A landslide includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows.

The biggest reason for a landslide is always that there is a slope and material goes down the slope because of gravity.

But other things also contribute to landslides:

• erosion by rivers, glaciers, or ocean waves makes slopes too steep
• rock and soil slopes made weak through saturation by snowmelt or heavy rains
• earthquakes create stresses that make weak slopes fail (see liquefaction, Hope Slide)
• volcanic eruptions produce loose ash deposits, heavy rain, and debris flows
• vibrations from machinery, traffic, blasting and even thunder may trigger failure of weak slopes
• weight from much rain or snow, stockpiling of rock or ore, from waste piles, or from buildings may stress weak slopes to failure and other structures
• groundwater pressure making the slope unstable
• in shallow soils, the removal of deep-rooted plants that bind the colluvium to bedrock

The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock.

Earthen slopes can develop a cut-spherical weakness zone. The probability of this happening can be calculated in advance using a simple 2-D circular analysis package. A primary difficulty with analysis is locating the most-probable slip plane for any given situation. Many landslides have only been analyzed after the fact.

Slope stabilisation methods in rock or in earth, can be collocated into three types of measure:

• Geometric methods, in which the geometry of the hillside is changed (in general the slope);
• Hydrogeological methods, in which an attempt is made to lower the groundwater level or to reduce the water content of the material;
• Chemical and mechanical methods, in which attempts are made to increase the shear strength of the unstable mass or to introduce active external forces (e.g. anchors, rock or ground nailing) or passive (e.g. structural wells, piles or reinforced ground) to contrast the destabilising forces.

For More Information: Landslide

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