Rockfall, landslides, debris flows

Mass movements (gravitational natural hazards) are downslope directed displacements of solid and/or loose rocks as well as soil material. As falling processes, they can occur quickly and suddenly. Landslides on the other hand, are slow, continuous processes.

Stieregg landslide, Grindelwald 2005
Stieregg landslide, Grindelwald 2005
©  Hansruedi Burgener

Summary

Falling processes are mass movements in which material, that has been broken out of the rock face along discontinuity surfaces (layering, foliation, jointing or fracture surfaces), travels the greatest part of the way in the air. One distinguishes between different rockfall categories depending on the size of the individual components, mobilized volume and falling speed.

Landslides are downslope directed, sliding displacements of portions of slopes consisting of solid and/or loose rocks as well as soil material. They are the result of a shear fracture and generally occur on moderately inclined to steep banks or slopes. The two main characteristics of landslides are the activity (annual velocity and velocity change or reactivation) and the depth of the sliding surface (base depth).

Debris flows are formed on relatively steep slopes and are a fast downward moving mixture of loose rock (mostly soil and vegetation cover) and a lot of water, without the presence or rather formation of a sliding surface. They often act destructively because they occur suddenly and develop rapidly.

Integrated Risk Management (IRM) is necessary
There will always be ground movements in Switzerland. Through Integrated Risk Management (IRM), the potential risks and damage can be prevented or limited with targeted measures. The development of the basis for risk, for example through event registers and hazard maps, is therefore indispensable.

Damage limitation through targeted measures

  • Regional development measures: a construction ban in high risk areas, rezoning, building regulation for new structures including property protective measures, usage restrictions, relocation of endangered facilities and infrastructure, keeping drainage corridors free, ensuring the space requirements etc.
  • Maintenance: preserve the discharge capacity of the water bodies, maintenance and repair of existing protective structures (e.g., emptying of sediment traps or rockfall protection nets)
  • Maintenance of protection forests
  • Technical measures: protective structures like barriers, retention ponds, drainage, levees, anchors etc. Where additional protective measures are necessary, these should be undertaken as naturally and according to landscape needs as possible
  • Organizational measures: monitoring, measuring and alarm systems, evacuation plans, temporary closure of transport corridors etc.

Who is who

Gravitational natural hazards: contacts

The Federal Office for the Environment (FOEN), the National Platform for Natural Hazards (PLANAT) and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) provide contact information on various forms of mass movements.

Data

The Federal Office for the Environment (FOEN), the Swiss Geological Survey as well as the Geodata portals of the cantons and the federal government provide visual access to the natural hazards data. Geocat.ch offers an ideal entrance to the search for such data. Numerous reports and illustrations are obtainable via FOEN.

Viewer, maps


Reports, explanations

Federal Office for the Environment


Geologische Gefahren

Contact

Hazard Prevention Division (FOEN)
E-Mail
Natural Hazards, PLANAT
E-Mail

Landslide (SilvaProtect-CH)