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Wipneus

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Re: PIG has calved
« Reply #300 on: March 11, 2015, 07:12:42 PM »
Thanks Wipneus. Could you add this frame to your animation from Feb 9?  I'm trying to get a sense of the rate of expansion- both width and length - of the crack.

The satellite is here in a different orbital position than in the two frames in that animation, with very different sun position. That influences the appearance of the crack, including width and length.
Unfortunately the image from Mar 10 when the Landsat was in the correct position was cloudy.

I plan to do some more analysis on the Sentinel images at some day though. I think a nice long sequence of those should be possible.
 

AbruptSLR

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Re: PIG has calved
« Reply #301 on: March 19, 2015, 10:25:49 PM »
I post this Terra image of Thwaites for March 19 2015, because I think that it is interesting that while there is some thin newly frozen sea ice, some of the older thicker fast sea ice has recently broken free from the east side of the Thwaites Eastern Ice Shelf.
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Re: PIG has calved
« Reply #302 on: March 23, 2015, 06:02:04 PM »
The attached image is from the Landsat8 satellite for March 17 2015.  To me this image indicates some of the impacts of the relatively high (recently accelerated) ice flow velocity of the PIIS, including: (a) shear cracks in the northern edge of the Southwest Tributary Glacier at its confluence with the PIIS; (b) a crevasse formation in the grounded glacial ice in the southwest corner between the PIIS and the Southwest Tributary Glacier; (c) widening of the "flexural" crack in the PIIS; (d) compressive folding of the floating glacial ice at the southwest corner of the PIIS; and (e) widening of the shear cracks at the southwest corner of the PIIS.

All of these indications encourage me to think that there may well be a major calving of the PIIS in the Nov to Dec 2015 timeframe.
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Re: PIG has calved
« Reply #303 on: March 25, 2015, 10:33:23 PM »
Just seen a report from the European Space Agency. Is this news?

This image combining two scans by Sentinel-1A’s radar shows that parts of the Pine Island glacier flowed about 100 m (in pink) between 3 March and 15 March 2015. Light blue represents stable ice on either side of the stream.

http://www.esa.int/spaceinimages/Images/2015/03/Pine_Island_Glacier_on_Sentinel-1A_s_radar
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AbruptSLR

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Re: PIG has calved
« Reply #304 on: March 25, 2015, 11:47:11 PM »
Geoff,

Thanks as this information was news to me; however, further up this thread Wipneus makes the following statement (which indicates comparable ice flow velocities)

"Here is a sequence composed of Landsat images (30m/pix) from Dec 4 and Feb 6, spanning a 64 day interval.
Measuring pixel movement, using the 15m native resolution, the ice moved about 701.5 meter. That translates to an average speed of 11 m/day, the highest figure that I measured yet."

Best
ASLR
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crandles

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Re: PIG has calved
« Reply #305 on: March 26, 2015, 01:06:55 AM »
one of the fastest ice streams on the continent, with an average of over 4 km per year

so 100m in 12 days is under 75% of average and 701.5m in 64 days is only just average or probably below average. Why is the fastest speed Wipneus measured likely to be below average? Is that odd or is there reason why it is difficult to measure when it is moving at above average speed?

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Re: PIG has calved
« Reply #306 on: March 26, 2015, 10:32:21 AM »
Didn't we find that surface winds over Nina periods slowed the warm water impacting the glacier front and so its flow rates? Now we have been nino or near nino for a while maybe we ought to expect the 'slowdown' in mass loss that we had been seeing now reverse as the surface winds swing around and warm waters are helped toward the calving front/grounding line?
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AbruptSLR

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Re: PIG has calved
« Reply #307 on: March 26, 2015, 04:03:06 PM »
one of the fastest ice streams on the continent, with an average of over 4 km per year

so 100m in 12 days is under 75% of average and 701.5m in 64 days is only just average or probably below average. Why is the fastest speed Wipneus measured likely to be below average? Is that odd or is there reason why it is difficult to measure when it is moving at above average speed?

