Abstract
On May 28, 2025, a high-altitude long-runout ice-rock avalanche-debris flow disaster occurred at the Birch Glacier in the Alpine region of Valais, southern Switzerland, completely destroying the downstream towns of Blatten and Ried, necessitating the emergency evacuation of over 300 residents, with one person reported missing. This study conducts a systematic investigation into the development characteristics, evolutionary processes, and disaster-forming dynamics of the "5.28" Birch high-altitude ice-rock avalanche-debris flow disaster, based on multi-temporal satellite remote sensing imagery, pre- and post-disaster unmanned aerial vehicle (UAV) data, slide-seismic signals, and on-site video recordings. Preliminary results indicate that, driven by the combined effects of global climate warming and freeze-thaw cycles, Nesthorn Peak, located on the southern flank of the upper Birch Glacier with a relative elevation difference of approximately 300 m, has frequently experienced rockfall events. The fallen debris continuously accumulated on the glacier surface, which not only attenuated glacial ablation but also enhanced the glacier's plastic flow, thereby intensifying frontal bulging deformation and crevasse propagation. Remote sensing interpretation reveals that over the past decade, the glacier area has expanded by approximately 44%, while the glacier tongue advanced by about 110 m. During the disaster event, approximately 3 million m³ of wedge-shaped collapse mass underwent high-altitude destabilization, continuously impacting and loading the lower Birch Glacier at a velocity of approximately 36 m/s. This triggered the overall instability of approximately 6 million m³ of glacier ice and its overlying debris, which subsequently transformed into a high-velocity, long-runout ice-rock debris flow that exited the gully mouth at an average velocity of approximately 64 m/s and came to rest after colliding with the opposite mountainside. Such high-altitude long-runout ice-rock geological hazards, which develop in high-cold, high-altitude extreme alpine regions, are widely distributed throughout the Himalayan orogenic belt in China, posing severe threats to the geological safety of major engineering projects. This research can provide valuable reference for relevant disaster prevention and mitigation efforts.
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Title: Study on the May 28 Birch High-altitude and Long-runout Ice-Rock Avalanche in the Swiss Alps
Authors: ZHANG Shi-lin², HUO Zi-hao¹, YANG Chao-ping¹, CHEN Fei-yu²
Affiliations:
¹ China Institute of Geo-Environment Monitoring, Technical Guidance Center for Geological Disaster Prevention of Ministry of Natural Resources, Beijing 100081, China
² Faculty of Geosciences and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
Abstract
On May 28, 2025, a high-altitude, long-runout ice-rock avalanche-debris flow disaster occurred at the Birch Glacier in the Valais Alps of southern Switzerland. The event completely destroyed the downstream towns of Blatten and Ried, necessitated the emergency evacuation of over 300 residents, and left one person missing. This study systematically investigates the development characteristics, evolutionary processes, and disaster dynamics of the May 28 Birch avalanche based on multi-temporal satellite remote sensing imagery, pre- and post-disaster UAV data, slide seismic signals, and on-site video footage.
Preliminary results indicate that driven by the combined effects of global warming and freeze-thaw cycles, Nesthorn Peak—located on the south side of the upper Birch Glacier with a relative relief of approximately 300 m—experienced frequent rockfalls. The fallen debris continuously accumulated on the glacier surface, which not only reduced glacial ablation but also enhanced the glacier's plastic flow, accelerating frontal bulging deformation and ice fracture propagation. Remote sensing interpretation reveals that over the past decade, the glacier area expanded by approximately 44% and the ice tongue advanced by about 110 m.
During the disaster, approximately 3 million m³ of wedge-shaped collapse mass became unstable at high altitude, continuously impacting and loading the lower Birch Glacier at a velocity of approximately 36 m/s. This triggered the overall instability of roughly 6 million m³ of glacier ice and overlying debris, which subsequently transformed into a high-velocity, long-runout ice-rock debris flow. The flow exited the gully mouth at an average speed of approximately 64 m/s before depositing upon colliding with the opposite mountain slope. Such high-altitude, long-runout ice-rock geological hazards, which develop in extreme alpine regions under cold and high-altitude conditions, are widely distributed across the Himalayan orogenic belt in China and pose serious threats to the geological safety of major engineering projects. This research provides valuable reference for relevant disaster prevention and mitigation efforts.
Keywords: Birch Glacier; Glacial fracture; High-altitude long-runout ice-rock avalanche-debris flow