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Fast clay is a material that originates from the marine environment, that is, it has previously been covered by seas of salt water. This means that land areas that had previously been the seabed may consist of more or less large areas of fast clay, for example in western Sweden, along the Göta river valley and around Lake Vänern, also in Norway, Finland and Canada.
– Quick clay itself is not dangerous and does not pose an immediate avalanche hazard, but it is good to know that it exists when you have to do earth work or excavation so you are careful Landslides can be dangerous if the topography is unfavorable, for example slopes, large level differences or sloping waterways, says HannaSofie Pedersen, head of the climate adaptation department at the Swedish Geotechnical Institute.
She explains that if there is a small landslide in such a place you can go down to the depth where the quick clay is and then the material becomes relatively solid like mush in consistency. In such a situation, the landslide can spread and cause further devastation similar to what happened in the Norwegian Gjerdrum.
– When municipalities in Sweden produce new detailed or general plans, it is always included that studies should be carried out to assess the risks of, among other things, landslides, landslides and erosion. It’s called geotechnical safety issues and there we have a function that supports the county administrative boards and municipalities in the process, more specifically that we review and comment on the data that they have sent us, says HannaSofie Pedersen.
Other problems include the “ordinary” clay found in most of Sweden, sandy soils, mud streams, and erosion. Erosion in particular is a concern along the Skåne and Halland coasts, where water slowly makes its way inland.
– The idea of our work is to capture these problems before starting to build. We and the Swedish Civil Contingency Agency also work with so-called landslide risk mapping, that is, we map areas to estimate the probability of landslides and the consequences of them, says HannaSofie Pedersen who mentions the mapping for Säveån, Norsälven, Göta älv and a continuum for Ångermanälven. .
How should ordinary people relate to these risks?
– As a resident, I don’t think you should be afraid of landslides or something like that. We have good conditions to catch the problem in time and a lot of preventive work is done, but it is clear that it is good if you as the owner are aware of what you have of land in the area so that you do not put large buildings on a slope, for example. where there’s clay underneath, says HannaSofie Pedersen.
