Ground Failure

Flows are gravitational mass movements down a slope in the form of a fluid. Flows often leave behind a distinctive, fan-shaped deposit where the landslide material has stopped moving (cf. British Geological Survey 2024)

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

Sub-categories of slides may be defined by the type of material (e.g., rock, soil, debris, or earth) and the velocity of the mass movement (cf. Cruden and Varnes, 1996; Hungr et al., 2014). Mud slides are here taken to be a sub-category of earth slides.

A topple is the forward rotation out of the slope of a mass of soil or rock about a point or axis below the center of gravity of the displaced mass (Cruden and Varnes, 1996).

Sub-categories of topples may be defined by the type of material (e.g., rock, soil, debris, or earth, modes of toppling (Goodman and Bray, 1976) and the velocity of the mass movement (cf. Cruden and Varnes, 1996; Hungr et al., 2014).

A gravitational mass movement (‘landslide’) is the downslope movement of soil, rock and organic materials under the effects of gravity, which occurs when the gravitational driving forces exceed the frictional resistance of the material resisting on the slope. Such movements may be terrestrial or submarine (GH0306) (cf. Cruden and Varnes, 1996). 

Subsidence is a lowering or collapse of the ground, caused by various factors, including groundwater lowering, sub-surface mining or tunnelling, consolidation, sinkholes, or changes in moisture content in expansive soils. Shrink-swell is the term applied to the behaviour of expansive soils. These are a group of soils that exhibit volumetric change in response to changes in moisture content, such that they shrink in response to desiccation and swell by hydration, resulting in ground subsidence and ground heave respectively (BGS, 2020). 

Sinkholes (also known as dolines) are depressions or holes in the ground caused by the dissolution, collapse or erosion of rock below the landsurface. This is one of several hazards that result in subsidence, i.e., lowering or collapse of the ground (adapted from USGS, no date; and BGS, no date). 

A submarine gravitational mass movement (‘Landslide’) is  the downslope movement of sediment or rock due to gravity, occurring when the downslope forces exceed the sediment's resistance to movement (Adapted from Lee et al., 2007). 

A rock, debris or earth fall is a fragment of rock (a block), body of debris or earth (here taken to include mud) detached by sliding, toppling, or falling, that falls from a vertical or sub-vertical cliff and proceeds down slope by bouncing and flying along ballistic trajectories or by rolling on talus or debris slopes (adapted from Highland and Bobrowsky, 2008). 

Rock spread: Near-horizontal stretching (elongation) of a mass of coherent blocks of rock as a result of intensive deformation of an underlying weak material, or by multiple retrogressive sliding controlled by a weak basal surface. Usually with fairly limited total displacement and slow movement (Hungr et al., 2014).

Liquefaction refers to the loss of strength experienced in loosely packed, saturated or close to saturated sediments at or near the ground surface in response to strong ground shaking, such as earthquakes, cyclic loading (repeated application of stresses), and vibration from machinery, or due to the development of excess pore water pressure resulting from a change in head or confining pressures. (c. AGI, 2017; USGS, no date).