Rock-ice avalanche-generated erosion behaviors at the Sedongpu gully, Tibet, China: New insights from the geomorphologic perspective

Abstract

In recent years, massive rock-ice avalanches frequently occur in the Sedongpu gully, forming an extensive dammed lake. Rock-ice avalanches not only threaten residents living in upstream and downstream areas, but also significantly change geomorphology. The gully geomorphology also experienced complicated alterations, due to distal motion distance and strong entrainment of debris flows, coming from the conversion of rock-ice avalanches. This study aims to determine the relation between dynamics erosion of rock-ice avalanches and geomorphology evolution during rock-ice avalanche events at the Sedongpu gully, where a large amount of moraine was distributed with five branch ditches. Field investigations, digital elevation models (DEMs), unmanned aerial vehicles (UAVs), multiphase remote-sensing images, topographic profiling, and InSAR monitoring are carried out to characterise the material changes, including composition, structure, transition, and deposits. Materials were entrained and scraped by debris flows and transported into the Yarlung Zangbo River. The total erosion volume of materials on the valley floor reached 980 million m³ from 2010 to 2021. Topographical profiling suggests that the most severe erosion also occurred in the midstream Sedongpu gully, with the maximum width of above 500 m. The overall elevation of the downstream valley increased by 50 m due to continuous deposits, and formed a large debris fans. The results might be helpful in further studies to reveal dynamic erosion geomorphology of rock-ice avalanches.