Thwaites Glacier Discussion

[jai mitchell]

From a friend:

A 2021 study on the Thwaites glacier by Wild et al. suggests that the Thwaites pinning point will detach from the sea bed and reach floatation within the next decade, which has some serious implications for the Eastern Ice Shelf, and in turn, the whole Thwaites Glacier. They suggest that the unpinning of the Eastern Ice shelf will be followed by breakup of the shelf, similar to that of the Western Glacier Tongue in 2009. This is likely to increase Ice discharge along a 45 km stretch of the grounding line. Once detached from the seabed at the pinning point, warm water will be able to circulate under the ice shelf and towards the grounding line, where the glacier will be melted from where it meets the rock. Therefore, the unpinning of the Thwaites Glacier is likely to cause rapid retreat and ice shelf destabilisation.

I couldn’t find any exact measurements of ice thickness at the pinning point, however this figure from Wild et al. (2021) illustrates ice thickness nicely.

If you want to read into this a little further have a look at this recent paper https://tc.copernicus.org/preprints/tc-2021-130/tc-2021-130.pdf

[FrostKing70]

The video links earlier in this thread include ice thickness.  You can also view the press conference on Youtube.  It is over an hour long, but has great (and concerning!) information.

[FrostKing70]

If I remember correctly, they were  predicting that the existing pinning point would be gone by 2024.

[baking]

If I remember correctly, they were  predicting that the existing pinning point would be gone by 2024.

I discussed above the different scenarios of "unpinning", "shearing", and "fracture" and their possible timelines.  If that doesn't help, this recent video has a good overview although he leaves out the "shearing" scenario.

[bluesky]

AGU 21 press conference, the threat from Thwaites Dec 13, 2021

[jai mitchell]

from the press report, the glacial thickness at the grounding line is 350 meters with the majority of it below sea level.  We won't experience ice cliff instability regimes for about a century under worst case scenarios (need about 100 meters above sea level)

[AbruptSLR]

from the press report, the glacial thickness at the grounding line is 350 meters with the majority of it below sea level.  We won't experience ice cliff instability regimes for about a century under worst case scenarios (need about 100 meters above sea level)

jai,

It is my opinion that ice cliff instability could occur along the location indicated by the heavy red arc sketched on the attached image sometime between 2030 and 2040.

Best,
ASLR

[oren]

Moved.

[baking]

Here is a 24 day GIF made from today's high resolution Sentinel-1A radar images of the base of Thwaites Ice Tongue.  There are three images, the first two show the "normal" 12 day progression of the glacier and the Tongue and the melange to the bottom.  The third image from today reflects the effect that the recent shift of Iceberg B22-A had on the sea ice near Thwaites.

The is similar to what was seen in September 2019, but in this case the effect reaches all the way to the base of the Tongue.

https://forum.arctic-sea-ice.net/index.php/topic,1760.msg230824.html#msg230824

[jai mitchell]

from the press report, the glacial thickness at the grounding line is 350 meters with the majority of it below sea level.  We won't experience ice cliff instability regimes for about a century under worst case scenarios (need about 100 meters above sea level)

jai,

It is my opinion that ice cliff instability could occur along the location indicated by the heavy red arc sketched on the attached image sometime between 2030 and 2040.

Best,
ASLR

Apparently the threshold for ice cliff instability is on the order of 250 meters but that has to be above sea level. Is that your understanding?  There are other effects that happen below sea level but they are much slower.

[IceConcerned]

The TEIS is moving quite fast ultimately. On its eastern side, we have flow that is getting into shape, with "destruction zones" (to take over the vocabulary of PIG) under formation on both sides, and a big calving in preparaation on the east and along the front. 
Warning : 2MB file

[IceConcerned]

And if we look at the ice sheet itself, things are not so rosy either. All fringes are slowly but surely crumbling, we can see lots of small bergs detaching from tha pinning points (plus the big long one, which seems to have decided to go out soon finally). The flat plain before the pinning zone is expanding laterally, causing the ouverture and expansion of cracks. ANd teh icebergs that were stuck between the TEIS and TIT are going away, allowing the movement westwards of the blocks corresponding to the oldest cracks to go on unimpeded.
Beware, 2MB file

[baking]

Only a 12-day GIF for me showing the sea ice off the tip of Thwaite's Tongue.

