This vast gorge might rival the Grand Canyon in splendor … if only it weren’t smothered by a couple of kilometers of ice. By stitching together data gathered by ice-penetrating radar equipment suspended from aircraft, researchers have discovered a massive canyon that has likely been hidden for millions of years. This unexpected, yet-to-be-named feature (colored mid- to dark brown in the exaggerated topography above) stretches 750 kilometers—about twice the length the Grand Canyon—from central Greenland (lower center of image) all the way to a fjord along the northwestern coast (top of image). It’s about as wide as the Grand Canyon (10 kilometers) and nearly half as deep at its deepest point (800 meters), the researchers report online today in Science. The proportions of the canyon, as well as its meandering path, suggest that the feature was carved by a great river well before the island was coated with ice, not by glacial action in the years since. Without the ice sheet that is now weighing down Greenland’s terrain, a river in the canyon would, on average, drop about 30 centimeters for every kilometer it flowed seaward, the team estimates. The continually dropping slope helps explain why northern Greenland, unlike Antarctica, has no large subglacial lakes: Meltwater that either forms at the base of Greenland’s ice sheet or ends up there after draining from the ice sheet’s upper surface flows away uninterrupted. This massive flow may also help explain the gargantuan channels on the underside of the floating ice shelf attached to the coast where this canyon meets the sea, the researchers contend. Previous studies have attributed those undersea channels—which measure between 1 and 2 km wide and extend up into the ice shelf as much as 400 meters—solely to the melting action of seawater.
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