WHEN THE MOUNTAIN COMES DOWN
Major natural events occur regularly in the Alps, posing significant challenges for people. With climate change progressing, glacier collapses, landslides, avalanches and floods are becoming increasingly frequent. Adaptations are necessary to keep the Alpine region safe to live in, use and visit in the future.
Whether and when rock faces become unstable depends on various factors, including topography, rock composition, weak zones, permafrost, frost and thaw cycles, glacier retreat, heavy precipitation, vegetation and earthquakes. Climate change often plays an indirect role, making it difficult to quantify its influence precisely.
However, experts agree on the case of the Spitze Stei above Kandersteg: the warming of the Alpine permafrost is contributing to the destabilisation of the rock masses on the slope. The absence of permafrost allows more water to penetrate the rock, accelerating the movement of the rock masses. At Spitze Stei, slide speeds of up to several metres per year are being measured. The municipality of Kandersteg hopes that the 16 million cubic metres of rock will break off piece by piece and that the protective measures taken will be sufficient to prevent a disaster in the valley.
At Spitze Stei above Kandersteg in the canton of Bern, an unstable mountainside in the permafrost zone is sliding (primary process) and could trigger a dangerous chain of events. It is expected that part of the slope will break off and that, during heavy rainfall, the deposited material may lead to debris flows in the Öschibach stream below Lake Oeschinen (secondary process) which could reach as far as Kandersteg. This could cause debris to accumulate in the Kander river, damming the river and leading to flooding (tertiary process).
Graphic: based on Nils Hählen (Natural Hazards Department, Canton of Bern); swissALTI 3D; SWISSIMAGE 10 cm (Federal Office of Topography swisstopo)
RISK REDUCTION FOR SPITZE STEI
Graphic: based on Nils Hählen (Natural Hazards Department, Canton of Bern); swissALTI 3D; SWISSIMAGE 10 cm (Federal Office of Topography swisstopo)
Graphic: Natural Hazards Department, Canton of Bern (modif.)
THE ROLE OF PERMAFROST
Permafrost in the Alps generally increases the strength of rock masses and thus their stability. It accounts for around 5% of Switzerland’s land area. Its condition is continuously monitored by the Swiss Permafrost Monitoring Network (PERMOS). The data shows that Alpine permafrost is warming and thawing at increasingly greater depths due to climate change.
THE BLATTEN CASE
In May 2025, an ice and rock avalanche buried the village of Blatten in the canton of Valais. Permafrost at Kleines Nesthorn played an important role here. Thanks to an excellent monitoring system, a warning was issued in good time before the event, allowing the inhabitants to be evacuated. However, the village was completely destroyed.
In the aftermath of the disaster, the discussion centres on questions such as the influence of climate change on the event and who will bear the financial consequences. Another particularly important issue is how to reliably predict catastrophic chains of events in the future. This will also determine whether areas at risk can continue to be inhabited. In addition, one question is becoming increasingly urgent: should a disaster always be followed by reconstruction?
Exhibit
ICE AND ROCK AVALANCHE, BIETSCHHORN / BLATTEN, Valais (2025)
On 28 May 2025, Blatten in the Lötschental valley (canton of Valais) was hit by a massive ice and rock avalanche. Following major rockfalls on the Kleines Nesthorn and a collapse of the Birch Glacier, approximately 9 million cubic metres of ice and debris crashed into the valley, burying the village of Blatten and parts of the hamlet of Ried. The village buildings were destroyed by the debris or flooded by the Lonza River, which was dammed up by the debris.
The area marked in black indicates the path of the rock, debris and ice masses. The dark blue line marks the glacier’‘s position shortly before the event. The light blue line shows the glacier’‘s position in 1938 at the time the relief was constructed by Eduard Imhof, then Professor of Cartography at ETH Zurich.
Bietschhorn relief 1:2000 (Eduard Imhof, 1938/1939);
on loan: ALPS Swiss Alpine Museum, Bern
Photo: Fabian Neyer (Terradata AG)