La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. copyright Engineering Applications Figure 5. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. This dynamic tectonic environment has created a spectacular landscape of rugged mountains and steep-walled valleys that compose much of the regions scenic beauty. [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. The landslide slumped as a coherent mass of material. The KCALTV video indicates that the landslide material mobilized simultaneously and nearly instantaneously into a highly fluid, rapidly moving debris flow. Deep-seated landslides can be triggered by deep infiltration of rainfall, which can take weeks or months to occur. The slippery zone is often made up of wet sediment. The content on this page is copyrighted under a Creative Commons Attribution 4.0 International license. 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 landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. La Conchita, coastal area of southern California. In a rotational slide the axis of rotation is roughly parallel to the contours of the slope. The cookies is used to store the user consent for the cookies in the category "Necessary". 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? These schematics illustrate the major types of landslide movement. They can easily overflow channels and severely damage houses, vehicles, or other structures. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. A) La Conchita, California The community of La Conchita in Ventura County, California experiences frequent landslides. Although landslides are primarily associated with mountainous regions, they can also occur in areas of generally low relief. If people continue to live in La Conchita, more lives will . You also have the option to opt-out of these cookies. Many readers will be familiar with the La Conchita landslide in California. Note the numerous landslides that have taken place in the area, including the large slide in 1995. The bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. 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. Landslide. The 2005 landslide occurred on part of a previous landslide that occurred in 1995. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. 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). During the winter season in California, beaches typically erode thereby allowing waves to reach further inland and to inundate the bottoms of coastal cliffs. 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. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). (See avalanche.) Since that time, other slides have occurred, covering at times cultivated land, roadways, and the community itself.[4]. This indicates that the landslide material, although it flowed rapidly, was quite viscous and pushed structures in front of it rather than flowing around them or filling them with mud, as sometimes occurs with fully saturated debris and mud flows. Figure 2. The lower part of the slope is siltstone, sandstone, and mudstone of the Pliocene Pico Formation (O'Tousa, 1995). This is the only mitigation effort the town undertook. There are various direct methods of preventing landslides, such as modifying slope geometry, using chemical agents to reinforce slope material, installing structures such as piles and retaining walls, grouting rock joints and fissures, diverting debris pathways, and rerouting surface and underwater drainage. 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. There is no reason to believe this pattern of landsliding will stop. From December 27, 2004, through January 10, 2005, the nearby city of Ventura received 378 millimeters (14.9 inches) of rainfall, only slightly less than its mean annual total of 390 millimeters (15.4 inches). Sometimes more than one type of movement occurs within a single landslide, and, because the temporal and spatial relationships of these movements are often complex, their analysis often requires detailed interpretation of both landforms and geological sections, or cores. Rotational slip. What type of slide is the La Conchita slide? The rising groundwater level within the 1995 deposit would thus have resulted from deeper recharge from rainfall infiltration upslope. Bits of rock fall off the cliff face, usually due to freeze-thaw weathering. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. 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. This cookie is set by GDPR Cookie Consent plugin. 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. Keefer, D.K., Wilson, R.C., Mark, R.K., Brabb, E.E., Brown, W.M., Ellen, S.D., Harp, E.L., Wieczorek, G.F., Alger, C.S., and Zatkin, R.S., 1987, Realtime landslide warning during heavy rainfall: Science, v. 238, p. 921925. The two major types of slides are rotational slides and translational slides. They write new content and verify and edit content received from contributors. 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. 3J). A few things, however, can be said. Parise, Mario, and Jibson, R.W., 2000, A seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the January 17, 1994 Northridge, California, earthquake: Engineering Geology, v. 58, p. 251270. Legal. Landslide | Definition, Types, Causes, & Facts | Britannica OF 05-1067, "La Conchita Ranch is sold for $2.5 million", "La Conchita Lawsuit Settled, But It's Not Over", "Settlement reached in La Conchita lawsuit", Assessing Landslide Hazard Over a 130-Year Period for La Conchita, California, https://en.wikipedia.org/w/index.php?title=La_Conchita_landslides&oldid=1134048066, 2005 natural disasters in the United States, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, The 2005 La Conchita landslide is the setting of, This page was last edited on 16 January 2023, at 19:34. National Oceanic and Atmospheric Administration, 1994a, Climatological data annual summaryCalifornia 1994: National Climatic Data Center, v. 98, no. A slide happens when a section of soil or rock suddenly gives way and moves down a slope. 4, p. 2224. 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). The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows. Share sensitive information only on official, secure websites. Falls are abrupt movements of masses of geologic materials, such as rocks and boulders, that become detached from steep slopes or cliffs (fig. Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. The La Conchita landslide in Ventura County is an example of a deep-seated landslide that has experienced both styles of movement (seeLandslide Hazards at La Conchita, California- Open-File Report 2015-1067). 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 most common types of landslides are described as follows and are illustrated in figure 3. In 1995, after a very wet January, the landslide did not move until more than a month later, during which time very little rain fell (fig. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water. [2] The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. If the overlying material moves as a single, little-deformed mass, it is called a block slide. The arcuate bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. It is often triggered by heavy rainfall. This also is consistent with the shallower, fluid mode of failure: shallow, rapid debris flows most commonly occur during periods of prolonged, intense rainfall with little or no lag time (Campbell, 1975; Keefer and others, 1987; Jibson, 1989). Geol 1014 Chapter 10 Flashcards | Quizlet In 1995, after an exceptionally wet winter, the landslide moved tens of meters (tens of yards) damaging nine houses. 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. Morton, D.M., 1971, Seismically triggered landslides above San Fernando Valley: California Geology, v. 24, no. 3C). Our editors will review what youve submitted and determine whether to revise the article. Colorado, and northern New Mexico) are complex in rock type and climate, and so the landslides there are also complex. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. C. Preferential weathering along fractures can cause blocks to become rounded. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. This was not the first destructive landslide to damage this community, nor is it likely to be the last. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). January 10, 2005 The La Conchita landslide then occurred on March 4. 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. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. Omissions? 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. Debris flows include <50% fines. Often referred to as "mudflows," debris flows are a type of landslide made up of a rapidly moving mixture of dirt, rocks, trees, and water (and sometimes ash) that start on a hillside and travel downvalley. The landslide recurred on part of a previous landslide in 1995.La Conchita, California. Overall, the models predict a re, Coastal cliff retreat, the landward migration of the cliff face, is a chronic problem along many rocky coastlines in the United States. 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 La Conchita area has experienced, and will likely continue to experience, a rather bewildering variety of landslide hazards. 1). 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. The town is located on a narrow coastal plain, with a steep . Figure 2. This area has experienced two massive landslides in the past decade: March 4, 1995, and January 10, 2005. Combination of two or more of the above types is known as a complex landslide. There were 10 confirmed fatalities. Even modest rain storms during normal, non-El Nio years can trigger post-wildfire debris flows. Contact between the flowing mass and the underlying material can be distinct, or the contact can be one of diffuse shear. British Geological Survey - What is a landslide? The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". Lateral spreads are distinctive because they usually occur on very gentle slopes or flat terrain (fig. Reading: Landslide Types and Processes | Geology | | Course Hero 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. [1] The USGS report stated that "no part of the community can be considered safe from landslides. Mudflow: A mudflow is an earthflow consisting of material that is wet enough to flow rapidly and that contains at least 50 percent sand-, silt-, and clay-sized particles. In southern California, at least 25 cm (10 in) of rainfall during the winter is needed to nearly saturate the ground. Debris flows include <50% fines. 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. Wofford, Michael, 2005, Ventura, California weather conditions. 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. 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 volume of material moved by the landslide was 2.8 cubic kilometers (0.67 mi 3) . Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Ultimately, the County prevailed against the plaintiffs on all claims. Coastal cliff failuresmay also occur simply as a result of heightened precipitation as well wave action makes cliffs inherently unstable, and rainfall may be the ultimate trigger for failure, even during times with little to no wave action. The 2005 landslide occurred on part of a previous landslide that occurred in 1995. These cookies ensure basic functionalities and security features of the website, anonymously. The materials may move by falling, toppling, sliding, spreading, or flowing. 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. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. 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. 8 What year did the landslide happen in Ventura CA? How can the hazards of landslides to humans be mitigated? 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. PDF Falling Into the Pacific: California Landslides and Land Use Controls Some materials with a loose, open sediment fabric will weaken if they are mechanically disturbed or flooded with water. There were 10 confirmed fatalities, unfortunately. The 2005 landslide occurred at the culmination of an extremely wet 2week period (fig. Earlier that morning, debris flows from canyons northwest of La Conchita reached Highway 101. 3E). 3F). Often the initial failure is a slump, but in some materials movement occurs for no apparent reason. Official websites use .gov Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. Photo taken March 8, 1995. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way.
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