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Author Topic: Larsen Ice Shelves A, B, D, E, F, G  (Read 13140 times)

FredBear

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #50 on: January 02, 2023, 04:15:05 PM »
Re: Reply 48, Larsen B embayment:-
That "spray" of ice coming from Vaughan Bay (below the Pederson Nunatak) has been running for more than six weeks and seems to be encouraging a clockwise flow round the old Larsen B embayment. I don't know what the mechanism has been to produce all the fine ice but the surface in Vaughan Bay looks to have been retreating?
The following image from Worldview also includes a smaller "spray" from a similar position from the old Larsen A embayment and the almost stationary Weddell pack ice beyond, with icebergs A76B & C.
« Last Edit: January 02, 2023, 11:21:47 PM by FredBear »

FredBear

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #51 on: January 17, 2023, 08:10:10 PM »
The Pederson Nunatak area (between the sites of Larsens A & B) has more discolourations leading down from the peaks(?) now - could this be loss of snow from old volcanic debris?
The sprays of bluish ice from a few glaciers on the edges of both of those Larsen embayments have still been occurring from time to time recently. Apart from that ice the amount of ice in the area seems to be historically low, although the ice in the Weddell Sea may not have retreated east away from the Antarctic Peninsular so far this year?
« Last Edit: January 17, 2023, 08:19:41 PM by FredBear »

paolo

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #52 on: February 05, 2023, 03:31:49 PM »
It's been a while since I should have told you about the DBE (Dinsmoor / Bombardier / Edgeworth) and HGE (Hektoria / Green / Evans) glaciers that have continued to calve!
I am therefore posting for each of the two groups:

> An animation with one image per quarter from Q1 2019 to Q1 2023.
Notes on these animations:
>> For the last image, that of Q1 2023, I did not take the first image of the quarter, as in the other cases, but that of 30/01
>> Between the images of Q1 2020 and Q2 2020 there is a shift, which indicates that a modification of the procedures took place: modifications of the algorithms and/or of the elevation information and/or of the image taking by the satellite (for example the area covered by an image is not the same any more); if I remember well baking had fallen once on this problem during the generation of an animation)
>> The images of the first quarters are very difficult to process because of the presence of water on the surface. I have lightened these images (so that the glaciers look more or less the same; this is the only operation I allow myself on the images), but there is no way to make the differences between the glacier and the ice melange more obvious 
I will make a post later on these lines and the history, but in the meantime I would like to point out that :
>> In the analysis of the animation, it should be taken into account that the front lines displayed are not aligned with the satellite images (the offset seems uniform)
>> Still regarding the front lines: no updates in this sector for versions 7.4 and 7.6 => the corresponding lines do not appear, they are respectively overwritten by the lines of versions 7.3 and 7.5. For the colour codes see my post of yesterday in the PIG thread.

> An animation to locate it using the images of the "Air Operations Planning Maps" (zoom in on this map) and "Coastal-Change and Glaciological Maps".

I start with the two animations related to the DBE and in a following post the two related to the HGE

Click to animate and click again to enlarge completely

paolo

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #53 on: February 05, 2023, 03:41:37 PM »
Continued with the two HGE animations

oren

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #54 on: February 05, 2023, 03:59:26 PM »
Thanks for these updates, paolo.
The retreats are extremely fast. It seems as soon as a calving occurs in a confluence - so as to create a separation between two joining glaciers - and the buttressing between them disappears, there is an almost immediate crumbling of the glaciers behind the junction.

