Glacial Moulin Formation Triggered by Rapid Lake Drainage
Moulins are the conduits that allow water melting on the surface of the Greenland Ice Sheet to drain to its base and cause the ice to flow faster. This study compared moulins mapped from satellite-images to computer simulations of stresses in the ice constrained by hourly, on-site ice velocity measurements from GPS stations. Most moulins in the study could only form from large ice stresses that occurred when a lake on the ice sheet surface drained to the bottom of the ice sheet.
Rare and brief lake drainages must be the cause of most of the moulins around the edges of the Greenland Ice Sheet, and they, therefore, have a lasting impact on the flow of water into the ice sheet and the changes in the flow of the ice this causes.
Moulins are the conduits that allow water melting on the surface of the Greenland Ice Sheet to drain to its base and cause the ice to flow faster. Forming a moulin in Greenland requires a crack on the surface that becomes filled with enough water to drive the crack all the way through the ice. However, a large fraction of moulins in Greenland forms away from the ice sheet’s crevasse fields, making their formation a mystery. We forced a model of ice sheet flow to match measurements of the ice speed measured by GPS every two hours. At most of the moulin locations in the area studied, the stresses predicted by the model were too small to fracture the ice and allow moulins to form during winter, spring, and most of summer. However, fracturing did occur at most moulin locations when large lakes on the surface of the ice drained catastrophically to the bed over a few hours. These rare and brief lake drainages must be the cause of most of the moulins, and they, therefore, have a lasting impact on the flow of water into the ice sheet and the changes in the flow of the ice this causes.