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Author Topic: PIG has calved  (Read 184936 times)

theoldinsane

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Re: PIG has calved
« Reply #550 on: May 16, 2016, 08:32:38 PM »
I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.

I point-out that another major calving event will occur for the PIIS along existing crevasses; it is only a question of when, and what will trigger such a calving (as impacting the grounded iceberg is not a requirement for such a major calving event).

Yes, but suppose you at some point in the future have a lot of grounded islands at the same time. Will they slow down the shelf via some kind of buttress effect (negative feedback) or will they help to speed up the calving through "change the compressive stress field in the PIIS" (positive feedback). Or has it no significance?

Each case is different.  While potential buttressing from a mélange is real, it is also temporary, and the amount and influence of the buttressing is dependent on geometry and dynamics.

Ok, thanks, in a few weeks we probably have the answer in this specific event.

oren

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Re: PIG has calved
« Reply #551 on: May 16, 2016, 09:05:41 PM »
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"

AbruptSLR

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Re: PIG has calved
« Reply #552 on: May 16, 2016, 09:13:38 PM »
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"

Numerous marine glaciers (like Jakobshavn) have already lost their ice shelves; and during those occurrences what you are describing did not occur.  Rather, basal melting due to warm ocean water thinned the ice shelves (as did ice flow velocity), until the calving events reached the grounding line.  After that cliff failures limited the size of the associated icebergs, which also frequently roll, resulting in reduced drafts.
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oren

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Re: PIG has calved
« Reply #553 on: May 16, 2016, 11:33:29 PM »
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"

Numerous marine glaciers (like Jakobshavn) have already lost their ice shelves; and during those occurrences what you are describing did not occur.  Rather, basal melting due to warm ocean water thinned the ice shelves (as did ice flow velocity), until the calving events reached the grounding line.  After that cliff failures limited the size of the associated icebergs, which also frequently roll, resulting in reduced drafts.

Thanks ASLR for your excellent answer. Now things are clearer.

solartim27

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Re: PIG has calved
« Reply #554 on: May 18, 2016, 08:06:43 AM »
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Wipneus

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Re: PIG has calved
« Reply #555 on: May 18, 2016, 08:29:55 AM »
Not quite there yet (or so it looks to me)


You are right, the ice island has not moved a bit.

Wipneus

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Re: PIG has calved
« Reply #556 on: May 19, 2016, 09:13:22 AM »
But now it did.

Wipneus

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Re: PIG has calved
« Reply #557 on: May 20, 2016, 06:23:10 PM »
The higher resolution IW images are better, even when scaled from 10 m/pix to 30 m/pix.

AbruptSLR

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Re: PIG has calved
« Reply #558 on: May 20, 2016, 07:02:30 PM »
The higher resolution IW images are better, even when scaled from 10 m/pix to 30 m/pix.

It is possible that the change in the stress field in the PIIS associate with this contact contributed to the calving event shown in the "notch" area of the PIIS.
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Wipneus

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Re: PIG has calved
« Reply #559 on: May 22, 2016, 11:04:46 AM »
Another animation of the collision. From this and the previous, I think the ice island is being deformed (by some process). The top of the island (that meets the glacier front) can be seen moving with the glacier and sideways. The opposite tip does not move so much, not fully explained by a rotation of the island.
The Red/Green image shows how each side from the island has moved between the Sentinel 1A visits and shows the same: the island's top moves more than the rest of the island.
All images scaled to 30m/pix.

Tor Bejnar

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Re: PIG has calved
« Reply #560 on: May 22, 2016, 03:07:03 PM »
In the later of the two images, I definitely see evidence of a 'new' crack going from near the upper right point of the iceberg (ice island?) toward the uppermost crack on the left side.  I see what I think is evidence of that uppermost left side crack extending further into the berg.  (I do not see the two cracks actually connecting.)  Besides this tiny bit of deformation, I imagine the entire iceberg is pivoting on the most significant (of, I presume multiple) grounding point that (estimating from the rotation indicated by the red/green image and looking at the 2-image movie) is fairly close to (but not at) the lower left point of the iceberg.
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Wipneus

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Re: PIG has calved
« Reply #561 on: May 30, 2016, 03:10:30 PM »
Latest Sentinel image is from 2016-05-30 and I compare it with one cycle ago 18th May.
I have rotated the images 0.3o and shifted to align the images of the ice island as good as I could in the Gimp. On this medium resolution (GRDM, 40m/pix) there is no unambiguous deforming visible: the island is moving as a whole.

