http://www.sciam.com/article.cfm?id=greenl...speeding-to-sea

"On July 29, 2006, there was a roughly 11-billion-gallon (0.044–cubic kilometer) lake that stretched more than two square miles (5.6 square kilometers) and covered the western portion of Greenland's massive ice sheet. In the span of 16 hours, it was gone. The reason: water pressure cracked through the more than half-mile (980-meter) thick ice, draining the lake as its water rushed through the new funnel and gathered below the giant ice sheet, raising it nearly four feet (1.2 meters) and moving it nearly three feet (0.8 meter) to the north.

"My co-workers and I had proposed models [in which] meltwater gets to the bed when a lake fills a crevasse, thus driving the crack down," says glaciologist Richard Alley of Pennsylvania State University who was not involved in the study. Now glaciologist "[Sarah] Das [and her colleagues] have observed it—more than Niagara plunging into Greenland!"

In fact, Niagara Falls's flow per second can be as fast as 202,000 cubic feet (5,720 cubic meters) of water; the glacial lake drained at pace of 307,237 cubic feet (8,700 cubic meters) per second. The meltwater below the glacier then flowed away through channels in the rock below, allowing the ice to subside back to its normal position. "