Halley Base and Brunt Ice Shelf

[interstitial]

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.

It is grounded on the leading edge.

[paolo]

I wanted to give an update on the future detachment of the BIS Iceberg.
To show the situation I focus on the McDonald Ice Rumple and I use the Sentinel1 high resolution images from 01/04/2022 to 12/06/2022, one image every 12 days (missing the image from 13/04)
For the alignment of the tiff images I use QGIS and I added as a reference the coastline of SCAR_ADD-Antarctic Digital Database (2020)
You can clearly see that there are three distinct blocks:
block A, i.e. the future large iceberg
block C, i.e. the part of the ice shelf that will remain
and block B, a small block wedged between the two, which under the pressure of A tends to turn slightly clockwise. When A calves, this block should also break away.
In any case, the widening of rifts A (between A and B) and B (between B and C) are impressive.
Now the whole thing can break completely at any time (or not  )

Click to animate (and click a second time to enlarge the images further)

[Phil.]

Approximately what size would that iceberg be?

[paolo]

These are the approximate estimates
The break line between block B and C is partly hypothetical

Click to enlarge (possibly twice for maximum extent)

PS: In the image of my previous post there was, at the bottom left, the scale (coloured black)

[paolo]

A small calving occurred at the McDIR (McDonald Ice Rumples), just next to the point of support on the McDIR of the second future iceberg (east of the McDIR).

In itself it is very small (scale bottom left), but it occurred in a critical point (the detachment of the future iceberg from the McDIR would produce an acceleration of its calving) and that is the reason for this report

In the animation, based on the images of 19/06 and 01/07, I use the notations of the previous post (blocks A, B and C) and add block D, the second future iceberg.

click to animate

[grixm]

Especially large widening of the rift in the most recent radar image. Attached is a comparison between the 30th and 18th of July.

[Stephan]

Thank you for that update.
Looks to me as if the great calving is happening in the not too distant future...

[crandles]

Does that cork shear in half?

continue rolling for a while then most of it come out with the big iceberg?

~20% shear off?

crumble into several or many pieces?

or something else?

[paolo]

I'm updating the animation using images from 01/04/2022 to 31/07/2022, one image every 12 days (the image from 13/04 is missing).
Don't neglect block "D" (see last image for notations) and the rift that separates it from C which is extending south of McDIR.
It is the pressure of this block that caused the two small calvings on the McDIR side. I wonder if at the end of the process (calving of A, B and D) the McDIR will not become detached from the BIS.

Click to animate and click again to enlarge (image 1500x1500px.)

PS: The tip of D is twisting and I have just noticed a very small calving 3km upstream (east, sea side) from McDIR

[IceConcerned]

It appears on the latest S1 SAR image that blocks A and B are ready to go.
As for block D, a destruction zone East of the ice rise could be the forebearer of the separation zone with the rise, once the separation eastwards is complete.

[grixm]

It appears on the latest S1 SAR image that blocks A and B are ready to go.
As for block D, a destruction zone East of the ice rise could be the forebearer of the separation zone with the rise, once the separation eastwards is complete.

Btw Sentinel-2 season is here so we have access to much clearer images than radar now.
The crack has extended all the way to the sea. The shelf itself is clearly no longer holding the main iceberg back to any meaningful degree, so it is grounded and/or held in place by fast ice, as we already mostly knew.

[FredBear]

Worldview today - is it clouds or the expected calving - something to watch    .     .  1st image today, will be cleaned up later?

[kassy]

Antarctic: Giant iceberg breaks away in front of UK station

A big iceberg roughly the size of Greater London has broken away from the Antarctic, close to Britain's Halley research station.

Sensors on the surface of the Brunt Ice Shelf confirmed the split late on Sunday GMT.

Currently, 21 staff are at Halley, maintaining the base and operating its scientific instruments.

...

Halley is positioned some 15km from the line of rupture.

BAS has an array of GPS devices in the area that relay information about ice movements back to the agency's HQ in Cambridge.

Officials will be inspecting satellite imagery when it becomes available. They will want to see that no unexpected instabilities emerge in the remaining ice shelf platform that holds Halley.

A similar sized berg, known as A74, calved in February 2021 further to the east. At the time, it was thought that its departure might initiate the latest breakaway, but these events are beyond any confident prediction.

