Pine Island Glacier (PIG) Calving and Discussion

[paolo]

Oren,
The position of the front is only the visible and final consequence of what is happening elsewhere: retreat of the grounding line, increase in speed, thinning of the glacier (upstream) and the ice shelf (downstream), loss of pinning points, including the weakening of the lateral shear, or even its loss, stresses inside the flow, …

Pinning point loss is detectable in satellite imagery in most cases, but not always, and if detectable, it may not be immediately detectable, especially in the case of Ice Rumples.
The speed has hardly changed in the last 10 years (it had changed before).
Migration of the grounding line, thinning of the glacier and ice shelf are not detectable from the images.
Existing stresses inside the stream may, in part, be visible on the surface through their surface expression, but with analysis.

Moreover, the retreat of the front line can occur well after the causes.

I have another idea to give a simplified vision of the process in progress and its progression and I will work on it, but you have to be patient, it takes me a long time, but it is the southern winter and if it stops calving a little and bothering us ...

But there could be an anticipation: the front line without going through the images, which, in general, are not easily available.

[baking]

Baking,
I'm going back to your post of 05/25
"The most likely outcome for the SWT seems to be a gradual recession of the front as the SIS continues to degrade.  I expect its velocity to increase slightly as the bend becomes shorter, but I don't think the SWT will ever move fast enough to form much of a tongue."

Glaciers can form tongues, even at low velocities, as an example just look at the Lucchitta glacier in front which, with a low velocity of 225 ma^-1, has a very nice tongue. (The SWT has a velocity of 1k ma^-1)

The Luccitta Glacier terminates in an ice shelf.  The chance of the SWT forming an ice shelf is even less likely than of it forming a tongue.  An before you go off to find another true ice tongue moving at a slower speed, let me point out that I said "I don't think the SWT will ever move fast enough to form much of a tongue" NOT "no glacier can form an ice tongue at that velocity."

SWT terminates in a relatively ice free bay and it would have a much harder time forming an ice tongue or an ice shelf than a similar glacier at another location.  Thwaites probably would not have its tongue if it didn't have the almost continual sea ice to support it.  Every 3-4 years the sea ice recedes for a couple of months and a large part of the Tongue floats away.

I usually post my analyses in response to a post that I consider to be particularly ambiguous or not terribly informative.  I try to make somewhat more concrete predictions in the hopes of sparking a discussion that pins down some alternative points of view.  Making predictions in the form of "anything can happen" or that something may happen "any day now" never seems terribly informative or useful to me.  I'd rather have a bunch of people making wrong predictions because I'd at least know what some people are thinking.  Unfalsifiable theories are useless.

[paolo]

The Lucchitta glacier was on the edge of an ice shelf, it is no longer and perhaps it is a condemned structure.
Anyway, after this answer:
" I usually post my analyses in response to a post that I consider to be particularly ambiguous or not terribly informative.  I try to make somewhat more concrete predictions in the hopes of sparking a discussion that pins down some alternative points of view.  Making predictions in the form of "anything can happen" or that something may happen "any day now" never seems terribly informative or useful to me.  I'd rather have a bunch of people making wrong predictions because I'd at least know what some people are thinking.  Unfalsifiable theories are useless.",
that makes me say what I've never said, and offensive in the back, I'm stopping any direct response to your posts.
I'll keep reading everything, and so I'll read you (what you say: sometimes is interesting, sometimes is wrong, as for everyone), but I don't think there's any possibility of a profitable dialogue with you anymore.
And I won't stop posting here.

[paolo]

No big news: the main Iceberg has moved off, the SIS Iceberg, the Crescent and a block of ice mélange, which should follow the Crescent, are still lying around.
The rifts of the MIS: mR2 and cR1, have not evolved, but remain threatening for the next few months.

[baking]

Today's 6-day high resolution GIF of the Southern Shear Margin shows that most of the melange in front of "Cork III" is a collection of sea ice and icebergs recently freed from their previous locations.  Less than half of the melange in front of the Cork remains intact after the recent calving.  An approximate border is shown in the second image, but some of the icebergs on the margin have moved slightly more than other ones nearby so the area disrupted after the calving may actually be larger than what I've shown.

[paolo]

I'm a little surprised, but I didn't find (by searching with google) any other echo of the calving than this one 
Wrong search or it's like this?

[Tor Bejnar]

I was remembering something about predictions concerning Cork 3.  Some discussion and predictions start around March 5^th above.  Any comments about how slow or fast events have developed in this part of Antarctica these 3 months?

[oren]

I'm a little surprised, but I didn't find (by searching with google) any other echo of the calving than this one 
Wrong search or it's like this?

Wrong search, at least judging by Steff Lhermitte. Short gif at link.
https://twitter.com/StefLhermitte/status/1265410528454811654

[paolo]

Tor,
Personally, a resurgence of the expression of tensions in the MIS with the extension of the existing rifts was expected, but not so abruptly. That's why I was following it attentively, for example in my post of 04/28 I wrote: "Conclusions: this will take time, but does not promise anything good", and in my post of 05/04: "We must not forget them ...".
But I didn't expect the sudden development on the 22nd of April with my general alert, an alert coming only one day before calving.
The existence of tensions in the MIS is not unknown and we have already seen in the past months their effects with the opening and the rapid evolution of the R2 and R3 rifts. But then the process had calmed down and proceeded more slowly and I thought that events would have happened more this fall.
Now I am afraid that in the next four months we will have new calvings and, as I wrote on the 24th, "I think that the PIG in the first sentinel-2 image will not look the same as it does today. "
For me the Cork3 is no longer important, it is the fortress in front of it that is disintegrating (the rifts cR1 and mR2 are still there).

EDIT : on 24/05 I posted my forecast for future calvings

[paolo]

Thank you Oren

He even reported the second calving

I'll keep the link

[baking]

I was remembering something about predictions concerning Cork 3.  Some discussion and predictions start around March 5^th above.  Any comments about how slow or fast events have developed in this part of Antarctica these 3 months?

The "Point" went faster then expected.  The Southern Ice Shelf calved much faster then expected.  But Cork III is still firmly attached to its section of Ice Shelf, and that is what I based my March 2021 prediction on.  Odds are the Cork III calving will be somewhat sooner than my original prediction, but probably still closer to that date than today.  Or at least that is what my observation of the first two Cork calvings told me.

Of course if that piece of shelf goes away, all bets are off.  I had predicted the "Crescent" would last longer than the "Keystone" but when the shelf it was attached to calved, that didn't matter anymore.

EDIT:  Looks like the next SIS calving might miss Cork III.  See image below.

[AbruptSLR]

I was remembering something about predictions concerning Cork 3.  Some discussion and predictions start around March 5^th above.  Any comments about how slow or fast events have developed in this part of Antarctica these 3 months?

The "Point" went faster then expected.  The Southern Ice Shelf calved much faster then expected.  But Cork III is still firmly attached to its section of Ice Shelf, and that is what I based my March 2021 prediction on.  Odds are the Cork III calving will be somewhat sooner than my original prediction, but probably still closer to that date than today.  Or at least that is what my observation of the first two Cork calvings told me.

Of course if that piece of shelf goes away, all bets are off.  I had predicted the "Crescent" would last longer than the "Keystone" but when the shelf it was attached to calved, that didn't matter anymore.

EDIT:  Looks like the next SIS calving might miss Cork III.  See image below.

Tor,

Of course, Point 2 might fail well before the next SIS calving; in which case Cork III could be liberated before the end of November 2020.

[paolo]

Tor,

I forgot to say that the evolution in the SIS was not unexpected and I started talking about it in February: "I think they will extend later in the SWT and will have to be followed as they may lead to significant calvings in the SWT."

