80-Mile Crack Threatens an Antarctic Ice Shelf

Its eventual breakup could add nearly 4 inches to global sea levels.

Photo: A 2013 satellite photo of the Larsen C ice shelf in Antarctica shows the rift, which has now grown to 80 miles in length and nearly 14 miles across. Credit: NASA Earth Observatory Scientists have been monitoring the deterioration of Larsen C, the Antarctic ice shelf that is roughly the size of Scotland and the fourth biggest on the southernmost continent. And their latest observations have them plenty alarmed.

Larsen C has a rift in it that's grown steadily over the past five years. But during this year's six-month-long Antarctic polar night, the crack's size increased by an astonishing 13 miles, according to a recent blog post by Project MIDAS, a British Antarctic research project, which was based upon satellite observations. The giant crack now measures about 80 miles long -- roughly the distance between New York City and Philadelphia -- and nearly 14 miles in width.

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"As this rift continues to extend, it will eventually cause a large section of the ice shelf to break away as an iceberg," the researchers wrote on Aug. 18.

The scientists published a paper last year which concluded that Larsen C was likely to undergo "calving," in which a piece of the ice shelf would break off. They calculated that would remove as much as 12 percent of the shelf, and leave the front of the shelf "at its most retreated position ever."

They say that the current progression of the rift makes that more likely than ever.

"Larsen C may follow the example of its neighbor Larsen B, which disintegrated in 2002 following a similar rift-induced calving event," they wrote.

Martin O'Leary, a glaciologist at Swansea University and one of the authors of the blog post, told the Washington Post that the amount of ice lost would be 2,316 square miles. That's nearly the size of the state of Delaware.

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O'Leary told the Post that it's difficult to predict exactly when Larsen C will break in two, because scientists don't yet have a good grasp of the processes which control its timing. "It's a lot like predicting an earthquake – exact timings are hard to come by," he said. "Probably not tomorrow, probably not more than a few years."

When ice shelves lose big pieces, it speeds up the flow of non-floating glacial ice from the shelf, which now is being held back. Researchers estimate that freeing that outflow would raise global sea levels by just under 4 inches, according to the Post.

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