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Author Topic: Pine Island Glacier (PIG) Calving and Discussion  (Read 441928 times)

blumenkraft

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2350 on: June 18, 2020, 12:59:45 PM »
Paolo, can you please also promise that the PIG will recover from now on? Perhaps it will work.  ;) ;)

Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2351 on: June 18, 2020, 05:28:56 PM »
How long will this permanent micro calving on both shear margins go on? At which place will there be a calving front which is supposed to be stable for years?
A recovery of PIIS is urgently needed but this wish will remain unheard of...
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baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2352 on: June 18, 2020, 08:11:07 PM »
How long will this permanent micro calving on both shear margins go on? At which place will there be a calving front which is supposed to be stable for years?
A recovery of PIIS is urgently needed but this wish will remain unheard of...
We are almost there, but I can't promise you years.  Maybe 18 months, depending.  But could be longer.  Here are predictions I made in May, March, and November:

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2353 on: June 18, 2020, 09:54:52 PM »
Stephan;
Even if we have to study all the elements from almost the grounding line and there is a lot of things to deepen (which I have started) we can still provide a first evaluation:
In the image (Sentinel1 of 16) in yellow are indicated the ice rumples and in green the tributaries...
The current moment of instability should last at least two years with a consolidation of a temporary resistance line where I placed the orange line with subsequent advances and successive calvings at that level. The SW-ZD will have disappeared and the point of resistance to the South will be given by the tributary.
But this is only temporary, the two pinning points given by the ice rise Evan's Knoll and the main SIS tributary not being able to provide solid support to the PIG.
This is the optimistic hypothesis, in the pessimistic hypothesis already in two years these two pinning points will start to crumble.
In any case in a few years, not many, will begin the retreat towards the red line.

Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2354 on: June 18, 2020, 10:49:47 PM »
The orange line would represent the most upstream calving front that PIIS has had since it was discovered. It would be bad. The red line is much much worse. I wonder which consequences a calving front of that position would have on the thickness, the flow speed further upstream and the stability (the evolution of new "zones of destructions" at the shear margins) would have on the ice shelf. And, beyond that, this destabilisation must have consequences for the position of the grounding line. [PS: Are there any plans for an update of the grounding line positions after the calvings 2017, 2018 and 2020? I think this would be very important]
Finally, SIS, SWT and the smaller NE-IS are also affected, because they would be exposed to open waters for many months of the year.

So I hope that you are wrong (but I don't think so).

What I'd like to see is a recovery, not a further retreat of PIIS.  >:(
It is too late just to be concerned about Climate Change

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2355 on: June 18, 2020, 10:52:37 PM »
Just a short question. Did anybody have a look after Cork? Is he still grounded between PIIS and Thwaites? Or have we lost this hero?
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baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2356 on: June 19, 2020, 12:38:24 AM »
I think we can at least say a bit more, or at least speculate, on the factors that will eventually cause the failure of what is shaping up to be the new stable calving front.  I think it makes sense to look at the strengths and vulnerabilities of each side independently.  Obviously the failure of one side will affect the other, so the weakest link in the chain will determine the stability of the whole. Or at least on this first approximation.

In the South, the "T11" tributary has proven to be a strong force shaping the shear margin.  It has held its own against the heavy upstream rifting.  The question is how long will this continue.

The downstream margin will certainly not last more than a few months and we can expect to see water lapping at the end of T11 by the Southern hemisphere Spring at the latest.  However, I am not seeing a long-term impact from this, but of course I may be wrong about it.

More important may be the strength of the Southern Ice Shelf in supporting T11.  The older, thinner parts of the shelf have been calving but that doesn't mean the bulk of the shelf won't still remain stable.  Of course the interaction with SWT will play a factor, but on the whole I expect it to have a positive effect in keeping the SIS in place.

Of course, it could also be some combination of the upstream rifting, the open water, and the loss of the SIS that does in the T11 pinning point.  Or it could be some other unforeseen factor, but I see the Southern Ice Shelf as the biggest determinant in the South right now.