4000m/365 = 11m/day, which equals the speed that Wipneus measured.  Furthermore, depending on how the researchers treat end dates, March 3rd to 15th might possibly be 11 days and not 12, so 100/11 = 9 m/day, which might be within the natural fluctuations of the PIIS ice flow (including ENSO, weather, & observational uncertainty).
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AbruptSLR

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Re: PIG has calved
« Reply #308 on: March 26, 2015, 10:43:37 PM »
Just for fun, I post the first attached Worldview image of the Ferrigno Ice Tongue on March 8 2015; and for comparison I provide the second attached image showing that the Ferrigno Ice Tongue surged in late Summer of 2012 and then calved back to its equilibrium condition by Feb 2013, and it seems to have stayed in equilibrium since then.
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Re: PIG has calved
« Reply #309 on: March 27, 2015, 08:10:44 AM »
From crandles post here, http://forum.arctic-sea-ice.net/index.php/topic,622.msg48780.html#msg48780

And a quote from Sciencemag http://news.sciencemag.org/climate/2015/03/antarctica-rapidly-losing-its-edge
Even so, the overall picture they report online today in Science is grim: The 18-year record suggests that the average loss in volume of Antarctica’s ice shelves across the entire continent has accelerated significantly in the last decade. From 1994 to 2003, the overall loss of ice shelf volume across the continent was negligible: about 25 cubic kilometers per year (plus or minus 64). But from 2003 to 2012, that number jumped to 310 cubic kilometers per year (plus or minus 74). That rapid acceleration was particularly apparent in the WAIS, where volume losses increased by 70% in the last decade. In the hot spots of the Amundsen and Bellinghausen seas, the ice shelves lost 18% of their thickness in less than 10 years.


The graph below is from the supplement that's free http://www.sciencemag.org/content/suppl/2015/03/25/science.aaa0940.DC1/Paolo-SM.pdf

AbruptSLR

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Re: PIG has calved
« Reply #310 on: March 27, 2015, 06:21:53 PM »
The attached Worldview image of the PIIS for March 27 2015 shows that the "notch" has extended slightly as compared to the March 17 2015 Landsat 8 image shown in Reply #302.
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Wipneus

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Re: PIG has calved
« Reply #311 on: March 29, 2015, 03:01:39 PM »
Detail of the "crack" with the Landsat 8 camera "moving" with the upstream part of the glacier.
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 

Yuha

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Re: PIG has calved
« Reply #312 on: March 29, 2015, 04:01:57 PM »
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 

It seems the downstream part is not moving straight downstream but quite a bit sideways too.

Shared Humanity

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Re: PIG has calved
« Reply #313 on: March 29, 2015, 04:43:41 PM »
With a continuous crack that grows this quickly, is it possible that the lead portion of  PIIS has already completely separated from the ice  behind it?

AbruptSLR

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Re: PIG has calved
« Reply #314 on: March 29, 2015, 05:58:26 PM »
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 

It seems the downstream part is not moving straight downstream but quite a bit sideways too.

Yuha,

You make a good observation; which could (possibly) be taken as evidence supporting my hypothesis that the next major calving event for the PIIS will first swing seaward from the Southwestern end of the calving face, thus pivoting about the pinnacle at the opposite end of the calving face.  If true this would represent a change in previous calving behavior and would support my "compressive field" interpretation (with the compression coming from the Southwest Tributary Glacier running into the PIIS) that I started outlining in Reply #225.

SH,

If my "compressive field" interpretation is correct then there is very little chance that the portion of the PIIS seaward of the (flexural) crack has completely separated from the upstream portion of the PIIS as at least the Southwest corner should still be in compression and the pinnacle is probably still restraining the Northeast end of the (flexural) crack.  Furthermore, 50-m of crack widening can easily be accounted for by stain deformations without any need for invoking rigid body translations/rotations.

Best,
ASLR
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AbruptSLR

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Re: PIG has calved
« Reply #315 on: April 08, 2015, 12:16:00 AM »
I am posting this April 7 2015 Terra image of Thwaites as it may well be the last of this season (due to cloud cover & loss of daylight), and it shows that while sea ice is current extending around Antarctica, locally it is still breaking-up north of Thwaites.
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Re: PIG has calved
« Reply #316 on: April 09, 2015, 11:00:17 AM »
The crack in hi-res Sentinel images. The images are from 2014-10-10 and 2015-04-08, separated by 180 days or 12 Sentinel cycles. The glacier moved in the middle about 1980.4 m, 11.0 m/day.
The images are aligned on the crack which is seen lengthening, widening and - if I read the shadows in this SAR image correct - deepening.

