Pine Island Glacier (PIG) Calving and Discussion

[Wipneus]

The way a calving crumbles.

[steve s]

I agree, Shared Humanity. Beautiful.

[Shared Humanity]

The shadows cast by the sun, low in the horizon, on the Sentinel 2 image and this latest crumbling suggests to me that the PIG is undergoing dramatic thinning. If you look at the upper left portion of the Sentinel 2 image, the shadow shrinks dramatically as you move towards the center of the berg just recently calved. Is there some way to calculate the freeboard of the thinner section and determine the thickness of the shelf here? Also, on the 2nd image, there are pronounced depressions (3 at least, perhaps as many as 5) that run through the ice shelf and terminate on the calving face exactly where the crumbling on the berg is occurring. Wouldn't these suggest canyons have formed on the underside of the shelf by warm waters flowing to the open sea? If this is so, the leading edge of the PIG may be far more susceptible to collapse than it would appear.

[Shared Humanity]

Wipneus....

Could you capture a Sentinel 2 image of the calved berg where these apparent depressions exist closer to the center of the berg) so that we can determine whether the shadows confirm the existence of the depressions? Also if these are caused by undulating height of the ice shelf is there any other reason than thinning of the glacier that would cause this? Perhaps scouring of snow on the surface of the glacier by winds?

[oren]

The rapid crumbling of the PIIS calf is scary. As if it was barely holding itself together before the calving.
p.s. the animation also shows another (very minor) calving at the eastern tip.

[Wipneus]

Wipneus....

Could you capture a Sentinel 2 image of the calved berg where these apparent depressions exist closer to the center of the berg) so that we can determine whether the shadows confirm the existence of the depressions?

I have uploaded the full image at
https://drive.google.com/open?id=0B8NUHa4P2gmlNzVrcldTUHQ1TXM

Download this in a sufficiently powerful PC (file size is about 600MB) and view with the Gimp or some other capable software.

[Wipneus]

More crumbling...

[Shared Humanity]

It would seem that most of the cracks are occurring in areas where the berg and ice shelf show depressions. Are these snow covered depressions actually deep fissures hidden from view?

[Adam Ash]

Interesting paper on ice-cliff instability, which presumably has relevance to all ocean-terminating glaciers.

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks
http://www.nature.com/nature/journal/v550/n7677/full/nature24458.html?WT.ec_id=NATURE-20171026&spMailingID=55217903&spUserID=NzE3MDU3OTQ1MDMS1&spJobID=1264650535&spReportId=MTI2NDY1MDUzNQS2

and an illustration of the concepts..
http://www.nature.com/nature/journal/v550/n7677/fig_tab/nature24458_F4.html

and all the figures at:
http://www.nature.com/nature/journal/v550/n7677/fig_tab/nature24458_ft.html

From the abstract...
'From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8, 9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11, 12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels.'
'Our findings demonstrate the effective operation of Marine ice-cliff instability (MICI) in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.'

[Adam Ash]

More crumbling...

Is this crumbling an indication that the ice generally has a lower structural strength than previously, where tabular bergs would hold together?  If so, this would suggest that the ice is warmer than before.  Unsurprising, if that is the case, tho troubling too.

[sidd]

Thanks for the link to the Wise paper. Nice. I attach Fig 4

sidd

[oren]

Thank you. Highly interesting, a pity it's pay-walled.
A MICI model supported by actual evidence on the seafloor, a strong argument indeed.

[Wipneus]

The disintegration of the PIG calving is subject of today's NASA Earth Observatory "image of the day":
https://earthobservatory.nasa.gov/IOTD/view.php?id=91203

One consequence is:

None of the fractured pieces are large enough to be named and tracked by the U.S. National Ice Center, which has removed B-44 from their table of tracked bergs.

That was quick.

[solartim27]

Nice time lapse video in this article.  Also includes Thwaites.
https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html?smid=tw-nytimes&smtyp=cur&_r=0

The animation above shows Pine Island glacier flowing into the Amundsen Sea from 2014 to 2017. Twice in that period, the glacier released an iceberg larger than 100 square miles.

[FishOutofWater]

Whoa, Wip, that was much too quick. Periodic formation of icebergs happened before the effects of climate change hit Antarctica, but this rapid disintegration looks like something else altogether. It has apparently disintegrated along lines of weakness caused by extension during flow. I suspect that there has been a substantial amount of melting on the underside of the glacier.

This does not bode well for the long term stability of PIG.

[oren]

Nice time lapse video in this article.  Also includes Thwaites.
https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html?smid=tw-nytimes&smtyp=cur&_r=0

The animation above shows Pine Island glacier flowing into the Amundsen Sea from 2014 to 2017. Twice in that period, the glacier released an iceberg larger than 100 square miles.

