LiveScience: Geoscientists have solved a decade-long mystery of how some of the large lakes that sit atop the Greenland ice sheet can completely drain billions of gallons of water in a matter of hours. In 2006, Greenland's North Lake, a 2.2 square-mile (5.6 square kilometers) supraglacial meltwater lake, drained almost 12 billion gallons of water in less than two hours. In a study published two years later, researchers determined that this astonishing phenomenon is possible because giant hydro-fractures (water-driven...