Geomorphological evolution of the Blanco Este River after recent eruptions of the Calbuco volcano, Chile

Abstract

In this paper, we retrace the geomorphological evolution of a 6.5 km-long segment of the Blanco Este River, which drains the Calbuco volcano in southern Chile, highlighting the geomorphic signatures of the disturbances caused by the 1961 and 2015 eruptions. In particular, we track the geomorphological changes and the evolution of the geomorphological units and discuss the underlying processes. In addition, we use the NDVI (Normalize Difference Vegetation Index) to characterise the vegetation recovery at the basin and the active channel scales. The reconstruction of the geomorphological changes is performed by means of photointerpretation and supervised classification image analysis. Moreover, we quantify braiding indices and active channel widths to characterise the fluvial corridor and to describe its evolution after the two eruptive events. It is found that the evolutionary trajectories of the Blanco River immediately after the eruptive events of 1961 and 2015 exhibited strong similarities. In fact, the major geomorphological adjustment of the Blanco Este River occurred during the first period of observation (19 years) after the 1961 eruption. Subsequently the river progressed gradually towards an advanced relaxation stage in 2014. For 53 years (between 1961 and 2014), the reduction of the active channel width was the dominant process, followed by erosion, which favoured the regeneration and consequent expansion of vegetation cover within the river corridor. The 2015 eruption reset the fluvial landform and a new cycle of sedimentation, braiding and formation of central bars began; the highly dynamic pattern is still observed today.