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paolo

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Re: PIG has calved
« Reply #1800 on: February 14, 2020, 06:53:16 PM »
Stephan and Blumenkraft, you're too focused to the last images, you have to step back and remember that these fractured areas have always been created (maybe less extensive) and that in the past they always reabsorbed further downstream. Maybe we are reaching a tipping-point relative to the NE-IS, but in order to show it we need other elements and other analyses than the image of the day. I am attaching an animation that I had already posted in December on this subject.
What I want to say is that we want to make predictions and that these predictions are realistic and come true, so we need to take time, accumulate information and explanations (and articles). But we have the time, even if the PIG is a glacier that goes fast (too fast), it is still a glacier ...

Blumenkraft the "blumencracks" are in the ice platform (they float, even if they are not far from the grounding line)

Stephan

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Re: PIG has calved
« Reply #1801 on: February 14, 2020, 07:15:54 PM »
Maybe I didn't write correctly enough. I do not mean the cracks uphill, but the beginning of the formation of ice mélange in the part that is already floating (ice shelf) which is visible in the lower and left side part of your fantastic gif from today (i.e. the fast moving area).
The cracks uphill may be an initiation of the separation of the slow flowing ice on land beyond the grounding line and the ice shelf itself.
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baking

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Re: PIG has calved
« Reply #1802 on: February 14, 2020, 07:29:30 PM »
paolo,
   Just because marginal shear rifts from previous years are smaller than this years, doesn't mean they've been reabsorbed or shrunk.  Perhaps they started out smaller.  Older rifts will obviously become less defined due to blowing snow and refreezing, but I'm not so sure about shrinkage.  It would take multi-year comparisons to say for sure.

Stephan,
   The marginal shear rifts move with the glacier and will eventually (5 years?) reach the calving front as we've seen happen this week on the Southern Margin.  Those Southern rifts were first detected in 1999 so it might take a while longer than 5 years.  The blumencracks are on stationary ice and who knows when they will come into play.  Right now the Northern margin is pinned to a grounding line around Evans Knoll.  If the front moves upstream from there, the margin will depend on the ice shelf that those cracks are on the upstream end of.  When the front gets to the shelf, how big those cracks will be is the question.  I'm still undecided at this moment.

blumenkraft,
   The blumencracks might be a sign that the ice shelf is moving slightly at the grounding line, or they may just be large crevasses (bergschrund) where the higher ice transitions to the ice sheet.  Whenever you mention the Northern margin I always want to so go look at the Southern margin at the opposite location and see all the crazy sh*t going on there.  Yet I don't know if it means anything except that the glacier has been moving faster and will in future move faster still.

EDIT: crazy sh*t = rifts extending from the margin into the Southern ice shelf at the upstream end, yet no significant impact on the strength of the ice shelf so far.  How the Southern ice shelf handles the eventual loss of the "melange" is different matter.
« Last Edit: February 14, 2020, 07:37:40 PM by baking »

Stephan

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Re: PIG has calved
« Reply #1803 on: February 14, 2020, 07:47:06 PM »
Stephan,
   The marginal shear rifts move with the glacier and will eventually (5 years?) reach the calving front as we've seen happen this week on the Southern Margin.
I should have calculated before I posted.  :(
The "blumencrack area" is around 35 km away from the calving at Evan's Knoll.
With 15 m/day flow speed it will take around 6 years to reach the position of the actual calving front, which, of course, may have shifted upstream until then. But 1 year is much much too fast...
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paolo

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Re: PIG has calved
« Reply #1804 on: February 14, 2020, 08:32:57 PM »
Baking,

Without investigating too much at the moment, I had followed the evolution of the fractures (individually) over time and it seems to me that there is (at least) a process of closure downstream. But I agree with you that we need to get out of each other's impressions and provide more elements. As far as I am concerned, I will try to do it in the following days (and I count on your opinion ...).

