|This information has been developed in association with Peter Dahlhaus, University of Ballarat.|
The term landslide is usually defined as: "the movement of a mass of rock, debris or earth down a slope". This international definition is used by the Australian Geomechanics Society and includes all forms of movement from debris creep to rock falls. The terminology used to describe a landslide depends on the information known about the processes and generally uses two nouns to describe material involved and the style of movement, e.g. a rock fall or a debris flow.
The landslide material is classified as either 'bedrock' or 'engineering soil'. Engineering soils are further subdivided into either debris (predominantly sand, gravel, cobbles and boulders) or earth (predominantly silt and clay). The five main types of movement are falls, topples, slides, spreads and flows.
Landslides near Scotts Creek
Landslides compared to Simplified Geology
Over 1 400 landslides have been mapped in various studies within south west Victoria and it is estimated that thousands more, of varying sizes, exist. All mapped landslides occur south of the western Victorian volcanic plain, where the geology, steeper terrain slopes and climate combine to provide the conditions required. Landslides vary in area from a few square metres to over 120 hectares and in volume from a few cubic metres to over ten million cubic metres. They are triggered by prolonged and/or intense rainfall, man-made changes to the landscape and rare earthquake events. The vast majority of landslides occur in two rock types, viz: the Otway Group rocks and the Gellibrand Marl.