Pine Island Glacier (PIG) Calving and Discussion

[baking]

It is obvious that the Keystone in reality is moving away from P1.

I have no idea what you are seeing unless you are confusing the Northwest corner for the Northeast corner.  I made a longer GIF and made it relative to Point 2 as a proxy for the main glacier.  The Northeastern corner of the keystone is clearly pushing against the adjoining iceberg even to the point of creating a visible compression at times.

[paolo]

Sometimes the PIG is very fast... 

[blumenkraft]

Boom! 

Amazing how some of the melange is still 'glued' to the new iceberg.

[Stephan]

A very short story about the newly named R1...
On the one hand fascinating, how fast things happen, on the other hand frustrating and alarming. How much further will MIS calve until it finds a state which is stable at least for one year

[blumenkraft]

BTW, the last frame in Baking's GIF (#2200) might be shot mid-calving. Fascinating!

[paolo]

The two images of the 22nd and the 23rd can't be well aligned, so I made an animation with the images of the 27th and the 23rd.
I highlighted the small piece, which came off the MIS together at the iceberg.
The fact that part of the ice mélange remained attached to it has already been highlighted by Blumenkraft
The cushioning mélange between b2 and the Keystone has dislocated...
In the next few days we will see where the mélange ice front will temporarily stabilize upstream.

[Stephan]

How large is the latest iceberg and is it big enough to be numbered?

[paolo]

Stephan,
Yesterday (post 2191) I gave a rough estimate: "EDIT3: The block is 11x4 km and about 35 km²"

[paolo]

Baking,
You can't go too far back in time, it all happened abruptly and far from the Keystone, and what happened here in the past is not the cause, 12 days is already a long time.
To estimate the relative movements I had taken a point not far from the NE point of the Keystone (400m). I re-did the measurement directly at the point (it is more laborious) and I find the same distance between the NE point and P1 (clearly within the limits of the test).
Between the Keystone and b2 there was a mixture of ice, but perhaps now the Keystone and b2 were touching each other directly.
From all this we can deduce at most a certain Keystone action on b2 and that's it.
b2 was not at all in direct contact with P1, far from it, between the two a mélange of icebergs.
I absolutely do not understand how you can seriously consider a Keystone action on P1 of this magnitude and at this distance.
The fact that we do not understand exactly what is happening in the MIS should not push you to choose unfounded hypotheses, it is better to admit and leave the mystery that exists, while waiting for a decisive observation or an article that will enlighten us.

[baking]

Glaciers move slowly and you need to observe them over long periods of time.  If you only look back a few days, of course sudden changes will appear mysterious.

[Stephan]

P2, now becoming the most exposed part of MIS, has increased its distance to Cork III, letting the gap between them be a little wider. I expect a flowing out of the unprotected icebergs between P2 and Cork III in the near future. Then Cork III will act like Cork II did some weeks ago and prevent the mélange upstream from flowing out into the sea.
P2 does look fragile and full of little cracks. I do not know how long it can withstand the forces of wind and currents.

What does today's calving mean for MIS's future? MIS has lost some weight, some area and some resistance. Will this loss lead to a speeding up? Has the bigger calving of February already increased MIS's flow speed? Any ideas?

[baking]

Since everyone is interested in the arch, or iceberg line (the icebergs being practically aligned), I just created an animation with high resolution and clear images from 05/02 to 17/04, to have a clearer idea about it.
The interval between the images is 12 days, but the image of the 29/02 is missing and there is therefore between the images of the 17/02 and that of the 12/03 a jump of 24 days, but the animation remains valid.
It seems to me that in this 72 days the whole has moved coherently, turning slightly and compacting, always slightly. So there was a little compression and this is good for the arch holding. If there is no external event this arch could hold without problems for 3 to 5 months.
If there is no external event this arch could hold for 3 to 5 months. But it's not very strong and there can always be surprises!

