Pine Island Glacier (PIG) Calving and Discussion

[Stephan]

Yes, and imagine, this comparison is just six days apart. No other place in Antarctica is moving as fast as PIIS does. In this case I have the impression, that SW tributary is also moving.

OT:
Did you recognize that B-22-A has turned backwards in NE direction the last days? It seems to be flowing freely now without pinning points. Hope it can escape into deeper seas to give room for new icebergs from Thwaites.

[blumenkraft]

Thanks for the confirmation, Stephan.

If it is really free-floating by now we will lose it to the ocean pretty soon.

But i bet the bathymetry has many more surprises. There are a lot of other grounded icebergs in the vicinity.

This will be exciting to watch this summer.

[baking]

OT:
Did you recognize that B-22-A has turned backwards in NE direction the last days? It seems to be flowing freely now without pinning points. Hope it can escape into deeper seas to give room for new icebergs from Thwaites.

This is a good catch.  Movement to the West (or NW) is "good" because it means the iceberg is becoming grounded again.  This is pretty much what it has been doing every few months lately.  Movement to the East (or NE) is "bad" because that is movement towards deeper water and possibly floating free (or at least farther away.)  It bears watching.

Of course, an iceberg of this age, condition, and size could also breakup under the stresses of being grounded, regrounded, and pushed by wind and currents.  Floating off intact seemed like the least likely scenario.

[Shared Humanity]

Would be cool to see it exit into the southern ocean essentially intact.

[oren]

Of course would be better to see it regrounded and stabilize Thwaites, but I dread that its recent movement opens up a lot of destabilization in the near future.

[IceConcerned]

A minor calving at the junction between PIG and SW tributary.
Tha cracks in the SW Tributary seem to have widened at htat point too

[Wipneus]

Crack detail, images 12 days apart. The widening getting faster mainly from the Wesy side.

[Stephan]

A minor calving at the junction between PIG and SW tributary.

Probably the same minor calving observed by analysing the EOSDIS comparison (circled in brown):
https://worldview.earthdata.nasa.gov/?v=-1765632,-371520,-1550592,-251328&p=antarctic&t=2019-10-19-T04%3A00%3A00Z&t1=2019-10-03-T00%3A00%3A00Z&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&l1=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&ca=true&cv=57

[vox_mundi]

[paolo]

Today no better images 
How long before the crash: weeks, days?

[oren]

Thanks for this VM. PIG (actually PIIS) will again be in record retreat very soon. Really bad situation.

[paolo]

Today no better images 
How long before the crash: weeks, days?

To complete my post the today's image and two images of the SW Tributary of 21 and 22 to show a micro-calving (west of SW Tributary)

[paolo]

Joint PIG- SW Tributary, it's going to crack: images of Sentinel of 09/14 and 10/24

[paolo]

PIG : the northern rift is joining the southern rift, 1.5 kilometer to join.
Images of Sentinel of 09/14 and 10/24

[Stephan]

Thank you for this update.
Any bets when the big calving will happen? [at the NE edge of PIIS the northern crack has grown a little bit but it still ends in the ice sheet without a joint second crack]

[blumenkraft]

+1

I've not seen these cracks before. Very eagle-eyesque, Paolo.

[blumenkraft]

Any bets when the big calving will happen?

Any second now. 

No, seriously! It's amazing it hasn't calved yet.

[paolo]

I would like to point out that in the southern rift (see previous post) we can see an iceberg still connected to the northern edge on 09-14, which detached and partially turned on 10-24: submerged part against the northern wall and part emerged against the southern edge, as can be inferred from the shadow and the fact that the width emerged is greater than the original width.

Which gives us an estimate of height of glacier (in this point): > 500 m 

[blumenkraft]

Amazing find, Paolo!

[Stephan]

The most frightening part is the bigger iceberg close to the calving front circled in black. I'd like to call it "cork". It has turned around counterclockwise in the last 6 weeks by approx. 10°. The smaller calving events (see postings earlier this day) have further exposed it to the sea. If it is lost, then the "zone of destruction" (circled in yellow) will be directly touched by open water. One of the icebergs in this area has turned over since Sep 14 (circled in blue, east of the "cork"). So there must be already thin sea ice covered sea between the bergs which allows them to turn over. New or widened cracks are marked in red.
Question to the experts: Have cracks of that size ever been observed so far upstream of the PIIS?

