Landslides and rockfalls
Some soils, especially clay soils on sloping ground or adjacent to water, is prone to landslides. Best of all is to avoid building on such sites, but if there are already buildings, it must be possible to assess the landslide risk and, where necessary, the measures to be deployed. This requires knowledge of the soil's properties and of the occurrence of previous landslides.
Around 5 per cent of Sweden's land area consists of clay and silt soils. A quarter of these soils, mainly clay soils, are considered to be prone to landslides. Natural disasters in Sweden caused by landslides cost society approximately SEK 200 million annually.
SGU's "Landslides and ravines" map viewer shows the locations of a large number of landslides in different parts of Sweden.
The natural process of erosion adjusts cliffs and slopes to a position of equilibrium. Small changes to this equilibrium can trigger landslides or rockfalls. Land uplift, the climate and human intervention in nature alters soil stability. Over the years, safe ground can therefore become unsafe.
A distinction is made between landslides and rockfalls
A landslide is a cohesive mass of soil that comes into motion. Landslides occur in silt and clay soils. Landslides can also occur in silty or clayey moraines if the moraine is saturated with water.
In a rockfall, blocks, stones, gravel and sand particles move freely.
Rockfalls occur in rock faces and in gravel and sand cliffs.
The common denominator is that both landslides and rockfalls can occur without warning.
In connection with landslides and rockfalls, mention is usually also made of ravines. The creation of ravines is a slower process than for landslides and rockfalls. They are primarily formed in areas where there is plenty of coarse clay, silt and fine sand. A ravine is often ten to twenty metres deep, V-shaped and has steep sides. The ravines usually branch out and have abrupt irregularities.
Soil characteristics have an influence
The ability of the soils to let through, absorb or retain water depends primarily on grain size and how hard the grains are packed.
The Skånestrand Project
SGU has mapped areas along Skåne's beaches, on the sea bed and on land, in order to obtain a better basis for assessing erosion susceptibility.
More information on landslides
The Swedish Civil Contingencies Agency (MSB), the Swedish Geotechnical Institute (SGI) and SGU are jointly responsible for the content of a section on landslides and rockfalls on the MSB website.