Jonathan Amos
@jcdamos.bsky.social
Journalist. Former BBC Science Correspondent. Way too interested in icebergs for my own good.
"Such records are vital for distinguishing between rapid grounding-line retreat, as is reported to have occurred at Hektoria Glacier, versus the retreat of a floating ice margin through “conventional” iceberg calving processes," says polar SAR specialist Frazer Christie at Airbus Defence and Space.
November 3, 2025 at 5:00 PM
"Such records are vital for distinguishing between rapid grounding-line retreat, as is reported to have occurred at Hektoria Glacier, versus the retreat of a floating ice margin through “conventional” iceberg calving processes," says polar SAR specialist Frazer Christie at Airbus Defence and Space.
But the paper has caused a stir because there is wide disagreement in the glaciology community about precisely where Hektoria had been fully grounded on bedrock due to a lack of high-accuracy satellite records.
November 3, 2025 at 5:00 PM
But the paper has caused a stir because there is wide disagreement in the glaciology community about precisely where Hektoria had been fully grounded on bedrock due to a lack of high-accuracy satellite records.
Swansea Uni co-author @adrianluckman.bsky.social put this Sentinel-1 movie together. "Although the paleo record indicates some very rapid retreats in the past, the pace of retreat of Hektoria Glacier and its neighbours is unprecedented in the observational record," Adrian says.
November 3, 2025 at 5:00 PM
Swansea Uni co-author @adrianluckman.bsky.social put this Sentinel-1 movie together. "Although the paleo record indicates some very rapid retreats in the past, the pace of retreat of Hektoria Glacier and its neighbours is unprecedented in the observational record," Adrian says.
Hektoria lost ~25km in 15 months, with 8.2km fragmenting in just the Nov/Dec of 2022. Naomi Ochwat et al point to a particular vulnerability: an "ice plain" - a big section of glacier ice sitting on flat seabed rock that suddenly goes afloat, spitting off icebergs like crazy.
November 3, 2025 at 5:00 PM
Hektoria lost ~25km in 15 months, with 8.2km fragmenting in just the Nov/Dec of 2022. Naomi Ochwat et al point to a particular vulnerability: an "ice plain" - a big section of glacier ice sitting on flat seabed rock that suddenly goes afloat, spitting off icebergs like crazy.
Ooops! It's happened again. The remnants of iceberg A23a have been caught on another Taylor Column, this time above the NorthWest Georgia Rise to the north of South Georgia BOT. The fragments have spun around and around for more than a month now.
October 4, 2025 at 1:09 PM
Ooops! It's happened again. The remnants of iceberg A23a have been caught on another Taylor Column, this time above the NorthWest Georgia Rise to the north of South Georgia BOT. The fragments have spun around and around for more than a month now.
Really clear view today of Iceberg A23a's big fragmentation event. Going back through the data, I think it happened on the 25th/26th. Image from NASA/Terra/Modis. Each new fragment is probably big enough to get a US National Ice Center designation. Likely A23g, A23h and A23i.
August 30, 2025 at 1:40 PM
Really clear view today of Iceberg A23a's big fragmentation event. Going back through the data, I think it happened on the 25th/26th. Image from NASA/Terra/Modis. Each new fragment is probably big enough to get a US National Ice Center designation. Likely A23g, A23h and A23i.
🚨🚨🚨Boom! Iceberg A23a looks to have undergone a major fragmentation event in the past 24 hours. I count at least three "daughter" bergs (g, h and i ?). Further satellite imagery will confirm. The last intact measurement I made was ~2,250 sq km. @bas.ac.uk
August 29, 2025 at 10:15 AM
🚨🚨🚨Boom! Iceberg A23a looks to have undergone a major fragmentation event in the past 24 hours. I count at least three "daughter" bergs (g, h and i ?). Further satellite imagery will confirm. The last intact measurement I made was ~2,250 sq km. @bas.ac.uk
Iceberg A23a update. It's lost another couple of large chunks in the past few days. Are we getting close to a major fragmentation event? Likely so.
July 15, 2025 at 3:07 PM
Iceberg A23a update. It's lost another couple of large chunks in the past few days. Are we getting close to a major fragmentation event? Likely so.
In case you were wondering... Iceberg A23a seen cruising around South Georgia today by Meteosat 12. The old berg still has an area of 2,846 sq km.
