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Author Topic: Thwaites Glacier Discussion  (Read 55998 times)

grixm

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Re: Thwaites Glacier Discussion
« Reply #300 on: September 22, 2020, 10:49:40 AM »
Overview of the whole Thwaites glacier back in March before the sun set, and now.

solartim27

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Re: Thwaites Glacier Discussion
« Reply #301 on: September 22, 2020, 04:55:23 PM »
From Peter Neff @icy_pete
Today is the first day of the #WAIS2020 West #Antarctic glaciology workshop! 🇦🇶❄️

If you registered, you can attend any session over the next two weeks. Zoom links in your inbox. 📬

Today: Grounding zones & ice shelves, Session 7
3-5pm Eastern
https://t.co/v3HfBXL0Tp https://t.co/IDzzmQhQ43

All sessions are recorded and available on YouTube  from @MinesGlaciology
https://www.youtube.com/channel/UC-nSFKCeciZh5KQtEgrJqmg
FNORD

baking

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Re: Thwaites Glacier Discussion
« Reply #302 on: September 26, 2020, 05:09:38 PM »
Another piece of Iceberg B22-A broke off from the older (Western) end earlier this month and floated off this week.  Click on the GIF below.  You can also see the amount of movement of B22-A.

AbruptSLR

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« Last Edit: November 25, 2020, 03:09:22 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

baking

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Re: Thwaites Glacier Discussion
« Reply #304 on: November 25, 2020, 04:15:07 AM »
I've been keeping a close eye on the sea ice off of Thwaites.  The Tongue is in such rough shape that I fear it could be devastated if the sea ice retreats much during this upcoming warm season.  It was protected by the fast ice it last year, but the year before it was very bad.  I am worried that it could be even worse this year.

AbruptSLR

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Re: Thwaites Glacier Discussion
« Reply #305 on: November 25, 2020, 03:36:16 PM »
I've been keeping a close eye on the sea ice off of Thwaites.  The Tongue is in such rough shape that I fear it could be devastated if the sea ice retreats much during this upcoming warm season.  It was protected by the fast ice it last year, but the year before it was very bad.  I am worried that it could be even worse this year.

I concur :(

Edit: For comparison the first image is from Sentinel-1 on Nov 27, 2017; while the second image is from Sentinel-2 on Nov 17 2020.
« Last Edit: November 25, 2020, 03:56:10 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

baking

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Re: Thwaites Glacier Discussion
« Reply #306 on: November 25, 2020, 04:28:47 PM »
I think this morning's Sentinel-1 image illustrates the threat of open water (in black) reaching the Tongue.

gerontocrat

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Re: Thwaites Glacier Discussion
« Reply #307 on: November 25, 2020, 05:36:45 PM »
Thwaites is becoming a hot potato. For someone like me, (i.e. too old, tired and lazy to understand the science) the linked article does help as it shows that the scientists are unsure of what the future holds except for one thing:- if GHG emissions are not reduced, by a lot, then it's whoops for sure.

https://yaleclimateconnections.org/2020/11/can-shearing-of-thwaites-glacier-slow-or-stop-if-humans-control-greenhouse-gas-emissions/
Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions?

Runaway sea-level rise resulting from retreat of Antarctica's Thwaites glacier depends on humans' substantially cutting GHG emissions.

Quote

Scripps Institution of Oceanography scientist Jeffrey Severinghaus opens the video pointing to someone’s gradually rolling a large round boulder down a hill: Stop pushing a few moments, and the boulder may pause, may sit in place. But in time, the pushing gets to the point that the boulder sets apace on its own. Severinghaus calls that a “runaway positive feedback,” something to be avoided. Is that runaway prospect inevitable? he asks rhetorically. “We are possibly in a collapse right now,” he says. “but I would say it’s not very likely.” There’s a “but” coming, as Severinghaus adds “but we can’t completely rule it out either.”

Severinghaus shares with climate scientist Eric Rignot, of the University of California, Irvine, a concern that so little is known about the underlying topography of the Antarctic ice sheets. “We know more about the topography of Mars than we know about the topography beneath Antarctic Ice,” he says. Rignot agrees, pointing to “not enough observations.”

