Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: Seumas on March 12, 2015, 10:28:58 PM

Title: Rift in Larsen C
Post by: Seumas 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 (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?

Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (http://forum.arctic-sea-ice.net/index.php/topic,322.0.html#lastPost)

Best,
ASLR
Title: Re: Rift in Larsen C
Post by: Seumas 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).
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (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
Title: Re: Rift in Larsen C
Post by: nukefix 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
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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
Title: Re: Rift in Larsen C
Post by: nukefix 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.
Title: Re: Rift in Larsen C
Post by: icefest 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...
Title: Re: Rift in Larsen C
Post by: nukefix 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..
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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/ (http://www.carbonbrief.org/blog/2015/05/antarctic-larsen-c-ice-shelf-at-risk-of-collapse-study-warns/)
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (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.
Title: Re: Rift in Larsen C
Post by: nukefix 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?
Title: Re: Rift in Larsen C
Post by: Rubikscube 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.
Title: Re: Rift in Larsen C
Post by: plinius 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).
Title: Re: Rift in Larsen C
Post by: Seumas 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 (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.
Title: Re: Rift in Larsen C
Post by: BornFromTheVoid 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/ (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.
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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:
Title: Re: Rift in Larsen C
Post by: jai mitchell on September 08, 2016, 05:18:31 PM
good paper on the upcoming Larsen C breakup

http://www.nature.com/articles/ncomms4707 (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.
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (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.”"
Title: Re: Rift in Larsen C
Post by: Sleepy 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.
Title: Re: Rift in Larsen C
Post by: Sleepy 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 (http://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.
Title: Re: Rift in Larsen C
Post by: iwantatr8 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 (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161124T001525_594C_S_1.final.jpg)
Title: Re: Rift in Larsen C
Post by: LRC1962 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/ (http://news.nationalgeographic.com/2016/11/foehn-winds-melt-ice-shelves-antarctic-peninsula-larsen-c/)
Quote
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.
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (http://mashable.com/2016/12/03/nasa-photo-crack-larsen-c-ice-shelf/?utm_cid=hp-n-1#Va1T32Dzwmqr)
Title: Re: Rift in Larsen C
Post by: oren 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.
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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.
Title: Re: Rift in Larsen C
Post by: charles_oil on December 04, 2016, 06:03:58 PM
Do we have an idea of depth - and the thickness / age of the dirty layer?
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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.
Title: Re: Rift in Larsen C
Post by: Tigertown on January 06, 2017, 06:26:50 AM
Hanging on by a thread now.
www.bbc.com/news/science-environment-38522954 (http://www.bbc.com/news/science-environment-38522954)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2F&hash=35d7d5d7526c9897dfb55501e320295a)
Title: Re: Rift in Larsen C
Post by: JD 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.
Title: Re: Rift in Larsen C
Post by: logicmanPatrick 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.

Quote
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 (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/ (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=89257)
http://earthobservatory.nasa.gov/IOTD/view.php?id=88708 (http://earthobservatory.nasa.gov/IOTD/view.php?id=88708)
http://svs.gsfc.nasa.gov/12449 (http://svs.gsfc.nasa.gov/12449)

Title: Re: Rift in Larsen C
Post by: Neven 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
Title: Re: Rift in Larsen C
Post by: Tigertown 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.
Title: Re: Rift in Larsen C
Post by: crandles 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 (https://www.eurekalert.org/pub_releases/2005-08/qu-isd080305.php)
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (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."
Title: Re: Rift in Larsen C
Post by: Hans on January 06, 2017, 10:44:34 PM
You now can make some money (http://www.paddypower.com/bet?action=go_event&category=SPECIALS&ev_class_id=45&ev_type_id=28524&ev_id=11685222&force_racing_css=&ev_desc=When%20will%20the%20next%20Iceberg%20detach%20from%20the%20Larsen%20C%20Ice%20Shelf) out of this rift. :D

<Changed the link; N.>
Title: Re: Rift in Larsen C
Post by: solartim27 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 (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170104T002328_0731_S_1.final.jpg)
Title: Re: Rift in Larsen C
Post by: georged 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.
Title: Re: Rift in Larsen C
Post by: oren 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.
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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
Title: Re: Rift in Larsen C
Post by: Sebastian Jones 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.
Title: Re: Rift in Larsen C
Post by: JD 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 (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.

Title: Re: Rift in Larsen C
Post by: silkman 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
Title: Re: Rift in Larsen C
Post by: A-Team on January 07, 2017, 01:39:40 PM
Quote
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.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar 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.
Title: Re: Rift in Larsen C
Post by: charles_oil 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.
Title: Re: Rift in Larsen C
Post by: johnm33 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.
(https://upload.wikimedia.org/wikipedia/commons/5/5e/M2_tidal_constituent.jpg)
from https://en.wikipedia.org/wiki/Tide (https://en.wikipedia.org/wiki/Tide) also check http://www.esr.org/polar_tide_models/Model_AntPen0401.html (http://www.esr.org/polar_tide_models/Model_AntPen0401.html)
Title: Re: Rift in Larsen C
Post by: iceman 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
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fimgur.com%2Fnt8oy90.png&hash=7cb46ab76e1ed290b29d405b3b081b56)
Title: Re: Rift in Larsen C
Post by: solartim27 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 (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
Title: Re: Rift in Larsen C
Post by: AbruptSLR 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 (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."
Title: Re: Rift in Larsen C
Post by: solartim27 on January 20, 2017, 07:25:39 AM
The linked article, entitled:"Larsen ice crack continues to open up",
http://www.nbc.com/blindspot/video/nor-i-nigel-aka-leg-in-iron/3446618 (http://www.nbc.com/blindspot/video/nor-i-nigel-aka-leg-in-iron/3446618)

I think that should be
http://www.bbc.com/news/science-environment-38686626 (http://www.bbc.com/news/science-environment-38686626)
Quote
"Although you might expect any extension to hasten the point of calving, it actually remains impossible to predict when it will break because the fracture process is so complex.
"My feeling is that this new development suggests something will happen within weeks to months, but there is an outside chance that further growth will be slow for longer than that.
Title: Re: Rift in Larsen C
Post by: Seumas on January 20, 2017, 10:41:19 AM
That's actually another update from the Project Midas team:

http://www.projectmidas.org/blog/larsen-c-rift-continues-to-grow/ (http://www.projectmidas.org/blog/larsen-c-rift-continues-to-grow/)

They send them out as press releases, so you'll see them in several places. But any time you spot that map with Wales as the size comparison, that's them  :D

EDIT: Though, oddly, there's always more detail in the BBC report than on their own blog. I guess the reporter gets more out of them!
Title: Re: Rift in Larsen C
Post by: iwantatr8 on January 20, 2017, 02:07:05 PM
Now this is an interesting tool for monitoring using Sentinel 2 images.

http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.58776309484115/lng=-61.321563720703125/zoom=10/preset=CUSTOM/layers=B05,B03,B01/maxcc=8/gain=0.4/time=2015-01-01 (http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.58776309484115/lng=-61.321563720703125/zoom=10/preset=CUSTOM/layers=B05,B03,B01/maxcc=8/gain=0.4/time=2015-01-01)|2017-01-13/cloudCorrection=replace/colCor=SenCor/
Title: Re: Rift in Larsen C
Post by: magnamentis on January 20, 2017, 03:04:43 PM
countdown to break away is running relentlessly, will take perhaps just one nice westerly storm to push that part into oblivion ( warmer waters after breaking away )
Title: Re: Rift in Larsen C
Post by: georged on January 21, 2017, 03:30:16 AM
That's actually another update from the Project Midas team:

http://www.projectmidas.org/blog/larsen-c-rift-continues-to-grow/ (http://www.projectmidas.org/blog/larsen-c-rift-continues-to-grow/)

They send them out as press releases, so you'll see them in several places. But any time you spot that map with Wales as the size comparison, that's them  :D

EDIT: Though, oddly, there's always more detail in the BBC report than on their own blog. I guess the reporter gets more out of them!

That rift width chart is perhaps the more concerning one right now. 500m is very large.
Title: Re: Rift in Larsen C
Post by: DrTskoul on January 21, 2017, 04:58:41 AM
Cracks in anisotropic materials are some wild unpredictable beasts... I think the scales have tipped over for LC...But I would not be surprised if it takes a rest first...
Title: Re: Rift in Larsen C
Post by: magnamentis on January 21, 2017, 01:35:16 PM
Cracks in anisotropic materials are some wild unpredictable beasts... I think the scales have tipped over for LC...But I would not be surprised if it takes a rest first...

you put that perfectly well, thanks for finding the right words :-)
Title: Re: Rift in Larsen C
Post by: solartim27 on January 23, 2017, 11:48:29 PM
I'm not sure if this is an advance, or just the change in satellite view, but it's only a couple of days difference.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg) (28 MB)

S1A_EW_GRDM_1SSH_20170118T000717_9C56_S_1.final.jpg  (30 MB)
Title: Re: Rift in Larsen C
Post by: DrTskoul on January 24, 2017, 12:01:09 AM
I'm not sure if this is an advance, or just the change in satellite view, but it's only a couple of days difference.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg) (28 MB)

S1A_EW_GRDM_1SSH_20170118T000717_9C56_S_1.final.jpg  (30 MB)

Seems like an advance....
Title: Re: Rift in Larsen C
Post by: swoozle on January 24, 2017, 02:54:55 AM
I'm not sure if this is an advance, or just the change in satellite view, but it's only a couple of days difference.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170123T001522_3CA4_S_1.final.jpg) (28 MB)

S1A_EW_GRDM_1SSH_20170118T000717_9C56_S_1.final.jpg  (30 MB)

But it looks like the earlier image (20170118) has the longer crack. Must be a trick of the lighting.
Title: Re: Rift in Larsen C
Post by: LRC1962 on January 29, 2017, 12:28:49 AM
http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think (http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think)
Quote
One puzzling aspect is how it managed to plow through areas of softer ice, called suture zones, that bind the ice from neighboring glaciers into one giant sheet.

"There's something different about that ice that slows it down or causes it to hang up for some period of time," says Dan McGrath, a glaciologist at Colorado State University. But, starting in 2014, that soft ice did very little to slow down this rift.

"We need to get to the bottom of understanding what changed that allowed this rift to progress as it has, and will other rifts follow suit," says McGrath, who spent four field seasons camped out on the Larsen C ice shelf.
Title: Re: Rift in Larsen C
Post by: magnamentis on January 29, 2017, 09:21:53 PM
http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think (http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think)
Quote
One puzzling aspect is how it managed to plow through areas of softer ice, called suture zones, that bind the ice from neighboring glaciers into one giant sheet.

"There's something different about that ice that slows it down or causes it to hang up for some period of time," says Dan McGrath, a glaciologist at Colorado State University. But, starting in 2014, that soft ice did very little to slow down this rift.

"We need to get to the bottom of understanding what changed that allowed this rift to progress as it has, and will other rifts follow suit," says McGrath, who spent four field seasons camped out on the Larsen C ice shelf.

best explanation that comes to my mind immediately is the stone that damages a car's front window and one thinks he can live with that small crack, only to find out that the crack will spread with each movement of the car (torsion) after all this is what happens, there is swell action, there is currents action and there is glaciers pushing out to sea action, sufficient sources for movement that will widen each crack until a part of the structures will detach one or the other way.

BTW i still think that, considering topography and prevailing winds, that there must be some kind of "Foehn" winds
heading down from the highs of the peninsula and sooner or later pusch that entire ice sheet out into the southern atlantic or beyond.
Title: Re: Rift in Larsen C
Post by: DavidR on February 01, 2017, 02:28:27 AM
http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think (http://www.npr.org/sections/thetwo-way/2017/01/16/509565462/an-ice-shelf-is-cracking-in-antarctica-but-not-for-the-reason-you-think)
Quote
One puzzling aspect is how it managed to plow through areas of softer ice, called suture zones, that bind the ice from neighboring glaciers into one giant sheet.

"There's something different about that ice that slows it down or causes it to hang up for some period of time," says Dan McGrath, a glaciologist at Colorado State University. But, starting in 2014, that soft ice did very little to slow down this rift.

"We need to get to the bottom of understanding what changed that allowed this rift to progress as it has, and will other rifts follow suit," says McGrath, who spent four field seasons camped out on the Larsen C ice shelf.

best explanation that comes to my mind immediately is the stone that damages a car's front window and one thinks he can live with that small crack, only to find out that the crack will spread with each movement of the car (torsion) after all this is what happens, there is swell action, there is currents action and there is glaciers pushing out to sea action, sufficient sources for movement that will widen each crack until a part of the structures will detach one or the other way.

I  would have thought the most obvious solution is the weight of unsupported ice. The ice is melting from the bottom and presumably most at the edges.   As this occurs the ice has to drop or the ratio of the ice above sea level to  below sea level will increase. Somewhere this is going to  cause a crack across the ice and  the creation of the crack will cause extra pressure at the ends of the crack causing the cracking to accelerate.  This rate of cracking would be greater that that caused by swell and currents.  If the crack occurs at a point that  has been thinned by under-ice currents it is easy to imagine that after the first section breaks off the next section is also vulnerable.

The soft ice might prevent the propagation of the crack if it was due to normal tides and currents but would not halt a crack caused by the weight of the ice seaward of the crack.   

Just a novices opinion!
Title: Re: Rift in Larsen C
Post by: oren on February 01, 2017, 06:55:28 AM
Just a novices opinion!
Excellent point DavidR (novice to novice...). Basal melt seaward of the crack is a very good explanation. I wonder if there are any papers on this issue.
Title: Re: Rift in Larsen C
Post by: magnamentis on February 01, 2017, 10:10:33 AM
Just a novices opinion!

a very logical and hence valid point IMO, most probably as usual it's a combo of factors while i would second your opinion to have the greater impact than the factors i mentionend. i'd put this on top of the list.

thanks for that input :-)
Title: Re: Rift in Larsen C
Post by: Seumas on February 07, 2017, 02:01:07 PM
The MIDAS folk have posted another update: a FAQ on the rift:

http://www.projectmidas.org/blog/rift-faq/ (http://www.projectmidas.org/blog/rift-faq/)
Title: Re: Rift in Larsen C
Post by: Susan Anderson on February 07, 2017, 04:10:54 PM
The New York Times webpage has an article on the rift, with excellent graphics, front and center today.
https://www.nytimes.com/interactive/2017/02/07/science/earth/antarctic-crack.html (https://www.nytimes.com/interactive/2017/02/07/science/earth/antarctic-crack.html)

(Everyone can access 10 free per month; their graphics won't copy.)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 07, 2017, 04:49:20 PM
There are always screenshots!
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 07, 2017, 08:21:02 PM
I sometimes wonder if what I'm seeing is what others are seeing.  To that end, I've made a screenshot of a PolarView image (http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20170207T075244_EA73_S_1.final.jpg) and put pairs of arrows showing where I see the rift.  The second image is to put it into the wider perspective: the one pair of arrows shows the area where I see the rift ending.  Because these are screenshots, looking at the 'original (http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20170207T075244_EA73_S_1.final.jpg)' may be more informative. (click images to enlarge)
Title: Re: Rift in Larsen C
Post by: solartim27 on February 07, 2017, 08:32:03 PM
I think the rift goes just to the left of your arrows.  Time will tell.
Title: Re: Rift in Larsen C
Post by: Tealight on February 09, 2017, 02:31:24 PM
First cloud free S2A image is in. I marked the end of the rift with GCP1 (Ground Control Point)

Link to Sentinel Playground
http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.38663858288848/lng=-61.14372253417969/zoom=11/preset=1_NATURAL_COLOR/layers=B04,B03,B02/maxcc=22/gain=0.3/time=2015-01-01|2017-02-09/cloudCorrection=none/colCor=/evalscript=
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 09, 2017, 04:30:20 PM
First cloud free S2A image is in. I marked the end of the rift with GCP1 (Ground Control Point)
Link to Sentinel Playground
http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.38663858288848/lng=-61.14372253417969/zoom=11/preset=1_NATURAL_COLOR/layers=B04,B03,B02/maxcc=22/gain=0.3/time=2015-01-01|2017-02-09/cloudCorrection=none/colCor=/evalscript=
Using this "Sentinel Playground" image, I see the rift going to the circle in the general location image and the enlargement that has two pairs of arrows pointing to the rift.  (The lineation - rift - extends slightly above the top pair.)  Tealight and I show different orientations, but the end point may be 'the same'.
Title: Re: Rift in Larsen C
Post by: georged on February 10, 2017, 05:32:31 AM
First cloud free S2A image is in. I marked the end of the rift with GCP1 (Ground Control Point)
Link to Sentinel Playground
http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.38663858288848/lng=-61.14372253417969/zoom=11/preset=1_NATURAL_COLOR/layers=B04,B03,B02/maxcc=22/gain=0.3/time=2015-01-01|2017-02-09/cloudCorrection=none/colCor=/evalscript=
Using this "Sentinel Playground" image, I see the rift going to the circle in the general location image and the enlargement that has two pairs of arrows pointing to the rift.  (The lineation - rift - extends slightly above the top pair.)  Tealight and I show different orientations, but the end point may be 'the same'.

Interestingly, at the end the rift appears to 'split' into several separate rifts. I'm not sure whether this is simply an artifact or real.

The rift is currently about 25km from the shelf edge. How would we describe the series of rift-like features approximately 100km north and south of the rift end?
Title: Re: Rift in Larsen C
Post by: Tony Mcleod on February 10, 2017, 07:50:07 AM
It would be amazing to be near the end of it and to hear it groaning and crackling. :o
Title: Re: Rift in Larsen C
Post by: BornFromTheVoid on February 16, 2017, 02:30:58 PM
Hey folks, were hosting a Q&A session on reddit.com/r/science today that might be of interest to some here

American Geophysical Union AMA: Hi Reddit, I’m Chris Borstad, and I’m here to talk about the peculiar nature of snow and ice related to avalanches and glaciers. Ask Me Anything!