click to open a 3.5 MB animation.

solartim27

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Re: PIG has calved
« Reply #317 on: April 21, 2015, 07:32:22 PM »
Looks like some cracks are forming at the top of the notch heading towards the larger middle crack? (From Polar View 4/19, 32MB pic http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150419T035507_7940_S_1.final.jpg )

Edit:  circled the area I was looking at
« Last Edit: April 21, 2015, 11:05:22 PM by solartim27 »
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nukefix

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Re: PIG has calved
« Reply #318 on: May 06, 2015, 05:51:38 PM »
Here's an RGB-composite of two S-1 acquisitions:

R = B = 19.4.2015
G = 1.5.2015

Movement of the crack in these 12 days appears to be approximately 200m ~= 17m/day ~= 6km/year.
« Last Edit: May 06, 2015, 10:30:24 PM by nukefix »

AbruptSLR

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Re: PIG has calved
« Reply #319 on: May 06, 2015, 06:36:56 PM »
nukefix,

Thanks for the great image & calcs.  If correct, your 17m/day represents a significant acceleration of the PIIS ice flow velocity from the 11m/day value that Wipneus calcs in earlier posts.

As we are currently in an El Nino condition and as the ABSL has been positioned for the past couple of months to direct/blow warm CDW directly in to the ASE (see the attached Earth 850 hPa Wind & MSLP Map for May 6 2015); which in past has been proven to accelerate PIIS ice velocities by advecting greater volumes of warm CDW directly beneath the ice shelf.

If so, then my forecast of a major PIIS calving event in the Nov to Dec 2015 timeframe still seems on track.

Best,
ASLR
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oren

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Re: PIG has calved
« Reply #320 on: May 06, 2015, 10:25:55 PM »
Here's an RGB-composite of two S-1 acquisitions:

R = B = 19.2.2015
G = 1.5.2015

Movement of the crack in these 12 days appears to be approximately 200m ~= 17m/day ~= 6km/year.

I guess the baseline is 19.4.2015 ?

nukefix

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Re: PIG has calved
« Reply #321 on: May 06, 2015, 10:29:47 PM »
ASRL, please note that my estimate has a much larger margin of error as I eyeballed the movement during 12 days, while Wipneus had 12*12=144 days so a much better signal to estimation error ratio. It would be interesting to check whether actual acceleration has taken place.

nukefix

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Re: PIG has calved
« Reply #322 on: May 06, 2015, 10:31:00 PM »
I guess the baseline is 19.4.2015 ?
Yes, thanks, fixed.

AbruptSLR

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Re: PIG has calved
« Reply #323 on: May 06, 2015, 10:59:51 PM »
ASRL, please note that my estimate has a much larger margin of error as I eyeballed the movement during 12 days, while Wipneus had 12*12=144 days so a much better signal to estimation error ratio. It would be interesting to check whether actual acceleration has taken place.

Thanks for the clarification.  It would be great if you could provide periodic updates through the dark austral winter.
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Wipneus

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Re: PIG has calved
« Reply #324 on: May 07, 2015, 07:08:54 AM »
Let me explain how I arrive at my estimated velocity from two images acquired from identical orbital positions:

- load the two images as layers in The Gimp;
- Clicking the visibly of the top layer you can detect whether parts of the images are out of alignment. Shift the images until the rocks in the images are perfectly aligned: remaining movements  are due to genuine ice movements;
- to measure the movement of some feature, e.g. "the crack", move the top layer again until the object is aligned to perfection. Note the number of pixels that the top image was shifted and calculate speed.

With images from 2015-04-20 and 2015-05-02 I measure a shift of 14x1pixels. At 10 m/pix and 12 days this translates to about 11.7 m/day.
The uncertainty in the procedure is at best 2 pixels (one pixel in both steps 2 and 3), but honestly could be two times that amount.
So my result would be reported as 12 +/-4 [m/day].

Of course letting the computer doing the alignment capable would reduce the uncertainty to sub-pixel values. To reliably detect acceleration it seems required.

nukefix

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Re: PIG has calved
« Reply #325 on: May 07, 2015, 12:26:55 PM »
Wipneus your estimate is better, it looks like I had a shift in the co-registration of images. I processed the data again and now I'm getting values close to 140m in 12 days.

