The British Antarctic Survey (BAS) has released new footage of the Larsen C ice shelf as it looks set to produce a giant iceberg.
The 175km-long fissure runs through the Larsen C on the eastern side of the Antarctic Peninsula.
If it propagates just 20km more, a block of ice a quarter the size of Wales will break away into the Weddell Sea.
Scientists gathered the new video footage while recovering instrumentation that had been placed on the ice shelf.
Uncertainty about the stability of the region means researchers cannot set up camp as they would normally do, and instead make short visits in a Twin Otter plane.
The most recent sortie enabled the researchers to fly along the length of the crack, which is 400-500m wide in places, to assess its status.
At 5,000 square kilometres, the iceberg would be one of the biggest ever recorded.
When it splits, interest will centre on how the breakage will affect the remaining shelf structure.
The issue is important because floating ice shelves ordinarily act as a buttress to the glaciers flowing off the land behind them.
Dr Paul Holland from BAS said: “Iceberg calving is a normal part of the glacier lifecycle, and there is every chance that Larsen C will remain stable and this ice will regrow.
“However, it is also possible that this iceberg calving will leave Larsen C in an unstable configuration. If that happens, further iceberg calving could cause a retreat of Larsen C.
“We won’t be able to tell whether Larsen C is unstable until the iceberg has calved and we are able to understand the behaviour of the remaining ice.”
The study of the Larsen C Ice Shelf is led by Swansea University through its MIDAS project, which involves BAS.