Hi Reddit! I am Chris Borstad, Associate Professor of Snow and Ice Physics at the University Centre in Svalbard (UNIS). Located at 78 degrees north, UNIS (www.unis.no (http://www.unis.no)) is the northernmost institution of higher education and research in the world. I am fascinated by snow and ice, and my research relates to processes that cause ice and snow to fracture. Most recently I have been studying the Larsen C ice shelf in Antarctica, where a massive crack in the ice is about to release an iceberg the size of Delaware! By improving our understanding of what caused this event and what the consequences are for the ice shelf, we hope to make better predictions of how other ice shelves around Antarctica will respond to a changing climate. I also study the physics of snow avalanches, a research interest that originated with a desire not to get caught in an avalanche myself while skiing in the backcountry. The most destructive types of avalanches occur after a large volume of snow is undercut by fractures. I am working to better understand these fascinating natural phenomena so that we can hopefully keep people out of harm’s way.
I will be back to answer your questions at 12 pm ET, Ask me Anything!
Follow me on twitter @RogueChrisB.


https://www.reddit.com/r/science/comments/5uer59/american_geophysical_union_ama_hi_reddit_im_chris/ (https://www.reddit.com/r/science/comments/5uer59/american_geophysical_union_ama_hi_reddit_im_chris/)
Title: Re: Rift in Larsen C
Post by: Espen on February 18, 2017, 07:01:41 PM
Larsen C rift expanding further:

Please click to enlarge and animate!
Title: Re: Rift in Larsen C
Post by: DrTskoul on February 18, 2017, 08:43:59 PM
Almost there....
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 18, 2017, 11:30:13 PM
I find it curious that the crack keeps going "up" (the image) and not "out" (to the coast).  Does anybody have ideas, or knowledge, about the stresses on or weaknesses in the ice shelf that would cause the crack to continue to propagate quasi-parallel to the coast?
Title: Re: Rift in Larsen C
Post by: DrTskoul on February 19, 2017, 12:39:47 AM
My experience with cracks in glassy materials is that they do not kink but smoothly change direction. So the crack would curve but not take a right turn unless there is a significant defrct. For the shelf a big hill ?
Title: Re: Rift in Larsen C
Post by: magnamentis on February 19, 2017, 12:43:15 AM
I find it curious that the crack keeps going "up" (the image) and not "out" (to the coast).  Does anybody have ideas, or knowledge, about the stresses on or weaknesses in the ice shelf that would cause the crack to continue to propagate quasi-parallel to the coast?

has to do with the structure from where the ice originates. glaciers for example use to crack more or less 90 degrees to their flowing direction and i could imagine that this ice is built on or close to land and drifting out, similar like a glacier's ice flows down the valley. there are many experts on glaciology in this forum who can certainly explain it better and/or rectify what's wrong with my assumption.
Title: Re: Rift in Larsen C
Post by: DrTskoul on February 19, 2017, 01:02:58 AM
Also the stress profile depends on the anchor points of the shelf.
Title: Re: Rift in Larsen C
Post by: iwantatr8 on February 19, 2017, 09:53:53 AM
Nature has an article on the shelf stresses here:

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

which contains the helpful image below, looks like a curve to the east can be expected soon.
Title: Re: Rift in Larsen C
Post by: Mozi on February 22, 2017, 06:59:29 PM
The British Antarctic Service has posted an article with an attached video of the rift - quite striking footage.

http://www.climatecentral.org/news/scientists-larsen-c-crack-21178 (http://www.climatecentral.org/news/scientists-larsen-c-crack-21178)

"On Tuesday, researchers with the British Antarctic Survey released new aerial footage showing the widening rift that threatens to tear the ice shelf asunder at any moment. The footage makes the immensity of the crack clear, as the yawning chasm stretches off into the horizon."

https://www.youtube.com/watch?v=WAM0tZB0aIc (https://www.youtube.com/watch?v=WAM0tZB0aIc)
Title: Re: Rift in Larsen C
Post by: Bill Fothergill on February 23, 2017, 10:48:08 AM
Here are some new links on the topic (although there is a fair bit of repetition between them)...

https://www.bas.ac.uk/media-post/new-footage-shows-rift-in-larsen-c-ice-shelf/ (https://www.bas.ac.uk/media-post/new-footage-shows-rift-in-larsen-c-ice-shelf/)

http://www.bbc.co.uk/news/science-environment-39055524 (http://www.bbc.co.uk/news/science-environment-39055524)


Regarding the earlier discussions about the crack mechanism(s) and the almost orthogonal relationship between the flow direction and the major stress axis ...

It's been a bloody long time since I've even thought about mechanics (it was covered in second year at University, and then more or less flushed out from what passes for a brain during that summer's vacation) but the bending/cracking idea makes perfect sense to me. (Although that doesn't mean very much!)

The bathymetry around Antarctica has lots of places where, as one moves towards the continent from the off-shore grounding line, the depth actually increases for a while.  That means that glaciers/ ice shelves are prone to serious undercutting. That would put the top surface of the ice into tension, whilst the bottom surface is in compression. This is a classic way to produce a fracture, and, like so many other aspects of climate change, it has a nasty feedback mechanism. As the crack propagates, it leaves less of the ice unfractured, with increasingly more of the bending moment being resisted by an ever-decreasing amount of ice.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on March 06, 2017, 08:11:05 PM
I've vaguely outlined in orange the end of the rift in the shelf and outlined in black a lineation that crosses the rift and goes to the coast.

Sentinel screenshot from PolarView (http://www.polarview.aq/antarctic) Acquired: 05-03-2017 19:14:40 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201703/S1B_EW_GRDM_1SSH_20170306T001440_FDBE_S_1.8bit.jp2). 

Is the "in black" lineation a weakness of some sort?
Title: Re: Rift in Larsen C
Post by: DrTskoul on March 06, 2017, 08:19:56 PM
I've vaguely outlined in orange the end of the rift in the shelf and outlined in black a lineation that crosses the rift and goes to the coast.

Sentinel screenshot from PolarView (http://www.polarview.aq/antarctic) Acquired: 05-03-2017 19:14:40 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201703/S1B_EW_GRDM_1SSH_20170306T001440_FDBE_S_1.8bit.jp2). 

Is the "in black" lineation a weakness of some sort?

Something big is coming....
Title: Re: Rift in Larsen C
Post by: bairgon on March 06, 2017, 09:22:18 PM
I noticed what looks like a warm foehn wind forecast for the 10th, blowing off the ice shelf. Maybe that will help things along?

https://earth.nullschool.net/#2017/03/10/1800Z/wind/surface/level/overlay=temp/orthographic=2.76,-66.17,1203/loc=-61.901,-67.389 (https://earth.nullschool.net/#2017/03/10/1800Z/wind/surface/level/overlay=temp/orthographic=2.76,-66.17,1203/loc=-61.901,-67.389)
Title: Re: Rift in Larsen C
Post by: iwantatr8 on March 07, 2017, 11:44:48 AM
Tor,

If you look at the Sentinel 2 image from 15th Feb

http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.70110969585656/lng=-61.219940185546875/zoom=10/preset=CUSTOM/layers=B05,B03,B02/maxcc=100/gain=0.3/gamma=1/time=2015-01-01|2017-02-15/cloudCorrection=replace/atmFilter=/evalscript=/showImage (http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.70110969585656/lng=-61.219940185546875/zoom=10/preset=CUSTOM/layers=B05,B03,B02/maxcc=100/gain=0.3/gamma=1/time=2015-01-01|2017-02-15/cloudCorrection=replace/atmFilter=/evalscript=/showImage)

It clearly shows that the end crack is much further north than the area where you have shown, the cloud cover in the last few weeks makes it difficult to track but it will be quite interesting to see if the summer has enough energy left to create the calving or if we will be waiting for next year.

Title: Re: Rift in Larsen C
Post by: Buddy on March 07, 2017, 06:29:44 PM
Apologies if this has been asked before....but is the Larsen C INCLUDED in the "sea ice" numbers....or are the ice shelve's NOT included in the sea ice numbers?

I guess to state another way....there seems to be 3 "types" of ice talked about:  Land ice, ice shelves, and sea ice.  For purposes of the various organizations that measure the "sea ice".....are the ice shelves included or excluded from their calculations?



Title: Re: Rift in Larsen C
Post by: DrTskoul on March 07, 2017, 07:17:06 PM
Apologies if this has been asked before....but is the Larsen C INCLUDED in the "sea ice" numbers....or are the ice shelve's NOT included in the sea ice numbers?

I guess to state another way....there seems to be 3 "types" of ice talked about:  Land ice, ice shelves, and sea ice.  For purposes of the various organizations that measure the "sea ice".....are the ice shelves included or excluded from their calculations?

Excluded
Title: Re: Rift in Larsen C
Post by: Buddy on March 07, 2017, 07:31:44 PM
Quote
Excluded

Thanks...

So what that means.....if someone is just looking at the "sea ice numbers" to study "albedo" for instance......those numbers are UNDERSTATING the downturn in the albedo effect from sea ice.....because any shelf ice "lost to melting" doesn't impact the sea ice numbers.

Now....I don't FOR A MINUTE believe that the scientists don't know that (I'm sure they do)....and hopefully work THAT into THEIR calculations.....but for a science novice such as me, it is one more piece of the puzzle that "goes the wrong way".

Because not only are we continuing to have less reflective sea ice.....we're losing ice shelves as well.  Just more "bad news" to plug in......unless ice shelves are GROWING somewhere else in the Antarctic.





Title: Re: Rift in Larsen C
Post by: solartim27 on March 07, 2017, 07:47:01 PM
Well, they get included when they break off, so sea ice will have a big jump soon (I think a year at least).
Title: Re: Rift in Larsen C
Post by: FredBear on March 07, 2017, 08:26:00 PM
But the ice shelf masks stay the same? So the floating iceberg counts as sea ice but the sea ice replacing it counts as ice shelf!
Title: Re: Rift in Larsen C
Post by: charles_oil on March 08, 2017, 12:32:19 AM

In the sea Ice around Antarctica thread the area is currently (record minimum) around 1,500,000 km2 so 5,000km2 - the size of the potential loss of the shelf is quite small in area % terms - probably lost within normally daily increase / decrease figures though it obviously represents a massive volume compared to thin, surface ice. 
See: Re: Sea Ice Extent around Antarctica (http://forum.arctic-sea-ice.net/index.php/topic,1759.msg105642.html#msg105642)                           
« Reply #561 on: March 07, 2017, 01:59:45 PM »


I can't seem to find any measures of arctic sea ice volume so dont know what fraction it would represent (or if it would skew the figures)
Title: Re: Rift in Larsen C
Post by: prokaryotes on April 14, 2017, 05:05:41 PM
The Making of an Iceberg
April 14, 2017
(https://eoimages.gsfc.nasa.gov/images/imagerecords/90000/90021/larsenc_msr_2017096.jpg)
Quote
In 2014, a crack began opening in the Larsen C Ice Shelf—a huge slab of floating ice along the Antarctic Peninsula. By April 2017, only 16 kilometers (10 miles) of ice separated the tip of that crack from the open sea.
Predicting when the cracking shelf will set loose an iceberg is a challenge because ice fracturing depends on several factors, some of which are poorly understood. The iceberg, which is likely to be the size of Rhode Island, could break off any time from days to years from now, according to scientists from Project MIDAS, a United Kingdom-based group that is monitoring the event.
https://earthobservatory.nasa.gov/IOTD/view.php?id=90021
Title: Re: Rift in Larsen C
Post by: oren on April 14, 2017, 07:42:48 PM
The Making of an Iceberg
April 14, 2017
Quote
In 2014, a crack began opening in the Larsen C Ice Shelf—a huge slab of floating ice along the Antarctic Peninsula. By April 2017, only 16 kilometers (10 miles) of ice separated the tip of that crack from the open sea.
Predicting when the cracking shelf will set loose an iceberg is a challenge because ice fracturing depends on several factors, some of which are poorly understood. The iceberg, which is likely to be the size of Rhode Island, could break off any time from days to years from now, according to scientists from Project MIDAS, a United Kingdom-based group that is monitoring the event.

I am surprised it's still attached...
Title: Re: Rift in Larsen C
Post by: prokaryotes on April 20, 2017, 08:11:19 PM
ESA video on Larsen C crack, includes insides into detection with Interferogram (using two radar images) https://www.youtube.com/watch?v=8PvCY7pBd-w (https://www.youtube.com/watch?v=8PvCY7pBd-w)

#interferometry
Title: Re: Rift in Larsen C
Post by: crandles on April 30, 2017, 05:22:15 PM
Some discussion at

http://www.bbc.co.uk/news/science-environment-39759329 (http://www.bbc.co.uk/news/science-environment-39759329)

though mainly about foen winds being more prevalent that realised.
Title: Re: Rift in Larsen C
Post by: Bill Fothergill on May 01, 2017, 11:28:08 AM
I noticed what looks like a warm foehn wind forecast for the 10th, blowing off the ice shelf. Maybe that will help things along?


Depends on how you are using the word "help".  ;)

See this BBC article (or possibly "antarcticle"?) on the Larsen C and the impact of the Foehn effect thereupon...
http://www.bbc.co.uk/news/science-environment-39759329 (http://www.bbc.co.uk/news/science-environment-39759329)

The BBC probably used this BAS press release as their source...
https://www.bas.ac.uk/media-post/new-insight-into-what-weakens-antarctic-ice-shelves/ (https://www.bas.ac.uk/media-post/new-insight-into-what-weakens-antarctic-ice-shelves/)

Other BAS articles on the Foehn effect can be found...
https://www.bas.ac.uk/?s=Fohn (https://www.bas.ac.uk/?s=Fohn)
Title: Re: Rift in Larsen C
Post by: 1rover1 on May 02, 2017, 05:20:17 PM

https://www.eurekalert.org/pub_releases/2017-05/su-air050217.php (https://www.eurekalert.org/pub_releases/2017-05/su-air050217.php)

https://scienceblog.com/493824/larsen-c-antarctic-ice-rift-spreads/ (https://scienceblog.com/493824/larsen-c-antarctic-ice-rift-spreads/)

The linked articles note the rift in the Larsen C ice shelf in Antarctica now has a second branch, which is moving in the direction of the ice front.  "While the previous rift tip has not advanced, a new branch of the rift has been initiated. This is approximately 10km behind the previous tip, heading towards the ice-front.  "This is the first significant change to the rift since February of this year. Although the rift length has been static for several months, it has been steadily widening, at rates in excess of a metre per day."
Title: Re: Rift in Larsen C
Post by: AbruptSLR on May 03, 2017, 04:20:36 PM

https://www.eurekalert.org/pub_releases/2017-05/su-air050217.php (https://www.eurekalert.org/pub_releases/2017-05/su-air050217.php)

https://scienceblog.com/493824/larsen-c-antarctic-ice-rift-spreads/ (https://scienceblog.com/493824/larsen-c-antarctic-ice-rift-spreads/)

The linked articles note the rift in the Larsen C ice shelf in Antarctica now has a second branch, which is moving in the direction of the ice front.  "While the previous rift tip has not advanced, a new branch of the rift has been initiated. This is approximately 10km behind the previous tip, heading towards the ice-front.  "This is the first significant change to the rift since February of this year. Although the rift length has been static for several months, it has been steadily widening, at rates in excess of a metre per day."

As a follow-up, the linked article is entitled: "The Larsen C Ice Shelf Crack Just Sprouted a New Branch". 

http://www.climatecentral.org/news/larsen-c-crack-new-branch-21409 (http://www.climatecentral.org/news/larsen-c-crack-new-branch-21409)

Title: Re: Rift in Larsen C
Post by: Shared Humanity on May 03, 2017, 07:54:21 PM
If you look at the angle that new branch is heading towards the sea, it aligns perfectly with the ice shelf that is pinned by the small island to the north. This is exactly where the berg will break free.
Title: Re: Rift in Larsen C
Post by: Seumas on May 18, 2017, 04:47:32 PM
An update from Project Midas as Larsen C begins to react to the rift:

http://www.projectmidas.org/blog/reacts-to-rift/ (http://www.projectmidas.org/blog/reacts-to-rift/)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on May 18, 2017, 06:21:39 PM
Although still connected by a (twisting) neck, they are calling it an iceberg!  I think the falling-in rift edges is mostly a reflection of the instability of tall cliffs (especially tall cliffs with fractured rock [or ice] around.  The taller the shelf edge, the faster it will fail (more or less).
Title: Re: Rift in Larsen C
Post by: Tony Mcleod on May 19, 2017, 02:06:09 AM
Appears to the laymens eye those 'slumping' blocks can only wedge the crack further apart a they move.
Title: Re: Rift in Larsen C
Post by: 1rover1 on May 31, 2017, 06:48:29 PM
The rift has grown by 17 km since May 25!
 
"In the largest jump since January, the rift in the Larsen C Ice Shelf has grown an additional 17 km (11 miles) between May 25 and May 31 2017. This has moved the rift tip to within 13 km (8 miles) of breaking all the way through to the ice front, producing one of the largest ever recorded icebergs. The rift tip appears also to have turned significantly towards the ice front, indicating that the time of calving is probably very close."

http://www.projectmidas.org/blog/another-step-closer/ (http://www.projectmidas.org/blog/another-step-closer/)

Title: Re: Rift in Larsen C
Post by: Dry_Land_Is_Not_A_Myth on June 01, 2017, 04:09:48 AM
When this detaches any thoughts on if it will no longer be counted in the nsidc Antarctic Sea Ice Extent? I've found size estimates that the ~2000 m^2 (~5000 km^2, to 1 sig fig), so it probably won't cause a notable dip in sea ice extent which is ~7 million km^2 (to 1 sig fig) if it was counted.
Title: Re: Rift in Larsen C
Post by: bairgon on June 01, 2017, 07:03:28 AM
See earlier in the thread for a discussion about that:

Apologies if this has been asked before....but is the Larsen C INCLUDED in the "sea ice" numbers....or are the ice shelve's NOT included in the sea ice numbers?
Title: Re: Rift in Larsen C
Post by: Lord M Vader on June 01, 2017, 07:44:39 PM
Larsen C is on the verge to break off: http://www.climatecentral.org/news/larsen-c-iceberg-breaking-off-21498 (http://www.climatecentral.org/news/larsen-c-iceberg-breaking-off-21498)
Title: Re: Rift in Larsen C
Post by: georged on June 04, 2017, 07:46:48 AM
Larsen C is on the verge to break off: http://www.climatecentral.org/news/larsen-c-iceberg-breaking-off-21498 (http://www.climatecentral.org/news/larsen-c-iceberg-breaking-off-21498)

It's rocketing away. (EASO map below)

https://twitter.com/adrian_luckman/status/871060621810335748 (https://twitter.com/adrian_luckman/status/871060621810335748)

Edit:

The Larsen Berg will be about the size of the Grand Canyon National Park or Delaware, or half the size of Puerto Rico when it is released, for context.
Title: Re: Rift in Larsen C
Post by: solartim27 on June 04, 2017, 08:57:24 AM
Here's a gif of the area from 17 Apr to 4 Jun.  Full size, so you'll need to click to animate and zoom in to the part you want to see (2.3 Mb).  The crack extension is barely discernable at this resolution.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.final.jpg)  (33 Mb)

S1A_EW_GRDM_1SSH_20170417T001453_DDEE_S_1.final.jpg (70 Mb)
Title: Re: Rift in Larsen C
Post by: magnamentis on June 04, 2017, 05:47:20 PM
Here's a gif of the area from 17 Apr to 4 Jun.  Full size, so you'll need to click to animate and zoom in to the part you want to see (2.3 Mb).  The crack extension is barely discernable at this resolution.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.final.jpg)  (33 Mb)

S1A_EW_GRDM_1SSH_20170417T001453_DDEE_S_1.final.jpg (70 Mb)

very nice, thanks, i think one can already guess where the growing fissure from the ocean in a 90 degree angle will meet the fissure that we're all watching for months now. it's clearly visible that the smaller ocean side fissure has grown into the shelf ice.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 05, 2017, 10:38:38 PM
PolarView has made an image from yesterday (2017-06-04 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.8bit.jp2)) available.  Here are three screen prints (blow-ups) showing the rift's right hand turn and it's relative position to the Larsen C shelf.  (Arrows point to the sharp curve.  Circles identify a 'blemish' on the rift. Location rectangles are approximate.)
EDIT:  The crack end progressed beyond the edge of the middle image (near the upper left corner) and way beyond the blow-up image.  The bend I identified is false!  and is where the rift ended about a year ago.
Title: Re: Rift in Larsen C
Post by: georged on June 06, 2017, 02:00:10 AM
PolarView has made an image from yesterday (2017-06-04 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.8bit.jp2)) available.  Here are three screen prints (blow-ups) showing the rift's right hand turn and it's relative position to the Larsen C shelf.  (Arrows point to the sharp curve.  Circles identify a 'blemish' on the rift. Location rectangles are approximate.)

Fascinating. Apologies if this has been asked, but how stable/active is the large rift below the Larsen Berg?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 06, 2017, 04:48:50 AM
I don't understand what you are asking ("Larsen berg" = 'Larsen C almost-a-berg'?), but if I did, I'm sure I wouldn't know.  I hope someone else can help!
Title: Re: Rift in Larsen C
Post by: magnamentis on June 06, 2017, 07:36:30 PM
let's see :-)

there are several other possibilities but this one's at list seamlessly connected ;)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 06, 2017, 08:24:59 PM
I was thinking along similar lines.  I see several lineations that might reflect zones of weakness leading to the coast (purple's), and there are the parallel-to-the-coast cracks (a couple green's drawn in) that could be incorporated in a 'final' rift path. EDIT: note: the rift's end is beyond the upper left corner of this image. (The suggested 'end' is where it ended a year ago.)
Title: Re: Rift in Larsen C
Post by: magnamentis on June 07, 2017, 01:17:37 AM
I was thinking along similar lines.  I see several lineations that might reflect zones of weakness leading to the coast (purple's), and there are the parallel-to-the-coast cracks (a couple green's drawn in) that could be incorporated in a 'final' rift path.

absolutely, it's all there, just for the fun of it i thought to lean out of the window a bit more than necessary, game on LOL. further i don't really like the "i knew it" stuff while avoiding the risk to
express those thoughts in advance, prefer to stand corrected by reality.

i think that there will be some scrambling along the final breaking lines, however, interesting to watch this coming :-)
Title: Re: Rift in Larsen C
Post by: iwantatr8 on June 07, 2017, 12:23:06 PM
I know that it's tempting to try and follow the crack visually but it's really difficult to do and the location that Tor highlights is actually where the crack ended last year.

