![]() ![]() The shelf is a floating slab of ice, several hundred meters thick, extending roughly 50 kilometers into the Southern Ocean, covering between 800 and 1,000 square kilometers. The Thwaites Ice Shelf begins where the massive Thwaites Glacier meets the West Antarctic coast. But it isn’t, Pettit says: “There are five or six different ways this thing could fall apart.” In satellite images, the center of the ice shelf looks stable. It meant that the ice’s underside was a rolling landscape-not what anyone expected. To Pettit, a glaciologist at Oregon State University in Corvallis, this was significant. When it does, the rest of the West Antarctic Ice Sheet behind it could flow right into the ocean, pushing up sea levels around the planet, flooding coastal cities worldwide.įrom a distance, the ice shelf looks flat, but as Pettit walked she saw the guide flags ahead of her rise and fall against the horizon-a sign that she was walking across an undulating surface. Pettit was studying defects within the ice, akin to hidden cracks in an enormous dam, that will determine when the ice shelf might crumble. But if that were the case, Pettit wouldn’t have been there. ![]() The Thwaites Ice Shelf appeared healthy on the surface. A row of red and green nylon flags, flapping in the wind on bamboo poles, extended into the distance, marking a safe route free of hidden, deadly crevasses. Pettit was surveying a part of Antarctica where, until several days before, no other human had ever stepped. The brittle snow crunched like cornflakes underneath her boots-evidence that it had recently melted and refrozen following a series of warm summer days. Any reuse without express permission from the copyright owner is prohibited.On December 26, 2019, Erin Pettit trudged across a plain of glaring snow and ice, dragging an ice-penetrating radar unit the size of a large suitcase on a red plastic sled behind her. CC BY-NC-ND 3.0Įxcept where otherwise noted, images are subject to copyright. (2017), West Antarctic ice shelf breaking up from the inside out, Eos, 98. If these sites are prone to rifting, we could potentially see more accelerated ice loss in Antarctica. They point out that there are many similar valleys farther up the glacier. The researchers note that this kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that there may be a significant collapse of the West Antarctic Ice Sheet in the next century. The satellite images provide the first strong evidence that these large Antarctic ice shelves respond to changes at their ocean edge in a way similar to that observed in Greenland. Long shadows cast across the ice drew the team’s attention to the valley that had formed there.Īlthough this is the first time researchers have witnessed a deep subsurface rift opening within Antarctic ice, they have seen similar breakups in the Greenland Ice Sheet, in spots where ocean water has seeped inland along the bedrock and begun to melt the ice from underneath. The origin of the rift would have gone unseen, too, except that the images that the researchers analyzed happened to be taken when the Sun was low in the sky. The valley is likely a sign of something researchers have long suspected: Ocean water can intrude far inland and remain unseen because the bottom of the West Antarctic Ice Sheet lies below sea level. The most likely explanation is that a crevasse melted out at the bedrock level, driven by a warming ocean, according to the researchers.Īnother clue that the center of the ice shelf is weak is that the rift opened in the bottom of a “valley” in the ice shelf where the ice had thinned compared to the surrounding ice shelf. This implies that something weakened the center of the ice shelf. But this particular rift originated in the center of Pine Island Glacier’s ice shelf and propagated out to the margins. Rifts usually form at the sides of an ice shelf where the ice is thin and subject to shearing that rips it apart. During this period, another, similar rift opened 6 miles (10 kilometers) farther inland of the first. The rift grew over 2 years until it set the iceberg adrift over 12 days in late July and early August 2015. saw a rift open in the surface of the ice shelf nearly 20 miles (32 kilometers) inland in 2013. A nearly 225-square-mile (588-square-kilometer) iceberg-nearly the size of Chicago- broke off from Pine Island Glacier in 2015, but it wasn’t until researchers were testing some new image-processing software that they noticed something strange in Landsat 8 satellite images taken before the event. ![]()
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