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Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2600 on: November 22, 2020, 04:23:57 PM »
paolo's postings (thank you - very well done as always) inspired me to introduce Triangle (see attached picture) in the Southern Shear Damage Zone, roughly 3 km long and up to 1 km wide.

In my opinion it is the first time that such a big rift appeared in the SIS so far upstream. The resulting iceberg (Triangle) is probably the biggest feature since Cork and Cork II. Triangle is attached to the SIS (the ice bridge is approx. 300 m) on its western side. It is also connected upstream by a bridge of ca. 400 m width. As the flow speeds are larger at the upstream end than at the Western SIS end the rift between Triangle and SIS will become larger. Probably Triangle will get more and more influenced by the much larger WNW flow of PIIS-MIS, and start to rotate counterclockwise. Therefore I expect a breakup of the upstream bridge before a breakup of the Western ice bridge.

The green arrows show the flow direction, the length of the arrows symbolizes the flow speed.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2601 on: November 22, 2020, 04:43:18 PM »
I think it was interesting to see (and follow) the behaviour of the last point of contact between the PIG and the SIS. Its resistance will determine the progress upstream of the damage zone.
Animation based on the images of 11/11 and 21/11

Click to animate

Not going to be able to hang on much longer, me thinks.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2602 on: November 23, 2020, 01:55:31 AM »
The sdmz has so little holding it together and goes so far upstream. I expect several major calvings this southern hemisphere summer/fall.

AbruptSLR

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2603 on: November 23, 2020, 05:25:23 PM »
The linked Peter Sinclair video, and the associated Yale Climate Connections article focuses on Thwaites Glacier, but I post these links here because the video contains very nice sequences of the damage to the PIIS southern shear zone in recent years, which is a positive feedback for further degradation of both the PIIS and the SWT ice shelf.

Scientists: Climate Action Can Slow Antarctica’s Ice Loss - YouTube

Title: "Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions?"

Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions? » Yale Climate Connections

Extract: "Let’s face it: Thwaites has the makings of being the lead role in an upcoming cli-fi thriller, one strong on emotion and drama but lacking something when it comes to hard science."

Edit: As my Youtube links do not seem to work, the same video can be seen at the following link.

https://skepticalscience.com//shearing-thwaites-slow-or-stop.html

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oren

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2604 on: November 24, 2020, 05:27:00 PM »
I think this is the video in question.


paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2605 on: November 27, 2020, 12:04:24 AM »
In this post :

> The update of the animation of the history of the front line on the North side. It is the same format as last time, I limited myself to add the front line on 05/02, therefore before the big calving in February.

> An animation relating to the future iceberg in the north using one image every 48 days from 24/03 to 19/11. It can be seen that the situation is changing, even if slowly. In particular the central rift, named B in the last image of the animation, has widened significantly and there have been small extensions of rifts A (to the north) and B which are now slightly closer together. Rift C (in the south) has not changed. This iceberg will surely calve, but you have to be patient.

> A commented image relating to the evolution of the rifts in the NDDZ (North Downstream Damage Zone). The speed of the NEIS varies from a speed close to the PIG at NSM to 0 near the Ice Rise Evan's Knoll (grounding line). Now that the downstream NEIS is no longer under pressure from the PIG, the NEIS has likely accelerated and there has been a shift in the velocity gradient towards the Ice Rise and, as a result, a partial shift of the stress (PIG/NEIS) from the NSM to the grounding line on the Ice Rise Even's Knoll side. This should lead to a widening of the DZ

> The update of the animation of the history of the front line on the South side, in which I have integrated the front line on 05/02/2020.

Other history of the front line will follow (SWT,NIS)

Click to animate and enlarge.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2606 on: November 27, 2020, 09:08:16 PM »
Today I'm going to post :

> an animation related to the SWT front line history, same characteristics as the PIG front line history posted yesterday

> The last image of this animation to which I added comments on the foreseeable future for SWT in the coming years