I add an animation with today's evolution: the ice mix above the Crescent is gone, the Crescent itself is taking off and the other iceberg is going to follow...

[paolo]

I'm adding a zoom in on the recently calved iceberg, just for the viewing pleasure...

[baking]

Of course, Point 2 might fail well before the next SIS calving; in which case Cork III could be liberated before the end of November 2020.

The calving of Point 2 could be both good and bad for Cork III.  Good in that it would no longer be pushing on the cork, rotating it, and causing strain on its Southern attachment point to the shelf.  Bad in that the loss of the point could expose the Northern side of the cork to open water.  As such a mixed bag, I don't think it would change my prediction for the cork.

[Stephan]

To reply #2262:
Is it just the low resolution of the second picture of your gif that fools me or has Cork III already left its connection to the SIS?

[blumenkraft]

As you can see by the blown away sea ice, it was quite windy in recent days.

Now an even stronger storm is forecasted!

Saturday, May 30

Hour 22: 24 m/s from northeast

Hour 23: 24 m/s from northeast

BTW, it's also quite warm, around freezing.

[paolo]

Sthephan,
This is an effect of the low resolution of the only image available today (at least until now) and different orbits.
It should hold up until the next MIS calving (but that's not sure), but no more.

[paolo]

Blumenkraft,
Thank you
I wanted to point out an incongruity in this weather site that I just discovered 
is it an error that have discovered and are in the process of correcting, hence the different pages in contradiction with each other?

[Stephan]

I add an animation with today's evolution: the ice mix above the Crescent is gone, the Crescent itself is taking off and the other iceberg is going to follow...

The crescent and her little sister south of her are too young, too small and too unexperienced to be set free into the wide wilderness of the Southern Ocean. Someone should go there and help them to stay close to their birth place... 

[blumenkraft]

Hmm, i was using this site >> https://www.yr.no/en/forecast/daily-table/2-6623299/Antarctica/Pine%20Island%20Glacier.

The charts there look quite similar, but the table view is very different.

[paolo]

My apologies, I hadn't put the links
First site:
https://www.yr.no/en/forecast/daily-table/2-6623299/Antarctica/Pine%20Island%20Glacier
the same as you and the second https://www.yr.no/place/Antarctica/Other/Pine_Island_Glacier/

EDIT :
On the second site I have just read the following announcement:
" "Observations" has moved. You will find this content on our new website under the weather forecast. "
What is indicated in the first link therefore seems to me to be preferable.
But that does not explain the difference, which is limited to the big gust of wind on Saturday evening.

[paolo]

Blumenkraft,
It's all cleared up, now the second link also gives the forecasts for Sunday and there's a big gale, but between 1h and 4h.
So it was just a matter of time being used...

[blumenkraft]

Good, Paolo!

[paolo]

By any coincidence, I just looked at a map and tilted: I had the wrong name, I had talked about the tongue of the Lucchitta glacier, it was the Velasco glacier (west of the NIS) !
I always confuse the two names.
Which made my post incomprehensible: the Lucchitta glacier ends in the NIS and has no tongue.
I wanted to correct the two concerned posts (2249, 2252), but I don't have the hand anymore.

[paolo]

Last calving follow-up:
The Crescent is now swimming in the bay and the SIS iceberg is jumping out of the springboard and diving in.

[paolo]

Yesterday there was no image relative to the front and today we discover the loss of an area of mixed ice between P2 and the Cork3

I post two images, high resolution, but of execrable quality, the first one related to calving and the second one related to rifts, not because there are novelties, but to remind that these two rifts are special watches (danger). In this last picture I marked with a small circle the end of the rifts

[Stephan]

There are some similarities of the actual situation (P2 / CorkIII) with the situation beginning April (P1 / Cork II). I wonder how long this situation will be stable until the next bigger calving occurs.

[paolo]

To show where the front is today and seen the quality of today's image I used the image from 23-05

[oren]

Paolo, I added the text from #2274 to #2249.

