Support the Arctic Sea Ice Forum and Blog

Author Topic: Pine Island Glacier (PIG) Calving and Discussion  (Read 442724 times)

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2450 on: July 22, 2020, 12:06:15 PM »
New calving at the NSM, animation based on the images of 10/07 and 22/07.

Click to animate

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2451 on: July 22, 2020, 12:32:30 PM »
PS: No significant changes in PIG rifts.

PS2: I am currently refining the process of calculating the velocities and I will soon publish the results (which will also take into account the last two images of 10/07 and 22/07) as well as the calving front histories: North and South (both covering the entire front).

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2452 on: July 22, 2020, 01:59:31 PM »
New crack in Cork 3 in 12-day GIF of the Southern Shear Margin.  Also the 12-day GIF of the Northern Shear Margin with absolute motion.

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2453 on: July 22, 2020, 02:10:49 PM »
Almost missed the new rift on T11 (Tributary 11) which may prove worrisome.  We've been pinning our hopes on it becoming the new 'pinning point' in the South, but this is its first sign of potential vulnerability.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2454 on: July 22, 2020, 02:20:56 PM »
Good point!
It's all the more worrying as it's the eastern edge of the T11 and further east it's the ice platform fed by small unnamed tributaries and is less robust!

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2455 on: July 22, 2020, 05:05:24 PM »
A quick analysis of the PIG
NSM:
Mini calvings should continue, but the distance between the two edges should decrease, leading to temporary stabilization.
The recently opened rift has stabilized and tensions tend to move further upstream where another rift has widened. This process should continue and new rifts should open upstream as the PIG progresses. There should be no more than marginal rifts (at least for the time being). I have named this rift system nmR1.
Towards the front the block that had not calved in February should remain attached to the PIG, the two rifts, north and south (the latter is out of the picture) having not moved in the last few months.

We can timidly hope that this front will stabilize temporarily.

SSM :
Large calvings linked to the cR1, smR2 and new rifts are inevitable in the following months. Along the margin mini calvings should continue up to the shear margin of T11, as we have just sadly discovered.
The resulting pinning point is not very strong, let's hope that T11 behind supports it properly and holds as long as possible!

But, good news, for the moment no opening of the new marginal rifts in the PIG.

Conclusions:
It seems to me that the most critical point is the SSM, which is to be watched very carefully in the coming months.

click to zoom in

Stephan

  • Nilas ice
  • Posts: 1336
    • View Profile
  • Liked: 468
  • Likes Given: 231
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2456 on: July 22, 2020, 10:23:50 PM »
Thank you both, paolo and baking, for these updates.
In my opinion the new rift in T11 is the start of an extension of the SWZD further upstream. In the last year(s) the upper end of this zone of destruction seemed quite stable to me.
It is too late just to be concerned about Climate Change

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2457 on: July 23, 2020, 07:30:01 PM »
I think we are seeing something similar on both margins which is expansion rifting as the PIG pulls away from the margins downstream of the pinning points.  This is basically approaching a new equilibrium as the new pinning points are established.  The loss of the old pinning point in the South at the SWT is causing the Northern pinning point to shift upstream to be between Evans Knoll and the new Southern pinning point at T11.

The major uncertainties are the location of the grounding line around Evan's Knoll which will affect the eventual location of the Northern pinning point and the stability of the Southern Ice Shelf and its support of T11 as the Southern pinning point

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2458 on: July 23, 2020, 09:24:56 PM »
I can see you're an optimist:
The pinning point at the NSM has a certain solidity (over a few months for sure, over a few years to be confirmed), but it must absolutely not go upstream, the grounding line is moving away from the NSM upstream!
The pinning point at the SSM is the one I see very badly: after the last fractures, it is now well beyond T11 (and moreover the eastern part of T11 is less thick than the rest of T11). I don't feel that I trust too much the other components of the SIS upstream of T11. In my opinion it can withstand a few months, but not a few years.
To undo a glacier takes time, but at the moment the PIG seems to me in a very bad position and a retreat in the next few years seems inevitable.
I only ask to be reassured, but what I see does not reassure me in any way.