> an animation related to the Ice Rise front line west of the SWT (and east of the Thwaites Glaciers). In this case I used images from 25/11/2019, 17/02/2020, 11/05/2020, 15/08/2020 and 07/11/2020, since changes in this area are much slower. The interval between images is therefore 84 days (except between 11/05 and 15/08 which is 96 days because of the missing image of 03/08).
We can notice :
>> that the movements of the front in this sector are concentrated in the period of the southern summer and autumn (between the image of 25/11/2019 and the image of 11/05/2020) and are practically absent in the following period (between the image of 11/05/2019 and the image of 07/11/2020)
>> that there are small tributaries with small advances and small retreats following calving, and that the front line has been stable during this year.
The stability of this Ice Rise, whose bottom is below sea level (except for a promontory to the west), and which is the left flank of the SWT, is important for the evolution of the SWT, whose health is declining : one can indeed foresee an increase in its speed and thus its thinning and the retreat of its grounding line which is not far from a more or less flat bed and frankly retrograde further west by rapidly descending to less than - 1000m (and I recall that the CDW has no problem to penetrate below the SWT, the bottom of the SWT being always less than -700m).  So it is to be followed, even if very spaced controls are enough. It will be necessary to follow especially the pinning points, in fact once lost there is a more pronounced retreat.
Be careful, this image is very long : 500 x 2000.

Click to animate and to enlarge the images.

Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2607 on: November 27, 2020, 09:20:16 PM »
Thank you paolo for these very valuable gifs. And please keep up this good work.  :)
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paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2608 on: November 29, 2020, 05:55:30 PM »
I'm finishing the posts related to the history of the front line with the NIS.
There are two animations, one for the eastern part of the NIS and one for the western part (the northern part of the NIS, not covered by this post will be processed later).
As for the SWT Ice Rise I use images with an interval of 84 days, from 25/11/2019 to 07/11/2020.

You will notice :

> that also in this case the movements take place mostly during the southern summer (between the image of 25/11/2019 and the image of 11/05/2020) and are very limited during the winter (between the image of 11/05/2019 and the image of 07/11/2020)

> Eastern NIS front: there were calvings only towards the NMS (top right) and in the center (recent calving), the pinning point (bottom of the picture) clearly remained stable and the rest of the front advanced. We can thus consider this part, where the Larter Glacier is flowing and part of the Lucchitta Glacier is rather stable for the moment.

> Western Front: Here there have been important calvings, the NIS is losing support on the pinning point at the bottom of the image and the Domage Zones to the North (on the left in the image) are extending towards the sea. In the near future we can foresee a sharp retreat of the front with loss of contact with the northern part of the NIS (bottom left corner) which would remain anchored to its pinning points waiting to melt and detach towards the sea.

I added the commented image of the NIS that I had posted a year ago (I limited myself to adding the names of the two NIS glaciers)

Click to animate and enlarge images

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2609 on: December 01, 2020, 11:38:51 PM »
Today's Sentinel2 image is good, even if it is not perfect like the one of 11/21.
It allows me to present you two animations:
> the first one is related to the SIS being shredded by the SWT
> the second one is relative to the NdD and, more precisely, to its right flank which is cracking more and more.

Click to animate

1rover1

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2610 on: December 02, 2020, 07:16:37 AM »
I'm mostly a longtime lurker here, but I must say the detailed analysis here is greatly helping my understanding of the dynamic forces at play.  It is apparent to me that as the main PIG has retreated, there is therefore less lateral or constraining forces on the adjacent ice sheets.   The lack of constraint combined with the difference in flow speed between adjacent ice streams is now causing them to  tear each other apart, thereby compounding the whole issue.  I'm sure this was obvious to others, but the clarity provided in the recent animations in how these mechanisms are working is fascinating, and somewhat terrifying.  Thank you everyone for the good work and intelligent conversation in here.   

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2611 on: December 06, 2020, 03:25:19 PM »
This 6-day GIF of the Southern Ice Shelf shows a pretty rapid expansion of the middle rift.

grixm

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2612 on: December 07, 2020, 06:44:12 PM »
Some debris discharge at the north side.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2613 on: December 12, 2020, 09:10:30 PM »
SIS rifts update:

All rifts widen and WmR3 and WmR4 expand, WmR4 ending in a family of parallel rifts and the WmR3 is reconnecting to these rifts.

For the animation I use the Sentinel1 images from 30/11 and 12/12

Click to animate and zoom

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2614 on: December 13, 2020, 07:33:16 PM »
It is with delay, but the Sentinel2 images of the 11th finally arrived and they are of quality!
Apart from the NSM and the "SIS rifts" there were no big changes, so I post only the animations related to these 2 points

Click to animate

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2615 on: December 18, 2020, 04:23:15 PM »
Today's 6-day GIF of the rifts on the Southern Ice Shelf.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2616 on: December 24, 2020, 05:51:25 PM »
Today's 6-day GIF of the widening rifts in the Southern Ice Shelf.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2617 on: December 25, 2020, 07:56:30 PM »
A calving in the north.

