Abstract

The rapid in situ drainage of supraglacial lakes drives transient accelerations in ice flow on the Greenland Ice Sheet and creates the surface-to-bed hydraulic pathways that deliver surface melt water to the ice-bed interface throughout the remainder of the melt season. Records of lake discharge, ice motion and passive seismicity capture the rapid drainage of a ∼ 4 km2 supraglacial lake through 1.1-km-thick ice in West Greenland. These observations allow detailed insight into the opening and closure of hydraulically-driven fractures and the transient acceleration in ice flow caused by the delivery of large volumes of water to the bed. Furthermore, the observed expansion of surface melt and supraglacial lakes to higher elevations in recent warm summers correlates with an acceleration in annually-averaged ice flow in the Greenland ice sheet’s interior. These observations contrast with the prevailing hypothesis that annually-averaged flow in the ablation area is regulated by slower winter flow following warmer, faster summers.