See attached picture.

[baking]

Question to the experts: Have cracks of that size ever been observed so far upstream of the PIIS?

Not an expert, but the Southern side of PIG always seems to become separated at the margins before the Northern side.  Certainly nothing new.  The Northern side calls the shots.  Stuff happens on the Southern side, but it is pretty much inconsequential to what happens to the North.

Attaching today's high resolution Sentinel-1 image to show that cracks begin to appear at the first widening of PIG and they become more pronounced at the second widening.  So the cracks actually start twice as far back as what you've shown in your image.

[paolo]

Analysis of the left edge (SW) of the PIG (see the two attached images of 09-14 and 10-24; the latter with notations):
1.   Moving 650 meters in 40 days
2.   Two new cracks have appeared and the southernmost one is 3.5 km
3.   The old crack, the southernmost already existed and did not move
After the crack of the join between PIG and SW Tributary, I think things will move quickly on this side
The only resistance being on the right side (NE)

[Stephan]

These cracks (and the higher one upstream) I was referring to when I posed that question yesterday.

[paolo]

Stephan
4 attached images relating to the left edge of PIG before joint with theSW Tributary
- 2017-01-26: no PIG cracks, no zone of iceberg
- 2018-01-27: no PIG cracks, but beginning of area of icebergs between PIG and the Ice Shelf
- 2019-01-31: no PIG cracks and area of icebergs between PIG and the Ice Shelf
- 2019-10-24: PIG cracks and area of icebergs between PIG and the Ice Shelf
It all started after the loss of the junction with the SW Tributary

[Stephan]

Thanks a lot, Paolo. I have recently begun to read all about the changes in the Arctic and Antarctic and joined the forum around one year ago. Therefore I did not "actively see" a much more intact PIIS and thought, this feature is not new. Of course I could have looked up previous years in Sentinel as you just did - I will do so in a minute...

And this also answers my question: There have NEVER BEFORE* been cracks of that size so far upstream on the PIIS


*means: modern times with sattelite imagery, not interglacials millions of years ago ;-)

[paolo]

I think that after the last join between the SW Tributary and PIG will broke (it should have already cracked!!) the big iceberg will detach (even if the right side will make resistance) and then we will see an acceleration of the retreat of PIG

[baking]

I am attaching a Sentinal-1 radar image from Jan. 8, 2016, the earliest the Alaskan Satellite Facility has available on their site.  This clearly shows the break-up of ice at the "second widening" point in my earlier post.

I think you will find that the break-up started at this point (circa 2014-15) and has since moved downstream with the glacier to the calving front.

It may be tied to the separation from the SW tributary, but most likely through a speed-up of the glacier as a whole that kept the ice from spreading out completely at the widening point.  The retreating grounding line could also be a factor.

[paolo]

Hello baking,
we agree, I would say more: the architecture of the ice sheet (PIIS) upstream of the former PIG - SW Tributary join it is still the same as in the past, it depends on the positioning of the glaciers forming the PIIS, with the areas of friction, compression and relaxation.
So of course, there was (left of the PIG) an area of crevasses perpendicular to the PIG (but not in the part of the PIIS corresponding to the PIG), crevasses solding together again downstream.
I think that following the loss of the anchor of the confluence PIG - SW Tributary (the current joint is an incoherent and temporary bric-a-brac of the PIG, piece of ice sheet and the SW Tributary) there has been an acceleration of the PIG whose effects we see now.
The area is still the same, but its conditions is not the same and moreover there is a formation of crevasses in the PIG itself (this was the question of Stephan), which suggests a subsequent retreat of the PIG
In conclusion: the increase in the speed of the PIG and his retreat has transformed and will transform this glacier as a constructive element of the PIIS into a destructive element of the PIIS

[paolo]

I took a reference point in PIG (left side) and a reference point in the PIIS to the left of the PIG and, using the images of 2019-01-31 and 2018-01-27 from my previous post, i calculated the moves

[baking]

It turns out that the rifting on the Southern shear margin of the Pine Island Glacier began in 1999 and started even higher upstream at the "First Widening" (cf. Reply #1070).

