Objective Intense amount of large ancient landslides are developing in the Himalayan region. In recent years, the problem of ancient landslide reactivation has become more and more prominent, and the potential hazards are serious. However, the mechanisms controlling the reactivation of ancient landslides under endogenic−exogenic dynamic coupling remain poorly constrained, which hinders accurate hazard predictions and risk mitigation strategies.

Methods Based on remote sensing interpretation, field investigation, engineering geological drilling and comprehensive monitoring, we analyze the development characteristics and reactivation factors of ancient landslide in Pangcun, Jiayu Township, Longzi County, Shannan City, Xizang. Numerical simulation is used to predict the movement process of landslide after instability and evaluate its potential risk.

Results The Pangcun landslide first slided in the middle to Late Pleistocene with a volume of about 18.9×10⁶ m³, and the landslide developed two layers of slip zones, with buried depths ranging from 6 m to 25 m and 25 m to 55 m, respectively. At present, the reactivation characteristics of the landslide are obvious, and the gravel soil accumulation formed by historical sliding is the reactivation and deformation area, which is strongly deformed on the left side and weakly deformed on the right side, and its deformation is obviously affected by rainfall, and the surrounding seismic activities also play a certain role in promoting its reactivation.

Conclusions Once the reactivation deformation area of the landslide occurs the whole instability, the maximum accumulation thickness of the slide body reaches 25 m, the maximum movement speed reaches 16.52 m/s, and the furthest distance reaches 175 m, which will seriously threaten the Pangcun residential area at the slope foot and the national highway G219. The study results have a certain significance for deepening the understanding of the ancient landslide reactivation mechanism in the Himalayan region and supporting the local disaster prevention and reduction work.