While stability far from assured, Greenland perhaps not headed down too slippery a slope

"We don't yet know what warming temperatures means for increased calving of icebergs from the fronts of these outlet glaciers," Joughin says.

Until now scientists have only speculated if, and how, surface meltwater might make it to bedrock from high atop the Greenland Ice Sheet, which is a half-mile or more thick in places. The paper "Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage," with Woods Hole Oceanographic Institution's glaciologist Das as lead author, presents evidence of how a lake that disappeared from the surface of the inland ice sheet generated so much pressure and cracking that the water made it to bedrock in spite of more than half a mile of ice.

The glacial lake described in the paper was 2 to 2 ½ miles at its widest point and 40 feet deep. Researchers installed monitoring instruments and, 10 days after leaving the area, a large fracture developed, a crack spanning nearly the full length of the lake. The lake drained in 90 minutes with a fury comparable to that of Niagara Falls. (The researchers were ever so glad they hadn't been on the lake in their 10-foot boat with its 5-horsepower engine and don't plan future instrument deployments when the lakes are full of water. They'll get them in place only when the lakes are dry.)

Measurements after the event suggest there's an efficient drainage system under the ice sheet that dispersed the meltwater widely. The draining of multiple lakes each could explain the observed net regional summer ice speedup, the authors write.

Along with Das and Joughin other authors on the two papers are Matt King, Newcastle University, UK; Ben Smith, Ian Howat (now at Ohio State) and Twila Moon of the UW's Applied Physics Laboratory; Mark Behn and Dan Lizarralde of Woods Hole Oceanographic Institution; and Maya Bhatia, Massachusetts Institute of Technology/WHOI Joint Program.

For more information:

Joughin, (206) 221-3177,

Das, , or contact PIO Mike Carlowicz, (508) 289-3340,

Alley, (814) 863 1700, (Note that Alley will be away from his office April 16)

Look for companion press release from WHOI, "Lakes of meltwater crack the top of Greenland's Ice Sheet, make some ice move faster," which also is being posted on EurekAlert, www.eurekalert.org/. Video is available for news media from WHOI, contact Carlowicz.