Giant Canyon Discovered Under Greenland Ice Sheet

Summer meltwater has drained through a snow-covered channel in Greenland. Scientists say that the Greenland Ice Sheet sits atop a canyon twice as long as the Grand Canyon. Photograph by James Balog, National Geographic

Imagine if you could pick up the Greenland Ice Sheet and see what lies beneath. Surely 1.7 million square kilometers of slowly thawing ice must rest on a massive pool of melted water, right?

Not necessarily, according to a study released today in the journal Science. Unlike the ice sheet covering Antarctica that sits atop numerous lakes, the Greenland Ice Sheet blankets a giant subglacial canyon nearly twice as long as the Grand Canyon located in Arizona. (Read: "Changing Greenland" in National Geographic magazine.)