Cyclic landslide-flood chains along a major mountain river

Abstract

Landslides are a crucial Earth surface process in mountain landscapes, rapidly transporting large amounts of sediment into lower-elevation areas, and periodically negatively impacting people and their livelihoods. Most studies focus on their immediate, local-scale impacts, but few recognize their remote impacts in mountain environments. In particular, major landslides along rivers can block river channels to form lakes through backwater inundation, posing a flood hazard to downstream areas. In 2018, two landslides occurred along the Baige section of the Jinsha River, eastern Tibetan Plateau, forming two landslide lakes and subsequently, causing two flood events. In this study, we explore the impacts of these events on hillslopes along the river banks, upstream and downstream of the Baige site. Using small baseline subset Interferometric synthetic-aperture radar (SBAS InSAR), we find many active landslides along the Jinsha River and detect a sudden acceleration in these instabilities following the 2018 events. We attribute upstream instabilities to an increase in river width and depth, related to the remains of the landslide dam, while downstream slope instability is likely caused by undercutting along the outburst route. Modelling indicates that failure of these newly detected landslides may block the river again and potentially extend the hazard chain. This work demonstrates that landslides along major rivers can initiate new instabilities, and that even a short-lived landslide-dammed lake can have long-term impacts on stability of hillslopes in river valleys.