In the North I see two major concerns.  One is the Shear Margin Rift that could work there way downstream.  There is some thinking that those rifts are being compressed and reabsorbed which might explain why they haven't progressed further downstream.  Or the newer rifts are just larger than rifts from previous years.  An increase in the velocity of PIG should make the shear margin rifting worse.  In any case, it should take at least a few years for these rifts to affect the Evan's Knoll pinning point.

The second concern is the shrinking grounding line around Evan's Knoll and the possibility that the margin may come completely disconnected from the Knoll.  There was research on the grounding line done with radar from sleds on the ice this past season and it may be a while before we see the  published data, but the researchers did tweet about their concerns.  This may show up as either the calving line never stabilizing near Evan's Knoll or perhaps a retreat after it has stabilized.  I currently see this as the biggest concern for PIG as a whole.

Others have mentioned the stability of the smaller triangular ice shelf to the Northeast.  I don't see any particular reason to worry about it myself.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2357 on: June 19, 2020, 01:19:41 AM »
This is the tweet I mentioned in the previous post:

https://twitter.com/geologicalJo/status/1205753120430710784

"Waited for a plane that never came today - currently shrouded in mist. Here's a pic from yesterday when John+Ash got lots of radar data suggesting a new grounding line exists around Evans Knoll. Very excited to be first to see results - john was pretty excited too!"

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2358 on: June 19, 2020, 04:40:48 PM »
I made another month-long GIF of the Point2-Cork3 interaction this time based on the series ending June 16 for a slightly different view.  (Motion is still relative to Point 2.)

My impression is that there is still a rather tenuous connection between from Point 2 through the broken end of Cork 3 to the "Almond" and the SIS.  It may be assisted by the triangular iceberg between Point 2 and Cork 3 I am calling the "Wedge" for now.

I think that the forces acting on them will cause this link to fail with the most likely result being that the end of Cork 3 will come lose along with the Almond, although Point 2 could give way first.

If Point 2 does not calve first, it could maintain contact on the remains of Cork 3 through the Wedge which would continue the pressure on Point 2 leading to its eventual calving.
« Last Edit: June 19, 2020, 04:50:32 PM by baking »

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2359 on: June 19, 2020, 06:28:37 PM »
Here is a GIF of Sentinel-2 visible light images from the last season (Sept. 2019 to March 2020) showing Cork 3 on the left and Point 2 moving right to left at the top.  You can see a prominence on Point 2 as it approaches and is about to meet with an attachment on Cork 3 that is to become the "Wedge."

I think this helps to explain both why the gap between Point 2 and Cork 3 downstream of the contact point is not significant and why the Wedge may play a important role since it may be still attached to the end or Cork 3.  In fact, the Wedge should probably be considered to be a part of Cork 3 until it becomes visibly separated.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2360 on: June 19, 2020, 07:09:53 PM »
The important area is where icebergs are piled up between the SIS and the PIG. It is these piles that can create, especially as a result of their rotation induced by the movement of the PIG, significant shear forces on the PIG itself, forces that have already caused damage and will, alas, do more damage. It is the rifts created by these forces that must follow.
No images today, for this reason I use the image of the 16th (that of the 18th being incomplete).

EDIT: Once there is no more material to build these destructive piles, the turbulent period we are living through will be over and the situation will move towards more stability.

EDIT2: I add a small diagram about destructive piles
« Last Edit: June 19, 2020, 07:42:38 PM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2361 on: June 19, 2020, 11:47:12 PM »
Below is a 6-month GIF of the "Cork 4"/"Point 3"/and upstream melange area of the Southern Shear Margin of high resolution visual light Sentinel-2 images from September 14 to March 2.  Next is a GIF of the last three months of Sentinel-1 radar images of the same area with all motion relative to Point 3.

Finally is a detailed Sentinel-2 image breaking down of what I see.  I have circled in green what I think are paolo's "destructive piles" so you can see that we are talking about the same area.

