Antarctic crack may release giant iceberg

A crack that could create a 5000-square-kilometre iceberg and destabilise one of the largest ice shelves in the Antarctic has branched out and is widening more quickly, a US scientist says.

The new fissure has turned toward the shelf's ocean edge, potentially speeding up the iceberg's process of breaking off, said Dan McGrath, a geophysicist with the US Geological Survey and a project partner with UK-based monitoring group Project Midas.

"It's taking basically a sharp hook toward the calving front," said McGrath, using a technical term to describe the ocean side of the ice shelf.

The new crack on the Antarctic's fourth-largest ice shelf Larsen C is an offshoot of a rupture that gained notice after growing dramatically in 2014.

Last year it was forecast to cause the separation of an iceberg within years.

The projected size of the iceberg is more than 300,000 times the size of the 125m one that sunk the Titanic, putting it among the largest on record.

While not getting longer, the original crack has continued to widen steadily, at a rate of about one-metre day, a rate that has increased since the new crack formed, according to a Midas report.

McGrath said the combination of the new crack and the faster widening could point to an imminent separation of the berg, even as soon as this summer.

The loss of so much ice would shrink the shelf by about 10 per cent, leaving it with the smallest area ever recorded.

It was reasonable to link the event and shrinking Antarctic ice shelves to global warming, Richard Alley, a glaciologist at Penn State University who is not connected with project, said.

An overwhelming majority of scientists say human activity - including the burning of oil, gas and coal - is the main driver of rising global temperatures.

Scientists warned in 2015 the loss of such a large mass of ice would create a "significant risk" of the shelf as a whole becoming unstable and breaking up.