Disappearing lakes in Greenland have long been a mystery to geologists and other researchers working to understand the strange glacial lakes. Now, a team of investigators believe they have solved the riddle behind this bizarre geological behavior.
Woods Hole Oceanographic Institution (WHOI) researchers, together with colleagues from the University of Washington, showed in 2008 that cracks can form in the bottoms of glacial lakes, capable of swallowing the water bodies entirely in just a couple hours. However, no one knew the mechanism that triggered these cracks until now.
North Lake, a supraglacial lake in southwestern Greenland where cracks and draining were first reported, was encircled by a ring of 16 GPS units. Movement of the ground around the 1.5-mile-long lake was carefully recorded during a trio of drainage events in 2011, 2012 and 2013.
Data revealed that six to 12 hours before a drainage event, the ice moved upwards and shifted. Researchers believe meltwater runs down vertical channels in the ice sheet that connect the surface to the base 3,215 feet below. Once enough water collects down there, it can lift the ice sheet, which builds tension in the ice beneath the lakes. If this gets too severe, the force can result in the creation of massive cracks. If the quantity of water in the lake is great enough, the water can expand the crack, leading to a runaway draining of the water down to the base of the ice sheet. Researchers estimated that, at its greatest flow, this lake drained water faster than the liquid flows over Niagara Falls.
"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. 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," said Laura Stevens of the Joint Program in Oceanography managed by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution (MIT/WHOI).
Some researchers had previously proposed that the mammoth weight of the water on the frozen lake bottom applied gargantuan pressure on the ice, finally resulting in the development of a crack. However, this theory could not explain why some of the lakes drained while others stayed in place. This new theory explains the mystery by explaining that both the initial fracture, as well as a large volume of water in the lake, is required for the water body to suddenly disappear.
Glacial lakes form as warming temperatures each spring melt ice in glaciers, which form lakes and ponds on the frozen surface.
Discovery of the means by which these glacial lakes suddenly disappear was published in the journal Nature.