The main feature I see is an attachment to Cork 4 that curls around like a scorpion's tail.  The question then becomes will icebergs 1 and 2 remain attached to Cork 4 through the tail while being pushed on from Icebergs 3, 4A, and 4B, and will they provide enough resistance to cause a rift above Point 3.  I think that due to the large number of rifts already created, it is unlikely that the tail will remain attached and provide any meaningful resistance.

But even unattached icebergs can clump together and provide some strength.  I think the most likely way for paolo's "pile" theory to work is shown in the orange arrows. It is possible that there is already some resistance here as shown by the large number of rifts created, but it is does not seem likely that it will hold up after all the rifting.

Lastly, the biggest problem is that icebergs will soon be able to escape to open water as shown by the blue arrow.

(Click the first GIF to play and the last image to see in full resolution.)

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2362 on: June 20, 2020, 12:48:18 AM »
1) The "destructive piles" have already done damage during the calving: opening and extension of R2 and R3 and opening of mR1 and mR2 and after the calving: opening cR1, extension mR1 and calving P1.
2) Currently the conditions for this type of destructive action are weaker, but they still exist. P2 is doomed, but we could see calving induced by cR1 and mR2 in the next few months (say late summer, autumn) and, in the more pessimistic hypothesis at the opening of a new rift upstream of mR2.
3) In general, this corresponds to a very particular situation, which has come to be created, and which, this autumn, we did not see (myself included), since we were looking elsewhere.
4) In general, for me it has been a call to order : from time to time, we must look at what is really going on, forgetting all previous hypotheses and ask ourselves if we have not forgotten something and if we are not blind to what reality is trying to show us.  I could invite others to do the same, but this is not my concern.
« Last Edit: June 20, 2020, 01:00:50 AM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2363 on: June 20, 2020, 01:16:14 PM »
The basic difference is that I see those icebergs getting caught between the Southern Ice Sheet and the moving PIG and creating and expanding rifts upstream while you seem to see them affecting rifts downstream which makes no sense to me.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2364 on: June 20, 2020, 02:07:03 PM »
1) The rifts open immediately downstream of the point of application of the shear forces, between the hold-back part and the part that is now free (no more shear downstream) (see diagram in the previous post).
2) There is still high shear on P3, hence the possibility of mR2 expansion. As for cR1 it is now open and its life is now independent of the SSM
3) The possible opening of a rift upstream of mR2 (my pessimistic hypothesis), caused by the disappearance or weakening of the shear on P3 and by the creation of a shear further upstream (or its reinforcement if it already exists), is what you refer to in your diagrams. This possibility is quite possible, but not absolutely certain.
4) Beware of dated images, the evolutions are fast: in one month the situation can be very different, and of "confused" images of Sentinel1, which do not allow to appreciate the forces in action. On the contrary, pay close attention to any changes in the rifts of the PIG, it is these changes that will alert us and inform us about the force field that applies to the PIG.We can then search in the ZD for their origin and the analysis of the ZD, thus framed, becomes very useful.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2365 on: June 21, 2020, 04:31:46 PM »
Here is a 6-day GIF of today's high resolution Sentinel-1 radar images of the Southern Shear Margin.  This one shows absolute motion so you can see just how much the melange is holding back the Pine Island Glacier.  Hint: Not so much.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2366 on: June 21, 2020, 05:29:43 PM »
I had already prepared an animation on the SSM (always 6 days), it is mainly dedicated to the monitoring of rifts. So I decided to post it.
Nothing exceptional, but the two rifts cR1 and mR1 are progressing. To highlight it I needed to use zoomed images and to view it it is therefore necessary to click (I apologize).
EDIT : and click twice for full resolution

Regarding the sentence of the previous post: "This one shows absolute motion so you can see just how much the mélange is holding back the Pine Island Glacier.  Hint: Not so much", I don't know if it should be considered seriously, as if the shear should slow down the PIG, or even stop it.

