Greenland's Vanishing Glacial Lake Mystery Solved with New Study

Each summer, Greenland's ice sheet begins to melt. Pockets of this melting ice create glacial lakes on the surface and, eventually, drain through cracks and crevasses to create a liquid layer over which massive chunks of ice can slide. Now, scientists have taken a closer look at these lakes to see if they could worsen the ice sheet's contribution to sea level rise.

"One of the big questions about the Greenland ice sheet is how much of the ice sheet [travels towards the coast] during the summer, and how much is entering the ocean," said Laura Stevens, one of the researchers, in a news release. "Our hypothesis that inland lakes are less likely to drain locally suggests the ice sheet in that region won't speed up. That's good news, at least for the time being."

In the summer of 2006, researchers visited Greenland to document the drainage of North Lake, a 10-meter-deep, 2-kilometer-wide lake on the western side of Greenland. Each summer, the lake, like many others, drained quickly, completely emptying in just a couple hours.

During its draining, the researchers set up one GPS station near the lake to record the surface of the ice. They identified a large fracture in the basin through which the water drained; however, they weren't quite sure what triggered this crack.

In 2011, the researchers returned and set up 16 GPS stations in two rings around the lake, and recorded the movement of the ice as the lake drained over three consecutive summers. They found that water will cause the ice above it to be jacked up like a dome. This creates tension at the surface that allows he ice sheet to start to fracture. Once this fracture gets beneath the lake, the water drains.

But will these draining lakes contribute to sea level rise? According to researchers, it's not much. Lakes further inland than North Lake and at higher elevation form over thicker ice. This means that the ice is unlikely to crack and cause drainage. In addition, they were fewer moulins near inland lakes, which prevents water from getting to the ground locally.

"It is critical to understand how and why these lakes drain in order to predict how much mass the ice sheet will contribute to sea-level rise in our warming climate," said Stevens. "We find that while lakes are forming inland, they probably won't drain by this...mechanism. The inland lakes will more likely drain their water via surface stream runoff, which transfers the water to the bed in more coastal areas of the ice sheet."

The findings are published in the journal Nature.

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