Support the Arctic Sea Ice Forum and Blog

Author Topic: Rift in Larsen C  (Read 54108 times)

Seumas

  • ASIF Lurker
  • Posts: 36
    • View Profile
Rift in Larsen C
« on: March 12, 2015, 10:28:58 PM »
Hi folks,

Thoughts on the developing rift in the Larsen C ice shelf? There's a paper at:

http://www.the-cryosphere-discuss.net/9/861/2015/tcd-9-861-2015.html

They don't say when it's likely to calf based on the current rate. Any speculation?


AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #1 on: March 12, 2015, 11:10:20 PM »
Seumas,

See the last several posts in the following linked thread:

http://forum.arctic-sea-ice.net/index.php/topic,322.0.html#lastPost

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Seumas

  • ASIF Lurker
  • Posts: 36
    • View Profile
Re: Rift in Larsen C
« Reply #2 on: March 12, 2015, 11:26:57 PM »
Ah, thanks AbruptSLR. I do read more than I post (or understand ;) ) but I somehow missed those.

What do you reckon to timeline for the rift to cause a major calfing? I understand that people can be reluctant to speculate, but are we talking 5 years, 15 years, 150 years?

Oh, and since I rarely post, I'd like to thank you for all your posts on various topics. I enjoy reading them even though I don't post on the threads myself (and I'm sure there are many like myself).

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #3 on: March 12, 2015, 11:39:57 PM »
Seumas,

My guess is that Larsen C ice shelf will have a major calving event in the next 5 +/- 3 years.

You can what the progress of the rift yourself by periodically checking the following link:

http://www.polarview.aq/antarctic

Thanks for the thoughtful words, as I work full-time & have a family it can be tricky finding time to post.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

nukefix

  • ASIF Citizen
  • Posts: 406
    • View Profile
Re: Rift in Larsen C
« Reply #4 on: March 13, 2015, 08:09:08 PM »
Intersting, I'm getting coherence and fringes on S-1 12-day interferogram over the area (1 & 13.3.2015). There'a a phase-discontinuity going until Pin 1. Unfortunately the orbits and/or flat Earth correction are off so there are phase-ramps all over the place. In addition I don't know where I am exactly related to the images in the article..  :P

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #5 on: March 13, 2015, 09:25:06 PM »
Intersting, I'm getting coherence and fringes on S-1 12-day interferogram over the area (1 & 13.3.2015). There'a a phase-discontinuity going until Pin 1. Unfortunately the orbits and/or flat Earth correction are off so there are phase-ramps all over the place. In addition I don't know where I am exactly related to the images in the article..  :P

nukefix,

Based on the shape of the calving face, I guess that your image is near the beginning of the crevasse at the Southern end of the ice shelf (in the attached image you can see that the shape of the ice nob at the Southern end of the two images match each other).

So if the motions implied by your interferogram are correct, it is conceivable that a major calving could occur in the next year of two (or more).

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

nukefix

  • ASIF Citizen
  • Posts: 406
    • View Profile
Re: Rift in Larsen C
« Reply #6 on: March 16, 2015, 10:27:05 AM »
InSAR is a great tool for monitoring the crack. The difference in motion two sides of the crack is visible even if the crack is much thinner than a resolution cell. Once the 2nd S-1 satellite is up routine InSAR monitoring of Larsen C should be possible.

icefest

  • ASIF Citizen
  • Posts: 258
    • View Profile
Re: Rift in Larsen C
« Reply #7 on: March 16, 2015, 02:41:20 PM »
If it's anything like TanDEM and WorldDEM you'll have to pay through the nose to get any data though...
Open other end.

nukefix

  • ASIF Citizen
  • Posts: 406
    • View Profile
Re: Rift in Larsen C
« Reply #8 on: March 16, 2015, 04:50:18 PM »
If it's anything like TanDEM and WorldDEM you'll have to pay through the nose to get any data though...
S-1 data is freely available, there are some bottlenecks for the moment though..

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #9 on: May 13, 2015, 01:29:51 AM »
The linked article focuses on a new "The Cryosphere" paper (out tomorrow) about the rapid rate of thinning of the Larsen-C ice shelf; which does not need any more global warming to get it to collapse (at some still uncertain future date).

http://www.carbonbrief.org/blog/2015/05/antarctic-larsen-c-ice-shelf-at-risk-of-collapse-study-warns/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #10 on: May 13, 2015, 04:41:33 PM »
Here is the reference, abstract & link (to an open access pdf) of the Holland et al 2015 paper on the stability (instability) of the Larsen C ice shelf.