[IceConcerned]

And still another one, this time about the tongue. It appears that it is now a tongue in name only, the icebergs are well separated and moving away. This movement seems to be accelerating (only 54 days between the last two images). Meanwhile, new crack are appearing behind and widening fast.

[IceConcerned]

And now two fixed pictures to show the extent of the cracks that have appeared in the pas months. Of particular concern for me is the one at the back of the TEIS, but seeing cracks appearing on the western side so much upstream is quite disqueiting too.
I am afraid we will know about MICI sooner than later.

[Stephan]

Thank you all for these animations. It really does not look good.
I think we can be lucky that open waters haven't reached (so far) Thwaites Ice Tongue or TEIS this austral summer.

[solartim27]

Lots of motion in the last couple of days.  I wonder if it can be residual effects of the tsunami.  Looking at Worldview along the coast, I was surprised how minimal the motion was in the closest areas after the 14th.  There were some ice shelves busted up, but I was expecting more damage.

[baking]

Tweet thread from Rob Larter (@rdlarter)

"I've been following changing sea ice distribution near #ThwaitesGlacier closely for the past couple of months to see if/when RVIB Nathaniel B Palmer and RV Araon might be able to get close to it. Access to the glacier is now looking increasingly unlikely this season."

https://twitter.com/rdlarter/status/1486474785882349568

[AbruptSLR]

from the press report, the glacial thickness at the grounding line is 350 meters with the majority of it below sea level.  We won't experience ice cliff instability regimes for about a century under worst case scenarios (need about 100 meters above sea level)

jai,

It is my opinion that ice cliff instability could occur along the location indicated by the heavy red arc sketched on the attached image sometime between 2030 and 2040.

Best,
ASLR

Apparently the threshold for ice cliff instability is on the order of 250 meters but that has to be above sea level. Is that your understanding?  There are other effects that happen below sea level but they are much slower.

It is my understanding at an ice cliff with a freeboard of about 110m above sea level is sufficient to trigger a slumping typed of ice cliff failure (see the first image), while at the location that I indicated by my red arc this freeboard is currently well over 140m (see the second image).

[baking]

It is my understanding at an ice cliff with a freeboard of about 110m above sea level is sufficient to trigger a slumping typed of ice cliff failure (see the first image), while at the location that I indicated by my red arc this freeboard is currently well over 140m (see the second image).

At the AGU press conference that has been linked above numerous times, a scientist reported on a recent study that modeled ice cliff instability and found that the threshold was closer to 140 meters.  Not yet published, but a little over the 100-110 meters previously theorized.

Of course, Marine Ice Cliff Instability (MICI) will most likely kick in after Marine Ice Shelf Instability (MISI) pushes the grounding line back past any stabilizing ridges and that won't happen until well after Thwaites Eastern Ice Shelf (TEIS) collapses, so this discussion has been getting ahead of itself.  TEIS is clearly in danger, but it is too soon to suggest that MICI is an imminent danger at the current grounding line.

I do think we will see MICI at Thwaites eventually, but when is the question, and I think we will see it coming well ahead of time.

[Stephan]

An update from the series "Just Have A Think" about Thwaites Glacier, its ice tongue and its Eastern Ice Shelf. The latest information from the US-UK Thwaites Glacier Project is included.

[baking]

@HotWaterOnIce arrived yesterday on Dotson Ice Shelf.  Not making it to Thwaites either this season.

https://twitter.com/HotWaterOnIce

[baking]

Cross-posting a 12-day GIF from the Icebergs thread showing the sea ice breaking up off the tip of Thwaites Tongue.  There is no longer any excuse for the Tongue not breaking up, at least at the end.

[baking]

Today's 12-day high resolution GIF shows the remaining sea ice West of the Tongue is breaking up.

[baking]

Today's 12-day GIF shows the Northern half of the Tongue breaking up with the surrounding sea ice.

[RoxTheGeologist]

That is absolutely terrible.

[Bernard]

For the casual visitor of this thread, not familiar with the size of the area, could it be possible to have a scale on those images? In km, if possible. 
Thx!