The "Blumencracks" are in a part of the shelf that moves, even if slowly, and you can see it even in the Blumenkraft animation (I don't know the dates of this animation). This part is driven by the movement of the MIS (and more precisely the part of the NE-IS driven by the MIS) further south. What is problematic is that this area is hardly fed upstream, the NE-IS is fed by a small tributary but further west and this area has behind it only ice rises. Indeed it was already thinner in 2012 (comparable to the shear zone, see attached picture).  It could be that the drive has passed a pinning point and that a vacuum could be created at the base of the ice rises immediately to the East. This is a point that deserves to be analysed and I will try, as far as I'm concerned, to do it in the following days ...

As for your 5 year forecast for the arrival of the fracture zone at the calving line, (EDIT) given that currently the SW boundary of this zone is about 30 km from the calving line, this would imply that you predict a 10 km retreat from the calving line to the north. Edit4 I'm not saying it's impossible, but at the moment it doesn't seem most likely (I'll try to evaluate as cleanly as possible what we lost on Evans Knoll with the current calving).

I have the impression that everything is moving at the moment and that we really have a lot of work to do.

Edit2 : I forgot to attach the image >:(
Edit3 : I have added to the image the notation for NE-IS
« Last Edit: February 14, 2020, 09:14:35 PM by paolo »

Stephan

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Re: PIG has calved
« Reply #1805 on: February 14, 2020, 08:59:49 PM »
This image is somehow shocking - dating from 2011, only nine years ago.
Evan's Knoll, just for clarity, is the brown dot (hill) right above the word "North Ice Shelf" and left from the word "Main Ice Shelf".
If I just do a quick interpolation into the future (which is, of course, not allowed in a scientific way), assuming a further linear retreat into 2029, then the calving front will be much further upstream and may have reached the "blumencracks" region (somewhere between the words "NE-IS" and "Ice Plain")...  :o
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paolo

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Re: PIG has calved
« Reply #1806 on: February 14, 2020, 10:13:11 PM »
Baking,
Concerning the history of NE-IS fractures, I attach two animations related to the PIG and it seems to me that these fractures also existed in the past (2000), even if their development was variable: sometimes more marked, sometimes less so and that they disappeared as they moved away from the zone of origin.  If the interpretation is correct and if I am not mistaken (very low resolution images), their age shows us that his fractures have reached the calving line until today without being noted ...

Twice click to animate and zoom the second image

baking

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Re: PIG has calved
« Reply #1807 on: February 15, 2020, 02:01:46 AM »
their age shows us that his fractures have reached the calving line until today without being noted
Good point, but again look at the south.  Much more extreme rifting and it did eventually reach the calving front.  It also rifted deep into the the ice shelf upstream.  I think the general lesson is that the effect will diminish as it moves downstream, but it can still reach the front if it is severe enough.

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Re: PIG has calved
« Reply #1808 on: February 15, 2020, 09:34:50 AM »
Calving in the cork area / ZOD. Line is approximate




blumenkraft

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Re: PIG has calved
« Reply #1809 on: February 15, 2020, 10:53:52 AM »
Thanks for reporting, Grixm! :)

So what're your guy's guesses? When will the zone of destruction be cleared?
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Stephan

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Re: PIG has calved
« Reply #1810 on: February 15, 2020, 11:38:43 AM »
(Sorry, just for the case I repeat myself)
As soon as Cork II and the remainders of Cork are gone, there is no reason why the icebergs in the zone of destruction stay where they are at the moment.
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Re: PIG has calved
« Reply #1811 on: February 16, 2020, 02:07:46 PM »
New hi-res just came in. Aligned at the calving front.
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paolo

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Re: PIG has calved
« Reply #1812 on: February 16, 2020, 02:48:31 PM »
You will find attached :

> an animation with the high resolution Sentinel1 images from 04/02 and 16/02.
the mR1 rift has extended moderately, but for the moment remains marginal (to be followed)

EDIT : The alignment is relative to mR1 we can notice that mR1 is widening and that the distance to mR2 is increasing.
I have also modified the animation by increasing the time for the 16/02 frame.