[paolo]

Oren,
thank you very much

[AbruptSLR]

There are some similarities of the actual situation (P2 / CorkIII) with the situation beginning April (P1 / Cork II). I wonder how long this situation will be stable until the next bigger calving occurs.

paolo's attached image from May 24, shows the rifts that will likely lead to the calving of P2 as CorkIII rotates about its aide-de-camp to thrust against P2.

[baking]

There are some similarities of the actual situation (P2 / CorkIII) with the situation beginning April (P1 / Cork II). I wonder how long this situation will be stable until the next bigger calving occurs.

There are a lot more differences than there are similarities.  Namely:

1. Cork 2 was paired with and immediately behind Cork 1.  While Cork 1 died its slow death, Cork 2 was slowly disintegrating.  Basically, being so close to Cork 1 meant that as Cork 2 rotated pieces would break off due to collisions with ice trapped behind Cork 1, While Cork 1 was free to "roll with the punches" if you will.

2.  Cork 3 had a companion behind it, the briefly named Cork 4, which suffered the same fate as Cork 2 except it didn't last nearly as long.

3.  Cork 3 is now at the front and it free to rotate without any resistance except for its sole companion wedge which will eventually break-off if it comes under pressure.  It is unlikely to damage Cork 3 in any serious way.

4.  Cork 2 was not in direct contact with the point and as such it was pushed by a melange that was pushed by the point, but it was not able to "push back" (except indirectly) on the Point.  What caused the Point to fail (After Cork 2 left the scene) was the arch of icebergs extending from the "Crescent" through the "Keystone" which provided the resistance between the SIS and the Point which eventually caused the Point to calve.

5.  On the other hand, Point 2 is in direct contact with Cork 3 and there will at least be a contest of wills.  Cork 3 may in fact go before Point 2 like Cork 2 did before the Point, but the most likely scenario seems to be that Point 2 will calve before Cork 3 leaves the Margin.  (I say "leaves the margin" because there is a good chance that if Cork 3 detaches before Point 2 calves that it could stay trapped in the margin between the SIS and Point 2 until it is freed by the calving of Point 2.)

[paolo]

As usual, micro-calving at the NSM

I also attach an animation related to the calving, before yesterday, of the ice mélange (images from 28/05 and 03/06)

EDIT: the first animation is aligned with the Ice Rise Evan's Knoll ( the MIS moves downstream) and the second animation is aligned with the MIS (and it's the SIS that moves upstream, but in reality it's the MIS that moves downstream).

[baking]

There are a few interesting things to see in today's image near the base of Point 2 where it attaches to the main PIG.  This is a 200% blow-up of the 6-day GIF and these items are faint, but I think only one might be an artifact or an old feature.

First thing to note is the small calving in the corner.  Not typically a big deal, but when combined with the others I think it is significant.

Second is circled in image two as #1 where the first transverse rift appears to join the calving front.  This could certainly be a cause for the small calving.  No apparent changes to the rest of the rift however.

Next is #2 which appears to be a new crack at the edge of the margin, below the second transverse rift and a possible calving line for Point 2.

Last is a faint line connecting both areas.  It was been noted before, but might be more significant now.

[paolo]

I will regularly check the Sentinel-1 images to monitor rifts, I note the real or supposed progress, but normally I don't publish the results anymore if they are not confirmed by the following images (I already had bad experiences this winter).
The previous post confirms me the right choice.
After analysis only remains the track, but very interesting, of a very likely new rift starting from the base of mR2. We'll see soon if it's a temporary fever due to tensions that are temporarily blocked elsewhere or if it will develop, which could lead to a very fast calving of P2. In any case P2 cannot hold a lot of temp and in three, four months maximum she should have calved with a nice piece of MIS.
I would like to take this opportunity to point out that I am monitoring very closely the extension of mR2 and a new rift that is developing further upstream from mR2 and that is creating a new point further upstream : P4.
Of course I am also closely monitoring the development of cR1.
The situation is very dynamic and there will be no shortage of surprises.