[baking]

For the casual visitor of this thread, not familiar with the size of the area, could it be possible to have a scale on those images? In km, if possible. 
Thx!

I have no idea how to put a scale on those GIFs, but here are some things that can help.

Low-resolution Sentinal-1 images (EW mode) are 40 meters per pixel.

High-resolution Sentinal-1 images (IW mode) are 20 meters per pixel.

So the Feb 3 image I posted earlier is low-res 700x700 pixels or 28km on a side.

I try to always mention the resolution and any changes in scaling.

Another rule of thumb is that small tabular icebergs tend to be about a km across.

I hope this helps.

[interstitial]

For the casual visitor of this thread, not familiar with the size of the area, could it be possible to have a scale on those images? In km, if possible. 
Thx!

I have no idea how to put a scale on those GIFs, but here are some things that can help.

Low-resolution Sentinal-1 images (EW mode) are 40 meters per pixel.

High-resolution Sentinal-1 images (IW mode) are 20 meters per pixel.

So the Feb 3 image I posted earlier is low-res 700x700 pixels or 28km on a side.

I try to always mention the resolution and any changes in scaling.

Another rule of thumb is that small tabular icebergs tend to be about a km across.

I hope this helps.

it is a bit of effort but the distance between latitude lines is a known quantity. It changes slightly but the distance is around 111 km. It varies by some small amount depending on which lines but it is not worth worrying about unless you need the precision. The polar view images shown include latitude lines. Use image J or whatever image processing software you prefer to measure the number of pixels for 111 km. A little division and you have the number of pixels per km. For low res 25 pixels per km. For high res 50 pixels per km. That is for the downloaded images any post processing can change things. In the image shown from the tip of the longer blue shaded region directly to the red line on right is about 31km.

[baking]

For the casual visitor of this thread, not familiar with the size of the area, could it be possible to have a scale on those images? In km, if possible. 
Thx!

I have no idea how to put a scale on those GIFs, but here are some things that can help.

Low-resolution Sentinal-1 images (EW mode) are 40 meters per pixel.

High-resolution Sentinal-1 images (IW mode) are 20 meters per pixel.

So the Feb 3 image I posted earlier is low-res 700x700 pixels or 28km on a side.

I try to always mention the resolution and any changes in scaling.

Another rule of thumb is that small tabular icebergs tend to be about a km across.

I hope this helps.

it is a bit of effort but the distance between latitude lines is a known quantity. It changes slightly but the distance is around 111 km. It varies by some small amount depending on which lines but it is not worth worrying about unless you need the precision. The polar view images shown include latitude lines. Use image J or whatever image processing software you prefer to measure the number of pixels for 111 km. A little division and you have the number of pixels per km. For low res 25 pixels per km. For high res 50 pixels per km. That is for the downloaded images any post processing can change things. In the image shown from the tip of the longer blue shaded region directly to the red line on right is about 31km.

Yes, 25 pixels/km = 40 meters/pixel and 50 pixels/km = 20 meters/pixel, but that image is low resolution so it is only 28km to a side.

And I only meant to say that I don't have the GIMP skills to put markings on a GIF.  If i need to mark something up I use Paint, but it can't make GIFs,

[Stephan]

For the casual visitor of this thread, not familiar with the size of the area, could it be possible to have a scale on those images? In km, if possible. 
Thx!

Just for information (first N↔S, then E↔W) of the sizes we are talking about:
Iceberg B-22 is ca. 45 * 80 km large
Thwaites Ice tongue measures around 60 * 30 km
Thwaites Eastern Ice Shelf has a size of about 55 * 25 km (due to its triangular shape a little difficult). The edges of this triangle measure about 60 * 60 * 50 km
Crosson Ice Shelf 65 * 55 km.

[paolo]

Baking, you make a mountain out of a molehill (you my animation master!)
You don't have to use Gimp or Paint, you can use both 
For the neophytes, I used Paint to make the mask (plain background on which I drew the scale and the label) and Gimp to draw the animation in the two images, to paste the mask (selection by background colour and inversion of the selection) and to assemble the images thus modified in the new version of the animation

Click to animate

[baking]

Fuzzy image from Worldview today, but it is pretty clear that the end (about 10km square) of the Tongue has separated from the rest.

