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paolo

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Re: PIG has calved
« Reply #2000 on: March 24, 2020, 06:44:34 PM »
Baking,
I disagree:

> the vector of the force exerted by the icebergs east of the Cork, which is the only force that applies to the Cork2, points well north of the base of the Cork2 (its direction passes off the base for more than half the length of the iceberg; just look at your animation) and, even though the iceberg is rigid, its very narrow base does not allow the force you are talking about to be transmitted to the SIS.  No, the cork2 can only rotate until its base disintegrates.

> The causes of SR1 and SR2 are clearly the same and other factors, such as Cork2, are only secondary actors. Moreover, SR2 is the most important and the one that is currently expanding the most and it shows no link with SSM. Moreover SR1 has formed very much inwardly, towards the SWT.The link with the SSM was given by the Cork, which opposed the push of the SWT being blocked to the north by the MIS. But now the Cork is no longer there.

You have to look at the big picture and not get lost in the details...

Currently I don't have access to the Sentinel2 images, so no images  >:( >:(

paolo

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Re: PIG has calved
« Reply #2001 on: March 24, 2020, 08:07:54 PM »
Still no Sentinel2 images, so I used the coherent Sentinel1 images from 29/01 (before calving), 10/02 (after calving), 22/02, 05/03 and 17/03 to show the evolution of the two rifts that appeared after calving: SR2 before and SR1 after.
The aim is to show what happens and how it happens, and there are no notations or indications to allow everyone to get an idea without preconceptions.

baking

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Re: PIG has calved
« Reply #2002 on: March 24, 2020, 09:00:54 PM »
Consider two hypotheses:

1.  The removal of "Cork I" allowed the northern movement of the Southern Ice Shelf (SIS) to accelerate which created (or caused the expansion of) the two transverse rifts in the SIS.

2.  The major calving of PIG along with the removal of "Cork I" caused the force of the upstream melange acting on "Cork II" to be directed at a point on the SIS, at an oblique angle.  This force was a factor in the formation of the northern most transverse rift in the SIS.

Both hypotheses could be true.  In particular, arguing for Hypothesis 1 does not negate Hypothesis 2.

paolo

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Re: PIG has calved
« Reply #2003 on: March 24, 2020, 09:31:06 PM »
Baking, you consider SWT and SIS ( all that is east of SWT) as a single unit, which does not correspond to reality, and you forget this hypothesis :
The SWT, comes from the west, in the past it turned completely to the NW constrained by the MIS. Following previous calvings, the direct constraint of the MIS being no longer there, its flow had taken the NNE direction constrained only by the Cork. Now that the Cork is no longer there, only the SIS opposes the SWT to take its natural direction, i.e. towards ENE, and the SIS directly takes the thrust of the SWT (and it does not have the capacity to resist without damage).

oren

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Re: PIG has calved
« Reply #2004 on: March 24, 2020, 10:00:23 PM »
Thank you baking for better explaining what I meant about the Cork II and the SIS.
Thank you Paolo for taking the time to respond in detail.

paolo

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Re: PIG has calved
« Reply #2005 on: March 24, 2020, 10:10:08 PM »
Question: Do you have access to Sentinel2 images?
I only access the first image, which is in the PC memory, and nothing else.

baking

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Re: PIG has calved
« Reply #2006 on: March 25, 2020, 03:38:21 AM »
the SIS directly takes the thrust of the SWT (and it does not have the capacity to resist without damage).
Yes, the SWT is pushing due West, but the SIS is pushing due North and the PIG is pushing due East.  Of the three, the PIG is moving much faster and is pushing much harder.  Also, it is probably not a coincidence that the location of the transverse rifts line up with possible pressure points on the Southern Shear Margin.

At the time that the downstream rift first formed, Cork II was much more firmly attached to the SIS.  It is a mistake to say that Cork II is not firmly attached today therefore it could never be a factor in the past.

paolo

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Re: PIG has calved
« Reply #2007 on: March 25, 2020, 10:48:55 AM »
Today only one low-resolution Sentinel1 image.
It seems to me that some of the Ice mélange has calved (it's up to you to judge)
Attached an animation based on the images of the 24th and 25th and the Sentinel2 image of the 16/03 with the addition (in yellow) of the area interested by this calving.
And has well early (as soon as I have time) for the next episodes of the soap opera baking-paolo

Edit : corrected the image with the area that calved
« Last Edit: March 25, 2020, 11:00:55 AM by paolo »

blumenkraft

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Re: PIG has calved
« Reply #2008 on: March 25, 2020, 10:57:26 AM »
So here is my theory why Cork II hasn't calved already.

