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Images: Scientists Find Trigger That Cracks Lakes

After long dark winters, sunlight returns to Greenland each spring and heat melts ice. The meltwater streams into depressions in the ice to form large supraglacial lakes. (Laura Stevens, Woods Hole Oceanographic Institution)
Thousands of supraglacial lakes form each summer on top of the Greenland Ice Sheet. Scientists had found that the lakes can drain completely within hours, sending torrents of water to the base of the ice sheet. That lubricates the interface between rock and ice, which allows the ice sheet to flow faster to the ocean. When more ice is discharged into the ocean, sea levels rise faster. (Laura Stevens, Woods Hole Oceanographic Institution)
To study supraglacial lakes, scientists over the last several summers have helicoptered atop the Greenland ice sheet to set up a research camp. Laura Stevens, a graduate student in the MIT-WHOI Joint Program in Oceanography, joined the team on the ice in 2013. (Laura Stevens, Woods Hole Oceanographic Institution)
A helicopter brings researchers and equipment to a supraglacial lake atop the Greenland Ice Sheet. If you look closely in the background, you can see the tents of the scientists’ ice camp. (Laura Stevens, Woods Hole Oceanographic Institution)
Over the last several years, researchers have established camps each summer on the Greenland Ice Sheet to study supraglacial lakes. (Laura Stevens, Woods Hole Oceanographic Institution)
In a tent in their ice camp, Woods Hole Oceanographic Institution scientists Mark Behn (left) and Sarah Das (right), and Ian Joughlin from the University of Washington, plan research strategy. (Chris Linder, Woods Hole Oceanograhic Institution)
To find out what triggers the sudden draining of supraglacial lakes, WHOI scientits Sarah Das (left) and Mark Behn and colleagues deployed a dense network of GPS units around a lake to record movements of the ice before, during, and after sudden drainage events. (© 2012 Chris Linder)
The scientists found that water spilled into moulins, or vertical conduits through the ice, and was transported to the base of the ice sheet. This accumulating water eventually created a bulge between the bedrock and the base of the ice, which floated the entire ice sheet. That exerted tension at the surface, underneath the lake. The stress built up until it was relieved by a sudden large crack in the ice below the lake. (Ian Joughin, University of Washington)
Water pours into a seemingly bottomless moulin on the ice sheet. But water eventually does reach a bottom: the bedrock below the ice. (Chris Linder, Woods Hole Oceanograhic Institution)
Graduate student Laura Stevens was lead author of a new study that identified a surprising trigger mechanism that causes large cracks to split open the bottoms of supraglacial lakes. The study was  published in the prestigious scientific journal Nature. (Sarah Das, Woods Hole Oceanographic Institution)
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