Thanks. These NYT animations are superb, especially the Thwaites one. The Thwaites discharge area is very "messy", and the animation helps understand what is going on where in there.

[Wipneus]

Good optical images are scarce at the moment: Sentinel 2 images have not been uploaded since the beginning of October while Landsat images are mostly cloudy. This Landsat 8 image from the 17th is still hazy, but the new crack can yet easily made visible by enhancing the contrast.

[crandles]

Antarctic glacier's rough belly exposed

The melting Antarctic ice stream that is currently adding most to sea-level rise may be more resilient to change than previously recognised.

New radar images reveal the mighty Pine Island Glacier (PIG) to be sitting on a rugged rock bed populated by big hills, tall cliffs and deep scour marks.

Such features are likely to slow the ice body’s retreat as the climate warms, researchers say.

http://www.bbc.co.uk/news/science-environment-42052072

Nature Communications

Diverse landscapes beneath Pine Island Glacier influence ice flow

The retreating Pine Island Glacier (PIG), West Antarctica, presently contributes ~5–10% of global sea-level rise. PIG’s retreat rate has increased in recent decades with associated thinning migrating upstream into tributaries feeding the main glacier trunk. To project future change  requires  modelling  that  includes  robust  parameterisation  of  basal  traction,  the resistance to ice flow at the bed. However, most ice-sheet models estimate basal traction from satellite-derived surface velocity, without a priori knowledge of the key processes from which it is derived, namely friction at the ice-bed interface and form drag, and the resistance to ice flow that arises as ice deforms to negotiate bed topography. Here, we present high-resolution maps, acquired using ice-penetrating radar, of the bed topography across parts of PIG. Contrary to lower-resolution data currently used for ice-sheet models, these data show a contrasting topography across the ice-bed interface. We show that these diverse subglacial landscapes have an impact on ice flow, and present a challenge for modelling ice-sheet evolution and projecting global sea-level rise from ice-sheet loss.

[AbruptSLR]

Such features are likely to slow the ice body’s retreat as the climate warms, researchers say.

If one only considers basal slide of the PIG, then the basal roughness of PIG's bed identified in the linked reference is good news, as it may slow future ice mass loss.  On the other hand, such basal roughness may do little to slow ice mass loss associated with any future cliff failures that PIG may experience in the coming decades, as Wise et al. (2017) demonstrates happened in the not too distant past:

Wise et al. (2017), "Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks", Nature 550, 506-510, doi:10.1038/nature24458

https://www.nature.com/articles/nature24458

Extract: "From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels.
...
Our findings demonstrate the effective operation of Marine ice-cliff instability (MICI) in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet."

See also:

http://glacierhub.org/2017/11/20/roundup-ice-cliff-instability-buffers-glacial-retreat/

[Susan Anderson]

Fascinating graphic and exposition. If there are more big rapid breakups, I'd guess (and it is only a guess) that means deeper iceberg breakoffs and more scraping, is that right?

[AbruptSLR]

Fascinating graphic and exposition. If there are more big rapid breakups, I'd guess (and it is only a guess) that means deeper iceberg breakoffs and more scraping, is that right?

Susan,
The topic of ice cliff failures and hydrofracturing has been discussed extensively in other threads, so I will only touch on this topic here.  The first attached image (see also the associated caption) shows Pollard et al. (2015)'s criteria for cliff failure in a marine glacier without hydrofracturing (I note that DeConto indicates that a lot of hydrofracturing will occur in key portions of West Antarctica well before GMSTA gets to 2.7C).  So without hydrofracturing cliff failures (at the grounding line) roughly occur when the portion of the cliff face above the water line equals, or exceeds, about 90 to 100m, in a water depth on the order of 800m; once the ice shelf has collapsed.

Once the Pine Island Ice Shelf collapses (say due to hydrofracturing if/when GMSTA nears 2.7C, which might be as soon as 2040 per the second attached image from Friedrich et al. (2016), assuming BAU warming until at least 2040), then there could be a lot of cliff failures of the PIG as at its grounding line it currently exceeds Pollard et al (2015)'s criteria.  This might result in an extensive ice mélange in front of the PIG, which might increase bottom gouging and might partially buttress the face of the PIG (thus temporarily stopping more calving).  However, I note that the ice mélange in front of the Jacobshavn Glacier in Greenland only provides limited buttressing of calving from its face.

Pollard et al (2015), https://doi.org/10.1016/j.epsl.2014.12.035

http://www.sciencedirect.com/science/article/pii/S0012821X14007961

Caption: "Fig. 2. Schematic cross-sections of an ice sheet approaching cliff failure. Ice flow is from left to right, from grounded ice to floating shelf. M = surface liquid runoff into crevasses. C = calving. O = oceanic basal melt. F = deformational flow across the grounding line. Red arrows show possible grounding-line movement. (a) With substantial ice shelf, and shallow surface slopes in the grounding zone. (b) After strong warming (large M,C,O) with the shelf nearly removed but still allowing shallow slopes. (c) With the shelf completely removed, exposing a vertical cliff > ∼100 m above sea level that undergoes structural failure, causing very rapid grounding-line retreat. Note that “cliff” failure can also occur at grounding lines with ice shelves, if the ice shelf provides little or no buttressing. It can occur in shallower depths than shown if the ice column at the grounding line is weakened by melt-driven hydrofracturing M"

Best regards,
ASLR

[Wipneus]

On the SW side new cracks have formed.

[AbruptSLR]

On the SW side new cracks have formed.

Not to sound like a Jeremiah, but this new cracking pattern in the PIIS looks to me like it could be associated with a coming major calving of the Southwest Tributary Ice Shelf; which might contribute to an eventual acceleration of the Southwest Tributary Glacier ice flow velocities.

[FredBear]

"Jeremiah", the movements of glacier, icebergs and cracks look too fast to bode well, I'm afraid   .   .   .   (even if the Sept. 22 calving only moved the calving face back to the 2015 position).

[Susan Anderson]

New from Earth Observatory https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=91470&src=nha

Pine Island Iceberg Under the Midnight Sun

acquired December 15, 2017 [note: to download large image (6 MB, JPEG, 5000x5000) go to link]

In September 2017, a new iceberg calved from Pine Island Glacier—one of the main outlets where the West Antarctic Ice Sheet flows into the ocean. Just weeks later, the berg named B-44 shattered into more than 20 fragments.

On December 15, 2017, the Operational Land Imager (OLI) on Landsat 8 acquired this natural-color image of the broken berg. An area of relatively warm water, known as a polyna, has kept the water ice free between the iceberg chunks and the glacier front. NASA glaciologist Chris Shuman thinks the polynya’s warm water could have caused the rapid breakup of B-44.

The image was acquired near midnight local time. Based on parameters including the azimuth of the Sun and its elevation above the horizon, as well as the length of the shadows, Shuman has estimated that the iceberg rises about 49 meters above the water line. That would put the total thickness of the berg—above and below the water surface—at about 315 meters.

[Wipneus]

Detail of the widening SW crack.

[oren]

Looks like a lot of widening given it's just 9 days between the images.

[maga]

The picture in Susan's entry shows several more cracks. They can also be seen from time to time in Aqua (Modis) pictures but not in such detail. I marked some of them.

[Grygory]

Amazing how grow new crack in pine island glacier
http://www.polarview.aq/images/106_S1jpgsmall/201801/S1A_IW_GRDH_1SSH_20180110T043545_BF1A_S_1.jpg but what's more amazing is what's happening at the next glacier:
http://www.polarview.aq/images/106_S1jpgsmall/201801/S1A_IW_GRDH_1SSH_20180110T043610_7729_S_1.jpg -This season mealting will by propobly rekord in this region Antarctic
if not wholly

[Tealight]

Sentinel2 started acquiring images of Antarctica again.

Click on the first image for full resolution of the new crack.

The second image shows one of the rifts 20km upstream, which has some ice-free spots in it. I'm wondering if the ocean heat was enough to melt the ice locally. There the ice can't just drift away like the calving front.

[solartim27]

The second image shows one of the rifts 20km upstream, which has some ice-free spots in it. I'm wondering if the ocean heat was enough to melt the ice locally. There the ice can't just drift away like the calving front.

I believe it's much to thick to melt through in a single spot.  Looks to me that it's from rifting and downstream bergs moving faster than the still attached parts.  With all the new rifts on that side, I think well see more frequent smaller calving of PIG.

[solartim27]

Nice gif from Landsat 8, dates 26 Dec to 11 Jan on this tweet
https://twitter.com/StefLhermitte/status/951967405890310145

[Bernard]

Nice gif from Landsat 8, dates 26 Dec to 11 Jan on this tweet
https://twitter.com/StefLhermitte/status/951967405890310145

Impressive images. Not only the extension of the crack, but the rapid move of the chunks of desintegrated B44. New calving by the end of this month, I would bet.

[ghoti]

His pinned tweet is also very impressive: PIG, the movie

https://twitter.com/StefLhermitte/status/918875349945126912

[Wipneus]

Another clear Sentinel image. An overview below is scaled to 60m/pix only shows the SW crack clearly.

There are two more cracks, indicated by arrow on the overview, shown in 10m/pix detail below. The first one was first noticeable after the latest big calving. The second one is rather new, and much further upstream. Perhaps the next big calving?