Click twice to animate and zoom in.

[paolo]

I wanted to check with the Modis images between 2001 and 2019 whether the recent situation of the SSM was completely exceptional or whether similar, albeit smaller, phenomena had already occurred or not. So I retrieved Modis images, one per year relative to the month of December (except for a few cases for which there were no images for the month of December).
I found some expected results, but also an intriguing fact:
I have noticed the exceptionality of recent events compared to the history of the last two decades: there are indeed two depressions in 2001 towards the SWT, one of which will give birth to two very localized small fractures, and which move slowly towards the front to calve in 2017, but nothing comparable to what has just happened.
The fracture downstream of the future Cork dates from 2014, in 2016 the fractures multiply downstream of the Arc Structure and in 2017, following the beginning of the collapse to the north, the fractures also extend upstream of the Arc Structure.
These fractures in tributary T11 are located where fractures had started further upstream along its SM to the east.
These results were expected or reasonable.
The more detailed analysis of recent years will be in a later post and will be based on the Sentinel-2 images, but I will anticipate the publication of this animation because of the unexpected result:
Between 2011 and 2016 we have the visual impression that the T11 tributary is pushing the MIS north?!?!
I think that, at least in part, this is an impression and not a fact (different snow cover, the MIS is moving and the structures we visualize are not the same, ...), but the visual effect is very intriguing and continues year after year, so I wanted to have your opinion.

[Stephan]

Thank you paolo for this impressive animation.
I asked a while ago whether the existence of the ZoD since 2017 is unprecedented, and I think the answer is yes, as far as we can go back with satellite images.
If you would be able to add 2019 (and early 2020) into the series it would be good to see how much of this glacier (this ice shelf) has further eroded in the last 2 of the 20 years. I think with the loss of pinning points (at first with the NIS, now with the merger of MIS and SWT) we have passed a tipping point. A stabilisation seems to be unlikely in the current situation, a further retreat must be expected.

PS: The northward move of the SSM from 2011 to 2016 is obvious.

[paolo]

For the moment I think that around 2010, 2011 the T11 tributary has, in its turn, increased speed and the extra mass of ice had to find its place. This must have created an excess of pressure between T11 and the MIS, which at least partly displaced the MIS flow (but the visual impression can be increased by other visual effects) and which, together with the shear force due to the movement of the MIS, could no longer be managed by deformation, but led to the destruction of the final part of T11, the part in direct contact with the MIS remaining attached to the MIS, which finally gave a dividing line that is not far from the old SSM line.

[paolo]

Stephan,
The last image is from December 2018 and the last Modis image I have is from March 2019. But as I wrote I will make a presentation (tonight or tomorrow), much more detailed, using the Sentinel-2 images for the 2016 / 2020 period, to finish with the Sentinel-1 images for the current period.

[paolo]

I discovered the archive of Landsat images, which I didn't know (a real Ali Baba's cave  , too bad that the images you can download have a limited extension, the ones used have the maximum extension  ) and I was able to make a new animation with much more detailed images related to the T11/MIS joint for the 2010-2016 period (still using the December images) and there there is no doubt anymore and there is no effect that comes into play.
So to summarize and complete this first analysis in broad outline and over a long period of time, before moving on to a more detailed examination of the recent period, we can already say :
The other two ZD's: NZD and SE-ZD have a completely different configuration and history than the SW-ZD. These two zones are a classic case of rift zones generated downstream of an Ice Rumple and followed downstream by the arrival of a tributary that recompacts the ice (pinning point).
They have always existed with more or less pronounced opening and closing cycles. These areas will become dangerous to the stability of the MIS once the downstream pinning point is lost. Indeed the fracture zone may extend to the front and empty and the shear forces on the MIS on their side may weaken considerably or even disappear almost completely.
On the contrary, the SW-ZD is born at the junction of tributary T11 with the MIS. The animation of the previous post shows that until 2014 this junction was made by deformation with possibly the exceptional opening and without consequence of a rift from time to time. From 2008/2009 T11 started to push the MIS to the North, probably due to an increase in speed (element to be checked later) and the strong shear on the right flank of T11 caused, from 2014 onwards, the opening of very deep fractures in T11 (fractures opening from the SM of T11 by reopening fractures generated upstream when T11 entered the SIS (in the following post there will be images on this subject). It can also be noted that the existence of the pinning point given by the SWT/MIS joint until 2017 has prevented the complete degeneration of this zone.