Project midas use the differential between these sentinel images to work out the movement and hence where the crack ends. visually this is best represented by this tweet by professor Luckman
https://twitter.com/adrian_luckman/status/871060621810335748

As you will see the crack end is much further north on the shelf and close to the whole front of the shelf will become a berg.

Title: Re: Rift in Larsen C
Post by: magnamentis on June 07, 2017, 04:18:29 PM
I know that it's tempting to try and follow the crack visually but it's really difficult to do and the location that Tor highlights is actually where the crack ended last year.

Project midas use the differential between these sentinel images to work out the movement and hence where the crack ends. visually this is best represented by this tweet by professor Luckman
https://twitter.com/adrian_luckman/status/871060621810335748

As you will see the crack end is much further north on the shelf and close to the whole front of the shelf will become a berg.

thanks for that input, seems more plausible because things are more smooth in that theory :-)
i just lack the profound knowhow to do more than guessing and/or following visible lines LOL

looking at this from the outside ( like turning the chessboard 180dg ;) i'd vote for the variant you provided, let's see, interesting all the way down till things happen which could take another while BTW.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 07, 2017, 06:17:36 PM
Thank you, iwantatr8, for pointing out my error.  (I've made "edit" notes in the previous posts.) The attached three screen prints show
1) the Larsen C shelf from PolarView (June 4, 2017 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.8bit.jp2) - same as my previous post) with a purple circle showing the general location of the real rift end plus a scale (and red box where I previously thought the rift ended)
2) the map published by MIDAS (http://www.projectmidas.org/feed.xml) on May 31 with an added scale
3) close up of the Larsen C shelf where the rift ends with solid arrows pointing to the rift and dashed arrows showing where the rift might be (two suggested paths are within the red rectangle).
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 08, 2017, 04:49:54 PM
A June 6, 2017 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1B_EW_GRDM_1SDH_20170606T234955_CB82_S_1.8bit.jp2) image seems to show less detail, but looking at the ice shelf coast in the area where the rift is likely to go (or went), I think I see (yes: speculation) a lineation at the coast (middle arrow in 'whiter ice' June 6 image) that is not pared with a lineation on the June 4 image (dashed arrow).  (The other two pairs of arrows identify duplicated lineations.)  On the "rift-end" June 6 (wider area) image, I discern a few curved lineations within the red location box, one of which might identify the late May hook. (June 6 and June 4 images are approximately to same scale and location, and location box is also approximate.)

I sure look forward to the next MIDAS (http://www.projectmidas.org/feed.xml) feed!
Title: Re: Rift in Larsen C
Post by: Thomas Barlow on June 16, 2017, 02:33:10 PM
This is the latest from Polar View.
Looks like the crack to the right of the rock is also opening up more?
Title: Re: Rift in Larsen C
Post by: Hans on June 21, 2017, 03:38:23 PM
According the Dutch news site nu.nl: "Scientists issued a warning on Wednesday to ships in Antarctica in the coming days. A giant ice plateau, as big as the island of Bali, is about to break loose."

Project Midas is mentioned in the text, but unclear to me who "the scientist" are.
Anybody knows a real source?
link :http://www.nu.nl/klimaat/4783929/schepen-bij-antarctica-gewaarschuwd-enorm-scheurend-ijsplateau.html (http://www.nu.nl/klimaat/4783929/schepen-bij-antarctica-gewaarschuwd-enorm-scheurend-ijsplateau.html)
Title: Re: Rift in Larsen C
Post by: RikW on June 21, 2017, 04:28:43 PM
And I think they have some of the numbers wrong:

Google translate:
As soon as the plateau breaks out of Antarctica, the sea level rises to 'only' a few centimeters. If all the "fixed ice" breaks, an increase of about four meters is expected. And if all the ice is melting on the continent, the sea level can rise by tens of meters.

If I remember correctly: 10 cm happens when the ice-shelf completely collapses and the gletsjers that "end" in the shelf also stream into the sea.

4m happens when west-antarctica melts completely, isn't it?


And a stupid question, the shelf is said to be 350 meters thick, so around 50m above and 300m below sea level?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 21, 2017, 05:22:41 PM
Per Wikipedia (https://en.wikipedia.org/wiki/Ice_shelf), about 1/9th of an ice shelf is above water.  1/9th of 350 m is nearly 40m (or just over 125 feet, for us flatlander Americans)
Title: Re: Rift in Larsen C
Post by: RikW on June 22, 2017, 02:39:12 PM
according to the dutch wikipedia it's 1/5th till 1/7th

Dutch:
Wel is zeker dat een ijsberg slechts voor een vijfde tot een zevende boven water ligt

Google translate:
It is certain that an iceberg is only for a fifth to a seventh above water

Love those differences...
Title: Re: Rift in Larsen C
Post by: gerontocrat on June 22, 2017, 02:54:23 PM
Would an iceberg float higher in seawater than in freshwater, especially if made of freshwater ?
Title: Re: Rift in Larsen C
Post by: oren on June 22, 2017, 05:18:14 PM
Per Wikipedia (https://en.wikipedia.org/wiki/Ice_shelf), about 1/9th of an ice shelf is above water.  1/9th of 350 m is nearly 40m (or just over 125 feet, for us flatlander Americans)
The wiki quote:
Quote
The density contrast between glacial ice, which is denser than normal ice, and liquid water means that only about 1/9 of the floating ice is above the ocean surface.

There are several factors:
Freshwater is lighter than seawater.
But, shelf ice is denser than normal ice.
And the shape of the iceberg matters. A huge tabular iceberg is relatiely uniform, but a small calved iceberg could be assymetric with its top part narrower and therefore floating higher in the water.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 22, 2017, 05:20:48 PM
Per an internet search, some generic information:
Quote
What percent of the volume of the iceberg is under water?

Remember that the density of ice is 0.92 g/mL, and the density of water is 1.0 g/mL (1.03 for salt water). This means that ice has nine-tenths, or 90 percent of water's density – and so 90 percent of the iceberg is below the water's surface.

Freshwater:  .92/1.0 = 92% below water line
Saltwater: .92/1.03 = 89% below water line

So yes, an iceberg floats slightly higher in salt water.  If you really want to see a difference, take your piece of ice shelf to Great Salt Lake [Utah, USA] (~1.17 g/mL (https://www.jstor.org/stable/1763347?seq=1#page_scan_tab_contents) yielding 78% below water line - or instead of 40 m. showing, 75 m. will tower over you [after digging out the bottom of the lake, 'cause it is only on-the-order-of 10 m deep!]).
Title: Re: Rift in Larsen C
Post by: FishOutofWater on June 23, 2017, 02:15:27 PM
Guardian article by an actual expert says that Larsen C detachment will happen within a few weeks, but is not attributing it to climate change. I will add that it's very tricky to determine if a natural process like iceberg formation in Antarctica is speeding up because of climate change. She thinks that this is a normal event.

So, while ice fracturing and surface melting may sound like signs of climate change in action in Antarctica, they are really part of the background against which we must look for real change. Real changes are happening there, and when we report them they need to stand out. Previous collapse events involved large amounts of surface melt that forms ponds on an ice shelf that had already weakened. We have not observed this on Larsen C. We will continue to monitor Antarctica by satellites and from the ground, but we will not cry wolf about an imminent collapse of Larsen C.

    Helen Amanda Fricker is a professor at the Scripps Institution of Oceanography


https://www.theguardian.com/science/2017/jun/23/melting-and-cracking-is-antarctica-falling-apart-climate-change (https://www.theguardian.com/science/2017/jun/23/melting-and-cracking-is-antarctica-falling-apart-climate-change)


Title: Re: Rift in Larsen C
Post by: pileus on June 28, 2017, 06:45:07 PM
Another update on the imminent event.

Antarctic ice shelf crack is moving at record speeds, poised to cleave off massive iceberg any minute

http://mashable.com/2017/06/28/antarctica-iceberg-larsen-c-ice-shelf.amp (http://mashable.com/2017/06/28/antarctica-iceberg-larsen-c-ice-shelf.amp)

In a June 28 blog post, the scientists report: "...The soon-to-be-iceberg part of [the] Larsen C Ice Shelf has tripled in speed to more than ten meters per day between 24th and 27th June 2017." This means that the crack has moved at least 33 feet per day during the course of this 4-day period.

This is "the highest speed ever recorded on this ice shelf," according to the researchers. Predicting the exact date that the iceberg will cleave off from the Antarctic continent is tricky, however, since it still remains attached to the ice shelf, but just barely.

"The iceberg remains attached to the ice shelf, but its outer end is moving at the highest speed ever recorded on this ice shelf," researchers wrote. "We still can’t tell when calving will occur -- it could be hours, days or weeks -- but this is a notable departure from previous observations."

The satellite scientists are depending on to detect changes in the progression of the fissure is known as Sentinel-1, a project of the European Space Agency. This satellite is able to detect subtle changes in ground movements and is used for both studying melting glaciers and ice shelves as well as earthquakes and other geological phenomena.

According to Project MIDAS scientists, the most recent data do not cover the tip of the ice rift, but a low resolution image taken just after midnight on June 28 "shows clearly that the iceberg remains attached to the ice shelf at its western end -- for now."
Title: Re: Rift in Larsen C
Post by: RikW on June 29, 2017, 08:57:10 AM
What speed are they reporting, the growth of the length of the rift or the width?

The way I read the pictures I'd the eastern? (right side) part of the soon-to-be-iceberg is moving away form the shelf with 20+/day, so the rift is widening fast
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on June 29, 2017, 03:00:32 PM
They couldn't "see" the growing end of the rift, so the rift growth "had" to be growing width, presumably measured near the rift's 'mouth'.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on June 29, 2017, 04:09:50 PM
Larsen C is pivoting away from the ice shelf. Still connected on one end, it is opening like a door on a hinge.
Title: Re: Rift in Larsen C
Post by: magnamentis on June 29, 2017, 07:59:30 PM
Larsen C is pivoting away from the ice shelf. Still connected on one end, it is opening like a door on a hinge.

does anyone have insight as to the attributes of shelf ice when it comes to bending and other physical deformation?

what i find quite interesting is that the ice seems to be bendable without breaking to a certain degree which is known, but to what degree that is would be interesting to know.

why? because that way one could predict the angle at which the remaining joint would brake which would mean a possible prediction a few days out only.

what would be interesting about that is that one could perhaps witness the breakup in real time once one knows where and when to watch closely.
Title: Re: Rift in Larsen C
Post by: solartim27 on June 29, 2017, 08:46:38 PM
Here's how it looks on Sentinel.  Jun 4 - 28
S1A_EW_GRDM_1SSH_20170628T001457_3D5F_S_1.final.jpg

S1A_EW_GRDM_1SSH_20170604T001456_985B_S_1.final.jpg
Title: Re: Rift in Larsen C
Post by: iwantatr8 on June 30, 2017, 12:35:28 PM
Nasa's Landsat 8 has taken some nice thermal images of the crack.

visit the EO here to see the update:
https://earthobservatory.nasa.gov/IOTD/view.php?id=90481&src=eorss-iotd
Title: Re: Rift in Larsen C
Post by: johnm33 on June 30, 2017, 05:14:08 PM
"bending ice shelves" just not Larsen http://www.esr.org/~padman/Antarctic_Tides/ice_shelf_motion.html#tide_view (http://www.esr.org/~padman/Antarctic_Tides/ice_shelf_motion.html#tide_view)
Title: Re: Rift in Larsen C
Post by: crandles on July 05, 2017, 12:28:15 PM
http://www.bbc.co.uk/news/science-environment-40492957 (http://www.bbc.co.uk/news/science-environment-40492957)
Giant 'white wanderer' poised to break free

Just 5km left:

Quote
A rift has grown across the edge of the Larsen C Ice Shelf. A thin, 5km-long section of the floating shelf is now all that prevents a 6,600-sq-km berg from drifting away into the Weddell Sea.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 05, 2017, 07:38:46 PM
Even Fox News:  Giant 'Delaware-size' iceberg set to break off Antarctica (http://www.foxnews.com/science/2017/07/05/giant-delaware-size-iceberg-set-to-break-off-antarctica.html)
Quote
Hurry up and read this, before it’s too late.

The Larsen C ice shelf is seconds/minutes/hours/days away from breaking off from Antarctica. When it does — if it hasn’t by the time you’ve finished reading this — it will become one of the largest icebergs on record.

Scientists have been monitoring the crack in the ice shelf for two years, since they first observed that it was growing at a significant rate. As of January, it was 111 miles long and tearing away from the mainland at a rapidly growing rate.
...
Accuracy could be greater, but their heart is in the right place.   ???
Title: Re: Rift in Larsen C
Post by: Mozi on July 05, 2017, 07:49:06 PM
'The giant berg, the size of Delaware (or 0.31 SWU, Standard Wales Units,)...'
Title: Re: Rift in Larsen C
Post by: solartim27 on July 07, 2017, 08:31:13 PM
Nice picture in this tweet.
Adrian Luckman (@adrian_luckman) tweeted at 2:53 PM on Thu, Jul 06, 2017:
Close-up of #Sentinel1 Larsen C interferogram - rift branches in all directions. See also: https://t.co/dCZI9Tegtz. Not one clean berg then! https://t.co/sxsCQFZsli
(https://twitter.com/adrian_luckman/status/883081372302266369?s=03)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 08, 2017, 11:13:13 PM
I cannot see tweets at work, so here are screenshots for others.  See also: Larsen C rift branches as it comes within 5 km of calving (http://www.projectmidas.org/blog/multiple-branches/).  I'm curious about the cracks shown north of the "2" and "8" in "(2.8 miles)"  Will the collection of soon-to-calf icebergs include that area? (Or are they old and re-sealed/dormant?)  I'm guessing we will have to wait another 6 days for more information (my understanding of the Sentinel-1 satellite schedule over this location).
Title: Re: Rift in Larsen C
Post by: maga on July 09, 2017, 12:32:01 PM
The rifts you mention were probably initiated during the last major calving there in 2005. They probably have a lot to do with pressure from Bawden ice rise and I assume that the calving event will include these rifts as well. Probably not good for the complete northern and central part of the ice shelf...(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Flarsc_2005009_1225_modis_ch02.png&hash=855322cc8e7b5234d4cc12db24756f31)
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 09, 2017, 04:26:27 PM
I finally found names for the two islands that serve to define the length of the new iceberg. The Bawden Ice Rise to the north and the Gipps Ice rise to the south. These two ice covered islands stabilize the shelf and are worth keeping track of.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 09, 2017, 04:31:16 PM
Nice article.

https://www.nytimes.com/interactive/2017/06/09/climate/antarctica-rift-update.html (https://www.nytimes.com/interactive/2017/06/09/climate/antarctica-rift-update.html)

Scientists fear that two crucial anchor points will be lost.

According to Dr. Rignot, the stability of the whole ice shelf is threatened.

“You have these two anchors on the side of Larsen C that play a critical role in holding the ice shelf where it is,” he said. “If the shelf is getting thinner, it will be more breakable, and it will lose contact with the ice rises.”

If the shelf front disconnects from the ice rises, a rapid retreat will be triggered.

Ice rises are islands overridden by the ice shelf, allowing them to shoulder more of the weight of the shelf. Scientists have yet to determine the extent of thinning around the Bawden and Gipps ice rises, though Dr. Rignot noted that the Bawden ice rise was much more vulnerable.

“We’re not even sure how it’s hanging on there,” he said. “But if you take away Bawden, the whole shelf will feel it.”
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 09, 2017, 06:52:34 PM
Given the very fractured nature of the ice shelf near the Gipps ice rise, I would be surprised if, once calved, the Delaware sized ice berg does not quickly fracture into many pieces.
Title: Re: Rift in Larsen C
Post by: johnm33 on July 09, 2017, 07:22:42 PM
Good chance it'll break free this week, full moon, low pressure system 954 on nullschool, so extreme high tides. http://www.esr.org/polar_tide_models/Model_AntPen0401_plot_large.png (http://www.esr.org/polar_tide_models/Model_AntPen0401_plot_large.png)
Title: Re: Rift in Larsen C
Post by: wili on July 11, 2017, 08:52:52 PM
New piece on this by rs: https://robertscribbler.com/2017/07/11/antarcticas-4th-largest-ice-shelf-is-about-to-melt-back-to-its-smallest-area-ever-recorded/

Antarctica’s 4th Largest Ice Shelf is About to Melt Back to its Smallest Area Ever Recorded

Quote
... Antarctica could be tipping toward instability far faster than previously imagined.

... the Larsen C ice shelf is about to shatter off a very large 5,800 square mile ice berg even as several smaller ice bergs also appear ready to form. This event, which is now imminent in the coming days, weeks, or at most, months, will break the Larsen C ice shelf back to its smallest area ever recorded even as it marks a period of increased instability and risk of ice shelf loss.

For recent scientific assessments show that Larsen C is lowering in the water — an indication that the shelf is thinning. Furthermore, when the gigantic, Delaware-sized, ice berg and its smaller siblings break off they will take with them two outer sections of a stabilizing compression arch. The compression arch, somewhat like the arch of a flying buttress, helps to balance structural stresses for the ice shelf.

If it were to be compromised in total, according to glacier scientists like Dr. Eric Rignot, Larsen C would soon be adding its name to the list of various ice shelves around the world that have already fallen due to the warming airs and waters produced by human-caused climate change.
Title: Re: Rift in Larsen C
Post by: lurkalot on July 12, 2017, 11:10:07 AM
BBC reporting that it has detached: http://www.bbc.co.uk/news/science-environment-40321674 (http://www.bbc.co.uk/news/science-environment-40321674)
Title: Re: Rift in Larsen C
Post by: Andreas T on July 12, 2017, 12:49:44 PM
yes the AQUA nighttime band31 https://go.nasa.gov/2u8atAA (https://go.nasa.gov/2u8atAA) is pretty definite. Lighter colour shows warmer (than ice  surface) seawater in the crack which given the low resolution of the thermal IR band is fairly wide (or does the low resolution make it appear wider?)
Title: Re: Rift in Larsen C
Post by: Seumas on July 12, 2017, 01:08:43 PM
My guess is that Larsen C ice shelf will have a major calving event in the next 5 +/- 3 years.

Technically correct, but right at the bottom end. Clearly you're too conservative with your predictions!  ;)

Project Midas has the full report: http://www.projectmidas.org/blog/calving/ (http://www.projectmidas.org/blog/calving/)
Title: Re: Rift in Larsen C
Post by: oren on July 12, 2017, 01:24:34 PM
ASLR is too conservative. That is a scary thought indeed.
Title: Re: Rift in Larsen C
Post by: crandles on July 12, 2017, 01:35:01 PM
Quote
There was some keen interest a while back when the crack, which spread across the shelf from a pinning point known as the Gipps Ice Rise, looked as though it might sweep around behind another such anchor called the Bawden Ice Rise. Had that happened, it could have prompted a significant speed-up in the shelf's seaward movement once the berg came off.

As it is, scientists are not now expecting a big change in the speed of the ice.

Hadn't appreciated that where it broke off mattered so much.
Title: Re: Rift in Larsen C
Post by: DoomInTheUK on July 12, 2017, 01:41:46 PM

Hadn't appreciated that where it broke off mattered so much.