[solartim27]

Some minor action at PIG and the Tributary glaciers.  Might see some more with the full moon this week.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SDH_20180129T042752_C43C_S_1.final.jpg   32 Mb

[FredBear]

& more cracking at the western edge of PIG 07.Feb.2018? (EODIS)

[solartim27]

Nice Lands at 8 image of a new rift.  Doesn't seem like we'll need to wait quite as long to see this one go.
https://mobile.twitter.com/StefLhermitte/status/964254595030618113

[Sciguy]

Solartim,

What is the scale on that photo?  Can you tell how far back from the edge the new rift is?

Also, are dots that appear to be small holes melt ponds?  If so, that's a troubling sign.

[Sleepy]

Eyeballing, something like 16 kilometres. The most troubling sign is that we are watching at all.
PIG calvings used to be on decadal timeframes. Adding that updated animation by Lhermitte as a gif.

[Shared Humanity]

What is most troubling about that GIF are the large, widening rifts that are appearing on the ice stream at the lower left. This ice stream serves to pin the main ice stream at the current calving front. If this ice were to calve, eliminating this pinning effect, we would see a rapid retreat of the main calving face IMHO.

[Shared Humanity]

Looking more closely at the GIF, there is another terrifying feature. There is another secondary ice stream from the very bottom of the GIF which enters into the main stream and flows parallel with it along the bottom. There are very rapidly growing rifts in this stream as well. I think we are very close (a few years at most) from a dramatic change in this glacier's behavior.

[solartim27]

Solartim,
What is the scale on that photo?  Can you tell how far back from the edge the new rift is?
Also, are dots that appear to be small holes melt ponds?  If so, that's a troubling sign.

There is a scale bar in the bottom corner, but the latter gif scale bar gives a better overview.  There are no melt ponds in that photo, but it has happened before.  See this post upthread for a nice shot.

Here is a photo of melt ponds on PIIS circa 2005:

The other glacier coming in off the side is referred to as the SW Tributary Glacier, widely discussed upthread and elsewhere.  To find more info on that use the search button up top.

[FredBear]

The widening crack in the PIG showing at the bottom of the Land Sat 8 image in Reply #737 (14 Feb) leads to a large square breaking off the SW tributary - which I thought was becoming much less attached in my smaller scale pic. (Reply #736, 07 Feb),    going,    going   .   .   

[Sleepy]

Looking more closely at the GIF, there is another terrifying feature. There is another secondary ice stream from the very bottom of the GIF which enters into the main stream and flows parallel with it along the bottom. There are very rapidly growing rifts in this stream as well. I think we are very close (a few years at most) from a dramatic change in this glacier's behavior.

Add what can't be seen.
https://www.cambridge.org/core/journals/annals-of-glaciology/article/ocean-access-beneath-the-southwest-tributary-of-pine-island-glacier-west-antarctica/EFF449338C7D7D088CCB7BC48D40B150/core-reader

Abstract

The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line.

[Shared Humanity]

Does not surprise me that research has already studied in detail these tributaries.

[LRC1962]

Not sure if this study has already been posted or exactly where it should go as it could be posted in many spots.
Interacting Antarctic glaciers may cause faster melt and sea level contributions
This IMO continues to reinforce the idea glaciers are much more unstable and intact much with each other then previously thought.

"This is a potentially really dynamic place between these two glaciers, and this is somewhere where further study is really warranted," said lead author Dustin Schroeder, an assistant professor of geophysics at the School of Earth, Energy & Environmental Sciences. "If this tributary were to retreat and get melted by warm ocean water, it could cause the melt beneath Pine Island to spread to Thwaites."

Sea-level rise has become a major global concern based on research showing extra ocean water from melting glaciers could swamp coastal areas around the world, contaminate drinking and irrigation water, threaten wildlife populations and hurt the economy. This new perspective on the Southwest Tributary shows melting beneath Pine Island may be currently or imminently causing the melting of Thwaites and speeding the rate of sea-level rise.

"These results show that the ocean is really starting to work on the edge of this glacier, which means that we're likely at the onset of it having an impact," Schroeder said.


Read more at: https://phys.org/news/2018-01-interacting-antarctic-glaciers-faster-sea.html#jCp

[solartim27]

Another small calving, with more rift expansion.  Interesting how the sea ice has kept the older bergy bits contained this year.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SDH_20180306T042751_8C9C_S_1.final.jpg

[FredBear]

solartim27, that small berg which looks like a new calving drifted south (up) from the earlier calving between March 3 & 4 on EOSDIS and stopped at the tip of the large iceberg (wriggled slightly on 5th March). However the widening crack is more obvious in your picture, lighting and clouds can be deceptive on a smaller scale.

[solartim27]

solartim27, that small berg which looks like a new calving drifted south (up) from the earlier calving

Nope, it's new.  Don't have time to do a gif now.  This is from 3 March
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20180303T040320_85E1_S_1.final.jpg