Post-eruption morphological evolution and vegetation dynamics of the Blanco River, southern Chile

Abstract

In this study, we analysed the morphological evolution of a channel segment in the Blanco River in southern Chile that was affected by the Chaitén Volcano eruption occurred in 2008–2009. Through a series of high-resolution satellite images from 2005 to 2019 that represents the entire pre- and post-eruptive dynamics and land covers, we tracked the geomorphological evolution of a 5.65-km-long river segment using channel form indices and also monitored the vegetation dynamics using object-based image analysis (OBIA). Discharge record for the Blanco River was also reconstructed to support the analysis of channel morphologic process. The study aims at examining whether a) the river channel is still adjusting 10 years after the eruption and if so, at what magnitude and, b) the recovered riparian vegetation plays a significant role in stabilising the river streambanks and terraces. We found that even 10 years after the eruption, the Blanco River channel planform is still adjusting, showing a simpler and stable channel configuration in the upstream reaches of the valley, where a certain degree of equilibrium appears to have been attained. More dynamic morphologies were observed in the reaches downstream that have to accommodate the arrival of large amounts of freshly eroded sediments. Our analysis showed that the occurrence of competent floods capable of reworking the river channel matches with the geomorphic indices and mark the post-eruption adjustments of the channel. Finally, the in-channel and riparian vegetation does not play a significant role in stabilising the active channel, streambanks, and terraces, reinforcing the recolonization of sedimentary active areas occurring elsewhere in the valley.

This research was developed within the frame of the project FONDECYT 1170413 funded by the Chilean Government. Authors acknowledge the support of the Economy and Knowledge Department of the Catalan Government through the Fluvial Dynamics Research Group (RIUS) SGR017-459.