The shear exerts a force on the PIG creating stresses in the PIG itself, but it doesn't slow it down in a detectable way.
« Last Edit: June 21, 2020, 05:36:13 PM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2367 on: June 21, 2020, 06:20:37 PM »
The shear exerts a force on the PIG creating stresses in the PIG itself, but it doesn't slow it down in a detectable way.
Then how does one detect it?

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2368 on: June 21, 2020, 06:29:45 PM »
But don't forget the NSM: mini-calving ...
Animation 6 days, the black line that crosses the images is due to the fact that the front is straddling two images and I had to re-paste the corresponding images.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2369 on: June 21, 2020, 06:40:10 PM »
Then how does one detect it?

The creation and evolution of marginal rifts...

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2370 on: June 21, 2020, 07:58:25 PM »
Then how does one detect it?
The creation and evolution of marginal rifts...
It still sounds like a circular argument to me.

Looks, it's all very simple.  My theory (shown in the red arrows below) is that the icebergs in the margin occasionally exert a lateral force on the glacier causing an upstream marginal rift.  We have evidence of Cork 3 being pinned both against the SIS and the PIG and rotating to extend its length  and forcing the two apart.  You can see both the Point and Point 2 moving to the North in the weeks before the calving of the Point in the GIF from Reply #2361.

Your theory seems to be the traditional creation of marginal rifts downstream of a pinning point, where the marginal ice upstream is held back and the downstream ice moves forward with the rest of the glacier (shown in blue.)  The theory is fine, except that you have no evidence for it.  The broken up ice in the melange is not showing any sign of slowing down to prevent the forward motion of the margin.  You can't just argue that the theory alone gives evidence for your pinning point.

oren

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2371 on: June 21, 2020, 08:21:07 PM »
I had already prepared an animation on the SSM (always 6 days), it is mainly dedicated to the monitoring of rifts. So I decided to post it.
Thanks. But why does it seem to be moving backwards? I am guessing it is locked on some feature which I was not able to identify. In any case, just wanted to say absolute motion animations are usually easier to digest and understand, at least for me.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2372 on: June 21, 2020, 08:36:27 PM »
Oren,
There was a small problem when aligning the images, I hadn't recorded and consequently the alignment of this animation, which should be on the PIG is not good.
I realized this a while after posting (when I closed the application used for image processing that asked me if I wanted to save  >:( ) and decided that it was too late to correct and that it wasn't too serious, the extensions remaining visible.  ;)

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2373 on: June 21, 2020, 09:42:18 PM »
Baking,
The stacks are constrained, by the configuration: the top attached to the PIG and the base attached to the SIS, to straighten and therefore to compress: more it is vertical (relative to the PIG) and more the distance between the base and the top is small.
If it is the last point of strong shear, then the game is done.

Concerning the fact of controlling in detail what happens in the ZD I notice that even with Sentinel2 is not a small matter, a small animation is not enough to show the force fields, in reality we risk to see what we want to see => demonstration value 0.
Indeed currently there are no more big blocks for which we can observe the deformations more easily: formation of the bulges, measure the shortening due to compression, deduce the direction of the compression, make precise diagrams of their possible movements and see the stresses and measure them, as we have done in some moments for the Cork. This is even more difficult with Sentinel1. As you can judge what happens between two blocks by looking at the white spot that separates it? And there are too few fractures to evaluate the forces in action.
It's like predicting the future by looking in the back of the coffee, it's a waste of time.

On the other hand, it might be interesting to see if an a posteriori analysis of what happened this winter, a real analysis, not two, three arrows drawn on a picture. It should be possible, but his request for time...

As regards cR1, this rift was born as an extension of mR1 beyond a point of resistance (a ridge), but, at least for me, and since the calving corresponding to the complete opening of mR1, it has become a central rift and it lives its life as a central rift under the constraints of a central rift. 

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2374 on: June 21, 2020, 10:33:34 PM »
Then how does one detect it?
The creation and evolution of marginal rifts...
It still sounds like a circular argument to me.

