One of Antarctica's largest ice shelves is nearing its breaking point， scientists warn. A colossal crack in this ice shelf， known as Larsen C， abruptly grew by 18 kilometers during the second half of December 2016. Members of Project MIDAS， an Antarctic research group， reported the crack's dramatic growth recently. This separating ice is now only about 20 kilometers from Larsen C's edge.

Satellite images in 2014 revealed that a crack in Larsen C rapidly extended across the ice shelf. If the crack reaches the ice shelf 's edge， it could snap off a Delaware-sized area of ice. Such a loss would reduce Larsen C's size by about 10 percent. That's enough to shrink the shelf to its smallest size in recorded history. And it could potentially kick start the shelf 's disintegration.

Daniela Jansen is a glaciologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven， Germany. She led the 2015 study. At that time， she had expected the crack might chip apart Larsen C within five years. "We should keep a close eye on Larsen C，" she had argued. "It might not be there for so much longer."

Larsen C covers about 55 000 square kilometers. That makes it the largest ice shelf along the Antarctic Peninsula. Since Larsen C's ice already floats in the ocean， the big break-off won't immediately raise global sea levels. But if the shelf collapses， then glacial ice could flow into the sea unabated and contribute to rising sea levels.

The scientists can't say for certain when Larsen C will break off. But they think it could be soon.

Usually， researchers camp on the shelf during the Antarctic summer to conduct their science. But this year， the British Antarctic Survey announced it would halt this practice. Scientists will still be allowed access to the area. But they will be restricted to day trips only — with rescue aircraft waiting nearby.