The discovery of an underwater mountain ridge could help solve the mystery of why Antarctica’s Pine Island glacier is vanishing so rapidly.

A robot submarine sent beneath the glacier’s floating ice sheet has shown that there is a ridge rising 400 metres from the sea floor. Until recently, the glacier would have rested on this ridge, preventing warm seawater from reaching the ice and melting it from underneath. But the submarine has shown that the glacier no longer rests on the ridge – it has thinned and now floats above it (Nature Geoscience, DOI: 10.1038/ngeo890).

“Once you tip the glacier off the ridge, it continues to …