3I). Landslides occur when gravitational and other types of shear stresses within a slope exceed the shear strength (resistance to shearing) of the materials that form the slope. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others. The 1995 landslide apparently occurred as a result of an extraordinarily wet year. Currently, we have insufficient data and understanding of the failure mechanisms of this landslide to adequately answer these questions, but it is clear that the hazard from renewed landslide movement is considerable. There are generally three types of creep: (1)seasonal, where movement is within the depth of soil affected by seasonal changes in soil moisture and soil temperature; (2) continuous, where shear stress continuously exceeds the strength of the material; and (3) progressive, where slopes are reaching the point of failure as other types of mass movements. Inspection of the site within a few hours of the landslide indicated that much of the deposit consisted of fairly dry material (James O'Tousa, RJR Engineering, personal commun., 2005). [3] Historical accounts support this. As discussed above, the 1995 landslide was relatively deep and primarily moved as a coherent slumpearth flow. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. Other hazards, such as flash floods and debris flows, now become the focus. Figure 1: Air photo of La Conchita, CA taken in 2002. 3F). Types of mass movement Flows are a mixture of water, rock and sediment. Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact, and so forth), Contrast in permeability and/or stiffness of materials, Fluvial, wave, or glacial erosion of slope toe or lateral margins. Landslides and Mass Wasting Compared to spatially extensive natural hazards like earthquakes, tornadoes, and hurricanes, landslides are relatively localized and usually impact a minimal number of persons. Landslides are a type of "mass wasting" which denotes any down slope movement of soil and rock under the direct influence of gravity. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. 1 it is The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. Share sensitive information only on official, secure websites.. Environmental & Historic Preservation Guidance, Real Estate, Lending or Insurance Professionals, State, Local, Tribal or Territorial Governments, Preparedness Activities, Research & Webinars, Voluntary & Community-Based Organizations, Environmental Planning & Historic Preservation, National Business Emergency Operations Center, Ventura County Public Works - Transportation Department. 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. copyright Engineering Applications Figure 5. Areas recently burned by wildfires are particularly susceptible to flash floods and debris flows during rainstorms. Landslides in the United States occur in all 50 States. Major types of landslide movements. If people continue to live in La Conchita, more lives will . Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. 1). Earthflow: Earthflows have a characteristic "hourglass" shape (fig. However, this still leaves some troubling questions unanswered. You also have the option to opt-out of these cookies. The 2005 landslide occurred at the end of a 15day period that produced record and nearrecord amounts of rainfall in many areas of southern California. The lush, green vegetation visible in the southeastern (lower right in photograph) part of the 1995 deposit clearly indicates that drainage on and within the 1995 landslide deposit concentrated water in the part of the mass that failed in 2005. 4). People were evacuated and the houses nearest the slide were completely destroyed. British Geological Survey - What is a landslide? U.S. Department of the Interior | U.S. Geological Survey The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies.
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