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.)

Scientists suggest the canyon—which runs as deep as half a mile (800 meters) and as long as 466 miles (750 kilometers)—is paleofluvial, meaning it originated as a system of rivers in Greenland's hard bedrock surface. According to this research, the canyon is part of an organized valley system that carries meltwater away from the inland ice sheet and funnels it toward coastal fjords connecting to the Arctic Ocean. (Related: