Eis ins Meer transportieren, mit entsprechenden Folgen für den globalen Meeresspiegel. Die Studie ist im „Journal of Geophysical Research: Earth Surface“ erschienen und frei erhältlich.

There will always be a new one, thats the nature of a glacier?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: FrostKing70 on February 07, 2019, 05:46:38 PM
Has anyone been able to find an animation which shows the location of the calving events and the new cracks?    From what I can tell, the flow is about 3,000 Ft / yr, so the face has moved ~9,000 feet, or a little less than 2 miles in since the 2016 calving.  The new cracks are 8 miles from the face, so if we assume it calves this summer, that would be a retreat of about 6 miles?

FK
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on March 29, 2019, 06:29:41 PM
Sentinel-hub images (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.92832172515881&lng=-61.808148454874754&zoom=8&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=100&gain=1.0&gamma=1.0&time=2018-09-01%7C2019-03-24&atmFilter=&showDates=false) of Petermann Glacier have started to be available this season - surprise, surprise, lots of snow, and the boundary between the end of the shelf and the start of fast ice is subtle (which I do not attempt to show). 

Below is a pair of 'natural' views of the crack I'm obsessed with. The one with "E" is east of the mid-glacier [or floating ice tongue or shelf] valley, and to my surprise, the one with "W" (includes the mid-glacier valley) appears to show some melt water [pale blue]. Shadows and exposed ice just look different - if I understand what I'm seeing.  Any real experts on interpreting these images out there? (Best image this week is from March 24.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on March 29, 2019, 09:21:59 PM
I am aware there are some movements around, but I do not expect a major calving this season, meaning a calving leaving an island of ice (an iceberg worth mentioning)  my observations around Greenland is we are in pause phase, but on the other hand I am listening to much to Led Zeppelin at moment then everything is relative. When the levee breaks comes to mind https://www.youtube.com/watch?v=4VZtQPdSIsk
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: iwantatr8 on April 03, 2019, 05:23:36 PM
Here's a nice clear Sentinel Image of the Petermann.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 04, 2019, 10:51:38 PM
""we find an average acceleration of 10%""...

""This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue.""

""if the trend of a retreating calving front continues, PG is likely to further accelerate in the future. We attribute this to a loss of buttressing caused by the retreat further upstream and a subsequent loss of friction with the fjords walls.""

""the observed speedup in 2016 suggests that the ice in the frontal part is already detached from the stabilizing fjord walls. ""

Calving Induced Speedup of Petermann Glacier.
- Martin Rückamp  Niklas Neckel  Sophie Berger  Angelika Humbert  Veit Helm
First published: 11 January 2019

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JF004775
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 04, 2019, 11:19:53 PM
Just for fun. In light of paper posted above.
I wonder which area they are saying has detatched from main tongue, and how significant that could be?

Click to view animated gif of glacier over 1 year.
- April 5 2018 -> April 4 2019:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 04, 2019, 11:31:36 PM
"Cracks herald the calving of a large iceberg from Petermann Glacier" - GeoSpace - Earth & Space Science.
""Cracks in the floating ice tongue of Petermann Glacier in the far northwest reaches of Greenland indicate the pending loss of another large iceberg.""

""Glaciologists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, Germany report in a new study that the glacier’s flow rate has increased by an average of 10 percent since the calving event in 2012, during which time new cracks have also formed – a quite natural process.""

""However, the experts’ model simulations also show that, if these ice masses truly break off, Petermann Glacier’s flow rate will likely accelerate further and transport more ice out to sea, with corresponding effects on the global sea level.""

https://blogs.agu.org/geospace/2019/02/06/cracks-herald-the-calving-of-a-large-iceberg-from-petermann-glacier/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 04, 2019, 11:52:01 PM
Or year to year:
I think you can kindof see it on my July 2017 post, in the zoomed in images and markings I made. It may have become clearer, maybe not much has changed structurally deep down.
https://forum.arctic-sea-ice.net/index.php/topic,53.msg120534.html#msg120534
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 09, 2019, 04:56:31 AM
Where's the grounding line on this?
Polar View April 8th

 
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: nukefix on April 09, 2019, 10:13:30 AM
Where's the grounding line on this?
Much farther upstream, see:

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7309C276E62C3B38C05CC4379A7C8028/S0022143016000836a.pdf/div-class-title-grounding-line-migration-from-1992-to-2011-on-petermann-glacier-north-west-greenland-div.pdf
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 13, 2019, 07:33:39 PM
Where's the grounding line on this?
Much farther upstream, see:

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7309C276E62C3B38C05CC4379A7C8028/S0022143016000836a.pdf/div-class-title-grounding-line-migration-from-1992-to-2011-on-petermann-glacier-north-west-greenland-div.pdf

Thanks!
Most of that stuff in the image must be basically floating then?
I've seen a site that shows altitude changes (breaking and lowering closer to sea-level before they fully break off) for glaciers in the Antarctic. Is there something like that for Arctic region?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 20, 2019, 03:48:52 AM
Changes.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on April 21, 2019, 03:29:04 AM
Changes
The main fissure, towards northern shore.
Click image for animation.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on April 21, 2019, 09:42:01 AM
Great GIF Thomas! Thank you.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on April 21, 2019, 01:48:05 PM
Great GIF Thomas! Thank you.
Indeed.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on April 26, 2019, 06:38:49 PM
I've been 'seeing things' for a long time (and sometimes conflicting with 'each other'), but maybe today you'll see 'it' in this GIF made from yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201904/S1B_EW_GRDM_1SDH_20190425T204146_96B0_N_1.8bit.jp2).  I see a trace of something (a crack?) the yellow line approximately follows .  [Click to play]   (Edit: approx. location of GIF in outline.  Petermann Fjord is 15 km wide.)

(I sure appreciate Thomas's GIFs too.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Darvince on April 27, 2019, 12:49:41 AM
I see it, but based on the shape and scale of the other cracks and the bends in them, I don't believe it is anything other than just noise at this point.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on April 27, 2019, 01:14:14 AM
I can see it, but only an animation (corrected for glacier movement) can "prove" if it's a crack and if it's new.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on April 27, 2019, 10:45:33 PM
I've been 'seeing things' for a long time (and sometimes conflicting with 'each other'), but maybe today you'll see 'it' in this GIF made from yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201904/S1B_EW_GRDM_1SDH_20190425T204146_96B0_N_1.8bit.jp2).  I see a trace of something (a crack?) the yellow line approximately follows .  [Click to play]   (Edit: approx. location of GIF in outline.  Petermann Fjord is 15 km wide.)

(I sure appreciate Thomas's GIFs too.)

At this point I belive it is only a UIO?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on April 28, 2019, 12:49:02 AM
an Unidentified Identified Object?
:)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on April 28, 2019, 01:01:07 AM
No an Undentified Ice Object.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on April 29, 2019, 09:03:00 PM
Further to what Thomas posted above (https://forum.arctic-sea-ice.net/index.php/topic,53.msg196224.html#msg196224) concerning a crevasse on the NW side of the glacier, the mid-glacier crevasse has also widened over the course of a year.  Images are from Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.86410948481816&lng=-61.06544494628906&zoom=10&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2018-10-01%7C2019-04-27&atmFilter=&showDates=true) (April 2018 and April 2019).  The date bars are 150 meters wide and about 38 meters tall.  The location of the crevasse is near the bottom of the image in this post (https://forum.arctic-sea-ice.net/index.php/topic,53.msg194449.html#msg194449).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on May 14, 2019, 03:19:24 PM
Different from the post above, these two SentinelHub Playground images are 28 days apart showing Petermann Glacier is moving about 3 meters per day (at this location).  The orange lines are in the dip of the mid-glacier stream valley on the April 14 and May 12 images.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on May 30, 2019, 06:54:58 PM
Melt ponds on Petermann, per May 29 Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.92820916597857&lng=-61.56394958496094&zoom=11&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=20&gain=0.3&gamma=0.9&time=2018-11-01%7C2019-05-30&atmFilter=ATMCOR&showDates=false) image.