> an image of the calving line of the densely packed ice zone with an indication of all calvings that occurred after 09/02. It will complete the blumenkraft animation.
« Last Edit: February 16, 2020, 02:56:37 PM by paolo »

blumenkraft

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Re: PIG has calved
« Reply #1813 on: February 16, 2020, 02:59:02 PM »
Oh, i didn't see the mR1 extension. Thanks, Paolo.
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paolo

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Re: PIG has calved
« Reply #1814 on: February 16, 2020, 03:04:59 PM »
I add a zoom relative to the rift that recently opened in the SIS. It appears to have joined the SWT

Click to zoom in

paolo

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Re: PIG has calved
« Reply #1815 on: February 16, 2020, 03:23:14 PM »
Blumenkraft,
I zoomed in and increased the time
It's not something exceptional, but it shows that this rift is not stationary.

EDIT : Excuse me, I misinterpreted your message (speed leads to mistakes) and I thought you don't see it. I'm not deleting the message, because the zoom is not useless.
« Last Edit: February 16, 2020, 04:45:51 PM by paolo »

Grygory

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Re: PIG has calved
« Reply #1816 on: February 16, 2020, 03:30:41 PM »
Is there anything that will block calving from the second destruction zone? Is undoing 100 W inevitable? :'(

Stephan

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Re: PIG has calved
« Reply #1817 on: February 16, 2020, 04:00:24 PM »
Thanks paolo and blumenkraft for the information and animations.
Cork II has lost the two icebergs that were attached to it. So the distance between it and the Point should be now around 1.5 km, which should facilitate the export of the icebergs from the zone of destruction.
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blumenkraft

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Re: PIG has calved
« Reply #1818 on: February 16, 2020, 04:10:28 PM »
Is there anything that will block calving from the second destruction zone? Is undoing 100 W inevitable? :'(

What do you mean with second destruction zone, Grygory?
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blumenkraft

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Re: PIG has calved
« Reply #1819 on: February 16, 2020, 04:14:22 PM »
Stephan, you are welcome. :)

I find it baffling, that it broke off where i thought was a pressure rig. I assumed it should be compacted and stronger there, but it seems to be a predetermined breaking point.
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Re: PIG has calved
« Reply #1820 on: February 16, 2020, 04:26:26 PM »


What do you mean with second destruction zone, Grygory?

blumenkraft

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Re: PIG has calved
« Reply #1821 on: February 16, 2020, 04:32:16 PM »
Oh yeah, we haven't named that one yet.

So, SDZ (second destruction zone) it is i guess. :)

I have no idea how this will propagate downstream ... sorry.

Paolo and Baking have ideas on that one upthread.

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Stephan

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Re: PIG has calved
« Reply #1822 on: February 16, 2020, 08:32:48 PM »
I find it baffling, that it broke off where i thought was a pressure rig. I assumed it should be compacted and stronger there, but it seems to be a predetermined breaking point.
blumenkraft,
the same idea came into my mind when I wrote the posting two days ago about Cork II. I did not ecpect these two (blue circled) rigs were weaker than the rest...
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paolo

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Re: PIG has calved
« Reply #1823 on: February 16, 2020, 08:36:19 PM »
Considering the cloud cover of today's Terra/Modis image (image attached) I don't expect much from today's Sentinel2 image. So I'm giving you two animations using the Sentinel2 image of 11/02:
  > The first one is based on the PIIS images of 2016-12-03, 2017-10-14, 2018-01-27, 2018-11-18, 2019-09-14 and 2020-02-11.
  > The second one is based on the images of 2018-11-18 and 2020-02-11, the last two calvings, and Edit : on from the same images with highlighting of the calving line to clearly show the differences in the positioning of these two calvings.

twice click to animate and to zoom in

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« Last Edit: February 16, 2020, 09:37:28 PM by paolo »

paolo

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Re: PIG has calved
« Reply #1824 on: February 16, 2020, 08:53:43 PM »
Stephan and Blumentkraft,
I don't understand your astonishment, the pressure of P1 can only induce the expulsion of the fragments indicated in the attached picture.

