Cracks cutting across Antarctica’s Brunt ice shelf are on course to truncate the shelf and release an iceberg about twice the size of New York City. This Copernicus Sentinel-2 image from February 7, 2019, shows two lengthening fractures: a large chasm running northward and a split, dubbed Halloween Crack, that has been extending eastwards since October 2016.

(European Space Agency)

At a Glance

Two cracks are close to converging on the Brunt Ice Shelf.The resulting iceberg could have a surface area of 660 square miles.Even at that size, the iceberg would not be among the largest calved off Antarctica.

An iceberg twice the size of New York City is about to break away from Antarctica's Brunt Ice Shelf.

Two cracks running across the shelf are only a few miles apart. The larger chasm had been stable for about 35 years, according to NASA, but about 2.5 miles a year.

The chasm is nearing a smaller rift, known as the Halloween Crack, that has been extending toward the east since October 2016.

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When the two cracks meet, the southern end of the ice shelf could , the European Space Agency said.

NASA says the resulting iceberg would cover at least 660 square miles in surface area. That would be the largest iceberg to break from the Brunt Ice Shelf since observations began in 1915. However, it would be small compared with other Antarctic bergs.

A chasm and the Halloween Crack are creeping closer to each other on the Brunt Ice Shelf off Antarctica. First image is from January 1986. The second is from January 23, 2019.

(NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey)

For example,in July 2017, covered 2,240 square miles in surface area. It was among the largest ever observed since satellite tracking began.

The cracks have resulted in a British research station being shut down for the third winter in a row because of safety concerns.

The Halley VI station, operated by the, used to be on the seaward side of the chasm but was moved about 14 miles to its current home in 2016-2017, according to the European Space Agency.

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It's unlikely that global warming is behind the creation of this iceberg.

“The Brunt ice shelf is relatively far south compared to the ice shelves that have calved dramatically on the Antarctic Peninsula,” Oliver Marsh, a British Antarctic Survey glaciologist, told National Geographic. “.”