Perhaps the melange behind it has some gluing effect. Meaning with this recent melange calving, there is glue lost and the calving of Cork II is now more likely.
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paolo

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Re: PIG has calved
« Reply #2009 on: March 25, 2020, 11:30:22 AM »
Blumenkraft,
The iceberg to the east of Cork2 pushes the latter, which is limited to rotating, relative to the base, without opposing any resistance, and, until the base manages to deform to allow this rotation (deformations which are minimal), nothing happens.
What amazes me is the absence of drive by the outgoing current, which, if in action, would lead to the calving of the Cork2 without any problem.
In the attached picture I indicate the movement of the iceberg, the consequent movement of the Cork2 and the minimal compression efforts due to the rotation of the Cork2.

paolo

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Re: PIG has calved
« Reply #2010 on: March 26, 2020, 09:50:10 AM »
Mini calving SWT side

The Corck2 it hangs on and always resists

paolo

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Re: PIG has calved
« Reply #2011 on: March 26, 2020, 11:10:20 AM »
For once we have close images (48 minutes between frames) it was worth creating an animation with the low resolution Sentinel1 image of 04h19m53s and the high resolution Sentinel1 image of 05h07m55s, even if we can't have exactly the same scale.

blumenkraft

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Re: PIG has calved
« Reply #2012 on: March 26, 2020, 11:46:46 AM »
Interesting indeed!

It also gives a hint on how less reliable the low res stuff is. Thanks for that, Paolo.
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Stephan

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Re: PIG has calved
« Reply #2013 on: March 26, 2020, 07:19:00 PM »
I think this mini-calving was overdue.
I checked the latest Sentinel image from 16.03.2020 and in my opinion there is a "pre-rift" further to the west through great parts of the SWT (dotted yellow line with a question mark in its middle). I think the next calving is already under preparation.
See attached picture.
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paolo

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Re: PIG has calved
« Reply #2014 on: March 27, 2020, 12:29:46 AM »
SR1 & SR2, the main player: the SWT

In the other world the SWT was an important but secondary actor, the MIS being clearly the main actor and it was necessary to start from it to analyze the SIS, in its entirety, including SWT.
The SWT was forced to turn 135° and was forced to turn, upstream, through the more western part of the SIS, and downstream, directly through the MIS. I remind you that this part of the SWT flow is completely floating and therefore not constrained by the seabed.

At the meeting between the SWT and the SIS along the right shear margin of the SWT, margin that I will call ESM (East Shear Margin) there were two forces that were exerted: the one due to the constraint to turn and the one due to the speed differential between the SWT and the SIS. These forces were not visible on the surface: not rifts. Indeed, the SIS was completely wedged and compressed between the SWT and the MIS.

There was a brief period of transition in which there was no longer direct contact between the SWT and the MIS, but only indirect contact by the Cork, which provided pressure on the SWT and the SIS. However, the SWT was no longer forced to turn 135°, but only 45°, and it had begun to increase its speed. However, the SWT was no longer forced to turn 135°, but only 45°, and it had begun to increase its speed.

In November I had measured a speed, at the calving front, for the fastest flow (east side of the SWT flow) and the result was 1.7km, to be compared with a "normal" speed of 1km (see attached picture).  Even though the speeds at the calving front may be higher if there are rifts opening, as was indeed the case, the difference is significant enough and, in any case, the calculated speed at the ESM, which is lower relative to the flow, was 1.25km. This speed fell to 0.6km in the SIS south of Cork, in line with the speeds of other times.

For the rest the old way of working of the SWT and SIS was not yet upset.

But towards the end, following the Cork's shift, the pressure that the Cork exerted on the SIS quickly weakened: not only did it weaken, but it also shifted more and more to the SWT.  And that's when SR2 appeared.

