How Arctic flow can snowball

For several years, scientists have worried that meltwater plunging from the surface of Greenland's ice sheet to the bedrock below has in effect greased the skids – accelerating the rate at which Greenland is losing ice.

Now, a team of researchers from the US and Britain suggests that while water under the ice is an important lubricant, it's unlikely to cause a catastrophic loss of Greenland ice as the climate warms. The more significant mass loss is likely to come from the speedup of glaciers that bring ice to the ocean. For the glaciers, lubricating of the underside appears to be less important than the loss of ice shelves along the coast that were grounded on the seafloor and acted as a brake on glacier movement.

Still, the team from the University of Washington, the Woods Hole Oceanographic Institution, and Newcastle University in Britain got a first-hand look at how powerful a lubricant icecap meltwater can be.

Their instruments recorded the loss of a lake covering some 2 square miles of icecap surface to a depth of up to 40 feet. Once water began working its way down a crevasse, the crack grew until it reached the ground a half mile below. The entire lake drained in less than two hours, with a peak flow higher than the average gush over Niagara Falls. The results of these studies appear at Sciencexpress, the online edition of the journal Science.