And a new crack in the south seems to have reached all across to the sea. A calving may be imminent.

baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2618 on: December 25, 2020, 08:15:35 PM »
There has been a lot posted here about the Southern Ice Shelf, so I thought I would review recent developments and the implications for Pine Island Glacier.

First is a 30-day GIF of the developing rifts on the Southern Ice Shelf.  Movement has been pretty much continuous, so it would appear that a significant calving is becoming imminent.

The Southern Ice Shelf (SIS) is being pushed from the West by the Southwest Tributary (SWT) and supports the "T11" Tributary as it is merges with the main trunk of the Pine Island Glacier (PIG.)  Ever since the PIG Ice Front retreated from its merger with the SWT, the SIS has been weakened by rifts and calving.  The danger is that the loss of SIS will weaken T11.  In particular, the current SIS rifts (red) could extend to the T11 (orange) leading to more calving at the end of T11 (yellow.)

Even a temporary retreat of T11 could lead to the upstream rifts in the Southern Shear Margin (SSM) spreading downstream and which could speed up and weaken the PIG.  Further retreat of the PIG ice front could result in a permanent disconnect between the PIG and T11 just as has occurred with the SWT.

This could also affect the Northern Shear Margin (NSM) if the loss of contact with T11 causes the NSM to pull further away from the stationary Evans Knoll grounding line.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2619 on: December 25, 2020, 10:34:34 PM »
Above all, a merry Christmas to all,

Not a lot of time at the moment, but I wanted to add some comments :

For the actual delimitation of T11 see the attached image

The progressive opening of the rifts, and more precisely of families of parallel rifts, as we can see better in the Sentinel2 images, shows not only the strong northward thrust printed on the SIS and T11 by the SWT, but also the resistance opposed, especially by T11, which gives precisely the extension of the rifts (of each rift) is very often done by opening the new parallel rifts.

This should quickly lead to important calvings that will cut T11 and thus eliminate any direct contact between T11 and the PIG.  Only the small unnamed tributary, east of T11, will remain to make the joint between T11 and the PIG. In addition, the ice mélange to the west of this tributary should gradually calve.

I don't see how this small tributary, even with the help of T1, can last for years, and in the years to come we will have to expect the extension east of DZ (Damage Zone) until it connects to the existing DZ upstream (SuDZ).
« Last Edit: December 25, 2020, 10:41:05 PM by paolo »

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2620 on: December 26, 2020, 05:02:01 AM »
Look at this video for the last six years of PIG:
https://movie-usa.glencoesoftware.com/video/10.1073/pnas.1912890117/video-1

I stand by my diagram since it shows the Eastern margin of T11 which is the part that joins with the main trunk of PIG and has the greatest effect on it.  Think of two multi-lane highways merging, where only the lanes closest to the other are the ones that have to do the merging.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2621 on: December 26, 2020, 12:09:54 PM »
I think the elevation map while out of date is helpful when looking at the southern margin. When looking at this map the current shelf edge is about where the Main ice shelf label is. The shelf edge currently is roughly perpendicular to the direction of ice flow. The protrusion left of the label is Evens Knoll. Given ice flows "downhill" the higher elevations flow towards the lower elevations. The shear margins are mostly light to dark blue parallel of the direction of ice flow and on either side. Near the rock face on either side of the ice plain label the shear margins have even lower elevation then the downstream shear margins near the ice edge.  The ice river is most constricted a bit upstream of the ice plain label. Once the ice edge retreated upstream of the southern ice shelf protrusion elevation and hence resistance on the southern shear margin decreases all the way to the base of the ice plain. The northern shear margin elevation also decreases all the way to base of the ice plain. The damage zones appear when the relative downstream pressure exceeds the lateral pressure by the shear strength of the ice. An increase in lateral tears near the base of the ice plane on the southern shear margin are a further indication of reduced lateral pressure on the shear margin.


In summary as the ice edge retreats upstream pressure on the sides of the ice flow decreases all the way to the base of the ice plane. Any tributaries real or perceived will not slow ice flow prior to the base of the ice plain.


In your merging highway analogy a traffic light is placed on one highway such that they are only allowed on when they will not cause traffic to slow. 

