Falling processes: National Platform for Natural Hazards

Large rockfalls and landslides are usually signalled in advance by increased rockfall activity.

In steep and rocky areas, blockfalls and rockfalls, rockslides (over 100 m3) or even landslides (with a rock volume of over one million m3) can occur. These processes are by no means limited to the mountains: this danger must be reckoned with wherever rock and rock formations appear on the surface. Large rockfalls and landslides are usually signalled in advance by increased rockfall activity.

The annual financial damage caused by falls is hardly significant in Switzerland. However, due to the usually strong impacts, they can have very drastic effects locally. Certain areas may not be populated due to the hazard, others must be temporarily evacuated (as in Brienz, GR in 2023) or - if no other option is available - permanently relocated (as in Horlaui, Weggis, LU in 2014). Infrastructure facilities such as roads and railway lines are often affected by rockslides and rockfalls.

Fact sheet «Fall processes» (2023)

Due to the spectacular images, fall trials often trigger a great deal of media coverage and corresponding consternation among the population

Effects of climate change

The risk of rockfalls and even rockslides is expected to increase due to climate change

Risk increases with climate change

The risk of rockfalls and even rockslides is expected to increase due to climate change: Thawing permafrost, more frequent frost and thaw cycles in warmer winters and increased heavy precipitation can lead to the destabilisation of rock faces.

Permafrostmonitoring

SLF, Rockfalls in permafrost

Monitoring and early warning

Monitoring of the moving rock face in Preonzo (TI) using ground-penetrating radar

Monitoring and early warning

Monitoring and early warnings primarily serve to ensure personal safety by evacuating the population from the danger zone in good time. Alternative transport routes are important for the infrastructure in the event of a closure. As it is usually not possible to avoid the fall processes, this leads to significant indirect costs (such as the temporary closure of the Gotthard A2 motorway).

Effective measures

The risk of rockfall can be minimised by protective forests and technical measures. In the case of rockfalls, these measures are significantly more expensive, more complex or cannot be implemented at all. In the case of rockfalls, there are not many options left to influence the process itself. Therefore, in terms of integral risk management, the focus is not on reducing the hazard alone, but on recording, assessing and controlling the risk - also in terms of a cost-benefit analysis - accompanied by an active risk dialogue. Examples of measures include

Spatial planning measures

Plan residential development in areas at risk
Issue building bans in high-risk areas
Designate differentiated hazard zones and restrict uses
Decide on conditions for new buildings and conversions in endangered areas

Land use and natural hazards

Technical measures

Construct or reinforce buildings and facilities in known rockfall areas using robust construction methods
Secure or dismantle localised fall sources
Build dams, especially if large volumes are expected
Stretch and maintain protective nets

SIA, Actions on supporting structures

Biological measures

Establish and maintain protection forests in the area of origin, transit and demolition

Organisational measures

Monitor known sources of danger
Organise alarm systems
(Temporarily) close traffic routes and hiking trails
Draw up evacuation plans, evacuate if necessary

BAFU, Monitoring systems for gravitational natural hazards (2020)

BAFU_BABS, Guidelines for operational planning for gravitational natural hazards (2020)

Spitze Stei: large-scale monitoring and structural measures

Above Kandersteg (BE) lies the unstable mountain flank ‘Spitze Stei’, which has been moving strongly for several years at a rate of several metres per year. As a result, there is not only frequent rockfall, but also the threat of large rockfalls of 100,000 to several million cubic metres - with debris flows posing a secondary danger. Since 2018, the movements have been monitored and measured using various instruments. To protect the settlement area below, a damming system and a debris deposit site were built in 2020 as an emergency measure. The municipality provides specialist information and publishes a bulletin at least once a week.

Kandersteg, Spitze Stei

Chronicle

Dramatic rock and landslides in the past

1806 Goldau

The landslide in Goldau (SZ) is the largest natural disaster in Switzerland to date, alongside the Basel earthquake (1356). The Rossberg landslide destroyed entire villages in just over three minutes on 2 September. 457 people and 323 animals lost their lives.

1881 Elm

Although the landslide in Elm (GL) with its devastating consequences had been announced on 11 September, over 110 people died - many because they wanted to witness the natural disaster as spectators. Around 10 million cubic metres of rock thundered into the valley as a result of slate exploitation and the persistent rain. 83 buildings, 4 bridges and 90 hectares of cultivated land were destroyed.

1991 Randa

On 18 April and 9 May, two demolitions with a total volume of 30 million m3 took place near Randa (VS). The railway line and road connection to Zermatt were interrupted and the Vispa River was filled in and dammed. No people were injured.

2012 Bellinzona

The area above Preonzo near Bellinzona (TI) had been on the move for years when the canton detected increased activity in April. The affected area in the outlet zone was evacuated and the cantonal road was closed. In the early hours of 15 May, part of it - around 220,000 m3 of rock - collapsed into the valley. Thanks to the evacuation, no people were injured.

2017 Piz Cengalo

On 23 August, three to four million cubic metres of rock fell down the Piz Cengalo in Bergell (GR). Several debris flows then travelled as far as the village of Bondo. Eight people lost their lives on a hiking trail. It was one of the biggest landslides in the last 100 years. Thanks to a debris retention chamber, most of the village remained undamaged.