July 7, 2025 at 3:43 PM
In case you were wondering... Iceberg A23a seen cruising around South Georgia today by Meteosat 12. The old berg still has an area of 2,846 sq km.
Iceberg D15a, grounded in the Amery Sea, is now officially "the world's biggest iceberg".
June 15, 2025 at 7:57 AM
Iceberg D15a, grounded in the Amery Sea, is now officially "the world's biggest iceberg".
Sentinel-1 has finally got a clear view of iceberg A23a (13/6/25). The berg is much diminished as it skirts around South Georgia. And the US National Ice Center has updated its stats: A23a is now only the world's second biggest berg at 829.79 sqNM, or 2846,11 sqKM.
June 15, 2025 at 7:57 AM
Sentinel-1 has finally got a clear view of iceberg A23a (13/6/25). The berg is much diminished as it skirts around South Georgia. And the US National Ice Center has updated its stats: A23a is now only the world's second biggest berg at 829.79 sqNM, or 2846,11 sqKM.
You can see the original grounded position in this BBC map. The berg is following the expected track, riding the prevailing current and hugging the continental shelf. It could always ground again. But if not, it should sweep around SG and go north.
June 4, 2025 at 2:41 PM
You can see the original grounded position in this BBC map. The berg is following the expected track, riding the prevailing current and hugging the continental shelf. It could always ground again. But if not, it should sweep around SG and go north.
The movement of iceberg A23a over the past seven days. It's moved about 80km to the southeast of the position where it grounded off the coast of South Georgia in early March. Zoomed in animation from Meteosat-12.
June 4, 2025 at 2:41 PM
The movement of iceberg A23a over the past seven days. It's moved about 80km to the southeast of the position where it grounded off the coast of South Georgia in early March. Zoomed in animation from Meteosat-12.
And I'm pretty sure now that A23a is no longer the "World's Biggest Iceberg". D15a is larger in my view. But only the US National Ice Center can make that determination and its listing doesn't yet reflect this.
June 1, 2025 at 6:25 PM
And I'm pretty sure now that A23a is no longer the "World's Biggest Iceberg". D15a is larger in my view. But only the US National Ice Center can make that determination and its listing doesn't yet reflect this.
Somebody's got itchy feet! Iceberg A23a has moved in the past couple of days. It grounded close to South Georgia back at the beginning of March. But the erosion and melting since then has clearly allowed it to break free. Does it now reground or sweep off around the island?
June 1, 2025 at 6:17 PM
Somebody's got itchy feet! Iceberg A23a has moved in the past couple of days. It grounded close to South Georgia back at the beginning of March. But the erosion and melting since then has clearly allowed it to break free. Does it now reground or sweep off around the island?
With days shortening at South Georgia (it's about 8 hours from sunrise to sunset), optical satellite coverage in the region is getting more restricted. Not so for Meteosat, which images the Europe/Africa hemisphere regardless of season. Hence we get a few views of iceberg A23a. Still grounded.
May 30, 2025 at 2:47 PM
With days shortening at South Georgia (it's about 8 hours from sunrise to sunset), optical satellite coverage in the region is getting more restricted. Not so for Meteosat, which images the Europe/Africa hemisphere regardless of season. Hence we get a few views of iceberg A23a. Still grounded.
There was a spectacular view of iceberg A23a on 3 May. Clear skies over the berg and South Georgia. By my measurement, A23a is no longer the world's biggest iceberg. At ~2850 sq km, it's now bested by D15a - but only just. The US National Ice Center will be the final judge on the matter.
May 6, 2025 at 9:49 AM
There was a spectacular view of iceberg A23a on 3 May. Clear skies over the berg and South Georgia. By my measurement, A23a is no longer the world's biggest iceberg. At ~2850 sq km, it's now bested by D15a - but only just. The US National Ice Center will be the final judge on the matter.
Mickey's recent GRL paper on trends/extremes in big Antarctic bergs is here: doi.org/10.1029/2024...
And you can read the Kirkham paper in Nature Comms here: doi.org/10.1038/s414...
And yours truly with the lead story on New Scientist online here: newscientist.com/article/2477... 😎
And you can read the Kirkham paper in Nature Comms here: doi.org/10.1038/s414...
And yours truly with the lead story on New Scientist online here: newscientist.com/article/2477... 😎
April 24, 2025 at 9:25 AM
Mickey's recent GRL paper on trends/extremes in big Antarctic bergs is here: doi.org/10.1029/2024...
And you can read the Kirkham paper in Nature Comms here: doi.org/10.1038/s414...
And yours truly with the lead story on New Scientist online here: newscientist.com/article/2477... 😎
And you can read the Kirkham paper in Nature Comms here: doi.org/10.1038/s414...
And yours truly with the lead story on New Scientist online here: newscientist.com/article/2477... 😎
This underscores thinking about Antarctica. Large calvings like A23a are not necessarily a sign of instability. “Rather, ice shelves disintegrate via death by a thousand cuts. We should be concerned when we stop seeing the large calving events,” Mickey MacKie tells me.
April 24, 2025 at 9:25 AM
This underscores thinking about Antarctica. Large calvings like A23a are not necessarily a sign of instability. “Rather, ice shelves disintegrate via death by a thousand cuts. We should be concerned when we stop seeing the large calving events,” Mickey MacKie tells me.
In Antarctica, megabergs calve from ice shelves. The recognition that tabular bergs once existed in the North Sea tells us the seaward margins of the retreating British and Irish Ice Sheet at the end of the last glacial maximum also had ice shelves.
April 24, 2025 at 9:25 AM
In Antarctica, megabergs calve from ice shelves. The recognition that tabular bergs once existed in the North Sea tells us the seaward margins of the retreating British and Irish Ice Sheet at the end of the last glacial maximum also had ice shelves.
"We can estimate from the extent of the scours and what is known about ancient sea levels that these bergs were probably five to a few tens of kilometres wide and perhaps a couple of hundred metres thick." ie Think blocks of ice the size of Cambridge or Bristol 😲
April 24, 2025 at 9:25 AM
"We can estimate from the extent of the scours and what is known about ancient sea levels that these bergs were probably five to a few tens of kilometres wide and perhaps a couple of hundred metres thick." ie Think blocks of ice the size of Cambridge or Bristol 😲
It's crazy to think the UK once had its own colossal icebergs. @jdkirkham.bsky.social et al have found the preserved scour marks the megabergs made when their undersides ploughed through the muddy bottom of the North Sea some 20k-18k years ago. 🧵
April 24, 2025 at 9:25 AM
It's crazy to think the UK once had its own colossal icebergs. @jdkirkham.bsky.social et al have found the preserved scour marks the megabergs made when their undersides ploughed through the muddy bottom of the North Sea some 20k-18k years ago. 🧵
US National Ice Center formally catalogues A23c, the big off-cut from grounded behemoth A23a. Daughter berg is ~130km² - or 2x Manhattan Island. A23a (~3,100km²) only needs to lose another ~30km² to hand "World's Biggest Iceberg" title to D15a (~3,070km²) in Amery Sea.
April 22, 2025 at 12:41 PM
US National Ice Center formally catalogues A23c, the big off-cut from grounded behemoth A23a. Daughter berg is ~130km² - or 2x Manhattan Island. A23a (~3,100km²) only needs to lose another ~30km² to hand "World's Biggest Iceberg" title to D15a (~3,070km²) in Amery Sea.
A big chunk has broken away from iceberg A23a, currently grounded at South Georgia. I calculate ~110 sq km. Looks to have fractured sometime on 11/12 April. It will get a US National Ice Center designation. It should be A23c, unless I'm mistaken.
April 16, 2025 at 9:12 AM
A big chunk has broken away from iceberg A23a, currently grounded at South Georgia. I calculate ~110 sq km. Looks to have fractured sometime on 11/12 April. It will get a US National Ice Center designation. It should be A23c, unless I'm mistaken.
You don't need to be a seismologist to look at this figure and understand the huge forces that ripped through Myanmar on March 28. The M7.7 quake ruptured fully 500km of the Sagaing Fault, moving its western flank north, with >3m of slip at the surface. Data from EU Sentinel satellites.
April 2, 2025 at 5:40 PM
You don't need to be a seismologist to look at this figure and understand the huge forces that ripped through Myanmar on March 28. The M7.7 quake ruptured fully 500km of the Sagaing Fault, moving its western flank north, with >3m of slip at the surface. Data from EU Sentinel satellites.