Holland, P. R., Brisbourne, A., Corr, H. F. J., McGrath, D., Purdon, K., Paden, J., Fricker, H. A., Paolo, F. S., and Fleming, A. H.: Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning, The Cryosphere, 9, 1005-1024, doi:10.5194/tc-9-1005-2015, 2015.

http://www.the-cryosphere.net/9/1005/2015/tc-9-1005-2015.html

Abstract. The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

nukefix

  • ASIF Citizen
  • Posts: 406
    • View Profile
Re: Rift in Larsen C
« Reply #11 on: May 14, 2015, 11:11:54 AM »
The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1).
These numbers do not make sense to me, the surveyed lowering is abt. 6.6cm per year of which 28cm per year is ice-loss?

Rubikscube

  • ASIF Citizen
  • Posts: 247
    • View Profile
Re: Rift in Larsen C
« Reply #12 on: May 14, 2015, 12:07:58 PM »
These numbers do not make sense to me, the surveyed lowering is abt. 6.6cm per year of which 28cm per year is ice-loss?

I would guess that the lowering of the ice only reflect a fraction of the total melting/thinning since most of the ice is resting below the water line. Maybe a slightly clumsy way to present the numbers.

plinius

  • ASIF Citizen
  • Posts: 403
    • View Profile
Re: Rift in Larsen C
« Reply #13 on: May 14, 2015, 12:52:58 PM »
don't find that clumsy. Also 28cm/year do not make even the full lowering - you need to add the firn air loss (then it makes totally sense, applying a factor of about 10 to the thickness loss for elevation).

Seumas

  • ASIF Lurker
  • Posts: 36
    • View Profile
Re: Rift in Larsen C
« Reply #14 on: July 12, 2016, 12:05:52 PM »
Update on this, following the rift up to Feb 2016:

http://hdl.handle.net/10013/epic.47801

Abstract:

The Larsen C Ice Shelf is the most northerly of the remaining major Antarctic Peninsula ice shelves and is vulnerable to changes in both to ocean and atmospheric forcing. It is the largest ice shelf in the region and its loss would lead to a significant drawdown of ice from the Antarctic Peninsula Ice Sheet. There have been observations of widespread thinning, melt ponding in the northern inlets, and, in the northern part, a speed-up in ice flow, all processes which have been linked to former ice shelf collapses. Previous studies have also highlighted the vulnerability of Larsen C Ice Shelf to specific potential changes in its geometry including a retreat from the Bawden and Gipps Ice Rise. In a change from the usual pattern, a northwards-propagating rift from Gipps Ice Rise has recently advanced towards the center of the ice shelf. It is now more than halfway towards calving a large section of the ice shelf and continues to widen. We followed the rift propagation on MODIS and Landsat imagery and,during the austral winter 2015, on Sentinel-1A radar data. Due to the very cloudy weather conditions during the austral Summer 2015 / 2016 the Sentinel data became an essential part of the monitoring. By calculating differential interferograms it was possible to clearly identify the active tip of the rift, which was not always obvious on the Landsat images. Further, surface velocities were derived from recent Sentinel-1A acquisitions by means of offset intensity tracking. In order to investigate a possible speed-up of the ice shelf we extended the study area to the north including Bawden ice rise.

BornFromTheVoid

  • ASIF Middle Class
  • Posts: 969
    • View Profile
Re: Rift in Larsen C
« Reply #15 on: August 18, 2016, 04:55:18 PM »
Another update on the Larsen C rift.
http://www.projectmidas.org/blog/a-growing-rift-in-larsen-c/

A growing rift on Larsen C

For almost two years now, we have been tracking the progress of a large rift in the Larsen C Ice Shelf. This rift, which may threaten the stability of Larsen C, has grown significantly and rapidly during the Antarctic polar night, which is now coming to an end. As of August 2016, the rift is now 22km longer than when satellites were last able to observe it in March of this year.