FredBear

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #55 on: February 05, 2023, 04:32:49 PM »
Re: Glaciers DBE and HGE.
The way that those rivers of ice have impinged on each other means that they must have backed up badly. Now the glaciers have retreated and separated the ice can flow so much freely - explaining why all the fine ice has been flooding into the old Larsen A & B embayments in the last couple of melt seasons.
I would expect that measurements would show large decreases in height and increases in flow rate of those glaciers    .    .    .
« Last Edit: February 05, 2023, 04:39:23 PM by FredBear »

paolo

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #56 on: February 05, 2023, 10:08:40 PM »
DBE
You will find attached :
> an animation of more zoomed S1 images (2000x3000 px) and with more frequent images (12 days instead of one quarter) from 01/12/2022 to 30/01/2023 (6 images)
> an animation (still 2000x3000 px) composed with the images :
>> S1 from 06/01/2023
>> S2 from 13/01/2023
>> S1 of 18/01/2023,
The S2 image allows a better interpretation of the S1 images

The retreat occurs between 25/12/2022 and 18/01/2023 and is a progressive retreat by successive calving as shown in the S1 images of 25/12/2022, 06/01/2023, 18/01/2023 and the S2 image of 13/01/2023.
The total retreat of Edgeworth Glacier is about 3 km

Click to animate and click again to enlarge completely

paolo

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #57 on: February 06, 2023, 02:04:17 AM »
HGE
You will find attached:
> an animation of more zoomed (in relation to the previous HGE animation) S1 images (2000x1600 px) and with more frequent images (24 days instead of one quarter). It covers the period from 02/10/2022 to 30/01/2023 (6 images). (Note
> an animation (still 2000x1600 px) composed with the images :
>> S2 from 13/01/2023 (very nice image)
>> S1 of 18/01/2023,

Note: the period shown for HGE is double that used for DBE, as in this case calving started in early November
Warning: as always, the global images for HGE are less zoomed in than those for DBE, as the calving area for HGE is much larger than that for DBE

The Hektoria Glacier has retreated more than 8 km, on average Green has retreated 2 km and Evans has retreated about 4 km

Click to animate and click again to enlarge completely

Often Distant

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #58 on: August 16, 2023, 02:51:03 AM »
Comparative recent capture.
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Often Distant

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #59 on: October 26, 2023, 11:46:12 PM »
The first gif spans recent months and is a close up high gamma visual of the dividing ice at the point of Gipps Ice Rise between Larsen C north and Larsen D south. Cracks encroach as days wear on. There may be some coming action. Potential small calvings seem to be approaching at north, and a long coming large calving may finally eventuate at the south. Ice west of Gipps may continue to remain largely constrained for years yet regardless. Yet it may not.

The second gif provides insights into potential shapes of future icebergs yet to break away from the vicinity. Weather conditions during summers reveal underlying ice dynamics within the usual white on white.

The third gif is rather rough, of northern Larsen D south of Gipps, from 2014. The first couple of images don't align with the rest, though are included anyway due to the lack of existing years.

The fourth gif is slightly further south Larsen D and spans just 4 years, with 4 images. An incredibly quick flowing glacier is smashing through the old shelf ice from behind at Smith Inlet. A cork was popped some years earlier. An omen.
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Often Distant

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #60 on: October 27, 2023, 12:17:51 AM »
A couple of long experimental animations of the northern sector of Larsen C spanning from 2014 to 2023, focusing on weather conditions during melting seasons that may display physical characteristics of the ice and shifting dynamics. The images don't align perfectly though it is quite consistent. Animations are split into two to gather similar satellite trajectory paths together. No sign of large imminent collapse at this end despite the situation south at Gipps Ice Rise. Hard to tell.

This is not one of the most worrisome of Antarctic ice shelves at the moment. Larsen C may be quite strong. Larsen D may soon be gone. I don't know.
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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #61 on: October 30, 2023, 06:37:42 AM »
Larsen A. Firstly 5 years, secondly 1 year. Click. Clock. Developing collapse. The weather may change quite a lot when it makes way for the winds. Glacial debris in the sea gives it something to aspire to. Perhaps if Larsen A breaks apart, much of it could become grounded and fasted in with multiple years of strengthening fast sea ice that it reforms as a shelf with the increasing flow from the glaciers. Maybe it doesn't really matter. Seas will rise fast due to many other more dramatic locations on the continent. It is similar to there being approaching comets.
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John_the_Younger

