However, dry flows of granular material are also possible. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. This dynamic tectonic environment has created a spectacular landscape of rugged mountains and steep-walled valleys that compose much of the regions scenic beauty. [3] Historical accounts support this. Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. TYPES OF LANDSLIDES 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. How many people died in the landslide on Rincon Mountain? There were 10 confirmed fatalities, unfortunately. (See avalanche.) 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. 3). [2], Geologic evidence indicates that landslides have been occurring at and near La Conchita for many thousands of years up to the present, on a geologically frequent basis. 3F). Share sensitive information only on official, secure websites. The two major types of slides are rotational slides and translational slides. The materials may move by falling, toppling, sliding, spreading, or flowing. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. There were 10 confirmed fatalities. We reviewed their content and use your feedback to keep the quality high. The catastrophic movement of the 2005 landslide damaged or destroyed 36 houses and killed 10 people. An official website of the United States government. There is a good web site where you can read and see pictures about the slide in La Conchita: By reading it I can tell you that the bluff above La Conchita has produced a variety of landslides over an extended period of time. 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. URL: https://pubs.usgs.gov/of/2005/1067/508of05-1067.html 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. What year did the landslide happen in Ventura CA? Some move slowly, while others can move rapidly with little notice. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges (fig. Future earthquakes, of course, also could trigger landsliding in the area (Harp and Jibson, 1995, 1996). 3E). Shallow landslides can occur at any time during the winter, but are more likely happen when the ground is nearly saturated. Even modest rain storms during normal, non-El Nio years can trigger post-wildfire debris flows. This cookie is set by GDPR Cookie Consent plugin. The judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible. Figure 2. A wall built after the 1995 landslide to keep minor landslide debris off the road was tilted forward and(or) overtopped in places by debris from the 2005 landslide (fig. However, dry flows of granular material are also possible. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. 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. [2] The top of the bluff was covered by avocado and citrus orchards. Debris flows include <50% fines. 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. 3I). On March 10, a subsequent debris flow from a canyon to the northwest (see canyon on left part of figs. On January 10, 2005, a major landslide occurred in La Conchita. 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. Shear strength is dependent mainly on two factors: frictional strength, which is the resistance to movement between the slope materials interacting constituent particles, and cohesive strength, which is the bonding between the particles. Since that time, landslides frequently have inundated roads, railroads, cultivated land, and more recently, the La Conchita community (O'Tousa, 1995). The ZIP Code is 93001, and the community is inside area code 805 . How can the hazards of landslides to humans be mitigated? 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. Although landslides are primarily associated with mountainous regions, they can also occur in areas of generally low relief. During and just after storms, existing coastal landslides may become reactivated and seemingly stable coastal cliffs may erode and fail rapidly. The slide covered 300 feet of Vista Del Rincon (VDR) Drive. [5] The Ranch was found 50% negligent because it did not provide for adequate drainage of its orchards during torrential rains and settled the suit. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. 3A). 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. 7). Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. While this preliminary report does not represent a detailed evaluation of those hazards, a few reasonable observations can be made. Agenda What is a landslide? Surface cracks in the upper part of the slope were noted as far back as the summer of 1994. 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). Types of Landslides 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 2005 event in La Conchita was a deep-seated landslide, which is characterized as 10-15 ft. deep. Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. The landslide killed 10 people, and destroyed or damaged dozens of houses. Study with Quizlet and memorize flashcards containing terms like A comprehensive term for any type of downslope movement of Earth materials is, What strategy has been suggested to stabilize the La Conchita, California, landslide?, In Yosemite National Park, strong bedrock influences the formation of what types of hillslopes? 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. What happened at La Conchita in 1995 and 2005? The following summary of the 1995 La Conchita landslide is extracted from O'Tousa (1995) and Anderson (Robert Anderson, RJR Engineering, 2005, personal commun.). The storm of March 23 also may have played a role in triggering initial movement of the hillside, which already was approaching instability due to longerterm seasonal rises in groundwater levels. The landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. 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 2005 La Conchita landslide occurred on January 10. However, you may visit "Cookie Settings" to provide a controlled consent. Know the Signs of a Deep-Seated Landslide Several smaller landslides occurred between the summer of 1994 and March 1995, when the large slide occurred. 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. 3F). Most of the excess rain fell in January, which had 623 mm (24.53 in) as compared to a normal rainfall of 108 mm (4.26 in). 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. La Conchita, coastal area of southern California. Landslide. 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. 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. If people continue to live in La Conchita, more lives will . The 2005 La Conchita landslide occurred at about 12:30 p.m. on January 10. The already loosened sediment from the 1995 landslide made the 2005 event a lot more catastrophic. This apparently resulted from a highly hazardous situation involving a twophased landslide mechanism: (1) a saturated, highly fluid layer at depth on which the landslide mobilized that (2) carried a thick layer of drier, much more viscous material that effectively acted as a battering ram. Triggered by earthquake shock or torrential rain in mountainous relief with steep gradients, a huge volume of avalanching rock or debris (of up to millions of metric tons) can reach a velocity of more than 50 metres (160 feet) per second and leave a long trail of destruction. A block slide is a translational slide in which the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass (fig. An idealized slump-earth flow showing commonly used nomenclature for labeling the parts of a landslide. They can easily overflow channels and severely damage houses, vehicles, or other structures. Many readers will be familiar with the La Conchita landslide in California. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. The La Conchita area has experienced, and will likely continue to experience, a rather bewildering variety of landslide hazards. landslide - Children's Encyclopedia (Ages 8-11), landslide - Student Encyclopedia (Ages 11 and up), California landslide halts rail service, homes evacuated. This cookie is set by GDPR Cookie Consent plugin. Photo by R.L. January 10, 2005 The sliding can extend downward and outward along a broadly planar surface (a translational slide), or it can be rotational along a concave-upward set of shear surfaces (a slump). Near a Slope? Earlier that morning, debris flows from canyons northwest of La Conchita reached Highway 101. These recent landslides spilled over U.S. Highway 101 in the Ventura County community that is located 25 miles south of Santa Barbara. While shallow, that. As such, the maps offer a partial answer to one part of the three parts necessary to predict the soil-slip/debris-flow process. The information in this publication provides an introductory primer on understanding basic scientific facts about landslidesthe different types of landslides, how they are initiated, and some basic information about how they can begin to be managed as a hazard. 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). The 2005 landslide involved few new materials and seems to have been a continuation of the original 1995 landslide. Hazards from these types of landslides can occur both at the bottom of cliffs (from burial) and at the tops of cliffs (from falling over). Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). Jibson, R.W., 1989, Debris flows in southern Puerto Rico, in Schultz, A.P., and Jibson, R.W., eds., Landslide Processes in Eastern North America and Puerto Rico: Geological Society of America Special Paper 236, p.2955.
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