The S-1 orbits are good enough that sub-pixel co-registration should be possible with orbit data alone. I'm trying to figure out how best to do it in the S-1 toolbox. It's quite easy to script the operations so that it would be possible to add new images to the stack semi-automatically each time a new image arrives.


solartim27

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Re: PIG has calved
« Reply #326 on: May 09, 2015, 09:38:04 AM »
Elvis hasn't left the building, but his bag is packed and he's heading for the elevator.
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AbruptSLR

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Re: PIG has calved
« Reply #327 on: May 10, 2015, 01:39:10 AM »
For what it is worth, per the attached Earth Surface Wind & Temperature Map for May 9 2015 for Antarctica; the surface air temperature at the PIG is about 1.8C.
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AbruptSLR

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Re: PIG has calved
« Reply #328 on: May 10, 2015, 03:43:52 PM »
Not to be the master of the obvious, but strong El Nino events telecommunicate atmospheric energy from the Tropical Pacific to the West Antarctic focused on the ASE.  Therefore, as we are currently in a mild El Nino condition and are projected to reach a strong El Nino condition as soon as July, the fact that the two attached NOAA daily temp, and temp anom, maps (respectively) for May 9 2015 show the ASE to currently be above freezing (with a temp anom of over 20 C); indicates to me that ice mass loss (& associated major/minor calving) will likely occur at an accelerated level for at least the next nine months (or for however long the current El Nino condition lasts).
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Wipneus

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Re: PIG has calved
« Reply #329 on: June 28, 2015, 03:19:04 PM »
Time for an update. I choose sentinel IW (10m/pix) images from May 2 and June 19, 48days or 4 Sentinel cycles.
The "crack" has widened by about 10-20m, now about 140m in the middle. It has also got quite visibly longer, especially to the West (right in the image).
Some of the cracks in the shearing region can be seen getting longer as well.
I estimate the main glacier has moved about 55x7 (down x left) pixels. That works out to about 11.6 m/day. No winter slowdown for the PIG.

Final image rendered at 20m/pix to keep the image size reasonable. Click to start the animation.

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Re: PIG has calved
« Reply #330 on: June 28, 2015, 10:28:27 PM »
That puppy does NOT have a lot of life left.  Within 2 years it will be toast...  Nice graphic.
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AbruptSLR

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Re: PIG has calved
« Reply #331 on: July 06, 2015, 09:59:53 PM »


The linked article indicates that between March 3 and March 15 2015, the PIG ice stream flowed at a rate of 4,000 m/yr, or 11 m/day; which very closely matches Wipneus' value:

http://www.livescience.com/50254-fast-flow-pine-island-glacier.html

One of West Antarctica's largest glaciers surged a staggering 325 feet (about 100 meters) in less than two weeks this month, the European Space Agency reports.
Two radar images from the ESA's Sentinel-1A satellite on March 3 and March 15 reveal parts of the enormous Pine Island Glacier and its floating ice shelf making a swift trek toward the sea. The wild race to sea is typical for Pine Island Glacier, which flows up to 13,120 feet (4,000 m) every year.

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solartim27

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Re: PIG has calved
« Reply #332 on: July 30, 2015, 10:35:01 PM »
BYE BYE
Edit:  GIFed it up, images from 7/17 to 7/30.  There was another shot at 7/23, with no sign of the collapse coming.

Edit:  Added the frame for the 23rd because you can see the ice field collapsing.
« Last Edit: July 30, 2015, 11:17:32 PM by solartim27 »
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AbruptSLR

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Re: PIG has calved
« Reply #333 on: July 30, 2015, 11:02:55 PM »
BYE BYE

That looks like ice bergs have split-off near the submerged pinnacle.

That looks like the break goes all the way back to the crack that Wipneus has been documenting (leaving a chunk of the shelf left dangling on the submerged pinnacle), this is a major calving event in the middle of the austral winter and could soon relieve some buttressing support for the SW Tributary Glacier.