Click twice to animate and zoom in

[paolo]

In this post I present in more detail the history of the SW-ZD between 2016 and 2019.
I have noted the main elements of the SW-ZD and the surrounding elements that are used to understand recent history in the Sentinel-2 image of 17/11/2019 and in the D.E. Shean et al. 2019-Figure3 elevation image. I have added an animation with the images relative to the 2016/2019 period (images relative to the month of November).
An analysis of the last period as well as possible futures will be the subject of other posts.
To remember :
> As said in the previous post at the junction between T11 and the MIS pre-existing fractures (see second image) have reopened and transformed into rifts that have completely cut this tributary in all its width. This block was then broken on the MIS side.
> the line of weakness represented by the arc structure caused the complete breaking of the block between Cork2 and Cork3 giving rise to the Keystone (a runt of Cork).
> MSS includes not only the ice provided by the PIG, but also the contribution of T_ and part of T11. Indeed the tearing of the rift-isolated blocks occurred inside T11 and not on its MIS-side SM. This structure on the South side of the MIS, integrating parts of the SIS, explains some weaknesses of this part, weaknesses that appeared during the partial calvings, in late 2019 and early 2020, of the tip of the future Big Iceberg.
> relative to the first pinning point of the first image we can note that currently there is no longer a direct join between T11 and MIS, but only between its SM to the East and the MIS. We can hope that the movement of T11 can recreate a more efficient joint at least for a while.

Click twice to animate and zoom in

[paolo]

Now let's turn our attention to the last few months and the effects of the SW-ZD on the MIS itself:
Indeed in the MIS the push towards the front is powerful and the problems start when the shear on one edge is not constant, but acts on precise zones and especially when these zones are no longer followed downstream by other zones with a shear of the same magnitude or even a shear zone at all. These shear differentials indeed determine tensions in the MIS that will create rifts that will extend to its center (remember that shear is not limited to the edge, but extends inside).
Image of 24/09/2019: the rifts R3 (downstream of P1) and mR1 (downstream of P2 do not exist yet)
The brake by the Cork on the downstream part of R2 is almost nil, because of its rotary movement, which no longer opposes the movement of the future Iceberg. Hence the rapid widening of R2. But, still because of its progressive rotation, the brake on P0 (the point downstream of P1) is not strong and will weaken later. This will cause, in October, the opening of mR1 in a first time, followed in a second time by the explosive opening of R3 and the entry into sleep of mR1. We can think that the Crescent/Keystone complex brake on P2 was initially stronger than the Cork2 brake on P1, but that quickly the latter, which is downstream, increased its action and became the main braking point of the MIS.
The result can be seen in the image of 23/12/2019.
In the final image of 16/03/2020 we see that P1 is free in its movement and that the action of the downstream brake is of the Crescent/Keystone complex on P2, which can only lead quickly to the calving of P2, which we have just witnessed, and the reactivation of mR2.
Another point to remember, in order to understand the events of this season, is that the edge of the PIG-fed part of the MIS is a point of resistance to the progression of rifts, which can lead to a temporary halt in their progression, or even to the birth of a separate, seamless extension beyond this point of resistance, and possibly to an extension in another direction as mR1 has recently done (in other words: stopping the extension of a rift may not mean that there is no more tension in progress).
In a next post I will analyze the present and the future, but already I invite you not to observe the SW-ZD with all the attention returned to its calving, but rather in the opposite direction: towards its braking action on the MIS, an action that can be extremely destructive.

