what is the landslide type of the la conchita?

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. Landslides in the United States occur in all 50 States. Future landslide activity could occur in the areas of the 1995 and 2005 landslides or in other areas and could damage or destroy any or all of the developed area. Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide (fig. Previous work at the USGS has identified both the areas of southwestern California most susceptible to shallow landslides and the rainfall conditions required to trigger slope failures. Subsequently, residents formed the La Conchita Community Organization (LCCO) to coordinate with government officials to determine the best way to protect the community. 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. 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). Agenda What is a landslide? These schematics illustrate the major types of landslide movement. National Oceanic and Atmospheric Administration, 1995a, Climatological data annual summaryCalifornia 1995: National Climatic Data Center, v. 99, no. It does not store any personal data. . Maps displaying where shallow landslides are most likely to occur are based on observation of previous landslide activity, topographic slope, and information on the bedrock material (seePreliminary soil-slip susceptibility maps, southwestern California-Open-File Report 2003-17). [2] The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. They can be deadly, however, and can cost billions of dollars to clean up. 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. In both 1889 and 1909, the Southern Pacific rail line running along the coast was inundated. Colorado, and northern New Mexico) are complex in rock type and climate, and so the landslides there are also complex. Earth materials can become detached from a steep slope without significant shearing, fall freely under gravity, and land on a surface from which they bounce and fall farther. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. Some materials with a loose, open sediment fabric will weaken if they are mechanically disturbed or flooded with water. This was not the first destructive landslide to damage this community, nor is it likely to be the last. In southern California, at least 25 cm (10 in) of rainfall during the winter is needed to nearly saturate the ground. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. February 1995 produced only about onethird of the normal rainfall, but a modest storm on March 23 produced 21 mm (0.81 in) of rain. What caused the Los Angeles landslide in 1995? Falls of large volume can trap enough air to facilitate the very rapid flow of rock or debris, forming rock avalanches and debris avalanches, respectively. The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. Figure 1. Figure 2. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. There are four different types of mass movement: The landslide, which occurred about 130 km northwest of Los Angeles, California, mobilized over 40,000 cubic yards of wet debris into a large scale debris flow (commonly referred to in the media as a mudslide) that flowed into a residential community at the foot of the slope, killing 10 persons and damaging or . D. All of these are correct <--------. Below is a summary of reports and maps to identify hazards associated with different types of landslides in this part of the state. The project engages emergency planners, businesses, universities, government agencies, and others in preparing for major natural disasters. The entrance to La Conchita is from the northbound lanes of Hwy 101. Debris flows include <50% fines. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges (fig. Since that time, landslides frequently have inundated roads, railroads, cultivated land, and more recently, the La Conchita community. 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. These types of landslides take weeks, even months, to happen. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. The 2005 La Conchita landslide occurred at about 12:30 p.m. on January 10. Like the northern part of the state, southern California is well known to be susceptible to landslides (seePreliminary soil-slip susceptibility maps, southwestern California- Open-File Report 2003-17). Unfortunately, this extraordinary landscape also presents serious geolo, This group of maps shows relative susceptibility of hill slopes to the initiation sites of rainfall-triggered soil slip-debris flows in southwestern California. How and why the same material failed twice in 10 years by fundamentally different mechanisms certainly will be the object of future research, and it is much too complex to analyze in detail at this time. Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material. The 2005 landslide occurred at the culmination of an extremely wet 2week period (fig. Days later, on March 10, a subsequent debris flow from a canyon to the northwest damaged five additional houses in the northwestern part of La Conchita. Please refer to the appropriate style manual or other sources if you have any questions. [2] The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080ft) long, and 30 meters (98ft) deep. Since that time, other slides have occurred, covering at times cultivated land, roadways, and the community itself.[4]. Figure 1: Air photo of La Conchita, CA taken in 2002. Hemphill, J.J., 2001, Assessing landslide hazard over a 130year period for La Conchita, California, in Association of Pacific Coast Geographers Annual Meeting, Santa Barbara, Calif., September 1215 2001. 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. [1] The USGS report stated that "no part of the community can be considered safe from landslides. 1). 