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #16 on: August 18, 2016, 05:41:58 PM »
Here are the figures from the article that BFTV just posted on the Larsen C rift extension thru August 2016:
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

jai mitchell

  • ASIF Upper Class
  • Posts: 1749
    • View Profile
Re: Rift in Larsen C
« Reply #17 on: September 08, 2016, 05:18:31 PM »
good paper on the upcoming Larsen C breakup

http://www.nature.com/articles/ncomms4707

Marine ice regulates the future stability of a large Antarctic ice shelf
    Bernd Kulessa, Daniela Jansen, Adrian J. Luckman, Edward C. King & Peter R. Sammonds

Abstract

The collapses of the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002 confirm the impact of southward-propagating climate warming in this region. Recent mass and dynamic changes of Larsen B’s southern neighbour Larsen C, the fourth largest ice shelf in Antarctica, may herald a similar instability. Here, using a validated ice-shelf model run in diagnostic mode, constrained by satellite and in situ geophysical data, we identify the nature of this potential instability. We demonstrate that the present-day spatial distribution and orientation of the principal stresses within Larsen C ice shelf are akin to those within pre-collapse Larsen B. When Larsen B’s stabilizing frontal portion was lost in 1995, the unstable remaining shelf accelerated, crumbled and ultimately collapsed. We hypothesize that Larsen C ice shelf may suffer a similar fate if it were not stabilized by warm and mechanically soft marine ice, entrained within narrow suture zones.
Haiku of Past Futures
My "burning embers"
are not tri-color bar graphs
+3C today

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #18 on: October 01, 2016, 05:17:43 PM »
The linked article is entitled: "Rift Speeds Up Across Antarctic Ice Shelf", and it discusses the rift extending itself across the Larsen C Ice Shelf:

http://www.climatecentral.org/news/rift-speeds-up-across-antarctic-ice-shelf-20752

Extract: "The rift working its way across the ice shelf is one of a larger grouping that has been present for more than 50 years, possibly formed by the stresses of the ice shelf pressing against a ridge on the seafloor below it.
This collection of rifts seemed to have reached an area called a suture zone, where the ice from glacier tributaries is mushed together in a complex mixture that seems to slow the rifts’ progression.
But the first post-winter satellite images from late August showed that this rift had managed to break across that zone and streak ahead; it now reaches about halfway across the ice shelf, parallel to its front.
When Daniela Jansen, a glaciologist at the Alfred Wegner Institute in Germany, first looked at those photos, “I was really surprised how fast this was developing,” she said.
Why it was able to progress so rapidly isn’t known. One possibility is that relatively warm, pliable marine ice that freezes to the bottom of the ice shelf — and is able to absorb more stress without cracking — may have melted, clearing a forward path for the rift.
Where the rift goes from here — and how fast it does so — is unknown. If it continues working its way northward, it will likely periodically slow down because there are more suture zones in its path. But if it changes direction and begins heading toward the ice front, it could cause an iceberg to calve, as the process is termed, much sooner.
“It’s akin to predicting an earthquake,” Khazendar said. “It’s a very, very complex problem.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Sleepy

  • Guest
Re: Rift in Larsen C
« Reply #19 on: October 02, 2016, 08:31:56 AM »
I only had a quick browse through some of the papers posted here and in the other thread by ASLR. What are the odds for it to break along the red line in the attachment?
Images inserted are from this image; S1A_EW_GRDM_1SSH_20160902T235854_9740_S_1.final.jpg at polarview.

Sleepy

  • Guest
Re: Rift in Larsen C
« Reply #20 on: October 31, 2016, 07:11:48 AM »
Nice image on polarview from the 28:th of October:
www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161028T075407_9491_S_1.final.jpg

The crack at the red line I marked in my comment above, extends at least to the 68°S line.

iwantatr8

  • ASIF Lurker
  • Posts: 39
    • View Profile
Re: Rift in Larsen C
« Reply #21 on: November 24, 2016, 10:35:08 AM »
Well today's S1A imagery shows quite an extension to the crack compared to the October images, and that the already open portion of the crack is widening.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161124T001525_594C_S_1.final.jpg

LRC1962

  • ASIF Citizen
  • Posts: 408
    • View Profile
Re: Rift in Larsen C
« Reply #22 on: November 28, 2016, 11:24:56 AM »
Found this interesting article. http://news.nationalgeographic.com/2016/11/foehn-winds-melt-ice-shelves-antarctic-peninsula-larsen-c/
Föhn winds may have escaped scientists’ notice because they don’t just blow during summer—some of their most impressive heat waves actually strike in the dead of winter, eroding glaciers at a time of year that no one thought possible.

