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 landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. If significant additional rainfall occurs, either this year or in future years, several landslide scenarios are possible: (a)deep movement of the 1995 deposit, as described above, (b) mobilization of the 1995 (and possibly the 2005) deposit into a rapid debris flow such as occurred on January 10, 2005, (c) triggering of subsidiary landslides from parts of the 1995 and 2005 deposits or scarps, (d) triggering of slumps and (or) earth flows on adjacent hillsides, and (e) triggering of rapid debris flows from various nearby slopes, particularly in ravines. This was not the first destructive landslide to damage this community, nor is it likely to be the last. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. 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. What year did the landslide happen in Ventura CA? 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. Figure 3. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. Of primary interest to the general public and various Governmental entities is the current state of hazard at La Conchita. 1995 and 2005, La Conchita, California: On March 4, 1995, a fast-moving earthflow damaged nine houses in the southern California coastal community of La Conchita. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Major landslides in La Conchita, California, La Conchita Community Organization (LCCO), Recent Landslides In La Conchita, California Belong To Much Larger Prehistoric Slide, Landslide Hazards at La Conchita, California, "Recent Landslides in La Conchita, California Belong to a Much Larger Prehistoric Slide, Report Geologists", Landslide Hazards at La Conchita, California. Such a failure scenario, involving a significant amount of dry material that fully mobilized on a saturated layer, indicates that most of the rain that fell on the surface of the 1995 deposit did not infiltrate but drained off the surface. Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. People were evacuated and the houses nearest the slide were completely destroyed. 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). The deposit covered approximately 4 hectares (9.9 acres), and the volume was estimated to be approximately 1.3 million cubic meters (1.7 million cubic yards) of sediment. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. The latter landslide killed 10 people, and destroyed or damaged dozens of houses. 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). The content on this page is copyrighted under a Creative Commons Attribution 4.0 International license. Actually there have been several sizes, types, and ages of landslides. Omissions? Click the image to open a larger version in a new window. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. This area has experienced two massive landslides in the past decade: March 4, 1995, and January 10, 2005. Coarse particles such as sand grains have high frictional strength but low cohesive strength, whereas the opposite is true for clays, which are composed of fine particles. Landslides pose a recurrent hazard to humans in most parts of the world, especially in regions that have experienced rapid population and economic growth. Below are publications associated with this project. The failure is caused by liquefaction, the process whereby saturated, loose, cohesionless sediments (usually sands and silts) are transformed from a solid into a liquefied state. { "10.01:_Why_It_Matters" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10.02:_Classifying_Mass_Movements" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10.03:_Erosion_and_Deposition_by_Gravity" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10.04:_Driving_and_Resisting_Forces" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10.05:_Landslide_Types_and_Processes" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10.06:_Putting_It_Together" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, { "00:_Front_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "01:_Science_of_Geology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "02:_Rock_Forming_Minerals" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "03:_Rocks_and_the_Rock_Cycle" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "04:_Soil" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "05:_Plate_Tectonics" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "06:_Earth\'s_Interior" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "07:_Crustal_Deformation" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "08:_Earthquakes" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "09:_Volcanic_Activity" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "10:_Mass_Movement" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "11:_Hydrology" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "12:_Geological_Implications" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "zz:_Back_Matter" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, [ "article:topic", "showtoc:no", "license:ccby", "licenseversion:40" ], https://geo.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fgeo.libretexts.org%2FBookshelves%2FGeology%2FFundamentals_of_Geology_(Schulte)%2F10%253A_Mass_Movement%2F10.05%253A_Landslide_Types_and_Processes, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), Original content from Kimberly Schulte (Columbia Basin College) and supplemented by, Creative Commons Attribution 4.0 International, Combination or two or more principal types of movement. What was different about the 2005 slide at La Conchita compared to the 1995 slide in the same place? If people continue to live in La Conchita, more lives will . There were 10 confirmed fatalities. Accessibility StatementFor more information contact us atinfo@libretexts.org. 4). Necessary cookies are absolutely essential for the website to function properly. Legal. La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. https://www.britannica.com/science/landslide, Geology.com - Landslide Hazard Information. In 199495, about twice as much rain761 mm (29.96 in)fell during that period (National Oceanic and Atmospheric Administration, 1994b, 1995b). Mudflow. 