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12-1 <br /> <br /> <br /> <br /> <br /> <br /> <br />12. LANDSLIDE/MASS MOVEMENTS <br /> <br /> <br /> <br /> <br />12.1 GENERAL BACKGROUND <br />A landslide is a mass of rock, earth or debris moving down a slope. Landslides may be minor or very large, and <br />can move at slow to very high speeds. Mudslides are rivers of rock, earth, organic matter, and other soil materials <br />saturated with water. They develop in the soil overlying bedrock on sloping surfaces when water rapidly <br />accumulates in the ground, such as during heavy rainfall or rapid snowmelt. <br /> <br />Landslides in hillside terrain can pose serious hazard to downslope property and structures. They can disrupt <br />roadways and other infrastructure lifelines, destroy private property, and cause flooding, bank erosion, and rapid <br />channel migration. A slide can move rapidly down slopes or through channels, and can strike with little or no <br />warning. It can travel miles from its source, growing as it descends, picking up trees, boulders, cars, and anything <br />else in its path. Although slides behave as fluids, they convey many times the hydraulic force of water due to the <br />mass of material they carry. <br /> <br />In spite of their destructive potential, landslides can serve beneficial functions to the natural environment. They <br />supply sediment and large wood to the channel network and can contribute to complexity and dynamic channel <br />behavior critical for aquatic and riparian ecological diversity. <br /> <br />12.1.1 Landslide/Mass Movement Causes <br />Slides are caused by a combination of geological and climate conditions and the influence of urbanization. They <br />can be initiated by storms, earthquakes, fires, volcanic eruptions or human modification of the land. Vulnerable <br />natural conditions are affected by human development and the infrastructure that supports it. In some cases, <br />irrigation increases the landslide potential. The following factors can contribute to slide formation: <br /> Change in slope of the terrain <br /> Increased load on the land <br /> Shocks and vibrations <br /> Change in water content <br /> Groundwater movement <br /> Frost action <br /> Weathering of rocks <br /> Removing or changing the type of vegetation covering slopes.