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. An unstable hillside The rain caused debris from an older landslide to fall about 150 feet. 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). By clicking Accept All, you consent to the use of ALL the cookies. Please select which sections you would like to print: Geographic Database Manager and Geographic Information Systems Analyst, Department of Geography, Royal Holloway, University of London, Egham, Surrey, U.K. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. After the 1995 landslide, the town of La Conchita built a retaining wall at the foot of the hill. The slippery zone is often made up of wet sediment. The ZIP Code is 93001, and the community is inside area code 805 . Debris flows also commonly mobilize from other types of landslides that occur on steep slopes, are nearly saturated, and consist of a large proportion of silt- and sand-sized material. The bluff above La Conchita consists of poorly indurated marine sediment of the Monterey and Pico Formations. 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. Wildfire can significantly alter the hydrologic response of a watershed to the extent that even modest rainstorms can produce dangerous flash floods and debris flows. The 1995 landslide apparently occurred as a result of an extraordinarily wet year. Many readers will be familiar with the La Conchita landslide in California. The January 2005 landslide was a debris flow that killed 10 people, and damaged 36 residential homes. 2 When was the last landslide in La Conchita? Although it is not uncommon for subsidiary debris flows to occur from the toes or scarps of existing landslides (Morton and Campbell, 1989), that is not what happened in 2005. O'Tousa, James, 1995, La Conchita landslide, Ventura County, California: Association of Engineering Geologists AEG News, v. 38, no. The most important fluidizing agent is water, but trapped air is sometimes involved. La Conchita ( / l kntit / ( listen); Spanish for "The Little Shell") is a small unincorporated community in western Ventura County, California, on U.S. Route 101 just southeast of the Santa Barbara county line. 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. The content on this page is copyrighted under a Creative Commons Attribution 4.0 International license. landslide - Children's Encyclopedia (Ages 8-11), landslide - Student Encyclopedia (Ages 11 and up), California landslide halts rail service, homes evacuated. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). Figure 3 shows LIDAR and falsecolor infrared images of the bluff above La Conchita and the surrounding area, and several sizes, types, and ages of landslides are visible. 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. However, you may visit "Cookie Settings" to provide a controlled consent. 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). The material moves as a single mass along a slippery zone. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. These maps em, 12201 Sunrise Valley Drive Reston, VA 20192, Preliminary soil-slip susceptibility maps, southwestern California, Southern California LandslidesAn Overview, Map of Historic and Prehistoric Landslides in Pacific Palisades, Landslides in Santa Monica Mountains and Vicinity, Preliminary Soil-Slip Susceptibility Maps for Southwestern California, Map of Fatal or More than $1 Million Damage in California from 1906 to 1984, Landslide Hazards at La Conchita, California, Southern CaliforniaWildfires and Debris Flows, National Assessment of Shoreline Change Part 4: Historical Coastal Cliff Retreat along the California Coast, Emergency assessment of post-fire debris-flow hazards for the 2013 Springs Fire, Ventura County, California, Coastal and Marine Hazards and Resources Program, Pacific Coastal and Marine Science Center, National assessment of shoreline change, part 4: Historical coastal cliff retreat along the California coast, Southern California Wildfires and debris flows, Southern California landslides-an overview, Landslide hazards at La Conchita, California, Groundwater and Streamflow Information Program, Geology, Minerals, Energy, and Geophysics Science Center, Soil slips, debris flows, and rainstorms in the Santa Monica Mountains and vicinity, southern California. 3 What was the main cause of La Conchita landslide in 2005? While every effort has been made to follow citation style rules, there may be some discrepancies. 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). As coastal populations continue to grow and community infrastructures are threatened by erosion, there is increased demand for accurate information regarding trends and rates of coastal cliff retreat. A translational slide is sometimes called a mud slide when it occurs along gently sloping, discrete shear planes in fine-grained rocks (such as fissured clays) and the displaced mass is fluidized by an increase in pore water pressure. Although many types of mass movements are included in the general term landslide, the more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. Once the smoke clears from a wildfire, the danger is not over!! They move very quickly. The slide covered 300 feet of Vista Del Rincon (VDR) Drive. Below are other science projects associated with this project. The volume of the landslide was estimated to be approximately 200,000 cubic meters with a surface 350 meters (1,150 feet) long and 80100 meters (260330ft) wide. YUARA SLUMP EARTHFLOW DEBRIS SLIDE ROCKFALL SCARP ORIGINAL LAND SURFACE -SLIP PLANE. What year did the landslide happen in Ventura CA? 4 What type of mass wasting took place in La Conchita? The latter landslide killed 10 people, and destroyed or damaged dozens of houses. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. 