Rock Collapse to Debris Slide Transition: Understanding the Dynamics and Hazard Implication

Mining-induced landslides in southwestern China are being more frequently reported, but quantifying the erosion-entrainment effect on their mobility requires further attention. This study reconstructs the December 3, 2004, Zuojiaying landslide in Guizhou, China, where a rainfall- and mining-triggered rock collapse evolved into a debris slide that claimed 44 lives. Field investigation and UAV-based digital elevation model are combined with RAMMS simulations to reproduce the landslide's dynamic characteristics and assess the effect of entrainment on runout. Back-calculated models suggest that the landslide volume increased from an initial 11,000 m³ to approximately 36,000 m³ due to entrainment. A sensitivity study shows that denser and more saturated erodible material in the transport zone substantially increases entrained volume. Comparison of scenarios with and without entrainment reveals that runout extends from ∼380 m to ∼430 m, with maximum deposit thickness increasing from ∼4 m to ∼7 m. A stage-wise analysis of the runout process emphasizes the critical role of erosion-entrainment in regulating mobility and the deposit characteristics of landslides, which includes four stages from rock collapse to debris slide. These findings provide quantitative constraints on substrate erodibility and entrainment that govern runout and deposit thickness, improving hazard assessment and zoning in areas with similar conditions.