A form of mass movement where the displaced material retains its form as it moves. Cruden and Varnes (USGS Fact Sheet 2004–3072) divide landslides into slides, falls, flows, topples, and lateral spreads. Probably the world’s largest landslide occurred in south-west Iran in 1937, when a segment of the Kabir Kuh ridge, about 15 km long, 5 km wide, and 300 m thick, slid off the mountain, with enough momentum to travel 20 km.

Landslides are prompted by an increase in pore pressure through snow melt, through precipitation, and through spring action. These all reduce the friction which binds the mass to the slope. See Hungr. et al. (2008) Geomorph. 96, 3–4 on the technique of constructing a regional magnitude-cumulative frequency curve for landslide prediction.

http://rainfallthresholds.irpi.cnr.it/ Worldwide database of empirical rainfall thresholds for the possible occurrence of landslides.