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Author Topic: Petermann Gletscher / Petermann Fjord / North West Greenland  (Read 156831 times)

Thomas Barlow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #500 on: June 19, 2017, 09:31:43 PM »
Oh, ok, Thanks!
Glad that's all it is.
Where you getting that image from?

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #501 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!
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ghoti

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #502 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

VeliAlbertKallio

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #503 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/

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #504 on: June 23, 2017, 05:51:34 PM »
The June 21 Polar View image 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.)
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #506 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)
« Last Edit: June 23, 2017, 08:36:33 PM by Tor Bejnar »
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #507 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)
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oren

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #508 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.

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #509 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.
« Last Edit: June 29, 2017, 05:29:50 PM by A-Team »

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #510 on: June 29, 2017, 05:15:01 PM »
"Hear Hear"!
Have a ice day!

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #511 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.
« Last Edit: July 01, 2017, 05:01:55 AM by A-Team »

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #512 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.
Have a ice day!

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #513 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.

"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."




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.
« Last Edit: July 01, 2017, 05:41:31 PM by A-Team »

Thomas Barlow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #514 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)

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #515 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).  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).
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #516 on: July 24, 2017, 08:34:13 PM »
Here is a GIF showing Sentinel Playground images of June 16, June 30 and July 19.  Is it changing light or is the crack widening?  The glacier is certainly progressing!
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Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #517 on: July 24, 2017, 09:50:01 PM »
I believe there will be no substantiel calving this calender year.
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #518 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.)
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Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #519 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.
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #520 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 image)
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Shared Humanity

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #521 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?

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #522 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.

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #523 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) 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.
« Last Edit: August 01, 2017, 08:49:18 PM by Tor Bejnar »
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Shared Humanity

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #524 on: July 26, 2017, 10:31:19 PM »
Thank you.

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #525 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:
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #526 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 gifs)
« Last Edit: July 27, 2017, 02:58:35 PM by Tor Bejnar »
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Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #527 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.
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #528 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...
« Last Edit: July 29, 2017, 10:28:34 PM by Tor Bejnar »
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Tealight

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #529 on: July 29, 2017, 10:19:17 PM »
The iceberg has broken into two main pieces and leaves towards Nares Straight.

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #530 on: July 31, 2017, 04:56:28 PM »
The smaller iceberg is eager to get away! Polar View image from July 30. (red dots on the two larger icebergs)
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Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #531 on: July 31, 2017, 05:52:26 PM »
I've attempted to show the curious crack near mid-glacier growing (widening), with Sentinel Playground 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.
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Andreas T

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #532 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.
...
Take a closer look

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.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #533 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 ...

hth.
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Often Distant

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #534 on: August 06, 2017, 10:23:05 AM »
Detached segments melting fast in the warm waters of the fjord.


Juan C. García

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #535 on: August 10, 2017, 01:01:39 PM »
Forget That Big Iceberg--A Smaller One in the Arctic Is More Troubling

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/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #536 on: August 11, 2017, 11:15:18 PM »
Forget That Big Iceberg--A Smaller One in the Arctic Is More Troubling

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.

Have a ice day!

logicmanPatrick

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #537 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.






supposed to be an animated gif.


polarview 12 Aug. 2017






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Thomas Barlow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #538 on: August 23, 2017, 06:58:04 PM »
Widening gaps.

31 Aug 2016 and 21 Aug 2017.