EDIT : I used the high-resolution Sentinel1 image from 10/02

EDIT2: Excuse me, I've added, in the picture, an expelled fragment that I had forgotten
« Last Edit: February 16, 2020, 09:04:02 PM by paolo »

AbruptSLR

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Re: PIG has calved
« Reply #1825 on: February 16, 2020, 10:56:05 PM »
What this thread has named the zone of destruction, ZOD, and the second destruction zone, SDZ, might better be considered as the southern shear margin for the PIIS between the southern ice shelf, SIS and the main ice shelf, MIS, as shown by the first attached image from Shean et al. (2019).  Furthermore, it seems to me that the majority of the icebergs in the ZOD came from the calving of the green area in the SIS surrounded by blue basal channel carved by the water circulation beneath the SIS shown in the second attached image, and I believe that the calving of the icebergs from this green area of the SIS is well illustrated by the third gif clip (requiring a click to start) assembled by paolo.  Also, I believe that the fourth image (also from paolo) of the SIS-SWT rift can also be seen in the first image, and that as this SIS-SWT rift widens both the SIS and the ice shelf for the SWT will be further destabilized

Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E., and Berthier, E.: Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica, The Cryosphere, 13, 2633–2656, https://doi.org/10.5194/tc-13-2633-2019, 2019.

https://www.the-cryosphere.net/13/2633/2019/

Finally, I note that the following linked AGU December 2019 presentation by Karen Alley et al. confirms that basal channels are frequently found beneath the shear margins of fast-flowing ice shelves like the PIIS.

Karen Alley et al (from a presentation at the December 2019 AGU Fall Meeting) discuss how basal channels in Antarctic ice shelves can work to destabilize such ice shelves leading to the type of accelerated calving as we have recently witness for the Pine Island Ice Shelf, PIIS.  In my opinion this behavior does not bode well for the stability of either the PIIS or the Thwaites Ice Tongue in coming decades.

C53C-1361 - Direct and indirect impacts of basal channels on ice-shelf stability

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/509049

Abstract
Basal channels are frequently found beneath the shear margins of fast-flowing ice shelves, where thinning due to channel formation likely contributes to reduced buttressing and decreased ice-shelf stability. Basal channels are also commonly found in the middle of ice shelves, particularly in areas where warm water is present. In either case, indirect effects on ice-shelf stability related to changes in buttressing and controls on basal melt rates are combined with direct effects, as stresses imparted by basal channels cause fractures, which may initiate calving events. We show that fractures form in association with basal channels on ice shelves throughout Antarctica, both at shear margins and at mid-shelf channels. Upstream channel growth is associated with channel deepening and the upstream propagation of channel-associated fractures on the Getz Ice Shelf. Because basal channels are widespread on Antarctic ice shelves, it is important to ascertain the balance of direct and indirect basal channel influences on ice-shelf stability and the capacity for basal channel change under evolving oceanic conditions.

PS: I find the posts offered recently in this thread to be helpful in better understanding just how rapidly the PIIS is currently being destabilized.
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blumenkraft

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Re: PIG has calved
« Reply #1826 on: February 17, 2020, 11:13:48 AM »
Thanks a lot, AbruptSLR!

Here a future iceberg at the calving front on its way to becoming an iceberg.

(Click to play)
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paolo

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Re: PIG has calved
« Reply #1827 on: February 17, 2020, 11:55:54 AM »
Blumenkraft,
If I understood well what you refer to, then you are mistaken, it is necessary to be careful when you compare images with different orbits (here I use the coherent image of 05/02)

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Re: PIG has calved
« Reply #1828 on: February 17, 2020, 12:28:46 PM »
You got me again with the different orbits, Paolo. One fine day i will get it, i swear. ;)
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baking

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Re: PIG has calved
« Reply #1829 on: February 20, 2020, 03:11:43 PM »
Surprising how uneven the height of the ice is at the new front.

https://twitter.com/houston_wellner/status/1230295550152597504

baking

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Re: PIG has calved
« Reply #1830 on: February 20, 2020, 03:19:05 PM »

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Re: PIG has calved
« Reply #1831 on: February 20, 2020, 06:40:42 PM »
Amazing photos!