Edit: GIF made with ezgif.com [curious, I had to open the GIF to run it.] showing change between May 22 and 29.  I moved one image to mostly remove the effect of the glacier tongue's movement (see change in lower right corner scale).  Lots of change in 7 days.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Stephan on May 30, 2019, 07:18:33 PM
Question to the experts: Is this usual for this time of the year or is it (much too) early to happen?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on May 30, 2019, 07:50:36 PM
This part of Petermann Glacier has earlier melt ponds in 2019 than in 2016, '17 or '18.  GIF made from images "dated" May 30 from these four years.  (Date of actual Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.89697573702526&lng=-61.434173583984375&zoom=10&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2018-11-01%7C2019-05-11&atmFilter=&showDates=false) image may be earlier, as the 2019 image is actually May 29.  I note the 2016 image has a 'different' shadow.)  You certainly can see the glacier tongue moving year by year!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on May 30, 2019, 07:57:27 PM
Beautifully aligned shadows in '18 and '19.  8)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 01, 2019, 11:26:56 PM
Following on what Tor showed.
Meltponds and fissures: June 1 2018 (left) 2019 (right)
Zoom in for meltponds for 2019.
Also, compare relative distance between two fissures June 1 2018 (red arrow) and 2019 (blue arrow).
(these are the main fissures in the middle of Petermann that have been discussed many times.)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 05, 2019, 02:54:07 PM
A lot of meltponds - June 5.
Click and zoom to view meltponds.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 05, 2019, 02:56:42 PM
These fissures look like they are ajoining.
Click to zoom in.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on June 05, 2019, 03:59:24 PM
Uniquorn's (https://forum.arctic-sea-ice.net/index.php/topic,53.msg187373.html#msg187373) and Espen's (https://forum.arctic-sea-ice.net/index.php/topic,53.msg187374.html#msg187374) posts in January fairly show the connection between the crevasses on the NE side of the Petermann Glacier tongue and the mid-glacier lateral crevasse.  Nice to see it with a different satellite.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 06, 2019, 02:33:31 AM
I knew I'd seen something like that somewhere, looked for it, couldn't find them. Thanks for those. The radar images showed it was there, and now it is visible on the surface to the naked eye, makes it tangible. I wonder if we'll see it more visible this summer.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on June 07, 2019, 12:02:43 PM
What a difference a day makes ... 24 little hours ...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 11, 2019, 03:42:06 AM
A lot of melt ponds.
Fissure extension getting more visible.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Csnavywx on June 11, 2019, 07:02:40 PM
Upcoming heatwave should cause those ponds to proliferate even more, putting additional hydro pressure on crevasses.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: longwalks1 on June 11, 2019, 08:38:09 PM
in re 617

My computer wallpaper is a Sentinel shot from June 18, 2016 is almost an an exact copy of the #617.  I might go back and add it to this post as a reference, but work beckons. 
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 11, 2019, 09:49:38 PM
Maybe one big difference.
(wait...2)  :)

June 18 2016:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 14, 2019, 10:07:36 PM
Comparing meltponds June 15 2016.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 14, 2019, 10:08:10 PM
Comparing meltponds June 15 2017.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 14, 2019, 10:08:37 PM
Comparing meltponds June 15 2018.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 14, 2019, 10:12:06 PM
Comparing meltponds June 14 2019.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 24, 2019, 04:16:16 AM
Ajoined.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 24, 2019, 04:17:17 AM
Ajoined.

adjoin (v.)
c. 1300, "unite (something to something else), ally" (a sense now obsolete); late 14c. as "be contiguous with, be adjacent to," from Old French ajoin- stem of ajoindre "join together, unite," from Latin adiungere "fasten on, harness, join to," from ad "to" (see ad-) + iungere "to bind together," from a nasalized form of PIE root *yeug- "to join." Meaning "be contiguous with, be in contact with" is from late 14c. The French word was Latinized 16c. to Modern French adjoindre. Related: Adjoined; adjoining.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 24, 2019, 04:32:22 AM
Petermann weak spot confirmed.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on June 24, 2019, 07:08:55 AM
When Thomas? This summer?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on June 24, 2019, 06:06:39 PM
When Thomas? This summer?
It is (as good as) one long fissure (red line), seen on the surface as of this week. The stresses on that fissure, now that they appear to be joined into one, must be huge, but I have no idea. If not this summer, I think next summer. Although this glacier is moving so fast now, it could even happen in winter.
Any significant tsunami (from landslides in the area, which happen once in a while with warming tundra), could also make a difference.
I'd be amazed if it lasts more than 18 months.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on June 24, 2019, 08:08:55 PM
Agreed. My best bet is this coming winter. When all that water in the cracks is going to freeze and expand, cracking it even more.