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #62 on: October 30, 2023, 07:37:25 AM »
Quote
Maybe it doesn't really matter. Seas will rise fast due to many other more dramatic locations on the continent.
As I understand it (and someone showed some maps a few months ago), sea level around Greenland will go down, basically, as Greenland's ice cap melts (until it's pretty much all melted), and sea level around Antarctica will go down as Antarctica's ice cap melts.  All due to the loss of gravity pull of the melting ice.  (Other sea level rise is due to expanding [warming] ocean water, and some is due to local conditions like sinking land [e.g., Louisiana's delta] and changing ocean currents.)

Therefore, I suspect that where icebergs ground around Antarctica will continue to be places icebergs will ground in the foreseeable future.  How much this will help ice shelves, I have no opinion.

FredBear

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #63 on: October 31, 2023, 01:11:09 AM »
For the past couple of years the areas formerly occupied by the Larsen A & B ice shelves have lost their covering of fast ice - in 2022 the ice was breaking up by September 1 (Worldview).
Sprays of ice have been coming from local glaciers and occasionally icebergs have traveled round the bays and may have impeded the complete clearance of ice from these areas.
Last summer the Weddell Sea pack ice was particularly slow moving along the eastern edge of the Antarctic Peninsular so icebergs A76B & A76C have been hanging around the area for the past year.
This may have had the knock-on effect of stabilising the fast ice so far this season but this might change soon as the main pack ice is beginning to move. It is not clear whether these particular icebergs are grounding or it is that the pack in the area is just slow moving but all other icebergs have eventually moved away.
Further to the east things are moving more rapidly, A80A has just split (giving rise to A80D) and A23A has been sailing north clear of the area.
« Last Edit: October 31, 2023, 01:20:57 AM by FredBear »

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #64 on: November 23, 2023, 08:14:51 AM »
A deeper delve.
Larsen remnants between A and B, unofficially referred to as the Seal Nunataks Ice Shelf, could calve any time without being very surprising. It is dependent on the ocean, surrounding ice and the weather as to when. It continues loosening grip regardless of when.

I attach a couple of long play Sentinel 1 IW HH animations as rough explorations. Ice flowing from the peninsula comes down from mountain slopes rather than through deep trough. On the western half of the images, most ice flow veers to fall southward to space vacated from Larsen B in the early 00's. On the Eastern half northward past the peaks, most flow falls into the bay vacated by Larsen A in the mid 90's. Rogosh Glacier used to flow across more volume at higher elevation eastward into the divide. Much of what flows down into the Larsen A remnant, is melt or rain water draining to the ocean beneath. The recent inner crack extensions appear to have been caused by thinning ice at the Rogosh tributary point by Cape Fairweather, increasing in velocity dropping with gravity at reduced feed less held back by Pedersen Nunatak, which will maybe need a name change to island. Since the tipping point, shockwave ripples still appear to flow through the shelf further expanding cracks. The once compacted thick ice has reduced in elevation in years since most compressing force detached and floated away. Ice that measured 200m thick quarter of a century ago could be much more than 50m thinner today.

The altering angles of sunlight can cause illusion of movement where they can be seen as portraying differing perspectives across the 3 dimensional space highlighting differing features at differing elevations. Multiple plays provide more information as many details are interesting to follow through time lapse. The first animation spans 2014 to present, and the second begins at 2016 from differing satellite orbital track. Images are mainly gathered over melt seasons when visuals are most vivid.  Gamma is not consistent. The third gif reduces the images down to 10 for a simpler quick display of activity over recent years.

Some shelf ice may remain for years yet among the ancient front east nunatak cluster to Robertson Island. It may also probably soon shatter and float away. It isn't what it used to be. There used to be one Larsen Ice Shelf renowned for its floating area size before it broke into all notes in the key of C major. It more than half melted away, mostly as icebergs in distant warmer waters. Larsen collapse hardly impacts sea level as far as most can see. It's millimeters.