After the calving more MIS action on the SWT and even on the western part of the SIS, if not on the margin (we'll see that in another post).
And it is on this occasion that SR1 also opens up in the middle of the SIS and rapidly expands to the ESM as well.  The fact that they both open in the middle of the SIS on the ESM side and extend to the ESM and that the most marked part is on the ESM side is the signature of the forces that generate them.

I attach:
> an image of the speeds indicated not only by color, but also by speed level lines, one line every 0.1km/y. I have added to this image:
 >> the glacier and SWT shear margin notations
 >> the current calving front (in pink)
 >> the dividing line between SWT and TG (in yellow)
NB: As soon as possible I'll recalculate the speeds based on the most recent images, to check if there are already some new features.
click to zoom in

> an animation related to the ESM based on the Sentinel2 images of 07-03-2018, 02-11-2018, 20-02-2019, ESM 14-09-2019 and 16-03-2020 which shows that in the last months the ESM has moved east. That is to say, the MIS being far away, the SWT is starting to impose its laws
EDIT: In the interpretation of this animation take into account that the ESM is moving northwards

> an animation relative to SR2 with images between 27-12-2019, date of appearance of SR2 and 01-02-2020, the date of the last image before calving (5 images; twice click to animate and zoom in)

> an animation relative to SR1 and SR2 with images between 11-02-2020, first image after calving, and date of appearance of SR1 and 16-03-2020 the date of the last image (3 images; twice click to animate and zoom in)

And in the next post (limit of 4 images):
> A zoom relative to the first appearance of SR2 (27-12-2019)
> A zoom relative to the first appearance of SR1 (11-02-2020)

A post on an analysis of the forces exerted on the Cork2 will soon follow.
« Last Edit: March 27, 2020, 01:08:02 AM by paolo »

paolo

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Re: PIG has calved
« Reply #2015 on: March 27, 2020, 12:32:08 AM »
attached the last two images:
> A zoom relative to the first appearance of SR2 (27-12-2019)
> A zoom relative to the first appearance of SR1 (11-02-2020)
twice click to zoom in
« Last Edit: March 27, 2020, 12:37:47 AM by paolo »

paolo

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Re: PIG has calved
« Reply #2016 on: March 27, 2020, 05:56:18 PM »
Attached an analysis of the Cork2 based on a satellite image of 16/03:
In green the center of rotation of the Cork2, its base and the trajectory, due to the rotary motion, of the current point of contact between Cork2 and the iceberg in the south which pushes it (here named A)
In red the movement of A as well as the corresponding pressure on the Cork2
In orange the decomposition of this pressure according to the direction towards the centre of rotation and its orthogonal direction.
I see three possible origins of the pressure from Cork2 on its base and therefore on the SIS:
> the fact that the pressure of A is not orthogonal to the direction towards the center of rotation (see decomposition)
> the fact that the base on the side opposite the centre of rotation must deform to allow rotation (but the deformations required are minimal)
> and probably the effect induced by the friction between Cork2 and A: indeed the two contact surfaces of Cork2 and A move one relative to the other, the direction of the rotational movement of the point of contact of Cork2 not being parallel to the movement of A.
All these effects exist, but are not major, and the history of SR1, which originated far from the base of Cork2 and has expanded and widened especially on the SWT side, clearly shows that they are not the main players and that, at most, they have contributed marginally.
As far as SR2 is concerned, it is obvious that there are no other actors than the SWT.

Stephan

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Re: PIG has calved
« Reply #2017 on: March 27, 2020, 06:47:32 PM »
When I months ago named this iceberg "Cork II" I couldn't imagine how famous it would become...
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Tor Bejnar

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Re: PIG has calved
« Reply #2018 on: March 27, 2020, 08:02:43 PM »
Stephan,
I'm glad you're calling Cork II an "iceberg" (one which appears to be frozen to a shelf [or something] at one end and is being pushed [and therefore rotated] by another iceberg).  Folks writing about this iceberg and other mélange as 'calving' was pushing my buttons.  Calving is the process of breaking a piece of shelf, glacier or large iceberg off of that shelf, glacier or iceberg, creating a 'new' iceberg.  Icebergs and melange stuck together by fast ice (or the slowly moving equivalent) is just that: stuck together.  When they break away, the fast ice (or whatever you want to call it) breaks or melts and releases the iceberg or melange.

