A growing threat of multi-hazard cascades highlighted by the Birch Glacier collapse and Blatten landslide in the Swiss Alps

Rapid atmospheric warming, especially at high altitude, leads to alpine mountain landscapes becoming more vulnerable to mass movements and consequently unstable. For example, decay of mountain permafrost contributes to rockfalls, landslides and debris flows; glaciers are retreating and losing mass at alarming rates, exposing unstable slopes that are more likely to fail; and meltwater, which collects in a growing number of glacial lakes, can pose an outburst flood hazard, putting communities and infrastructure downstream at risk of damage. Occurring now with increasing frequency, these natural phenomena often combine to create complex multi-hazard cascades that are more powerful and have a greater reach down-valley than a singular isolated event. Combined with increasing population and infrastructure and economic activity in high mountains, there is therefore increased vulnerability of society to natural hazards in high alpine mountains, as has been experienced in the Swiss Alps in 2025, with the collapse of the Birch Glacier and the destruction of the alpine village of Blatten. Here, we review the physical processes of this recent event, their impact on environment, people and economy, and consider what can be learned from them.