Forming Conditions and Failure Mechanism of Clustered High-Position Ancient Landslides in Linka Township, Basu County, Tibet Autonomous Region, China

Southeast Tibet, located at the southeastern margin of the Qinghai-Tibet Plateau, is characterized by active plate tectonics and intense topographic relief, making it a high-incidence area for large high-position landslides. To investigate the forming mechanisms of large high-position landslides in Southeast Tibet, ancient landslides in Linka Township, Basu County, were identified through remote sensing interpretation to establish a landslide inventory. GIS-based spatial analysis and statistical methods were then applied to characterize their spatial distribution and determine the dominant controlling factors. Finally, four representative high-position ancient landslides near Ziga Village were selected for field investigation to further examine their forming mechanisms. Remote sensing interpretation identifies 51 high-position ancient landslides, all located on deeply incised valley flanks, primarily concentrated along the slopes of the Nujiang and Waqu rivers. Statistical analysis reveals that lithology and topographic relief are the primary environmental controls on their distribution. Ancient landslides are most likely to develop in sandstone-slate strata and in areas with relief between 1 000 and 1 600 m. Field investigations of four typical ancient landslides near Ziga Village in Linka Township reveal that they all developed in fragmented rock masses induced by long-term flexural toppling. The widespread occurrence of moderately to steeply dipping, layered, weakly metamorphosed sandstone and slate—typical topple-prone rock masses—in the landslide areas of Linka Township, combined with the sliding directions of ancient landslides generally aligning with or opposing the dominant bedding orientation, suggests that toppling was likely a widespread pre-existing failure mechanism prior to the formation of these ancient landslides.