click to zoom in

EDIT: The only positive points are:
that in the North the NE-IS fracture, caused by the movement of the PIG, has gradually moved away from the Ice Rise, which may lead to a structure with some stability and at least partial closure of the rift zone...
and that in the South there have been, at least for the time being, no new marginal rifts in the PIG
« Last Edit: July 23, 2020, 09:36:04 PM by paolo »

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2459 on: July 23, 2020, 11:16:17 PM »
SSM: Come to think of it, maybe it's better that way. Indeed a pinning point based on thinner, but deformable ice can resist for a while, unlike T11, formed, especially in its western and central component, of very thick ice, and which provided strong resistance, but ended up breaking and shattering the PIG in front of it.
And perhaps the robustness of T11 could be used, in a more positive way, to provide behind an effective support to the future pinning point.

It only remains to follow and see the evolution.

The fact remains that, in any case, in a more or less near future, we may witness the beginning of the great retreat.

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2460 on: July 28, 2020, 04:51:01 AM »
12-day GIF of the Southern Shear Margin.  Nothing too surprising compared to the one from July 22.

oren

  • Moderator
  • First-year ice
  • Posts: 6196
    • View Profile
  • Liked: 2252
  • Likes Given: 1891
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2461 on: July 28, 2020, 04:54:21 AM »
Thanks baking. The only surprise for me is that the "almond" hasn't popped yet. Maybe the sea ice is helping to keep it in place, but I doubt it can avoid calving soon as it is pushed by the cork behind it.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2462 on: July 28, 2020, 09:38:49 AM »
Oren,
The fact that the "Almond" held and still holds is really a surprise:
> There is a strong compression between Cork3 and the SIS, which together with the stresses generated by the movement of the "Almond", whose point is moving away from the base of Cork3, caused the Cork3 to burst into three pieces (given the pressure Cork3 could not slide along the "Almond" and the point of Cork3 remained attached to the point of the "Almond").
> On the SIS side, the base of the "Almond" is small and partially off-centre in relation to the forces, even if the main pressure at the moment must be in the South.

 If we had Sentinel2 images we might have some elements to understand, but with Sentinel1 images is not possible.

I don't think that the sea ice has anything to do with it (given the forces that are exerted), it is rather necessary to take into account that in this sector the SIS (T11) is very thick.

Even if the moment is dragging on, I still believe that calving can occur at any time.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2463 on: July 28, 2020, 10:14:33 AM »
Mini calving at NSM (animation using images from 24/07 and 28/07)

click to animate

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2464 on: July 28, 2020, 02:54:12 PM »
Here is a higher-resolution 6-day GIF of the Northern Shear Margin, but the images are from different angles so beware the radar shadow artifacts.  I think it shows the calving is just some of the melange getting lose.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2465 on: July 28, 2020, 03:19:00 PM »
I don't quite understand what you're getting at; there's clearly a very fractured area at the NSM, but it's large pieces of ice shelf, which could still be reattached before calving, by the way.
In the picture below we can see a big iceberg (I checked and it was not present in the previous pictures).

EDIT: Looking in yesterday's partial image (it did not show the NSM, Ice Rise Even's Knoll side) we can notice this iceberg for the first time, which implies that the calving took place before this image (yesterday I had noticed a lot of garbage at sea, but missing the image containing the north side of the NSM I could not conclude).
« Last Edit: July 28, 2020, 03:31:04 PM by paolo »

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2466 on: July 29, 2020, 02:14:25 PM »
I am starting to catch up and you will find attached the history of the PIG calving front since the big calving of 09/02 based on the Sentinel1 images of 17/02 + n * 12 days (last image that of 22/07), the image of 29/02 being missing.
The calving front has been cut in two parts: North and South, they overlap and therefore give the global vision.
I give two versions: white background and Sentinel1 image of the 22/07.

click to zoom in

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2467 on: July 29, 2020, 09:23:50 PM »
I wanted to add a lighter version:
with two intervals of 24 days: 17/02, 12/03 and 05/04,
and three intervals of 36 days: 05/04, 11/05, 16/06 and 22/07,
and adding little comments.