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2622 on: December 27, 2020, 01:13:18 PM »
Small emptying of the NdDZ ( Northern downstream Damage Zone)
Animation with the two images (low resolution) of yesterday and today.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2623 on: December 27, 2020, 03:25:40 PM »
To visualize T11 you must first go through the speeds, only then you have to visualize its structures and landmarks in the satellite images!
There are several possibilities:
> Articles: e.g. MacGregor et al. 2013; see first image
> Worldview (MEaSUREs Ice Velocity (Antarctica)); see second image ( to view Worldview images use the link "https://worldview.earthdata.nasa.gov/?v=-1697696.534747684,-365927.62785400957,-1501088.534747684,-273511.62785400957&p=antarctic&t=2011-12-30-T18%3A25%3A07Z&l=Coastlines,MEaSUREs_Ice_Velocity_Antarctica,MEaSUREs_Ice_Velocity_Greenland,Reference_Labels(hidden),Reference_Features(hidden)".
> From "MEaSUREs Phase-Based Antarctica Ice Velocity MAP, Version 1" (using Panoply). I post :
>> a zoom on the SIS, linear scale, saturation for speeds < 200m/y and >700m/y
>> a general view of the PIG, logarithmic scale.
These data are not recent, but do provide a good delineation of T11. It is a powerful tributary with a discharge comparable to that of SWT and more than half that of T9 (see Larour et al. 2012).
Indeed, even if the speed (northward direction) is limited, this tributary is very wide and thick.

Very wide images, click to enlarge.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2624 on: December 30, 2020, 01:20:49 AM »

Paolo
If I understand things initially you were saying that t11 was contributing significant side pressure as shown in A with significant side pressure somewhere in the middle of the southern shear margin. With arrow length roughly represent pressure. I was thinking that elevation of the southern shear margin indicated the greatest side pressure was near the ice edge and was smaller further away from the ice edge. This is represented by shortening arrows. My diagram does not show that I didn't think this side pressure was very significant. After reading an article on the effects of damage on the southern shear margin that t11 is not (as I thought) providing significant to the main flow. When the pig was flowing slower the side pressure on the shear margin was such that the main flow did not exceed the strain rate. At that time the ice sheared at the shear margin. Something changed and the velocity of the main flow increased enough to exceed the maximum strain rate resulting in tears perpendicular to the shear margin. These tears became the damage zone. The damaged shear zone provides substantially reduced resistance to the main flow because the ice no longer has to shear ice on that side. Further the main flow ice on the shear margin side is free floating. A number of other parameters also influence the main flow rate but sorting out which is cause and effect is difficult.
An interesting article on the subject https://www.pnas.org/content/117/40/24735

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2625 on: December 30, 2020, 01:23:46 AM »
The article in my previous post has a large but excellent animation of the PIG.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2626 on: December 30, 2020, 05:16:30 PM »
Today's 6-day GIF shows a rapid expansion of the new extension of the first rift on the Southern Ice Shelf.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2627 on: December 30, 2020, 08:57:26 PM »
I don't expect it will hold on much longer. When it goes, a bit more SWT resistance will be lost.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2628 on: December 30, 2020, 11:52:41 PM »
Scott Manley explains Synthetic Apperture Radar used by Sentinel-1 (most of the images in this thread.)


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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2629 on: January 06, 2021, 06:34:45 AM »
Another in a series of 6-day GIFs of the Southern Ice Shelf.

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2630 on: January 06, 2021, 12:17:29 PM »
Calving on the north side of the NdDZ ( Northern downstream Damage Zone )

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2631 on: January 06, 2021, 02:00:10 PM »
PIG looks to me to have accelerated from moving 12 m/day to 13m/day in the last year. That is a rough estimate from the graphs not the data.
http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3&image_date=201225_201231#output
That is not good at all.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2632 on: January 06, 2021, 08:14:08 PM »
I follow this thread daily and the increase in velocity is worrying: To me, it looks like the strain along the edges of the glacier can no longer be taken up using ductile flow - and is therefore undergoing brittle failure (rather like an earthquake). My guess is as this happens the resistance to flow from the edges of the glacier will be significantly reduced, leading to an increase in velocity, and propagation of the points of failure; a runaway positive feedback. It's not exactly MICI but there is a similarity: The ice can no longer support the forces that it's subject to and is failing in a brittle and catastrophic fashion.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2633 on: January 06, 2021, 10:01:14 PM »
PIG looks to me to have accelerated from moving 12 m/day to 13m/day in the last year. That is a rough estimate from the graphs not the data.
http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3&image_date=201225_201231#output
That is not good at all.
Thanks for sharing. It is really worrying.
A plot of the velocity change at some defined spots over time would be quite interesting. Maybe the acceleration is accelerating over time, because some of the shelf and pinning points have been lost over the years and the evolution of the damage zones additionally helps a speeding-up?
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baking