Would be a bummer when it happens in winter though. We would rely on radar and couldn't actually see it visually via Sentinel.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 03, 2019, 04:08:03 PM
Petermann Fjord is 'starting' to clear out of seasonal fast ice.  From yesterday's Sentinel-hub Playground (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=81.16542636368189&lng=-62.47650146484375&zoom=9&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=20&gain=1.0&gamma=1.0&time=2019-01-01%7C2019-07-02&atmFilter=ATMCOR&showDates=false).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on July 03, 2019, 04:50:08 PM
It's also losing melt pond water via draining.

Which could indicate bottom melt.

Gif showing 30.06. vs. 02.07.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on July 05, 2019, 08:19:26 PM
A rather big melt event at Petermann today.

Tomorrows Sentinel shots should show a bluening.

This is the M8 band via RAMMB-SLIDER. Dark grey indicates unstructured snow (aka water), and brightness indicates intact snow structure (aka freshly fallen snow).

Correction: On second thought, this might be caused by rain!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on July 06, 2019, 08:35:35 AM
Tomorrows Sentinel shots should show a bluening.

Confirmed!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on July 06, 2019, 10:16:19 AM
The melt ponds on the fast ice have grown due to the rain.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Niall Dollard on July 10, 2019, 09:56:56 PM
Fast ice on the move.

Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: ghoti on July 11, 2019, 10:42:34 PM
New post about Petermann including two videos from 2015.

https://icyseas.org/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 11, 2019, 11:44:58 PM
4 videos at icyseas (https://icyseas.org/2019/07/04/petermann-glacier-videos-science/):
1st video:  Petermann Glacier is bbbiiiiggg!
2nd video:  "tides" are melting Petermann Glacier.

Andreas Muenchow, in his July 3rd post (https://icyseas.org/2019/07/03/whats-happened-at-petermann-gletscher-since-the-industrial-revolution-150-years-ago/), gives the posters on this thread a shout-out!  How cool is that?

Also, from the July 3 post:
Quote
Furthermore, a new sophisticated computer model of Petermann Gletscher reveals that the loss of this large “still attached” ice island is already gone from the glacier in terms of the friction that it provides along the sidewalls. Another way of putting this, all it takes is a little wiggle or bump and the separation will become visible. Dr. Martin Rueckamp just published this study in the Journal of Geophysical Research.
JGR link (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JF004775)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Andreas Muenchow on July 12, 2019, 05:49:53 PM
Thank you for the kind words, Tor.

My student (now Dr. Washam) just published his last dissertation paper on Petermann Gletscher's melting processes. It appeared this week in the Journal of Glaciology and can be accessed openly free of charge at https://www.cambridge.org/core/journals/journal-of-glaciology/article/summer-surface-melt-thins-petermann-gletscher-ice-shelf-by-enhancing-channelized-basal-melt/4F111AFFBE670992E7AAD21359561F1B (https://www.cambridge.org/core/journals/journal-of-glaciology/article/summer-surface-melt-thins-petermann-gletscher-ice-shelf-by-enhancing-channelized-basal-melt/4F111AFFBE670992E7AAD21359561F1B):

From moored ocean observations below the ice-shelf, surface weather, and ice-penetrating radar data at hourly intervalls we concluded that

"...We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base …"
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: b_lumenkraft on July 12, 2019, 07:05:41 PM
OMG, those videos are awesome.

Problem with them, i have so many questions now.  ::)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 17, 2019, 11:02:31 PM
While we are waiting for Petermann to calve, just a reminder we are also loosing a lot of ice next door to Petermann Fjord,and that is on top of Washington Land, the ice caps here will soon be history:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Alphabet Hotel on July 19, 2019, 09:28:25 PM
Ice has cleared from the mouth of the glacier.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 19, 2019, 09:57:49 PM
except for the fast ice in that protected northern (right) corner.

Pretty picture.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Alphabet Hotel on July 26, 2019, 04:07:42 PM
Melt is way up.

click for full resolution
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: DrTskoul on July 26, 2019, 05:52:33 PM
Melt is way up.

click for full resolution

That is a beautiful blue!!!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Stephan on July 26, 2019, 09:25:38 PM
Is this comparable with "the big melt year" 2012 or had it been worse then?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Alphabet Hotel on July 26, 2019, 10:23:16 PM
Is this comparable with "the big melt year" 2012 or had it been worse then?
I think this is worse, but I don't really have any proof that it is.