Of interest will be whether new weather regime could set in with wider ocean current and wind channels unsettling freeze. Waters may attract large icebergs that could get grounded for decades, which would be less interesting than what is happening to where the icebergs originate from. Less studied ice shelves and glacial tongues of greater consequence clearing from around the continental mainland bring bigger drama due to their larger ice catchment constrainment. Many a fragile precipice. Though soon due giant calvings of very old ice, much of Larsen may well outlast the precarious Brunt across the Weddle. Larsen collapses are not much of an indication of what will eventuate when more massive Antarctic ice shelves disappear. Maybe microcosm to thousandfold or millionfold. Seas are set to rise more rapidly through coming seasons as larger ice unsets. They rise where most people are settled. They rise where wars are fought over land that will be sea floor. They may rise as tsunamis upon where most nuclear technology is situated. Electronics and communications may go inaccessible, though largely cause of it. Larsen is lightweight.
« Last Edit: November 23, 2023, 08:39:50 AM by Often Distant »
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gerontocrat

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Re: Larsen Ice Shelves A, B, D, E, F, G
« Reply #65 on: January 10, 2024, 03:56:42 PM »
This is about the sea ice that forms where Larsen A & B iceshelves used to be.

Given that the Weddell sea ice melting season has been so slow, it is interesting that such a big clearout of sea ice has happened.

It comes from NASA's Earth Observatory website

https://earthobservatory.nasa.gov/images/152280/sea-ice-blues-off-the-antarctic-peninsula
Quote
Sea Ice Blues off the Antarctic Peninsula

With the arrival of summer in the southern hemisphere, sea ice that clung to the Antarctic Peninsula through austral winter 2023 is now letting go.

The seasonal transformation is visible in this pair of images, acquired by the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA’s Aqua satellite on December 19, 2023 (top), and January 1, 2024 (bottom). The images are centered on the Larsen A and B embayments on the peninsula’s eastern side.

The embayments are named for the ice shelves that once floated here as part of the greater Larsen Ice Shelf. In the past three decades, two large sections of the ice shelf (Larsen A and B) have collapsed: Larsen A in 1995 and Larsen B in 2002. Larsen C, south of this image, still hangs on but its “coastline” changed dramatically in 2017 when it spawned a massive iceberg.

Instead of ice shelves—the floating extension of glacial ice from land—the Larsen A and B embayments now often contain seasonal sea ice—frozen seawater that floats on the ocean surface, often covered with snow. Much of this sea ice, known as “fast ice,” clings to coastlines and ice shelves. Fast ice can help resist against the seaward flow of glaciers on land and slow their contribution to sea level rise, though fast ice is less effective at this buffering effect compared to a much thicker ice shelf.

Sea ice that grows over the course of a single winter, also known as first-year sea ice, often breaks up and clears out of the Larsen A embayment in summer. (Note that there are exceptions, especially between 2011 and 2021.) This season, by December 19, the transition became noticeable when meltwater (blue) pooled atop parts of the fast ice. According to the National Snow and Ice Data Center, melt-related features did not extend onto the nearby ice sheet or ice shelf (as of December 15).

By January 1, the ice had fractured and drifted freely into the Weddell Sea. “The Prince Gustav Channel, Larsen Inlet, and Larsen A are all now clear of first-year sea ice, and the Larsen B embayment is getting chipped away at the front,” said Christopher Shuman, a University of Maryland, Baltimore County, glaciologist based at NASA’s Goddard Space Flight Center.

It remains to be seen if, and when, the remaining sea ice in the Larsen B embayment will clear out this summer. Sea ice in the embayment broke apart over the span of a few days in January 2022 after persisting there for more than a decade. It cleared out again in summer 2023.

NASA Earth Observatory images by Wanmei Liang, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Kathryn Hansen.
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