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2634 on: January 07, 2021, 01:19:31 AM »
A plot of the velocity change at some defined spots over time would be quite interesting. Maybe the acceleration is accelerating over time, because some of the shelf and pinning points have been lost over the years and the evolution of the damage zones additionally helps a speeding-up?
The data is available for 6+ years, both along-flow and across-flow.  Someone just needs to download 700+ files and extract the raw data.  Then figure out the best way to smooth the velocity data points to get a velocity over time measure that can be used to estimate acceleration over time.  Tying in the major calving events would be a bonus.  Also would be nice if it was in a Jupyter notebook format so we could all play with it.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2635 on: January 07, 2021, 10:50:10 AM »
The sentinel-2 image from yesterday is crap, but it does show one thing. A little calving in the south.

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2636 on: January 11, 2021, 02:04:50 PM »
Yesterday's Sentinel2 image was not good, but that of day before yesterday wasn't so bad, unfortunately it only covers the NW part of the SWT.

Anyway, I can publish two images :
> the Ice Rumple that finishes the SWT in the west, showing its progressive degradation
> the Ice Rise bordering the SWT to the west, showing its almost complete detachment from the SWT 

Click to enlarge

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2637 on: January 11, 2021, 10:37:36 PM »
I recently talked about the MEaSUREs Ice Velocity (Antarctica) data that can be viewed through Worldview or downloaded and viewed with Panoply (more than 6 GB anyway). I would like to add the image from Christianson et al. 2016 which provides a very readable image of PIG/PIIS velocities with countor lines for each 100m/yr interval (first image posted).

As already mentioned, the problem is that these data are from 2011.

There are also very up-to-date images on the  site "http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3": a complete image of the PIG/PIIS (see second image) and a zoom on the part further upstream (see third image).They are produced every 6 days and are posted with a certain regularity (but there are delays).   Anyway the colors displayed give an idea of the speeds, but they do not allow to quantify them too precisely.

These images, even if they give us more qualitative than quantitative information, are important: to visualize the evolutions (comparison between the images at different dates) as well as to validate observations made by us directly from the satellite images. I also remind you that for some parts of the PIG/PIIS we do not have the possibility to calculate velocities from satellite images because of the lack of usable reference points and that the images on this site are therefore the only source of recent information.

The site also publishes, every 6 days, the diagrams of the calculated velocities along the two lines "Along-Flow" and "Across-Flow", line that you will find on the second image. I will talk about these diagrams in a future post.

Click to enlarge

Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2638 on: January 11, 2021, 10:40:21 PM »
It is a really bad thing.
Please have a look at some pictures I presented here around one year ago (Dec 06, 2019 - Jan 05, 2020 - Jan 22, 2020 - March 16, 2020) and look at the "Zone of Destruction = now Damage Zone" and the close link between the ice rise and the SWT that is now almost completely broken. Has SWT sped up and/or changed its flow direction?
It is too late just to be concerned about Climate Change

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2639 on: January 11, 2021, 10:49:31 PM »
Stephan,
there is no longer the PIG pushing the SWT against the Ice Rise and the SWT took the opportunity to modify its flow (further north)

Stephan

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2640 on: January 11, 2021, 10:53:31 PM »
...which will open up the damage zone even further in the future. Can the ice rumples prevent a complete calving of the northwestern end of the SWT or will it end up with a (much) further inland calving front and some grounded icebergs around the ice rise??
It is too late just to be concerned about Climate Change

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2641 on: January 11, 2021, 11:08:19 PM »
I think that the direction of the SWT will gradually change and there will be detached ice anchored to the Ice Rumple for a time before a full calving.
And that the Domage Zone will extend upstream.

uniquorn

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2642 on: January 12, 2021, 03:44:14 PM »
PIG Along-Flow, Across-Flow ice speed and Ice Velocity from Images Pairs since may2018
http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3
Quote
Hogg, A., A. Shepherd, N. Gourmelen (2015) A first look at the performance of Sentinel-1 over the West Antarctic Ice Sheet, FRINGE 2015, Frascati, Italy, 23-27 March 2015.