I get the feeling that it's more 'hope' than 'know'. We'll get a better idea of how much it matters in a year or so.....I'm still trying to work out how much Gin I'll need.
Title: Re: Rift in Larsen C
Post by: wili on July 12, 2017, 02:49:52 PM
Guardian is on it now, too: https://www.theguardian.com/world/2017/jul/12/giant-antarctic-iceberg-breaks-free-of-larsen-c-ice-shelf (https://www.theguardian.com/world/2017/jul/12/giant-antarctic-iceberg-breaks-free-of-larsen-c-ice-shelf)

Iceberg twice size of Luxembourg breaks off Antarctic ice shelf

Satellite data confirms ‘calving’ of trillion-tonne, 5,800 sq km iceberg from the Larsen C ice shelf, dramatically altering the landscape


Quote
A giant iceberg twice the size of Luxembourg has broken off an ice shelf on the Antarctic peninsula and is now adrift in the Weddell Sea.

Reported to be “hanging by a thread” last month, the trillion-tonne iceberg was found to have split off from the Larsen C segment of the Larsen ice shelf on Wednesday morning after scientists examined the latest satellite data from the area.

The Larsen C ice shelf is more than 12% smaller in area than before the iceberg broke off – or “calved” – an event that researchers say has changed the landscape of the Antarctic peninsula and left the Larsen C ice shelf at its lowest extent ever recorded.
Title: Re: Rift in Larsen C
Post by: Thomas Barlow on July 12, 2017, 02:56:17 PM

Iceberg twice size of Luxembourg breaks off Antarctic ice shelf

Quote
A giant iceberg twice the size of Luxembourg has broken off an ice shelf on the Antarctic peninsula and is now adrift in the Weddell Sea.


Yup. There it goes.
(from my screenshot of NASA Worldview today)
Title: Re: Rift in Larsen C
Post by: Thomas Barlow on July 12, 2017, 02:59:59 PM
.
Title: Re: Rift in Larsen C
Post by: VeliAlbertKallio on July 12, 2017, 10:57:16 PM
Larsen A --> Larsen B --> Larsen C --> Ronne Ice Shelf. It is a tragedy.  :'( 20 years maximum for R & R.  :(  I cannot see any reason that these chippings would end here but ever shoutwards...

Once upon a time was the Year 1995 and a fellow called Larsen Alpha: Statement on Ice Failure by Juan Pedro Brückner, the Director of the Argentinean Matienzo Base in Antarctica (attached).

Ban ki-Moon is always with us!  ??? He so much wanted climate to be on Rio+20 summit in 2012. I am enclosing his Larsen Beta statement as an image here.

I gave evidence on sea level rise risk (a good collection of links for Parliamentarians to browse many varied new phenomena - many familiar from here in ASIF, few others not yet discussed in ASIF): https://www.academia.edu/33000316/MPs_to_review_UKs_role_in_Arctic_sustainability_-_24th_April_2017.docx (https://www.academia.edu/33000316/MPs_to_review_UKs_role_in_Arctic_sustainability_-_24th_April_2017.docx)
Title: Re: Rift in Larsen C
Post by: AbruptSLR on July 12, 2017, 11:49:22 PM
ASLR is too conservative. That is a scary thought indeed.

The referenced post was from March 2015, so 5 +/- 3 years would be from March 2017 to March 2023, so at least the calving was within my margin of error ;)
Title: Re: Rift in Larsen C
Post by: RoxTheGeologist on July 13, 2017, 01:19:39 AM

Time to lock this thread....:)?
Title: Re: Rift in Larsen C
Post by: Juan C. García on July 13, 2017, 01:28:03 AM
One of the biggest icebergs in recorded history just broke loose from Antarctica

https://www.washingtonpost.com/news/energy-environment/wp/2017/07/12/one-of-the-biggest-icebergs-in-recorded-history-just-broke-loose-from-antarctica/?utm_term=.9b079763ae4c&wpisrc=al_alert-hse&wpmk=1 (https://www.washingtonpost.com/news/energy-environment/wp/2017/07/12/one-of-the-biggest-icebergs-in-recorded-history-just-broke-loose-from-antarctica/?utm_term=.9b079763ae4c&wpisrc=al_alert-hse&wpmk=1)
Title: Re: Rift in Larsen C
Post by: Thomas Barlow on July 13, 2017, 02:10:00 AM

Time to lock this thread....:)?
No. Where will it go? Will it break up? Who owns it?
Title: Re: Rift in Larsen C
Post by: Csnavywx on July 13, 2017, 02:23:53 AM
ASLR is too conservative. That is a scary thought indeed.

The referenced post was from March 2015, so 5 +/- 3 years would be from March 2017 to March 2023, so at least the calving was within my margin of error ;)

This officially leaves the shelf in a concave formation. With the re-arrival of the +PDO/+ENSO favored phase and the encroachment of the -9C annual isotherm on the shelf, the time of stability for Larsen C may be running out.
Title: Re: Rift in Larsen C
Post by: AbruptSLR on July 13, 2017, 03:16:04 AM
ASLR is too conservative. That is a scary thought indeed.

The referenced post was from March 2015, so 5 +/- 3 years would be from March 2017 to March 2023, so at least the calving was within my margin of error ;)

This officially leaves the shelf in a concave formation. With the re-arrival of the +PDO/+ENSO favored phase and the encroachment of the -9C annual isotherm on the shelf, the time of stability for Larsen C may be running out.

Maybe the rest of the ice shelf will collapse before my March 2023 timeframe ends. :o
Title: Re: Rift in Larsen C
Post by: RobertM on July 13, 2017, 03:43:17 AM
Greetings ASIF, long time lurker here, moved to post by the Larsen C event!

It is fascinating to read the media reaction: many glaciologists seem to be falling over themselves to say there is no reason to think there is any connect to climate change here. I find that weird. Anyway, what I wanted to ask about is this. Dr Adrian Luckman has several times cited a 2015 Scripps study (e.g., in today's Guardian and in theconversation.com) as measuring thickening of Larsen C. As I read the study, it says Larsen C is thinning:

"Volume loss from Antarctic ice shelves is accelerating",  Paolo et al Science, 2015: "On the eastern side of the Antarctic Peninsula... the regional ice-shelf thinning rate of 3.8 ± 1.1 m/decade is about half of that on the western side. The onset of thinning for Larsen C has progressed southward, which is consistent with climate-driven forcing discussed in earlier studies. The highest thinning rates on Larsen C (with local maximum thinning of 16.6 ± 8.1 m/decade) are near Bawden Ice Rise."

The Bawden Ice Rise is exactly where the iceberg finally detached.

Secondly, until today I was following the Larsen C rift in the context of John Mercer's 1978 predictions. Today I looked into it a little more. The detachment point is around the -12C isotherm (https://www.researchgate.net/publication/240424228_Holocene_climate_and_glacial_history_of_the_northeastern_Antarctic_Peninsula_The_marine_sedimentary_record_from_a_long_SHALDRIL_core (https://www.researchgate.net/publication/240424228_Holocene_climate_and_glacial_history_of_the_northeastern_Antarctic_Peninsula_The_marine_sedimentary_record_from_a_long_SHALDRIL_core)), whereas the shelves that have collapsed or started to collapse, consistent with Mercer's theory, to the north and west, are all markedly warmer, above the -9 C isotherm. The newspaper articles say there are no reports of surface meltwater on Larsen C.

So my question is, is there any mechanism by which warming of the air, even if it remains below freezing for most of the summer, could have weakened the shelf and contributed in some way?
Title: Re: Rift in Larsen C
Post by: Pmt111500 on July 13, 2017, 05:09:51 AM
Proposing the name 'Reagan Iceberg' for the piece of ice shelf that irreversibly separated from the glaciers of West Antarctica. This would be because of the slow pace of heat accumulation in the ocean, the 'thermal inertia' which is too technical an expression for many. This just means that the water takes a while to warm up and the heat that was applied in 1980s would have done the same, though a bit later, possibly in 2030s. Thus we could expect the "Iceberg Tillerson of Drumpfistan" to be launched by the chinese conspirators in 2040s. This would be way larger since the ego size and stupidity difference.
Title: Re: Rift in Larsen C
Post by: CraigsIsland on July 13, 2017, 08:03:57 AM
ASLR is too conservative. That is a scary thought indeed.

The referenced post was from March 2015, so 5 +/- 3 years would be from March 2017 to March 2023, so at least the calving was within my margin of error ;)

Jeez. I was hoping the scary stuff from Antarctica and Greenland would’ve been decades out. Like 5+ feet after 2040 maybe.

Are you surprised by this break? What’s the next “big” event In Antarctica?

This officially leaves the shelf in a concave formation. With the re-arrival of the +PDO/+ENSO favored phase and the encroachment of the -9C annual isotherm on the shelf, the time of stability for Larsen C may be running out.

Maybe the rest of the ice shelf will collapse before my March 2023 timeframe ends. :o
Title: Re: Rift in Larsen C
Post by: AbruptSLR on July 13, 2017, 10:30:34 AM
Are you surprised by this break? What’s the next “big” event In Antarctica?

I believe that the next "big' event in Antarctica will be a major calving event for the Pine Island Ice Shelf within the next one to nine months.
Title: Re: Rift in Larsen C
Post by: Adam Ash on July 13, 2017, 10:42:34 AM
Thinking out loud... (sorry!)
While a naive view of the impact of this calving would be to see the remainder of the ice shelf do a prompt shuffle to the east, relieving buttressing on land-based ice, I guess the major effect will be increased exposure of the remainder of the ice shelf to open-ocean tidal and thermal dynamics. 

It will be interesting to watch for signs of the prompt disintegration of the remainder (which seems unlikely at this stage) and instead I guess we will just continue to see the edge chewed away. 

Is there any feature of the ocean floor shape which would alter current dynamics now the calving is done? 

It will be interesting to watch the berg's movement from here - it will give us an idea of the net outcome of currents etc acting on it.

Another sign of the times!
Title: Re: Rift in Larsen C
Post by: AbruptSLR on July 13, 2017, 11:12:48 AM
For those who are not aware, more background discussion on trends for Larsen C can be found in the linked thread entitled: "Discussion of the Antarctic Peninsula"

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

Title: Re: Rift in Larsen C
Post by: numerobis on July 13, 2017, 01:46:29 PM
RobertM: on the march for science Facebook post, Robert Grumbine mentioned the in-retrospect obvious point that the temperature at the base is barely freezing, while at the surface it's very cold. So there's a temperature gradient through the ice shelf.

Higher temperature at the surface, even a warming from -35 to -30, means a larger region inside the slab of ice that's "warm" and therefore "soft" (in relative term of course), which means it can move faster.
Title: Re: Rift in Larsen C
Post by: Adam Ash on July 13, 2017, 02:41:05 PM
https://www.space.com/37472-nasa-images-show-massive-iceberg-separation.html?utm_source=notification (ftp://www.space.com/37472-nasa-images-show-massive-iceberg-separation.html?utm_source=notification)

This site shows a good time series of the crack's development.  The ice further inland is none too cohesive, with numerous cracks parallel to the current break line showing over recent years. 

It looks more like the ice shelf is held in position by shore-ward currents than any great degree of internal connectivity.
Title: Re: Rift in Larsen C
Post by: Thomas Barlow on July 13, 2017, 02:54:36 PM
Greetings ASIF, long time lurker here, moved to post by the Larsen C event!

It is fascinating to read the media reaction: many glaciologists seem to be falling over themselves to say there is no reason to think there is any connect to climate change here. I find that weird.

Yes, it would be abnormal if there was no such thing as global warming going on.
Title: Re: Rift in Larsen C
Post by: magnamentis on July 13, 2017, 08:47:39 PM

Time to lock this thread....:)?

better to amend the name as it was done with the US election thread so that the content remains accessible within the same thread and the discussion will continue seamlessly, this is my proposal, others will make the choice.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 13, 2017, 09:41:06 PM
A June 6, 2017 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201706/S1B_EW_GRDM_1SDH_20170606T234955_CB82_S_1.8bit.jp2) image seems to show less detail, but looking at the ice shelf coast in the area where the rift is likely to go (or went), I think I see (yes: speculation) a lineation at the coast (middle arrow in 'whiter ice' June 6 image) that is not pared with a lineation on the June 4 image ([see June 8 post]).  (The other two pairs of arrows identify duplicated lineations.)  ...
The actual rift (July 12 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_IW_GRDH_1SSH_20170712T080213_54FF_S_1.8bit.jp2)) reached the edge approximately where my 'middle' arrow identified a new lineation.  Cool!  (Chance?) (images are approximately the same area)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 13, 2017, 09:54:30 PM
Here is 'just the rift end' at 106%.  From the June 8 post's scale, the rift at its end is about 1/2 km wide. Now looking forward to all the 'little' icebergs that we were 'promised'!
Title: Re: Rift in Larsen C
Post by: VeliAlbertKallio on July 14, 2017, 12:55:15 AM
Does anyone know whether 10,000 km2 has been added to the global sea ice area to offset the lost segment of Larsen C ice shelf. When it will be included in the global sea ice area, if not already?  ???
Title: Re: Rift in Larsen C
Post by: Peter Ellis on July 14, 2017, 01:54:09 AM
Does anyone know whether 10,000 km2 has been added to the global sea ice area to offset the lost segment of Larsen C ice shelf. When it will be included in the global sea ice area, if not already?  ???
Global sea ice area is currently 14.75 million (Antarctic) plus 8.04 million (Arctic) = 22.79 million km^2. Feel free to mentally add 10,000 km^2 to make 22.80 million instead.

It changes global sea ice area by less than one twentieth of one percent.
Title: Re: Rift in Larsen C
Post by: VeliAlbertKallio on July 14, 2017, 10:52:03 AM
I am aware of that but the figures given by many sites for sea ice go to the last decimal points. There are a lot more ice shelves to go and for the Weddel and Ross Seas the overall percentage is very high. For the same argument we could just omit CAA and the Black Sea / Caspian Sea / Baltic Sea NH sea ice figure but to my understanding, these are calculated to overall winter tally.

Does anyone know whether 10,000 km2 has been added to the global sea ice area to offset the lost segment of Larsen C ice shelf. When it will be included in the global sea ice area, if not already?  ???
Global sea ice area is currently 14.75 million (Antarctic) plus 8.04 million (Arctic) = 22.79 million km^2. Feel free to mentally add 10,000 km^2 to make 22.80 million instead.

It changes global sea ice area by less than one twentieth of one percent.
Title: Re: Rift in Larsen C
Post by: FredBear on July 14, 2017, 01:35:10 PM
   .   .   .   but VeliAlbertKallio the satellites have difficulty even with meltponds!! (& clouds, & coastlines, & 15% cut-offs, etc.).I'm sure we can live with the limitations. It is only 12% of the 4th largest iceshelf on the earth  .   .   .   there's bigger nits to pick?
Title: Re: Rift in Larsen C
Post by: Pmt111500 on July 14, 2017, 01:43:57 PM
It would be kind of fun if the sea ice charts would show 'very old ice' with an estimate of years to develop to such a berg. I guess in this case there should be a number of over at least 8200. Probably much more.
Title: Re: Rift in Larsen C
Post by: oren on July 14, 2017, 01:49:20 PM
VAK, I think the direct answer to your question is: when the land mask is updated. Have no clue when that might happen though.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 14, 2017, 03:35:28 PM
A screen shot from the middle of the rift (July 12 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_IW_GRDH_1SSH_20170712T080213_54FF_S_1.8bit.jp2)) very nicely shows the relative movement of the iceberg and the ice shelf: a classic transverse fault.  All arrows are parallel and the three sets of collinear arrows have the same spacing between their butt ends.  (Is there some deformation in the iceberg or is my arrows' angle slightly off?)
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 15, 2017, 05:10:54 PM
Could the movement of the ice berg be caused by currents in the Weddell Sea? Are there persistent southerly currents down the peninsula toward the Ronne Ice Shelf?
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 15, 2017, 05:14:03 PM
Oh. And what the heck is with all of the penguins on this map?
Title: Re: Rift in Larsen C
Post by: Shared Humanity on July 15, 2017, 05:18:31 PM
It would appear that the ocean currents actually flow north along the peninsula.
Title: Re: Rift in Larsen C
Post by: Forest Dweller on July 15, 2017, 07:40:20 PM
Here is 'just the rift end' at 106%.  From the June 8 post's scale, the rift at its end is about 1/2 km wide. Now looking forward to all the 'little' icebergs that we were 'promised'!

Cool image.
The chunk of ice in the middle shows it came from above so there must be a surface flow heading south.
Some slushy ice entering the crack as well further indicates that.
The little map posted above has the currents heading north however.
Guess not at the surface...
Title: Re: Rift in Larsen C
Post by: johnm33 on July 15, 2017, 08:11:50 PM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esr.org%2Fpolar_tide_models%2FModel_CATS2008a_plot_large.png&hash=4d785d75d45259de91683e295d1d5dec)
The dark blue circles are the amphidromic points, around which the tides turn clockwise. I believe they drive the currents, that is the currents are residual persistent flows driven by tidal movements.
Image from http://www.esr.org/ptm_index.html (http://www.esr.org/ptm_index.html)
Title: Re: Rift in Larsen C
Post by: charles_oil on July 16, 2017, 10:56:43 AM

Good CNN movie about Larsen C berg at


http://edition.cnn.com/2017/07/14/world/sutter-iceberg-antarctica-climate-change/index.html (http://edition.cnn.com/2017/07/14/world/sutter-iceberg-antarctica-climate-change/index.html)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 16, 2017, 10:41:51 PM
The July 16 Sentinel image from PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_EW_GRDM_1SSH_20170716T072938_42E9_S_1.8bit.jp2) shows the south end of the rift.  This screen shot is at 50% enlargement ("ensmallment"?)
Title: Re: Rift in Larsen C
Post by: Hefaistos on July 17, 2017, 05:33:38 PM
Starts to break up now on the edge, according to satellite imagery from Deimos Imaging.

https://www.rt.com/viral/396558-larsen-c-iceberg-satellite/ (https://www.rt.com/viral/396558-larsen-c-iceberg-satellite/)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 19, 2017, 05:52:50 PM
There appears to be some fast ice growing in the young rift between Larsen C and Iceberg A68 (and friends). PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1B_IW_GRDH_1SSH_20170718T080131_89CE_S_1.8bit.jp2) screen print.
Project MIDAS (http://www.projectmidas.org/feed.xml) offers this (screen shot of part of their post's graphic with scale moved and Iceberg label recreated):
Quote
... a new rift appears to be extending northwards (towards the top left) and may result in further ice shelf area loss. Although this new rift will probably soon turn towards the shelf edge, there may be a risk that it will continue on to Bawden Ice Rise, a crucial point of stabilisation for Larsen C Ice Shelf.
Title: Re: Rift in Larsen C
Post by: magnamentis on July 19, 2017, 11:02:28 PM
@Tor Bejnar

is "fast ice" the correct term for ice growing between an iceberg and an ice-shelf?

the question is mean seriously not that you think there would be sarcasm or something i just don't know and like to learn about terms as much as i can, this term just did never cross my mind in this context, hence your feedback will be very appreciated.
Title: Re: Rift in Larsen C
Post by: charles_oil on July 19, 2017, 11:46:48 PM

Tor - I think link to Midas should be:  http://www.projectmidas.org/ (http://www.projectmidas.org/)


or: http://www.projectmidas.org/blog/larsen-c-responds/ (http://www.projectmidas.org/blog/larsen-c-responds/)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 20, 2017, 12:22:18 AM
fast ice (http://nsidc.org/cryosphere/glossary/F)
Quote
ice that is anchored to the shore or ocean bottom, typically over shallow ocean shelves at continental margins; fast ice is defined by the fact that it does not move with the winds or currents.

