Landslides with multi-slip surfaces in reservoir areas: Occurrence and geomorphic and geological controls

Reservoir landslides represent a significant geohazard in the context of global hydropower expansion, particularly those with multiple slip surfaces. However, the regional occurrence and controlling factors of multi-slip surface landslides (MSSLs) remain poorly understood, posing challenges for hazard prediction and mitigation. In this study, we have undertaken a comprehensive inventory of MSSLs based on geological investigations in the Three Gorges reservoir area, China, over the past two decades, and evaluated the geomorphic and geological controls on their distribution and process mechanisms. The results indicated that MSSLs are unevenly clustered along the bank slopes of the Yangtze River and near fold cores, displaying distinct types and developmental characteristics across three subregions of different topography and lithology settings. The combined effects of river erosion, geological structures, and bedrock with weak layers largely determine their occurrence. In contrast, the impacts of topography and distance to faults are moderate or negligible. MSSLs showed a distinct preference for specific strata (T 2 b and J 2 s) and slope intervals (15°–25°), where their proportion was approximately twice that of all landslides in the same range. These landslides are commonly composite deposits formed through multistage mass movements during valley geomorphic processes, driven by the interplay of episodic tectonic uplift, river incision, and palaeoclimatic changes since the Middle Pleistocene. We proposed conceptual models for their multistage evolution, emphasizing the significance of lithology and slope structure in governing MSSL evolution, and further explaining the spatial variability in MSSL distribution patterns. The findings contribute significantly to the early identification, hazard prevention, and mitigation in MSSL-active areas.