Key glacier in Antarctica is cracking from the inside out

Pine Island rift
© Rift in Pine Island Glacier ice shelf, West Antarctica, photographed from the air during a NASA survey flight on Nov. 4, 2016. (Nathan Kurtz/NASA)

New discovery points to troubling signs for the West Antarctic Ice Sheet, the collapse of which would prove catastrophic.

In 2015, a 225-square-mile iceberg in Antarctica made the headlines when it parted ways with its “mother,” the Pine Island Glacier. The Pine Island Glacier and its partner, the Thwaites Glacier, bound the edge of the West Antarctic Ice Sheet, one of the most active ice sheets on the continent. The two glaciers work to plug up the ice flow, in a way, and keep nearly 10 percent of the West Antarctic Ice Sheet from escaping into the sea. Scientists believe that the collapse of the Ice Sheet would lead to a sea-level rise of nearly 10 feet. More than half of the world's freshwater is frozen in Antarctica.

Recently, when testing new image-processing software, researchers from Ohio State University (OSU) noticed something unusual in satellite images taken before the 2015 breakup, as described by OSU:

In the images, they saw evidence that a rift formed at the very base of the ice shelf nearly 20 miles inland in 2013. The rift propagated upward over two years, until it broke through the ice surface and set the iceberg adrift over 12 days in late July and early August 2015.

The ice is breaking from the inside out. And while similar behavior has been seen in breakups of the Greenland Ice Sheet, it’s the first time we’ve known of a deep subsurface rift opening within Antarctic ice.

"Rifts usually form at the margins of an ice shelf, where the ice is thin and subject to shearing that rips it apart," he explained. "However, this latest event in the Pine Island Glacier was due to a rift that originated from the center of the ice shelf and propagated out to the margins. This implies that something weakened the center of the ice shelf, with the most likely explanation being a crevasse melted out at the bedrock level by a warming ocean."

It’s thought that because the bottom of the West Antarctic Ice Sheet lies below sea level, ocean water can sneak in inland, yet remains unseen. However, one indication of this would be the formation of valleys in the ice as it melts from below.

"The really troubling thing is that there are many of these valleys further up-glacier," Howat adds. "If they are actually sites of weakness that are prone to rifting, we could potentially see more accelerated ice loss in Antarctica."

"It's generally accepted that it's no longer a question of whether the West Antarctic Ice Sheet will melt, it's a question of when," Howat says. "This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes."

See the 2015 breaking away from the mothership in the series of Sentinel-1A satellite images below.

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