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Author Topic: Halley base shut down and new crack in Brunt shelf  (Read 46670 times)

grixm

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #150 on: March 14, 2021, 09:48:19 PM »
Today the iceberg was pushed back into the shelf. I don't know if this image is from right before or after it undoubtedly made contact, but I wonder if the impact affected the other cracks, like a battering ram.

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #151 on: March 14, 2021, 11:34:34 PM »
Even at slow speeds i bet the forces involved in a collision are impressive.

Stephan

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #152 on: March 15, 2021, 08:12:33 AM »
Just imagine you were sitting in a little boat cruising close to the new calving front and then the new iceberg moves back where it came from... Outch!
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FredBear

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #153 on: March 15, 2021, 10:46:48 AM »
There will be bits of icy debris (like "growlers") that would soften any impact by being crushed first, creating localised damage to both 'berg and ice shelf before any dislocation of the shelf. We will see     .     .     .
P.S. The iceberg seems to have moved out again today in the first image from Worldview.
« Last Edit: March 15, 2021, 04:02:13 PM by FredBear »

crandles

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #154 on: March 15, 2021, 04:31:11 PM »
Just imagine you were sitting in a little boat cruising close to the new calving front and then the new iceberg moves back where it came from... Outch!

My reaction was who would be stupid enough to do that.

Well shows what little I know:
https://www.bbc.co.uk/news/science-environment-56404142
Mega-iceberg A74: German ship squeezes through narrow ice channel

Stephan

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #155 on: March 15, 2021, 08:47:04 PM »
Thank you for that link, very interesting.
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grixm

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #156 on: March 19, 2021, 08:59:10 AM »
Hmmmmm.. Is it just me or has the main crack grown?

In the latest S-1 image, compared to the last one from the exact same angle 12 days ago, you can see a new/stronger line in between the previous two crack tips. I don't see exactly this line on any of the other S-1 images from other angles in between the two dates, either.

Or am I just being fooled by random image compression artifacts again?

oren

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #157 on: March 19, 2021, 10:20:38 AM »
It does appear so, but certainly could be an artifact.

Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #158 on: March 19, 2021, 12:00:33 PM »
March 6 - March 18 2021:

Please click to enlarge and animate!
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Stephan

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #159 on: March 19, 2021, 09:11:16 PM »
...a little bit confused at first glance.
It looks like this is a mirror image, N to the left and W up ?!?
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Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #160 on: March 20, 2021, 08:21:57 AM »
...a little bit confused at first glance.
It looks like this is a mirror image, N to the left and W up ?!?

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grixm

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #161 on: March 20, 2021, 09:02:41 AM »
New close-up s-1 images, but it's still very hard to say if the crack grew or not.

On the other hand, there is some activity east of the knoll where ice is pushed into it, some smaller bergs might calve there soon.

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #162 on: March 20, 2021, 11:05:20 AM »
Grixm,
I had already prepared the animation for the Chasm1 and I saw that you had already published your animation.
However, I decided to publish mine as well (also aligned with the McDonald Ice Rumple, the only difference being that I enlarged the scale of the image by a factor of 2, in my image one pixel corresponds to 10m) because this animation can help to show that Chasm1 is indeed connecting to the rift on the Ice Rumple side and that the calving should not be long in coming (during April, or even at the end of March)
As for the Hallowin Crack, indeed the part of the shelf in contact with the Ice Rumple is being pushed northwards, and the whole block north of the rift should start to separate completely from the shelf at least in its western part, but it could even calve completely very soon.
There is nothing to say, after months of waiting, now this shelf is moving and moving fast...


Click to animate (double click to enlarge completely)

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #163 on: March 20, 2021, 08:15:23 PM »
Espen,
Stephan was not confused by the fact that North was on the left and not on top, but by the fact that the image is mirrored (e.g. in the second posted image North is on top and West is on the right...)
But it's true that if you look at it from Denmark, i.e. from the bottom relative to the surface, and not from space, i.e. from the top, this is indeed what you see  ;) ;D

I would like to take this opportunity to welcome you to Antarctica, your contributions will be much appreciated

baking

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #164 on: March 20, 2021, 08:41:30 PM »
Espen is probably using the raw Sentinel 1 data.  Checkout https://www.polarview.aq/antarctic for images that have been processed to conform to polar coordinates and adjusted for the elevation and the shape of the earth.

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #165 on: March 20, 2021, 08:46:01 PM »
Baking,
I, Grixm and all the others also use Polarview, but we don't mirror the image

PS: if I look north, then Chasm1 must be on the left and Hallowin Crack on the right

Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #166 on: March 20, 2021, 09:55:30 PM »
While doing the first animation I noticed a new smal crack but I did not think it was worth reporting, it is seen expanding in the red circle below (animation):

"I would like to take this opportunity to welcome you to Antarctica, your contributions will be much appreciated"
When is the next flight?
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baking

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #167 on: March 21, 2021, 06:06:20 AM »
Baking,
I, Grixm and all the others also use Polarview, but we don't mirror the image
I can tell you use Polarview, if only because of the distinctive blue tint.  Espen is using the raw level-1 files from ESA that are grayscale and are mirror image and follow the satellite orbit.  They appear as a mirror image because the data is presented top-down and left-to-right as it is acquired.

Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #168 on: March 21, 2021, 08:47:00 AM »
Yes Baking is right, I only use raw data from Sentinel 1 and 2 and the various Landsat projects.
I find it easier to work with.
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paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #169 on: March 21, 2021, 09:06:09 AM »
Baking,
Thanks for the information.

Espen,
Can you please mirrored your images?

Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #170 on: March 21, 2021, 09:27:47 AM »
Baking,
Thanks for the information.

Espen,
Can you please mirrored your images?

What do you mean?
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paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #171 on: March 21, 2021, 10:25:00 AM »
Espen,
Below is your image and the correct image

Espen

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #172 on: March 21, 2021, 11:42:43 AM »
Here is a new animation including March 7 - March 19 2021:

Please click on image to enlarge and animate!
Have a ice day!

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #173 on: April 01, 2021, 12:05:10 PM »
In the Sentinel1 image of 31/03, Chasm1 seems to be joining the northern front (image S1 enlarged 1:2)
I also report a hint of a rift extending Chasm1 further upstream.

Click to enlarge

iwantatr8

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #174 on: April 07, 2021, 01:41:45 PM »
Lovely new image from the 5th on polar view.

more Crack 1 and halloween crack movement around the MIR, nothing momentus yet but certainly more movement.

it will be interesting what happens when much of the shelf is detatched from the MIR...

last time it happened there was a significant accelleration of the shelf until it reattached.

grixm

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #175 on: April 11, 2021, 05:25:32 PM »
Does my eye spy more cracking?

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #176 on: April 11, 2021, 10:05:42 PM »
I present a commented animation (consistent images from 30/03 and 11/04) showing :
> That the Chasme1 rift is narrowing slightly, at least in its northern part. I had already had this feeling when I looked at the Grixm animation and I wanted to know for sure. Especially when zooming in it seems clear to me and it can't be an effect induced by different orbits, the orbit being the same. The only explanation I can see is a stronger push to the north of the upstream part of the Ice Shelf, induced by the recent calving. This could, perhaps, delay the calving, but I don't think by much.
> The complex behaviour of the tip of the future iceberg north of the Halloween Crack. It will burst soon and induce, afterwards, the calving of this new Iceberg!

Click to animate


ADD: to see some of the effects better, zoom in

FredBear

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #177 on: April 12, 2021, 01:59:40 AM »
Yes, the crack appears to be narrowing which implies that the nascent iceberg is resisting being shoved out to sea, perhaps tending to rotate?
A question:- But are we pushing the images to their limits - the "borders" of many features "fluff" in and out slightly, perhaps due to lighting?
Thanks again for the updated images that keep us all in touch with developments.

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #178 on: April 12, 2021, 06:20:28 AM »
I hope I get the names right. The crack that grows toward the haloween crack alternately looks to have cracked and not cracked several times. The issue is even if a new burg forms from the ice shelf it is grounded near the shelf edge and can not move anywhere even if the crack finishes. The only real hope of that ice floating free is if it eventually grinds off a few houndred meters elevation of rock. While the forces involved are probably sufficient I would not even venture a guess what the time would be other than not in the next few years. The pressure release when the new iceburg formed may result in some redirection of ice flow as the shelf is probably still under tension.

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #179 on: April 14, 2021, 06:16:00 PM »
I disagree with the following comment:
"The issue is even if a new burg forms from the ice shelf it is grounded near the shelf edge and cannot move anywhere even if the crack finishes. The only real hope of that ice floating free is if it eventually grinds off a few hundred meters elevation of rock. While the forces involved are probably sufficient, I would not even venture a guess what the time would be other than not in the next few years. The pressure release when the new iceberg formed may result in some redirection of ice flow as the shelf is probably still under tension."

Indeed:
* In Antarctica all the underwater peaks have been extensively eroded during the ice ages, there are no peaks that can break off and be swept away by the pressure of a glacier and eroding takes geological time.
* A friction point does not block the advancement of an ice shelf (or a glacier), it only slows it down, and can eventually deform and crack the ice shelf and divide its flow in two, see for example the action of the McDonald Ice Rumple.
* The Brunt Ice Shelf moves westwards in its entirety, even if the speed of its southern part (Chasm 1 side) is more accentuated (see for example the animation below based on the images of the end of the southern summers 2001-2020, the 2002 being missing)
* The Brunt Ice Shelf meets the McDonald Bank to the west which has maximum heights that can touch the thicker parts of the ice shelf. There is therefore an irregular friction that is not visible on the surface. This has nothing to do with the action of the McDonald Ice Rumple (in the animation the last image contains the geographical information).
* The Brunt Ice Shelf last calved between 1915 and 1958 and most probably calved shortly before 1958 and the current front line already exceeds the hypothetical line that the front had at the time of calving (see the two images posted below)
* The partial (and most likely temporary) shrinkage of Chasm 1 on the McDonald Ice Rumple side, which I mentioned in my previous post, may be due to a temporary increase in friction on the McDonald Bank side and/or an acceleration of the left side of the Halloween Crack (related to the recent calving? ) and/or to an action of the southern part of the tip of the block to the north of the Halloween Crack (indeed this part, which is blocked by the McDonald Ice Rumple, seems, relative to the other elements, to rotate counterclockwise and could therefore exert a pressure towards the south and contribute to this narrowing). This would therefore be a temporary phenomenon.

