Causal phenomena

Downslope transport of soil and rock resulting from naturally occurring vibrations, changes in direct water content, removal of lateral support, loading with weight, and weathering, or human manipulation of water courses and slope composition.

General characteristics

Landslides vary in types of movement (falls, slides, topples, lateral spread, flows), and may be secondary effects of heavy storms, earthquakes, and volcanic eruptions. Landslides are more widespread than any other geological event.

Predictability

Frequency of occurrence, extent and consequences of landslides may be estimated and areas of high risk determined by use of information on area geology, geomorphology, hydrology and climatology and vegetation.

Factors contributing to vulnerability

Settlements built on steep slopes, softer soils, cliff tops
Settlements built at the base of steep slopes, on mouths of streams from mountain valleys
Roads, communication lines in mountain areas
Buildings with weak foundations
Buried pipelines, brittle pipes
Lack of understanding of landslide hazard

Typical adverse effects

Physical damage - Anything on top of or in path of landslide will suffer damage. Rubble may block roads, lines of communication or waterways. Indirect effects may include loss of productivity of agricultural or forest lands, flooding, reduced property values.
Casualties - Fatalities have occurred due to slope failure. Catastrophic debris slides or mudflows have killed many thousands.

Possible risk reduction measures

Hazard mapping
Legislation and land use regulation
Insurance

Specific preparedness measures

Community education
Monitoring, warning and evacuation systems

Typical post-disaster needs

Search and rescue (use of earth removal equipment); medical assistance; emergency shelter for homeless

Impact assessment tools

Damage assessment forms