Also, this attached image show the condition of the Thwaites Ice Shelf/Tongue on July 30 2015, per Polarview
« Last Edit: July 30, 2015, 11:38:32 PM by AbruptSLR »
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Re: PIG has calved
« Reply #334 on: July 30, 2015, 11:58:01 PM »
Spectacular. It looks like the SE corner got a sizable forward nudge as well, but failed to snap. I'm looking forward to a closer inspection of the central crack, and your further analysis of course.
« Last Edit: July 31, 2015, 12:17:08 AM by Rubikscube »

AbruptSLR

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Re: PIG has calved
« Reply #335 on: July 31, 2015, 12:31:29 AM »
Spectacular. It looks like the SE corner got a sizable forward nudge as well, but failed to snap. I'm looking forward to a closer inspection of the central crack, and your further analysis of course.

Rubikscube,

I believe that you are referring to the NW corner that nudged forward; however, I believe that it has snapped free of the rest of the PIIS but that it is grounded on the submerged pinnacle shown in the attached image (showing the mid-January 2014 grounding line location).  I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Best,
ASLR

PS: South is to the right of this image
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Re: PIG has calved
« Reply #336 on: July 31, 2015, 01:21:52 AM »
For those who have a hard time imagining how compression from the SW Tributary Glacier could contribute to today's calving pattern, I re-post the attached image showing how a solid subjected to external compressive loading develops internal stress patterns that kick out laterally, thus causing splitting tension parallel to the axis of compressive loading>
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Re: PIG has calved
« Reply #337 on: July 31, 2015, 05:20:44 AM »
Nice,scary,catch, tanx. PIG is approx 20-25Km across ?

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Re: PIG has calved
« Reply #338 on: July 31, 2015, 09:11:06 AM »
Wonderful. Here is a sequence 12 days apart, that means the Sentinel is in identical orbital position.
Resolution of the image is 120m/pixel, implying the width of the image is about 68km.

There are hi-res images available from the 24th and 25th, but I have some trouble downloading it from the data hub. The zip files keep being corrupted in different positions.
« Last Edit: July 31, 2015, 12:00:13 PM by Wipneus »

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Re: PIG has calved
« Reply #339 on: July 31, 2015, 11:58:15 AM »
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

oren

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Re: PIG has calved
« Reply #340 on: July 31, 2015, 03:40:47 PM »
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.

AbruptSLR

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Re: PIG has calved
« Reply #341 on: July 31, 2015, 04:17:59 PM »
Nice,scary,catch, tanx. PIG is approx 20-25Km across ?

Yes, for convenience I provide the attached 2012 image with an embedded scale in km's for reference.
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Re: PIG has calved
« Reply #342 on: July 31, 2015, 04:20:39 PM »
Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.

The rapid lengthening and widening of various cracks is itself part of the collapse process that ultimately result in the ice breaking off. I believe that is what is being referred to.

I believe that you are referring to the NW corner that nudged forward;

Yes, wrong hemisphere :)

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Re: PIG has calved
« Reply #343 on: July 31, 2015, 04:30:40 PM »
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

Oren, look at he dates. The collapse happened some time between July 25 and July 30.

AbruptSLR

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Re: PIG has calved
« Reply #344 on: July 31, 2015, 04:30:59 PM »
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.

If you look at the sketch in Reply #336, you will see that compression from the Southwest Tributary Glacier (at right angle to the PIIS), creates the splitting tension crack shown by Wipneus, but which also creates a lateral (downstream) kick at the middle of the ice shelf.  As the Northwest corner of the ice shelf is pinned at the bottom by a submerged pinnacle, it is natural (by fracture mechanics) that the lateral (downstream) kick would form a failure mechanism by extending the splitting tension crack down to the Southwest corner (which is not pinned).  Which this calving mechanism is formed (as shown in Wipneus's animation) it is just a matter of time, kinematics and boundary conditions for the lateral (downstream) kick to calve-off the middle wedge of an iceberg shown by solartime27 (leaving the Northwest iceberg pinned in place but rotated and the Southwest iceberg floating away faster than the middle wedge).
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A-Team

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Re: PIG has calved
« Reply #345 on: July 31, 2015, 04:36:19 PM »
I slap myself on the head: this collapse has been visible for most of July.

Let's keep an eye then on the new crack, top center below. The fact remains, even if Sentinel scenes are auto-streamed into a video, somebody has got to watch that video. However it's feasible to set up an auto-alert by differencing frames, not so dissimilar to wildlife camera motion detectors.

