Interplay of Freeze-Thaw Cycles and Avalanche Impact on Glacial Landslide-Debris Flow Geohazard Chain in the Southeastern Tibetan Plateau

Southeast Tibet suffers increasing hyper-mobility cascading geohazards, especially during the warm season. The glacial debris flow on 10 September 2020 in the Zelunglung Basin, transformed from a moraine landslide, exemplifies such geohazards, yet the landslide initiation or evolution process remained obscure. Literature deduced rock-ice avalanche can trigger moraine landslides and freeze-thaw cycles modify moraine deposit integrity, but their interplay effect is rarely touched. Here, we combined satellite remote-sensing, post-event investigation and multi-physics modeling to reveal these questions. Field investigations and satellite data suggest that a small rock-ice avalanche likely triggered a moraine landslide, setting off the cascading event with the evolution process as a small rock-ice avalanche (0.45-Mm³) → impact on moraine deposit → moraine landslide (1.14-Mm³) → glacial debris flow, where avalanching-moraine landslide is the key link, regarding the volume amplifying effect. Utilizing multi-physics modeling, we explored the interplay of freeze-thaw cycles and avalanche impacts on moraine deposit stability. Numerical results validate the avalanche as a primary instigator. Under such avalanche impacts, moraine deposits predominantly fail in warm seasons. Elevated water content from ice melting within moraine deposits, intensified during thawing and restrained during freezing, creates a conducive environment for excess pore pressure build-up and subsequent liquefaction when subjected to avalanche stresses, leading to transformation to debris flows. Thus, the seasonal freeze-thaw cycles exhibit a control effect on the key link and the whole chain. Our findings suggest increasing attention to potential locations of rock-ice avalanches through earth observation and seismic monitoring systems for hazard prediction and risk mitigation, particularly in warm seasons.