This is what you said a month ago.  It is all correct except that the compression of the arch caused the buttress (The Point or P1) to give way sooner than expected.  No magic needed.

[oren]

Thanks for all the updates here. I am very concerned (again). The abrupt new calving points to the fact already discussed herein that the PIG is very far from stable at the moment. The speed of events is disturbing and feels like a slow-motion collapse. Calving used to be spaced over several years, and then we had to wait months, now it's something new every few weeks, not to mentioned the bits and pieces that break away almost daily. It's true that this thread's coverage is much more detailed than in the past, but I think that hardly explains the new phenomenon.
Indeed it is possible that the significant loss of buttressing/friction on the south side, while the north side is still going along as it used to, is creating a host of new stresses on the main ice shelf and could lead to further disintegration.
In addition, any newly calved iceberg is immediately swept away, preventing a buildup of iceberg mélange that could slow down the process, unlike the behavior at next-door neighbor Thwaites, and unlike the behavior of some past PIG icebergs. These days they are smaller, immediately shatter, and also seem to be shallower so that none have been grounding anywhere.

[Stephan]

It may be a little bit OT, but I'd like to know whether Eric Rignot is following the discussions in this forum. For me he was the one to have a good explanation of what is going on (what is going wrong, actually) with PIG and Thwaites. I remember some of his presentations years ago. Today the situation is much worse than then. The ice shelf is thinner, faster, shorter, and the ZOD didn't exist years ago...

[baking]

It may be a little bit OT, but I'd like to know whether Eric Rignot is following the discussions in this forum.

I doubt it.  I think the experts know that what happens at the ice front is "water over the dam" at this point, and the real science is done at the grounding line and above.  Also, Eric proclaimed that the West Antarctic Ice Sheet is already doomed a number of years ago and he has seemed to switch focus to East Antarctica (Denman and Totten Glaciers) which are still salvageable.  His group also does modeling of ice sheet balances which are useful for predicting future sea level changes.

[paolo]

Baking,
You misinterpret the use of the word "mystery" in my post.
I'll say it again: there is a speed differential between the north and south side of the MIS that has always existed in the last few years (it already existed 10 years ago). This induces tensions in the MIS. The expression of these tensions depends and is influenced:
> by the pinning point downstream, that was the SWT, but now it's gone...
> by the shear caused by the SIS, shear which is now very low in the downstream part.
It is deduced that the effects of this differential are now much more visible and explosive.
Furthermore, this differential is probably increased due to the loss of the pinning point and the very low shear.
It is these effects that explain the rapid opening this fall of the R2 and R3 rifts and later their explosive expansion (extension and widening).
It is these same effects that more recently explain the explosive opening of the new cR1 rift and today's calving.
This is not mysterious at all.
On the other hand, to go out of the general framework and to arrive at more detailed predictions: when these effects will be noticed (visualization) and at what speed, this is much more difficult, since it depends on the structure of the ice shelf (existing points of weakness and points of resistance) and on the state of the tensions at the time of the analysis, and we don't have these elements.
But if we want to be able to make realistic forecasts, let's not run behind players who are only completely secondary, or even without any influence at all at the global level.

[paolo]

Image quality was terrible, it didn't move much after calving, only the tip of the iceberg moved a bit away from the ice shelf, not enough to make an animation.
This is the calm after the storm and while waiting for the next ones:
> To the North the constant decay in small pieces of the NSM will continue and there's a consistent piece that in the next few months will break off,
> In the South there is the gradual decay of the SWZD and on the MIS side, the development of existing rifts as well as the birth of new rifts can be expected.
In my opinion, in the coming months the PIG will continue to signal itself, with a small voice and from time to time thunderbolts.

[baking]

PIG is in an unstable transition and will continue with minor calving until a new temporary stability is restored.

The Northern Shear Margin will continue to retreat until it reaches the upstream side of the Evans Knoll grounding line.

On the Southern Shear Margin, the melange in front of Cork III will float off but the cork will hold into 2021.  The new point will most likely calve before Cork III gives way.  The melange behind Cork III will not give much additional resistance once exposed.

The SWT/Southern Ice Shelf Margin will be more interesting as the SSM recedes.  We can expect the SWT to chip away at the SIS.

Besides the eventual new point calving, we will see other calving on portions of the PIG ice front, but no massive calving of the entire front until the new stability is achieved.

[blumenkraft]

Could a diagonal calving front form?

PIG icebergs calving off do that at ~ square angle to the floating direction.

[Stephan]

The last months saw a faster and more intense calving at the SW edge of PIIS-MIS, due to the lack of stability around the zone of destruction (ZOD) at the south shear margin (SSM/SIS) and probably due to a stronger current beneath. But minor calvings along Evan's Knoll on the NE edge have always made up a little bit for that difference. One must also take into account that on the NE side there is also an issue with structural integrity and thickness because of the speed differential between MIS and the NE-IS.
In the end I think that a slight preference for calving on the SW side will continue until the upper end of the ZOD has reached the calving front. But I can not imagine a diagonal calving front.

[AbruptSLR]

...
On the Southern Shear Margin, the melange in front of Cork III will float off but the cork will hold into 2021.  The new point will most likely calve before Cork III gives way.  The melange behind Cork III will not give much additional resistance once exposed.

...

Baking,  in your first attached image you acknowledge that Cork III is bearing against Point 2 and that the compressive force associated with this bearing is causing new rifts to form in Point 2 (see your second attached gif animation).  It is my opinion that as soon as Point 2 calves (which your statement above indicates that you believe will happen before Cork III gives way) that Cork III will also give way at the same time, long before March 2021.

[baking]

Could a diagonal calving front form?

PIG icebergs calving off do that at ~ square angle to the floating direction.

PIG has had a diagonal calving front for decades, but it has flopped and flippped at least a couple of times.  The only issue is that some old transverse rifts or cracks formed at one angle and will cause more jagged calving until transverse rifts form at the new angle.  The stresses however end up shaping the front in a rough manner until then.

[baking]

...
On the Southern Shear Margin, the melange in front of Cork III will float off but the cork will hold into 2021.  The new point will most likely calve before Cork III gives way.  The melange behind Cork III will not give much additional resistance once exposed.

...

Baking,  in your first attached image you acknowledge that Cork III is bearing against Point 2 and that the compressive force associated with this bearing is causing new rifts to form in Point 2 (see your second attached gif animation).  It is my opinion that as soon as Point 2 calves (which your statement above indicates that you believe will happen before Cork III gives way) that Cork III will also give way at the same time, long before March 2021.

The rapid loss of the point certainly points to an accelerated schedule, but for now I will stick to an approximate October calving of "Point 2" and Cork III hanging on until March.  But I won't be too surprised if I am wrong.

[paolo]

I am attaching three images relating to the rifts already existing and the calvings they will induce in the coming months:
The north side is more stable and will be limited to a slow nibbling of the small ice shelf north of the MIS, a very narrow band wedged between the Ice Rise Even's Collins and the MIS, subject to the tensions induced by the speed differential of the neighbors: Ice Rise: zero speed and MIS: 4km/year, and without downstream protection. The MIS itself it should come out without too much damage, except for the iceberg that did not come out during the February calving and will do so by taking its time.
The south side is the most unstable. I thought it was interesting to follow the dismemberment of the SW-ZD, since it provided a small aid to the MIS, not as a pinning point, but by shearing, and I thought that by staying in place for a little while it would have helped to slow down the retreat of the MIS. One can only conclude that her support to the MIS is clearly insufficient and that the MIS tensions are tearing its southern side apart without hindrance.  Beyond the existing rifts we can expect the birth of new rifts further upstream, with downstream clearances leaving the upstream parts unprotected. And I'm afraid this will continue until we reach the next upstream pinning point we've already discussed. And the SW-ZD? Now is only a secondary actor following events and it has lost much of its interest to me.
The center and between the two and will synchronize between the two sides.

