Study on the dynamic erosion process of rock-ice avalanches and the characteristic of geomorphic evolution

Abstract

[Objective] The dam-break floods triggered by rock-ice avalanches in the river channel are highly destructive to downstream towns and major hydropower projects. To reveal the relationship between the dynamic erosion of rock-ice disaster chains, geomorphic evolution, and river damming, [Methods] taking the Sedongpu Gully in southeastern Xizang as an example, the study employed multi-source and multi-temporal optical remote sensing image interpretation, DEM differencing, UAV aerial surveys, and field investigations to explore the process of ice-rock chain movement transformation and its geomorphic effects. [Results] The research indicates that since 2010, the source areas of rock-ice avalanches have mainly been concentrated on steep slopes above 4,000 meters in altitude, with a maximum cumulative erosion depth of approximately 75 meters. In the valley section at an altitude of 3 000~4 000 m, erosion is predominant. The maximum cumulative erosion depth in the 5 km long valley is approximately 300 m, and the maximum widening width of the valley exceeds 500 m. The area below 3 000 m is a flowing accumulation zone, where the maximum cumulative accumulation thickness exceeds 50 m, and the accumulation blocking the riverbed has caused it to rise by more than 40 m. Influenced by the curved terrain of the valley, debris flows/mudflows not only erode the base but also exhibit strong lateral erosion on the bank slopes. The cumulative volume of unstable bank slopes on the concave bank exceeds 4×10⁷ m³, with a re-migration rate of the accumulation body reaching 75%, providing a material supply for the volume amplification effect of the disaster. [Conclusion] During the long-distance movement of ice-rock debris flows, their high-speed impact not only causes rapid erosion and deepening of the valley floor but also leads to erosion damage and widening of the concave bank slope due to centrifugal force at bends. The result ing landslide deposits are subsequently scraped and entrained again, amplifying the disaster volume, accelerating the transportation of valley materials, and promoting geomorphic evolution.

Keywords

rock-ice avalanche / Sedongpu Gully / debris avalanche/flow / lateral erosion / geomorphic evolution / landslides / influencing factors / disaster chain