The new ice attached to (and growing off of) the Larsen C ice shelf is fast ice.  The new ice that is attached to the iceberg (ice island) is not fast ice, as long as the iceberg is drifting around.  If the iceberg stops moving for a bit, there will temporarily (at least) fast ice between the two.  I rather expect the iceberg to get stuck in the winter fast ice later this SH winter. (But I'm not an iceberg expert.)
Title: Re: Rift in Larsen C
Post by: magnamentis on July 20, 2017, 01:33:32 AM
thanks, before learning this i thought fast ice is fastened to land which apparently was wrong ;)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 21, 2017, 06:51:15 PM
Iceberg A68 is wrecking havoc on the frozen sea ice off of Larsen C Ice Shelf: at least for now.  The crack through the fast ice shown here (PolarView 11 pm on July 18 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_EW_GRDM_1SSH_20170718T235039_92A9_S_1.8bit.jp2)) isn't apparent on the 8 am image (posted above).  It is interesting to see how much the little icebergs have moved in 15 hours.  The largest of the small icebergs is about 5 x 12 km in size.
Title: Re: Rift in Larsen C
Post by: solartim27 on July 22, 2017, 05:25:27 PM
The rifts behind the initial crack show signs of widening.  This could get interesting fast (or not).  28 Jun to 22 Jul  Click required, then you'll want to zoom in

S1A_EW_GRDM_1SSH_20170722T001458_4661_S_1.final.jpg
S1A_EW_GRDM_1SSH_20170628T001457_3D5F_S_1.final.jpg
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 24, 2017, 03:55:34 PM
I figured out a fallacy in my July 14 post (http://forum.arctic-sea-ice.net/index.php/topic,1175.msg120803.html#msg120803).  The relationship between Iceberg A68 and the remaining Larsen C Ice Shelf is not just a transverse fault, although it looks pretty much like one within the red oval.  The purple arrow pairs are collinear and equally gapped.  One set shows the actual relative movement, the other pair doesn't.  (Whereas the red pair of arrows shows actual relative movement.) (PolarView image from July 22 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_EW_GRDM_1SSH_20170722T001458_4661_S_1.8bit.jp2).)

PS: the paper linked by this post may explain my July 14 behavior!
...
link (http://www.synthesisips.net/blog/dynamic-versus-static-systems/)
An excellent paper on how students in Earth and Atmospheric Sciences have difficulty in conceptualizing complex systems.
Students’ Understanding of Complex Dynamic Systems (http://www.sci.ccny.cuny.edu/~raia/Publications/Raia_v53n3p297.pdf)
Title: Re: Rift in Larsen C
Post by: johnm33 on July 24, 2017, 07:28:11 PM
Tor that makes better sense, the tide arrives from the south and given the inertia of this block isn't going to push it north in a hurry, but something has to give so it begins to rotate.
Title: Re: Rift in Larsen C
Post by: Susan Anderson on July 28, 2017, 08:21:44 AM
Was just over at Earth Observatory where they used parallel parking as a metaphor.
https://earthobservatory.nasa.gov/ (main site because Hudson Bay ice is most recent fwiw)

https://earthobservatory.nasa.gov/IOTD/view.php?id=90627&eocn=home&eoci=iotd_grid
A Fracturing Berg in the Polar Night
Quote
“The back-and-forth movement of A-68 looks akin to maneuvering a parallel-parked car out of a tight parking space—like an Austin Powers three-point turn,” said Christopher Shuman, a cryospheric scientist at NASA’s Goddard Space Flight Center and the University of Maryland, Baltimore County.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 28, 2017, 07:54:23 PM
Nothing exceptional (per my eyes) re A68.  Here's a screen shot from yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1A_EW_GRDM_1SSH_20170727T002304_C976_S_1.8bit.jp2) image. (click for larger view; use link for looking at details)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on July 31, 2017, 01:56:42 PM
A68's northern mini-bergs from the July 30 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201707/S1B_IW_GRDH_1SSH_20170730T080132_221A_S_1.8bit.jp2) image.  (The Polar View Antarctica (http://www.polarview.aq/antarctic) page gives access to recent images.)
Title: Re: Rift in Larsen C
Post by: AbruptSLR on August 03, 2017, 02:08:44 AM
With the cracks still spreading in the remaining Larsen-C Ice Shelf, the world (& satellites) will be watching to see how itself integrity holds-up:

Title: “Cracks are still spreading where that massive Antarctic iceberg broke free”

https://www.theverge.com/2017/8/2/16081998/ice-berg-larsen-c-ice-shelf-collapse-antarctica-climate-change (https://www.theverge.com/2017/8/2/16081998/ice-berg-larsen-c-ice-shelf-collapse-antarctica-climate-change)

Extract: “Cracks continue to spread on the Antarctic ice shelf where a trillion-ton iceberg roughly the size of Delaware broke free in July, scientists say.”
Title: Re: Rift in Larsen C
Post by: J Cartmill on August 05, 2017, 01:23:59 PM
New high res pictures from deimos imaging

http://www.businessinsider.com/larsen-c-iceberg-satellite-pictures-2017-8/#deimos-1-and-deimos-2-follow-similar-orbits-and-work-together-to-image-the-same-spots-on-the-ground-in-medium-and-very-high-resolution-1 (http://www.businessinsider.com/larsen-c-iceberg-satellite-pictures-2017-8/#deimos-1-and-deimos-2-follow-similar-orbits-and-work-together-to-image-the-same-spots-on-the-ground-in-medium-and-very-high-resolution-1)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fstatic1.businessinsider.com%2Fimage%2F598354be4fc3c01c008b4f7d-1200%2Fheres-how-those-images-fit-together-in-the-larger-context-of-the-ice-shelf.jpg&hash=868eb6a1e4fd04b9d6f070cc1ff2cd13)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on August 06, 2017, 06:30:40 AM
August 5 PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201708/S1A_IW_GRDH_1SSH_20170805T080214_1BFD_S_1.8bit.jp2) of the northern corner with the several 'little' icebergs with A68.

Also, fast ice, bergy bits and a gap between fast ice and new ice growing on A68 - near the southern end of A68.
Title: Re: Rift in Larsen C
Post by: Susan Anderson on September 16, 2017, 03:22:32 AM
Earth Observatory has posted a new picture of iceberg A68:

Daylight Returns to Larsen C
https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90968&eocn=home&eoci=nh (https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90968&eocn=home&eoci=nh)

(https://eoimages.gsfc.nasa.gov/images/imagerecords/90000/90968/larsenc_tmo_2017254.jpg)

Quote
In August 2017, polar night loosened its grip on the Antarctic Peninsula and daylight began to illuminate the region. That means scientists are getting their first sunlit looks at the massive iceberg that broke away from the Larsen C ice shelf in July. This natural-color image was captured on September 11, 2017, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite.

For about a week before this image was acquired, offshore winds pushed sea ice away from the shelf and out to sea. The remaining thin layer of frazil ice (gray mottled streaks on the dark ocean) does not offer much resistance, letting iceberg A-68A and its companions more easily move about the ocean. Already, scientists have watched the passage widen between A-68A and the front of the ice shelf, and the smaller bits spread out.

NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE). Caption by Kathryn Hansen.
Title: Re: Rift in Larsen C
Post by: crandles on September 22, 2017, 08:04:41 PM
Big Antarctic iceberg edges out to sea
http://www.bbc.co.uk/news/science-environment-41366504 (http://www.bbc.co.uk/news/science-environment-41366504)

Quote
But the latest satellite imagery now indicates the near-6,000 sq km block is swinging out into the Weddell Sea.

(https://ichef.bbci.co.uk/news/660/cpsprodpb/94D1/production/_97979083_1.jpg)
Title: Re: Rift in Larsen C
Post by: Susan Anderson on October 05, 2017, 05:29:15 AM
A couple of days back Earth Observatory had new imagery (dated 16 September), but Crandles' is obviously more recent. That thing is moving fast for something so big.

(https://eoimages.gsfc.nasa.gov/images/imagerecords/91000/91052/larsen_oli_2017259.jpg)

https://earthobservatory.nasa.gov/IOTD/view.php?id=91052&eocn=home&eoci=iotd_grid (https://earthobservatory.nasa.gov/IOTD/view.php?id=91052&eocn=home&eoci=iotd_grid)
Title: Re: Rift in Larsen C
Post by: bligh8 on October 06, 2017, 04:13:06 PM
Modeling tabular icebergs submerged in the ocean

Key Points: A novel-modeling framework is developed to explicitly model large tabular icebergs submerged in the ocean. Tabular icebergs are represented using Lagrangian elements that drift in the ocean, and are held together by numerical bonds Breaking the numerical bonds allows us to model iceberg breakup and calving.                         

Abstract: Large tabular icebergs calved from Antarctic ice shelves have long lifetimes (due to their large size), during which they drift across large distances, altering ambient ocean circulation, bottom-water formation, sea-ice formation, and biological primary productivity in the icebergs’ vicinity. However, despite their importance, the current generation of ocean circulation models usually do not represent large tabular icebergs. In this study, we develop a novel framework to model large tabular icebergs submerged in the ocean. In this framework, tabular icebergs are represented by pressure-exerting Lagrangian elements that drift in the ocean. The elements are held together and interact with each other via bonds. A breaking of these bonds allows the model to emulate calving events (i.e., detachment of a tabular iceberg from an ice shelf) and tabular icebergs breaking up into smaller pieces. Idealized simulations of a calving tabular iceberg, its drift, and its breakup demonstrate capabilities of the developed framework.

http://onlinelibrary.wiley.com/doi/10.1002/2017MS001002/pdf (http://onlinelibrary.wiley.com/doi/10.1002/2017MS001002/pdf)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on October 25, 2017, 07:37:06 PM
The Polar View  (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201710/S1A_IW_GRDH_1SSH_20171025T073754_119A_S_1.8bit.jp2)image of A-68A shows the 'large' iceberg between A-68A and the Larsen C migrating northward (toward the left in the image) [or sucked northward into the low pressure 'void'] as the ice island's southern end pivots further into the Weddell Sea.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on October 31, 2017, 06:48:33 PM
The current PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201710/S1B_IW_GRDH_1SSH_20171031T073712_AF86_S_1.8bit.jp2)  image shows the ice island continuing to move away from the coast (at least at its south end - with North being toward the left in the image) with the 'large' [~10 km] iceberg continuing to be sucked northward.  Of perhaps greater interest is the large area of open water that has opened up to the east (that's 'the top-side' in the image) of A-68A.  Because of the location of the darker and brighter icebergs [each ~4 km long - about 40 km from the left edge of the image] in the previous and current images, it is clear the ice is 'moving out' and not just melting. (Larsen C Ice Shelf is at the 'bottom' of the image.)
Title: Re: Rift in Larsen C
Post by: oren on November 01, 2017, 12:39:45 AM
Thanks for the updates Tor.
Title: Re: Rift in Larsen C
Post by: charles_oil on November 02, 2017, 02:08:51 AM


Great pictures from Operation Icebridge of A68


# 3) The western edge of iceberg A68 and the new edge of Larsen C Ice Shelf in the distance:


https://www.facebook.com/NasaOperationIcebridge/photos/pcb.1490399277703754/1490382397705442/?type=3&theater (https://www.facebook.com/NasaOperationIcebridge/photos/pcb.1490399277703754/1490382397705442/?type=3&theater)



Do we know how high the broken face is ?
Title: Re: Rift in Larsen C
Post by: solartim27 on November 07, 2017, 06:38:27 PM
Here's a portion of yesterday's Polar View image.  Is the shelf on the right side considered to be part of Larsen C?  It's rift might have reached the edge of the shelf, if not it's real close.  The new rifts on the main part of Larsen C are also expanding.  Going to be an interesting summer.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20171107T001502_D6E4_S_1.final.jpg
Title: Re: Rift in Larsen C
Post by: Susan Anderson on November 07, 2017, 09:23:17 PM
Shared this elsewhere but repeating here in case it's of interest: today's look at Nullschool surface temps show many above freezing in the region. Click on spot (greens seem to be the ones) for local temperature:
https://earth.nullschool.net/#current/wind/surface/level/overlay=temp/orthographic=-54.33,-82.99,568 (https://earth.nullschool.net/#current/wind/surface/level/overlay=temp/orthographic=-54.33,-82.99,568)
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 07, 2017, 09:34:30 PM
Here's a portion of yesterday's Polar View image.  Is the shelf on the right side considered to be part of Larsen C?  It's rift might have reached the edge of the shelf, if not it's real close.  The new rifts on the main part of Larsen C are also expanding.  Going to be an interesting summer.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20171107T001502_D6E4_S_1.final.jpg

Yes, that is part of Larsen C. Also, that island where the shelf is pinned is one of two key islands that contribute to the overall stability of the shelf. If the shelf were to recede from this island (Gipps Ice Rise) or the one to the north (Bawden Ice Rise), the entire shelf will be at risk.

Here is an article covering concerns that scientists have about these two pinning points.

https://www.nytimes.com/interactive/2017/06/09/climate/antarctica-rift-update.html
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 08, 2017, 03:54:22 PM
I am fascinated by the dramatic rifting that is visible on Larsen C from the Joerg Peninsula suture zone south. Does this rifting suggest a relatively fragile ice shelf as compared to the northern section of the shelf? If so, the Gipps ice rise may be the Achilles heel of the entire shelf.

Can anyone explain what rifting on a shelf suggests?

Also, the portion of Larsen C that originates from glacier R must be moving slower than the ice on either side, correct?  The rifting/fracturing, on this section of the shelf looks very different. Is this section even more fragile?

We are entering the first melt season since the major calving. Larsen C will be riveting this year. Get your popcorn.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 08, 2017, 04:14:12 PM
Larsen C is seeing temps significantly above 0C.
Title: Re: Rift in Larsen C
Post by: Susan Anderson on November 08, 2017, 04:30:39 PM
@SharedHumanity:

Thanks for the terrific visuals on both temps and configuration. Do you know if the "warmth" is abnormal for this time of year?
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 08, 2017, 04:36:00 PM
The entire peninsula is experiencing temperatures much higher than normal.
Title: Re: Rift in Larsen C
Post by: Susan Anderson on November 08, 2017, 04:54:57 PM
Thanks again, also for the reminder to use Climate Reanalyzer. Those visuals are mind boggling. It's tempting to go all extreme on potential melt of the WAIS this year, but I'll try to calm down, remembering what happened to Arctic melt hype so far. Scary monsters.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 08, 2017, 05:03:38 PM
Positive anomalies over the peninsula are expected to weaken but West Antarctica stays warm. Based on expert analysis here provided by others, I don't expect WAIS to contribute significantly to sea levels for many decades.
Title: Re: Rift in Larsen C
Post by: pileus on November 15, 2017, 05:03:20 AM
Some more photos from a mission on Sunday,

https://gizmodo.com/nasa-captures-stunning-close-up-photos-of-antarcticas-m-1820432241
Title: Re: Rift in Larsen C
Post by: solartim27 on November 16, 2017, 05:23:20 PM
Nice Landsat 8 image from this tweet
https://twitter.com/StefLhermitte/status/931094514730721280?s=17
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 17, 2017, 02:00:39 AM
Wouldn't surprise me if we had more tabular bergs breaking free this melt season.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on November 20, 2017, 07:58:28 PM
Interesting look at the thin new ice between A-68A (top) and the Larsen Shelf (bottom).  As the iceberg moves out, the new ice has to decide if it'll be fast ice (remaining attached to the Larsen Shelf) or stay with the iceberg, or go its own way.  I wonder if sea ice is still growing or if it is in retreat in this area.  Image from PolarView 2017-11-18 (http://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20171118T073754_524F_S_1.final.jpg) via the Polarview website (http://www.polarview.aq/antarctic).
Title: Re: Rift in Larsen C
Post by: gerontocrat on November 21, 2017, 03:27:06 PM
HYCOM's 30 day Antarctic sea ice thickness gif shows well how the thickest ice collects into the SW corner of the Weddell Sea and is persistently pushed north along the coast until sent into oblivion in an easterly direction by the WSW polar winds.

Perhaps this is why Larsen C seems to be pivoting from the southern end in an anti-clockwise direction with the pivot at the northern end.

Anyway, "that is my theory and it belongs to me" (pace Monty Python).

Title: Re: Rift in Larsen C
Post by: johnm33 on November 21, 2017, 04:46:28 PM
My guess it's the tides (https://www.esr.org/wp-content/uploads/2017/07/Antarctic_Tide_10min.mp4) from https://www.esr.org/research/polar-tide-models/
Title: Re: Rift in Larsen C
Post by: gerontocrat on November 22, 2017, 02:07:51 PM
HYCOM's 30 day Antarctic sea ice thickness gif shows well how the thickest ice collects into the SW corner of the Weddell Sea and is persistently pushed north along the coast until sent into oblivion in an easterly direction by the WSW polar winds.

......Larsen C seems to be pivoting from the southern end in an anti-clockwise direction with the pivot at the northern end.

Anyway, "that is my theory and it belongs to me" (pace Monty Python).

More evidence to support "my theory and it belongs to me".

The first image below is Antarctic Sea Ice drift yesterday in the Weddell Sea (from Jaxa). Note the circular movement pushing sea ice SW into the corner, then North along the coast and finally NE out to sea. This seems to be a pattern often repeated and sometimes much stronger.

The second image is surface winds today in Antarctica. (from cci-reanalyzer). The West to East circumpolar winds are well away from the continent with a low formed over the Weddell Sea between the main polar winds and the shore. this pattern is also oft repeated.

PS:- And I have added HYCOM's 30 days of Antarctic Sea Ice Drift - click to start animation
Title: Re: Rift in Larsen C
Post by: Tealight on December 10, 2017, 11:04:48 PM
Iceberg A-68A has drifted far enough from the ice shelf to begin it's journey north-east (towards the top of the image) and follow the small piece that has broken of earlier. If it keeps up with the speed of the smaller piece it might be gone in just a few years.
Title: Re: Rift in Larsen C
Post by: gerontocrat on December 18, 2017, 11:25:45 PM
What a strange website go find an animation of what is happening to 68a

http://uk.businessinsider.com/antarctica-iceberg-a68-calving-animation-satellite-photos-2017-12?r=US&IR=T




Title: Re: Rift in Larsen C
Post by: sesyf on December 20, 2017, 08:32:04 PM
Of course we all know how much ice is underwater but for the general piblic it might be instructive to show how much ice there really is...
Title: Re: Rift in Larsen C
Post by: gerontocrat on December 21, 2017, 01:17:45 PM
Of course we all know how much ice is underwater but for the general piblic it might be instructive to show how much ice there really is...
A mass of 1 trillion tonnes and an area of 5,800 km2 gives an average thickness of about 170 metres, of which about 20 (?) are above and 150 (?) below the surface.

