An ice-filled "Grand Canyon" a mile deep has been discovered in the Antarctic.
The giant rift valley lies beneath the Ferrigno Ice Stream, a 15-mile long glacier flowing into the sea in western Antarctica.
Scientists believe it may be linked to high levels of ice loss from the region.
Experts made the find using ice-penetrating radar towed a distance of 1,500 miles over the flat ice surface.
Lead researcher Dr Robert Bingham, from the University of Aberdeen, said: "What we found is that lying beneath the ice there is a large valley, parts of which are approximately a mile deeper than the surrounding landscape.
"If you stripped away all of the ice here today, you'd see a feature every bit as dramatic as the huge rift valleys you see in Africa and in size as significant as the Grand Canyon. This is at odds with the flat ice surface that we were driving across - without these measurements we would never have known that it was there.
"What's particularly important is that this spectacular valley aligns perfectly with the recordings of ice-surface lowering and ice loss that we have witnessed with satellite observations over this area for the last 20 years."
The research, reported in the journal Nature, shows that the ice-filled rift basin is connected to the warming ocean.
This may have an impact on present-day ice loss, which is greater here than in other parts of Antarctica. Some West Antarctic glaciers are shrinking by more than a metre per year.
Co-author Dr Fausto Feraccioli, from the British Antarctic Survey, said: "The newly discovered Ferrigno Rift is part of a huge and yet poorly understood rift system that lies beneath the West Antarctic Ice Sheet. What this study shows is that this ancient rift basin, and the others discovered under the ice that connect to the warming ocean can influence contemporary ice flow and may exacerbate ice losses by steering coastal changes further inland."