Quote
Great shot. How high are those ice cliffs?
Quote
Difficult to measure from a distance of about 500m, which is as near as we're going. However, in places we see the bottom of the ice face at about 400 m depth in water column sonar data. Based on a freeboard calculation this implies a cliff height of around 50 m.

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Re: PIG has calved
« Reply #1832 on: February 20, 2020, 07:15:47 PM »
After reading this message on one of the photos:-
"There has been a trend in thinning of the ice shelf by several m/or for at least 3 decades, but the overall position of the calving front didn't change much. With each of the 4 calving events since 2015 though the front has stepped back. It seems to be a new trend."
Robert Larter    @rdlarter

I wonder if the calving face is tending towards a constant height or just a thinning (or warming) retreat??

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Re: PIG has calved
« Reply #1833 on: February 20, 2020, 07:29:18 PM »
I presume I'm seeing snow or broken up ice crystals blowing off the shelf (and not ship exhaust from an unseen boat around the corner).  I wonder what portion of snow gets blown into the sea, or how far from the coast is it where snow does not get blown, ultimately, out to sea [within a year] (and in the Arctic, what portion gets blown into leads).
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Re: PIG has calved
« Reply #1834 on: February 20, 2020, 08:41:50 PM »
I presume I'm seeing snow or broken up ice crystals blowing off the shelf (and not ship exhaust from an unseen boat around the corner).  I wonder what portion of snow gets blown into the sea, or how far from the coast is it where snow does not get blown, ultimately, out to sea [within a year] (and in the Arctic, what portion gets blown into leads).
It snows a lot in Antarctica.  A lot.  Whatever blows off the ice into the sea is probably inconsequential.

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Re: PIG has calved
« Reply #1835 on: February 21, 2020, 02:33:45 PM »
Sentinel2 very little hope of a decent picture.
Sentinel1 low resolution and rather nebulous, but we'll do with it: I'm attaching two zoom on the possible extensions of the old rifts: R1 and R3.

and thanks Baking for the pictures

EDIT: North of the extension of the old rift R1 there are old NEIS fractures.
Added less zoomed but wider image


Click twice to zoom in the second and third image
« Last Edit: February 21, 2020, 02:53:47 PM by paolo »

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An uncharted island in Pine Island Bay
« Reply #1836 on: February 21, 2020, 11:49:18 PM »
An uncharted island in Pine Island Bay has recently been discovered:

https://www.nature.com/articles/d41586-020-00489-4



Quote
A scientific expedition off the coast of Antarctica earlier this month spotted an island that appears on no maps — a finding that demonstrates how quickly the continent is changing as a result of climate change.

“I think I see rocks,” shouted an officer aboard the RV Nathaniel B. Palmer as the ship passed through Pine Island Bay, Antarctica. After consulting their charts, the crew realized they were looking at a brand-new island.
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baking

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Re: An uncharted island in Pine Island Bay
« Reply #1837 on: February 22, 2020, 12:10:46 AM »
An uncharted island in Pine Island Bay has recently been discovered:
This was the area.  I think I count three.

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Re: PIG has calved
« Reply #1838 on: February 22, 2020, 06:02:49 AM »
Robert Larter (@rdlarter) Tweets:
"The northern edge of the Pine Island Glacier ice shelf front is just about clinging on to the shallow water around Evans Knoll. When a future calving event causes it to lose contact here I think the northern part of the ice shelf front may step back more rapidly."

https://twitter.com/rdlarter/status/1231003758500499456

This is what I've been saying, although I don't think it will be the next calving event, but it will probably be the second big one.  The glacier advances (pushes the front forward) pretty rapidly and the next calving event will probably be another lopsided one with the Southern margin retreating more than the Northern, but after that watch out.

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Re: PIG has calved
« Reply #1839 on: February 22, 2020, 06:03:50 AM »
So, is this the reason PIG has taken so much time for calving? I mean, those islands might have acted as pinning points?
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paolo

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Re: PIG has calved
« Reply #1840 on: February 22, 2020, 09:49:07 AM »
Blumenkraft,
The island discovered is not in front of the calving line of the PIIS, no action on it.
It is when the MIS reached the NIS, that there were rumple ices (under water therefore) in front of the NIS.
Currently the only ice rumples are below the western part of the SWT, and the temporary blocking action on the small icebergs detached from the SWT in the past months has been seen.
The problem is that your time is not glacier time...  ;)
Even if I was a bit lucky, the fact that I had planned early February as my final calving date should tell you something.