Click twice to zoom in



blumenkraft

  • Guest
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2468 on: July 29, 2020, 09:44:11 PM »
This is marvelous, Paolo. :)

Stephan

  • Nilas ice
  • Posts: 1336
    • View Profile
  • Liked: 468
  • Likes Given: 231
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2469 on: July 29, 2020, 10:18:25 PM »
paolo,
thank you. Two likes earned.
It is very interesting, instructive and also artistic.
kind regards Stephan
It is too late just to be concerned about Climate Change

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2470 on: July 30, 2020, 03:51:36 PM »
I'm worried that the "Almond" may have slipped today.  Here are two 12-day GIFs of Cork3 enlarged 4x.  The first ends today, the second ends three days ago for comparison purposes.  I think I'm seeing more slippage in the first, but it also may be just the acquisition angle.

IceConcerned

  • New ice
  • Posts: 37
    • View Profile
  • Liked: 17
  • Likes Given: 7
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2471 on: July 30, 2020, 05:19:58 PM »
Well, what is sure is that the cork has suffered another significant break
IMHO it will not hold much longer

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2472 on: July 30, 2020, 05:28:58 PM »
It's been slipping slowly for days, but it's still tight between the middle piece of the Cork3 and the SIS, its been days that it should be swimming in the bay.

Denied by the resilience of the PIG in other cases, I refrained from intervening and limited myself to saying that calving can occur at any time.

You are braver!   

Tor Bejnar

  • Young ice
  • Posts: 3550
    • View Profile
  • Liked: 608
  • Likes Given: 380
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2473 on: July 30, 2020, 07:26:07 PM »
We're 5 weeks past the winter solstice and the ice hasn't hardly slowed down (says this casual watcher).  Is this typical for the PIG?

Edit (per B_'s question below):  I'm noticing posts showing the 'half (or 7/8ths) calved ice' ball-bearings, corks and related melange moving along, cracks opening and the like.  Glaciers advance in the summer a little faster than in the winter, at least where it is warmer, I recall learning (and I watched one moving faster in the afternoon than in the morning).
« Last Edit: July 30, 2020, 08:07:21 PM by Tor Bejnar »
Arctic ice is healthy for children and other living things.

blumenkraft

  • Guest
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2474 on: July 30, 2020, 07:29:03 PM »
What do you mean, Tor? The sea ice or the glacier?

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2475 on: July 30, 2020, 07:53:50 PM »
The speed of the PIG, the tensions induced by its progression and therefore its calvings are not influenced by the seasons and the presence of sea ice has practically no influence, as do summer temperatures.
Perhaps in the future, as a result of a subsequent rise in summer temperatures, summer phenomena could appear that would inflate calving in that season. 
This is not the case at the moment.

EDIT: What changes is that we don't have the images from Sentinel2, which would give us a better view of the state of the PIG.
  :(

EDIT2: What is not normal is having two big calvings a year apart, and then continuing with large calvings.
What can be translated by a significant receding of the calving front
« Last Edit: July 30, 2020, 08:01:36 PM by paolo »

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2476 on: August 04, 2020, 12:56:36 PM »
The PolarView service has been very poor lately, no high definition images yesterday and the day before yesterday, today a low resolution and poor-quality image ...

The Almond refuses to go out to sea and clings on.

Mini calving at NSM: small animation based on the images of 31/07 and 04/08, => different orbits (we do with what we have!), aligned, at best, on the front side of Evan's Knoll.

PS: not much time at the moment, the speed update is still in the works, but it will come soon

Click to animate


paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2477 on: August 05, 2020, 11:15:52 PM »
No news on the PIG side.

So I post an animation of the SWT on the SIS side.
This animation, based on the high resolution images of 24/07 and 05/08, is aligned with the SIS, which highlights the movement of the SWT, or more precisely of its eastern part (which is the only one visualized in this animation), relative to the SIS.
I remind you that it is the part of the SWT that moves the fastest, the speed decreasing further west, to become very low at its western end, where Ice Rumples are located.

We can also notice the widening of the rifts in the SWT itself and in the SIS in front of it.
This leads to the possibility of future calvings on the SWT and on the SIS, the causes being the speed differential in the SWT itself and between the SWT and SIS.

Click to animate

interstitial

  • Grease ice
  • Posts: 567
    • View Profile
  • Liked: 198
  • Likes Given: 76
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2478 on: August 06, 2020, 07:27:15 AM »
Can you even get speed from anything but the high resolution images?

