General term for the transfer of Earth material down hillslopes. It includes four main categories: flow, slide, fall (see rock fall), and creep. Of these, creep is the most important if least spectacular. It is the result of gravity acting on material that has lost cohesion, typically as a result of an increase in water content. An avalanche is a rapid and often destructive flow of rock or snow. A slide (or landslide) is a comparatively rapid displacement of Earth material over one or more failure surfaces which may be curved or planar. Failure on an arcuate surface is typical of clays, and gives rise to rotational slides such as those of Folkestone Warren, England.