The rift on Antarctica’s Brunt ice shelf has torn itself away from the glacier resulting in a massive iceberg that is known as A74. British Antarctic Survey has been monitoring the glacier for years. The shelf was at its largest extent for over 100 years.
The Brits have relocated their research station twice since 2016 as the cracking ice was a lethal threat.
Surface instruments confirmed that the iceberg tore loose today and is now floating and/or scraping the Weddel seafloor of life.
The event is not a result of climate change but rather a natural break off of the glacier’s leading edge. Nor have scientists detected climate impacts of any kind to Brunt. The shelf was overdue for this break. The glacier is closely monitored as the iceberg could be a serious threat to shipping.
The ice shelf is near the Antarctic Peninsula where rapid changes on and under the shelves are accelerating.
The first indication that a calving event was imminent came in November 2020 when a new chasm – called North Rift – headed towards another large chasm near the Stancomb-Wills Glacier Tongue 35 km away. North Rift is the third major crack through the ice shelf to become active in the last decade.
During January, this rift pushed northeast at up to 1 km per day, cutting through the 150-m thick floating ice shelf. The iceberg was formed when the crack widened several hundred metres in a few hours on the morning of 26th Feb, releasing it from the rest of floating ice shelf.
The glaciological structure of this vast floating ice shelf is complex, and the impact of ‘calving’ events is unpredictable. In 2016, BAS took the precaution of relocating Halley Research Station 32 km inland to avoid the paths of ‘Chasm 1’ and ‘Halloween Crack’.
Since 2017, staff have been deployed to the station only during the Antarctic summer, because during the dark winter months evacuation would be difficult. ‘Chasm 1’ and ‘Halloween Crack’ have not grown in the last 18 months.
5-years of Sentinel-1 data shows sea ice and icebergs moving past the Brunt Ice Shelf. Watch the cracks form on the crevassed ice shelf. The Antarctic Coastal Current moves in an anti-clockwise direction. Will this be the direction the new #A74 iceberg moves in? @esa @NERCscience pic.twitter.com/TcMeg6mIEW
— SENSE Earth Observation CDT (@EoCdt) February 26, 2021
“This is a dynamic situation. Four years ago we moved Halley Research Station inland to ensure that it would not be carried away when an iceberg eventually formed. That was a wise decision. Our job now is to keep a close eye on the situation and assess any potential impact of the present calving on the remaining ice shelf. We continuously review our contingency plans to ensure the safety of our staff, protect our research station, and maintain the delivery of the science we undertake at Halley.”
— Stef Lhermitte (@StefLhermitte) February 26, 2021