A glacier described as the "world's most dangerous" is showing worrying signs of collapse, after scientists found an 1,000ft tall cavity growing beneath the ice.
The Thwaites Glacier from West Antarctica has about 182,000 square km.
The icy monster "backstops neighbouring glaciers that would raise sea levels an additional 8 feet (2.4 metres) if all the ice were lost", Nasa warned.
Before they made the discovery, Nasa researchers were looking for gaps between ice and bedrock at the bottom of Thwaites where ocean water flows in and melts the glacier from underneath.
Thwaites glacier in western Antarctica.
However, the researchers say that the size and growth rate of the hole surprised them.
"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.
Scientists used a combination of ice-penetrating radar flown on NASA planes and European satellite data to capture what's going on. Researchers combined the NASA data with data from Italian and German spaceborne synthetic aperture radars.
"[The size of] a cavity under a glacier plays an important role in melting", Milillo says.
Antarctica has been constantly losing ice in the last decades as global warming became more pronounced. However, huge quantities of this colossal ice cube have melted away over the past three years as a result of climate change, contributing to around 4 percent of global sea level rise.
The cavity highlight the need for further observations to have a better idea of just how fast sea levels will rise.
That's important to know, since Thwaites now accounts for about 4 percent of 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. This suggests that the glacier lying on the ground, much weaker than expected.
The gaping mouth is located at the base of the Thwaites Glaciers, which is considered by many to be one of the most unsafe in the world due to its massive size. "We are discovering different mechanisms of retreat", Milillo explains. The melting of this glacier could lead to as much as 10 feet of sea level rise over the next century or so.
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.