Wipneus

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Re: PIG has calved
« Reply #562 on: May 31, 2016, 06:47:00 PM »
Same as yesterday, but now with two higher resolution images (IW, or 10 m/pix, here shown at 20 m/pix).
Somehow I had to rotate the images 0.55o to align them, nearly twice as yesterday.

Anyway, no unambiguous deformation of the ice island visible.

(needs a click to animate)

AbruptSLR

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Re: PIG has calved
« Reply #563 on: May 31, 2016, 07:25:41 PM »

Anyway, no unambiguous deformation of the ice island visible.


While there is no unambiguous deformations of the grounded iceberg (ice island); I note that there is clearly a new shear-tension crack in the notch area; which supports my prior projection that we may well witness a new major calving event for the PIIS in the late July to August, 2016 timeframe.
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Wipneus

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Re: PIG has calved
« Reply #564 on: June 03, 2016, 08:51:39 AM »
Here is an animation of a detail of the ice island (hi-res IW, 10m/pix sclaed to 5m/pix) that may show new cracks developing. It is all very vague and perhaps just noise, have a look.

Tor Bejnar

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Re: PIG has calved
« Reply #565 on: June 03, 2016, 05:28:36 PM »
Thanks.  I've been 'seeing things' (cracks, I contend) on the low-res image pairs, some of which match your hi-res image pairs (but they don't all match).  Time will tell which are phantom and which are physical.
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AbruptSLR

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Re: PIG has calved
« Reply #566 on: June 03, 2016, 06:44:35 PM »
Thanks.  I've been 'seeing things' (cracks, I contend) on the low-res image pairs, some of which match your hi-res image pairs (but they don't all match).  Time will tell which are phantom and which are physical.

I note that it is likely that when the next major calving event happens for the PIIS (possibly in the late July to August timeframe) that the newly calved icebergs may either refloat the grounded/pinned "ice island", or alternately cause it to fracture into smaller free-floating icebergs.
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Wipneus

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Re: PIG has calved
« Reply #567 on: June 08, 2016, 08:22:00 AM »
The low res (EW or 40m/px) image of 6 June hints at something similar in the same spot.

solartim27

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Re: PIG has calved
« Reply #568 on: June 12, 2016, 08:59:54 PM »
A large chunk breaks off the island.  Looks like break up will come pretty soon.
Dates are May 30 and Jun 11
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final
S1A_EW_GRDM_1SSH_20160530T045153_044B_S_1.final
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AbruptSLR

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Re: PIG has calved
« Reply #569 on: June 12, 2016, 11:00:23 PM »
A large chunk breaks off the island.  Looks like break up will come pretty soon.
Dates are May 30 and Jun 11

Great catch.  However, it is possible/likely that this calving event from the iceberg was associated with rotational restraint offered by the chunk that broke-off.  Now that the rotational restraint is no longer active, perhaps the pinned iceberg is more stable (from fracturing) than before this event. 

In any event, it will be interesting to see what happens next.
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Wipneus

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Re: PIG has calved
« Reply #570 on: June 13, 2016, 09:10:11 AM »
The pressure on the pointed tip of the ice island seems to have done it.

In the same time frame another calving on the other side of the glacier.

Animation from hi-res (IW) images, scaled to 70m/pix for size.

AbruptSLR

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Re: PIG has calved
« Reply #571 on: June 13, 2016, 10:45:05 AM »

In the same time frame another calving on the other side of the glacier.


Just for the record, the "... calving on the other side of the glacier" is actually a calving from what MacGregor et al 2013 calls the Southwest (SW) Tributary Glacier (which flows out of the Thwaites Basin) as in the first attached image, as well as in the second attached image from Ng 2015 (with a hat-tip to A-Team).
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notjonathon

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Re: PIG has calved
« Reply #572 on: June 24, 2016, 01:57:01 AM »
ALSR--

It looks like the moving front of the glacier is pivoting the ice island around. That should put some torsional pressure on weaker sections of the island and encourage further breakup.

Also, do the new calving fronts (the cracks further up the ice) actually calve when they reach the present front point, or is there significant retreat going on? I should know, but trying to follow everything that's going on in both the Arctic and Antarctic taxes my memory.

AbruptSLR

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Re: PIG has calved
« Reply #573 on: June 24, 2016, 05:06:47 AM »
notjonathon,

The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.

Best,
ASLR
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oren

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Re: PIG has calved
« Reply #574 on: June 24, 2016, 08:31:16 AM »
Wow. Two developments at the same time in this slow-moving monster.
The ice island is doomed one way or another, but the tributary glacier supplies part of the buttressing of the PIG. Calving there could speed up calving of PIG itself.

solartim27

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Re: PIG has calved
« Reply #575 on: June 30, 2016, 11:31:51 PM »
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11
S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final.jpg
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AbruptSLR

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Re: PIG has calved
« Reply #576 on: June 30, 2016, 11:38:31 PM »
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.
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crandles

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Re: PIG has calved
« Reply #577 on: July 01, 2016, 01:54:41 AM »
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.

Suggests a single pinning point else it wouldn't have rotated so far?

Rotation centre doesn't seem close to any edge. Might break up but if it doesn't, it would seem PIG has to advance a long way to push it off its pinning point.

magnamentis

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Re: PIG has calved
« Reply #578 on: July 01, 2016, 11:43:40 AM »
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.

having fun reading this what i just wanted to post which is great, i like common sense if it makes sense LOL
http://magnamentis.com
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Adam Ash

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Re: PIG has calved
« Reply #579 on: July 01, 2016, 02:33:16 PM »
Seems from those two images that the rotation is about a point in from the edge. 

The small bay at the top of the image and the grid line stay put during the switch between images, but you can see that the calving face advanced some towards the rotated slab.  So it may not be long before it gets a nudge from the glacier which may dislodge it some.

First image is or rotation, second shows my identification of points, normals and arcs which derive a fair idea of roughly where the centre of rotation is (was).

Tor Bejnar

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Re: PIG has calved
« Reply #580 on: July 01, 2016, 04:33:28 PM »
I think it is possible that the iceberg (ice island?) is slipping on the single pivot point, preventing Adam Ash's arcs from defining a single point.  A third day's addition to the image layers would expose this possibility.  (I wish I had the software to do what Adam did   :'()
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Adam Ash

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Re: PIG has calved
« Reply #581 on: July 02, 2016, 10:40:01 AM »
Hi Tor!  My diagram shows the 'berg is rotating about the single pivot point defined by the small magenta circle with a cross in it, among the normal rays.  All the arcs are from that centre point.

A single pivot point is likely to be under enormous strain and wont last long, I suspect.

Software used is Gimp (for the graphics and GIF) and BricsCad for the line work, and the W10 Snipper tool.

solartim27

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Re: PIG has calved
« Reply #582 on: July 04, 2016, 06:00:18 PM »
No apparent changes, looks like we need to wait for the next contact from the glacier.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160703T033009_71B9_S_1.final.jpg
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Adam Ash

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Re: PIG has calved
« Reply #583 on: July 12, 2016, 09:19:52 AM »
This Modis mosaic dated 20160711 seems to suggest that the berg has swung back in against the coast.  The 4km resolution is not clear, but the berg should show and there is no sign of the berg in its previous location.