...

Essentially, you are requesting a model (numerical and/or physical) analysis beyond a PhD dissertation level analysis such as the linked document:

Title: "The Flow Dynamics and Buttressing of Ice Shelves" by MARTIN G. WEARING 2016

http://nora.nerc.ac.uk/id/eprint/515803/1/Martin%20Wearing%20-%20Thesis%20-%20Final%20Version.pdf

Extract: "PIG Ice Shelf The Pine Island Glacier (PIG) area is dominated by high along-flow strain rate. This can be seen in Figure 3.17c, where there is high strain rate both in the grounded ice stream and in the margins of the shelf. While the ice is grounded, high strain rates are found across the entire width of the ice stream, with particularly high along-flow strain rates at the grounding line. However, once the ice begins to float, these high strain rates are restricted to the margins of the shelf. This indicates that the flow in the grounded section is accelerating towards the coast, while there is relatively little extensional flow in the floating shelf. The margins of both the grounded and floating sections of the ice flow are areas of high shear rates, which can be seen in Figure 3.17d. Here high strain and shear rates would lead to low effective viscosity, which in turn would allow higher strain and shear rates to be achieved. In Figure 3.17d the colour scale is saturated at 0.05 yr−1 , which corresponds to a shear stress of 135 kPa for ice with a Glen’s Flow Law rheology and a rate factor appropriate for ice at 0◦C. This sits within the range of critical stresses (90-320 kPa) for crevassing as found in field measurements (Vaughan, 1993). When compared with the MODIS image in Figure 3.17a, it is clear that large areas of damage are present on PIG ice shelf.

From the experimental results, it is clear that properties in the margins of the shelf are crucial for determining the shelf flow dynamics and thickness profile. In the geophysical data it is apparent that the margins of ice shelves are often areas with high levels of deformation, with high values of shear and strain rate. These properties of the flow field are linked to the presence and formation of fractures and crevasses, which are observed in the MODIS data. Comparing these crevasse features in ice-shelf margins with the Principal Strain Rates and Axes indicates that the 1st Principal Strain Axes are aligned at 45◦ to the margin and correspond to positive 1st Principal Strain Rates angled towards the central section of the flow. These features are associated with negative 2nd Principal Strain Rates, with the 1st and 2nd Principal Strain Axes aligned at 90◦ . This is due to the shear flow between the stationary, grounded-ice or bedrock and the fast flowing ice shelf. These areas of damaged ice, in the shelf margins, with weak effective viscosity allow high levels of deformation to be achieved. The negative component of the Principal Strain Rates is indicative of shear flow and implies that these areas generate resistance to flow, thereby making a positive contribution to buttressing.

The important role that shear margins play was highlighted with an assessment of the flow speed at ice-shelf calving fronts. It was shown that for ice shelves with intact shear margins (with comparable rheology in the margins and the centre of the shelf) and that are laterally confined by pinning points at the calving front, then the flow at the centre of the calving front conforms to the scaling relationship u ∝ w(eH) 3/4 , proposed by Hindmarsh (2012). For those shelves with weak or damaged margins or those that are not laterally confined at the calving front, the flow speed at the calving front is greater. This is because they are subject to reduced resistance from the lateral boundaries."

Edit: I underlined the last two sentences of my extract from the Wearing (2016) dissertation as the bottom line is that damaged shear margins offer reduced resistance to the flow of ice in the ice shelf and thus the ice flows faster than it would if the shear margin was not damaged, but that there is still some small amount of resistance offered even by a confined ice mélange such as by the southern shear margin of the PIIS (Pine Island Ice Shelf).
« Last Edit: June 21, 2020, 11:19:22 PM by AbruptSLR »
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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2375 on: June 22, 2020, 02:47:03 AM »
Baking,
I had the images I used for the SSM front history, so I used them to make an absolute motion animation. There is no change in the trajectory of P2, no northward shift.
In your animation there was a problem with the alignment on P2 and one can easily understand the origin of the problem, there are no clearly identifiable and punctual points on P2.
It is therefore an artifact.

