Investigation of a shallow high-locality landslide-induced debris flow in an alpine valley: A case study of the Ridi debris flow, Kangding, Sichuan Province, China (August 3, 2024)
摘要
High-locality landslide–debris flow chains (HLDCs) in alpine mountainous regions are highly destructive; however, their remote locations often hinder detailed observation and understanding. The Ridi HLDC, which occurred on August 3, 2024, in the eastern Tibetan Plateau, illustrates the landslides-to-debris flow transformation and their threat to infrastructure. This study uses satellite and unmanned aerial vehicle imagery, field investigations, and meteorological records to analyze this cascading hazard. Results reveal that the Ridi HLDC began as a cluster of high-locality landslides in the upper Ridi Ravine. The displaced mass traveled downslope through gullies, mixed with slope runoff, and evolved into slope-type debris flows. These flows merged into the Ridi Ravine, forming a single gully-type debris flow that eroded the bed and banks, widening the channel and increasing discharge. The Ridi Valley’s alpine ravine topography features an elevation range exceeding 4000 m, steep slopes, and an ample water supply from glaciers, snowmelt, and rainfall. Along with intense cryogenic weathering, these conditions facilitate the formation of a thin soil or highly weathered rock layer on steep slopes, predisposing the region to landslides and debris flows. Meteorological data from stations at different altitudes in the study area revealed that a rainfall event preceded the Ridi HLDC. Rainfall intensity increased with altitude, peaking at approximately 3500 m, identifying intense rainfall as the primary trigger for the landslides. This study enhances the understanding of the geomorphological and meteorological factors driving HLDCs in alpine regions, thereby providing valuable insights for hazard assessment and mitigation in similar environments.