Other nearby features shown to help you locate (the Molar and the Bite).

solartim27

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Re: PIG has calved
« Reply #584 on: July 12, 2016, 05:08:56 PM »
This Modis mosaic dated 20160711
Where is this from?  It's winter there. 
Edit:  Never mind, found it on the Polar view Mosaics tab.  Since Worldview has it as dark, I always figured that was dark too.
Edit:  Matches the worldview image for 20160405.
« Last Edit: July 12, 2016, 05:44:59 PM by solartim27 »
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Adam Ash

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Re: PIG has calved
« Reply #585 on: July 13, 2016, 09:19:32 AM »
Thanks for checking Solar..  I assumed Modis was radar so immune to day/night.  You could be right.

Will wait for the next pass of S1.

solartim27

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Re: PIG has calved
« Reply #586 on: July 17, 2016, 09:02:02 PM »
Nothing exciting, some rotation and advance.  6/30 to 7/17.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg

S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
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Re: PIG has calved
« Reply #588 on: July 31, 2016, 05:23:44 PM »
Sequence of Sentinel 1 images scaled to 30m/pix to capture both the ice island and the crack. The island seems to move freely and will probably be parallel with the calving front before significant pressure will be applied. I estimate the gap at least 60 pixels or 1.8 km wide, at an average speed of 10m/day it will take us into 2017 when that happens. In that time frame something else may break of course.

Adam Ash

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Re: PIG has calved
« Reply #589 on: August 03, 2016, 09:48:54 AM »
The centre of rotation has not moved far where it was a month ago.  First image 1 July, second image 31 July 2016. 

(Apologies for not rotating the images to the same orientation)

steve s

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Re: PIG has calved
« Reply #590 on: August 03, 2016, 03:34:13 PM »
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg. Both crevasses are either racing thinning to free the berg by breaking it up, or they are products of thinning.

Any guesses as to when the berg will drift free?

AbruptSLR

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Re: PIG has calved
« Reply #591 on: August 03, 2016, 04:53:37 PM »
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg. Both crevasses are either racing thinning to free the berg by breaking it up, or they are products of thinning.

Any guesses as to when the berg will drift free?

I believe that the crevasses that we see are left-over from shear stresses while the ice shelf was shearing against the adjacent landmass/shoring.  Also, I believe that the berg will drift free when the PIIS calves again sometime between next week and the end of November 2016.
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Tor Bejnar

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Re: PIG has calved
« Reply #592 on: August 03, 2016, 06:21:44 PM »
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg.
...
I saw those also, but didn't write anything because I've seen what I thought were extending cracks that didn't amount to anything, and the apparent extensions may have been due to changing angles (the ice island is rotating) rather than growing cracks.  (Or growing cracks could stop growing...).

If these are real, the island could break 'any day' (what do I know), but would likely split if hit by a new ice island or berg or tongue.
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solartim27

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Re: PIG has calved
« Reply #593 on: August 12, 2016, 06:36:05 AM »
More rotation and advance.  The crack in the glacier seems to extend quite a bit, but it could just be differences in the view.  Jul 24 - Aug 10
S1A_EW_GRDM_1SSH_20160810T045157_3C95_S_1.final.jpg
S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg
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Re: PIG has calved
« Reply #594 on: August 12, 2016, 08:48:17 AM »
More rotation and advance.

... and the ice island lost a shard ("bottom" left corner).

solartim27

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Re: PIG has calved
« Reply #595 on: August 23, 2016, 03:09:59 PM »
Ice island has spun 'downstream', but it doesn't look free floating yet.  The next impact will send it on its way, if it doesn't break off before.
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solartim27

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Re: PIG has calved
« Reply #596 on: August 28, 2016, 05:45:22 AM »
What a tease.
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nukefix

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Re: PIG has calved
« Reply #597 on: August 28, 2016, 04:09:23 PM »

Wipneus

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Re: PIG has calved
« Reply #598 on: August 29, 2016, 04:04:11 PM »
Turned back (or 270 degrees forward, who knows).

solartim27

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Re: PIG has calved
« Reply #599 on: September 03, 2016, 04:16:07 AM »
Ice island has broken free.  Aqua 9/2
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