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johnm33

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Re: Rift in Larsen C
« Reply #300 on: May 18, 2018, 12:43:51 PM »
The point of contact has broken.

from polarview

johnm33

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Re: Rift in Larsen C
« Reply #301 on: May 26, 2018, 10:37:47 AM »
Nice shot of the continued break-up

from polarview

crandles

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Re: Rift in Larsen C
« Reply #302 on: July 09, 2018, 02:30:59 PM »
The 'monster' iceberg: What happened next?

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

Susan Anderson

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Re: Rift in Larsen C
« Reply #303 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
« Last Edit: July 12, 2018, 08:41:25 PM by Susan Anderson »

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Re: Rift in Larsen C
« Reply #304 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



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.

johnm33

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Re: Rift in Larsen C
« Reply #305 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.


polarview

Tor Bejnar

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Re: Rift in Larsen C
« Reply #306 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 image from today.

[Edit:  they were also touching on 2018-08-17.]
« Last Edit: August 22, 2018, 06:52:42 PM by Tor Bejnar »
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Tor Bejnar

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Re: Rift in Larsen C
« Reply #307 on: August 22, 2018, 09:00:17 PM »
No longer 'rejoined' as of the 22nd.  No evidence of the cracks noted two days ago.
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Tor Bejnar

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Re: Rift in Larsen C
« Reply #308 on: August 24, 2018, 06:51:59 PM »
The new Larsen C cracks are more obvious in the PolarView image from today.
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oren

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Re: Rift in Larsen C
« Reply #309 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.

Tor Bejnar

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Re: Rift in Larsen C
« Reply #310 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 - not shown).  The screen shot of yesterday's image (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.
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Grygory

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Re: Rift in Larsen C
« Reply #311 on: August 31, 2018, 09:04:44 PM »
I think that in four days this iceberg will hit with more force

johnm33

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Re: Rift in Larsen C
« Reply #312 on: September 01, 2018, 12:20:50 AM »
Gary look at the size 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.

gerontocrat

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Re: Rift in Larsen C
« Reply #313 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.


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Tor Bejnar

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Re: Rift in Larsen C
« Reply #314 on: September 01, 2018, 04:03:27 AM »
I understand the 'small' ice island at the top of this image (from March) is A68-B.  Only much smaller pieces have also broken off (but maybe totaling about the same area [volume] than A68-B).
(A68-B is approximately 20 km long.  See post #300 above for the major 'other' iceberg sloughing - which also shows A68-B.)
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Darvince

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Re: Rift in Larsen C
« Reply #315 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

lurkalot

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Re: Rift in Larsen C
« Reply #316 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

Tor Bejnar

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Re: Rift in Larsen C
« Reply #317 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 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 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.
« Last Edit: September 05, 2018, 06:14:16 PM by Tor Bejnar »
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Grygory

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Re: Rift in Larsen C
« Reply #318 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.

jacksmith4tx

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Re: Rift in Larsen C
« Reply #319 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.”
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maga

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Re: Rift in Larsen C
« Reply #320 on: September 07, 2018, 12:20:40 PM »

Tor Bejnar

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Re: Rift in Larsen C
« Reply #321 on: September 07, 2018, 08:40:39 PM »
A68-A in perspective:
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Stephan

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Re: Rift in Larsen C
« Reply #322 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.

charles_oil

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Re: Rift in Larsen C
« Reply #323 on: September 07, 2018, 09:45:47 PM »
Yes = please show as a larger image - i cant see anything even when downloaded / zoomed - thanks !

gerontocrat

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Re: Rift in Larsen C
« Reply #324 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.
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johnm33

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Re: Rift in Larsen C
« Reply #325 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/
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.

Tor Bejnar

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Re: Rift in Larsen C
« Reply #326 on: September 11, 2018, 03:51:44 PM »
A68-A is on the move.  Two-framed GIF (from PolarView) goes from "20180910T235812" (nearly midnight at the end of September 10) to "20180911T080126" (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
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Tor Bejnar

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Re: Rift in Larsen C
« Reply #327 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), 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'.
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Tor Bejnar

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Re: Rift in Larsen C
« Reply #328 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, so 60º in 8 weeks.
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FrostKing70

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Re: Rift in Larsen C
« Reply #329 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?

johnm33

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Re: Rift in Larsen C
« Reply #330 on: September 17, 2018, 10:32:52 PM »
Grounded?
Link from Maga,320 above has animation. Looks like the ridge extends underwater.


from here
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[?].

FrostKing70

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Re: Rift in Larsen C
« Reply #331 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!

Tor Bejnar

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Re: Rift in Larsen C
« Reply #332 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]
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gerontocrat

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Re: Rift in Larsen C
« Reply #333 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 ?
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lurkalot

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Re: Rift in Larsen C
« Reply #334 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.

Tor Bejnar

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Re: Rift in Larsen C
« Reply #335 on: September 19, 2018, 04:32:53 AM »
From Johnm33's link, 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.
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litesong

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Re: Rift in Larsen C
« Reply #336 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.

johnm33

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Re: Rift in Larsen C
« Reply #337 on: September 19, 2018, 11:08:53 AM »
Thanks Tor, there just happens to be a polarview that illustrates your point.
 


It looks like a small island chain will emerge from the ice thereabouts.

Tor Bejnar

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Re: Rift in Larsen C
« Reply #338 on: September 20, 2018, 07:47:07 PM »
...
Incidentially, today's PolarView offers the best image of the battering-ram caused (or assisted) cracks in Larsen C. 
...
Looking at an 'old' Project MIDAS 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.
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maga

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Re: Rift in Larsen C
« Reply #339 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.



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Re: Rift in Larsen C
« Reply #340 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?" .

Tor Bejnar

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Re: Rift in Larsen C
« Reply #341 on: September 22, 2018, 07:43:54 PM »
...
An additional 10º rotation, per yesterday's PolarView image, so 60º in 8 weeks.
Yesterday's Polar View (Sept. 21) image 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.
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Re: Rift in Larsen C
« Reply #342 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.

oren

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Re: Rift in Larsen C
« Reply #343 on: September 22, 2018, 08:39:47 PM »
Thanks to all posters regularly updating this thread.

Tor Bejnar

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Re: Rift in Larsen C
« Reply #344 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.
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Tor Bejnar

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Re: Rift in Larsen C
« Reply #345 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 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).
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Re: Rift in Larsen C
« Reply #346 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.