In any case there will be calving, even if we cannot predict whether in a few weeks, months, or in 2022 (or even in 2023).
What will be important to observe during the calving will be the new front line created by the calving: if it appears as a point towards the McDonald Ice Rumple, with the rest of the front well to the east, then the future break-up of this pinning point is on track and, consequently, the break-up of this ice shelf as well.

Click to animate and to enlarge the images

oren

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #180 on: April 15, 2021, 05:25:52 AM »
Paolo, thanks for the long term animation and the analysis. Just a little comment, it is best to make the delay on the last frame larger, as it is hard to read all the text in such a short time.

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #181 on: April 15, 2021, 02:20:17 PM »
I disagree with the following comment:
"The issue is even if a new burg forms from the ice shelf it is grounded near the shelf edge and cannot move anywhere even if the crack finishes. The only real hope of that ice floating free is if it eventually grinds off a few hundred meters elevation of rock. While the forces involved are probably sufficient, I would not even venture a guess what the time would be other than not in the next few years. The pressure release when the new iceberg formed may result in some redirection of ice flow as the shelf is probably still under tension."


the images are an overlay of the research at from https://tc.copernicus.org/articles/13/545/2019/
and a Sentinel 1 image.


In the images the alternating black and white line is the grounding line and the green circles are potential pinning points. What I meant was given the grounding line and potential pinning points. The section of Ice shelf shone has mostly (perhaps completely) cracked from main shelf it is not going to float off anytime soon. From what is visible it looks like it will break off any day but with bathymetry information it is unlikely to ever do that. I do not think there is anything with what I meant to disagree with though without the images and reference article it may not have been clear what I meant.

paolo

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #182 on: April 15, 2021, 09:34:56 PM »
Interstitial,
1) The authors do expect a calving event and study the possible consequences: "In the immediate future, this will be determined by the direction of propagation of the tip of Chasm 1, the dynamics and geometry of the expected calving event, and the subsequent response of the remaining ice shelf."

2) The black and white contour of your first image, is the predicted grounding line (see my first posted image; in this image the current grounding line is line 4 in white).

3) The green circles indicate possible past and present pinning point (see my second posted image). Note: If you compare with the second image in my previous post you can see that the 1958 front line is upstream of some of these potential pinning points.

4) As can be seen in the third image posted, again from this same article, the ice shelf is generally too thin to touch the bottom. For the three lines examined see the three lines in red in my second image.

You will find another representation of the McDonald Bank in the fourth picture

In conclusion there is no constant and strong pinning clinging except in the area of the McDonald Ice Rumple.

This does not mean that the iceberg cannot remain pinned for some time after calving (see the example of a recent calving of the PIG, where an iceberg had hung around for some time)

Click to enlarge
« Last Edit: April 16, 2021, 02:57:34 AM by paolo »

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Re: Halley base shut down and new crack in Brunt shelf
« Reply #183 on: April 16, 2021, 07:45:45 AM »
Interstitial,
1) The authors do expect a calving event and study the possible consequences: "In the immediate future, this will be determined by the direction of propagation of the tip of Chasm 1, the dynamics and geometry of the expected calving event, and the subsequent response of the remaining ice shelf."

2) The black and white contour of your first image, is the predicted grounding line (see my first posted image; in this image the current grounding line is line 4 in white).

3) The green circles indicate possible past and present pinning point (see my second posted image). Note: If you compare with the second image in my previous post you can see that the 1958 front line is upstream of some of these potential pinning points.

4) As can be seen in the third image posted, again from this same article, the ice shelf is generally too thin to touch the bottom. For the three lines examined see the three lines in red in my second image.

You will find another representation of the McDonald Bank in the fourth picture

In conclusion there is no constant and strong pinning clinging except in the area of the McDonald Ice Rumple.

This does not mean that the iceberg cannot remain pinned for some time after calving (see the example of a recent calving of the PIG, where an iceberg had hung around for some time)

Click to enlarge



I read a previous paper that talked about  two grounded areas near the tip of the brunt ice shelf and showed a more defined underwater ridge between the Mcdonald Ice Rumple and the tip of the brunt Ice shelf. As I recall its bathymetry appeared much more precise. I searched for it and found this more recent paper. At first glance the images seemed to show what I read about before so I used them without reading the paper. Without the older paper I can not check to see whether my understanding of it was flawed or if something has changed since then.


I concede that this paper does not support what I was saying.