Click twice to zoom in.

[sidd]

Mr. Paolo,

You are doing a very good job. Perhaps you might write up a short version and submit to the cryosphere journal ?

https://www.the-cryosphere.net/index.html

sidd

[Stephan]

paolo,

thanks a million for the pictures, the gif and the explanations. Keep on doin' the excellent work. Very much appreciated.

[oren]

I join the applauds. I have never noticed (at an awareness level) the push of T11 and the complete crumbling of the left side of the stream in the last few years, though others may have. Long term animations can reveal this kind of process easily.
A small note, wherever you write to "twice click", I should let you know a single click is enough, at least in my browsing experience.

[Phoenix]

Merci beaucoup paolo and also a big thanks to baking.  The thread is enriched by having multiple perspectives and the dialogue between the two of you helps to try and grasp what is going on.

[paolo]

First of all a thank you!
After which I must inform you that the mystery thickens!
I wanted to check the speed of T11 and I downloaded the Landsat images to estimate its speed in the last twenty years and, after a first very quick estimate I find that the speed is unchanged, let's say around 390 my-1 matching the values already known! Calmly I would make the precise estimates, which I would communicate to you, but I no longer expect the solution of the margin of the MIS retreat problem to be a major T11 surge. We will therefore have to turn back to the MIS itself since I do not see how T11 could have pushed the MIS at a constant speed!
This is a result that I find unexpected and, for the same reason, very interesting.
I will also try to better qualify and quantify the retreat of the margin of the MIS.
That said, it doesn't change anything in the SW-ZD analysis, if not the explanation of the SIS debacle from 2016 onwards. It would no longer be the product of an increase in pressure between the MIS and T11.  Indeed this hypothesis must have been erroneous, in the sense that a major pressure compacts the shelf and therefore tends to keep it whole, so much so that downstream the SWT/MIS joint was still very solid! It is on the contrary a decrease of the compression that makes possible the widening of the rifts.
As usual it is by formulating hypotheses which are wrong that we advance towards the solution ...

[paolo]

With regard to the PIG/MIS flow issues, the idea of a regular and constant flow in time must be abandoned. Indeed, differences in the time of basal or lateral shear can induce changes in velocity (and thus volume) and, in the ice shelf, spreadings, i.e. undulations of the edges of the flow, which the other small tributaries undergo, undulations which then migrate downstream.
To show a history of the modifications of the SSM I took advantage of the new high resolution image source to make two animations on the SSM: the first one on the SW-ZD and the second one on the SE-ZD. The regions covered by these two animations overlapping each other we have a panoramic view of the SSM. There is one image per year, if possible from January, otherwise from February or December. There are no images for 2006.

Click to animate (and a second click to zoom in completely)

[Stephan]

A big thank you again, paolo.
SWZD: In my opinion the general thinning of PIIS in the last years has finally become so severe that it partially breaks up in the tension between fast flowing MIS and slow flowing T11/SIS. In former times these different flow speeds put some harm to the glacier, but it was too thick to be observed by satellite. Since 2017 the obvious destruction took place. Let me put an analogy which does - of course - not fit. Think about a snow layer on an uneven slope with small boulders on it (take the Freya webcam as example). If you have 30-40 cm of fresh snow then everything is covered and you can't see the stones. If it starts melting, then the larger stones and also steeper slopes start to appear. This is what 2017-2020 PIIS/SWZD appears to me. In the end there will be no ice left. I can not imagine any circumstance that heals the ZOD to get back a full and healthy ice cover.
SEZD: I am shocked how it has changed in the last years. Another "calving" in 2019→2020. I didn't really follow that, as I was focused on the Cork and its neighbours as well as on the SWT ice rise.