But they were shocked to find the hole and then "surprised" to see its "size and explosive growth rate".
"We have suspected for years that Thwaites was not tightly attached to the bedrock beneath it", said Eric Rignot of the University of California, Irvine, and NASA's JPL.
Scientists spotted the concealed void thanks to a new generation of satellites, Rignot noted. All the data was then processed using a technique called radar interferometry to show how the ground below the surface is moving between images.
And if all the ice in neighboring glaciers were to melt, it would raise global sea levels by approximately eight feet (2.4 meters), which would spell disaster for the majority of the world's coastal populations, accounting for upwards of 80 percent of the entire human population. The growing cavity is the red mass at the center. They used NASA's ice-penetrating radar to get their data. 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.
A large cavity has formed under what has been described as one of the world's most unsafe glaciers, and could contribute to a significant bump in global sea levels, said Nasa scientists. For instance, the 100-mile-long (160 kilometers) glacier front has different rates of retreat in its grounding line (where the sea ice meets the ocean's bedrock) depending on where you look.
The glacier isn't retreating uniformly.
From 1992 to 2011, the centre of the Thwaites grounding line retreated by almost 14 kilometres.
The glacier has been coming unstuck from a ridge in the bedrock at a steady rate of about 0.6 to 0.8 kilometers a year since 1992. Despite this stable rate of grounding-line retreat, the melt rate on this side of the glacier is extremely high.
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