Landslides occur because of the sudden soil liquefaction caused by external solicitations such as vibrations induced by an earthquake, or massive rainfalls.
[1][2][3] Quick clay is found only in countries close to the north pole, such as Russia; Canada; Norway; Sweden; and Finland; and in Alaska (United States); since they were glaciated during the Pleistocene epoch.
It results in a stronger electrostatic repulsion between negatively charged clay platelets which can more easily become dispersed and form stable suspensions in water (peptization phenomenon).
[6] At this point, there was only the formation of very strong marine clay, which is found all over the world and highly stable, but with its own unique geotechnical problems.
Quick clay deposits are rarely located directly at the ground surface, but are typically covered by a normal layer of topsoil.
[4] In modern times, areas known to have quick clay deposits are commonly tested in advance of any major human development.
It is not always possible to entirely avoid building on a quick clay site, although modern engineering techniques have found technical precautions which can be taken to mitigate the risk of disaster.
For example, when Ontario's Highway 416 had to pass through a quick clay deposit near Nepean, lighter fill materials such as polystyrene were used for the road bed, vertical wick drains were inserted along the route and groundwater cutoff walls were built under the highway to limit water infiltration into the clay.