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.

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?

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

Further information about the exhibit

The costs of climate-related disasters such as droughts, forest fires, floods, heavy rainfall, storms and mass movements are borne by insurance companies, governments, those affected and aid organisations. Low-income people in the Global South are particularly hard hit: without insurance, they have to pay for the damage themselves – often losing everything. Many of these countries also have little government funding for reconstruction.

Whether major greenhouse gas emitters should pay for climate damage is politically controversial. The link between emissions and individual disasters is difficult to prove. However, pressure is growing on wealthier countries to contribute to the costs. The Loss and Damage Fund was established in 2025 to help particularly vulnerable countries cope with the consequences of climate change.

In the long term, costs will rise for everyone: infrastructure must be made more crisis-proof, emergency plans improved and aid expanded. Insurance will also become more expensive as risks increase.

The consequences of climate change are becoming increasingly noticeable, especially for insurance companies and reinsurers. According to Munich Re, natural disasters – 93% of which are weather-related – caused damage amounting to USD 320 billion in 2024. Only around USD 140 billion of this was insured.

This insurance gap affects millions of households and businesses. When basic infrastructure such as energy plants or agricultural land is affected by extreme weather events, it can disrupt entire (global) production chains.

As weather events become more extreme, insurance costs rise, for example for storms, hail, drought or flooding. If the risks become too great, insurers and reinsurers (who cover global risks) pull out. Preventive measures can reduce risks, damage and thus costs.

One example is hail insurance in Switzerland, which has been in existence since 1880. Almost 70% of agricultural land is insured. Measures such as hail nets can reduce crop losses and premiums – a win-win for farmers and (re)insurers. By promoting such protective measures, the insurance industry is also contributing to climate change adaptation.

On 28 May 2025, Blatten in the Lötschental valley in the canton of Valais was hit by a massive ice and rock avalanche. Following major rockfalls on the Kleines Nesthorn and a glacier collapse on the Birch Glacier, around 9 million cubic metres of ice and debris broke loose, crashed into the valley and buried 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.

One person lost their life, but around 300 residents were evacuated in time. The damage amounts to around 320 million Swiss francs. The municipality is planning to rebuild, but experts advise against rebuilding the village in the same location.

This is the first ice and rock avalanche in Switzerland that has been proven to have destroyed a residential area.

In Switzerland, landslides and similar events are considered natural disasters and are covered by building insurance. This is compulsory in most cantons – but not in Valais. Anyone in Blatten who was not insured has lost everything and must pay for the reconstruction themselves. According to the Swiss Insurance Association, the damage could amount to several hundred million Swiss francs – not including public infrastructure such as roads.

The municipality is already planning ‘New Blatten’. The costs are high and will only be partially covered by private insurers. The canton of Valais has pledged CHF 10 million in emergency aid, and the federal government CHF 5 million. A disaster fund is being considered. A national fundraising campaign by Swiss Solidarity has raised around CHF 21 million – including for private hardship cases. Even in well-insured Switzerland, there are gaps in insurance coverage that mostly affect less privileged sections of the population.

Video: SRF, Tagesschau, 30.05.2025, minute 8:27 – 10:47

The Swiss Confederation‘s natural hazard agencies work closely with researchers to promote the monitoring of natural hazards in Switzerland. The planned ETH Swiss GeoLab in Lucerne will evaluate Earth observation data continuously recorded by sensors, drones and satellites. The data will be used for modelling and risk assessments in order to identify hazards at an early stage and to plan and implement protective measures.

On 28 May 2025, Blatten in the Lötschental valley in the 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, around 9 million cubic metres of ice and debris broke loose, crashed into the valley and buried 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 had been dammed up by the debris.

Video: SRF, Einstein, 02.10.2025, minutes 3:58 – 5:42 / 7:24-9:31 / 20:19-24:20

One person died in the ice and rock avalanche in Blatten. Around 300 residents were evacuated in time. The damage amounts to around 320 million Swiss francs. The municipality is planning to rebuild. However, experts advise against rebuilding the village in the same location.

This is the first ice and rock avalanche in Switzerland that has been proven to have destroyed a residential area. Modern simulation technology can be used to model the course of the ice and rock avalanche. This also allows future risks to be better assessed.

Simulation: Johan Gaume (ETH Zurich & WSL-SLF)

High-resolution images are used for precise 3D reconstruction. These serve as a basis for modelling and for situation assessment by experts and authorities.

Video: Terradata AG, Helimap

On 3 October 2024, a rockslide occurred directly above Martinsloch on the Grosses Tschingelhorn. The fact that approximately 100,000 m³ of rock thundered downhill went unnoticed for several days because the mountain, including Martinsloch, was shrouded in fog. It was only when the fog lifted that the changed silhouette of the Grosses Tschingelhorn revealed that a large mass of rock must have fallen. The time of the rockslide was then reconstructed with the help of ground vibrations recorded by nearby earthquake stations belonging to the Swiss Seismological Service.

