Expansion of man-made developments into fire-prone wildlands has created situations where wildfires can destroy lives and property, as can the flooding and debris flows that are common in the aftermath of the fires. There are five basic categories of flows that differ from one another in fundamental ways. 3B). A landslide can be defined as follows: [T]he movement of a mass of rock, debris, or earth down a slope. 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). Similar combinations of large ancient landslides and smaller, recently active landslides also are present in areas southwest of the 1995 and 2005 landslides. Accessibility StatementFor more information contact us atinfo@libretexts.org. 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. [1] The USGS report stated that "no part of the community can be considered safe from landslides. Earthflow: Earthflows have a characteristic "hourglass" shape (fig. 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. They can be deadly, however, and can cost billions of dollars to clean up. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. The 2005 landslide occurred on part of a previous landslide that occurred in 1995. The 11ha (28acre) community was first established in 1924 when subdivision created about 200 lots that mostly contain singlefamily residences. A few things, however, can be said. 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. 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. What mitigation took place after the La Conchita slide? O'Tousa, James, 1995, La Conchita landslide, Ventura County, California: Association of Engineering Geologists AEG News, v. 38, no. landslide - Children's Encyclopedia (Ages 8-11), landslide - Student Encyclopedia (Ages 11 and up), California landslide halts rail service, homes evacuated. 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. As such, the maps offer a partial answer to one part of the three parts necessary to predict the soil-slip/debris-flow process. 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. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. A classification system based on these parameters is shown in table 1. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. An official website of the United States government. The most important fluidizing agent is water, but trapped air is sometimes involved. In 1995, after an exceptionally wet winter, the landslide moved tens of meters (tens of yards) damaging nine houses. [3] Historical accounts support this. Contact between the flowing mass and the underlying material can be distinct, or the contact can be one of diffuse shear. What happened in the La Conchita landslide 2005? 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. After covering the road with 7-8 feet of debris, the slide stabilized. U.S. Department of the Interior | U.S. Geological Survey Below are other science projects associated with this project. Figure 3: Some major types of mass movements. Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. The content on this page is copyrighted under a Creative Commons Attribution 4.0 International license. Although rainfall intensities were not extreme, moderate to highintensity rainfall persisted for more than 2 weeks, and the landslide occurred at the culmination of this 15day highrainfall period (fig. copyright Engineering Applications Figure 5. Landslides in the United States occur in all 50 States. This is a typical type of landslide. 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. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water. Although landslides are primarily associated with mountainous regions, they can also occur in areas of generally low relief. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. Morton, D.M., 1971, Seismically triggered landslides above San Fernando Valley: California Geology, v. 24, no. This cookie is set by GDPR Cookie Consent plugin. La Conchita is a small Pacific coastal community that lies between Santa Barbara, CA and Ventura, CA. Saturated soil (soil filled with water) flows down a slope. 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. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. 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. What are various methods available for deploying a Windows application? On January 10, 2005, a major landslide occurred in La Conchita. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. 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. Analytical cookies are used to understand how visitors interact with the website. This is a typical type of landslide. 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. 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. Where did the La Conchita . 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 . 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. 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. 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. October 17, 2022. 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. This website uses cookies to improve your experience while you navigate through the website. 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. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others (figs. The rising groundwater level within the 1995 deposit would thus have resulted from deeper recharge from rainfall infiltration upslope. It does not store any personal data. Below are publications associated with this project. Ultimately, the County prevailed against the plaintiffs on all claims. Alaska and Hawaii also experience all types of landslides. 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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. Types of landslides Factors contribute to landslides Landslide in Utah. Wave energy is also typically higher during the winter, and particularly during El Nio events, thereby exacerbating the potential for coastal erosion. 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. 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. 2 When was the last landslide in La Conchita? There is also a need for a comprehensive analysis of cliff retr. [2] The top of the bluff was covered by avocado and citrus orchards. These include oversteepening of the base of the slope, such as by natural erosion or excavation, and loading of the slope, such as by an inflow of water, a rise in the groundwater table, or the accumulation of debris on the slopes surface. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Toppling failures are distinguished by the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks (fig. This cookie is set by GDPR Cookie Consent plugin. A complete prediction of the process would include assessments of where, when, and how big. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. The material moves as a single mass along a slippery zone. The main mass that failed is on the southeastern margin of the larger ancient landslide that encompasses the entire front of the bluff (see fig. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. URL: https://pubs.usgs.gov/of/2005/1067/508of05-1067.html 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. In a rotational slide the axis of rotation is roughly parallel to the contours of the slope. 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. Eyewitness accounts indicate, however, that similar to 2005, dust was in the air and much of the deposit included relatively dry material. A large section of the hillside slid down and buried several homes after receiving almost 30 inches of rain that winter. However, you may visit "Cookie Settings" to provide a controlled consent. Below is a summary of reports and maps to identify hazards associated with different types of landslides in this part of the state. 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. La Conchita landslides - Wikipedia [6] NOAA uses this information to provide early warning for debris flows in areas affected by the fire. Prudence would certainly dictate, however, that we anticipate renewed landslide activity during or after future periods of prolonged and(or) intense rainfall. Lesson All About Landslides: Land on the Run - TeachEngineering.org In both 1889 and 1909, the Southern Pacific rail line running along the coast was inundated. The materials may move by falling, toppling, sliding, spreading, or flowing. The 2005 landslide occurred at the end of a 15day period that produced record and nearrecord amounts of rainfall in many areas of southern California. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. [2] It lies on a narrow strip of land about 250 meters (820 feet) wide between the shoreline and abutting a 180-meter (590ft) high bluff. Landslide Hazards at La Conchita, California - USGS Click the image to open a larger version in a new window. Articles from Britannica Encyclopedias for elementary and high school students. 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.