2018 CSDMS meeting-128
Deterioration of the eastern margin of the Colonia Glacier, northern Patagonia: the end of a glacially-dammed alpine lake?
Lago Cachet Dos (LC2) is a glacially-dammed lake adjacent to the Northern Patagonian Ice Field (NPIF), formed by the blockage of Cachet Basin (CB) by the Colonia Glacier. This glacier has experienced rapid (~1-2 km) retreat of its terminus as well as ~1-2 m/yr of thinning, documented over the past several decades. Furthermore, the glacier has exhibited a change in hydrologic regime and the frequency of high energy glacial lake outburst flood (GLOF) events since 2008. These historical changes appear to be coupled with regional climate change; summer mean maximum and minimum temperatures in nearby Cochrane show a steady increase since 1971, whereas winter mean maximum temperatures show cooling in the 1970s and 1980s, followed by gradual warming with rapid acceleration in the 2000s-present. Preliminary correlations with a recently installed weather station at Sol de Mayo (~12 km downstream of the Colonia Glacier terminus) show a strong positive correlation with the Cochrane data, indicating these climate changes are regional and not local and thereby have implications for the evolution of other alpine basins of the NPIF and perhaps glaciers on a global scale. Recent observations from unmanned aerial vehicle (UAV) flights, satellite imagery, and geologic mapping suggest unprecedented glacier deterioration near the southern limit of CB. An UAV flight in January 2016 revealed that during GLOF events, the lake drained through a large hole at the base of the glacier. Upon entering this chasm, the water made a sharp east turn (towards the bedrock abutting the glacier’s eastern margin) and appeared to flow beneath the ice at this point. Subsequently, a large (~2km long x 100 m wide) supra-glacial channel has opened directly above the drainage hole, effectively separating the glacier from bedrock. Ice elevation data reveal that healing of this channel may not be possible under the current climate regime, suggesting the basin could be experiencing a long-term (over human timescales) shift to fluvial deposition from a dominantly lacustrine environment, corresponding to an inability to impound water associated with the glacier's retreat. Basin stratigraphy indicates these oscillations between lacustrine and fluvial conditions have occurred repeatedly throughout the Holocene, but the timing of these changes are poorly constrained. Optically stimulated luminescence (OSL) dating of CB sediments will be applied to identify the timing and periodicity of these depositional shifts, with the broader goal of linking these oscillations with local and regional climate and stability of the Colonia Glacier.