Integrated hydrology and glacier dynamics: Key outcomes from the RESPONDER project on Store glacier, Greenland

Fast flowing outlet glaciers drain the Greenland Ice Sheet by transporting ice from the interior to its marine-terminating margins. In contrast to the widely studied land-terminating ice margin, where flow has decreased over the last several decades, outlet glaciers are flowing faster, posing a global risk of accelerated sea level rise. Here we report outcomes from the interdisciplinary RESPONDER project, focusing on Store Glacier in West Greenland. Using GPS-assisted drones with high accuracy, we tracked meltwater pathways and found surface water to descend rapidly to the bed when supraglacial lakes are intercepted by extensional fractures forming along pre-existing structural weaknesses. The subglacial drainage path was located initially through hydropotential analysis and subsequently by the frequency of tremors and icequakes recorded in a passive seismic network, while GPSs recorded uplift. We used a hot-water drill to gain access to the bed at specific targets, which included the shore of a rapidly draining lake, and the drained lake floor where a moulin subsequently delivered a significant, but varying supply of surface water to the basal drainage system. The basal water pressures were high, sometimes above floatation. The pressures also varied according to moulin discharge, with in-phase variations reflecting hydrological connectivity at the bed, whereas out-of-phase variations in a borehole just 50 m away reflect a purely mechanical response there. We report deep crevasse penetration from optical televiewing as well as outcomes from distributed temperature sensing with a fiber optic cable, in what may be the first glaciological application in Greenland. This experiment revealed so far unidentified englacial heat sources and a 100-m-thick layer of basal temperate ice, which may have formed from energy originating at the surface.