Engineering Insights from the 2025 Blatten Glacier Collapse

On 28 May 2025, the Birchgletscher in Valais, Switzerland, collapsed under the combined load of rock debris and ice, triggering a high-velocity rock-ice avalanche that partially buried the village of Blatten and dammed the Lonza River. The collapse occurred within 40 seconds, releasing approximately 20 million tons of mixed material down a 1,200-metre vertical drop, traveling at speeds close to 200 km/h. The glacier, which had exhibited unusual behavior since 2019, was covered in accumulated debris from repeated avalanches off Kleines Nesthorn. The increasing mass and melting water significantly accelerated the ice flow before failure.

ETH Zürich researchers identified several contributing factors to the collapse. These included increased basal pressure from englacial water, basal shear stress from added debris, and movement in the unstable terrain above. Data shows the glacier’s thickness had increased at its snout due to debris insulation, reducing melt yet amplifying stress loads. The collapse involved approximately 2.9 million m³ of ice and 6.4 million m³ of debris. The entire lower glacier section has now disappeared, and a new lake has formed behind the rock-ice deposit. This cascade event, though unique in scale, shares mechanisms with past events observed both in Switzerland and globally.

According to the ETH and University of Zürich teams, anthropogenic climate change likely played a key role in the failure. Since the 1980s, the region has seen rising permafrost degradation, loss of perennial snow cover, and increased atmospheric exposure of bedrock. These changes have reduced rock slope stability through repeated freeze-thaw cycles and facilitated water infiltration. While geological preconditioning was a factor, the researchers suggest that climate-related processes amplified the instability, leading to the catastrophic collapse witnessed in Blatten.