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Large-scale landsliding is an extremely important geological process in shaping landscapes in the Tibetan Plateau. In this research, an ancient river-damming landslide with an estimated debris volume of 4.9 × 107 m3, located in the upper Jinsha River, SE Tibetan Plateau, was studied. The landslide once formed a dam over 60 m high and blocked the river. Lacustrine sediments, composed of silty clay with particle sizes of 0.002–0.25 mm, are intermittently distributed along both banks, extending about 6.5 km upstream. The OSL dating indicates that the lacustrine sediments have an age of 2.6 ± 0.2 ka. Detailed field investigation and theoretical analysis was performed to investigate the characteristics, potential cause and mechanism of the landslide. The results suggest that the landslide was most likely triggered by buckling of planar rock slabs under gravity. It may start as a translational sliding along the weak interlayer composed of mica schist at the upper part of the slope and then formed buckles by curving amphibolite rock beds near the slope toe. The hillslope has still been affected by gravitational deformations, with geomorphology characterized by tension cracks, buckle folds, and small landslide scars distributed on the slope surface, suggesting that the evolution of the river valley caused by buckling deformation has not achieved equilibrium. [ABSTRACT FROM AUTHOR]