“They seem to impart a lot more melt onto the ice shelf than we had imagined,” says Adrian Luckman, a glaciologist at Swansea University in the United Kingdom, who studies this region of Antarctica. The winds result from subtle changes in the atmospheric circulation due to climate warming; they could have major consequences.
Since short lived, unless your timing is right or are expecting you, you would never know it happened.
"All truth passes through three stages: First, it is ridiculed; Second,  it is violently opposed; and Third, it is accepted as self-evident."
       - Arthur Schopenhauer

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #23 on: December 04, 2016, 03:03:08 PM »
The linked article is entitled: "NASA photo reveals a startling 300-ft-wide rift in Antarctic Ice Shelf", see the attached image from Nov 10 2016, which will eventually grow to calve an iceberg the size of Delaware:


http://mashable.com/2016/12/03/nasa-photo-crack-larsen-c-ice-shelf/?utm_cid=hp-n-1#Va1T32Dzwmqr
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

oren

  • ASIF Upper Class
  • Posts: 1572
    • View Profile
Re: Rift in Larsen C
« Reply #24 on: December 04, 2016, 04:24:06 PM »
The linked article is entitled: "NASA photo reveals a startling 300-ft-wide rift in Antarctic Ice Shelf", see the attached image from Nov 10 2016, which will eventually grow to calve an iceberg the size of Delaware:
The resolution is so amazing.

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #25 on: December 04, 2016, 05:52:17 PM »
The linked article is entitled: "NASA photo reveals a startling 300-ft-wide rift in Antarctic Ice Shelf", see the attached image from Nov 10 2016, which will eventually grow to calve an iceberg the size of Delaware:
The resolution is so amazing.

Yes, it really emphasizes how much darker (with lower albedo) the surface ice layers are as compared to the deeper ice.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

charles_oil

  • ASIF Citizen
  • Posts: 181
    • View Profile
Re: Rift in Larsen C
« Reply #26 on: December 04, 2016, 06:03:58 PM »
Do we have an idea of depth - and the thickness / age of the dirty layer?

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #27 on: December 04, 2016, 06:29:23 PM »
Do we have an idea of depth - and the thickness / age of the dirty layer?

I do not know, but I would not be surprised to find-out that the dirty layer began when the ozone hole induced an increase in the circumpolar westerly wind velocities.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Tigertown

  • ASIF Upper Class
  • Posts: 1629
    • View Profile
Re: Rift in Larsen C
« Reply #28 on: January 06, 2017, 06:26:50 AM »

JD

  • ASIF Lurker
  • Posts: 5
    • View Profile
Re: Rift in Larsen C
« Reply #29 on: January 06, 2017, 01:21:15 PM »
But according to the article:

"The researchers say that this is a geographical and not a climate event. The rift has been present for decades, they say, but it has punched through at this particular time."

This also made the news on Radio 3 this morning, but the news item stressed that this was a natural event. 

Does anyone know how old the Larsen C shelf is?  I presume that ice shelves don't calve in the same way glaciers do, so I find it difficult to see how this can be a "natural" event unrelated to global warming.

logicmanPatrick

  • ASIF Citizen
  • Posts: 244
    • View Profile
    • The Chatter Box
Re: Rift in Larsen C
« Reply #30 on: January 06, 2017, 02:16:07 PM »
Do we have an idea of depth - and the thickness / age of the dirty layer?

I estimate that the dark layer is from 10 to 30 feet deep, based on visual cues in available images and the dimensions given by, e.g. NASA.  Note that the actual rift is in the shadow of what I wouyld call the debris pile.

The IceBridge scientists measured the Larsen C fracture to be about 70 miles long, more than 300 feet wide and about a third of a mile deep. The crack completely cuts through the ice shelf but it does not go all the way across it – once it does, it will produce an iceberg roughly the size of the state of Delaware.
https://www.nasa.gov/image-feature/rift-in-antarcticas-larsen-c-ice-shelf

It is very difficult to determine the age of the dark layer from images and available data.  Warm föhn winds scour the snow from time to time, snow which would otherwise form ice.  Note that the 'dark' ice layer is simply the most recently compacted snow.  A 'boots on the ground' image would show it as dark blue.
Föhn winds - http://news.nationalgeographic.com/2016/11/foehn-winds-melt-ice-shelves-antarctic-peninsula-larsen-c/

The presence of what I call a debris pile indicates from its size that the wind direction is constant.  The pile results from turbulence as the wind flows over the rift.

