Iceberg 'hanging by a thread' after sudden growth in rift

An iceberg a quarter the size of Wales is poised to break off from an ice shelf in Antarctica, scientists have said.

The Larsen C Ice Shelf is primed to lose an area of more than 5,000 square kilometres (1,900 square miles), after a rift in the ice shelf grew suddenly by around 18km (11 miles) in the second half of December.

Just 20km (12 miles) of ice now connects the vast iceberg to the rest of the shelf, according to researchers from the Midas project, which has been studying the stability of the Larsen C Ice Shelf for three years.

Lead researcher, Swansea University's Professor Adrian Luckman, said the iceberg was now "hanging by a thread".

When it calves off, the Larsen C Ice Shelf will lose more than 10% of its area, fundamentally changing the landscape of the Antarctic Peninsula, and making the shelf less stable, the experts said.

The current event is not an ice shelf collapsing, but Larsen C may, in years or decades to come, follow the course of the Larsen B Ice Shelf which splintered and collapsed in the space of a month in 2002, they said.

Ice shelves hold back the ice on the land, and their collapse can allow glaciers behind them to discharge into the sea quicker - with a potential impact on sea levels.

While warming temperatures in the Antarctic will not have helped the stability of the ice, the growth in the fissure was not "directly" associated with climate change, Prof Luckman said.

"This is a rift that is decades old, it is more likely that we can put this down to a natural development of the rift."

But he said: "In the 1990s Antarctica was one of the fastest warming places on Earth. It's started to cool down a little bit but long term this is a warming place.

"That can't have helped, I'm sure that's part of the explanation of wider ice shelves collapsing. But we can't directly attribute this to climate change."

In June the crack grew 20km (12 miles) in a short space of time, before the latest growth in the rift in December.

While the calving of the iceberg is "inevitable", the researchers could not say exactly when it will happen - though it could be months before it goes.

"It's not predictable, it very much depends on the local weather conditions. These events are basically chaotic and unpredictable," Prof Luckman said.

Project Midas is based at Swansea University and Aberystwyth University, with support from the British Antarctic Survey and other partners, and is funded by the National Environment Research Council.