Halley Base and Brunt Ice Shelf

[grixm]

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.

[interstitial]

Even at slow speeds i bet the forces involved in a collision are impressive.

[Stephan]

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!

[FredBear]

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.

[crandles]

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]

Thank you for that link, very interesting.

[grixm]

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]

It does appear so, but certainly could be an artifact.

[Espen]

March 6 - March 18 2021:

Please click to enlarge and animate!

[Stephan]

...a little bit confused at first glance.
It looks like this is a mirror image, N to the left and W up ?!?

[Espen]

...a little bit confused at first glance.
It looks like this is a mirror image, N to the left and W up ?!?

[grixm]

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]

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]

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 

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

[baking]

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]

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]

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?

[baking]

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]

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.

[paolo]

Baking,
Thanks for the information.

Espen,
Can you please mirrored your images?

[Espen]

Baking,
Thanks for the information.

Espen,
Can you please mirrored your images?

What do you mean?

[paolo]

Espen,
Below is your image and the correct image

[Espen]

Here is a new animation including March 7 - March 19 2021:

Please click on image to enlarge and animate!

[paolo]

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]

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]

Does my eye spy more cracking?

[paolo]

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]

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.

[interstitial]

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]

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]

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.

[interstitial]

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]

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

[interstitial]

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.

[grixm]

The recently calved iceberg is speedily on the move, and it grazed/crashed into the tip of the ice sheet on its way south-west. Some debris came loose from both the sheet and berg. See attachment 1.

Maybe it was because of this impact, but the cracks seems to have grown a bit further since 2 weeks ago. See attachment 2.

[FredBear]

The BBC reports the movement of A74, says it has not caused the nascent Brunt iceberg to calve yet:-

https://www.bbc.co.uk/news/science-environment-58192348

[iwantatr8]

So I think it may have finally calved but the image is being processed now....

a quick look at polarview shows that the critical IW sentinal image is missing from the pass on the 15th...

https://www.polarview.aq/antarctic
I guess we will need to wait for this to be released...

[Tealight]

Sentinel 2 captures the ice shelf again.

Even though there are thin clouds you can still see below. The crack made a nearly 90 degree right turn towards the McDonald Ice Rumple and the so called "Halloween crack".

The other nearby exiting crack extending from the ocean is only 1.7km away. The "Halloween crack" is still 3.8km away.

Hard to say if it was caused by a collision with the iceberg A74 or a natural change in direction.

[paolo]

As expected the tip of the "future iceberg", linked to the Halloween Crak, has just calved producing two icebergs. This "future iceberg" has almost lost all contact with the McDonald Ice Rumple
Posting:
> today's image (Sentinel1 low resolution)
> and the Sentinel2 images of 24/09

Click to enlarge

[grixm]

Two sentinel-2 comparison animations between today and March.

[paolo]

Update of 30/09 (using the Sentinel2 image published by Grixm):
Calving of a small iceberg: the junction between the McDonald Ice Rumple and the "future Iceberg" becomes ever weaker ....
But for the calving of the "future Iceberg" it will be necessary to wait for its detachment to the east, and that is another story ...

I attach the update of the image I published yesterday

Click to enlarge

Update:
I wanted to add an animation based on the Sentinel2 images of 9/24 and 9/30, which allowed me to see that the new calving also includes the part, very fractured coast McDonald Ice Rumple and not only the splintering of the joint between The "future Iceberg" and the McDonald Ice Rumple, as I had indicated in the first image

Click to enlarge animate

[FredBear]

The main Chasm 1 crack looks to have widened on today's clearer Worldview - is the iceberg slipping out to sea or is it just an artifact    .     .     .    ? (The fast-ice to the south had disappeared sometime after 19/12/2021).

P.S. The cloud formations in the downloaded image are not the same as I saw in Worldview and any change in Chasm 1 nothing like so obvious - updated already???

[FredBear]

No significant changes to the Brunt Ice Shelf to date - another false alarm from me! Sorry.

D28 is heading around the north-west of the Stancomb-Wills Glacier tongue to join a number of other icebergs (paolo mentions "the armada" in  Antarctic Icebergs « Reply #458) which had broken off Queen/Dronning Maud Land during the winter, drifting around the area in the video mentioned below:-

I did find the following article on ice shelves - and on the Brunt page, at the bottom there is a YouTube about icebergs drifting near Brunt. I think most of these were melting in the South Atlantic in 2019/20 having traveled west across the top/north of the Weddell Sea?

http://www.cpom.ucl.ac.uk/csopr/brunt/index.html

B15AA, having come down the coast from the north, sailed westwards towards the Antarctic Peninsular by 2020, whereas A74 calved from the Brunt Ice Shelf earlier last year and has traveled south, following the coastline. I wonder what the "Armada" will do? (Also will any impact the potential iceberg, Brunt West, vacated by the Halley base?).

[paolo]

Still no S2 image, so I offer you a high definition S1 image.

It seems that the fracture is now almost complete.To better identify it, the attached image has been enlarged (200%)

To be watched ...

To display it with the right definition click twice

[paolo]

Today a nice Sentinel2 image:

I'm sorry for myself, but the rifts are still a long way from joining and we'll have to wait a lot longer

Click to enlarge

[FredBear]

It seems the British Antarctic Survey continues to operate Halley as a summer station with winter activity automated.
A recent small blog item with links to Halley operations:-

https://www.bas.ac.uk/blogpost/blog-happy-at-halley

[grixm]

I just noticed this crack here, doesn't look like anyone has reported on it before, even though it has been visible for at least a few months. It has been growing over the antarctic summer. It's located north of the "Halloween crack", next to the big calving last year. It's about 30% of the way to connecting with the Halloween crack which would result in another big calving.

[paolo]

Grixm,
Indeed is interesting and to follow.
Attached is a high definition S1 image (1px=10m) of today as a first base for the follow-up during the next months of the southern winter (more S2). The new fracture is well visible.

Very large image (1600x900 px, that is 16x9 km),
Click twice to enlarge completely

PS : the fracture starts at the top left and the "Halloween crack" is on the right

[Andreas T]

This is a sentinel 2 image from 17.2 in NDWI for better contrast.
The crack look slightly longer than in January. But of course it is unlikely that breaking this last stretch of unbroken ice of less than 1km would make the huge piece of ice shelf drift away suddenly. Something else must be holding it in place, either some grounding or refrozen ice along older parts of the crack.

[paolo]

This is the S2 image from 13/03/2022 (1px = 10m; overall dimensions 10 x 7 km), most likely the last image of the season.

Click to enlarge