Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods

Changes in the velocity of large outlet glaciers and ice streams in Greenland and Antarctica are important for ice-sheet mass balance and hence sea level(1). Mass loss in large parts of both ice sheets is being driven by the recent accelerations of outlet glaciers(2-5) in response to unknown or poorly constrained climatic or internal perturbations in their boundary conditions. Surprisingly active networks of subglacial lake drainage have recently been found beneath the Antarctic ice sheet and tentatively linked to the onset of fast ice flow(6-8). Here we report an observed acceleration of ice velocity on Byrd Glacier, East Antarctica, of about 10% of the original speed between December 2005 and February 2007. The acceleration extended along the entire 75 km glacier trunk and its onset coincided with the discharge of about 1.7 km(3) of water from two large subglacial lakes located about 200 km upstream of the grounding line. Deceleration coincided with the termination of the flood. Our findings provide direct evidence that an active lake drainage system can cause large and rapid changes in glacier dynamics.