Where exactly is this?
It is on the Brunt Ice Shelf, which is the floating protrusion of glaciers that have flowed off the Antarctic continent into the Weddell Sea. On a map, the Weddell Sea is that sector of Antarctica directly to the south of the Atlantic Ocean. The Brunt is on the eastern side of the sea. Like all ice shelves, it will periodically calve icebergs. Prior to this latest berg and A74, the last major chunk to come off the Brunt was in 1971.

Was the breakaway anticipated?
Absolutely. Just not its timing. Scientists continuously monitor any major cracks in the Brunt, and had noticed one particular split - dubbed Chasm One - start to open up again after decades of dormancy. Recent years had seen the propagation of Chasm One accelerate, resulting now in the complete separation of a block of ice that is about 150-200m thick.

...

Just how big is the new berg?
Estimates put it at around 1,550km² - nearly 600 square miles. That's big by any measure. It's city-sized. The job of naming icebergs falls to the US National Ice Center. Because the new block is in the Antarctic quadrant that runs from 0 degrees longitude to 90 degrees West), it will carry the letter "A" in its designation. It's likely to be called A81. The "81" refers to its place in the sequence of major calvings in the region. The similarly sized berg that broke away from the Brunt to the east of Halley was called A74.

...

https://www.bbc.com/news/science-environment-60825387

[paolo]

For the initial announcement (later picked up by the BBC) see the BAS (British Antarctic Survey) website:
https://www.bas.ac.uk/media-post/brunt-ice-shelf-in-antarctica-calves-giant-iceberg/?utm_source=miragenews&utm_medium=miragenews&utm_campaign=news

[solartim27]

BAS posted an image from Suomi
https://twitter.com/BAS_News/status/1617789496048906240?t=605XlHqmMLkVrBwUM5vYfQ&s=19

[grixm]

Bwoah it actually happened 

[HapHazard]

Wow, thar she blows!

[paolo]

I used EO Browser to access the S3 images and discovered the "Enhanced True Color Visualization" display mode which gives better results than the image published above.
In particular the "Cork" Iceberg is better visualized and we can also see that the Chasm1 has generated several other Icebergs (even if some of them may be, in part, thickened fast ice

Click to enlarge the image

I also found a Tweet from BAS with a small animation   

https://twitter.com/i/status/1617859038586482691

[gerontocrat]

Smashing images

https://www.bbc.co.uk/news/science-environment-64390797
The EU's Sentinel-2 satellite has obtained a crystal clear image of Antarctica's new monster iceberg.

The 1,550-sq-km (600-sq-miles) frozen block broke away from the Brunt Ice Shelf late on Sunday GMT.

Its detachment occurred close to Britain's Halley research station, which sits just 20km upstream from the line of rupture.

The base and its 21 occupants are all secure. Officials see no need for an evacuation.

Concerns had been expressed that a major Emperor penguin colony near the breakaway could have been disrupted.

The Emperors breed on sea-ice attached to the coast - so-called "fast ice".

But the new Sentinel-2 picture clearly shows the stains from the birds' excrement, or guano, to be on an ice platform that remains intact.


The guano stains are visible from space

The imagery on this page was processed by Ben Wallis, from the Institute for Climate and Atmospheric Science at the University of Leeds.

click image to enlarge, and click maximise for full size

[paolo]

The S2 image is indeed available.

The overall image being in gerontocrat's post I add three zooms on the Chasm1 and its icebergs and, in a following post, a zoom on the Halloween Crack and a further zoom on the McDonnald Ice Rumple (MIR).

This Ice Rumple, which is a pinning point of the BIS, will be followed very closely !

Click twice to completely enlarge the image

[paolo]

Continued from previous post

Click twice to completely enlarge the image

[FredBear]

Bit of a precarious life for those Emperor chicks if they are not ready to swim, I assume the parents probably have stopped feeding them by now??

Reports are that chicks are mature in December/January so this years brood may have left already - if they haven't they may gain a shorter walk to the water!

[paolo]

During the night we had the first S1 image (low resolution), hence this animation (2000x2000 px)

Click to animate and click again to enlarge the image completely

PS : To these images are added, as I will do systematically, the information relative to the front and grounding lines provided by :
>> MEaSUREs Antarctic boundaries (in green; with data for the years 2007/2009)
>> USNIC_Antarctic Ice Shelf Data (yellow; from early 2019)
>> SCAR_ADD-Antarctic Digital Database (v7.3; orange; from early 2020)
>> SCAR_ADD-Antarctic Digital Database (v7.4; in red; from early 2021)
>> SCAR_ADD-Antarctic Digital Database (v7.5; in purple; from early 2022)
In this sector version 7.3 is no more recent than the USNIC version and is overwritten by it.