[paolo]

PS: I didn't put any date because I think that in the current state the behavior of the PIG has become too unstable, and in the next four months we could have important developments as well as nothing happening, even though I think that the PIG in the first sentinel-2 image will not look the same as it does today. Let's get used to breaking news

[IceConcerned]

The quality is very poor, but I have the impression that the blocs from the SIS are getting loose.
Not sure due to the image quality, but also a feeling that the Crescent is moving, along with more melange.

[paolo]

I confirm, it's a direct consequence of yesterday's calving, I'm attaching a slightly more zoomed image that I had already prepared before discovering your post

[baking]

Here is a 6-day high resolution GIF focused on the Southern Ice Shelf (and with improved alignment) from May 17 and 23 followed by today's low-resolution calving.  You can see the middle rift ("1.5") spreading in the second image, but other than that no sign of the impending calving event.

[baking]

What's next for the Southern Ice Shelf?  If the current trend continues, "Rift number 2" should connect with "Cork III" but that is quite a long trip and there would seem to be a strong likelihood that it would calve before it gets there.

[Stephan]

It is incredible. Another major calving two days after a major calving. Will there be major calvings every two hours in the next future? When does this stop?

[Stephan]

Here is a 6-day high resolution GIF focused on the Southern Ice Shelf (and with improved alignment) from May 17 and 23 followed by today's low-resolution calving.  You can see the middle rift ("1.5") spreading in the second image, but other than that no sign of the impending calving event.

Thank you baking for this information. I think a new rift sR4 is visible in the second last picture.

[paolo]

Finally the high resolution image arrived and you can clearly see what you could only perceive in the low resolution image: the iceberg between SR1 and SR1.5 it has no more connection to the SWT and therefore it has already calved.
I calculated the total area of the two calvings (23 and today), including the ice mélange, and I find 68km2 

[paolo]

Stephan,
The two calvings are linked, with the first calving removing all pressure on the Crescent, thus freeing up any obstacle to the second calving.
The new rift, which was already reported a few days ago (17/05), will be named, when it is more developed, but its name will be SR3. In fact it is the fourth in order of distance from the sea, but the second one was born after SR1 and SR2 we had to name it SR1.5 => SR1, SR1.5, SR2 and the upcoming SR3.

[paolo]

Post Calving SWT-SIS:

On the SIS side:
SR2 will probably expand, but I think it will branch off to the front line long before Cork3.
The future SR3 should become an "official" rift recognized by all.
The tensions that had been expressed through the opening of the rifts SR1 and SR1.5 should be carried further upstream and the opening of another rift further upstream (SR4) is quite possible.

On the SWT side :
There will be consequences, but these are harder to predict and will be slower to happen. I am torn between a crumbling of the SWT on the East side on the one hand, and a SWT resistance with minor losses and the beginning of a Tongue formation on this side on the other hand.
Having said that, the part of the SWT north of SR1.5, a rift that has already extended into the SWT, seems doomed. And this glacier is not in balance with the speed differential between the slower west side and the faster east side.

The SWT will have to be carefully monitored and studied.

[baking]

I've included a comparison GIF of the SWT from March 2019 as reference.  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. 

[Stephan]

I think the SWT is in a dangerous position. It now has two calving fronts that are directly attackable by the ESE → WNW directed current. In addition there are cracks (or precursor cracks) visible. I wouldn't be too surprised if relatively soon another calving completes the series. At least at the red line a calving will happen in the not too distant future.

[baking]

Not much happened today except that some more of the melange floated off.

[paolo]

To help those who follow this forum less closely, to situate the events of this year's PIIS, I wanted to trace the calvings.
I based myself on the image of the 01/02
The lines drawn are relative to the PIIS losses and do not correspond to the current position of the front that has moved since 01/02.