I just finished looking at most of the west coast between Jakobshavn and Humboldt and it's just crazy. Melting everywhere, giant sheets of bare ice exposed, icebergs spreading all over the place in the open sea. It looks like the days and days of melting in some areas is really starting to have an effect.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on July 29, 2019, 03:42:57 PM
Temperatures at Peterman Glacier are pretty high?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on July 29, 2019, 04:03:58 PM
Thomas, i agree it's warm there but you placed the dot slightly wrong (Nares Land that is i think), not Petermann. :P
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 29, 2019, 06:12:32 PM
Temperature at Petermann:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on July 29, 2019, 06:17:50 PM
That's interesting!

GFS has it much colder.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 29, 2019, 06:26:32 PM
Even B_ doesn't have Petermann Glacier location right.
From Petermann's Glacial History (https://petermannsglacialhistory.wordpress.com/), see that Petermann Glacier is off of Hall Basin, the place where Nares Strait widens (and opposite Lady Franklin Bay).  (For all the place names in the area, go to Greenland Maps (https://forum.arctic-sea-ice.net/index.php/topic,277.0.html) thread.)

[Espen has the location right.  Of course, I'd believe him over my own research...]
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on July 29, 2019, 06:47:36 PM
Even B_ doesn't have Petermann Glacier location right.

Damn!  :-\

I blame Nullschool! :P
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 29, 2019, 08:24:21 PM
Since one year ago, the lateral mid-glacial crevasse has increased in width (~44 m to ~56m at the right side of the GIF below) and is clearly longer by about 1150 meters (yellow [approximate] trace).  For scale, the date bars are approximately 620 m wide and 100 m tall.  Images from Sentinel Playground here (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.84032814311632&lng=-61.34717558976263&zoom=12&preset=CUSTOM&layers=B01,B02,B03&maxcc=86&gain=1.0&gamma=1.0&time=2018-01-01%7C2018-07-28&atmFilter=&showDates=true&evalscript=cmV0dXJuIFtCOEEqMixCMDMqMSxCMDIqMV0K) and here (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.85127397294049&lng=-61.37237550923601&zoom=12&preset=CUSTOM&layers=B01,B02,B03&maxcc=86&gain=1.0&gamma=1.0&time=2019-01-01%7C2019-07-28&atmFilter=&showDates=true&evalscript=cmV0dXJuIFtCOEEqMixCMDMqMSxCMDIqMV0K). [requires a click]

Interesting that some melt ponds are smaller this year.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on July 30, 2019, 05:05:58 PM
Breaking Old News
Another calving at Petermann Gletscher, this time probably the oldest satelite documented calving at Petermann, the calving happened sometimes in the 1976 melting season, notice the front of Petermann at that time reached all the way to the mouth of Petermann Fjord.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: DrTskoul on July 30, 2019, 05:37:58 PM
Not
Broken old news
??

 Very cool find. Thank you!!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 30, 2019, 06:47:21 PM
On the 'left' (southwest) side of Petermann Glacier are several crevasses, 'one' of which may soon met up with the lateral mid-glacier crevasse (see post above (https://forum.arctic-sea-ice.net/index.php/topic,53.msg217286.html#msg217286)).  Here is a one-year (two frame) GIF showing how they have grown. Sentinel-hup Playground images from 2018 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.84983001885807&lng=-61.5399169921875&zoom=13&preset=CUSTOM&layers=B01,B02,B03&maxcc=86&gain=1.0&gamma=1.0&time=2018-01-01%7C2018-07-31&atmFilter=&showDates=true&evalscript=cmV0dXJuIFtCOEEqMixCMDMqMSxCMDIqMV0K) and 2019 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=80.86044284998277&lng=-61.56515121459961&zoom=13&preset=CUSTOM&layers=B01,B02,B03&maxcc=86&gain=1.0&gamma=1.0&time=2019-01-01%7C2019-07-29&atmFilter=&showDates=true&evalscript=cmV0dXJuIFtCOEEqMixCMDMqMSxCMDIqMV0K).  For scale, the date bars are approximately 620 m wide and 100 m tall. The 'top' crevasse has lengthened about 2.6 km.  (The dark area on the left is shadow from the land looming over the side of the glacial tongue.) [requires a click]

Edit:  obviously, the glacier has advanced during this year.  The two images were adjusted so that a particular stream meander would be un-moved.  The result is the top of the images appear fixed while the lower parts of the GIF appear to rotate counterclockwise.  I think this is caused by the rifts on the NE side of the tongue (or shelf) opening faster than on the ones on the SW side (here pictured), causing this future ice island to rotate a little, even while still attached to the rest of the floating ice shelf.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on July 30, 2019, 08:51:20 PM
Cross-post - a copy belongs here ...
The linked reference implies that the stability of the ice in the Petermann catchment is likely less stable than consensus climate scientists currently assume:

Chambers, C., Greve, R., Altena, B., and Lefeuvre, P.-M.: On the possibility of a long subglacial river under the north Greenland ice sheet, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-141, in review, 2019.

https://www.the-cryosphere-discuss.net/tc-2019-141/

Abstract. Does a long subglacial river with a source deep in the interior of the Greenland ice sheet, drain into the sea at the Petermann Glacier grounding line? Basal topographic data shows a segmented valley extending from Petermann Fjord into the centre of Greenland, however the locations of radar scan lines, used to create the bedrock topography data, indicate that valley discontinuity is due to data interpolation. Simulations where the valley is opened are used to investigate effects on basal water and ice sheet sliding. The simulations indicate that the opening of this valley results in an uninterrupted water pathway from the interior along the valley that alters ice sheet sliding in the Petermann catchment and in areas of west Greenland. Along its length, the path of the valley progresses gradually down an ice surface slope causing a lowering of ice overburden pressure that could enable water flow along its path. The fact that the valley base appears to be relatively flat and follows a path along the interior ice divide that intersects the east and west basal hydrological basins, is presented as evidence that its present day form developed as a consequence of the overlying ice sheet rather than prior to ice sheet inception. Though considerable uncertainty remains, the results are consistent with a present day active long subglacial river system. The results raise issues concerning the need to better observe, understand, and simulate the complicated basal hydrology of the Greenland and other ice sheets.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Sterks on July 31, 2019, 12:35:28 AM
If it means something to you I did this gif for my own amusement comparing early June to recent date. But I can see you use much bigger zoom and quality to study the crevasses etc.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: DrTskoul on July 31, 2019, 01:18:34 AM
Neat!!!
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on July 31, 2019, 10:09:34 AM
Nice animations Tor and Sterks. Note the 2017 typo.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Sterks on July 31, 2019, 10:58:00 AM
Nice animations Tor and Sterks. Note the 2017 typo.
Thanks, Ah didn't catch that, the Sentinel-hub app puts those labels. I'd swear these images are 2019
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: grixm on July 31, 2019, 12:06:00 PM
Nice animations Tor and Sterks. Note the 2017 typo.
Thanks, Ah didn't catch that, the Sentinel-hub app puts those labels. I'd swear these images are 2019

Are you sure about that? Looks to me like your pictures are indeed from 2017. Here's a gif comparison between 2017 and now (click). Notice the shape and position of the the edge, and compare to your image.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 02, 2019, 01:35:09 AM
You guys probably knew about this, but this is Petermann Glacier.
Huge hidden canyon under Greenland ice sheet may have flowing water:
https://www.newscientist.com/article/2211583-huge-hidden-canyon-under-greenland-ice-sheet-may-have-flowing-water

I don't have access to New Scientist but here is the Wiki page about the canyon, which they are now saying may have flowing water under it:
https://en.wikipedia.org/wiki/Greenland%27s_Grand_Canyon
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 02, 2019, 04:44:11 PM
I've seen sediment saturated waters coming from Petermann almost every day since the fast ice is gone. I always wondered where it came from. Now i know.

Thanks, Thomas, great info.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 04, 2019, 03:43:49 PM
RE: Sediments

