Beneath Greenland's ice, a grand canyon


British and American scientists watching Greenland's massive ice sheet have found what appears to be a 460-mile "megacanyon" far beneath the frozen surface of the world's largest island.

Airborne radar images taken by the U.S. space agency NASA and compiled by scientists at the University of Bristol revealed the canyon's existence, Bristol glaciologist Jonathan Bamber said Thursday. It's buried under the layer of ice that blankets Greenland, a covering up to 3 kilometers

(1.9 miles) thick.

The gouge is about 50% longer than Arizona's 277-mile Grand Canyon, but not as deep -- ranging from 650 feet to about 2,600 feet (200 to 800 meters), Bamber said. It runs from the middle of Greenland to its northern shore, on the Arctic Ocean, and it's likely to have been covered over by ice for 4 million years.

"It's a continuous canyon. It's pretty deep. It very much looks like it predates the ice sheets," Bamber said. "We think it's indicative of a river system that was here before the ice sheet was there, and which perhaps was modified by the ice sheet cover some, but not much."