More images and videos of Larsen B -
http://earthobservatory.nasa.gov/IOTD/view.php?id=89257
http://earthobservatory.nasa.gov/IOTD/view.php?id=88708
http://svs.gsfc.nasa.gov/12449

si hoc legere scis nimium eruditionis habes

Neven

  • Administrator
  • ASIF Governor
  • *****
  • Posts: 4068
    • View Profile
    • Arctic Sea Ice Blog
Re: Rift in Larsen C
« Reply #31 on: January 06, 2017, 02:45:20 PM »
As always, British scientists go out of their way to stress their scientific reticence. And then the press puts on its running shoes.

Phlegm, blegh.  ;D
Il faut cultiver notre jardin

Tigertown

  • ASIF Upper Class
  • Posts: 1629
    • View Profile
Re: Rift in Larsen C
« Reply #32 on: January 06, 2017, 03:41:42 PM »
 
Does anyone know how old the Larsen C shelf is?  I presume that ice shelves don't calve in the same way glaciers do, so I find it difficult to see how this can be a "natural" event unrelated to global warming.
It can be an otherwise natural event, while at the same time having been sped up by climate change. Then the unnatural timing has consequences.

crandles

  • ASIF Upper Class
  • Posts: 1776
    • View Profile
Re: Rift in Larsen C
« Reply #33 on: January 06, 2017, 04:12:55 PM »
Does anyone know how old the Larsen C shelf is? 

No, but Larsen A was present for 4000 years and Larsen B present for at least 10,000 years per wikipedia referencing
https://www.eurekalert.org/pub_releases/2005-08/qu-isd080305.php

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #34 on: January 06, 2017, 07:24:46 PM »
The linked article entitled: "The crack in this Antarctic ice shelf just grew by 11 miles. A break could be imminent.", indicates that the Larsen C ice shelf could calve soon.

https://www.washingtonpost.com/news/energy-environment/wp/2017/01/06/the-crack-in-this-antarctic-ice-shelf-just-grew-by-11-miles-a-break-could-be-imminent/?utm_term=.0f82630f19a0

Extract: "A growing rift on the floating Larsen C ice shelf on the Antarctic peninsula — a rift that grew dramatically by another 11 miles last month, according to a team of scientists watching it closely — is setting the shelf up for an imminent loss of nearly 2,000 square miles of ice, these scientists say. That’s larger than Rhode Island and almost as big as Delaware."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Hans

  • ASIF Lurker
  • Posts: 23
    • View Profile
Re: Rift in Larsen C
« Reply #35 on: January 06, 2017, 10:44:34 PM »
You now can make some money out of this rift. :D

<Changed the link; N.>
« Last Edit: January 07, 2017, 11:14:25 AM by Neven »

solartim27

  • ASIF Citizen
  • Posts: 429
    • View Profile
Re: Rift in Larsen C
« Reply #36 on: January 06, 2017, 11:06:19 PM »
Here's a shot of the area.  Back in December the crack was just past the Latitude line.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170104T002328_0731_S_1.final.jpg
FNORD

georged

  • ASIF Lurker
  • Posts: 48
    • View Profile
Re: Rift in Larsen C
« Reply #37 on: January 07, 2017, 12:52:40 AM »
The linked article entitled: "The crack in this Antarctic ice shelf just grew by 11 miles. A break could be imminent.", indicates that the Larsen C ice shelf could calve soon.

If the rift is complete by the end of the southern summer (mid-Feb), how long would you think it would take before it separates from the main shelf?

And given the size and depth of the shelf, it seems like it might take years to melt out, wherever it eventually finds itself. Is this correct?

A final note - it seems like the major medium term impact of this loss will be to increase the insolation of the sea surrounding the EAIS, and change winds and local climatic conditions. Eventually much more of Larsen will go, and these changes will be more dramatic.

oren

  • ASIF Upper Class
  • Posts: 1572
    • View Profile
Re: Rift in Larsen C
« Reply #38 on: January 07, 2017, 01:18:22 AM »
And given the size and depth of the shelf, it seems like it might take years to melt out, wherever it eventually finds itself. Is this correct?
Looking at past Antarctic icebergs of similar sizes, it could melt over 5-10 years if it broke up and the pieces were carried north, or it could take decades if it remained fairly whole and kept to Antarctic waters. I guess the time to melt/breakup depends on initial iceberg thickness. The Larsen C iceberg is expected to be 350m thick, while other icebergs came from larger shelves and may have been up to 800m thick.
Note there have also been cases of such icebergs colliding with ice tongues on their journey and breaking off new icebergs.