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2479 on: August 08, 2020, 05:12:25 PM »
A few 12-day high resolution GIFs, all at 2x enlargement.

Cork3 showing rapid disintegration.

Upstream T11 tributary rift expanding.

Third rift forming on the Southern Ice Shelf (SIS) where it meets the Southwestern Tributary (SWT).

Stephan

  • Nilas ice
  • Posts: 1336
    • View Profile
  • Liked: 468
  • Likes Given: 231
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2480 on: August 08, 2020, 09:45:01 PM »
To say it politely, I am not satisfied with what happens to PIIS and its surroundings.  :(
Thank you baking for this update.
It is too late just to be concerned about Climate Change

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2481 on: August 09, 2020, 02:43:10 PM »
Just to round things out, we finally have a good high-resolution image of the Northern Shear Margin, so here is a 18-day GIF, also a 2x enlargement to match with the ones in my previous post.

The melange looks vulnerable, and the calving of the northern ice shelf could be a sign that the ice there is not very thick, but the marginal rifts did not grow in length or in number.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2482 on: August 10, 2020, 07:13:06 PM »
I'd like to make an update on the NSM.

I'll use yesterday's high-resolution image that I commented on.
In this image I have embedded an image with elevations, and thus thickness, (David E. Shean et al. 2019; data used first half of 2010) and velocities (WorldView 2011).

The NE-IS is fed upstream by a small tributary and, far to the east, by ice overflowing the Ice Rumples next to the PIG (north of the ZD). The ice of this IS is carried westward by the PIG and pushed towards the funnel between the Ice Rise Evan's Knoll and the PIG itself, where it recompacts.
This is the final part of the funnel that is visible in the image.
In the funnel the movement is parallel to the PIG and the speed gradually changes from zero, Ice Rise side, to that of the PIG itself, PIG side.
As for the thickness we can estimate it at 500m, see more.

Currently the movement of the PIG and the induced tensions lead to the opening of small marginal rifts in the NE-IS orthogonal to the PIG and the pieces of IS between two rifts are bent by the movement of the PIG until complete detachment and calving. This is the area indicated in red in the image (I also added a zoomed image of this area, image from the day before yesterday).
This area creates, PIG side, a shear force (even if relative), which ensures a progressive increase of the shear as we go upstream without abrupt increases.  As a result there is almost no formation of marginal rifts in the PIG (which is positive).
Downstream there is final detachment of the pieces of IS with dynamic calvings: rapid initial movement of the icebergs and in many cases, given their size, their turning over.
This field of rifts, as well as the calving front migrate upstream and nothing seems to be able to stop this process, the only thing that can be hoped for is that this process is as slow as possible.

Clearly upstream, where the funnel widens, the process can only accelerate and there will be reunification with the already existing ZD and thus a detachment of the NE-IS from the PIG. But this process is expected to take several years.
What could accelerate it is a collapse of the part of the NE-IS already detached from the PIG and which currently provides support to the NE-IS upstream: this part is under pressure from the NE-IS upstream but it should resist, moving without breaking, for some time.

Following the detachment of the PIG from the NE-IS there may be some mini calvings (PIG side), one has recently arrived, but they should remain anecdotal.

To the west, on the front line, the large iceberg left over from the big calving (see third picture), already half detached from the PIG, should resist for a while.Indeed the rifts indicated r1 and r2 in the image are widening contentedly but their progression is slow (there is no modification of the rifts r3 and r4). This calving should have no effect on the PIG.

Click to enlarge

interstitial

  • Grease ice
  • Posts: 567
    • View Profile
  • Liked: 198
  • Likes Given: 76
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2483 on: August 10, 2020, 11:15:44 PM »
Paolo:
Thanks for your posts Paolo. Is that elevation map recent? When?

IceConcerned

  • New ice
  • Posts: 37
    • View Profile
  • Liked: 17
  • Likes Given: 7
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2484 on: August 11, 2020, 12:16:35 PM »
Paolo
I think you underestimate the crack you labeled ""C*. On the contrary I think it is the portend of a very serious future calving (going from the current diagonal to a new perpendicular front as you predicted some weeks ago)

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2485 on: August 11, 2020, 02:04:38 PM »
From my post: "This area creates, PIG side, a shear force (even if relative), which ensures a progressive increase of the shear as we go upstream without abrupt increases.  As a result there is almost no formation of marginal rifts in the PIG."