What the general public would make of that I dunno.
Title: Re: Rift in Larsen C
Post by: Mozi on December 21, 2017, 02:24:50 PM
As a member of the general public, my reaction to that is "that's a lot of ice."
Title: Re: Rift in Larsen C
Post by: gerontocrat on December 21, 2017, 03:42:39 PM
If spread out over the ocean in a 1 meter thickness iceberg 68A would cover an area of just under 1 million square kilometres, which is 4 times the area of the UK

Yes, it is a lot of ice, but in the context of the Antarctic Ice Sheet it is but a smidgeon.
Title: Re: Rift in Larsen C
Post by: Susan Anderson on December 21, 2017, 07:35:29 PM
What a strange website go find an animation of what is happening to 68a

http://uk.businessinsider.com/antarctica-iceberg-a68-calving-animation-satellite-photos-2017-12

The huge and growing number of people in all walks of life who are aware here in the US are animated by a strong need to overcome the rot at the top. Meanwhile,Business Insider and other outlets are looking for material of interest. Unfortunately, Larsen C break is eye candy for sensationalists, but it still moves people towards paying attention.
--
[edit: OT rant removed with apologies to anyone who saw it here. best to all, susan]
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on December 21, 2017, 07:45:47 PM
further to A-68A's ice volume
... or 1/10 of one inch covering all the Earth's oceans!
Title: Re: Rift in Larsen C
Post by: Martin Gisser on December 21, 2017, 08:54:42 PM
What a strange website go find an animation of what is happening to 68a

http://uk.businessinsider.com/antarctica-iceberg-a68-calving-animation-satellite-photos-2017-12

The huge and growing number of people in all walks of life who are aware here in the US are animated by a strong need to overcome the rot at the top. Meanwhile,Business Insider and other outlets are looking for material of interest. [...]
I hope this isn't just an "east coast elite" impression, but extends to "flyover America"...
Title: Re: Rift in Larsen C
Post by: Susan Anderson on December 22, 2017, 12:59:30 AM
@Martin Gisser: Me too. Our survival depends on it. But I think so, optimistically (from Boston, a home of elitist America). I cannot lose hope. There is no other life.
Title: Re: Rift in Larsen C
Post by: Grygory on December 25, 2017, 12:39:05 PM
A- 68a will collide again with larsen c? Will there be more icebergs?
http://www.polarview.aq/images/106_S1jpgsmall/201712/S1A_EW_GRDM_1SSH_20171225T001500_4E3F_S_1.jpg

Title: Re: Rift in Larsen C
Post by: gerontocrat on December 25, 2017, 04:13:21 PM
A- 68a will collide again with larsen c? Will there be more icebergs?
http://www.polarview.aq/images/106_S1jpgsmall/201712/S1A_EW_GRDM_1SSH_20171225T001500_4E3F_S_1.jpg
Weather-forecast.com says all quiet in the weddell sea now and for the days ahead. No wind = no drift (usually tending north at Larsen c location). When winter comes maybe a different story. Sea ice drift can then be something awesome.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on January 08, 2018, 09:42:25 PM
Today's Polar View (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1A_IW_GRDH_1SSH_20180108T080214_4DAA_S_1.8bit.jp2) shows how much A-68A has moved since breaking off the Larsen C Shelf in July 2017 (about 35 km, net).  Obviously, it did not move in a straight line!  The 'little' icebergs (one with a purple dot) started out at the southern end of the ice island (link to July 16 post (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg121101.html#msg121101)).
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on January 18, 2018, 04:25:11 PM
Looks like some open water off of the eastern side of Ice Island A-68A, per yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1A_IW_GRDH_1SSH_20180117T073751_268C_S_1.8bit.jp2).  A different PolarView image from yesterday  (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1A_EW_GRDM_1SSH_20180118T001459_1B12_S_1.8bit.jp2)shows the entire ice island.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on January 26, 2018, 02:36:58 PM
Yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1B_EW_GRDM_1SDH_20180125T235803_D6F0_S_1.8bit.jp2) shows some recently broken off icebergs (or else they are holding on by a thread).  These were predicted by the Project MIDAS (http://www.projectmidas.org/feed.xml) folks last July.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on January 30, 2018, 09:32:45 PM
Is there going to be a collision?  The 'little' iceberg has scooted out of the way (see previous image, above, from 5 days ago).  Exciting times!  The A68-A Ice Island has moved about 200 meters northwards in these 5 days, I reckon. Today's PolarView image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1A_EW_GRDM_1SSH_20180130T001459_4567_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 01, 2018, 06:30:07 PM
Today's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201802/S1A_IW_GRDH_1SSH_20180201T080214_81EC_S_1.8bit.jp2) shows about 500 m separation between the ice island and the shelf.
Title: Re: Rift in Larsen C
Post by: FrostKing70 on February 01, 2018, 07:12:02 PM
I am curious about the rift below the Gipps Rise (bottom right on the posts which show it).   Does anyone know if that is a "stable/ not growing" rift or is is growing?   If it is growing, would the predicted rift direction remove the Gipps Rise as an anchor point?

 

Title: Re: Rift in Larsen C
Post by: FredBear on February 01, 2018, 10:03:54 PM
The ice edge is growing outwards to the south of Gipps ice rise and has filled the bay (where the ice is shown overlaid in grey in the following picture).

https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1175.0;attach=54638;image

To me it looks like the large rift could grow to create a calving but because the ice has been growing beyond the accepted margin it may be inhibited/prevented from happening? Anyway, these rifts can grow slowly for many years before breaking (c.f. A68).
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 05, 2018, 04:39:03 PM
Today's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201802/S1B_EW_GRDM_1SDH_20180205T001417_E436_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 05, 2018, 07:55:13 PM
Wind and Sea Ice drift in the SW Weddell sea has been zilch for months. But when winter comes things are often very very different. (as a typical image from HYCOM last May shows)

So I guess 68a ain't gonna move much until then.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 05, 2018, 09:51:59 PM
Ice Island A-68A 'drifted' north about 20 km during the past week.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 05, 2018, 11:34:53 PM
Ice Island A-68A 'drifted' north about 20 km during the past week.
is that a lot, or is it a little ? I confess I have no knowledge at all about how fast large bergs can move around.
Title: Re: Rift in Larsen C
Post by: magnamentis on February 05, 2018, 11:44:26 PM
Ice Island A-68A 'drifted' north about 20 km during the past week.
is that a lot, or is it a little ? I confess I have no knowledge at all about how fast large bergs can move around.

an example from the Harbour Authority Of Twillingate   Twillingate, NL A0G 4M0
An iceberg drifts at about 0.2 m/s or 0.7 k/hr. The speed that an iceberg drifts depend on various factors such as, size, shape, currents, waves and wind.

i think this is very individually different, up there they move relatively fast due to the labrador current while on the other hand the 20km for that huge and specific berg is faster than it has travelled before that. it's all relative :-)

https://www.youtube.com/watch?v=8ObLZUWgMgU
Title: Re: Rift in Larsen C
Post by: johnm33 on February 06, 2018, 12:05:06 AM
Ice Island A-68A 'drifted' north about 20 km during the past week.
Tides have been huge this last few days.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 06, 2018, 12:27:16 AM
Ice Island A-68A 'drifted' north about 20 km during the past week.
Tides have been huge this last few days.
Supermoon effect?
Title: Re: Rift in Larsen C
Post by: johnm33 on February 06, 2018, 11:18:46 AM
'supermoon?' I guess so
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 06, 2018, 02:09:48 PM
Ice Island A-68A 'drifted' north about 20 km during the past week.
is that a lot, or is it a little ? I confess I have no knowledge at all about how fast large bergs can move around.
20 km in 7 days is not a lot, it is a little.

The little table below says if that 20 km took 7 days, the average speed was 0.033 metres per second, as opposed to average speed of icebergs subject to the Labrador current of 0.2 metres per second. On the one hand, 68A is huge as is its inertia. But once moving, somewhat difficult to stop. 20 km movement is an impressive performance by the supermoon.

The first images below show how the SW Weddell Sea is currently a dead spot for cyclones, as it has been for most days in the summer. This seems to me why the sea ice theere is more or less stuck.

Winter seems to be very different. The last image shows a typical sea ice drift image from JAXA in winter (September) caused by cyclones forming between the circumpolar vortex and the coast of the Weddell Sea. Ice is pushed West and then North right alongside Larsen C. Methinks in a few months we will see real northward drift of Larsen C as this is the normal and persistent weather pattern. "That is my theory and it belongs to me!" (pace Monty Python)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 06, 2018, 03:29:48 PM
Ice Island A-68A 'drifted' north about 20 km during the past week.
is that a lot, or is it a little ? I confess I have no knowledge at all about how fast large bergs can move around.
I reported on January 30 that the ice island had moved about 200 meters during the previous 5 days.  From mid July to January 30 (6.5 months), the ice island moved a net (through more of a wolf pattern than a crow pattern) 50 km, so the recent movement is relatively fast.

From above (0.2 km/hr) and from the internet (http://www.icebergfinder.com/iceberg-facts.aspx) (0.7 km/hr), I get 33 to 115 km per week movement 'doable'.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 06, 2018, 04:06:32 PM
HYCOM's snapshot archive from 2017 suggests that active cyclones and strong sea ice drift could start as early as late Feb or early March. Winter comes early at 70 degrees south.
Title: Re: Rift in Larsen C
Post by: SteveMDFP on February 12, 2018, 07:15:19 PM
Here's a very interesting article about research on the sea and sea floor underneath A68:

UK team set for giant Antarctic iceberg expedition
http://www.bbc.com/news/science-environment-43008058 (http://www.bbc.com/news/science-environment-43008058)
Quote
British Antarctic Survey marine biologist Dr Katrin Linse, who is leading the mission, said that the calving of the iceberg, which has been named A68, provides researchers with "a unique opportunity to study marine life as it responds to a dramatic environmental change".
Title: Re: Rift in Larsen C
Post by: Sleepy on February 13, 2018, 05:30:03 PM
A nice and closer view of that little ice cube:
https://twitter.com/emm_pearce/status/963167751018827776 (https://twitter.com/emm_pearce/status/963167751018827776)
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 20, 2018, 04:30:10 PM
Here's a very interesting article about research on the sea and sea floor underneath A68:

UK team set for giant Antarctic iceberg expedition
http://www.bbc.com/news/science-environment-43008058 (http://www.bbc.com/news/science-environment-43008058)
Quote
British Antarctic Survey marine biologist Dr Katrin Linse, who is leading the mission, said that the calving of the iceberg, which has been named A68, provides researchers with "a unique opportunity to study marine life as it responds to a dramatic environmental change".
The expedition ship leaves port on Wednesday. But which port ? The article does not say, of course. Long way from UK to Larsen C

https://www.theguardian.com/environment/2018/feb/20/scientists-race-to-explore-antarctic-marine-life-revealed-by-giant-iceberg
Title: Re: Rift in Larsen C
Post by: Sleepy on February 20, 2018, 04:48:14 PM
RRS James Clark Ross (ZDLP) is in Port Stanley:
https://www.marinetraffic.com/en/ais/details/ships/shipid:780940/mmsi:740339000/vessel:ZDLP (https://www.marinetraffic.com/en/ais/details/ships/shipid:780940/mmsi:740339000/vessel:ZDLP)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 20, 2018, 07:44:27 PM
Since February 1 (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg140741.html#msg140741), A68-A moved about 19 km (in 18 days), so about 7 km/week.  Screen print from yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201802/S1B_IW_GRDH_1SSH_20180219T080131_D5CE_S_1.8bit.jp2).  However, most of the movement happened before February 5 (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg141092.html#msg141092) (1 km/week).
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 20, 2018, 07:56:21 PM
A68-A moved about 19 km (in 18 days), so about 7 km/week.  Screen print from However, most of the movement happened before February 5 (1 km/week).

How many Kms to escape the peninsula? is it likely to get trapped by winter ice, or will winds help it on its way. " I want to know!", or will I have to just wait and see.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 20, 2018, 08:54:08 PM
If A68-A continues northeastward along the Antarctic Peninsula, its leading end needs to travel about 600 km to pass Joinville Island (just off the northern tip of the peninsula).  It has traveled about 70 km in 7 months.  At this rate, it will take about 5 more years for the leading end to emerge north of the peninsula.  Although A68-A is about 200 km long, when the ice island gets that far north, I suspect it will be caught by the Antarctic Circumpolar Current and will not take an additional year or two to be clear of the peninsula.  (I'll probably break into significant smaller ice islands before then, and the pieces will travel separately.)

The Polar View (http://www.polarview.aq/antarctic) screen shot shows a snap shot (showing most of A68-A) of the frame highlighted in yellow.  The tip of the Antarctic Peninsula (land is outlined in purple) is in the 3rd frame northeast of this one.

The Antarctic Iceberg Tracking Database (http://www.scp.byu.edu/data/iceberg/) shows where icebergs have traveled.

(Disclaimer:  I am not an ice expert.)
Edit:  a couple typos fixed.



Title: Re: Rift in Larsen C
Post by: Susan Anderson on February 23, 2018, 06:47:18 PM
@Tor Bejnar, that is a fantastic resource.

disclaimer: I'm even less expert than you.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 23, 2018, 07:25:27 PM
If A68-A continues northeastward along the Antarctic Peninsula, its leading end needs to travel about 600 km to pass Joinville Island (just off the northern tip of the peninsula).  It has traveled about 70 km in 7 months.  At this rate, it will take about 5 more years for the leading end to emerge north of the peninsula. 

(Disclaimer:  I am not an ice expert.)

I am not an ice expert.  -anybody who knows more than me is, in my eyes, an expert. So I will ask the expert two questions.

To the casual eye the iceberg tracker says the majority of icebergs originate from the shores of the Weddell Sea (or  pushed along the shore from the East?). True or false?

During the last winter HYCOM (and even the JAXA Sea Ice Drift Images) showed really strong movement along the Weddell Sea from East to West and then North up along the coast until exiting the peninsula into the Westerlies. It looked as if strong cyclones often developed between the west to east circumpolar vortex and the shore with strong easterlies along the shoreline. Could this not hurry the Larsen C beastie on its way?

ps: I am with Ms Anderson - what a super resource. Every day my environment folder bulges more and more at the seams.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 23, 2018, 08:15:30 PM
Replying just to be polite...
True or False?  No idea.
Hurrying the beastie?  No idea, except that I think Ice Shelf Larsen C and Ice Island A68 (now A68-A - whatever happened to A68-B  :'() got a divorce and that A68 would like folks to use its chosen name, A68-A.  (I don't like the idea of old acquaintances calling me my ex's beastie  >:()  [I guess I am an expert at junior high humor.  The year I left junior high school they closed it down and former 7th grades went to the expanding middle school, with the 8th and 9th graders going into the high school.  Therefore, I do not have to apologize to current junior high school students, for there are none where I came from.]
Title: Re: Rift in Larsen C
Post by: Susan Anderson on February 23, 2018, 08:42:08 PM
@
Here's a very interesting article about research on the sea and sea floor underneath A68:

UK team set for giant Antarctic iceberg expedition
http://www.bbc.com/news/science-environment-43008058 (http://www.bbc.com/news/science-environment-43008058)
Quote
British Antarctic Survey marine biologist Dr Katrin Linse, who is leading the mission, said that the calving of the iceberg, which has been named A68, provides researchers with "a unique opportunity to study marine life as it responds to a dramatic environmental change".
The expedition ship leaves port on Wednesday. But which port ? The article does not say, of course. Long way from UK to Larsen C

https://www.theguardian.com/environment/2018/feb/20/scientists-race-to-explore-antarctic-marine-life-revealed-by-giant-iceberg

New Zealand or southern Chile? My New Yorker (favorite resource) had a terrific article about Worsley's expeditions, including a centennial Shackleton one, that describes the process of getting out there and resources available to them. The quote below is a very small part of a 25 page special with great pix. I know they allow 5 articles a month free. https://www.newyorker.com/magazine/2018/02/12/the-white-darkness (https://www.newyorker.com/magazine/2018/02/12/the-white-darkness)

Quote
the new expedition would be composed of descendants of men who had explored alongside Shackleton. They would try to reach Shackleton’s farthest point on January 9, 2009—exactly a hundred years after he did—and then press on to the South Pole, completing, in Gow’s words, “unfinished family business.”

Worsley listened in amazement. Here was the chance of a lifetime.
....
Worsley, Gow, and Adams planned to begin their journey south of New Zealand, on Ross Island. The island is bound by the Ross Ice Shelf, which extends over the Ross Sea and is the largest body of floating ice in the world—more than 180,000 square miles and, on average, more than a thousand feet thick. Because the Ross Ice Shelf is easier to reach by sea during the summer than other parts of the continent, and because it is relatively smooth and stretches nearly 600 miles toward the heart of Antarctica, it was the starting point for expeditions to the South Pole during the golden age of Antarctic exploration. Shackleton and Scott and Amundsen all began their expeditions on the shelf.
....
On October 30, 2008, Worsley, Gow, and Adams arrived in Punta Arenas, on the southern tip of Chile. They went to a warehouse owned by a company named Antarctic Logistics & Expeditions. During the summer, between 30,000 and 40,000 tourists visit the continent, nearly all of them travelling on small cruise ships. Worsley’s party had hired A.L.E. to provide logistical support, which included transporting them by airplane to their starting point on Ross Island.
Title: Re: Rift in Larsen C
Post by: FredBear on February 24, 2018, 06:21:13 AM
gerontocrat, on: February 23, 2018, 07:25:27 PM you asked where the icebergs in the Weddell sea started out. In the topic "Antarctic Icebergs" I said:-

"Some other 'bergs are heading off from the Weddell Sea in the direction of South Georgia - b15z (15*7nm), b15t (25*6nm), c28b (21*14nm) and b09f (20*8nm) are fairly clear.

A new recruit has been b15aa (11*6nm) which came round the bend from the east above the Brunt ice shelf (about October 24 2017) and has been drifting round in small circles all this summer season, rather than going south towards Brunt."

b15 was a huge berg from the Ross Sea, so its remains (b15z, b15t) have travelled in a westerly direction 3/4 of the way round Antarctica before heading north into the South Atlantic Ocean.

b15aa was doing cart-wheels round the coast last year, and after being freed from the winter pack, was continuing but stalled. It is now drifting away from the shore - is it going to take a short cut towards the Antarctic Peninsular, drift north, or continue south round the Weddell Sea? Time will tell!

Title: Re: Rift in Larsen C
Post by: Sleepy on February 24, 2018, 10:49:36 AM
@
Here's a very interesting article about research on the sea and sea floor underneath A68:

UK team set for giant Antarctic iceberg expedition
http://www.bbc.com/news/science-environment-43008058 (http://www.bbc.com/news/science-environment-43008058)
Quote
British Antarctic Survey marine biologist Dr Katrin Linse, who is leading the mission, said that the calving of the iceberg, which has been named A68, provides researchers with "a unique opportunity to study marine life as it responds to a dramatic environmental change".
The expedition ship leaves port on Wednesday. But which port ? The article does not say, of course. Long way from UK to Larsen C

https://www.theguardian.com/environment/2018/feb/20/scientists-race-to-explore-antarctic-marine-life-revealed-by-giant-iceberg

New Zealand or southern Chile?
Susan, I posted a link dírectly after gerontocrat's question above with the exact (and live) location of RRS James Clark Ross:
RRS James Clark Ross (ZDLP) is in Port Stanley:
https://www.marinetraffic.com/en/ais/details/ships/shipid:780940/mmsi:740339000/vessel:ZDLP (https://www.marinetraffic.com/en/ais/details/ships/shipid:780940/mmsi:740339000/vessel:ZDLP)

So, on Feb 20:th the ship was still in Port Stanley, Falkland Islands.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 24, 2018, 11:44:51 AM

b15 was a huge berg from the Ross Sea, so its remains (b15z, b15t) have travelled in a westerly direction 3/4 of the way round Antarctica before heading north into the South Atlantic Ocean.


perhaps this post should be in the Antarctic Icebergs thread, for as Sleepy remarked, A68-A is now divorced from Larsen C.

travelled in a westerly direction 3/4 of the way round Antarctica - Watching Antarctica weather and sea ice drift over the last year I was struck how the West to East polar vortex was consistently well off shore, and from it often strong lows developed between it and the shore, often with strong Easterlies along the coast. Perhaps most of the time only when icebergs reach the peninsula at the SW corner of the Weddell Sea is the drift forced north until the Vortex can pick them up and send them out to their slow death.

