However, you may visit "Cookie Settings" to provide a controlled consent. Explain why. Publications. For those who aren't, La Conchita a small (population about 340 people), unincorporated seaside village located on the Pacific coast north of Los Angeles (Fig. Southern California lies astride a major tectonic plate boundary defined by the San Andreas Fault and numerous related faults that are spread across a broad region. Where did the La Conchita . Separation occurs along discontinuities such as fractures, joints, and bedding planes, and movement occurs by free-fall, bouncing, and rolling. When was the last landslide in La Conchita? Of primary interest to the general public and various Governmental entities is the current state of hazard at La Conchita. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. An official website of the United States government. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. Note the numerous landslides that have taken place in the area, including the large slide in 1995. Background rates of coastal cliff erosion are variable along the California coast (seeNational Assessment of Shoreline Change Part 4: Historical Coastal Cliff Retreat along the California Coast - Open File Report 2007-1133) and tied to the rock or soil strength of the cliffs among other factors, but these measurements of historic coastal cliff retreat provide indications of places most susceptible to coastal landslides. Several smaller landslides occurred between the summer of 1994 and March 1995, when the large slide occurred. Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). Note the numerous landslides that have taken place in the area, including the large slide in 1995. During the winter season in California, beaches typically erode thereby allowing waves to reach further inland and to inundate the bottoms of coastal cliffs. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. landslide, also called landslip, the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). The latter landslide killed 10 people, and destroyed or damaged dozens of houses. In southern California, at least 25 cm (10 in) of rainfall during the winter is needed to nearly saturate the ground. Other classification systems incorporate additional variables, such as the rate of movement and the water, air, or ice content of the landslide material. This report describes my field observations and provides a description of the La Conchita area and its landslide history, a comparison of the 1995 and 2005 landslides, and a discussion of continuing landslide hazards in the La Conchita area. Recent Landslides in La Conchita, California Belong to a Much Larger These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Rockslides and other types of slides involve the displacement of material along one or more discrete shearing surfaces. National Oceanic and Atmospheric Administration, 1995a, Climatological data annual summaryCalifornia 1995: National Climatic Data Center, v. 99, no. When coherent material, either bedrock or soil, rests on materials that liquefy, the upper units may undergo fracturing and extension and may then subside, translate, rotate, disintegrate, or liquefy and flow. This slower rate also is suggested by eyewitnesses who stated that some residents were able to outrun the advancing flow, which would not have been possible at the higher upslope velocity. From December 27, 2004, through January 10, 2005, the nearby city of Ventura received 378 millimeters (14.9inches) of rainfall, only slightly less than its mean annual total of 390 millimeters (15.4inches). They write new content and verify and edit content received from contributors. 10.5: Landslide Types and Processes is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts. A translational slide typically takes place along structural features, such as a bedding plane or the interface between resistant bedrock and weaker overlying material. This information provides tools to help make PDF files accessible. They can easily overflow channels and severely damage houses, vehicles, or other structures. The La Conchita area has experienced, and will likely continue to experience, a rather bewildering variety of landslide hazards. What type of mass wasting took place in La Conchita? Since only about 15 percent of the 1995 deposit remobilized in 2005, could the remainder also mobilize into a rapid debris flow, or is it more likely to remobilize as a deep slump? 5 and 6). What caused the Los Angeles landslide in 1995? The timing of the two landslides with respect to the triggering storms is of primary interest. Coherent blocks of material subside into the weaker substrate, and the slow downslope movement frequently extends long distances as a result of the retrogressive extension from the zone of origin, such as an eroding riverbank or coastline. 1 What type of slide is the La Conchita slide? Even in the absence of additional significant rainfall this year (2005), the remainder of the 1995 landslide could still remobilize, most likely as a deep slumpearth flow similar to that in 1995. Debris flows are commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes and mobilizes loose soil or rock on steep slopes. In 2005, after a 15-day period of near-record rainfall, a larger area failed rapidly, remobilizing part of the 1995 slide. These hazards are mitigated mainly through precautionary means such as restricting populations from susceptible areas, limiting land use, installing early warning systems, and building structures such as piles and retaining walls. The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to improve resiliency of communities to natural disasters including earthquakes, tsunamis, wildfires, landslides, floods and coastal erosion. 