Landslide-lake outburst floods accelerate downstream hillslope slippage

The Jinsha River, which has carved a 2-4 km 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 100 km 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 >2 m. Among them, three moving hillslopes similar to 80 km 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.

Automated summary

The Jinsha River, one of the largest SE Asian rivers, experienced two landslide-lake outburst floods after the 2018 Baige landslides. Using Sentinel-2 images, researchers found that the floods widened the active river channel by 54% and triggered major landslides at least nine locations for 15 months. One year later, three moving hillslopes 80 km downstream from the Baige landslides slumped more than 10m after the floods.