Preliminary analysis of the mechanism in the July 16, 2022 Gaojiashan cascading hazard: a landslide-induced debris flow in Southwest China

Debris flows can be triggered by landslides and lake outbursts, constituting cascading hazards that pose threats to life and property. However, cascading mechanisms are poorly understood due to the complex energy transfer and material transformation among precipitation, landslides, floods, and debris flows. Here, we aim to identify the cascading mechanisms and key controls of the Gaojiashan debris flow and provide insights applicable to other cascading hazards. Our study integrates field measurements and numerical simulations, combining data on runoff discharge, landslide stability, overtopping volume, and debris-flow discharge. We show that gravity-driven high-altitude water sources control the weakening and entrainment of sediment sources in cascading. Water convergence and seepage due to intense precipitation, elevate pore pressure and weaken sediment sources, triggering landslides and initiating cascading hazards. Water from the overtopped landslide impulse wave, combined with runoff, entrained wet gully bed materials, and formed the debris flow. A physical approach that accounts for the strength of wet sediment sources and the paths of unstable water release in mountains may therefore be applicable for assessing cascading hazards. This work provides a reference for reducing the losses caused by cascading hazards.