An avalanche is a mass of snow and ice falling suddenly down a mountain slope and often taking with it earth, rocks and rubble of every description (WMO, 1992).

A mud flow is a flow of water so heavily charged with sediment and debris that the flowing mass is thick and viscous (WMO and UNESCO, 2012).

A rock slide is a movement of a mass of soil or rock on an individualized failure surface (Dennis and Didier, 2019).