Formation mechanism and quantitative risk analysis of the landslide-induced hazard chain by an integrated approach for emergency management: A case study in the Bailong River basin, China

The landslide-debris flow-river blockage hazard chain is one of the most common types of geological hazard chain in mountainous areas, seriously threatening human life and property across an extensive geographical area. The development of approaches for the rapid investigation and prediction of multi-hazard chains can play a significant role in reducing the number of casualties and economic losses. Here, taking the Lijie landslide-debris flow-river blockage in the Bailong River basin as a case study, we used remote sensing methods, geophysical technology, numerical simulations and empirical formulas to develop an integrated approach for analyzing the mechanisms, multi-hazard prediction and quantitative risk assessment induced by this geological hazard chain. The reactivation process of the Lijie landslide is composite retrogressive sliding. The steep slopes and highly fractured bedrock with low strength are the principal internal factors, and heavy rainfall in 2020 and spring freeze-thaw effect are the principal triggering factors. The deposited landslide material is eroded and transformed into a channel-type debris flow under high rainfall conditions. The steep terrain and abundant finegrained material provides favorable conditions for a viscous debris flow with a long runout, which is usually followed by secondary disasters associated with river blockage. Our results indicate that under rainfall conditions with a 100-year return period, the Bailong river will be completely blocked by the landslide-induced debris flow. And there will be an estimated 5.84 million CNY of economic losses caused by the multi-hazard chain, which is 2.6 times the losses directly caused by the landslide. Our integrated approach is practicable in an emergency context and useful for local administrators to rapidly develop strategies for multi-hazard chain prevention and mitigation, based on information about the transformation mechanisms of the multi-hazard chain, potential hazard-affected areas, damaged degree of elements at the risk, and incurred economic losses.