Treffer: 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. Plain Language Summary: Southeast Tibet is experiencing more frequent hyper‐mobility cascading geohazards due to global warming, especially in summer. The triggering mechanisms and evolution process of these hazards, including the glacial debris flow in the Zelunglung Basin on 10 September 2020, are still unclear. A previous study inferred that rock‐ice avalanches trigger moraine landslides, while freeze‐thaw cycles modify moraine deposit stability, but their combined effect is rarely explored. In this study, we used satellite remote‐sensing, post‐event investigation, and multi‐physics modeling to address these gaps. Satellite data indicated that a small rock‐ice avalanche likely triggered a moraine landslide and the subsequent cascading event. The hazard chain was rock‐ice avalanche → impact on moraine deposit → moraine landslide → glacial debris flow, with avalanching‐moraine landslide being the key link with volume amplification effect. Multi‐physics modeling confirmed the avalanche as the primary instigator, with moraine deposits mainly failing during warm seasons. Increased water content from ice melting during thawing created conditions for excess pore pressure generation and liquefaction under avalanche impact, leading to the evolution into debris flows. Our study appeals increased attention to areas prone to rock‐ice avalanches using earth observation and seismic monitoring techniques, especially during warm seasons, for hazard prediction and risk mitigation. Key Points: Remote sensing and numerical modeling reveal a hazard chain type: rock‐ice avalanche → impact on moraine → moraine landslide → debris flowFreeze‐thaw cycles control moraine landslide proneness under avalanche impact by water content and excess pore pressureSmall avalanches can trigger moraine landslides that amplify volume and enhance mobility for cascading geohazard chain in warm season [ABSTRACT FROM AUTHOR]

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