The Thwaites Glacier in Antarctica is unstable and at a high risk of collapse, according to scientists mapping its retreat.

The Thwaites Glacier is one of the largest glaciers on the world, approximately 80 miles wide and 925 miles long, roughly the size of the island of Britain, or a little larger than Florida. It is between 800 and 1200 meters deep for most of its length, and it is not floating ice, which means that should it melt, it will contribute measurably to sea level rise. Some sources call it the ‘Doomsday glacier‘ due to the threat it poses. Some estimates put the possible rise as high as three feet.

In 2020, scientists studying the glacier discovered a ‘warm’ outflow from the glacial bed, of water as warm as 2 degrees Celsius. Any water warmer than freezing coming from a glacier is ominous. This warmer water erodes the connection between the glacier and the ground beneath it, which is below sea level. If the glacier should melt far enough to become floating ice, the meltwater and the displacement of the floating ice together will cause sea level rise. The warmer flow also threatens the floating shelf ice that protects the lower foot of the glacier from erosion by the ocean, which is always above freezing.

According to a recent study published by Nature Geoscience, seabed evidence of the prior movement of the Thwaites Glacier shows that it has periodically become partially floating and retreated extremely rapidly, sometime in the last two centuries. With the erosion of the ice shelf, however, scientists believe that if this happens again, the glacier will not recover.

“Thwaites is really holding on today by its fingernails, and we should expect to see big changes over small timescales in the future — even from one year to the next — once the glacier retreats beyond a shallow ridge in its bed,” Robert Larter, a marine geophysicist and one of the study’s co-authors from the British Antarctic Survey, said in the release.

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