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #39 on: January 07, 2017, 01:26:13 AM »
The linked article entitled: "The crack in this Antarctic ice shelf just grew by 11 miles. A break could be imminent.", indicates that the Larsen C ice shelf could calve soon.

If the rift is complete by the end of the southern summer (mid-Feb), how long would you think it would take before it separates from the main shelf?

And given the size and depth of the shelf, it seems like it might take years to melt out, wherever it eventually finds itself. Is this correct?

A final note - it seems like the major medium term impact of this loss will be to increase the insolation of the sea surrounding the EAIS, and change winds and local climatic conditions. Eventually much more of Larsen will go, and these changes will be more dramatic.

I would expect that after calving the associated iceberg will drift into the main Antarctic Circumpolar Current, ACC, within a few months, and once there I expect that it will circle Antarctica for one to several decades.  While the impact of this single calving event will be relatively small, it does indicate a trend towards a non-linear increase in calving events potentially (all around Antarctica but particularly in the AIS and the WAIS) within a few decades if we stay close to BAU forcing
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Sebastian Jones

  • ASIF Lurker
  • Posts: 23
    • View Profile
Re: Rift in Larsen C
« Reply #40 on: January 07, 2017, 02:01:54 AM »
@jd:  "I presume that ice shelves don't calve in the same way glaciers do, so I find it difficult to see how this can be a "natural" event unrelated to global warming."
But they do calve the same way that glaciers do, ice shelves can be thought of as extensions of the glaciers that feed them. Another way to think of them is as floating piedmont glaciers. They grow as the glaciers grow, and periodically, big chunks break off.

JD

  • ASIF Lurker
  • Posts: 5
    • View Profile
Re: Rift in Larsen C
« Reply #41 on: January 07, 2017, 08:39:11 AM »
Thanks Sebastian.  Looking at the paper that Seumas linked to at the start of this thread,

http://www.the-cryosphere-discuss.net/9/861/2015/tcd-9-861-2015.html

you can see the ice flow and how it will periodically calve.

The conclusion from the paper was interesting, particularly that this event may take it back to a new minimum since the last interglacial and that it may also put the ice shelf into an unstable configuration that might lead parts of it to collapse.

The reduction in area of Larsen C Ice Shelf under Scenarios
I and II of 9 and 12% respectively will be significant, but
will of course not contribute to immediate sea level rise since
the floating ice already displaces its own weight of seawater.
The predicted ice loss is also not unprecedented: in the late
1980s a calving event removed 14% of Larsen C Ice Shelf
(Cook and Vaughan, 2010). The real significance of this new
rift to this ice shelf is two-fold. First, the predicted calving
will reduce its area to a new minimum both in terms of direct
observations, and probably since the last interglacial period
(Hodgson et al., 2006). Second, unlike during the 1980s,
but highly comparable to the development of Larsen B Ice
Shelf between 1995 and 2002, the resulting geometry may
be unstable. According to the stress-flow angle criterion, our
calving scenarios lead to a range of unstable outcomes from
partial to significant. Under our modest rift propagation Scenario
I, immediately following the predicted calving event,
the central part of the ice front will be unstable and prone to
persistent calving of small ice blocks as the principal strain
works to open existing fractures. It is not clear how quickly
the velocity of a real ice shelf will be able to adapt to the
new boundary conditions, but even if this is rapid, the margin
of stabilizing ice becomes very narrow. Under Scenario
II, the unstable part of the new ice front is considerably larger
and, even if the flow field adapts quickly to the new geometry,
parts of the calving margin remain unstable and prone
to run-away calving of a similar nature to Larsen B Ice Shelf
between 1995 and 2002. Assessing the stress field according
to Doake et al. (1998), Scenario II would also be considered
as an unstable calving front.

Our model demonstrates that the newly developing rift
presents a considerable risk to the stability of the Larsen C
Ice Shelf.


silkman

  • ASIF Citizen
  • Posts: 206
    • View Profile
Re: Rift in Larsen C
« Reply #42 on: January 07, 2017, 09:02:48 AM »
As Hans pointed out in an earlier post, the bookies are now on to this story.

Paddy Power is offering 6 to 1 on the calving to take place in January but February and March are joint favourites at 7 to 2.

