How does BGS classify landslides?

The classification of landslides by the BGS follows the scheme based on Varnes (1978) and Cruden & Varnes(1996). The scheme terminology is also that suggested by the Unesco Working Party on the 'World Landslide Inventory' (WP/WLI 1990, 1993).

The main classification criteria are:

  • type of movement (falls, topples, slides spreads, flows), and
  • type of material involved in the movement (rock, debris, earth)

Combining movement and material type terms enables an appropriately descriptive landslide name to be formulated. Naming can become more detailed with the addition of other descriptive details related to activity state, water content , rate of movement, etc., if known (e.g. active, complex, extremely rapid, dry rock fall-debris flow).

Only a small selection of the wide spectrum of landslide types that may develop in nature are shown here.

Land lip types

Movement types

Falls: masses are detached from steep slope/cliff along surfaces with little or no shear displacement (e.g. joints/fissures) and descend mostly through air by free fall, bouncing or rolling.
Topples: movements of rock, debris or earth masses by forward rotation about a pivot point.
Rotational slides (slumps): masses slide outwards and downwards on one or more concave-upward failure surfaces that impart a backward tilt to the slipping mass, which sinks at the rear and heaves at the toe.
Translational (planar) slides: movements occur along planar failure surfaces that may run more-or less parallel to the slope.
Spreads: involve the fracturing and lateral extension of coherent rock or soil masses due to plastic flow or liquefaction of subjacent material.
Flows: slow to rapid movements of saturated or dry materials which advance by flowing like a viscous fluid, usually following an initial sliding movement. Some flows may be bounded by basal and marginal shear surfaces but dominant movement of the displaced material is by flowage.
Complex slides: involve a type of movement style that combines two or more of the main movement types (fall, topple, slide, spread, flow) occurring in sequence. Complexity may be indicated by combining the main movement terms, e.g. complex rotational earth slide-earth flow (or complex slump-earth flow).

References

Varnes, DJ. 1978. Slope movement types and processes. In Special report 176: Landslides: Analysis and Control, Transportation Research Board, Washington, D.C.
Cruden, DM & Varnes, DJ. 1996. Landslide types and processes. In Special Report 247: Landslides: Investigation and Mitigation, Transportation Research Board, Washington D.C..
WP/WLI. 1990. A suggested method for reporting a landslide. Bulletin of the International Association of Engineering Geology, No. 41.
WP/WLI. 1993. A suggested method for describing the activity of a landslide. Bulletin of the International Association of Engineering Geology, No. 47.