Click to play
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Dietrich on August 05, 2019, 05:16:29 PM
Replying to move the counter.  Can't let this thread stay at 666.   The GIS response is scary enough on it's own
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 05, 2019, 05:22:29 PM
That's almost heroic, Dietrich. Thank you. :)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on August 05, 2019, 05:34:43 PM
There is a poll concerning Petermann Glacier and the timing for the creation of the next ice island.
https://forum.arctic-sea-ice.net/index.php/topic,2862.msg219270.html#msg219270
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 05, 2019, 05:39:58 PM
Thanks, Tor. Cool idea.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 15, 2019, 10:27:16 PM
Teeny tiny calving yesterday. Is this the beginning?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on August 15, 2019, 11:38:43 PM
Well, it is the beginning of a ~60 m wide iceberg!  (and several smaller ones)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 16, 2019, 03:05:52 AM
Another calving at Petermann Gletscher, this time probably the oldest satelite documented calving at Petermann, the calving happened sometimes in the 1976 melting season, notice the front of Petermann at that time reached all the way to the mouth of Petermann Fjord.
How many kilometres retreat of the face do you think that is from the mouth of the fjord in '75 to where it is today?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on August 16, 2019, 03:51:59 AM
Surely you can figure that out - hint:  Petermann Fjord is 15 km wide.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 27, 2019, 04:03:43 AM
Surely you can figure that out - hint:  Petermann Fjord is 15 km wide.
So you don't know.
Ok.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Thomas Barlow on August 27, 2019, 04:05:08 AM
More observations of Petermann evolution:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mabarnes on August 27, 2019, 06:19:48 AM
Crazytown.  July 29-August 25 ... click to animate in new window.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: IceConcerned on August 27, 2019, 08:12:55 AM
Most significant for me is the opening of the western cracks, down the cliff
This is a true change in behaviour compared with previous observations
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 29, 2019, 07:23:20 PM
~15-day increment, from 01.08.

Please correct me if i'm wrong, but it looks to me as if all those huge cracks are filled with water?

How deep are those 'melt ponds'?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Shared Humanity on August 29, 2019, 08:48:06 PM
I don't think those are melt ponds. Those are fractures in the glacier that have been growing wider and the water is open water.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on August 29, 2019, 09:23:59 PM
My understanding matches SH's.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 29, 2019, 09:30:59 PM
Haha, OK.

This is a body of water sitting on a body of ice caused by melting ice. I know it's usually not called melt pond, but that's the closest i knew. This is why i put it in air-quotes.  ;D

But how deep do they go? Is this known?
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mabarnes on August 29, 2019, 09:47:55 PM
I believe the final end of the glacier is riding on a layer of water beneath it, as evidenced every time a giant berg breaks off and floats away ... I remember one that made the news in August 2012.  Those same cracks appeared in pretty much the same place in August 2018 (pic attached).

I'm far from fully informed on this kind of thing, but I think the end of most glaciers is actually floating on water beneath, and there's a "grounding" line upstream where it's still riding on land.  Maybe this has something to do with it...?  Perhaps somebody more knowledgeable on glaciers can help enlighten on this?  Interesting stuff....
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 29, 2019, 09:58:15 PM
OMG, of course! Seawater makes sense!  :o

I thought the glacier was thicker then...
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: longwalks1 on August 29, 2019, 10:00:09 PM
Maybe look at
The Ice Shelf of Petermann Gletscher, North Greenland
 and its Connection to the Arctic and Atlantic oceans

Andreas Münchow 1 , Associate Professor, University of Delaware, Newark, DE 19716, U.S.A.
Peter Washam, Graduate Student, University of Delaware, Newark, DE, U.S.A.

My copy is a pre-official release, I don't see the doi. 

Pg 5   About 60 meters thick at terminus.     Between 2010 and 2012 the ice sheet went from 86 to 41 km long. 

I should update some of my sources for this glacier,  search Münchow , he went back a couple years ago. 
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: longwalks1 on August 29, 2019, 10:03:17 PM
Via his web site (

*Washam, P., K. Nicholls, A. Muenchow, and L. Padman: "Summer surface melt thins Petermann Gletscher ice shelf by enhancing channelized basal melt," J. Glac., doi:10.1017/jog.2019.43, 2019.

*Washam, P., A. Muenchow, and K. Nicholls: "A decade of ocean changes impacting the ice shelf of Petermann Gletscher, Greenland," J. Phys. Oceanogr., 48, 2477-2493, 2018.

*Ryan, P. and A. Muenchow: "Sea ice draft observations in Nares Strait from 2003 to 2012," J. Geophys. Res. Oceans, 122, doi:10.1002/2016JC011966, 2017.

