Glacial Lake Drainage

Thousands of supraglacial lakes form each spring and summer on top of the Greenland Ice Sheet as sunlight returns to the region. Many lakes disappear within hours when large cracks form below them, draining the lakes and sending torrents of water to the base of the ice sheet. To learn what triggers this phenomenon, a team of scientists installed a network of GPS units around a lake.

The depression directs the flow of ice downward, compressing ice on either side together at the bottom of the depression. As melting increases, more streams feed the expanding lake.

An outflow stream from the lake spills water into the moulin, which transports it to the base of the ice sheet.

Thousands of supraglacial lakes form each spring and summer on top of the Greenland Ice Sheet as sunlight returns to the region. Many lakes disappear within hours when large cracks form below them, draining the lakes and sending torrents of water to the base of the ice sheet. To learn what triggers this phenomenon, a team of scientists installed a network of GPS units around a lake.

In 2006, scientists at WHOI and the University of Washington discovered that cracks can form suddenly at the bottom of lakes on the Greenland Ice Sheet and drain the lakes within hours. To learn why these cracks, or hydrofractures, form, the researchers installed a network of GPS receivers to record subtle movements of the ice before, during, and after a sudden drainage. In 2015, the researchers published a new study that revealed a fascinating sequence of forces and events that triggers the cracks. The water drains to the bedrock, lubricating the flow of ice to the sea and accelerating sea level rise.

These cracks, called hydrofractures, drain the entire lake within an hour or two. Water flows out of the lake bottom faster than the water goes over Niagara Falls. The influx of water at the base of the ice sheet causes the ice sheet to slide faster toward the coast. That accelerates the outflow of ice from land to sea and causes sea levels to rise faster.