MacGregor 2012 "Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011"

https://www.cambridge.org/core/journals/journal-of-glaciology/article/widespread-rifting-and-retreat-of-iceshelf-margins-in-the-eastern-amundsen-sea-embayment-between-1972-and-2011/A7DF1034DE3833AFA25ABB83894976F6

Figure 1b below shows the location of the rifts in 2011 (my red arrows for reference) and the following from page 463: "Rifting along the southern shear margin 40–60km upstream of the terminus began in 1999."

So the rifting is 20 years old but has in that time moved downstream 60km, or 3km/year, which is close to the average speed of PIG over that time-frame.

I will note that the rifting has caused the separation of the Southern Ice Shelf (SIS) from the main glacier so now you are also seeing calving from the SIS.  I will try to highlight what I mean by this in a subsequent post.

[baking]

Here are two close-up Sentinel-1 radar images of the margin between Pine Island Glacier (PIG) and the Southern Ice Shelf (SIS) from April 11 and October 26, 2019, and a GIF comparing the two so movement can be more easily seen.

I've labeled the first image to show the areas that are considered to be the PIG, SIS, and the South West Tributary (SWT.)  They are all part of one big ice shelf, but they move relative to one another so it is important to make the distinction.  The Southern Shear Margin (SSM) rift is the continuation of a rift that started 60km upstream in 1999.  I show that the rift ends short of the ice front.

There is calving from the SIS where it meets the SSM rift.  I think it is reasonable to assume that when the rift reaches the ice front that the "melange" of ice from the calving will eventually float off and we may see additional calving from the SIS causing a retreat of the calving front into the SIS.

I do think that Stephen is correct to call the terminal iceberg a cork, although if the PIG calves it will become a moot point.   It is probably safe to say that within the next six months that either the PIG will calve or the cork will "pop."

But I do not see the SSM rift or the SIS calving as a threat to PIG since the northern margin is faster that the southern and it drives the calving of PIG.  It is however potentially a threat to the SIS and the South West Tributary.

[oren]

But I do not see the SSM rift or the SIS calving as a threat to PIG since the northern margin is faster that the southern and it drives the calving of PIG.  It is however potentially a threat to the SIS and the South West Tributary.

Thanks for these great posts baking. Just a question:
Isn't the northern margin faster because of the SWT pressure? Isn't it quite possible that the southern margin will accelerate following loss of "cork" and SWT contact?

[paolo]

Hello, it's been a long time since I follow this forum, but before I had no time to study scientific articles (I limited myself to reading them very diagonally) and to intervene. In addition, my English is very primitive, see null (and I hope you will forgive me the nonsense that I will probably write, with the help of the automatic translator).
Summarize:
1)   Before 1999 (thanks baking for the article I'm going to read) no rifting => plastic deformation between PIG and SIS. The birth of the rifting being due to an increase in the speed of the PIG (in fact it cannot be induced by the retreat of the grounding-line, since here the SSI was already floating)
2)   2018-10 : break de la jointure entre PIG et SW Tributary. Currently there is no direct join (as I said in post 1077 "the current joint is an incoherent and temporary bric-a-brac of the PIG, piece of ice sheet and the SW Tributary"), but only via an Iceberg of the SIS (Southern Ice Shelf)
3)   SIS side Southern Shear Margin (SSM) (see post 1073):
a)   2017-01: rifts up to 4 km in length, no icebergs
b)   2018-01: beginning to create icebergs and ice-free zones
c)   2019-01: iceberg area and no more strict contact between PIG and SIS
d)   2019-10: the area of icebergs is slightly reduced following the progress of the SIS (it advances by 400 /500 m per year towards the PIG (with an angle of 45 degrees, see post 1078). Still no strict contact between SIS and PIG
4)   PIG side SSM 2019-10: Opening of two new rifts in PIG (side SSM), in a month, including one of 3.5 km (see post 1071). The old rift further south has not changed.
5)   PIG side "ice front": widening of rifts
I think that, the pseudo-join PIG SW Tributary being giving in, we had an advance of the PIG sizeable. But now there is only one area of friction: The Northern Shear Margin NSI, SSI being currently frictionless, hence the tension on the south side of the PIG and the creation of the two new rifts
Future :
1)   Breaking the pseudo-join
2)   PIG Iceberg detachment once the north side has broken
3)   At least partial emptying of ISS icebergs
4)   New iceberg of the PIG very soon with substantial retirement of the PIG
5)   In a year or two the SIS will come again into contact with the PIG (see above), but without the SW Triburary it shouldn’t change much

