Abstract
Water at glacier beds has been repeatedly linked to short term ice-velocity fluctuations and plays a key role in theoretical models of glacier surging. However, the details of water storage in the surge cycle, including where and when water accumulates and drains, remain unclear. Here, we use seismic noise interferometry to monitor changes in water volume near the glacier bed through the surge cycle at Sít’ Kusá, Alaska, and infer evolution in the structure of the drainage system. Within the reservoir zone, we identify multi-year water accumulation during quiescence in a poorly connected basal drainage system, followed by a rapid decrease in basal water volume driven by a reorganization toward a better-connected system that coincides with surge termination. This multi-year cycle is overlain by similar dynamics at the seasonal timescale that modulate annual increases in ice velocity within the reservoir zone. We speculate that reorganization of subglacial drainage and increases in connectivity between previously isolated water volumes can play a central role in the onset of high ice velocities during both seasonal speedups and surges. Our findings regarding the long-term evolution of water storage near the bed fit well within enthalpy-based models of glacier surging.