Mountain hazards on the rise- The collapse of Birchgletscher, Switzerland
Global climate change is profoundly altering high mountain environments, intensifying both the frequency and magnitude of natural hazards. Warming temperatures, shifting precipitation patterns, and changes in cryospheric processes are driving complex transformations that increase the risk of catastrophic events such as landslides, glacial lake outburst floods (GLOFs), rockfalls, avalanches, and debris flow.
On, Wednesday, 28th of May, 2025 around 15:24 CEST, a glacier in Swiss Alps called the Birchgletetscher collapsed due to the weight of accumulating rock debris and materials sourced from multiple rock avalanches from a peak above the glacier called Nesthorn. This event lead to havoc and rapid flow of debris down the valley, engulfing a beautiful mountain village called Blatten. There have been a lot of speculations among scientists and researchers, of what exactly led to the collapse of the Birch Glacier. Due to evidence of multiple such events happening around the glacier way back since 1990s, this glacier was continuously under observation. Some preliminary understanding about the situation has shed some light on what could be the potential cause of this event, and whether it could be attributed to climate change (we will discuss this later).
A recent report published by the Laboratory of Hydraulics, Hydrology and Glaciology in ETH Zurich (see below in further reading), listed out some possible explanations about the driving factors-
The rock mass deposition over the glacier increased pressure on the temperate glacier, enhancing meltwater production leading to ice flow acceleration (estimated at up to 10 m/day), causing basal shear stress and shear heating. Combined with snowmelt, rainfall, and rapid landslide motion, these factors likely exceeded the glacier bed’s stability threshold, contributing to the eventual glacier failure. Approximately 2.9 million cubic meters of ice and 6.4 million cubic meters of rock and debris, totaling around 20 million tons were mobilized. The mass fell over an elevation drop of 1200 meters, releasing a significant amount of potential energy. The avalanche reached the valley floor in approximately 40 seconds, moving at an average speed of 200 km/h. Upon impact, the debris-ice mixture buried the village of Blatten and dammed the Lonza River. Within two days, a stream channel developed through the deposit, stabilizing the water level of a newly formed lake behind the dam.
Attribution to Climate Change
Climate change plays a critical role in amplifying mountain hazards by driving rapid environmental changes in high-altitude regions. Rising global temperatures are accelerating glacier melt, leading to the formation and expansion of unstable glacial lakes that can burst catastrophically. Simultaneously, the thawing of permafrost is destabilizing rock faces and slopes that were once frozen and structurally stable, triggering an increase in rockfalls, landslides, and debris flows. Unprecedented and intense rainfall events, often occurring over melting snow or ice, further saturate mountain slopes and increase hydrostatic pressure, compounding the risk of slope failures and floods. These processes often interact, creating complex hazard cascades- such as landslides into glacial lakes that generate glacial lake outburst floods (GLOFs) or hazards such as glacier collapses like the one we discussed. The warming-driven transformation of the cryosphere, combined with extreme weather events, is fundamentally altering hazard dynamics in mountainous regions, posing escalating threats to downstream communities, infrastructure, and ecosystems.
Further reading/visuals:
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