Seismo Lab Seminar

Greenland ice flow is highly responsive to surface meltwater input into the subglacial hydrological system; however, the mechanisms that control this relationship remain poorly constrained. Season variations in ice velocity are most often explained by two competing hypotheses that make contradictory predictions for long-term ice sheet behavior in a warming climate: a self-regulating subglacial hydrological system, or a sediment-controlled system with evolving till strength. We use integrated seismic and geodetic observations in western Greenland to test these hypotheses. We show that the large influx of meltwater to the basal hydrologic system following a rapid supraglacial lake drainage weakens and mobilizes basal sediments, leading to an acceleration in ice flow and increased sensitivity to subsequent runoff variations. As the melt season ends, the sediment restrengthens, leading to a reduction in ice velocity. Our results provide the first continuous, seasonal constraints of basal sediment control on ice sheet dynamics, provide new evidence for the role of supraglacial lake drainages in modifying basal sediment strength, and highlight the need for future work to better understand the distribution of subglacial sediments and the effects of predicted increased runoff and expansion of lakes on future ice flow and sea level rise.