“The accident of where it is, is that Thwaites can cause tremendously more sea-level rise by itself than these others can,” says Penn State climate scientist Richard Alley. He notes that some models show the unending shearing and collapse of Thwaites ice “keeps going,” but says other models hold that the shearing can be constrained – and the resulting sea-level rise kept “small, slow, and expected” – if greenhouse emissions can be substantially reduced, and soon.
That’s a point Twila Moon, scientist with the National Snow and Ice Data Center, fully buys into. “All of these different elements of the cryosphere” in the future will look “dramatically different if we are taking very strong action to reduce GHG emissions, versus if we are following a path like today.”


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AbruptSLR

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Re: Thwaites Glacier Discussion
« Reply #308 on: November 25, 2020, 06:26:52 PM »
Thwaites is becoming a hot potato. For someone like me, (i.e. too old, tired and lazy to understand the science) the linked article does help as it shows that the scientists are unsure of what the future holds except for one thing:- if GHG emissions are not reduced, by a lot, then it's whoops for sure.

https://yaleclimateconnections.org/2020/11/can-shearing-of-thwaites-glacier-slow-or-stop-if-humans-control-greenhouse-gas-emissions/
Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions?

Runaway sea-level rise resulting from retreat of Antarctica's Thwaites glacier depends on humans' substantially cutting GHG emissions.

Quote

Scripps Institution of Oceanography scientist Jeffrey Severinghaus opens the video pointing to someone’s gradually rolling a large round boulder down a hill: Stop pushing a few moments, and the boulder may pause, may sit in place. But in time, the pushing gets to the point that the boulder sets apace on its own. Severinghaus calls that a “runaway positive feedback,” something to be avoided. Is that runaway prospect inevitable? he asks rhetorically. “We are possibly in a collapse right now,” he says. “but I would say it’s not very likely.” There’s a “but” coming, as Severinghaus adds “but we can’t completely rule it out either.”

Severinghaus shares with climate scientist Eric Rignot, of the University of California, Irvine, a concern that so little is known about the underlying topography of the Antarctic ice sheets. “We know more about the topography of Mars than we know about the topography beneath Antarctic Ice,” he says. Rignot agrees, pointing to “not enough observations.”

“The accident of where it is, is that Thwaites can cause tremendously more sea-level rise by itself than these others can,” says Penn State climate scientist Richard Alley. He notes that some models show the unending shearing and collapse of Thwaites ice “keeps going,” but says other models hold that the shearing can be constrained – and the resulting sea-level rise kept “small, slow, and expected” – if greenhouse emissions can be substantially reduced, and soon.
That’s a point Twila Moon, scientist with the National Snow and Ice Data Center, fully buys into. “All of these different elements of the cryosphere” in the future will look “dramatically different if we are taking very strong action to reduce GHG emissions, versus if we are following a path like today.”



I am not very good at graphics but hopefully the three attached images will give readers a better appreciation that the calving front for icebergs from the base of the Thwaites Ice Tongue is rapidly approaching the southern face of the subglacial cavity in the Thwaites Gateway leading down into the BSB (Byrd Subglacial Basin).  The first image is from the Peter Sinclair video you linked to of an image from the austral 2017-18 summer season showing the location of the subglacial cavity at the base of the Thwaites Ice Tongue circa 2017, with only initial fracturing of the ice over the subglacial cavity (which I have previously termed the 'Big Ear', inside the zone called T1 in the image).  The second image created by baking shows a Sentinel-1 image from May 21, 2020 showing that the calving front has moved close to the southern side of the Big Ear subglacial cavity.  The third image from Sentinel-2 on November 17, 2020 shows that the icebergs floating over the top of the Big Ear subglacial cavity while still constrained from floating way when the local sea ice melts, but are much less constrained than they were in May 2020.  Once the icebergs floating over the Big Ear subglacial cavity do float away, they will likely expose a bare ice cliff face that is subject to a MICI-type of failure leading directly into the BSB.

Edit: The fourth image is a Landsat photo from 2018 showing growing crevasse-damaged areas near the grounding line of the Thwaites Ice Tongue base; with much less crevasse-damage than shown in the third image of a Sentinel-2 photo from Nov 2020.
« Last Edit: November 25, 2020, 10:44:34 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Stephan

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Re: Thwaites Glacier Discussion
« Reply #309 on: December 27, 2020, 09:18:38 PM »
New calving at Thwaites Glacier.

