NASA Finds Giant Cavity in Antarctica's Thwaites Glacier

thwaites glacier
The Thwaites Glacier. NASA/OIB/Jeremy Harbeck

An enormous cavity has been discovered at the base of the Thwaites Glacier in Antarctica. The void, deep beneath the surface of the ice, is estimated to be about 1,000 feet tall and could have contained around 14 billion tons of ice.

NASA said the cavity is "one of several disturbing discoveries" made about the Thwaites Glacier—a 100 mile wide river of ice that is disintegrating and will one day collapse.

Understanding the unstable glacier is important for future predictions about sea level rise. It holds enough ice to raise ocean levels by around two feet. Thwaites also serves as a backstop to other Antarctic glaciers—if they subsequently collapsed, sea levels could rise by another eight feet.

In 2010, NASA started an airborne campaign to survey the polar regions. A radar was used to peer through the ice to see to the bottom of the glacier. Scientists have long thought the glacier was not connected to the bedrock below, and they had expected to find some gaps along the base of the ice. However, the size of the cavity came as a big surprise—it was about 2.5 miles wide, six miles long and 1,000 feet tall. Researchers estimate the ice melted in the space of just three years. Findings are published in Science Advances.

"[The size of] a cavity under a glacier plays an important role in melting," lead author Pietro Milillo, from NASA's Jet Propulsion Laboratory, said in a statement. "As more heat and water get under the glacier, it melts faster. We are discovering different mechanisms of retreat."

Scientists were also able to chart the rate of retreat and ice loss, finding a "complex pattern," where some sectors retreated faster with more melting than others. They found the "grounding line"—the point where the ice lifts off the bedrock and extends out into the ocean—is shifting. Thwaites' grounding line is currently retreating, meaning more of the glacier's underside is exposed to the water, increasing the rate of ice melt.

The newly discovered cavity sits on the western side of the glacier, where the melt rate was found to be fastest. "On the eastern side of the glacier, the grounding-line retreat proceeds through small channels, maybe a kilometer wide, like fingers reaching beneath the glacier to melt it from below," Milillo said.

thwaites glacier cavity
Changes in surface height at Thwaites Glacier's grounding line. Sinking areas are in red and rising areas are in blue. The growing cavity is the red mass at the center. NASA/JPL-Caltech

He said he is now preparing for another expedition. The International Thwaites Glacier Collaboration is a joint project between the U.S. National Science Foundation and the British National Environmental Research Council with the aim of getting a better understanding of the glacier and how it will respond to climate change in the future.

"Detailed studies of the grounding zone and its specific regime of ice melt will therefore be critical to explore in more detail using numerical models, remote sensing data, and in situ observations to improve our characterization of the retreat of Thwaites Glacier near its grounding line, its rate of mass loss, and, in turn, projections of its contribution to global sea level rise in decades to come," the authors conclude.