Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event

Understanding the dynamic response of glaciers to climate change is vital for assessing water resources and hazards, and subglacial hydrology is a key player in glacier systems. Traditional observations of subglacial hydrology are spatially and temporally limited, but recent seismic deployments on and around glaciers show the potential for comprehensive observation of glacial hydrologic systems. We present results from a high-density seismic deployment spanning the surface of Lemon Creek Glacier, Alaska. Our study coincided with a marginal lake drainage event, which served as a natural experiment for seismic detection of changes in subglacial hydrology. We observed glaciohydraulic tremor across the surface of the glacier that was generated by the subglacial hydrologic system. During the lake drainage, the relative changes in seismic tremor power and water flux are consistent with pressurization of the subglacial system of only the upper part of the glacier. This event was not accompanied by a significant increase in glacier velocity; either some threshold necessary for rapid basal motion was not attained, or, plausibly, the geometry of Lemon Creek Glacier inhibited speedup. This pressurization event would have likely gone undetected without seismic observations, demonstrating the power of cryoseismology in testing assumptions about and mapping the spatial extent of subglacial pressurization.This work was made possible in part by hard work in the field by Margot Vore, Daniel Bowden, Galen Kaip, and the students and staff of the 2017 Juneau Icefield Research Program. We especially thank Matt Beedle for provision of the photogrammetrically-produced DEM of Lake Linda, following lake drainage. This work was also aided by the advice of Mike Gurnis and Rob Clayton. We thank Paul Winberry and two anonymous reviewers for their helpful feedback, which improved this paper greatly. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. This work was made possible in part by a University of Idaho seed grant, #FY18-01. DEM provided by the Polar Geospatial Center under NSF-OPP awards 1043681, 1559691, and 1542736.Ye