Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage

Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid (< 2 hours) drainage of a large supraglacial lake down 980 meters through to the bed of the Greenland Ice Sheet initiated by water- driven fracture propagation evolving into moulin flow. Drainage coincided with increased seismicity, transient acceleration, ice- sheet uplift, and horizontal displacement. Subsidence and deceleration occurred over the subsequent 24 hours. The short- lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially. The integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup.