Landslide-lake outburst floods accelerate downstream hillslope slippage

Abstract

The Jinsha River, which has carved a 2-4km deep gorge, is one of the largest SE Asian rivers. Two successive landslide-lake outburst floods (LLFs) occurred after the 2018 Baige landslides along the river. Using Sentinel-2 images, we examined the LLF impacts on downstream river channels and adjacent hillslopes over a 100km distance. The floods increased the width of the active river channel by 54%. Subsequently, major landslides persisted for 15 months in at least nine locations for displacements >2m. Among them, three moving hillslopes ∼80km downstream from the Baige landslides slumped more than 10m 1 year after the floods. Extensive undercuts by floods probably removed hillslope buttresses and triggered a deformation response, suggesting strong and dynamic channel-hillslope coupling. Our findings indicate that infrequent catastrophic outburst flooding plays an important role in landscape evolution. Persistent post-flood hillslope movement should be considered in disaster mitigation in high-relief mountainous regions.