[oren]

The bad news continue...

[Bernard]

Thanks all for the scale information!

[Stephan]

A short distance check:
Thwaites Glacier Ice Tongue had a length of 55 km from its very tip until the black grounding line in EOSDIS on Jan 31. After the break-up of the fast ice/sea ice/ice mélange the new tip has a distance of 40 km to the black grounding line in EOSDIS. Roughly a good third of length was reduced in just four days...

[uniquorn]

rough area measurement and poor quality rammb, jan31-feb4
might be useful for movement.

[paolo]

The S2 images of 03 and 04 are available and are of very good quality.
Unfortunately the image of 04 only covers the eastern end of the Tongue, but I find that the animation produced from these two images still gives useful information, so I post it

Click to animate

[uniquorn]

Possibility that the arch completes?

[paolo]

I add the S1 low resolution animation with the images of 03/02 and 05/02, the movement continues

Click to animate and enlarge

[baking]

Here is my 12-day low-res GIF of the end of Thwaites Tongue.  Image is 40km by 32km.

[paolo]

I am making available two very high resolution (10m per px) S1 images of the Thwaites Glacier Tongue from today:
> TGT downstream S1 06-02-22: 3400 x 3400
> TGT upstream S1 06-02-22: 3550 x 3550

Very large images, click twice to enlarge completely

[paolo]

I am also posting an image of today's very high resolution S1 image from the TEIS

Very large image, click twice to enlarge completely

[baking]

Here is today's 12-day high-resolution GIF of Thwaites Tongue.  Image is 48km on each side.

[baking]

1-day GIF of the Tongue.

[Tor Bejnar]

Thanks, Baking.  The different movements of some individual icebergs (compared with other bergs in the vicinity) is interesting.

[steve s]

The uniformly western direction of movement is surprising to me, as is the amount of movement in one day, and the sharp dividing line between the moving and other bergs. Seems more akin to sea ice breakup than previous losses of the Thwaites' Tongue's tip did.

[baking]

The uniformly western direction of movement is surprising to me, as is the amount of movement in one day, and the sharp dividing line between the moving and other bergs. Seems more akin to sea ice breakup than previous losses of the Thwaites' Tongue's tip did.

Excellent point.  There are still a lot of similarities, such as being tied to the seasonal break-up of sea ice, but in the past the pieces that broke away were still clumps of smaller icebergs frozen together.  This time, the individual icebergs had separated long ago and, when the sea ice broke up, they just seem to scatter.  More like a melange than an ice tongue.

[paolo]

I am wary of the impressions one can get from being focused on the present all the time and I wanted to get a historical view of Thwaites Glacier Tongue. So I made an animation of it with S1 images related to the month of February from 2017 to 2022.
Warning: the last image of 2022 is that of 03 and is therefore previous to the Tongue break-up (but as far as the elements we want to highlight are concerned, this is not important)
This animation shows that the positioning of the break-up front is not unusual (see 2018).
What is being progressively degraded is the structural strength of the Tongue and especially the crevasse creation front which is migrating upstream, as the damage zone between the TGT and TEIS.
It is hard to believe that it was this Tongue that produced B-22!
It is certain that this Tongue will evolve into a conglomerate of icebergs awaiting departure to the open sea and its function of supporting the TG upstream, currently still exercised, will be at least very weakened

Click to animate and enlarge

[FredBear]

The modern Thwaites Ice Tongue lacks the old pinning point which used to hold the calved icebergs together in a block. Because the modern icebergs get more loosely frozen in by sea ice they are much more free to break apart. This year there has also been sea ice flowing into Pine Island Bay from the north (and particularly on the eastern side) which has left the easiest route for the calvings from the tongue to move in the direction of the north-west as the blockage by B22A lessens, subject to risk of being blocked or grounding before they reach the polynya in the west.

The old Thwaites Ice Tongue consisted of a block of icebergs wedged together which broke off as a unit to form B22A, which has been unable to move away much for 20 years. A subsequent smaller calving from the tongue in 2012 did manage to avoid any major grounding and passed east and north of B22A before traveling west to melt north of the Ross Sea six years later.