Quantifying environmental controls on the magnitude of glacial lake outburst floods and the resulting impacts to hydrology and geomorphology: Lago Cachet Dos, Patagonia, Chile
AuthorJacquet, Jonathan Daniel
AdvisorMcCoy, Scott W
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The sudden release of water from an ice-dammed lake poses substantial hazard to the downstream environment, but the degree to which peak discharge depends on environmental variables that change with climate remains unclear. We combine in situ measurements of environmental variables with high-resolution discharge measurements from a glacier-dammed lake, Lago Cachet Dos (LC2), to evaluate environmental conditions that influence the peak discharge of observed glacial lake outburst floods (GLOFs). Since April 2008, 20 GLOFs have initiated out of LC2, located on the eastern edge of the Northern Patagonia Icefield, Chile and flooded areas along the Rio Colonia- Rio Baker system. GLOF frequency has averaged 1-3 events annually and calculated peak discharges exiting LC2 have ranged widely from 2,000 to >15,000 m3/s. We show that, consistent with physics-based theory, increasing water volume released, lake temperature, and the rate of meltwater input into the glacially dammed lake all increase the peak discharge of observed GLOFs. Additionally, we quantify the hydrologic and geomorphic response to episodic GLOFs using multi-temporal satellite imagery and field observations. Peak discharge exiting the source lake exceeded 15,000 m3/s, but became progressively muted downstream. At ~40 km downstream, peak discharges were generally < 2000 m3/s, but still > 15 times the median discharge. The GLOFs resulted in > 40 m of downcutting and erosion of ~25 x106 m3 of sediment from the source lake basin and a non-steady channel configuration downstream. Our results suggest that more accurate predictions of GLOF magnitude from ice dammed lakes can be made by incorporating additional measurements of environmental conditions and that quantifying GLOF water and sediment fluxes in the Colonia system may provide insight into potential changes that similar fluvial systems could experience after the onset of large floods.