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A massive crack in one of Antarctica's largest ice shelves is very close to breaking point, and when it fractures it will create an iceberg bigger than Kangaroo Island.
The Larsen C ice shelf is located on the Antarctic Peninsula, which juts out towards South America.
A large fracture, which has been growing across the ice sheet for decades, has recently started to accelerate, said Sue Cook, a glaciologist from the Antarctic Climate and Ecosystems Cooperative Research Centre.
According to the latest data by a team of UK scientists, the fracture ripped open by 17 kilometres in the last week of May and turned towards the ocean.
Dr Cook said the lengthening fracture was within 13 kilometres of the sea, and there was nothing to stop it fracturing.
When it breaks it will create an iceberg of 5,000 square kilometres.
"We expect this to go pretty quickly from here," Dr Cook said.
What is an ice shelf?
An ice shelf is a section of ice that juts out into the sea.
Snow from the interior builds up and flows out to the edge of the continent. At the edges it thins, and because ice is less dense than water, it sits on top of the ocean instead of on the sea bed.
"So you have this transition from where the ice is on ground moving to a point where it is moving out into the ocean."
What happens when an iceberg breaks off?
The iceberg is massive, so it's likely to be a slow process.
"You might have seen videos of icebergs up in Greenland and they crash and roll and turn in [a] very violent process," Dr Cook told the World Today.
"In Antarctica, it doesn't tend to be quite as sudden or as dramatic. They move away much more slowly from the ice shelf."
What impact will it have on the ice shelf?
The Larsen C ice shelf, which is Antarctica's fourth largest ice shelf, covers an area of 46,500 square kilometres.
"The iceberg that's about to come off will be about 10 per cent of the ice shelf area," Dr Cook said.
It's normal for icebergs to break off ice shelves.
"Ice shelves are constantly flowing into the ocean losing a bit off the end," she said.
"It might not really have a big impact on the ice shelf."
But, she said, it could also destabilise the ice shelf causing it to quickly disintegrate.
That's exactly what happened in 2002 to the neighbouring ice shelf Larsen B.
"The Larsen C is the next one we think that might happen to.
"We're not sure if it's going to happen now, or further in the future."
Could this affect sea levels?
This iceberg itself won't increase sea levels because it is breaking off from floating ice.
But there will be increases in sea levels if the entire ice shelf breaks up.
"If you remove an ice shelf, all of the glaciers that used to feed into it start putting more ice out into the ocean and that's where you get your potential contributions to sea level rise," Dr Cook said.
She said when the Larsen B ice shelf disintegrated in 2002, the glaciers that flowed into it more than doubled in speed.
"If the Larsen C were to collapse, then we'd expect to see a similar acceleration of its tributary glaciers," Dr Cook said.
She said the glaciers feeding into the Larsen C ice shelf contained about 10 centimetres of global sea level equivalent, but it's very unlikely that all of that would go.
What's causing it to happen?
Dr Cook said it was really hard to pin down exactly why this is happening.
The Antarctic Peninsula is rapidly warming, but there is no evidence to link this event to climate change.
"In this case it is really hard to say whether it has something to do with global warming or not," Dr Cook said.
Dr Cook said once this iceberg calved, the front of the shelf would have moved back to the furthest point that's ever been recorded.
"So that implies that there is a process that is causing it to move more ice than it has in the past," she said.
How are we monitoring the ice shelf?
Scientists are monitoring the ice shelf using radar data from satellites.
But Dr Cook said there was no way to reliably predict when an ice shelf would break up.
"It's one of the things we'd like to be able to do better, because all of our sea level rise predictions could be affected quite a lot by this."