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paolo

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Larsen D
« on: November 12, 2020, 04:38:28 PM »
BIG calving at Larsen D !

Large image, click to animate

gerontocrat

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Re: Larsen D
« Reply #1 on: November 12, 2020, 05:13:17 PM »
BIG calving at Larsen D !
Scale? please pretty please
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paolo

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Re: Larsen D
« Reply #2 on: November 12, 2020, 05:30:45 PM »
The scale was displayed at the bottom left, next to the date, in the second image (post-calving image: 12/11). ;)

Stephan

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Re: Larsen D
« Reply #3 on: November 12, 2020, 07:13:30 PM »
The scale is only visible when the picture is zoomed.

It is a real massive calving event. Did anyone of us have it on his agenda?

Thank you paolo for sharing this information with us.
It is too late just to be concerned about Climate Change

paolo

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Re: Larsen D
« Reply #4 on: November 12, 2020, 07:56:28 PM »
Here is the history of the front lines of 06/11 and 12/11. I have differentiated a part that probably is not part of the ice shelf and is simply very thick sea ice (multi-year). I added the estimate of the area that calved.

click to enlarge

interstitial

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Re: Larsen D
« Reply #5 on: November 12, 2020, 08:39:44 PM »
Here is the history of the front lines of 06/11 and 12/11. I have differentiated a part that probably is not part of the ice shelf and is simply very thick sea ice (multi-year). I added the estimate of the area that calved.

click to enlarge
all of the grey is not ice shelf but multiyear sea ice but thanks for the update.

paolo

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Re: Larsen D
« Reply #6 on: November 12, 2020, 10:52:11 PM »
Interstitial,
Thank you, I had doubts myself, but it must be very thick, and almost simulates the appearance of an ice platform.
So I applied a very strict criterion, and I find a line parallel to the blue-coloured part in the Sentinel1 image (the displacement corresponding to the advance of the ice shelf).
Below is the result and you can see that this calving remains very impressive.

Click to enlarge

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Re: Larsen D
« Reply #7 on: November 13, 2020, 12:52:11 AM »
Interstitial,
Thank you, I had doubts myself, but it must be very thick, and almost simulates the appearance of an ice platform.
So I applied a very strict criterion, and I find a line parallel to the blue-coloured part in the Sentinel1 image (the displacement corresponding to the advance of the ice shelf).
Below is the result and you can see that this calving remains very impressive.

Click to enlarge

It is an impressive calving and you can't really tell from the satellite image how thick they are. This calving was predicted by the same scientist who predicted the last one that occurred a bit north of this one. She didn't give an exact time table but I believe this was within her predicted time. Thanks for pointing this out. They seem to do nothing for so long I stop checking then BAM! something happens.

The ice shelf does advance from the blue boundary. I just wish I knew when the boundary was created so I can estimate how fast some of those glaciers are moving. The Ronne ice shelf has extended well beyond its boundary but I don't think it is moving very fast. It may have already calved too. IDK

oren

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Re: Larsen D
« Reply #8 on: November 13, 2020, 09:39:14 AM »
For the sake of less knowledgeable readers, whom I represent quite well, here is the short text from Wikipedia about Larsen D, and a map of the locations of the various Larsen ice shelves.
I would greatly appreciate if anyone can match the animation location relative to the map, or if anyone can post an overview image showing the regions surrounding the calving area.

Quote
The Larsen D Ice Shelf is between Smith Peninsula in the south and Gipps Ice Rise. It is considered to be generally stable. Over roughly the past fifty years it has advanced (expanded) whereas comparable George VI, Bach, Stange, and Larsen C ice shelves have retreated (to a much greater net extent). The most recent survey of Larsen D measured it at 22,600 km2. There is fast ice along the entire front. This makes it difficult to interpret the ice front because the semi-permanent sea ice varies in thickness and may be nearly indistinguishable from shelf ice.


FredBear

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Re: Larsen D
« Reply #9 on: November 13, 2020, 02:21:57 PM »
Earlier this year (July) iceberg A69 broke off from the extreme northern edge of Larsen D, just south of the "island' at the end of Larsen C.This 'berg then quickly broke into two named parts:-
https://www.natice.noaa.gov/doc/PR%20-%2020200708%20-%20Iceberg%20A-69A-B.pdf

The new breakage is offshore & south of the peninsular embedded in the ice shelf just south of the Larsen "D" tag on the previous map but nothing has been given the "A-70" iceberg tag yet. This indicates that the break-out is not significant enough to merit naming an individual big iceberg (although some of the 'bergs look as big as the bits of A69, some ice is likely to be accumulated sea ice)?

paolo

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Re: Larsen D
« Reply #10 on: November 13, 2020, 03:29:56 PM »
Oren,
You will find enclosed :
> An animation with the two Sentinel1 images in their integrality with the scale and the indication lof two landmarks
> A simplified image of the Antarctic Peninsula with the two landmarks
> A detailed map of the Antarctic Peninsula

Click to enlarge and to animate the first image (very large images, to enlarge them completely click twice)

oren

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Re: Larsen D
« Reply #11 on: November 13, 2020, 04:52:45 PM »
Thank you paolo.

paolo

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Re: Larsen D
« Reply #12 on: November 13, 2020, 09:29:25 PM »
Interstitial,
I looked in Worldview which gives the speeds, but relative to 30/12/2011 and I find a maximum speed of 400 m/yr in the middle between Steele Island and Butler Island and 160 m/yr between Butler Island and Cape Mackintosh

"https://worldview.earthdata.nasa.gov/?v=-1795024.1235806216,913897.3490050219,-1598416.1235806216,1006313. 3490050219&p=antarctic&t=2011-12-30-T18%3A25%3A07Z&l=Coastlines,MEaSUREs_Ice_Velocity_Antarctica,MEaSUREs_Ice_Velocity_Greenland,Reference_Labels(hidden), Reference_Features(hidden),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden)"

I checked the speed of a point between Steele Island and Butler Island, for which Worldview gives a speed of 280 m/yr in 2011, using the Sentinel2 images from 23/10/2019 and 17/10/2020 and I find, for the same point, a speed of 340 m/yr (± 12 m/yr taking 2 px as error).

Even if the oldest Sentinel1 image of the zone dates only from 09/07/2020 (120 days before the one of 06/11/2020), which makes a too narrow base to calculate speeds of a few hundred meters per year, I wanted to make a test anyway and, for this same point, I find a speed of 365 m/yr (happy coincidence, an error of only one pixel corresponds to an error of 60 m/yr!).

We can conclude that, at least for this point, there was a significant acceleration (25%).

For the moment no more detailed analysis, this sector does not fit, for the moment, in my schedule.

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Re: Larsen D
« Reply #13 on: November 14, 2020, 09:47:34 AM »
If I did not make a mistake the letters are the snow covered rises that look like snow covered boulders too me. A is not sure B is Dolleman I. C is Steele I. D is Ewing I. The numbers are the calving's. #1 is A68a the long skinny one that is still mostly intact and some speculate that it will crash into an Island soon. #2 is A69 #3 Just happened. I made images too but the image files are too big.                                                                                                               

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Re: Larsen D
« Reply #14 on: November 14, 2020, 09:50:12 AM »
Thanks paolo. That is a lot slower than PIG. I knew it would be I just wanted the comparison.