How 156 m water level rise triggered the Wangjiashan landslide: Unraveling its spatiotemporal deformation and triggering mechanisms via multi-tech observations

The Wangjiashan landslide， one of the most active and hazardous landslides triggered during the initial stage of 156 m impoundment at the large-scale Baihetan Hydropower Project， provides crucial insights into the mechanisms of reservoir-induced landslides. This study integrates space-air-ground-subsurface deformation observations to characterize the landslide's complex evolution， elucidates the phase-based spatiotemporal deformation and triggering mechanisms of the Wangjiashan landslide during the impoundment of the Baihetan Hydropower Project， and comparatively analyzes different deformation observation techniques. The results show that different techniques characterized the multi-scale spatiotemporal deformation characteristics of the Wangjiashan landslide. Based on the integrated multi-technique observations， the deformation evolution of the Wangjiashan landslide after impoundment can be divided into three phases: gradual acceleration (Phase I)， rapid displacement (Phase II)， and deceleration and stabilization (Phase III). Sharp reservoir level fluctuations dominated the Wangjiashan landslide deformation via coupled buoyancy， softening， and pore pressure effects， while no consistent rainfall control was identified. Different landslide deformation observation techniques are inherently complementary; however， each is constrained by distinct operational conditions. This study underscores the critical influence of reservoir-level variations on large ancient landslides， offers new evidence for interpreting their spatiotemporal evolution， and provides practical value for hazard prevention and mitigation in major hydropower projects.