Video: SRF, Schweiz aktuell, 15.10.2024

The causes of the rockfall are currently being investigated. The Grosse Tschingelhorn is composed of Verrucano rock, which is highly fractured. At the point of collapse – an exposed rock ridge – the rock is also exposed to extreme temperature fluctuations and heavy rainfall, which promote further disintegration of the rock. As a result, the mountain has been in motion for some time – and continues to be so today. It is being monitored accordingly and, where necessary, equipped with sensors. There is no threat to the village of Elm, as the break-off point is far away. The hiking trails remain open as they are outside the danger zone.

Simulation: TectonicArena Sardona

On 16 April 2024, a rockslide occurred on the 3,970-metre-high Piz Scerscen (GR). Several million cubic metres of rock, debris, snow and ice rolled 5.5 kilometres through the Roseg Valley. As the valley is uninhabited, there was no damage to property or injury to persons. The area is popular with mountaineers, but fortunately no one was out and about during the landslide, which lasted only two minutes. The mass movement was modelled in detail by researchers at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). Ein direkter Zusammenhang mit dem Klimawandel wurde bisher nicht untersucht. A direct link to climate change has not yet been investigated.

On 23 August 2017, approximately 3 million cubic metres of rock broke loose in a permafrost area at an altitude of around 3,000 metres on Piz Cengalo and crashed down onto a glacier field. The enormous energy of the impact caused the ice to melt, forming a large debris flow. This rolled through the Bondasca Valley into the village of Bondo, which fortunately escaped major damage. The danger was known: after the first rockfalls in 2011/12, monitoring systems had been installed on the unstable mountain slopes and a catch basin and warning systems had been built for the village.

Video: SRF, Schweiz aktuell, 23.08.2022, minute 8:42 – 9:31

Despite the installation of monitoring and warning systems, eight hikers lost their lives in the landslide on Piz Cengalo. The deaths led to legal proceedings: the public prosecutor‘s office investigated two experts from the Graubünden Office for Forest and Natural Hazards, an external geologist and two representatives of the municipality ‘for multiple counts of negligent homicide’, as the Bondasca Valley, where the hikers died, should have been closed as a precautionary measure. The case is being heard before the Regional Court in Maloja.

Video: SRF, NewsApp, 23.08.2022

From May to August 1994, a major landslide occurred in Falli-Hölli (FR), slowly destroying an entire holiday village.

After the earth movements were discovered (cracks in the ground and buildings), all holiday guests were evacuated. The building insurance company took over the ruins of the resort for a sum of 15 million Swiss francs. The area has been closed off ever since. In the spring of 1995, the landslide more or less came to a halt, and in 1996 the remains of the resort were removed as far as possible. Since then, nature has been reclaiming the area.

Video: SRF, Schweiz aktuell, 21.04.1995, minute 07:14 – 08:05

Even before the settlement was built, i.e. long before the landslide, a geological report classified the terrain near Falli-Hölli as prone to landslides, but this was ignored.

A lesson was learned from the disaster throughout Switzerland: today, there are systematic hazard maps that show the types of natural hazards that occur and their intensity (risk). These hazard maps are implemented in building regulations, which govern where construction is permitted, under what conditions and where it is not.

Between 18 April and 9 May 1991, two major landslides occurred, bringing a total of approx. 30 million m³ of rock into the valley and cutting off the village of Randa (VS) from the outside world. The railway line and roads were buried, and the Vispa river was dammed up over a length of 1.3 km. Thanks to the efforts of the Swiss Army, a new track for the Matterhorn Gotthard Railway and a bypass road were quickly built. In addition, a 20-metre-deep channel was dug through the rubble to allow the dammed water to drain away. Nevertheless, parts of Randa were flooded during storms in July and August 1991.

Video: SRF, Schweiz aktuell, 10.05.1991, minute 00:59 – 03:53

Miraculously, no lives were lost in the landslides in the spring of 1991. However, the mountain is still active today and is under constant surveillance. Various sensors, radar monitoring and an automated alarm system have been installed.

Natural disasters in Randa have been documented since the Middle Ages. Collapses of the Bisgletscher glacier often buried the village in ice avalanches, causing deaths and property damage. The Bisgletscher glacier is listed in the inventory of dangerous glaciers in Switzerland and is also under constant observation.

On 30 August 1965, part of the Allalin Glacier broke off and an avalanche of ice and debris destroyed the barracks at the Mattmark Dam construction site. Eighty-eight workers, including many migrant workers, lost their lives.

After the disaster, questions arose as to why the barracks had been built in the danger zone. Seventeen people were charged with negligent homicide but were acquitted by the courts. A year later, construction of the dam continued and it was completed in 1967.

Video: Der Gletschersturz von Mattmark, Beitrag der Schweizer Filmwochenschau vom 03.09.1965 (Schweizerisches Bundesarchiv J2.143#1996/386#1177-1#1*), minute 15:24 – 15:45

On 10 April 1939, large boulders broke away from the unstable Flimserstein rock face above Fidaz in the canton of Graubünden (see also Flims rockslide). They buried the Sunnehüsli children‘s home, which was located below the 400-metre-high rock face. Eighteen children lost their lives.

The mountainside above Fidaz remains unstable and is constantly monitored by sensors. Occasional rockfalls from the wall are part of everyday life for the villagers.