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. But opting out of some of these cookies may affect your browsing experience. [6] Morton, D.M., and Campbell, R.H., 1989, Cyclic landsliding at Wrightwood, southern California, in Sadler, P.M., and Morton, D.M., eds., Landslides in a semiarid environment with emphasis on the inland valleys of southern California: Inland Geological Society, Riverside, Calif., v. 2, p. 174182. The worst of these was the tragic slide on January 10, 2005 when a huge rain-caused side killed 10 residents. There were 10 confirmed fatalities, unfortunately. Where did the La Conchita . A) La Conchita, California The community of La Conchita in Ventura County, California experiences frequent landslides. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. Falls are abrupt movements of masses of geologic materials, such as rocks and boulders, that become detached from steep slopes or cliffs (fig. 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. A .gov website belongs to an official government organization in the United States. Contact between the flowing mass and the underlying material can be distinct, or the contact can be one of diffuse shear. As such, the maps offer a partial answer to one part of the three parts necessary to predict the soil-slip/debris-flow process. 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. Debris flows include <50% fines. Another factor that affects the shear strength of a slope-forming material is the spatial disposition of its constituent particles, referred to as the sediment fabric. This is a typical type of landslide. "[1], La Conchita is a small community located on the southern California coastline between Ventura and Santa Barbara. The landslide occurred on part of a previous landslide that occurred in 1995. Analytical cookies are used to understand how visitors interact with the website. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. ) or https:// means youve safely connected to the .gov website. Several smaller landslides occurred between the summer of 1994 and March 1995, when the large slide occurred. 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. There is also a need for a comprehensive analysis of cliff retr. In both 1889 and 1909, the Southern Pacific rail line running along the coast was inundated. 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 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. Campbell, R.H., 1975, Soil slips, debris flows, and rainstorms in the Santa Monica Mountains and vicinity, southern California: U.S. Geological Survey Professional Paper 851, 51 p. Harp, E.L., and Jibson, R.W., 1995, Inventory of landslides triggered by the 1994 Northridge, California earthquake: U.S. Geological Survey OpenFile Report 95213, 17 p. Harp, E.L., and Jibson, R.W., 1996, Landslides triggered by the 1994 Northridge, California, earthquake: Bulletin of the Seismological Society of America, v. 86, no. The cookies is used to store the user consent for the cookies in the category "Necessary". This mode of movement would most likely be relatively slow (compared to 2005) but still could pose serious hazards to property and, perhaps, life. This information provides tools to help make PDF files accessible. What happened at La Conchita in 1995 and 2005? The project also helps to. The slope material liquefies and runs out, forming a bowl or depression at the head. Wildland fires are inevitable in the western United States. What mitigation took place after the La Conchita slide? 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. The 2005 landslide mobilized the south flank of a larger landslide that occurred in March 1995, and destroyed 9 homes. Landslides in the United States occur in all 50 States. Ultimately, the County prevailed against the plaintiffs on all claims. 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. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. 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. 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. Entrapped snow and ice may also help mobilize such flows, but the unqualified term avalanche is generally used to refer only to an avalanche of snow. The town of La Conchita, California, experienced major landslides in 1995 and 2005. On March 4, 1995, the hill behind La Conchita failed, moving tens of meters in minutes, and buried nine homes with no loss of life. Near a Slope? 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. The movement of the same landslide mass in 1995 and 2005 by two very different mechanisms, and with markedly different results, is difficult to explain. Eyewitness accounts indicate, however, that similar to 2005, dust was in the air and much of the deposit included relatively dry material. 3H). 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. National Oceanic and Atmospheric Administration, 1994a, Climatological data annual summaryCalifornia 1994: National Climatic Data Center, v. 98, no. Language links are at the top of the page across from the title. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. 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. Let us know if you have suggestions to improve this article (requires login). What about the remaining 1995 deposit? In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as "mudslides.". They can be deadly, however, and can cost billions of dollars to clean up. Areas recently burned by wildfires are particularly susceptible to flash floods and debris flows during rainstorms. 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). These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. The 1995 slide was 120 m (400 ft) wide, 330 m (1100 ft) long, and covered approximately 4 ha (10 acres). 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. Secure .gov websites use HTTPS D. All of these are correct <--------. 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. This mode of movement suggests that the landslide formed as a result of rising groundwater levels in response to deep infiltration of antecedent seasonal rainfall. La Conchita, CA. B. Weathering attacks corners from three sides and so these are preferentially removed. Figure 4. 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.

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