Research on the Development Characteristics and Formation Mechanism of the Lagang Giant Long-Runout Landslide Along the Yarlung Zangbo Fault Zone, Tibetan Plateau, China

Affected by the continuous collision and compression of the Indian plate and the Eurasian plate, the Tibetan Plateau has strong neotectonic movements, frequent earthquakes, and strong river erosion. A series of large-giant long-runout landslides formed and caused river blocking-dam breaking disaster chain events, which induced extremely severe disasters and simultaneously had an important impact on geomorphological evolution. In the area of Lagang Village, Jiacha County, Tibet, a long-runout landslide is found along the Yarlung Zangbo fault zone, named the Lagang landslide. The investigation and research show that the Lagang landslide developed in the conglomerate of the Triassic Luobusha Group. The maximum movement distance of the sliding body is 3407 m, the maximum height difference is 965 m, the original collapse body volume is approximately 0.37-0.43×10 8 m 3 , and the landslide volume is 0.6-0.75×10 8 m 3 . Giant boulders remain on the landslide accumulation, with a single block size of 40 m×25 m×15 m. The Yarlung Zangbo fault passed from the middle part of the ancient landslide almost straightly, and the landslide dammed the Yarlung Zangbo River. Combining the 10 Be of boulders of the sliding body on the surface and the 14 C geological dating data of the sediments exposed by the exploratory trench and the simulation analysis of the Massflow movement process, it is believed that the landslide was formed at approximately 4713-8710 a B.P., and it might be caused by the strong earthquake that occurred along the Yarlung Zangbo fault zone. The formation of the landslide disaster chain has experienced four stages: the development of the trailing edge structure surface - penetration, high-speed ejection from the parent body, high-speed impact-debris flow-river blocking, and dam break-late self-stabilization. The research results of this paper are of great significance for advancing research on the mechanism of long-runout landslides in the eastern Tibetan Plateau, research on geological hazards in active fault zones, and disaster prevention and mitigation.