Title: Re: Rift in Larsen C
Post by: johnm33 on February 24, 2018, 01:33:28 PM
In order to move north bergs have to be accelerated eastward by about 5kph for every 20k travelled [needs checking], or their inertia will press them against the peninsular. So they need to get caught up in a powerful current or tidal movement to 'escape' antarctica. If you look at the 600 s lat. you'll see that for practical purposes a berg, going n, is moving directly away from the axis of rotation, and that the 600lat. is approx half the distance the equator is from that axis, thus the surface speed (https://68.media.tumblr.com/f6959257bf4c7b28be5a0da1ae16a52a/tumblr_mzv5b7Sljz1s3dn7vo1_1280.png) is approx half that at the equator. We know there's a powerful clockwise tidal flow through Weddel. 
https://earth.nullschool.net/#current/ocean/surface/currents/overlay=sea_surface_temp/azimuthal_equidistant
The icebergs escaping but not from Weddel look more like rare events, but worth looking into, given their similarities, as/when time permits.
Title: Re: Rift in Larsen C
Post by: gerontocrat on February 24, 2018, 02:14:13 PM
hullo Johnm33,

putting my answer to your most informative post in the Antarctic Icebergs thread. A68-A is now divorced from Larsen C

cheers

Gerontocrat
Title: Re: Rift in Larsen C
Post by: Susan Anderson on February 24, 2018, 10:23:39 PM
@Sleepy, thanks, that's an interesting link. (Out of my depth here, but I was intrigued by the Worsley story.)
Title: Re: Rift in Larsen C
Post by: Sleepy on February 25, 2018, 09:42:44 AM
Susan, the ships name was mentioned in the BBC article that Steve posted. If you know the ships name, you can often find their call sign, in this case: ZDLP.
Title: Re: Rift in Larsen C
Post by: FredBear on March 02, 2018, 01:02:13 PM
I see the Larsen C expedition to explore the newly cleared sea bed has been abandoned for this year.

http://www.bbc.co.uk/news/science-environment-43257289

The RRS James Clark Ross (ZDLP) seemed to head for the western side of the Antarctic Peninsular earlier, so I did wonder whether it would send scientists across by air as the sea ice did not look good (or was too good?) in satellite images of the East this year.
Title: Re: Rift in Larsen C
Post by: RikW on March 02, 2018, 03:45:34 PM
https://www.telegraph.co.uk/news/2018/03/02/penguin-super-colony-discovered-antarctic-danger-islands-pictures/

When i read this article the first thing I thought "A-68 will probably hit the island and wipe-out the colony..."

and then I thought, what happens when A-68 will hit an island like that, will it even be noticed on such an island because it won't hit the island but it will get grounded near the island probably, and will it stay grounded for a long time?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on March 19, 2018, 05:16:25 PM
Looks like A68-A has moved about 4 km in 4 weeks. (Polar View (http://www.polarview.aq/antarctic) - today's image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201803/S1A_EW_GRDM_1SSH_20180319T001459_AB59_S_1.8bit.jp2))
Title: Re: Rift in Larsen C
Post by: Shared Humanity on March 19, 2018, 08:44:47 PM
So how close is A68 to the Bawden ice rise? What effect if any could A68 have on this crucial pinning point for Larsen C?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on March 19, 2018, 09:56:49 PM
reference (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg140741.html#msg140741)

They've been closer. 

To your question, "What effect?",  I don't know, but I'm watching!
Title: Re: Rift in Larsen C
Post by: Shared Humanity on March 20, 2018, 01:46:30 AM
Thanks. So a little under 2 km.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on March 20, 2018, 01:54:58 AM
That reference link shows A68 closer to Larsen C but that is not the Bawden ice rise. The ice rise is the step feature that is just north of A68 on the picture you just posted. A little less than 2 km separates them. This island serves to pin the Larsen C glacier, providing essential stability to the entire shelf. There is a 2nd, the Gipps Ice Rise (Island) further south that performs the same function.
Title: Re: Rift in Larsen C
Post by: Sleepy on March 20, 2018, 08:50:05 AM
So what's the time frame here until Bawden and Gipps doesn't do their job anymore and A68 leaves port without doing damage. A few more years, or less? If the future resembles Larsen B, it might collapse down to Kenyon Peninsula rather quickly after they fail, maybe even down to a lesser straight line between Kenyon and Churchill:

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1175.0;attach=36823;image)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on March 30, 2018, 07:53:41 PM
A68-A has move south a bit since I last posted.
full image link (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201803/S1B_EW_GRDM_1SDH_20180329T074514_A409_S_1.8bit.jp2)
Polar View (Antarctica) (https://www.polarview.aq/antarctic)

Still about 800 meters separate ice shelf from ice island.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on April 20, 2018, 03:25:21 PM
Not much movement lately...
Today's PolarView image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201804/S1B_IW_GRDH_1SSH_20180420T080132_29B9_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on April 25, 2018, 05:34:15 PM
Did something go 'bump in the night'? (less than 100 m separation)
From today's Polar View image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201804/S1B_EW_GRDM_1SDH_20180425T000613_ADE8_S_1.8bit.jp2).
Okay, not quite 'night', per Worldview.
Title: Re: Rift in Larsen C
Post by: FrostKing70 on April 25, 2018, 09:08:48 PM
I am not familiar enough with this area to understand the bottom picture.   Would you kindly explain what it shows?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on April 25, 2018, 09:51:09 PM
This help? EOSDIS WorldView link (https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2018-04-25-T00%3A00%3A00Z&z=3&v=-3320728.238890833,194181.89075177791,-740248.2388908334,2078341.890751778) (Enlarging from this linked view will show more clearly the features roughly outlined below.)
Title: Re: Rift in Larsen C
Post by: FrostKing70 on April 25, 2018, 09:59:26 PM
Thank you, with that I can now tie it together!
Title: Re: Rift in Larsen C
Post by: AbruptSLR on May 02, 2018, 08:27:08 PM
With climate change coming the Larsen C ice shelf is a dead-man walking:

Title: "‘Foehn winds’ causing Antarctica’s Larsen C ice shelf to melt in winter"

https://www.carbonbrief.org/foehn-winds-causing-antarcticas-larsen-c-ice-shelf-to-melt-in-winter

Extract: "Parts of Antarctica’s Larsen C ice shelf are melting in the depths of winter, when temperatures typically stay well below freezing, research finds.

Between 2015 and 2017, around 23% of the annual surface melt across the ice shelf occured in the winter months, according to results taken from field and satellite observations."
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on May 14, 2018, 05:35:32 PM
Icebergs have broken off A68-A (I'm curious why/how) and image showing the least distance I've seen between ice island and shelf (since the original separation).  Today's PolarView  (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201805/S1B_IW_GRDH_1SSH_20180514T080134_2D24_S_1.8bit.jp2)image from PolarView Antarctica (https://www.polarview.aq/antarctic).
Title: Re: Rift in Larsen C
Post by: Shared Humanity on May 14, 2018, 05:50:50 PM
Looking at this image, I am very concerned about the condition of Larsen C where it is attached to the Bawden ice rise. Those pronounced troughs (melt streams?) on the northern half of the island suggests the shelf is losing its grip on the rise, a crucial pinning point that stabilizes the entire shelf. The southern half looks bad as well with the dark portion of the ice shelf that runs parallel to the island.

When the shelf breaks free, I expect to see a rapid collapse of this portion of the shelf.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on May 14, 2018, 07:04:39 PM
The 'fingers' at (or north of) the Bawden Ice Rise in today's image look like the image Tealight posted in December (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg135971.html#msg135971) dated 2017-12-09 (reproduced here).
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1175.0;attach=55882;image)These looked similar in a ProjectMIDAS (http://www.projectmidas.org/blog/larsen-c-responds/) lower-resolution image dated 2017-07-12 (partial screen print below).

Shared Humanity's concern may be the apparent weakness on the 'left' side of the Bawden Ice Rise which may be more developed than it was 5 months ago.

For educational purposes:
Quote
An ice rise (https://en.wikipedia.org/wiki/Ice_rise) is a clearly defined elevation of the otherwise totally flat ice shelf, typically dome-shaped and rising 100 to 200 metres above the surrounding ice shelf. An ice rise forms where the ice shelf touches the rocky seabed because of an elevation in the seabed that remains below sea level.
Quote
Bawden Ice Rise (https://en.wikipedia.org/wiki/Bawden_Ice_Rise) (66°59′S 60°50′WCoordinates: 66°59′S 60°50′W) is an ice rise, 8 nautical miles (15 km) long and 2 nautical miles (4 km) wide, near the edge of the Larsen Ice Shelf, 41 nautical miles (76 km) east-southeast of Cape Alexander, Graham Land. The feature, which may consist of more than one ice rise, was mapped on a British Antarctic Survey (BAS) radio echo sounding flight from Adelaide Island in February 1975, and named by the UK Antarctic Place-Names Committee in 1985 after John Bawden, who was with BAS from 1971 and was Finance Officer, 1973–78.

I wonder if the bit of A68-A that recently broke off got stuck on (submerged) rocks...
Title: Re: Rift in Larsen C
Post by: Shared Humanity on May 14, 2018, 07:19:17 PM
The 'fingers' at (or north of) the Bawden Ice Rise in today's image look like the image Tealight posted in December (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg135971.html#msg135971) dated 2017-12-09 (reproduced here).
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1175.0;attach=55882;image)These looked similar in a ProjectMIDAS (http://www.projectmidas.org/blog/larsen-c-responds/) lower-resolution image dated 2017-07-12 (partial screen print below).

Shared Humanity's concern may be the apparent weakness on the 'left' side of the Bawden Ice Rise which may be more developed than it was 5 months ago.

For educational purposes:
Quote
An ice rise (https://en.wikipedia.org/wiki/Ice_rise) is a clearly defined elevation of the otherwise totally flat ice shelf, typically dome-shaped and rising 100 to 200 metres above the surrounding ice shelf. An ice rise forms where the ice shelf touches the rocky seabed because of an elevation in the seabed that remains below sea level.
Quote
Bawden Ice Rise (https://en.wikipedia.org/wiki/Bawden_Ice_Rise) (66°59′S 60°50′WCoordinates: 66°59′S 60°50′W) is an ice rise, 8 nautical miles (15 km) long and 2 nautical miles (4 km) wide, near the edge of the Larsen Ice Shelf, 41 nautical miles (76 km) east-southeast of Cape Alexander, Graham Land. The feature, which may consist of more than one ice rise, was mapped on a British Antarctic Survey (BAS) radio echo sounding flight from Adelaide Island in February 1975, and named by the UK Antarctic Place-Names Committee in 1985 after John Bawden, who was with BAS from 1971 and was Finance Officer, 1973–78.

I wonder if the bit of A68-A that recently broke off got stuck on (submerged) rocks...

Not talking about the fingers of ice north of Bawden. I'm looking at where the ice is in contact with the island. There are very visible troughs/depressions/rifts which come into contact with the island.

IMHO, the very dark portions of the ice shelf that run the entire length of the island are evidence of thinning and the 4 pronounced dark spots on the northern half that terminate each of the 4 troughs that run towards the island are due to melt or rifting.
Title: Re: Rift in Larsen C
Post by: johnm33 on May 14, 2018, 10:42:59 PM
"I'm curious why/how"
 It's worth considering the tides rotating clockwise through Weddel, being inhibited by the island, and forcing the island north. The islands cliffs are what 200ft high?, the warmer waters passing through are going to find the shallowest way through at the north end of the island, eventually cutting a deep gouge on the underside, maybe? It does look like some of the ice directly north of the island is new which may indicate deeper warm waters surfacing and briefly clearing the ice.
Title: Re: Rift in Larsen C
Post by: johnm33 on May 18, 2018, 12:43:51 PM
The point of contact has broken.
(https://puu.sh/Aoqhd/66a94ced11.jpg)
from polarview (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201805/S1A_EW_GRDM_1SSH_20180518T001501_1DAB_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: johnm33 on May 26, 2018, 10:37:47 AM
Nice shot of the continued break-up
(https://puu.sh/AtdP2/c974b91cf1.jpg)
from polarview (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201805/S1B_EW_GRDM_1SDH_20180525T235806_2B57_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: crandles on July 09, 2018, 02:30:59 PM
The 'monster' iceberg: What happened next?

https://www.bbc.co.uk/news/science-environment-44745734
Title: Re: Rift in Larsen C
Post by: Susan Anderson on July 12, 2018, 08:36:15 PM
The 'monster' iceberg: What happened next?

https://www.bbc.co.uk/news/science-environment-44745734

Thanks. Good informative article. This slightly off topic for here, but anyway: Antarctica's troublesome 'hairdryer winds' https://www.bbc.co.uk/news/science-environment-39759329 (https://www.bbc.co.uk/news/science-environment-39759329)
Title: Re: Rift in Larsen C
Post by: Susan Anderson on July 19, 2018, 06:49:37 PM
Earth Observatory put out a new article about A68:

Iceberg A-68A has moved a relatively short distance in the year since it calved from the Larsen C Ice Shelf: Iceberg A-68A has moved a relatively short distance in the year since it calved from the Larsen C Ice Shelf/b] https://earthobservatory.nasa.gov/images/92420/one-year-adrift-but-not-far (https://earthobservatory.nasa.gov/images/92420/one-year-adrift-but-not-far)

(https://eoimages.gsfc.nasa.gov/images/imagerecords/92000/92420/a68_tir_2018182.jpg)

Quote
A-68A’s sluggishness is not surprising. When it calved, the berg was about the size of Delaware and weighed more than a trillion tons. Dense sea ice in the Weddell Sea has made it harder for currents, tides, and winds to move all of that mass. The iceberg has also become stuck at times when its north end encounters the shallow water near Bawden Ice Rise, an ice-covered rock outcrop.

Still, Iceberg A-68A has seen plenty of motion. Throughout the year, tide cycles have shuffled the berg back and forth like a driver trying to get out of a tight parallel-parking spot. Its north end has been repeatedly smashed against Bawden Ice Rise, fracturing and reshaping its northern edge. Also notice how the southeastern edge appears to have grown in area. This is not part of the original iceberg; it is fast ice that has come fastened to the edge of the berg as it shoves through the ice pack.

A-68A will continue this dance in moonlight, as the darkness of austral winter continues through early August. Thermal images ... an important tool for Adrian Luckman and the UK-based Project MIDAS, which has been monitoring the iceberg and how its calving affects the Larsen C Ice Shelf.

There’s no telling how much longer A-68A will stay “stuck” in the Weddell Sea. The smaller A-68B is a good example of the path taken by many Antarctic bergs, as they are carried by currents out of the Weddell and northward toward South Georgia and the South Sandwich Islands.
Title: Re: Rift in Larsen C
Post by: johnm33 on July 19, 2018, 11:19:58 PM
It's actually rotated somewhat this month and is now more broadside on to the tides, i guess once the ice clears it could be moved north more rapidly.  In one of the recent shots from polarview it was hard against the shelf.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FAZBLx%2F2498cec567.jpg&hash=70ebc9b54b872363c60b53455ac0067f)

polarview (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201807/S1A_EW_GRDM_1SSH_20180718T235851_E53B_S_1.8bit.jp2)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on August 20, 2018, 07:46:59 PM
Ice Island A-68A is currently kissing the Larsen C Shelf.  You can see the consequent conchoidal cracks (at least two) in the Larsen C around the point of contact.  Detail has two drawn lines approx. 1 cm to the right of two cracks.  It appears to me that some (or most) of the ice island's 'nose' will peel, too.  PolarView (https://www.polarview.aq/antarctic) image from today (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201808/S1B_EW_GRDM_1SDH_20180820T074522_06FF_S_1.8bit.jp2).

[Edit:  they were also touching on 2018-08-17 (https://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SDH_20180817T235811_732D_S_1.final.jpg).]
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on August 22, 2018, 09:00:17 PM
No longer 'rejoined' as of the 22nd (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201808/S1A_EW_GRDM_1SSH_20180822T001507_8990_S_1.8bit.jp2).  No evidence of the cracks noted two days ago.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on August 24, 2018, 06:51:59 PM
The new Larsen C cracks are more obvious in the PolarView (https://www.polarview.aq/antarctic) image from today (https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20180824T080207_660C_S_1.final.jpg).
Title: Re: Rift in Larsen C
Post by: oren on August 24, 2018, 06:59:39 PM
I keep worrying that the iceberg will somehow crash into the ice shelf and cause a massive shattering or cracking. It's probably for nothing, as I guess the momentum is not there and there is no way to acquire it. But I wouldn't rest easily if I had such a static bull at my china-shop doorstep.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on August 31, 2018, 05:19:42 PM
The A68-A Ice Island and the Larsen C met up again on the 29th (per PolarView  (https://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SDH_20180829T235811_138B_S_1.final.jpg)- not shown).  The screen shot of yesterday's image (https://www.polarview.aq/images/105_S1jpgfull/S1B_IW_GRDH_1SSH_20180830T080126_3B8A_S_1.final.jpg) (below) is much clearer.  Comparing the Larsen C coastline within the little yellow circle (about 3.5 km long) with the image posted on August 24 shows some 'contact caused erosion'.  The cracks in the Larsen C, however, appear unchanged to me.
Title: Re: Rift in Larsen C
Post by: Grygory on August 31, 2018, 09:04:44 PM
I think that in four days this iceberg will hit with more force
Title: Re: Rift in Larsen C
Post by: johnm33 on September 01, 2018, 12:20:50 AM
Gary look at the size (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201808/S1B_EW_GRDM_1SDH_20180829T235811_138B_S_1.8bit.jp2) of it! https://go.nasa.gov/2otEBC2 I don't recall if it's 200ft or mts high just now but there's a serious keel to shift.
Title: Re: Rift in Larsen C
Post by: gerontocrat on September 01, 2018, 02:01:07 AM
A-68 is (was) 5,800 km2 and 1 trillion tonnes giving an average thickness of about 170 metres.
It is a little bit smaller now.

Have some bits just broken off? Wordview images attached.


Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 01, 2018, 04:03:27 AM
I understand the 'small' ice island at the top of this image (from March (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg146413.html#msg146413)) is A68-B.  Only much smaller pieces have also broken off (but maybe totaling about the same area [volume] than A68-B).
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1175.0;attach=98483;image) (A68-B is approximately 20 km long.  See post #300 above for the major 'other' iceberg sloughing - which also shows A68-B.)
Title: Re: Rift in Larsen C
Post by: Darvince on September 03, 2018, 01:09:12 PM
Wow, it seems to have moved an extremely impressive distance for such an enormous iceberg since gerontocrat posted the last clear day on Worldview:

https://go.nasa.gov/2wM66L1
Title: Re: Rift in Larsen C
Post by: lurkalot on September 05, 2018, 01:34:52 PM
Seems to have turned 90 degrees in a very short time and could be starting to make its escape:

www.bbc.co.uk/news/science-environment-45421315
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 05, 2018, 06:03:09 PM
From that BBC article:
Quote
...
"Until recently, the iceberg was hemmed in by dense sea-ice in the east and shallow waters in the north.

"Now, a strong foehn wind blowing eastwards off the ice shelf in early September has pushed the southerly end of the iceberg out into the Weddell Gyre. This persistent clockwise drift of ocean waters and floating sea-ice flowing north past the Larsen Ice Shelf has rotated A-68 out into the Weddell Sea.

"Here, it is much more free to begin moving away and be carried further north into warmer waters."
...
Incidentially, today's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1A_IW_GRDH_1SSH_20180905T080208_ABEA_S_1.8bit.jp2) offers the best image of the battering-ram caused (or assisted) cracks in Larsen C. (enlargement on the original is clearly possible)  Yesterday's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1A_EW_GRDM_1SSH_20180904T235854_042D_S_1.8bit.jp2) of the entire ice island shows some ~year old fast ice having broken off.  Comparing with 19 July 2018 image above, A68-A has rotated about 50º in 6 weeks.
Title: Re: Rift in Larsen C
Post by: Grygory on September 05, 2018, 08:40:44 PM
A - 68A It rotates very fast. I think that it will soon break and divide into smaller icebergs.
Title: Re: Rift in Larsen C
Post by: jacksmith4tx on September 06, 2018, 06:30:23 PM
"No one is entirely sure where A68 might end up. But researchers are most excited about the home the iceberg is vacating."
https://futurism.com/a68-huge-iceberg-moving/
Quote
When A68 separated from the Antarctic ice shelf, it opened up a doorway into a pristine underwater ecosystem. Researchers predict this area of the ocean has remained undisturbed for some 120,000 years, but now that it’s exposed to sunlight and open-air conditions, there’s no telling what kinds of interesting changes could take place.

