Two rifts on the Brunt Ice Shelf in Antarctica are close to creating an iceberg over 560 square miles in size. Scientists say the calving event could happen any day now.

The resulting iceberg from the break will be about twice the size of New York City (shown rotated here).

Scientists say the break could trigger further retreat of the shelf. Without support from the McDonald Ice Rumples, the ice flow may get faster.

An image from Feb. 27 showed them converging toward islands of ice called the McDonald Ice Rumples. The islands provide support for ice on the shelf that flows westward.

An image captured on Dec. 30, 2016, showed the two rifts advancing through the shelf after being stable for about 30 years.

“This calving is a huge one for Brunt,” said Eric Rignot, a climate scientist at the University of California, Irvine, who has done extensive research on polar ice. “Brunt put that ice in store for probably a century and is about to let it go.”