A landslide is a sudden movement of a large section of a valley side, sea cliff or man-made cutting. Landslides are more common in wet weather because water seeps into the rocks, lubricates them and makes them more likely to slip. The Severn Gorge is famous for its river landslips.

Landslides are especially common along coasts made of soft rocks. The Yorkshire coast and Dorset coasts in England have more landslides than almost anywhere else in the world.

Another place where landslips are common is where a river bend cuts into a valley side. In both cases the cause is the same: the land at the foot of the cliff is removed by waves or river and the weight of the cliff above is no longer supported.

It is almost impossible to say when a landslip will occur, and landslips are so large that the ground cannot be shored up because the cost would be so high. For this reason building houses on tops of soft-rock cliffs and below cliffs is usually not allowed.