Assessment of a catastrophic rock avalanche in the West Mongolian Altai Mountains

A giant rock avalanche that resulted in the formation of a dammed lake was discovered during geological mapping in the valley of the Dund Tsenkher Gol River, Munhkhairkhan Soum, Western Mongolian Altai. Field and satellite data (WorldView-2 and SENTINEL-1) were used to obtain a geomorphological description of the landslide and a 3D geometric reconstruction of the rock avalanche. With deposits exceeding 14 million cubic meters in volume, the rock avalanche is one of the largest catastrophic landslides in the world. The rock avalanche was controlled by tectonic setting. The slope instability was favored by the presence of NW-SE and NE-SW trending fault systems, steep foliation and morphology. The rock avalanche was likely triggered by an earthquake related to the activity of the Tolbonuur and Hovd faults. Although the area is sparsely populated, the settlement of Munhkhairkhan Soum is threatened by rockfalls or even by rock avalanches that could be triggered by future earthquakes along these faults.