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Wipneus

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Re: PIG has calved
« Reply #700 on: October 15, 2017, 11:32:33 AM »
The way a calving crumbles.

steve s

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Re: PIG has calved
« Reply #701 on: October 16, 2017, 10:28:52 AM »
I agree, Shared Humanity. Beautiful.

Shared Humanity

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Re: PIG has calved
« Reply #702 on: October 16, 2017, 03:54:10 PM »
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.
« Last Edit: October 16, 2017, 04:05:33 PM by Shared Humanity »

Shared Humanity

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Re: PIG has calved
« Reply #703 on: October 16, 2017, 04:02:11 PM »
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

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Re: PIG has calved
« Reply #704 on: October 18, 2017, 12:41:55 AM »
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

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Re: PIG has calved
« Reply #705 on: October 18, 2017, 08:37:09 AM »
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

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Re: PIG has calved
« Reply #706 on: October 25, 2017, 06:48:02 PM »
More crumbling...

Shared Humanity

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Re: PIG has calved
« Reply #707 on: October 25, 2017, 08:10:04 PM »
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

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Re: PIG has calved
« Reply #708 on: October 26, 2017, 03:51:38 AM »
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.'
« Last Edit: October 26, 2017, 03:58:14 AM by Adam Ash »

Adam Ash

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Re: PIG has calved
« Reply #709 on: October 26, 2017, 03:54:36 AM »
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

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Re: PIG has calved
« Reply #710 on: October 26, 2017, 04:36:02 AM »
Thanks for the link to the Wise paper. Nice. I attach Fig 4

sidd

oren

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Re: PIG has calved
« Reply #711 on: October 26, 2017, 08:41:15 AM »
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

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Re: PIG has calved
« Reply #712 on: October 28, 2017, 11:46:32 AM »
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

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Re: PIG has calved
« Reply #713 on: October 31, 2017, 05:44:22 PM »
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.
FNORD

FishOutofWater

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Re: PIG has calved
« Reply #714 on: October 31, 2017, 06:20:17 PM »
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

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Re: PIG has calved
« Reply #715 on: November 01, 2017, 12:47:37 AM »
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

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Re: PIG has calved
« Reply #716 on: November 20, 2017, 06:35:49 PM »
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

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Re: PIG has calved
« Reply #717 on: November 20, 2017, 07:49:15 PM »
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

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Re: PIG has calved
« Reply #718 on: November 20, 2017, 08:24:00 PM »
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/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Susan Anderson

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Re: PIG has calved
« Reply #719 on: November 20, 2017, 09:34:47 PM »
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

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Re: PIG has calved
« Reply #720 on: November 20, 2017, 10:52:01 PM »
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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Wipneus

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Re: PIG has calved
« Reply #721 on: December 11, 2017, 06:16:09 PM »
On the SW side new cracks have formed.

AbruptSLR

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Re: PIG has calved
« Reply #722 on: December 11, 2017, 06:50:26 PM »
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.
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FredBear

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Re: PIG has calved
« Reply #723 on: December 12, 2017, 02:15:52 AM »
"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

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Re: PIG has calved
« Reply #724 on: December 22, 2017, 05:22:20 AM »
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

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Re: PIG has calved
« Reply #725 on: December 23, 2017, 01:13:24 PM »
Detail of the widening SW crack.

oren

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Re: PIG has calved
« Reply #726 on: December 23, 2017, 10:49:32 PM »
Looks like a lot of widening given it's just 9 days between the images.

maga

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Re: PIG has calved
« Reply #727 on: December 26, 2017, 03:57:38 PM »
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

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Re: PIG has calved
« Reply #728 on: January 10, 2018, 10:02:50 PM »
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

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Re: PIG has calved
« Reply #729 on: January 13, 2018, 01:30:48 PM »
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

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Re: PIG has calved
« Reply #730 on: January 13, 2018, 04:11:07 PM »
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.
FNORD

solartim27

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Re: PIG has calved
« Reply #731 on: January 14, 2018, 01:22:02 AM »
Nice gif from Landsat 8, dates 26 Dec to 11 Jan on this tweet
https://twitter.com/StefLhermitte/status/951967405890310145
FNORD

Bernard

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Re: PIG has calved
« Reply #732 on: January 14, 2018, 10:58:42 AM »
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

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Re: PIG has calved
« Reply #733 on: January 14, 2018, 04:18:24 PM »
His pinned tweet is also very impressive: PIG, the movie

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