Analysis of Channel Morphology and Large Wood Characteristics Through Remote Images in the Blanco River After the Eruption of the Chaitén Volcano (Southern Chile)

Abstract

Volcanic eruptions drastically affect fluvial systems, modifying channel morphology and processes of supply and transport of sediment and wood material, destroying vegetation and reducing infiltration rates on hillsides. This work aims to study the morphological changes and the distribution of large wood (LW) material along the Blanco River after the eruption of the Chaiten volcano in May 2008 using aerial and satellite images. Four different images from pre and post-eruption conditions were used: a satellite image from 2005, an aerial one from 2009, and two satellite images from 2012 and 2013. To assess river morphology, the active channel was digitized in all the images; and LW assessment was carried out by digitizing every individual element as polyline and wood jams as polygons. Results showed a general increase in the channel width, being the most notable change between 2005 and 2009. The same occurred in the case of LW supply, both individual elements and wood jams within the active channel increased significantly between 2005 and 2009 but there were no statistically significant differences comparing 2009, 2012 and 2013 images. This drastic event provided an opportunity to study post-eruption situation in the Blanco River, and with the results obtained it was possible to verify that the shape of the channel and presence of LW were strongly affected by the volcanic eruption.