Why Greenland Ice Sheet's Massive Glacial Lakes are Suddenly Draining

First Posted: Jun 03, 2015 05:35 PM EDT

Scientists may have discovered why massive glacial lakes atop the Greenland Ice Sheet drain suddenly. They've found a surprising mechanism that triggers cracks where the water drains.

"Our discovery will help us predict more accurately how supraglacial lakes will affect ice sheet flow and sea level rise as the region warms in the future," said Laura Stevens, the lead researcher, in a news release.

In order to find out what triggers the sudden lake drainages, the researchers deployed a network of 16 GPS units around North Lake, a 1.5-mile-long supraglacial lake in southwest Greenland, where the scientists first documented large-scale cracks and lake drainages. The researchers used these instruments to record movements of the ice before, during, and after three rapid lake drainages in the summers of 2011, 2012 and 2013.

So what did they find? In the six to 12 hours before the lake cracked and drained, the ice around the lake moved upward and slipped horizontally. Meltwater had actually begun to drain through a nearby system of moulins, which are vertical conduits through the ice, which connect the surface to the base of the ice sheet. The accumulated water created a bulge that floated the entire ice sheet, creating tension at the surface underneath the lake. The stress builds up until it's relieved by a sudden, large crack in the ice below the lake.

"In some ways, ice behaves like Silly Putty-if you push up on it slowly, it will stretch; if you do it with enough force, it will crack," said Stevens. "Ordinarily, pressure at the ice sheet surface is directed into the lake basin, compressing the ice together. But, essentially, if you push up on the ice sheet and create a dome instead of a bowl, you get tension that stretches the ice surface apart. You change the stress state of the surface ice from compressional to tensional, which promotes crack formation."

The findings reveal a bit more about how these cracks form and, in turn, how this water drains. This, in turn, may allow researchers to better predict melting in the future.

The findings are published in the journal Nature.

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TagsGreenland Ice Sheet, Climate Change, Glacial Lakes, Climate