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<br /> <br />2021 Multijurisdictional Local Hazard Mitigation Plan <br /> <br />While small landslides are frequently a result of human activity, the largest landslides are often naturally <br />occurring phenomena with little or no human contribution. The sites of large landslides are typically areas of <br />previous landslide movement that are periodically reactivated by significant precipitation or seismic events. <br /> <br />12.1.2 Landslide/Mass Movement Types <br />Common types of slides are shown in Figure 12-1. The most common is the shallow colluvial slide, occurring <br />particularly in response to intense, short-duration storms. The largest and most destructive are deep-seated slides, <br />although they are less common than other types. <br /> <br /> <br /> <br /> <br /> <br />Deep Seated Slide Shallow Colluvial Slide <br /> <br />Bench Slide Large Slide <br /> Figure 12-1. Common Types of Landslide <br /> <br />12.1.3 Landslide/Mass Movement Risk Areas <br />Landslides are typically a function of soil type and steepness of slope. Soil type is a key indicator for landslide <br />potential and is used by geologist and geotechnical engineers to determine soil stability for construction standards. <br />In general, landslide hazard areas are where the land has characteristics that contribute to the risk of the downhill <br />movement of material, such as the following: <br /> A slope greater than 33 percent <br /> A history of landslide activity or movement during the last 10,000 years <br /> <br /> <br />12-2