High-position landslides in Southeast Tibet can evolve into long-runout hazard chains by entraining loose alluvial or colluvial deposits along steep valleys. Intensified rainfall, glacier melt, and snowmelt may increase deposit saturation and groundwater level, thereby altering entrainment and landslide mobility. This study investigates these hydro-mechanical effects using a two-point two-phase material point method.
A flume-scale numerical model is developed to simulate the interaction between a sliding mass and erodible valley deposits. The solid skeleton and pore water are represented by separate material points, enabling coupled deformation, pore-pressure evolution, and solid–fluid interaction during rapid motion. Four scenarios are considered by varying the saturation states of the sliding mass and the deposit. The simulations compare effective stress, kinetic energy, entrained volume, deposition morphology, and runout distance.
The results show that saturation reduces effective stress and shear resistance, promoting deposit entrainment and enhancing landslide mobility. The saturated–saturated case exhibits the strongest entrainment and longest runout, whereas the dry–dry case remains more localized with limited basal scraping. These findings indicate that the hydro-mechanical state of entrainable valley deposits plays a key role in controlling the transition from slope failure to long-runout landslide hazard chains in Southeast Tibet.
 

material point method,hazard chains,impact-induced entrainment