.pdf Muenchow, A., L. Padman, *P. Washam, and K. Nicholls: "The ice shelf of Petermann Gletscher, North Greenland, and its connection to the Arctic and Atlantic Oceans," Oceanography, 29 (4), 89-95, 2016.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 29, 2019, 10:06:16 PM
Link >> https://tos.org/oceanography/assets/docs/29-4_munchow.pdf

Should be ~175 meters thick where the big cracks are.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: grixm on August 29, 2019, 10:06:38 PM
The water in the rifts is definitely sea water, it may enter from the sides or the rifts may extend to the bottom of the glacier where there's also water because it's floating. Here are some different perspectives on how rifts in the petermann glacier look close up:


(https://nsidc.org/sites/nsidc.org/files/icelights/files/2011/09/Double_glacier.png)

(https://icyseas.files.wordpress.com/2012/07/imgp3241.jpg)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on August 29, 2019, 10:09:10 PM
Awesome Grixm, thank you.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mabarnes on September 03, 2019, 08:48:29 PM
Was checking out Petermann today - the plot thickens.  For reference I put together a graphic of the last giant floe I remember (July 2012) along with yesterday's view of the glacier from the same source.  Looks like the tongue of the glacier has advanced idk, 8-10 km since 2012.

While doing this, I also looked at yesterday's high-res image and danged if my "floater" conception needs revision - there's visible (what sure looks like) rock as the floor of the cracks.  Now I'm wondering if it's "just" an uneven grounding line, maybe meltwater pulses below the glacier cause the cracking ... stumped, at least for now.

Anyway, that's all I have, curious as always....
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on September 03, 2019, 09:03:33 PM
there's visible (what sure looks like) rock as the floor of the cracks.

Hmm... It's either melting rocks or ice.  ;)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mabarnes on September 04, 2019, 12:38:56 AM
Well hallelujah ... it does look like ice.  Dirty or very thin.  Guess it's re-freezing given the temps.  Thanks man ....

(BTW - anybody know where the grounding line actually is?)
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: mabarnes on September 05, 2019, 03:12:11 AM
Shout out - for the humor and civility to Blumenkraft.  After I stopped laughing, I read the entire topic stream (next time, in advance eh) ... the cracks have been a big issue since 2016.  For what it's worth, and since I didn't see it on here yet, here's the most cited paper I could find on the Petermann ice tongue, it's speed, the grounding line, all that.  Sharing is caring ... I'm told lol.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL031765
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on September 05, 2019, 06:59:33 AM
Aww, thank you Mabarnes!  :D
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on September 06, 2019, 12:24:16 PM
A very impressive image from Petermann taken by the the NASA Icebridge Team September 4 2019:
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on September 30, 2019, 07:23:12 PM
How oceans interact with Greenland’s last floating glaciers via Icy Seas

Link >> https://icyseas.org/2019/09/30/how-oceans-interact-with-greenlands-last-floating-glaciers/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: oren on October 01, 2019, 02:18:00 AM
Big Kudos to Andreas Muenchow and his team for this super-important work. Grants should be 10 or 100 times as large, more holes should be drilled near the grounding line, and in other ice-shelf glaciers where physically possible (Pine Island Glacier? Nioghalvfjerdsbrae 79N?) to monitor the situation and collect data sets over a long time span. This should be a top priority project for humanity.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: johnm33 on October 01, 2019, 11:53:21 AM
Nice catch B-l thanks, looking forward to Padmans (https://www.esr.org/staff/laurence-padman/) work from this mission.
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Espen on October 22, 2019, 03:37:52 PM
Although I expected a real calving in 2019 which obvisously did not happen, the cracks at the port side of the glacier are still extending further towards each others.
The cracks are shown with a red 1. and 2.   
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on October 22, 2019, 03:42:57 PM
Wait a second, is it going backward??
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: Tor Bejnar on October 29, 2019, 03:13:37 PM
Me and my lineations.  Red circles one. (See thread (https://forum.arctic-sea-ice.net/index.php/topic,2862.0.html) that started with a poll that asked when a crack would occur in this area, including an enlargement of this lineation from October 2.)  Orange circles a lineation 20 km upstream.  (Petermann Glacier is about 15 km wide in the red circle [okay, oval] area.) Screen print from Polar View (https://www.polarview.aq/arctic) image from 2019-10-28 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201910/S1B_EW_GRDM_1SDH_20191028T195241_0291_N_1.8bit.jp2).
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on December 03, 2019, 05:46:13 PM
Finally some info! \o/

Blog: “Back in Petermann Fjord”

https://polar.se/en/news/blog-back-in-petermann-fjord-english/
Title: Re: Petermann Gletscher / Petermann Fjord / North West Greenland
Post by: blumenkraft on December 06, 2019, 08:22:04 PM
Tor, i think i'm seeing something!

Link >> http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201912/S1B_EW_GRDM_1SDH_20191205T193552_C744_N_1.8bit.jp2