| Summary: | Catastrophic drainage of glacier-dammed lakes can have significant downstream impacts. The role of the little-studied englacial hydrological system is investigated during the filling and drainage of an ice-marginal lake dammed by the Kaskawulsh Glacier in Yukon, Canada. Geophysical and hydrometeorological instruments were deployed to monitor the hydrology and dynamics of the lake--glacier system. Water-balance calculations reveal that of the ~44.1 million cubic metres of water in the catchment at peak lake level, the subglacial and englacial reservoirs store approximately 55% and 22%, respectively, compared to 23% in the subaerial lake. Abrupt changes in ice-shelf uplift rates, associated with fracturing and faulting, are linked to the redistribution of englacial water (1.6--6.6% estimated water content) based on borehole water-pressure and radar reflection-power data. Characterizing the dynamic coupling of the reservoirs, and the abrupt nature of connections between them, represents an advance in our conceptual understanding of glacier lake outburst floods.
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