“You’ll have sunlight, you’ll have phytoplankton, and you’ll begin to get zooplankton and fish in there pretty quickly,” marine ecosystem researcher Phil Trathan told Live Science in October. “So, it will be sort of a chain reaction — as you get productivity happening then you’ll get more species coming in, and so there will be quite significant changes over relatively short time scales.”
Title: Re: Rift in Larsen C
Post by: maga on September 07, 2018, 12:20:40 PM
Nice animation from Adrian Luckman:
https://adrianluckman.wordpress.com/2018/09/05/iceberg-a68-escapes-into-the-weddell-gyre/ (https://adrianluckman.wordpress.com/2018/09/05/iceberg-a68-escapes-into-the-weddell-gyre/)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 07, 2018, 08:40:39 PM
A68-A in perspective:
Title: Re: Rift in Larsen C
Post by: Stephan on September 07, 2018, 09:38:10 PM
I think it is useful to show this little 35 pixel something in the bigger context.
When Larsen C was about to calve I quickly calculated this effect on the ice extent around Antarctica. Its size (although it is a really big iceberg) is much too small to be presented in the two-digit daily JAXA figures.
Title: Re: Rift in Larsen C
Post by: charles_oil on September 07, 2018, 09:45:47 PM
Yes = please show as a larger image - i cant see anything even when downloaded / zoomed - thanks !
Title: Re: Rift in Larsen C
Post by: gerontocrat on September 08, 2018, 01:58:03 AM
I think it is useful to show this little 35 pixel something in the bigger context.
When Larsen C was about to calve I quickly calculated this effect on the ice extent around Antarctica. Its size (although it is a really big iceberg) is much too small to be presented in the two-digit daily JAXA figures.
Antarctic Sea Ice is, they say, generally 1 to 2 metres thick. The Berg is 5,800 km2 with an average thickness of about 170 metres. That is equivalent to 650,000 km2 of 1.5 metre thick ice.

It is a lot more than 35 pixels, but they are stacked up vertically.
Title: Re: Rift in Larsen C
Post by: johnm33 on September 09, 2018, 04:45:22 PM
Nice animation from Adrian Luckman:
https://adrianluckman.wordpress.com/2018/09/05/iceberg-a68-escapes-into-the-weddell-gyre/ (https://adrianluckman.wordpress.com/2018/09/05/iceberg-a68-escapes-into-the-weddell-gyre/)
Agreed, hope I'm the only one who missed the ice getting stuck on the arc of Bawden rise, it also shows a link between movement away from the shelf and sudden movement north. Now all set to rotate around the rise.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 11, 2018, 03:51:44 PM
A68-A is on the move.  Two-framed GIF (from PolarView (https://www.polarview.aq/antarctic)) goes from "20180910T235812 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_EW_GRDM_1SDH_20180910T235812_1723_S_1.8bit.jp2)" (nearly midnight at the end of September 10) to "20180911T080126 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_IW_GRDH_1SSH_20180911T080126_7D64_S_1.8bit.jp2)" (8 am on September 11).  The Sept. 11 image shows the gap in the ice on the ice island's southern side.  Looks to be about 5 km in 8 hours. Pretty nimble, if you ask me!  The winds are blowing, per Windy.com (https://www.windy.com/?-69.006,-57.854,5)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 13, 2018, 08:22:15 PM
I find it interesting that A68-A has move a little northward since the 11th, but the 'ice debris' south of it has mostly 'caught up' (Polarview 20180913T074523 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_EW_GRDM_1SDH_20180913T074523_BC0C_S_1.8bit.jp2)), so that icebergs are approximately the same distance from the ice island as they were on the 10th.  The ice-free (or apparently ice-free) area south of A68-A on the 11th has 'disappeared'.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 17, 2018, 05:53:48 PM
...
Comparing with 19 July 2018 image above, A68-A has rotated about 50º in 6 weeks.
An additional 10º rotation, per yesterday's PolarView image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1A_EW_GRDM_1SSH_20180916T235854_A463_S_1.8bit.jp2), so 60º in 8 weeks.
Title: Re: Rift in Larsen C
Post by: FrostKing70 on September 17, 2018, 08:02:18 PM
Is it grounded on the bottom left?   Seems to be the point it is rotating about.

Any idea what it will take to lit off and move with the current / wind?
Title: Re: Rift in Larsen C
Post by: johnm33 on September 17, 2018, 10:32:52 PM
Grounded?
Link (https://adrianluckman.wordpress.com/2018/09/05/iceberg-a68-escapes-into-the-weddell-gyre/) from Maga,320 above has animation. Looks like the ridge extends underwater.

(https://puu.sh/BwCwA/1b6958ad31.jpg)
from here (http://www.maps.arcgis.com/apps/View/index.html?appid=86a9728459aa4d18b4444b74d330832e/)
My guess is the tides will rotate it around the grounding point, we're at first quarter[moon] so the tides will begin to pick up peaking again in a week or so maybe another 100 in two weeks time[?].
Title: Re: Rift in Larsen C
Post by: FrostKing70 on September 18, 2018, 03:15:27 PM
Thank you, "grounded" may not be the correct term, but it obviously conveyed the intent!  Yes, I missed the comment above about the ridge, too!
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 18, 2018, 10:32:30 PM
A-68A is from the orange shaped area and is now in the yellow shaped area.
[forgive my poor drawing skills]
Title: Re: Rift in Larsen C
Post by: gerontocrat on September 18, 2018, 11:16:36 PM
A-68A is from the orange shaped area and is now in the yellow shaped area.
[forgive my poor drawing skills]
OK, I am dumb, but what on earth is that feature all down the left of the image ?
Title: Re: Rift in Larsen C
Post by: lurkalot on September 19, 2018, 01:11:17 AM
"OK, I am dumb, but what on earth is that feature all down the left of the image ?"

I had assumed the mountain peaks of the Antarctic Peninsula but may be completely wrong.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 19, 2018, 04:32:53 AM
From Johnm33's link (http://www.maps.arcgis.com/apps/View/index.html?appid=86a9728459aa4d18b4444b74d330832e/), the ridge on the left in my previous post is in the lower center below.  The Peninsula's tip is on the left.  Looks like a rocky ridge to me, but 'unrelated' to the "Rise" near where A68-A currently resides.  I think it is sure possible that the ice island is at least intermittently grounded in this current locale.
Title: Re: Rift in Larsen C
Post by: litesong on September 19, 2018, 06:19:42 AM

Time to lock this thread....:)?
No. Where will it go? Will it break up? Who owns it?
After 14 months, maybe we'll get some answers now.
Title: Re: Rift in Larsen C
Post by: johnm33 on September 19, 2018, 11:08:53 AM
Thanks Tor, there just happens to be a polarview (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_EW_GRDM_1SDH_20180918T075244_68BC_S_1.8bit.jp2) that illustrates your point.
 
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FBxsVA%2Fc88077e06d.jpg&hash=6f86dc6339e3028b391f9ca0c5547255)

It looks like a small island chain will emerge from the ice thereabouts.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 20, 2018, 07:47:07 PM
...
Incidentially, today's PolarView (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1A_IW_GRDH_1SSH_20180905T080208_ABEA_S_1.8bit.jp2) offers the best image of the battering-ram caused (or assisted) cracks in Larsen C. 
...
Looking at an 'old' Project MIDAS (http://www.projectmidas.org/feed.xml) image, I see what I called "battering-ram caused (or assisted) cracks" were in place in July 2017.  I'm now not certain the contact between shelf and ice island did anything to the cracks.
Title: Re: Rift in Larsen C
Post by: maga on September 22, 2018, 11:53:40 AM
Well, we can look at the first Sentinel pictures of the year to try to answer this question. It looks like not much happened. The cracks in that opened when the berg was still attached are still there and the old cracks to the northeast didn't really open up. But one can see three small new cracks along the innermost old one... The effects of the repeated collisions between the berg and the shelf seem to be mostly limited to the (shelf) ice edge where ice was piled up.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2F&hash=35d7d5d7526c9897dfb55501e320295a)
Title: Re: Rift in Larsen C
Post by: FredBear on September 22, 2018, 03:13:19 PM
Is it grounded on the bottom left?   Seems to be the point it is rotating about.

Any idea what it will take to lit off and move with the current / wind?
The southern end of A68-A seems to have moved northeast, away from the coast, since 10/09/18, while the northern end has continued to rotate anti-clockwise, so the iceberg now looks to be free.

The questions are  "Does it sweep all before it?" or "Does the seaice back up behind it?" and "Will it continue rotating?" .
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 22, 2018, 07:43:54 PM
...
An additional 10º rotation, per yesterday's PolarView image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1A_EW_GRDM_1SSH_20180916T235854_A463_S_1.8bit.jp2), so 60º in 8 weeks.
Yesterday's Polar View (Sept. 21) image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_EW_GRDM_1SDH_20180921T081715_822C_S_1.8bit.jp2) shows the ice island about 20 km away from the shelf (at their closest), while it was about 15 km away on September 16th.  'Doesn't act grounded now.
Title: Re: Rift in Larsen C
Post by: johnm33 on September 22, 2018, 08:37:54 PM
Looks like the ice that's broken off is grounded, and that the big one will have to pivot around the upper point once it's finished pivoting on the lower point.
(https://puu.sh/Bze4C/b85aa16572.jpg)
Title: Re: Rift in Larsen C
Post by: oren on September 22, 2018, 08:39:47 PM
Thanks to all posters regularly updating this thread.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 22, 2018, 08:57:20 PM
I cannot put the Sept. 16 and 21 images together, but here they are, showing no pivot points.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on September 25, 2018, 09:47:12 PM
Further to my previous post, here is a GIF showing the above referenced Sept. 16 image with this July 23 image (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201809/S1B_IW_GRDH_1SSH_20180923T080127_C339_S_1.8bit.jp2) showing no pivot points - A68-A is currently moving away from the Larsen C Ice Shelf (southeastward, about 14 km in 7 days).  From this view of just this one end, it looks like the whole ice island is continuing to rotate counter-clockwise (at least a little).
Title: Re: Rift in Larsen C
Post by: Phil42 on September 28, 2018, 01:18:52 PM
The iceberg and all the surrounding ice have drifted quite a distance southward in the last 2 days. I would estimate the distance ~5km.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on October 19, 2018, 07:13:28 PM
A68-A has drifted southwestward this past month, with a little more (5º?) counter-clockwise rotation. [PolarView (https://www.polarview.aq/antarctic) image from here (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201810/S1B_IW_GRDH_1SSH_20181017T080127_84AD_S_1.8bit.jp2)]  The ice island has now rotated about 95º from when it first separated from the Larsen C Shelf (and, of course, the pivot-end has relocated northwards).
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on October 26, 2018, 07:47:59 PM
Rifts in the Larsen C Ice Shelf are evident in this 2018-10-20 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-67.16336023061045&lng=-60.928287506103516&zoom=12&preset=92_NDWI&layers=B01,B02,B03&maxcc=100&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-10-20&atmFilter=&showDates=true) Sentinel-hub Playground image.  The 'about-to-separate' iceberg looked about the same on 2018-02-28 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-67.15243164298412&lng=-60.91215133666992&zoom=12&preset=92_NDWI&layers=B01,B02,B03&maxcc=100&gain=1.0&gamma=1.0&time=2015-01-01%7C2018-02-28&atmFilter=ATMCOR&showDates=true), and the 'propagating crack' looked even longer back then (but is clearer in some ways now).
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on November 08, 2018, 07:20:04 PM
The largest iceberg near A68-A is looking for some action (OR … has moved a lot since October - see above (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg177652.html#msg177652)).  Chisel and hammer-stone   OR   Nut-cracker?  [PolarView (https://www.polarview.aq/antarctic) image link (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201811/S1B_EW_GRDM_1SDH_20181108T081715_C7D7_S_1.8bit.jp2)]
Title: Re: Rift in Larsen C
Post by: Shared Humanity on November 08, 2018, 08:08:44 PM
What are all of the gray spots on the ice berg? Those can't be melt ponds.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on November 08, 2018, 09:29:59 PM
Definitely not melt ponds!  It is very cold (from a human perspective) there, I'm sure.  PolarView doesn't create visual-light-like images, but uses other parts of the electro-magnetic spectrums. (These details are not my forte.)  I like these because they "see" through clouds and night's (and winter's) darkness.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on November 21, 2018, 05:49:47 PM
The Ice Island A68-A has rotated about 115º in 6 months, but the pivot end hasn't moved diddlysquat. 

The largest iceberg in the area (current, lower, image) has, in the meantime, moved about 125 km northwards, squeezing through what I'll call an ice-strait.  (1st image from a May 18 post by johnm33 (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg154891.html#msg154891) [conveniently at the top of this thread's page 7]; 2nd image from PolarView (https://www.polarview.aq/antarctic) on November 20 (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201811/S1B_EW_GRDM_1SDH_20181120T081715_5644_S_1.8bit.jp2).) 

I'm going to postulate, now, that intermittent grounding keeps A68-A where it is; no point is clearly 'actually' stuck in one place for any length of time.  A GIF covering multiple images might show if any spot does get stuck (becoming a fixed (if temporary) pivot point).
Title: Re: Rift in Larsen C
Post by: FredBear on November 30, 2018, 09:33:37 PM
The Ice Island A68-A continues to inch(!?) northwards over the last 10 days, with the narrower 'tail' getting further from the coastal ice shelf.

Perhaps more importantly for the region, there is now a blue tint to the remains of the Larsen A & B shelves and also the ice further off-shore (From arctic.io 2018-11-30). Caused by adiabatic winds from the peninsula melting snow from the surface (+insolation)?
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on December 17, 2018, 06:11:58 PM
A-68A has move about 20 km northward this past month.  I'm guessing it will escape the shoals near Bawden Ice Rise soon (if it hasn't already).
Title: Re: Rift in Larsen C
Post by: litesong on December 17, 2018, 06:42:31 PM
A-68A has move about 20 km northward this past month.  I'm guessing it will escape the shoals near Bawden Ice Rise soon (if it hasn't already).
........ as the yearly Antarctic sea ice decrease loses its ability to hold onto A-68A.
Title: Re: Rift in Larsen C
Post by: FredBear on December 18, 2018, 01:49:40 PM
So far the sea ice has been building to the south and east of A68A (which seems to be blocking the gyre) , but dispersing to the NW.
On 13/12/2018 A68B had drifted in line with the point of the peninsular between Larsens A & B, just SE of a large sea ice floe. Also appears about level with the north of A68A.

The iceberg B15AA has been drifting across the Weddell Sea, but it is moving more slowly than the surrounding sea ice (which is now breaking up quite rapidly.). This demonstrates that icebergs can impede the movement of the  thinner sea ice.
Title: Re: Rift in Larsen C
Post by: FrostKing70 on December 18, 2018, 04:35:14 PM
I wonder if it will break into at least 3 chunks soon, especially if the bottom end stays grounded....
Title: Re: Rift in Larsen C
Post by: johnm33 on December 18, 2018, 06:29:06 PM
Wouldn't be surprised if it 1/2 rotated again before breaking.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on December 18, 2018, 10:56:05 PM
From an enlargement of the left side of A-68A (PolarView (https://www.polarview.aq/antarctic)) dated 2018-12-17@23:41:58 (https://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SDH_20181217T234158_0F83_S_1.final.jpg) (just over 18 minutes before midnight), I don't see current support for the cracks propagating in the suggested manner. Am I missing something?  But for sure, we'll see one way or another.  I do see the possibility of a ~2 x ~10 km scab braking off in this area. (sea ice on the left; A-68A on the right and top)
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on December 27, 2018, 04:41:28 PM
The southern end of Bawden Ice Rise has a rim of open water now, per this Sentinel-hub image from December 19 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-66.88794891180316&lng=-60.2299690246582&zoom=13&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=97&gain=1.0&gamma=1.0&time=2018-06-01%7C2018-12-19&atmFilter=&showDates=false). The first image (of mp4) is the NDWI rendering of bands (to identify the setting), and the second image is the 'Natural Color' rendering (exact same area).
Title: Re: Rift in Larsen C
Post by: Tealight on January 21, 2019, 09:51:18 PM
A nice view of A-68A today showing the rifts in a lot more detail than usual. A small part even broke off since the last picture posted here in December.
Title: Re: Rift in Larsen C
Post by: IceConcerned on February 04, 2019, 02:59:41 PM
Apparently new cracks appeared recently on the shelf, a big chunk seems ready to get loose.
Title: Re: Rift in Larsen C
Post by: Shared Humanity on February 04, 2019, 05:43:26 PM
Those fractures are getting dangerously close to the Bawden Ice Rise. Would hate to see the ice shelf lose this pinning point.
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 21, 2019, 02:16:23 AM
IceConcerned,
You will notice the cracks are little changed from one and two years ago, see here (https://forum.arctic-sea-ice.net/index.php/topic,1175.msg173776.html#msg173776), for example.  Yes, they look ready to let loose!
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on February 25, 2019, 05:06:49 PM
I'll probably start posting A68A images in the Antarctic Icebergs (https://forum.arctic-sea-ice.net/index.php/topic,2245.msg141174.html#msg141174) thread (after this one).  I estimate (with the assistance of a small protractor) the ice island has rotated 175º since forming.  That's quite a bite where it is (was?) grounded.  PolarView (https://www.polarview.aq/antarctic) image from yesterday (http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201902/S1B_EW_GRDM_1SDH_20190224T001423_4DFD_S_1.8bit.jp2).
Title: Re: Rift in Larsen C
Post by: FredBear on February 25, 2019, 11:26:25 PM
If A68A drifts into the bay it could replace the old Larsen B ice shelf!?? - no, the ice in the shelf area still seems to flush out.
This berg hasn't moved much this summer (but more than last year) - maybe it will move more in the winter.
The sea ice/icebergs in the Weddell Sea have been concentrated on the western & southern sides (apart from the lee of A68A) this year, but their location is very variable from year to year. Rather less total ice than recent years?
Title: Re: Rift in Larsen C
Post by: sqwazw on July 14, 2019, 07:14:41 AM
BBC has a nice animation of the past 6 months, it has moved north quite a lot in the interim:

https://www.bbc.com/news/science-environment-48920168 (http://"A68: World's biggest iceberg is on the move")
Title: Re: Rift in Larsen C
Post by: bligh8 on July 21, 2019, 05:37:04 PM
Turbulence Observations beneath Larsen C Ice Shelf, Antarctica

Peter E.D. Davis  Keith W. Nicholls
First published: 16 July 2019 https://doi.org/10.1029/2019JC015164 .. paywall

Abstract

Increased ocean‐driven basal melting beneath Antarctic ice shelves causes grounded ice to flow into the ocean at an accelerated rate, with consequences for global sea level. The turbulent transfer of heat through the ice shelf‐ocean boundary layer is critical in setting the basal melt rate, yet the processes controlling this transfer are poorly understood and inadequately represented in global climate models. This creates large uncertainties in predictions of future sea‐level rise. Using a hot‐water drilled access hole, two turbulence instrument clusters (TICs) were deployed 2.5 and 13.5 meters beneath Larsen C Ice Shelf in December 2011. Both instruments returned a year‐long record of turbulent velocity fluctuations, providing a unique opportunity to explore the turbulent processes within the ice shelf‐ocean boundary layer. Although the scaling between the turbulent kinetic energy (TKE) dissipation rate and mean flow speed varies with distance from the ice shelf base, at both TICs the TKE dissipation rate is balanced entirely by the rate of shear production. The freshwater released by basal melting plays no role in the TKE balance. When the upper TIC is within the log‐layer, we derive an under‐ice drag coefficient of 0.0022 and a roughness length of 0.44 mm, indicating that the ice base is smooth. Finally, we demonstrate that although the canonical three‐equation melt rate parameterization can accurately predict the melt rate for this example of smooth ice underlain by a cold, tidally‐forced boundary layer, the law of the wall assumption employed by the parameterization does not hold at low flow speeds.

bligh
Title: Re: Rift in Larsen C
Post by: DrTskoul on July 21, 2019, 08:31:11 PM
Cool article!!
Title: Re: Rift in Larsen C
Post by: Tor Bejnar on October 10, 2019, 08:05:31 PM
A look at part of Larsen C today... GIF from Sentinel-hub Playground from 2019-10-10 and 2018-12-10 (The October 2018 image just wasn't as clear as the December one.)  Area (annotated) screen print from 2019-10-10 (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-67.17102061822038&lng=-61.431427001953125&zoom=9&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=100&gain=0.2&gamma=0.5&time=2019-04-01%7C2019-10-10&atmFilter=&showDates=false).

This part of the Larsen C shelf has moved ~0.6 km in one year (October to October).  The most major cracks appear unchanged, but minor cracks appear to be more developed.  I think it's cute that the shore-bound iceberg broke in half at some point this past year.