Followed by auto-posting and subsequent Typepad notifications, maybe in the future an auto-journal submission that robotic crawling could utilize use for review articles, future sea level rise revisions and proportionate auto-increasing of carbon taxes.

Do you have earlier frames handy? To date the new crack, see when it developed, whether it is progressing. Also one longitudinal crack, bottom left, seems to pre-date the horizontal developments.

It is parallel to the main one because there is more frictional drag on the right side, meaning transverse shear leading to brittle failure. Petermann also has this half-herringbone pattern. The ice in the middle perhaps has a different character, maybe colder. The whitish areas on the sides where motion transitions from 3/12 pixels a day to 0 might be warmer, softer, smoother so more reflective of the radar beam.

In glaciology, they would go on here about the Cauchy stress tensor, deviatoric stress component, strain rates and so forth. It's all in Cuffey & Paterson or at this user-friendly Antarctic link below. There was a nice graphical display on that recently for Larsen B. http://www.antarcticglaciers.org/modern-glaciers/longitudinal-stress/

Fascinating to watch how gaps in the crack get filled in. The piece about to shatter is pivoting, somewhat awkwardly, causing secondary longitudinal cracks to extend on the right side. Here is a shorter smaller faster version of W's animation for any busy ice executives who might stop by.
« Last Edit: July 31, 2015, 05:26:00 PM by A-Team »

Yuha

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Re: PIG has calved
« Reply #346 on: July 31, 2015, 04:50:12 PM »
I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Another possible factor in the collapse is the thinning of the ice shelf.
Those cracks parallel to the flow probably happened along grooves carved by warmer water flowing out of the cavity under the shelf. This event shows that the grooves are now deep enough to be significant weak points in the ice shelf. We may be entering a new era in the PIIS evolution.

AbruptSLR

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Re: PIG has calved
« Reply #347 on: July 31, 2015, 05:25:22 PM »
I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Another possible factor in the collapse is the thinning of the ice shelf.
Those cracks parallel to the flow probably happened along grooves carved by warmer water flowing out of the cavity under the shelf. This event shows that the grooves are now deep enough to be significant weak points in the ice shelf. We may be entering a new era in the PIIS evolution.

Excellent points, and I expect the new splitting tension crack that A-team discusses will likely result in another major calving event within two years or less, and a repetition of this mechanism will progressive move the PIIS calving face upstream, thus progressively relieving buttressing from the SW Tributary Glacier which will progressive induce the adjoining Thwaites Glacier ice flow velocities to accelerate.
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crandles

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Re: PIG has calved
« Reply #348 on: July 31, 2015, 05:45:55 PM »
I expect the new splitting tension crack that A-team discusses will likely result in another major calving event within two years or less, and a repetition of this mechanism will progressive move the PIIS calving face upstream, thus progressively relieving buttressing from the SW Tributary Glacier which will progressive induce the adjoining Thwaites Glacier ice flow velocities to accelerate.


It seems to me the 2013 calving happened at the point where the northern end of that crack reached almost exactly the same point as the northern end of the latest crack has just reached.

See
http://www.bbc.co.uk/news/science-environment-23249909
(linked in first post of this thread)

Is the buttressing from the rock at the northern side the critical point, and wouldn't that continue for a while possibly with thinner glacier possibly moving faster and calving more frequently but at the same point?

(Note I probably don't know what I am talking about and could easily be misjudging the position to be about the same.)



A-Team

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Re: PIG has calved
« Reply #349 on: July 31, 2015, 06:03:59 PM »
It seems to me the 2013 calving happened at the point where the northern end of that crack reached almost exactly the same point as the northern end of the latest crack has just reached.

That would be just like Petermann Glacier which is pinned by rock walls and deflected tributaries instead of other glaciers.

Antarctica is a really big place -- here is thecorrect bounding box at Sentinel for Pine Island Glacier. This will pull out the files that Wipneus used for the animation above. (So many disintegrating ice shelves, so little time.) I found a slightly more recent 28 July scene that is GRDM EW (medium resolution, extra wide) rather than being the IW series. It will have distorted geometry and so cannot be easily added as an animation frame.

I added the rift two years up the road at full IW resolution (which does not add that much detail).

S1A_EW_GRDM_1SSH_20150728T032153_20150728T032257_007005_009832_866D
« Last Edit: July 31, 2015, 09:25:55 PM by A-Team »