[baking]

But I do not see the SSM rift or the SIS calving as a threat to PIG since the northern margin is faster that the southern and it drives the calving of PIG.  It is however potentially a threat to the SIS and the South West Tributary.

Thanks for these great posts baking. Just a question:
Isn't the northern margin faster because of the SWT pressure? Isn't it quite possible that the southern margin will accelerate following loss of "cork" and SWT contact?

That's a good point, Oren.  In the MacGregor 2012 paper cited above, there is a discussion on page 463 of why the Northern Margin has been faster than the Southern, some of which has to do with the "loss of buttressing" due to rifting from the Northern Ice Shelf.  Although it is not clear if that is the full explanation.  So one thing to watch for would be an acceleration of the Southern Margin.

[paolo]

Baking,
This is what I try to explain in my previous post:
1.   Strong Resistance NSM
2.   SSM currently no resistance
3.   The pseudo join PIG-SWT that begins to give way (widening of two large rifts crossing the PIG, especially the one to the south)
=> Acceleration PIG side SSM
=> Opening of new rifts further south (side SSM)

[paolo]

PIG on the north side it moves, but not much.
Below are two images of 09-14 and 10-24.
In the second image I added the differences

[baking]

Just for laughs I tried to measure the velocity of both margins of Pine Island Glacier of the past 7 months.  I took Sentinel-1 satellite images from March 24 and October 26, 2019, and lined up the images as best I could for both sides, just above the new large crack.  It was not terribly scientific, and the detail on the Northern Margin was pretty fuzzy, but within a reasonable margin of error I think my findings were significant.

Over the 216 days there was a ten pixel different between the sides, or 200 meters, which is 350 meters per year.  What's interesting was that the Southern Margin was moving faster, 4450 m/year, versus 4100 m/year for the Northern Margin.

Considering that the Northern Margin was moving much faster in 2011, this is a big change and probably attributable, at least in part, to the rift on the Southern Margin that now extends almost 60km.

I will need to find more recent publications to see if this has been noted already.

Turns out this information is available in pretty much real-time:
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=3

[blumenkraft]

Great find, Baking!

What is causing this in your opinion?

[baking]

What is causing this in your opinion?

I will try to summarize everything so far.  For background through 2011, I have to suggest the folowing paper.  The figure below are from there.

MacGregor 2012 "Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011"

https://www.cambridge.org/core/journals/journal-of-glaciology/article/widespread-rifting-and-retreat-of-iceshelf-margins-in-the-eastern-amundsen-sea-embayment-between-1972-and-2011/A7DF1034DE3833AFA25ABB83894976F6

The first figure (1a) labels the Northern and Southern Ice Shelves.  Ice shelves where multiple ice streams come together are like "merges" in heavy traffic.  More ice is coming in than can leave and everything slows down to the point that the ice shelf "buttresses" the incoming glaciers.

By 2011, (see figure 1b) Pine Island Glacier had rifted from the Northern Ice shelf and the Northern Shear Margin of PIG had substantially increased in speed.  There is an extensive discussion of this in MacGregor 2012 on page 463 of the PDF.