12). LockA locked padlock This dynamic tectonic environment has created a spectacular landscape of rugged mountains and steep-walled valleys that compose much of the regions scenic beauty. Spreads occur as the result of liquefaction caused by water saturation or earthquake shock in such substrates as loess, a weakly cemented wind-lain silt. Historical accounts and geologic evidence show that landsliding of a variety of types and scales has been occurring at and near La Conchita for many thousands of years, and on a relatively frequent basis, up until the present. This is a typical type of landslide. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. The Southern Pacific rail line that extends along the coastal strip was inundated by landslide debris in 1889 and again in 1909, when a train also was buried (Hemphill, 2001). In southern CA, the USGS has also identified the rainfall conditions required to trigger post-wildfire debris flows. But opting out of some of these cookies may affect your browsing experience. This website uses cookies to improve your experience while you navigate through the website. The 2005 landslide occurred on part of a previous landslide that occurred in 1995. Lateral spreading in fine-grained materials on shallow slopes is usually progressive. What type of slide is the La Conchita slide? U.S. Department of the Interior | U.S. Geological Survey About USGS/ Science Topics/ Maps, Products & Publications/ Education/Publication: FAQ. Figure 3. In 2003, only three children lived in town; today, there are more than 30, said Mike Bell, chairman of the La Conchita Community Organization, formed after the 2005 landslide to address safety . 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. This is the only mitigation effort the town undertook. PDF Falling Into the Pacific: California Landslides and Land Use Controls The town is located on a narrow coastal plain, with a steep . Although there are multiple types of causes of landslides, the three that cause most of the damaging landslides around the world are these: Original content from Kimberly Schulte (Columbia Basin College) and supplemented by Lumen Learning. Figure 1: Air photo of La Conchita, CA taken in 2002. Wofford, Michael, 2005, Ventura, California weather conditions. In low-relief areas, landslides occur as cut-and-fill failures (roadway and building excavations), river bluff failures, lateral spreading landslides, collapse of mine-waste piles (especially coal), and a wide variety of slope failures associated with quarries and open-pit mines. What mitigation took place after the La Conchita slide? 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. Once the smoke clears from a wildfire, the danger is not over!! The 2005 landslide involved few new materials and seems to have been a continuation of the original 1995 landslide. Get a Britannica Premium subscription and gain access to exclusive content. The tragedy came 10 years after the hill collapsed in 1995 when nine homes were lost. What are various methods available for deploying a Windows application? The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. Experts are tested by Chegg as specialists in their subject area. The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. 3E). Landslides are described and classified in various ways depending upon the material (s) involved, mode of movement, rate of movement, and the water, air or ice content of the landslide material (see Figure 4). Evacuation order lifted at La Conchita, but officials warn area is The January 2005 landslide was a debris flow that killed 10 people, and damaged 36 residential homes. 4, p. 2224. Week 14 Lecture on Landslides - Landslides When gravity - Studocu 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. Different landslide scenarios are more or less likely to occur as a result of different specific rainfall conditions, and no part of the community can be considered safe from landslides. The failure starts suddenly in a small area and spreads rapidly. A few things, however, can be said. The neighborhood of La Conchita has suffered from large landslides in the recent past that have wiped out homes and even killed people. Sometimes more than one type of movement occurs within a single landslide, and analysis of each requires detailed interpretation of landforms and geological sections. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. Examine Figure 1 (an oblique air photo of the slide features on the coast at La Conchita), Figure 2 (a close-up view of the. Debris-flow source areas are often associated with steep gullies, and debris-flow deposits are usually indicated by the presence of debris fans at the mouths of gullies. Since that time, landslides frequently have inundated roads, railroads, cultivated land, and more recently, the La Conchita community. The 11ha (28acre) community was first established in 1924 when subdivision created about 200 lots that mostly contain singlefamily residences. La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. The most common types of landslides are described as follows and are illustrated in figure 3. A lock () or https:// means youve safely connected to the .gov website. Historical accounts dating back to 1865 have reported landslides in the area around La Conchita as being a regular occurrence (Hemphill, 2001).
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