Animation with the images from 12/03 to 16/06, 12 days interval.
Click to animate.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2376 on: June 22, 2020, 02:57:25 AM »
I apologize for the volume of the previous animation, but I didn't want there to be any doubts... ;)

I attach here a reduced version for readers with network capacity problems.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2377 on: June 22, 2020, 10:33:53 AM »
I didn't want to waste time on something that was completely secondary, at least for me, but ...

In the attached picture I have marked in red the rotation point of the Cork3 and the almond.
As a consequence of the rotation of these two elements the distance between the two blue circles tends to increase. If the Cork3 remains attached to the almond it results in an effort of extension on the Cork3 on the interface Cork3/Almond and compression on the Almond.
This implies that the rift in Cork3 was caused by the fact that it remained attached to the tip of the Almond and did not slide southward along this interface (any sliding being very difficult because of the pressure induced by the PIG).  The Almand being compressed in both directions : East/West and North/South remained intact. For the rift in the SIS there are no problems, it is indeed the direct consequence of the pressure from the PIG.
The movement of the tip of the Cork3 is parallel to the movement of the PIG, or even begins to diverge.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2378 on: June 22, 2020, 02:20:08 PM »
Here is today's 6-day GIF of the SSM with all motion absolute (showing the clear NE movement of Point 2.)

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2379 on: June 22, 2020, 02:38:34 PM »
Sorry, what I'm seeing is movement in the same direction as the rest of the PIG.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2380 on: June 22, 2020, 03:42:07 PM »
Sorry, what I'm seeing is movement in the same direction as the rest of the PIG.
Which is my point.  You can't look at the absolute motion of a glacier moving Northeast and say you see no Northern movement.  You can only look at relative motion of one part of the glacier vs. another, which is what I did.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2381 on: June 22, 2020, 03:54:49 PM »
Sorry, like I said, that's what I did.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2382 on: June 22, 2020, 04:37:19 PM »
I add an animation all parts of the PIG walk as one man to the West-North-West

EDIT: Maybe you don't consider south side micro-calving...
« Last Edit: June 22, 2020, 04:44:37 PM by paolo »

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2383 on: June 27, 2020, 05:01:08 PM »
Today's 6-day high resolution GIF from Sentinel-1 radar images of the Southern Shear Margin.  All motion is absolute.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2384 on: June 27, 2020, 05:52:53 PM »
BTW, Stephan, Cork I is still at the same spot grounded. No movement.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2385 on: June 28, 2020, 08:20:37 AM »
Thank you for looking after Cork.  :)
It is too late just to be concerned about Climate Change

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2386 on: June 28, 2020, 09:05:33 AM »
Sure thing. :)

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2387 on: June 28, 2020, 03:40:41 PM »
I think a calving in the east is imminent.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2388 on: June 28, 2020, 04:02:45 PM »
I think a calving in the east is imminent.
North?

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2389 on: June 28, 2020, 04:21:30 PM »
This rift is a remnant of the great calving.
It is to be followed (and I follow it), but and it moves very slowly, very slowly .
See the animation based on two images with an interval of 48 days
I highly doubt that a calving is imminent, even though the PIG may surprise us...
Moreover I think the most likely extension is in the direction of the already existing rift at the NSM.

click to animate

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2390 on: June 28, 2020, 04:34:03 PM »
While watching my animation of the previous post I just noticed a strange and very interesting fact: a deformation of the PIG with an increase of the distance between the two tips of the future iceberg:
Indeed the animation is centered on the northern tip and the southern tip is moving away (I have already rechecked the enlargement of two Sentinel1 images is strictly the same and they are clearly coherent)

EDIT: I've just done a test again starting directly from PolarView images with two direct extractions with GIMP and there's nothing to do, there's a relative movement.
This is something to dig into...
« Last Edit: June 28, 2020, 05:06:27 PM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2391 on: June 28, 2020, 05:32:04 PM »
The most significant thing I'm seeing in the North is the increasing marginal rifts just upstream from the front.  This long-term GIF seems to show that the PIG is slowly pulling away from Evan's Knoll.  This might also explain the explain the expansion along the front as the compression against the Northern margin is eased.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2392 on: June 28, 2020, 06:01:25 PM »
1) Movements in my animation :
I have just measured the two extremities of the future iceberg with GIMP and I see that the distance between them is not modified, and what changes is the angle which passes from 18.20° to 18.46°.
So this is not a deformation, but a rotation induced by the speed differential already observed when moving along the front from North to South.

2) NSM: the NE-IS, under the shearing action of the PIG, is deepening, as already documented in my previous posts. It's progressive, calving downstream creating fractures further upstream (there is no more protection by the ice shelf downstream). The positive side being that even if calvings are moving upstream, they are slowly moving away from the Ice Rise Even's Knoll, which could lead to a slowing down or even a temporary stabilization.
As for the calving announced by BK, he will intervene, but most probably in a few months, and it seems to me secondary in relation to the stability of the PIG.
« Last Edit: June 28, 2020, 06:08:22 PM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2393 on: June 28, 2020, 06:44:27 PM »
If you set motion to the fixed end I think it becomes clear that the only movement you are seeing is some flexing at the margin.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2394 on: June 28, 2020, 08:11:35 PM »
Baking,
When we have find a problem and we want to verify and quantify it, the best is to start from the images provided by PolarView without transformations and use the "Measure" function of Gimp, which gives the distance between two points as well as the direction of the segment, and the only possible errors are the determination of the two points and they are minimal!

I used the two inner vertexs, further East, each well marked by a rift.
Indeed I considered as more stable, relative to the external vertex (more to the West), which in 48 days can more easily undergo micro calvings.

The response of the measurements on both images is immediate and clear:

> the distance between these two points remains unchanged and I have found exactly the same value, not even to the nearest pixel! (Lucky chance)
 > there is a clockwise rotational movement of 0.26° (in 48 days), which can be explained by a speed differential: proceeding along the front from North to South east to west there is an increase in the PIG speed.

Animations are useful to visualize problems (and discover them, as in this case), but are not a measure!
« Last Edit: June 28, 2020, 10:28:29 PM by paolo »

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2395 on: June 28, 2020, 10:12:45 PM »
> there is a clockwise rotational movement of 0.26° (in 48 days), which can be explained by a speed differential: proceeding along the front from east to west there is an increase in the PIG speed.
North to South?  Looks to me like the center of the PIG is moving faster than the Northern Margin.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2396 on: June 28, 2020, 10:29:13 PM »
My apologies and thank you, I just corrected my post.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2397 on: July 03, 2020, 06:58:05 PM »
Today's 6-day GIF of high-resolution Sentinel-1 radar images of the Southern Shear Margin.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2398 on: July 03, 2020, 11:02:04 PM »
Monitoring of PIG rifts :
Attached two animations related to the PIG rifts: North side and South side, with images from 21/06, 27/06 and 03/07.
These last 12 days no news and no clear modifications. Moreover the rendering of the images is not identical which does not facilitate the analysis of the possible modifications.
All these rifts are currently not very active and evolve very slowly.
But we know that they can suddenly accelerate, so follow them carefully.
On the ZD side in the animation of Baking we can note:
> that the fine is being expelled, after which the Cork3 debacle will follow.
> that the icebergs upstream are packing up against the Cork4 preparing for the possible new stress point.

EDIT: My apologies, corrected the second animation (the images of the 21st and 27th were in reverse order)
« Last Edit: July 03, 2020, 11:11:09 PM by paolo »

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2399 on: July 04, 2020, 01:40:05 PM »
Mini-calving at the NSM.
For the animation, not having the image of the 28/06, I used the image of the 29/06, the two orbits are thus not identical.