IceConcerned,
I don't underestimate them, but I found that the rift opened up and spread quickly, but then stopped developing very quickly, a sign that there were strong but episodic tensions. If there are no changes we may see in the future the opening of other rifts further upstream, but without major development.These rifts should develop over time, but slowly, and thus lead to a "normal" calving rhythm.  Of course this is not completely assured and I am watching this sector very carefully, but for the moment it seems to me that we can be a little optimistic (not too much) about this, and in the current catastrophic situation we need a little optimism.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2486 on: August 11, 2020, 02:08:54 PM »
Interstitial,
From my post: "In this image I have embedded an image with elevations, and thus thickness, (David E. Shean et al. 2019; data used first half of 2010) and velocities (WorldView 2011)."

These data are therefore sufficiently recent and the current elevation should not and cannot be very different.

interstitial

  • Grease ice
  • Posts: 567
    • View Profile
  • Liked: 198
  • Likes Given: 76
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2487 on: August 12, 2020, 04:55:10 AM »
Interstitial,
From my post: "In this image I have embedded an image with elevations, and thus thickness, (David E. Shean et al. 2019; data used first half of 2010) and velocities (WorldView 2011)."

These data are therefore sufficiently recent and the current elevation should not and cannot be very different.

Respectfully 10 years ago the leading edge of the Ice shelf was much further away from this location. From my limited understanding ice shelves thin substantially near the leading edge. I base this mostly on not to scale diagrams of ice shelfs in publications. Perhaps the ice shelf has retreated faster than thinning of the shelf edge occurs. IDK I was hoping I could compare it to older elevation maps and see if  it is much thinner now or if it is about the same. I think their are one or more satellites that determine elevations daily or nearly so but I have not taken the time to look. I just wonder how that interacts with retreat of the shelf edge.

I know elevation is related to thickness because the ice is floating but do you happen to how thick the ice would be for an ice shelf with 60 m of ice above the waterline? Thanks


paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2488 on: August 12, 2020, 03:14:32 PM »
Dear Interstitial,
First of all a small precision, I had said "data used first half of 2010", hearing 2010/2015. Indeed Shean et al. 2019, as can be seen in figure 6 of their article, see first picture attached, use data from 2008 to 2015. In particular, the most recent data used are from 2015.

If we look at the 2014 data, zoomed in the attached second image: figure6 (g) (I did not consider the 2015 image which presented an area without data at the NSM), we can notice that the data displayed are extremely similar to the one of their elevation presentation figure that I used in my previous post, image that I attach in its entirety: third image attached.

Moreover it is necessary to take into account that the maximum melting is given by the CDW to the grounding line this water which, cooled, passes under the ice platform, with a more limited melting, to go out finally to the calving front. There is no remarkable melting on the front line, except towards the exit of the existing channels under the ice platform. One of these channels is located at the NSM.
A figure, again from Shean et al. 2019, for melt rates is attached as the fourth image.

As a last remark I remind you that the period of high CDW, with a strong regression of the grounding line, goes back to the years 2000-2010, and that it weakened thereafter (with a lower speed of regression of the grounding line).

Conclusions :
> These data are sufficiently current.
> Melting depends on the history: the path of the ice and its speed (and thus the rate and duration of melting), but not on the current situation.
> The values shown in Shean et al. 2019 remain valid.

As for the thickness estimate, the estimate given in my previous post was not intended to be precise, but only to alert to the fact that it was consistent.
To answer you and be more precise, from the qualitative data of the image (color) we can deduce a thickness of 400 / 450 using the formula elevation + (elevation-10.6) * 0.915 / (1.028-0.915) (the 10.6m corresponding to the existence of the firn; I had found this formula during the analysis of the arc structure in the SIS and I had validated it with the results: elevation/draft displayed by Mankoff et al. 2012 figure2 relating to the PIIS; this value was also consistent with values of thickness and average density found in another article relating to the PIG, even if more upstream; which gives 460m for an elevation of 60m).