MacGregor 2012 also mentions is the rift that started on the Southern Shear Margin in 1999, 60 km back from the ice front where the glacier widens to the south.  (Red arrows added to figure 1b.)  This rift has grown and is about to reach the ice front which means that PIG is effectively no longer buttressed by the Southern Ice Shelf either.

So the first result of this is that PIG is moving faster, up by 10% in the last 5 years.  If the Southern side continues to move faster than the Northern, you could see future cracks forming in the North and spreading to the South, the opposite of what PIG has been doing.  I would foresee a strong likelihood that the ice front will retreat about 15km above the current point in the next 3-5 years.  For reference, say the point at 100 degrees West and 75 degrees South on the Northern Margin.  This would also make calving on the Southern Ice Shelf easier, and maybe the SW Tributary.

[baking]

I saw these cracks yesterday in the Southern Shear Margin Zone.  I don't think they are significant for the locations of future calving from the main glacier unless they extend out of the shear margin zone and cross the line of the shear margin of the glacier.

There is a discussion with real experts here:
https://twitter.com/bert_polar/status/1188585451071983616

Of course, this does fit in with the discussion about about the eventual breakup of this rift/shear zone and all that follows.

[blumenkraft]

I think it is happening.

Those 2 pictures where taken today. The first one (the low-res one) was taken 04:57 GMT, the second one was taken 09:52 GMT. It's either the low-res picture doesn't see the crack (perhaps a weird angle) or it has cracked massively between those times. I think it's the later.


(Sorry for the badly lined up pictures, but when i wanted to correct it, PolarView wouldn't load anymore)

Click to play!

[baking]

As a continuation of the shear margin discussion, this recent paper discusses the effect of shear margins on major glacier calving events.

"Troughs developed in ice-stream shear margins precondition ice shelves for ocean-driven breakup"

Authors: Karen E. Alley, Ted A. Scambos, Richard B. Alley and Nicholas Holschuh

https://advances.sciencemag.org/content/5/10/eaax2215

[paolo]

blumenkraft,
The first hypothesis is the right one, in well-before images the rifts are similar to the second image
We have to wait and, in my opinion, first advent will be rather side SWT

[baking]

I think it is happening.

Those 2 pictures where taken today. The first one (the low-res one) was taken 04:57 GMT, the second one was taken 09:52 GMT. It's either the low-res picture doesn't see the crack (perhaps a weird angle) or it has cracked massively between those times. I think it's the later.


(Sorry for the badly lined up pictures, but when i wanted to correct it, PolarView wouldn't load anymore)
Click to play!

I don't see it.  I looked at the last two high-res Sentinal-1 radar images from Oct. 26 and 31 and I don't see and enlargement.  There is a difference in angle of about 60 degrees which makes some features darker in the earlier image, but nothing seems significant.  Here is a GIF of what I saw.  Resolution is important.

[blumenkraft]

blumenkraft,
The first hypothesis is the right one

Ok, guys, striking arguments. I should have looked back on hi-res pictures myself. m)

[Stephan]

Update PIIS Nov 3, 2019.
A new Sentinel picture is available.
I compared it intensively with the picture from Oct. 24.
No relevant changes at the two large cracks. They have widened and lengthened very little. New cracks (red lines) appear SE of the "cork" which reveals tension and pressure in that area. The cork has turned a little bit more counterclockwise. The gap S of it (yellow line) has widened. A lot is on the move around the "cork".
I wonder whether the "cork" or the large cracks will calve next...

See attached picture.

[blumenkraft]

Oh cool! Thanks for the hint, Stephan.

Here is for comparison as GIFs.

Click to play.

[baking]

What rendering and effects are you guys using on Sentinel Hub?

[blumenkraft]

Normally "return [B8A*1,B03*1,B02*1]" does well.

For spotting melt ponds "return [B8A*2,B03*1,B02*1]" is great.

Playing with gain and gamma sometimes helps me.

Loving to hear what you guys do. Are there any tricks and tips?

[Stephan]

Oh cool! Thanks for the hint, Stephan.

Here is for comparison as GIFs.

Click to play.

Thanks for the animations. It looks like the "cork" is only glued at its W/SW edge and ready to move away any time...