Landslide

Abstract

Landslides are a near-global hazard, but are most common in areas of high relief where steep and moderate slopes are common. Landslides are classified according to type of movement (falls, topples, slides, slumps, flows, sags), type of material (rock, unconsolidated sediments), and velocity (slow, fast). The most important cause of landslides is geology – failure generally occurs on weak planes in rock, including stratification, foliation, joints, or faults; and poorly lithified rocks and non-lithified sediments are generally more prone to failure than lithified materials. Almost as important is water, which increases the mass of the earth material and therefore the gravitational driving force; water also penetrates joints, fractures, and permeable strata, possibly elevating pore-water pressures to the threshold of failure. Landslide triggers are related to, but distinct from, causes. They are the phenomena that raise the slope above the threshold of failure. The most common triggers of landslides are severe storms, earthquakes, volcanic eruptions, and human activity. In the case of human activity, loading the top of an unstable slope or removing material from its base may trigger a landslide, as both increase the gravitational driving force on the slope. Human activity, however, can also increase the stability of a slope, for example, by loading the toe of the slope or by dewatering unstable materials. Landslide hazards can be mitigated by land-use restrictions, monitoring, warning systems, and corrective and defensive structures.