4). Short-term stresses imposed by earthquakes and rainstorms can likewise contribute to the activation of landslides. The plaintiffs also sued the County of Ventura for damages, claiming that a wall that the County built at the base of the landslide caused or contributed to the landslide. The tragedy came 10 years after the hill collapsed in 1995 when nine homes were lost. 45. La Conchita (1995) La Conchita landslide, Ventura County. Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). 3F). On January 10, 2005, a landslide struck the community of La Conchita in Ventura County, California, destroying or seriously damaging 36 houses and killing 10 people. Debris flow: A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as a slurry that flows downslope (fig. But opting out of some of these cookies may affect your browsing experience. An increase in water content, resulting from either natural causes or human activity, typically weakens sandy materials through the reduction of interparticle friction and weakens clays through the dissolution of interparticle cements, the hydration of clay minerals, and the elimination of interparticle (capillary) tension. The town of La Conchita, California, experienced major landslides in 1995 and 2005. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. 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). In addition, an accessible version of Acrobat Reader 6.0, which contains support for screen readers, is available. The primary regions of landslide occurrence and potential are the coastal and mountainous areas of California, Oregon, and Washington, the States comprising the intermountain west, and the mountainous and hilly regions of the Eastern United States. Back scarp of ancient landslide Scarp of small recent landslide 1995 landslide Figure 2: Close-up image of the 1995 landslide event at La Conchita, CA. The 1995 landslide had a horizontal length, vertical length, and depth of 120 x 330 x 30 m and covered approximately 10 acres with a volume of 1.3x106 m3. Casualties in the United States are primarily caused by rockfalls, rock slides, and debris flows. Articles from Britannica Encyclopedias for elementary and high school students. Based on the opinion that surface water infiltration from irrigation contributed to the landslide, seventy-one homeowners sued La Conchita Ranch Co. in Bateman v. La Conchita Ranch Co. National Oceanic and Atmospheric Administration, 1994a, Climatological data annual summaryCalifornia 1994: National Climatic Data Center, v. 98, no. On January 10, 2005, a major landslide occurred in La Conchita. A few things, however, can be said. Legal. The 2005 La Conchita landslide occurred on January 10. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screenreading programs that synthesize text as audible speech. Necessary cookies are absolutely essential for the website to function properly. In 1995, after an exceptionally wet winter, the landslide moved tens of meters (tens of yards) damaging nine houses. We also use third-party cookies that help us analyze and understand how you use this website. This type of movement can subsequently cause the mass to fall or slide. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. There were 10 confirmed fatalities. This cookie is set by GDPR Cookie Consent plugin. The volume of the landslide was estimated to be approximately 200,000 cubic meters with a surface 350 meters (1,150 feet) long and 80100 meters (260330 ft) wide. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 . URL: https://pubs.usgs.gov/of/2005/1067/508of05-1067.html The term "landslide" describes a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill, or a combination of these. The 1995 slide was 120 m (400 ft) wide, 330 m (1100 ft) long, and covered approximately 4 ha (10 acres). Over time, upslope ponding of water by such back-tilted blocks can enlarge the area of instability, so that a stable condition is reached only when the slope is reduced to a very low gradient. A spread is the complex lateral movement of relatively coherent earth materials resting on a weaker substrate that is subject to liquefaction or plastic flow. Types of mass movement Flows are a mixture of water, rock and sediment. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. Officials in Southern California say a coastal landslide closed a historic cultural center, shut down rail service in the area and forced the evacuation of nearby residences. On January 14, 2005, at the invitation of the California Geological Survey, I visited La Conchita with James O'Tousa, contract geologist for Ventura County, and Pamela Irvine, Janis Hernandez, and Terry Jones, all from the California Geological Survey. 3F). This is a typical type of landslide. La Conchita is a small Pacific coastal community that lies between Santa Barbara, CA and Ventura, CA. 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. This was not the first destructive landslide to damage this community, nor is it likely to be the last. 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. What type of mass wasting took place in La Conchita? Little or no newly failed material was involved in the landslide; rather, it consisted of a remobilization of the southeastern portion of the 1995 landslide deposit, involving about 200,000 m3 (250,000 yd3) (James O'Tousa, RJR Engineering, personal commun., 2005). The deep mode of failure in 1995 is consistent with this delay: deeper landslides commonly are triggered by deep infiltration of rainfall, which can take weeks or months to occur (for example, Morton and Campbell, 1989). c) Slides: A slide is the downslope movement of a soil or rock mass occurring dominantly on the surface of rupture or relatively thin zones of intense shear strain.
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