There is, by the way, something called "post-calving mélange" (which, I'm sure, is melange formed from generally small bits of ice that broke off a large piece of ice [like a glacier] that stayed together).  Mélange is a term for both loose ice debris (packed together) as well as frozen-together debris.  The 'original' mélange, in a geological sense, "is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies. Both tectonic and sedimentary processes can form mélange. "
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baking

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Re: PIG has calved
« Reply #2019 on: March 27, 2020, 08:13:20 PM »
Calving is the process of breaking a piece of shelf, glacier or large iceberg off of that shelf, glacier or iceberg, creating a 'new' iceberg.
Tor,
I don't want to quibble over definitions.  Words are just words.  But I think you may be unaware of the history of "Cork II."  It is in fact a piece of the shelf and still attached.  It is surrounded by melange, but it is not melange itself.  I agree that to call a loosening of the melange a "calving" is a misnomer, but when "Cork II" gives way it will most likely be an explosive event deserving of the name.

blumenkraft

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Re: PIG has calved
« Reply #2020 on: March 27, 2020, 08:16:18 PM »
I was wondering about that, Tor.

When melange freezes onto the shelf and then breaks up, it's not a calving. This is what you are saying, isn't it?
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Tor Bejnar

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Re: PIG has calved
« Reply #2021 on: March 27, 2020, 08:45:11 PM »
Thanks, Baking.  B_ (in January) had a GIF showing a long history of the zone (mostly Cork I?) which I called "a crushable re-forming (smaller and smaller) set of ball bearings."  (The surface texture on a recent image of Cork II looked different from the surface on the neighboring shelf, too.)  But I'll accept that 'this' ball bearing never actually separated from the shelf.

Yes, B_, breaking up fast ice (with whatever is frozen in it) is just breaking up fast ice.  It may be a significant event, like the breaking up of ice jams on a river in the spring or the (often) annual release of built-up mélange from a fjord in mid-late summer.
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paolo

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Re: PIG has calved
« Reply #2022 on: March 27, 2020, 09:11:03 PM »
Tor is right about some of the posts, such as those related to iceberg and mixing release  in the NE of Cork2.
For those cases I suggest the term "Release", do you agree?

paolo

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Re: PIG has calved
« Reply #2023 on: March 27, 2020, 10:11:44 PM »
Tor,
to find the origins of the shear-induced texture of Cork2 (caused by the MIS), I propose a two-year history of the Corks: Cork and Cork2

paolo

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Re: PIG has calved
« Reply #2024 on: March 27, 2020, 10:51:53 PM »
I had already posted a recent and very detailed bathymetric image of the PIG, but it did not cover the inside of the PIG.
I just found this image with the entire PIG and, thinking it could be useful to others, I am sharing it with you. In this picture the division between PIG, SWT and TG is indicated.
I have added the name to the SWT and the area that supplies the NIS (yellow).

twice click to zoom in

Tor Bejnar

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Re: PIG has calved
« Reply #2025 on: March 28, 2020, 01:04:43 AM »
Thanks, Paolo.  Excellent GIF showing where the limits of the texture 'has always been'!

Although I glance at this thread daily, I don't study the contributions, and obviously miss a great deal.  I appreciate you (plural = 'you-all') correcting with straight forward explanations, etc., my occasional misstatements.
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baking

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Re: PIG has calved
« Reply #2026 on: March 28, 2020, 04:24:41 AM »
paolo,
You keep posting images that prove my point.  I couldn't help but notice this one.

paolo

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Re: PIG has calved
« Reply #2027 on: March 28, 2020, 07:28:25 AM »
Baking,
not at all, the two rifts clearly have opposite signatures.
The similarity, to a casual look, comes from the fact that the directions are parallel.
But they're reversed and you can see that

twice click to zoom in

EDIT
PS: it's a world that's changing completely and we mustn't be blinded by the past.

