April 26, 2019

There's A Huge Cavity Under Antarctica's Most Endangered Glacier

01 February 2019, 08:12 | Dale Webster

A massive cavity two-thirds the size of Manhattan is shown in

A massive cavity two-thirds the size of Manhattan is shown in

The Thwaites Glacier, the largest outflow channel of the vulnerable West Antarctic Ice Sheet, now has a huge subterranean hole.

According to NASA, the cavity once contained some 14 billion tons of ice, most of which has supposedly melted in last three years. The glacier itself is about as big as the state of Florida, and, if melted completely, could raise sea levels by some 2 feet globally, the scientists say.

Changes in surface height at Thwaites Glacier's grounding line.

NASA researchers say the mysterious cavity is growing at an "explosive" rate.

"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it", co-author Eric Rignot of the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, California, said in a press release.

Scientists spotted the concealed void thanks to a new generation of satellites, Rignot noted.

The cavity, reported in the Science Advances journal, was revealed by ice-penetrating radar in NASA's Operation IceBridge - an airborne campaign beginning in 2010 that studies connections between the polar regions and the global climate. Researchers combined the NASA data with data from Italian and German spaceborne synthetic aperture radars.

Lead author Pietro Milillo of JPL says the size of the cavity under the glacier "plays an important role in melting". The common thread among them is the infiltration of relatively warm ocean water below the ice, thinning it and causing the glaciers to flow out to sea faster.

The cavity can be seen in the center of the GIF in deep red.

The scientists have calculated that the melting glacier has already contributed to about 4 percent of the total global sea level rise. This summer, the U.S. National Science Foundation and the British Natural Environmental Research Council are launching the International Thwaites Glacier Collaboration, a five-year field project that aims to get to the bottom of the glacier's processes and features.

"We are discovering different mechanisms of retreat", Millilo said.

The glacier is retreating in the face of the warming ocean and is thought to be unstable because its interior lies more than two kilometres below sea level while, at the coast, the bottom of the glacier is quite shallow. The glacier has retreated at a steady rate of about 0.4 to 0.5 miles (0.6 to 0.8 km) annually since 1992, the researchers found. Despite this stable rate of grounding-line retreat, the melt rate on this side of the glacier is extremely high. The disappearance of the ice mass would cause sea levels to rise by about two feet as well as making surrounding glaciers more likely to melt rapidly-which could cause an eight foot rise.

Researchers hope the new findings will help others preparing for fieldwork in the area better understand the ice-ocean interactions.

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