Giant cavity found eating away at Antarctic glacier from underneath

Glaciers are kind of an endangered species in our rapidly-warming world, and unfortunately scientists keep finding new threats to them. NASA's ongoing Operation IceBridge has now found a gigantic cavity underneath Thwaites Glacier in West Antarctica, which shows that the area has suffered even more drastic ice loss in recent years than previously thought – and it's accelerating.

Thwaites Glacier is roughly the size of Florida, and by itself reportedly holds enough ice to raise the global sea level by 2.1 ft (65 cm). Worse still, it stands between the warming waters and neighboring glaciers, so if it goes others are expected to follow soon enough.

That makes Thwaites an important target for study. As part of Operation IceBridge, specialized planes fly over the frozen continent a few times a year and take radar readings of the ice below. The radar could peer through the ice and examine how much ice had been lost underneath.

Although it was expected that some ice loss had occurred, the team was surprised to see exactly how much was missing. The radar revealed a cavity measuring almost 1,000 ft (300 m) tall underneath Thwaites Glacier, big enough to have once contained 14 billion tons of ice. The majority of that had melted away in just three years.

"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it," says Eric Rignot, co-author of the study. "Thanks to a new generation of satellites, we can finally see the detail."

Located on the western side of Thwaites Glacier, the cavity was created as warmer waters lapped at the bottom of the glacier over the years, and unfortunately, it's a vicious cycle. The more the hole grows, the more ice is exposed to water, which speeds up the melting. This pushes the grounding line – where the ice meets the bedrock below – further and further inland, destabilizing the glacier.

Data shows that between 1992 and 2017, the grounding line on the western side of Thwaites Glacier has been retreating at a steady rate of between 0.4 and 0.5 mi (0.6 to 0.8 km) per year. The situation is worse on the eastern side, where the retreat rate has doubled – from 0.4 mi (0.6 km) per year between 1992 and 2011, to 0.8 mi (1.2 km) per year between 2011 and 2017.

Strangely enough, even though the retreat rate is worse on the eastern front, the melt rate is higher on the western side of the glacier. The researchers aren't sure why that is, but it does go to show that interactions between the ice and the ocean are much more complex than previously thought.

The International Thwaites Glacier Collaboration is preparing to embark on a field study on the ground during the Southern Hemisphere's next summer, in late 2019 and early 2020. The researchers on the current study hope that these new results will help inform that team's work.

"Such data is essential for field parties to focus on areas where the action is, because the grounding line is retreating rapidly with complex spatial patterns," says Pietro Milillo, lead author of the study.

The research was published in the journal Science Advances.

Source: NASA JPL