A vast and previously unmapped gorge 800 meters (half a mile) deep has been found under ice in Greenland, comparable in size to parts of the Grand Canyon in the United States, scientists said.
Other studies have also revealed a rift valley entombed in Antarctica's ice in 2012 that scientists said may be speeding the flow of ice towards the sea, and a jagged "ghost range" of mountains buried in Antarctica in 2009 similar to the Alps.
"It's remarkable to find something like this when many people believe the surface of the Earth is so well mapped," lead author Jonathan Bamber, of the University of Bristol in England, said of the canyon described in Friday's edition of the journal Science.
"On land, Google Street View has photographed just about every building in every major city," he told Reuters of the study, using ice-penetrating radar and carried out with colleagues in Canada and Italy.
The canyon is 750 km (470 miles) long in central and north Greenland and comparable in scale to parts of the Grand Canyon that is twice as deep - 1.6 km - at its deepest, they wrote. The Greenland canyon is buried under about 2 km of ice.
About as long as the Rhone river in France and Switzerland, the ravine was probably cut by an ancient river that eroded rocks as it flowed north before temperatures cooled and ice blanketed Greenland 3.5 million years ago, they wrote.
The gorge probably still plays a role in draining some meltwater from beneath the ice sheet.
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