Ice velocities in a west Greenland glacier during the summer can exceed its velocity during the winter by 220%, according to a study published online this week in Nature Geoscience. The findings are important for understanding the response of glacier movement to surface melting and to changes in the water drainage system beneath the glacier.

Ian Bartholomew and colleagues used GPS receivers along a 35-km transect into the western margin of the Greenland ice sheet to measure ice velocity throughout summer 2008 and into the subsequent winter season. The scientists found increases in glacier speed that coincided with an uplift of the glacier surface, indicative of the delivery of surface melt water to the glacier bed. Further inland, glaciers sped up later in the year.

The authors conclude that if summer melt seasons become longer and more intense, glacier acceleration events in response to meltwater will reach further inland, thus drawing ice from a larger area of the ice sheet.