EL PASO COUNTY NATURAL HAZARDS CLEARINGHOUSE
				Landslides A general definition is the movement of a mass of land down a slope.  The land can be composed of rock, earth and artificial fill or any of the above combinations.  Landslides occur when layers of earth, with different geological compositions, separate and the top-most layer begins to descend down the slope.  A common cause of layers separating is water seeping through pores in the earth and underlying sandstone, and saturating layers of clay or shale.  When these layers become saturated they become slippery; gravitational forces overcome the loss of friction holding the layers together and movement begins.  Common names for landslides include (but are not limited too): debris slide, earthflow, slope failure, unstable slope, lateral spreading, colluvium and displaced claystone.
Sidewalk, originally straight, deformed by underlying landslide - Colorado Springs Click on thumbnails for more landslide pictures and some of their effects
Links Colorado Geological Survey Hazards Information Hazards Publications U.S. Geological Survey Landslide Photos http://landslides.usgs.gov/html_files/landslides/slides/landslideimages.htm National Landslide Hazards Program Hazards Information Mitigation Information U.S Geological Survey - Landslide Publications and Reports Fema- Landsides and Mudflows Colorado Office of Emergency Management
More on landslides from CGS Special Publication 6 & 12 Mitigation Many methods of mitigation can be designed for active or potentially active landslide areas. These generally fall into four categories: 1) change of slope shape, 2) drainage management, 3) retaining structures, and 4) special treatments. Change of slope shape methods include excavating the entire slide, benching, excavating the upper part of the slide increasing the weight and resistance to movement of the lower part of the slide (loading), and a combination of excavation and loading. Land Use The above mitigation techniques can be quite costly, particularly for large landslide areas, and are often used only as a last resort or to protect expensive structures. Even then they may be temporary and in the long run ineffective. In general, recognition and avoidance of landslide areas with all structural land uses is desirable. Significant earth moving or structural use of the land nearly always justifies a thorough analysis of the landslide potential prior to construction, landslide-prone areas are unavoidable and mitigation measures must be utilized to fit the circumstances. Mitigation Procedures Having properly identified a region as being prone to landslide failure, several approaches can be taken in attempting to utilize the area. Avoidance Some non-conflicting use could be designated for the area, whereby losses would be minimal in the event of failure. One such use is green belting, or open space including certain types of agricultural use. Non-conflicting use Where the proposed use is simply not compatible with an existing slide hazard, the hazard is best avoided by selective use of available development land and complete avoidance of high-risk areas.
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