A huge iceberg the size of Greater London broke away from Antarctica near the British research station Halley.
Sensors on the surface of the Brunt Ice Shelf confirmed the rupture late Sunday GMT.
There are currently 21 staff at Halley who maintain the base and operate its scientific instruments.
They are out of danger and will continue working until they are picked up early next month.
The British Antarctic Survey (BAS) operates the station in a limited role pending calving.
Halley is about 15 km from the rupture line.
BAS has a number of GPS units in the area that relay information on ice movements back to the agency’s Cambridge headquarters.
Officials will check satellite images as they become available. They will want to see if there are any unexpected instabilities on the remaining ice shelf platform where Halley is located.
A similarly sized mountain known as A74 calved in February 2021 further east. At the time, it was thought that his departure could be the beginning of the last escape, but these events are beyond all certain predictions.
Where is it exactly?
It is located on the Brunt Ice Shelf, which is a floating projection of glaciers that have drained from the Antarctic continent into the Weddell Sea. On the map, the Weddell Sea is a sector of Antarctica located directly south of the Atlantic Ocean. Brunt is on the eastern side of the sea. Like all ice shelves, it will periodically calve icebergs. Before the last peak and the A74, the last big piece to fall off Brunt was in 1971.
Was the escape anticipated?
Absolutely. It’s just not his time. Scientists are constantly monitoring any major cracks in Brunt and have noticed that one particular crack – dubbed Chasm One – is starting to reopen after decades of dormancy. In recent years, the spread of Chasm One has accelerated, resulting in the complete separation of a block of ice about 150-200 m thick.
What about Halley station now?
The British base consists of a series of modules on skis that allow it to be moved away from the advancing ice shelf. When Chasm One was seen coming back to life, the decision was made to move Halley 23km “upstream” – a task completed in early 2017. Had this relocation not taken place, Halley would now be sitting in a very dangerous position on the escape iceberg.
What about people in the area?
During the Antarctic winters, BAS removed all its personnel from Halley. He didn’t want to be in a situation where he had to evacuate people at a time of year when the polar night lasts 24 hours and weather conditions can be terrible. It’s summer in Australia now, so if a small crew needs to be removed from the station, it can be done quickly and safely.
How big is the new berg?
Estimates say about 1,550 km² – almost 600 square miles. It’s big in every way. It’s the size of a city. The task of naming the icebergs belongs to the US National Ice Center. Since the new block is in the Antarctic quadrant, which runs from 0 degrees longitude to 90 degrees west, it will carry the letter “A” in its designation. It will probably be called A81. The “81” refers to its place in the sequence of major calvings in the region. A mountain of similar size that broke away from Brunt east of Halley was named A74.
What happens then?
The calving of large mountains from the shelf structure can lead to an acceleration of ice flow. Before calving, Brunt swam westward at a speed of about 3 m/day. If it’s experiencing acceleration now, it could affect the behavior of other cracks in the area. In particular, scientists are keeping a very close eye on the rift they call the Halloween Rift. It is located north and east of Halley and spreads away from the base. Scientists will want to watch his reaction if he does. Much will depend on what happens in the so-called McDonald Ice Rumples – a raised area of the seafloor that catches the bottom of the Brunt Shelf and usually helps to immobilize it.
Is this climate change happening?
No. Mountain calving on the front edge of the ice shelf is a very natural behavior. The shelf likes to keep its balance, and throwing up mountains is one way it balances the accumulation of snowfall and the influx of more ice from the glaciers feeding the land. Unlike on the Antarctic Peninsula across the Weddell Sea, scientists have not detected climate change in the Brunt region that would significantly alter the natural process described above. Moreover, estimates indicate that Brunt was at its greatest for at least 100 years before calving. The famous explorer Sir Ernest Shackleton noted the much smaller shelf structure as he passed by on his ill-fated Imperial Trans-Antarctic Expedition 1914-1917. There was definitely going to be a significant calving.