Video: SRF, Schweiz aktuell, 10.05.2021, minute 05:19 – 06:59

On 11 September 1881, a devastating rockslide occurred in Elm in the canton of Glarus. Excessive quarrying of slate slabs on Martinsberg had made the slope unstable. Around 10 million cubic metres of rock broke loose and crashed down into the valley. 114 people lost their lives and the village was severely damaged.

Swiss geologist Albert Heim investigated the event in detail and his analysis shaped modern research into landslides in the Alps. Elm is still considered a textbook example of man-made natural disasters.

After a summer of heavy rainfall, a flank of the Rossberg near Goldau broke away on 2 September 1806 and crashed into the valley as an extremely fast debris flow. The debris even spilled up around 100 metres on the opposite side of the valley and triggered a flood wave in Lake Lauerz. The entire village of Goldau was buried within a few minutes.

The landslide received widespread media coverage throughout Europe in the 19th century. It marked the birth of the first Swiss fundraising campaign.

Video: SRF, Wege aus Katastrophen, 14.03.2021, minute 00:10 – 01:32

Decades before the rockslide in 1806, increasing cracking, rockfalls, open crevices and broken roots had been observed on Rossberg. Animals fled the danger zone before the disaster struck. However, the people of Goldau did not seek safety.

Goldau became the first scientifically studied rockslide: the sloping rock layers of the Lower Freshwater Molasse (mainly Nagelfluh) on the Rossberg lost their support after the Ice Age and have since broken away in numerous rockslides.

The rockslide of 1806 can be attributed to deep weathering of thin marl layers, which, after several rainy years, ultimately led to the formation of a continuous fracture and slip surface on which the Nagelfluh banks of the Rossberg slid down.

The improper extraction of soapstone for the production of fireproof cookware led to the instability of Mount Conto above the trading town of Piuro in Bregaglia (formerly GR). On 4 September 1618, disaster struck: within a very short time, 6 million cubic metres of rock broke loose and buried the entire settlement. The Mera River was dammed by the debris and only found a new outlet around the debris cone after 90 minutes. The old village of Piuro was completely destroyed and is considered the Pompeii of the Alps, with approximately 1,200 deaths. The new Piuro was rebuilt in a different location (Italy).

Video: Municipality of Piuro

In 1512, a massive rockslide from Monte Crenone (now Pizzo Magn) buried the Blenio Valley near Biasca in the canton of Ticino. This created a dam of rock debris over 60 metres high, which dammed up the Brenno River to form the so-called ‘Lago di Malvaglia’. When this dam burst in 1515, the flood wave inundated the entire Magadino plain, including the city of Bellinzona.

The population of Biasca accused the inhabitants of Malvaglia of using witchcraft to free themselves from the reservoir. However, in the trial of 1517, the defendants from Malvaglia were acquitted.

The rockslide near Flims almost 10,000 years ago is considered the largest known mass movement in the Alps. Despite numerous research projects, the causes of the rockslide remain unclear. It may have been triggered by extreme precipitation or an earthquake.

Simulation: TectonicArena Sardona

The eastern main fault line of the landslide follows the Flimserstein for many kilometres, while the western fault line is barely visible in the terrain. The upper sliding surface with the northern fault line can be walked on near Cassons. The huge debris cone formed by landslide deposits is best seen today in the gorge near Ruinalta (see photo). Several landslide dams formed along the upper Rhine Valley, which triggered flood waves after dam breaches that can be traced as far as Lake Constance. Even today, the Flimserstein is considered unstable (see landslide near Fidaz, 1939) and is permanently monitored with sensors.

The retreat of the Great Aletsch Glacier is destabilising the valley flanks in the area where the glacier tongue currently lies. In the Moosfluh area (above Riederalp), the entire slope is sliding and tilting deeply towards the remaining glacier. The mountain station of the Moosfluhbahn was built in the area where the slope movement began. It has a flexible design and can adapt to even the smallest movements in the terrain, which are detected by continuous monitoring using surveying and GPS. The mountain station is considered an example of innovative solutions in the Alpine region. The municipality of Riederalp is supported in this by universities.

Video: SRF, 10vor10, 21.06.2016, minute 21:05 – 24:43

The village of Brienz, threatened by a large permanent landslide, debris flows and rockfalls, and its unstable mountainside have been monitored for decades and have been undergoing intensive geological investigation since 2017.

Video: SRF, 10vor10, 16.06.2023, minute 1:09 – 2:51

With the ‘red’ phase being declared again in summer 2025, the village may no longer be entered on a regular basis. After a quieter period in autumn 2025, rockfalls increased again in November 2025.

Video: SRF, Schweiz aktuell, 20.06.2025, minute 0:01 – 2:35

In the worst case scenario, up to 2.2 million cubic metres of rock could fall on the village (as of summer 2025). If the situation continues to worsen, the municipal management team would declare a ‘blue’ alert. In the worst case scenario, rapid mass movements could then reach the Albula.

Numerous simulations by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and ETH Zurich are examining the ranges and speeds of the various scenarios in detail.

Simulation: Johan Gaume (ETH Zurich & WSL-SLF)