Glacial-lake outburst flood effects on Colonia River morphology, Chilean Patagonia

Rio Colonia, a tributary of the Baker River, drains the Northern Patagonia Icefield, and is experiencing a new cycle of Glacial-Lake Outburst Floods (GLOFs). The sudden draining of c. 200 hm3 from glacier-dammed Cachet 2 Lake, results in a 3-5 fold increase in discharge in Baker River, Chile's largest. Suspended sediment concentration also increases 8-fold and load 10 to 20-fold, totalling almost 5% of the annual load.Yet baseline studies of one of the dams of a US$7 billion hydropower project to flood the confluence doesn't consider GLOF dynamics. Moreover, Patagonia, the world largest complex of icefields and temperate glaciers, is experiencing warming trends and higher glacial-river flows. And the region is one of the largest unknowns in the global sediment flux to oceans. Here we compare present morphology and dynamics with the 1967-2007 outburst-free period and the previous outburst cycle that ended in 1968, with particular focus on the Colonia/Baker river confluence. Floodplain vegetation cover shows significant changes. Implications for a recently approved Baker dam are discussed.