Quantifying lateral bedrock erosion caused during a hyperconcentrated flow in a narrow alpine limestone gorge

Abstract

Here, we show results of an unprecedented LiDAR dataset quantitatively determining the lateral bedrock erosion of a narrow limestone gorge during an extreme hyperconcentrated flow. The comparison of two point clouds prior and post to the June 15th hyperconcentrated flow event provide information about the massive breakout of particles and abrasion of the channel walls. With a multiscale model to model cloud comparison analysis, we can show that particles from 0.0001 m3 and 3.5 m3 were eroded from the subvertical limestone gorge walls. A total of 20.9 m3 of massive bedrock was eroded in the observable part of the channel with 90 % of the particles being smaller than 0.15 m3. We delimited two main erosion processes during the hyperconcentrated flow event: shearing of particles that reach into the flow and particles with predefined failure surfaces, and abrasion along the whole channel, detectable by LiDAR if the changes are > 3 cm. This study provides quantitative evidence for massive rock erosion processes in alpine gorges that could also control rock gorge formation and evolution over Holocene/Lateglacial time scales.