Abstract

The Blanco River basin (Patagonia, southern Chile) was highly altered by the 2008-2009 eruption of Chaitén Volcano. Pyroclastic density currents, lahars and remobilized sediment and channel reworking additionally obliterated floodplain forests, filling the lower course of the river with several meters thick volcanic sediments and large wood. Field surveys during January and March 2015 and 2016 in three 80 m-long study reaches of the active channel showed large wood load fluctuations between 64-316 m3 /ha. Following these first surveys, large wood and wood jam volumes were calculated using the structure from motion technique taking advantage of drone surveys. Between 3 and 4 years after the first surveys, total wood volume has increased attaining 101-757 m3 /ha. Data indicate that the large wood volume is not decreasing with time and that it is higher in the upstream reaches, suggesting that the river is still adjusting downstream after the disturbance, recruiting wood from different sources.