Remark: in my post of 28/08 (post 2465) I highlighted an iceberg, which apparently turned over and which can therefore give an idea of the thickness.



« Last Edit: August 12, 2020, 05:09:56 PM by paolo »

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2489 on: August 15, 2020, 12:00:52 PM »
Mini calving at the MSM NSM, but this time the modalities are different: the calving is not "explosive", a sign that the tensions were small and therefore the icebergs were already almost separated.
The field of rifts is now very wide and this new regime could herald a further upstream migration from this area. The almost pinning point to the North is not very solid and our hopes that the northern front will resist for a while rest on it! To be followed with attention !
« Last Edit: August 15, 2020, 01:07:07 PM by paolo »

oren

  • Moderator
  • First-year ice
  • Posts: 6196
    • View Profile
  • Liked: 2252
  • Likes Given: 1891
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2490 on: August 15, 2020, 12:35:34 PM »
I was asking myself what MSM was, feeling lost again in all the acronyms, when I realized it is just a typo...  8)
Northern Shear Margin.

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2491 on: August 15, 2020, 05:31:10 PM »
Here are a couple of 6-day high-resolution GIFs, both scaled x2.

First is the NSM, same as paolo's except with absolute alignment which I think shows better what happened.  A few small icebergs in the melange were released and at least one turned on it's side (the dark patch in the radar image showing less reflexivity.)

Second is Cork 3, and the almond seems to be slipping even faster, moving at the same speed as PIG, so no longer attached and just held in place by friction at this point.  I'm not the first to say it, but I wouldn't be surprised if it gave away any day now.

Stephan

  • Nilas ice
  • Posts: 1336
    • View Profile
  • Liked: 468
  • Likes Given: 231
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2492 on: August 15, 2020, 07:50:15 PM »
Thank you baking and paolo.
It looks like the Almond is the "real cork" at the SSM as Cork III has disintegrated into three separate icebergs. It seems a wonder to me that it is still connected to the SIS. "Any day now" a calving of parts of the ZOD seems possible for me.
It is too late just to be concerned about Climate Change

interstitial

  • Grease ice
  • Posts: 567
    • View Profile
  • Liked: 198
  • Likes Given: 76
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2493 on: August 16, 2020, 08:07:07 AM »
Paolo
Thanks for your response I have been meaning to get back to you. Warm CDW is not the mechanism I was thinking of or any other form of melting. I was thinking acceleration of glacier speed near the front edge. In order for that to work calving would need to be upstream of the region of high speed motion. It did not calve into the lower speed region so my thinking was flawed.

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2494 on: August 20, 2020, 05:35:05 PM »
Six day high resolution GIF of the cork.  The "Almond" is still hanging in there.

Tor Bejnar

  • Young ice
  • Posts: 3550
    • View Profile
  • Liked: 608
  • Likes Given: 380
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2495 on: August 20, 2020, 06:31:51 PM »
The SIS must have Velcro or honey - first Cork II (iirc), now the Almond!
Arctic ice is healthy for children and other living things.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2496 on: August 21, 2020, 12:52:41 PM »
At NSM calving the melange that formed after the previous calving
(images from 15/08 and 21/08; alignment on the edge, Ice Rise Evan's Knoll side)
« Last Edit: August 21, 2020, 12:57:42 PM by paolo »

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2497 on: August 26, 2020, 04:46:52 PM »
Today's 6-day GIF of the Southern Shear Margin, slip sliding away.

paolo

  • Grease ice
  • Posts: 585
    • View Profile
  • Liked: 203
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2498 on: August 26, 2020, 05:39:05 PM »
The emptying of the NSM continues (its speed is a bit worrying...)
Since the image of the previous calving was from 21/08 and therefore from a different orbit than the image of today and since the two images do not align as I would like (moreover today's image is a collage of two images) I will provide the two images separately.

Click to zoom in

baking

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 146
  • Likes Given: 9
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2499 on: August 27, 2020, 03:16:12 PM »
Here are today's 6-day GIF's for the Northern and Southern Shear Margins.  Northern Margin shows the continued clearing of the melange seen yesterday.

In the South, note that the Point is again being pushed to the North and the widening of the rift.  This is the first we've seen of this in months, but the odds still seem to be that the almond will slip lose first before Point calves.  We shall see.