Lakes of meltwater can crack Greenland's ice and contribute to faster ice sheet flow

Researchers captured this first sunset of summer over the Greenland ice sheet on July 22, 2007. A meltwater drainage channel lurks below. Click here for more information.

Thousands of lakes form on top of Greenland’s glaciers every summer, as sunlight and warm air melt ice on the surface. Past satellite observations have shown that these supraglacial lakes can disappear in as little as a day, but scientists did not know where the water was going or how quickly, nor the impact on ice flow.

Researchers have hypothesized that meltwater from the surface of Greenland’s ice sheet might be lubricating the base. But until now, there were only theoretical predictions of how the meltwater could reach the base through a kilometer of subfreezing ice.

“We set out to examine whether the melting at the surface—which is sensitive to climate change—could influence how fast the ice can flow,” Das said. “To influence flow, you have to change the conditions underneath the ice sheet, because what’s going on beneath the ice dictates how quickly the ice is flowing. If the ice sheet is frozen to the bedrock or has very little water available, then it will flow much more slowly than if it has a lubricating and pressurized layer of water underneath to reduce friction.”

In the summers of 2006 and 2007, Das, Joughin, and colleagues used seismic instruments, water-level monitors, and Global Positioning System sensors to closely monitor the evolution of two lakes and the motion of the surrounding ice sheet. They also used helicopter and airplane surveys and satellite imagery to monitor the lakes and to track the progress of glaciers moving toward the coast.

Glaciologist Sarah Das (left) and graduate student Maya Bhatia examine a crevasse near a recently drained meltwater lake basin in Greenland. Click here for more information.

The most spectacular observations occurred in July 2006 when their instruments captured the sudden, complete draining of a lake that had once covered 5.6 square kilometers (2.2 square miles) of the surface and held 0.044 cubic kilometers (11.6 billion gallons) of water. Like a draining bathtub, the entire lake emptied from the bottom in 24 hours, with the majority of the water flowing out in a 90-minute span. The maximum drainage rate was faster than the average flow rate over Niagara Falls.