All best viewed at half speed.
« Last Edit: January 12, 2021, 05:37:43 PM by uniquorn »

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2643 on: January 12, 2021, 04:52:36 PM »
Before switching to speeds "Along-Flow" and "Across-Flow" I would like to show the possibilities we have with the data from "MEaSUREs Ice Velocity (Antarctica)" and the applications Panoply and Gimp :
> The first image is given by pasting the 5 images using the following speed intervals: 0-1000 m/yr, 1000-2000 m/yr, 2000-3000 m/yr, 3000-4000 m/yr and 4000-5000 m/yr.During the pasting the colors of the extreme intervals around 1000, 2000, 3000 and 4000 are lost and these zones appear white (you will find the five color scales at the bottom of the image).
During the pasting the colors of the extreme intervals around 1000, 2000, 3000 and 4000 are lost and these zones appear white (you will find the five color scales at the bottom of the image).
> The second uses the 0-250 m/yr scale to highlight the upstream movements of the PIG and these tributaries.

The possibilities opened to us, from these data, to better know the structures of the PIG and these tributaries seem obvious to me.

Click to enlarge

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2644 on: January 12, 2021, 05:17:09 PM »
I would like to start by posting the images of the "Along-Flow" speeds that can be found in the articles and that give us a good history :
These 4 images are from Rignot 2008, Mouginot et al. 2014, Han et al. 2016, and Jeong et al. 2016 and cover the period from 1973 to 2016.
One can note the gradual acceleration overall, but also strong accelerations (for example in 2001, 2003, 2005, 2006, 2010 and 2014) and temporary slowdowns (for example in 2002, 2011 and 2012).


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paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2645 on: January 12, 2021, 05:36:27 PM »
Regarding the animation "Along-Flow" presented by uniquorn, I would like to present, in this post :
> a shorter animation: from 17/02/2020 to 25/12/2020 and slowed down to allow a better evaluation of the displayed information. We can notice that the lines drawn by the points, even when they are sharper and less scattered, have the tendency to oscillate (these movements are to be taken into account when estimating from a particular graph).
> a post-calving animation with the images from 17/02/2020 to 12/03/2020 to which I added the speed information in km/yr).
> a recent animation with the images from 01/12/2020 to 25/12/2020 to which I have added the speed information in km/yr).
These last two animations are later slowed down

Click to animate

paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2646 on: January 12, 2021, 05:39:39 PM »
Same thing "Across-Flow"

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paolo

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2647 on: January 12, 2021, 07:44:21 PM »
To finish these posts related to the PIG/PIIS speeds I wanted to point out that the site "http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3" gives access to a zip file containing the text files containing the data related to the "Along-Flow" and "Across-Flow" speeds from 22/11/2015 to 31/12/2019 (not recent data!)
But the site allows an individual download of the files of the first half of 2020.

You will find below two diagrams related to the 22/06/2020 for comparison: the one provided by the site and the one calculated from the data provided by the site and using a rolling average over two km.
I find that the gain of information that we have by constructing the graph is not exceptional and that therefore, taking into account that we do not have the most recent data, we can limit ourselves to using the diagrams provided.

But in the zip I also found images of the PIG/PIIS (1km per pixel) from 14/06/2017 to 31/12/2019 (there are other earlier images, but they don't cover the front) that can be useful to create animations or for studies on the last years.

Click to enlarge

oren

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2648 on: January 13, 2021, 04:59:11 AM »
Superb posts in this thread, and highly disturbing. The PIG is clearly accelerating, admittedly it's what one would expect given the shortening of the ice shelf and the removal of SWT buttressing, but with this data it is confirmed.
Can anyone make a chart of the speed over time? For a selected point (or multiple points) on the PIG/PIIS, the speed shown for that point, preferably averaged to avoid the fluctuations observed in the animations.

uniquorn

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Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2649 on: January 13, 2021, 10:51:38 AM »
A larger version of Ice Velocity from Images Pairs for an overview. Apologies for the fast speed, it's the only way I know how to compress a slow 53MB gif down to 2.1MB. For analysis, best to download it and view frame by frame. (or better, download the original .png files, the ani is half size, cropped)
jul2018-dec2020
The images differ in size by a few pixels so the ani jumps around a bit

I'm quite new to panoply so the third image should be treated with some caution. It focuses on a smaller area from 0-160m. Some of the settings are included in the capture.
x,y coordinate scaling may not be quite right
STD x,y velocity probably not so interesting.
« Last Edit: January 13, 2021, 05:35:41 PM by uniquorn »