PS2: look at the whole and each time carefully consider the scene and the actors of the moment.
« Last Edit: March 28, 2020, 07:36:51 AM by paolo »

Stephan

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Re: PIG has calved
« Reply #2028 on: March 28, 2020, 09:35:50 AM »
Tor,
to find the origins of the shear-induced texture of Cork2 (caused by the MIS), I propose a two-year history of the Corks: Cork and Cork2
Thank you paolo for this impressive series of the development of the Cork / Cork II area. I looked at the origin of SR2 which was clearly developed from a "depression" of the SIS, visible by the different shading of the area. I compare this with the actual development of the SWT, where I found a comparable "precursor" that I posted yesterday. In contrast to that the position of SR1 could not be detected by a "precursor depression".
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paolo

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Re: PIG has calved
« Reply #2029 on: March 28, 2020, 10:47:47 AM »
Release updates of mini icebergs and ice mixture

Animation from 25/03 to 28/03 (Sentinel1 low resolution)

paolo

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Re: PIG has calved
« Reply #2030 on: March 28, 2020, 11:22:32 AM »
Stephan,
I have summarized the two cotraints applying to the shear margin.
I may be wrong, but I do not think that the structures we see on the SWT are strictly and directly related to the rifts in the SIS, although there may be an indirect link.

tybeedave

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Re: PIG has calved
« Reply #2031 on: March 29, 2020, 10:34:21 AM »
paolo,

I could wear our my mouse clicking 'like' on your posts.

ty so very much for your excellent work

td
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baking

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Re: PIG has calved
« Reply #2032 on: March 29, 2020, 04:25:03 PM »
Here is another Sentinel-1 6-day GIF of "Cork II" and the Southern Shear Marging.  This is getting repetitive.

Stephan

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Re: PIG has calved
« Reply #2033 on: March 29, 2020, 05:45:30 PM »
The gap between Cork II and the SIS is widening and widening. Iceberg "A" keeps pushing and won't stop doing so.
I wonder whether the little iceberg in the NW of Cork II helps it maintained and prevents its calving from SIS?
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Re: PIG has calved
« Reply #2034 on: March 29, 2020, 05:51:44 PM »
I don't know, Stephan, but if it had any 'power' over Cork II, would it not function as leverage, popping it off of the SWT even more?

BTW, you can nicely see how the current is active, taking melange with it in the latest hi-res.
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paolo

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Re: PIG has calved
« Reply #2035 on: March 29, 2020, 06:12:25 PM »
I had prepared a commented animation, but Baking preceded me.
I publish it anyway for the added information.
I used the images from the 17th and today, with 12 days interval to highlight residual movements. I added an arrow on a reference point of the Cork2 and another arrow on a reference point of the iceberg A, the iceberg east of the Cork2, to show the shift of the Cork2 relative to A.
The images are aligned with the eastern part of the SIS to show the residual motion of the western part of the SIS, motion induced by the SWT drive.
As far as Cork2 is concerned, it should be remembered that the modest pressure of Cork2 on the SIS, whose origin I described in a previous post, is sufficient to keep it attached to the SIS. A similar speech can be made for the small iceberg B in the west of Cork2 (B is irrelevant for the rest and I only mention it as a curiosity).

The image is very zoomed, click twice to animate and zoom in.

IceConcerned

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Re: PIG has calved
« Reply #2036 on: March 30, 2020, 04:35:02 PM »
In the mean time, a new calving occurred on the NIS

paolo

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Re: PIG has calved
« Reply #2037 on: March 30, 2020, 05:50:06 PM »
Thank you IceConcerned,
It's the demonstration that many eyes can see better than two...  ;)
I attach an animation based on three high-resolution Sentinel1 images:
> 08h46m-29-03
> 04h35m-30-03
> 09h26m-30-03
Remarks :
> Relative to the NIS this is a significant calving
> NIS calvings are much less explosive than MIS calvings, with less tension here.

