Field and numerical investigations of the highest natural dam in the Jinsha River catchment formed by the Wangdalong landslide

The Baqu-Maiqu segment of the upper Jinsha River lies within the Jinsha River suture belt and is an area of numerous paleo-landslide dams due to its complex geological conditions. The Wangdalong paleo-landslide dam is located on the left bank of the upper Jinsha River. It is one of the highest landslide dams and formed the largest dammed lake on the river, which has had a significant effect on the geomorphological evolution of the Jinsha River. In this study, we undertook photogrammetry, field investigations, drilling, stereographic-based kinematic analysis, and discrete element modeling to examine the characteristics, formation, and evolution of the Wangdalong landslide. The Wangdalong landslide dam is ∼1700 m long and ∼3000 m wide, with a volume of ∼4 × 10 8 m 3 . The actual dam height is 454 m and ∼77 m of the landslide dam remains uneroded on the modern riverbed, making it the highest fully river-blocking landslide dam identified in the mainstream of the Three Rivers region. The formation of the Wangdalong landslide was related to wedge failure controlled by the Wangdalong Fault and foliation of the slate rocks. The modeling results show that the Wangdalong landslide had five evolutionary stages, with a maximum average landslide velocity of up to 49.66 m/s, while the model is highly sensitive to the assumed static friction coefficient. Our field and quantitative investigations provide reliable constraints on the geological cause of the landslide and its emplacement mechanisms, along with the extent of the disaster-affected area. These results can guide rapid decision-making during future similar landslide events.