Comparing the EOSDIS pictures from Nov 26 and Dec 25 a new rift (approx. 6 km long) is visible close to the grey line which once represented the grounding line. I painted a green line right to this new rift.

To be further examined on Sentinel images.

See attached picture. Might need a click for magnification.
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baking

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Re: Thwaites Glacier Discussion
« Reply #310 on: December 27, 2020, 10:05:31 PM »
Just a quick and dirty GIF of the calving front versus almost 2 years ago.  Not seeing much a retreat.

baking

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Re: Thwaites Glacier Discussion
« Reply #311 on: January 10, 2021, 07:06:24 AM »
I've noticed a recent increase in movement of Iceberg B22-A recently, so I thought I would give an update.  I post about B22-A here instead of the Iceberg thread because it is still close enough to Thwaites to affect the sea ice that helps to stabilize Thwaites to some extent.

The GIF below shows the movement of B22-A over the past 22 months.  It can be separated into three phases: 1) March 2019 to April 2020, Northward Movement; 2) April 2020 to October 2020, Westward movement (with calving from the western end); and 3) October 2020 to January 2021, Northward movement again.  All three phases resulting in approximately the same distance moved, so you can see that the velocity just about doubled between each phase (12 months to 6 months to 3 months.)  It is this increase in speed that is most concerning.

There is some rotation during this movement, but it hasn't resulted in a pattern yet.  Alternating between clockwise and counter-clockwise rotation, the orientation hasn't changed much over time.

The second image shows three areas of shallow water that tend to keep B22-A in place.  A peak on the eastern end, shallows on the western end, and another shallow to the Southwest near Bear Peninsula.  One concern is that the recent calving from the older Western end of the iceberg may allow it to rotate away from the shallows.  Of course, further movement to the West could also free it from the Eastern Peak.

The bathymetry under B22-A has never been accurately mapped, so it is hard to make predictions.  But observing the motion over time give us clues to where the iceberg is grounding and how it might float off, or at least float far enough away to change the sea ice off of Thwaites and neighboring glaciers.

interstitial

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Re: Thwaites Glacier Discussion
« Reply #312 on: January 10, 2021, 01:08:53 PM »
I was just looking at b22 A movement. It is clearly moving more and I suspect that process will continue. I conjecture the reason is probably bottom melt. I am not sure we will know. My guess is it will continue move northward this year but will escape next southern melting season.

baking

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Re: Thwaites Glacier Discussion
« Reply #313 on: January 10, 2021, 04:06:04 PM »
Below is a 3-day GIF of the land-fast sea ice off of Thwaites Tongue.  There had been no significant change since late November.  The next two months will be critical for this season.  Remember the glacier tongue is constantly pushing on the sea ice so that helps to weaken it.  The Tongue has been weakened by many fractures over the past two years and exposure to open water would be very destructive.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #314 on: January 10, 2021, 06:58:56 PM »
Thank you baking, for this update.
I noticed two bigger icebergs from the sea south of B-22 were flushed towards the bottleneck at the SW edge of B-22 (where the shallow sea is). I am curious whether they can make it through this gateway or whether they will ground there, making ice flow out through the bottleneck more difficult than it already is.
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baking

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Re: Thwaites Glacier Discussion
« Reply #315 on: January 10, 2021, 07:13:53 PM »
As a comparison with last year, here is the land-fast sea ice off of Thwaites Tongue from March 23-25, 2020, with the discussion at:
https://forum.arctic-sea-ice.net/index.php/topic,1760.msg256340.html#msg256340

As it turns out, the sea ice began refreezing in early April 2020, so nothing significant came from that break-up.

The previous year, 2019, was a different story.  The earliest image I have from February 16, 2019, shows the area almost completely free of sea ice.  Shortly afterwards, most of the icebergs at the lower right side of the image floated off en masse.

It sure looks like 2021 will be worse than 2020 (at least in this part of the Antarctica) but too soon to say if comparisons with 2019 are warranted.