EDIT: most likely there were two calvings, even if they were close together: the small iceberg first and the big one afterwards.


twice click to animate and zoom
« Last Edit: March 30, 2020, 05:56:12 PM by paolo »

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Re: PIG has calved
« Reply #2038 on: March 30, 2020, 08:24:20 PM »
Very much welcome Paolo, and thanks for the animation I concur with your interpretation.
I take this opportunity to thank you for your very didactic and (in my opinion) mechanically very accurate posts, it is a real delight

Coming back to the NIS I think that the crevassed chunk just south of the last calving is very fragilised and the cracks there have widened since your last post on the matter

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Re: PIG has calved
« Reply #2039 on: March 31, 2020, 06:26:57 PM »
High winds tomorrow forecasted.
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paolo

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Re: PIG has calved
« Reply #2040 on: April 04, 2020, 04:34:14 PM »
No, it's not to announce that the Cork2 has left the ice shelf...  ;) ;D

It is only to communicate a small observation, really small, but one that may be useful in our future observations:

Today there was a strong SE wind and in the image you can see the ice trails.
But in places protected from the wind we can see ice trails pushed only by the current and therefore having another direction.

blumenkraft

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Re: PIG has calved
« Reply #2041 on: April 04, 2020, 04:45:15 PM »
If the forecast is correct, the high winds will prevail for the upcoming (4-5) days.
Everyone who can must self-isolate.

grixm

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Re: PIG has calved
« Reply #2042 on: April 05, 2020, 10:49:24 AM »
Some stuff has happened since the forum went down yesterday.

Small calving in the north near Evans Knoll (click to play gif).

Discharge/movement near the cork. Also it looks like the small berg in front of the cork has somewhat separated and is no longer connected to the cork, just the ice sheet (barely).

And a new rift on the Southern Ice Shelf, in between the two others.

paolo

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Re: PIG has calved
« Reply #2043 on: April 05, 2020, 11:58:07 AM »
Grixm,
Good call for calving up north.

I had already prepared an animation related to SSM that I am adding to your post.

Notes on the animation (6 day):
The alignment point is the east side of the SIS.
Cork2: the pivot moved later on
B: is no longer in contact with Cork2 and is almost completely detached from SIS. He can only calve from one moment to the next.
C: because of D it's spinning
D: because of C its tip is moving south (get closer to SIS)
SIS: the west side, driven by the SWT, is moving to the N

Edit : The icebergs A, B, C and D are indicated in the animation.

Twice click to animate and zoom in
« Last Edit: April 05, 2020, 12:09:19 PM by paolo »

baking

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Re: PIG has calved
« Reply #2044 on: April 05, 2020, 11:59:12 AM »
Here's a 6-day GIF of "Cork II" and the new "Rift 1.5" in the Southern Ice Shelf.

baking

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Re: PIG has calved
« Reply #2045 on: April 05, 2020, 12:14:42 PM »
Also, not sure why, but this 6-day GIF of the Northern Shear Margin shows a little more detail of the calving and suggests that additional calving will be soon to follow.

blumenkraft

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Re: PIG has calved
« Reply #2046 on: April 05, 2020, 12:17:14 PM »
How in hell can Cork II and B stand?

There is strong wind attacking from above. There is a strong current attacking from below. There is A pushing and pushing.

I genuinely don't understand this robustness...
Everyone who can must self-isolate.

paolo

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Re: PIG has calved
« Reply #2047 on: April 05, 2020, 02:42:47 PM »
Blumenkraft,
"A" can't induce a speed of "Cork2" greater than his, the wind is negligible, considering the masses involved.What intrigues me is the current and especially for B which is already practically detached from the SIS ....

paolo

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Re: PIG has calved
« Reply #2048 on: April 05, 2020, 04:22:55 PM »
I wanted to check on the small calvings between the NIS and the NEIS.

This area around the Evan's Knoll ice rises is undergoing the stresses induced between the SWward movement of the NIS (driven by the Larter Glacier) and the NWward movement of the NEIS (driven by the MIS).

Attached a high-resolution Sentinel1 animation with a 24-day interval.

Double-click to animate and zoom in

Stephan

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Re: PIG has calved
« Reply #2049 on: April 05, 2020, 09:02:41 PM »
Thank you all for these interesting and very detailed updates.

It seemed to me that at the SE flank of Cork II (NE from the attachment point of iceberg A) a minor calving had taken place. I checked the area with the latest Sentinel picture from March 16; at that place there has been thicker ice mélange on March 16 which now seemed to have followed the other thinner mélange that left the "bay" some days ago, so there was no "real" calving.

On the eastern edge of SWT the rift seemed to have widened even more (grixm's gif), bit this may be due to different angles of the satellite; I don't know.
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