[FredBear]

I am continuing to report developments around A81 here as it has not moved far.
The 1st. year fast ice that broke away from the south of the iceberg has crumbled as it drifted south along the coastline.
The main iceberg has started to rotate anticlockwise around its south-eastern tip, allowing the "cork" (reply 220) to slide down the cavity between the iceberg and the remaining old shelf. This may be indicating that the coastal current is likely to push A81 on its way shortly?
There is one larger piece of ice drifting around in circles in the dark sea off Brunt which indicates there is no great impetus for A81 to drift westwards at the moment.

[FredBear]

Monitoring by the BAS has registered that the remaining part of the Brunt Shelf is moving more rapidly:-

https://www.bbc.co.uk/news/science-environment-66685821

[kassy]

The Brunt is an amalgam of ice, about 150-200m (500-650ft) thick, that has come off the Antarctic continent and pushed out into the Weddell Sea.

This buoyant mass has had an outward speed, historically, of 400-800m a year. But there has been a dramatic acceleration, from about 900m a year at the start of 2023 to 1,500m by August.

The data comes from precise GPS measurements around Halley and radar observations by the European Union's Sentinel-1a satellite.

The acceleration follows the calving of two major icebergs from the leading edge of the Brunt - a 1,300-sq-km (500-sq-mile) behemoth called A74, in February 2021, and an equally mammoth slab called A81, in January this year.

A74's impact was minimal but A81 appears to have released the shelf from a shallow section of seafloor that normally pins it in place and slows the seaward momentum.

What is more, these calvings - and there was another smaller one in June - have prompted new areas of stress in the ice shelf.

Prof Luckman said: "The Brunt has lost contact with this pinning point, known as the McDonald Ice Rumples, and, as a consequence, it has speeded up and is thinning. And you can actually now see cracks starting to open up at the grounding line (the zone where ice coming off the continent becomes buoyant), to the west and south of Halley."

Some of the relevant details.

There is no need to quote whole articles but i like it when people at least point out some of the important parts.

[solartim27]

Nice time lapse in this article
https://phys.org/news/2023-09-brunt-ice-shelf-calving-giant.amp

[Often Distant]

It looks like this ice shelf also carries potential to break away at any moment. It seems it could be due this season. If there's still a research base on the floating ice it could be floating away soon.

I attach a couple of animations. The first one focused on the coast. Ice streams are accelerating, breaking in and sliding to the sea. The Brunt Ice Shelf appears to have no stable grounding. The shelf looks effectively separated from Coats Land all across in near a straight line to the old Stancomb-Wills tongue. Note the ice across the tongue behind the land mass top right. It looks like Stancomb-Wills could open wider and alter direction northward with increasing velocity. Rock mass at the point of Dronning Maud Land looks like it is shifting with changing flow dynamics, and it very may well actually be doing what it appears to be doing. It could carry potential to burst open in quite a large sea lifting event of proportions unknown. Ice flow from the continent looks due to alter drastically from all sides.

The second gif zooms out to view the shelf, and the third gif zooms in on the comparatively tiny Dawson-Lambtom Ice Stream at the far right edge of the shelf. The shelf held back much bigger streams.

[Often Distant]

A couple of up to date animations with Sentinel 2 spanning 7 years. The first one is a zoom in on the ice rise named McDonald Ice Rumples, which may no longer be rumples since it mostly detached from the ice shelf that formed it. An unpinning point. The second gif looks at Stancomb-Wills. Brunt is brittle, slipping more than little.

[Often Distant]

Further update. Firstly Sentinel 1 of the previous 12 months looping forward and reverse like a breathing lung, with an image from 2016 added for comparison. The second gif uses Sentinel 2 zooming in south west, back and forth 6 years. The other two are across to the eastern side at the divide with Riiser-Larsen Ice Shelf and also loop back and forth 6 years with Sentinel 2.

[IceConcerned]

A new iceberg has just formed (but not yet detached) on Brunt IS, freeing most of the tabele south of Halloween crack

[paolo]

Now the big iceberg has come off 

Sentinel1 low-res image

Very large image, double-click for best view

PS: you'll find the scale at bottom left and the north direction at top left.