Remember, the bookmakers are seldom wrong :)

https://sports.paddypower.mobi/#sport/45/competition/28524/event/11685222

A-Team

  • ASIF Upper Class
  • Posts: 1882
    • View Profile
Re: Rift in Larsen C
« Reply #43 on: January 07, 2017, 01:39:40 PM »
reticence: "The researchers say that this is a geographical and not a climate event. The rift has been present for decades, they say, but it has punched through at this particular time."
This is really pathetic. In conflict with recent thinning, recent warming, recent widening, previous dead-ending of numerous parallel cracks, recent other collapsing Larsen ice shelves. Actually I could not locate this quote from the scientists involved, 'geographical event' is not a scientific term, so it may be an editorial overlay (so as to not offend the Business Council) or the reporter just putting a personal take on it.

The animation below looks at various enhancement schemes for accurate determination of the crack tip.
« Last Edit: January 07, 2017, 03:21:17 PM by A-Team »

Tor Bejnar

  • ASIF Upper Class
  • Posts: 1497
    • View Profile
Re: Rift in Larsen C
« Reply #44 on: January 07, 2017, 05:29:12 PM »
When I look at A-Team's 2nd image in his slide show, I see the lineation defined by the rift extending quite a distance beyond the arrow, expecially at a higher magnification.  I am not certain the crack extends all this distance, for the lineation may be 'geographical' in nature and not structural.  (There are plenty of lineations around!  I was looking at them last night at a higher magnification.)  But I think the state of the Larsen C Rift is more fragile than the suggested-by-the-arrow (but not stated) end-of-the-rift location.
Arctic ice is healthy for children and other living things.

charles_oil

  • ASIF Citizen
  • Posts: 181
    • View Profile
Re: Rift in Larsen C
« Reply #45 on: January 08, 2017, 01:03:25 AM »
I imagine the biggest short term variable force acting is tidal - so full moon in a few days - 12th Jan then on the 10th Feb and then the 12th March... though I havent found an easy to consult tide table.

johnm33

  • ASIF Middle Class
  • Posts: 758
    • View Profile
Re: Rift in Larsen C
« Reply #46 on: January 09, 2017, 11:58:10 AM »
Tides are large at the new moon too, and surprisingly large on the west coast of the peninsular.
About 80cm according to this and moving south to north, so if they gain any purchase on the calving peice it could just shift.

from https://en.wikipedia.org/wiki/Tide also check http://www.esr.org/polar_tide_models/Model_AntPen0401.html

iceman

  • ASIF Citizen
  • Posts: 261
    • View Profile
Re: Rift in Larsen C
« Reply #47 on: January 18, 2017, 12:59:40 PM »
Warm spell beginning this weekend around the Antarctic Peninsula.  Not sure how this interacts with other short-term factor such as tides, föhn winds, or even telekinetic wave action from distant storms.  But at this point it won't take much more for the rift to go the rest of the way.  I had thought the giant ice slab would hang on 'til near the end of the melt season, now my guess is a week from today.  That would be just over a month after the solstice - early enough for significant insolation gain near the rump portion of Larsen C, as georged notes above.

West Antarctic 22 Jan 2017 forecast 18 Jan


solartim27

  • ASIF Citizen
  • Posts: 429
    • View Profile
Re: Rift in Larsen C
« Reply #48 on: January 18, 2017, 06:16:22 PM »
Here is a zoomed in screen grab, and a gif of the rift tip from Jan 12 to Jan 18.  Looks like a lot of propagation over the 6 days.  I think the big factor over whether the berg breaks off this year or next year is if it turns towards the coast, or continues to the left of the picture.  It looks to me like it has reached some sort of surface feature, like a drainage channel, heading to the coast.  (Or is it a crack to thin for the resolution?)

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170118T000717_9C56_S_1.final.jpg  (30 MB)

S1B_EW_GRDM_1SSH_20170112T000635_65E1_S_1.final.jpg
FNORD

AbruptSLR

  • ASIF Emperor
  • Posts: 12987
    • View Profile
Re: Rift in Larsen C
« Reply #49 on: January 20, 2017, 03:58:38 AM »
The linked article, entitled:"Larsen ice crack continues to open up", and attached image adds details to solartim's last post

http://www.bbc.com/news/science-environment-38686626

Extract: "The rift in the Larsen C Ice Shelf has grown a further 10km since 1 January.
If the rift propagates just 20km more, it will free a tabular berg one-quarter the size of Wales."
« Last Edit: January 23, 2017, 11:51:27 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