A landslide is a downslope movement of rock or soil, or both, occurring on
the surface of rupture—either curved (rotational slide) or planar (translational slide) rupture—in which much of the material often moves as a coherent or semicoherent
mass with little internal deformation. It should be noted that, in some cases, land-
slides may also involve other types of movement, either at the inception of the failure or later, if properties change as the displaced material moves downslope.
This section provides descriptions and illustrations of the various types of land-
slides. Understanding the characteristics of the specific type of landslide hazard in
your area is vitally important to consider when planning or adopting appropriate miti-
gative action to lessen the risk of loss and damage. The type of landslide will deter-
mine the potential speed of movement, likely volume of displacement, distance of
run-out, as well as the possible effects of the landslide and the appropriate mitigative measures to be considered.
Landslides can be classified into different types on the basis of the type of move-
ment and the type of material involved (please see References 9 and 39). In brief,
material in a landslide mass is either rock or soil (or both); the latter is described as earth if mainly composed of sand-sized or finer particles and debris if composed of coarser fragments. The type of movement describes the actual internal mechanics of
how the landslide mass is displaced: fall, topple, slide, spread, or flow. Thus, land-
slides are described using two terms that refer respectively to material and movement (that is, rockfall, debris flow, and so forth). Landslides may also form a complex fail- ure encompassing more than one type of movement (that is, rock slide—debris flow).
For the purposes of this handbook we treat "type of movement" as synonymous
with "landslide type." Each type of movement can be further subdivided according
to specific properties and characteristics, and the main subcategories of each type are described elsewhere. Less common subcategories are not discussed in this handbook but are referred to in the source reference.
Direct citations and identification of sources and references for text are avoided in the body of this handbook, but all source materials are duly recognized and given in the accompanying reference lists
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