Greenland's 'grand canyon' was part of a large river system before an ice sheet covered it millions of years ago, a new study says. Now it appears to be a vital part of the island's plumbing.
Running from deep within the island's interior north to Greenland's northwest coast, the canyon measures at least 470 miles long, six miles across at its widest, and as many as 2,600 feet deep – reaching its widest and deepest points near the coast. The Grand Canyon, by comparison, is 277 miles long, 18 miles wide, and 6,000 feet deep.
The portrait points to how little scientists know about what lies beneath the world's great ice sheets. It also could help researchers understand how the ice sheet and melt water are working together to feed outlet glaciers along a coast where glaciers have been thinning at an increasing pace within the past decade.
Mapping Greenland's hidden landscape is important "so we can understand how the ice sheet is presently routing mass out toward its edges and how the ice sheet and water underneath the ice will interact," says Mark Fahnsetock, a geophysicist at the University of Alaska at Fairbanks.
In addition, the discovery could help solve a longstanding riddle: Why does Antarctica's ice sheet have lakes underneath it, but Greenland's ice sheet apparently does not? For the region the canyon traverses, the answer may be that the island has more efficient plumbing, says Dr. Fahnsetock, who was not involved in the study.
The first hints that the island's ice sheet, nearly two miles thick, was hiding such a feature emerged in the later 1990s. But the evidence was limited. No one anticipated a canyon of such magnitude.
The canyon lacks features that would signal it was formed by glaciers, suggesting that its predates the initial appearance of glaciers there about 38 million years ago, according to the team led by Jonathan Bamber, a glaciologist at the University of Bristol in Britain. His team built a profile of the canyon using 40 years of ice-penetrating radar data, which show the canyon meandering in ways that suggest it was carved by a large river system.