Huge long-runout landslide characteristics and formation mechanism: A case study of the Luanshibao landslide, Litang County, Tibetan Plateau

In the Tibetan Plateau, the complex geological tectonic background causes frequent earthquakes, together with the abnormal climate change, there are many large or even huge geological hazards, causing serious consequences. In this paper, based on the interpretation of remote sensing and the analysis of field geological survey, geophysical prospecting, trenching, and geological dating data, the authors studied the development characteristics of the Luanshibao landslide and investigated its formation mechanism. The Luanshibao long-runout landslide has the following features① The Luanshibao landslide is located on the northeastern margin of the Maoyaba Basin in Litang County, western Sichuan. The sliding direction of the landslide is perpendicular to the northwestern segment of the Litang-Dewu fault, with the top part of the Luanshibao landslide approaching the current snow line. ②The maximum sliding distance of the Luanshibao landslide is 3.83km; the elevation difference between the back wall of the landslide and the accumulation zone at the leading edge is approximately 820m, with a sliding body volume of approximately 0.64×10⁸~0.94×10⁸m³ and an average sliding velocity of approximately 53.25m/s. ③ The dating data indicate that the Luanshibao landslide occurred at about 1980±30a BP. ④ The compositional lithology of the landslide rocks is mainly granite, and the joint fractures are developed as cracked rocks under the impact of long-term tectonic dynamics and freezing weathering. The analysis indicates that the Luanshibao landslide has been substantially affected by the fault structure, terrain topography, and ancient climate change, and its formation mechanism is complicated① Since the Holocene, the Litang-Dewu fault has experienced frequent, strong earthquake activity. The strong earthquakes resulting from the fault activity might have been one of the main factors for the formation of the Luanshibao landslide. Under the impact of earthquakes, the seismic wave at the top of the slope would be "amplified", producing a vertical acceleration greater than the horizontal acceleration. The rock bodies experienced shock expansion and were thrown, forming the longrunout landslide. ② Dating back to approximately 2000a BP, the temperature change in the Tibetan Plateau area was relatively large, and the large-scale glacial activity occurring in this period was most likely one of the main factors behind the formation of the Luanshibao landslide. ③ The combination of earthquakes and climate change seems to have been one of the conditions causing the occurrence of the Luanshibao landslide, forming a complete chain of geological disasters, i.e., earthquake→avalanche→rockfall→ high speed debris flow.