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Re: PIG has calved
« Reply #1841 on: February 22, 2020, 10:30:21 AM »
The island discovered is not in front of the calving line of the PIIS, no action on it.

Oh, thanks for the clarification, Paolo. I misunderstood.
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paolo

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Re: PIG has calved
« Reply #1842 on: February 22, 2020, 10:33:33 AM »
Baking,
I agree with you that it won't be with the next calving.
- Even though the effects of the calving are not over and more small calvings will take place in the north, the current line is not stabilized,
- and even if the advance of the MIS will destabilize and fracture subsequently the final part of the NEIS,
I don't think for the moment that the narrow band of NEIS supported by the ice rises "Evens Knoll" will be completely disintegrated at the next big calving.
What is clear is that the narrow band of the NEIS, which is composed of :
- the ice of the NEIS further upstream driven by the MIS.
- and almost static ice from the "Evens Knoll" ice rises,
will not be regenerated: once lost, it is lost forever.
In addition, the upstream portion of the NEIS will not be able to effectively slow down the calving line retreat and there is already a detachment between the NEIS and the MIS at the eastern end of the NEIS.

PS: I remind you that NEIS denotes the part of the NIS still in contact with the MIS (the one upstream of the ice rises "Evens Knoll").

EDIT: But in any case nothing can stop the 40 km retreat from the calving line and the only reasonable question is when

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« Last Edit: February 22, 2020, 10:42:39 AM by paolo »

baking

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Re: PIG has calved
« Reply #1843 on: February 22, 2020, 04:45:54 PM »
Nice clear high definition images today of the Southern Shear Margin (AKA "The Zone of Destruction.")  Here is a 6-day GIF post-calving showing that the glacier marches on and is bringing most of the melange with it.  Cork II and it's crew of helpers look very fragile.

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Re: PIG has calved
« Reply #1844 on: February 22, 2020, 05:08:49 PM »
Wow! Marching indeed...  :o
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Tor Bejnar

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Re: PIG has calved
« Reply #1845 on: February 22, 2020, 06:27:03 PM »
Now, why did "We are marching to Pretoria" come to mind?
At least I have the 'right' hemisphere!  :-\
edit: fixed link

« Last Edit: February 22, 2020, 07:19:13 PM by Tor Bejnar »
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blumenkraft

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Re: PIG has calved
« Reply #1846 on: February 22, 2020, 06:46:01 PM »
Tor, why would you give me such an earworm. Now my brain is marching to Pretoria...

 ;D
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Re: PIG has calved
« Reply #1847 on: February 22, 2020, 07:14:17 PM »
Thank you baking for that animation. Indeed, Cork II and the remnants of Cork look very weak and tired. One-two weeks further and they will break off the SIS??
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Re: PIG has calved
« Reply #1848 on: February 22, 2020, 07:29:30 PM »
Today's microcalving from another perspective.
You see the outwash of ice mélange close to Cork II (circled in blue) from EOSDIS.
In addition I circled in yellow the iceberg derived from the latest SWT calving, located close to the ice rise at the northern tip of SWT. It looks like it is grounded - all other icebergs from the big calving have already left the scenery.

Btw - "Cork tracking" will be very difficult. I have tried to, but to do this I need clear Sentinel pictures. When I find him, I will dedicate him a posting in the iceberg thread.

Does anyone know whether SWT's ice is thicker than PIIS-MIS' ice, so it can more easily ground in shallow waters?

See attached picture
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Re: PIG has calved
« Reply #1849 on: February 22, 2020, 08:00:48 PM »
"Cork tracking" will be very difficult

Nah, no problem with EO-Browser. :)

It's grounded ATM.
« Last Edit: February 22, 2020, 08:12:24 PM by blumenkraft »
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