Click twice to zoom in

[Stephan]

paolo,
I guess you can read my mind. This picture was one I planned to make and to post here. Thank you for doing that so well. 

[oren]

Yes, thank you Paolo. I recommend adding a legend somewhere though.

[Stephan]

The red line is the major calving including Cork in February 2020. The yellow line includes minor calvings including Cork II in March and April 2020. The orange line summarizes the double calving of the Point, the Keystone, the Crescent and the northern part of SIS from this weekend.

PS: Apart from Cork III and Point 2 there are no other named places left. Let's see how these icebergs, rifts and edges develop to find a common understanding by giving them names and/or numbers in the future.

[paolo]

Oren asks, Paolo executes 

Click twice to zoom in

EDIT: I don't remember that there were so many calvings

[oren]

Thank you. I have been following all the updates here in detail, but we have some readers who may be newbies or lurkers who could greatly benefit from the extra information.

[Phoenix]

As one of the lurkers who follows this thread, I appreciate the effort and admire the passion you guys are putting into documenting the West Antarctic glacier retreat. I'm grateful that ASIF provides a home base where such documentation and analysis can be done.

There does seem to be a little bit of 'faster than expected' sense of what you are observing.

Figuratively speaking, I'm following along and observing the trees, but not necessarily understanding the connection to the larger forest. If you have some sense of whether the things you are seeing represent status quo retreat or point to accelerating retreat, some insights on the big picture would be appreciated. I'm familiar with the concepts like MISI and MICI and have been following Eric Rignot's work for a few years so i'm curious if your observations lead you to believe we might be witnessing meaningful acceleration.

Back to lurking....keep up the great work. 

[interstitial]

Paolo's image with a scale bar. I always need a scale bar to remind myself how big those minor calvings are.

[bluice]

After the large February calving the consensus on the forum was that this would be followed by the swift emptying of SW ZOD.

Is this what we have been witnessing in the form of consequantial calving events? The glacier is not stable along the southwestern shear zone.

[paolo]

I'm adding the current cumulative calving totals to the north.
The little mouse is patiently nibbling on the pinning point, the last defense to avoid the great retreat.

[paolo]

bluice,
As I said in my post of May 24th:
"The south side is the most unstable. I thought it was interesting to follow the dismemberment of the SW-ZD, since it provided a small aid to the MIS, not as a pinning point, but by shearing, and I thought that by staying in place for a little while it would have helped to slow down the retreat of the MIS. One can only conclude that her support to the MIS is clearly insufficient and that the MIS tensions are tearing its southern side apart without hindrance.  Beyond the existing rifts we can expect the birth of new rifts further upstream, with downstream clearances leaving the upstream parts unprotected. And I'm afraid this will continue until we reach the next upstream pinning point, we've already discussed. And the SW-ZD? Now is only a secondary actor following events and it has lost much of its interest to me."

[oren]

I think the best method to show the long term acceleration is to make an animation of the whole front with a proportional timescale, for example 1 or 2 or 4 images per month, over the last 10 years or so.
If images are not available from certain times, one can double the previous image, so as to maintain the sense of time.
I have seen several such animations on Twitter (Steff Lhermite for example) but they do not cover the final acceleration this year. The best animation would be rather large, rather slow, and have a pause at the end, to enable the viewer to take in the developments. A date or year counter would be quite helpful. Animation should be fixed to grid, not to any moving point. This will enable the viewer to follow the gradual dance of forward movement and calving, the net of which is the retreat.
I am not doing this myself unfortunately due to severe lack of time (and abilities), but if anyone is able and willing it would be much appreciated.

[paolo]

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)

That said, I'm also thinking more of a retreat, but I think we have to examine all the hypotheses and stay open and I prefer to take my time before providing an analysis/prediction (it's not useful to rush, it's not useful for the forum).

In any case it deserves to be studied (it's a door for CDWs to the back of the Thwaites)

Edit: 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.

<Modified at paolo's request. O>