Many readers will be familiar with the La Conchita landslide in California. 3D). Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This mode of movement would most likely be relatively slow (compared to 2005) but still could pose serious hazards to property and, perhaps, life. [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. 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 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. Figure 8 shows an aerial photograph of La Conchita taken in September 2004. landslide, also called landslip, the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). The materials may move by falling, toppling, sliding, spreading, or flowing. Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. Explain why. Figure 4. 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. While shallow, that. Schuster. Contact between the flowing mass and the underlying material can be distinct, or the contact can be one of diffuse shear. 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. 3). 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. 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. Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. Photo by Pam Irvine, CGS. Eyewitness accounts indicate, however, that similar to 2005, dust was in the air and much of the deposit included relatively dry material. They write new content and verify and edit content received from contributors. Articles from Britannica Encyclopedias for elementary and high school students. Historical accounts dating back to 1865 have reported landslides in the area around La Conchita as being a regular occurrence (Hemphill, 2001). While this preliminary report does not represent a detailed evaluation of those hazards, a few reasonable observations can be made. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. 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. Little or no newly failed material was involved in the landslide; rather, it consisted of a re-mobilization of the southeastern portion of the 1995 landslide deposit, involving about 200,000 m3 (250,000 yd3). The slippery zone is often made up of wet sediment. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. The volume of material moved by the landslide was 2.8 cubic kilometers (0.67 mi 3) . During and just after storms, existing coastal landslides may become reactivated and seemingly stable coastal cliffs may erode and fail rapidly. [2] The top of the bluff was covered by avocado and citrus orchards. On March 10, a subsequent debris flow from a canyon to the northwest (see canyon on left part of figs. In 1995, after an exceptionally wet winter, the landslide moved tens of meters (tens of yards) damaging nine houses. Figure 1: Air photo of La Conchita, CA taken in 2002. 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. 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. 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. landslide - Children's Encyclopedia (Ages 8-11), landslide - Student Encyclopedia (Ages 11 and up), California landslide halts rail service, homes evacuated. La Conchita landslide verdict - The Landslide Blog - AGU Blogosphere The landslide destroyed 13 houses and severely damaged 23 others. 1) Based on your observations of the 1995 La Conchita landslide, do you think the slide is classified as a slump, an earthflow, a debris slide, or a rockfall (see Figure 3)? 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. What was different about the 2005 slide at La Conchita compared to the 1995 slide in the same place? Rock of both formations is very weakly cemented and has been regionally associated with extensive landslide activity (Morton, 1971; Harp and Jibson, 1995, 1996; Parise and Jibson, 2000). 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. LockA locked padlock The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. On March 4, 1995 at 2:03 p.m. PST, the La Conchita landslide failed and moved tens of meters in only a few minutes. The town of La Conchita, California, experienced major landslides in 1995 and 2005. However, dry flows of granular material are also possible. The cookie is used to store the user consent for the cookies in the category "Performance". Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. The materials may move by falling, toppling, sliding, spreading, or flowing. Wofford, Michael, 2005, Ventura, California weather conditions. 10.5: Landslide Types and Processes - Geosciences LibreTexts The lower part of the slope is siltstone, sandstone, and mudstone of the Pliocene Pico Formation (O'Tousa, 1995). People were evacuated and the houses nearest the slide were completely destroyed. The material moves as a single mass along a slippery zone. When was the last landslide in La Conchita? The landslide occurred on part of a previous landslide that occurred in 1995. We also use third-party cookies that help us analyze and understand how you use this website. 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. 13, 52 p. National Oceanic and Atmospheric Administration, 1995b, Climatological dataCalifornia, JanuaryMarch 1995: National Climatic Data Center, v. 99, no. 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. 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. After covering the road with 7-8 feet of debris, the slide stabilized. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. 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. https://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html, Combination or two or more principal types of movement. "[4], Coordinates: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}342150.5N 1192645W / 34.364028N 119.44583W / 34.364028; -119.44583. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as "mudslides.". The neighborhood of La Conchita has suffered from large landslides in the recent past that have wiped out homes and even killed people. Since that time, landslides frequently have inundated roads, railroads, cultivated land, and more recently, the La Conchita community. National Oceanic and Atmospheric Administration, 1995a, Climatological data annual summaryCalifornia 1995: National Climatic Data Center, v. 99, no. 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. A classification system based on these parameters is shown in table 1. Actually there have been several sizes, types, and ages of landslides. Major types of landslide movements. The landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. What mitigation took place after the La Conchita slide? These cookies will be stored in your browser only with your consent. The landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Please refer to the appropriate style manual or other sources if you have any questions. The movement near the head of the slide is largely downward, exposing a steep head scarp, and movement within the displaced mass takes place along internal slip planes, each tending to tilt backward. What happened at La Conchita in 1995 and 2005? Types of mass movement Flows are a mixture of water, rock and sediment. Reported landslides began in 1865. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water. There were 10 confirmed fatalities, unfortunately. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others. Landslide Preparedness | U.S. Geological Survey But the mud stopped before reaching the homes, said county Geologist Jim O'Tousa. Future landslide activity could move into the same areas that recently have been damaged or could mobilize in other directions that could damage any or all of the developed area. 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. A. Weathering affects rocks from the outside in, forming an outer weathered zone or rind. They can be deadly, however, and can cost billions of dollars to clean up. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. 1). Landslides can also be activated by processes that weaken the shear strength of a slopes material. 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 1995 landslide), and Figure 3 (some common types oflandslides). Sometimes more than one type of movement occurs within a single landslide, and analysis of each requires detailed interpretation of landforms and geological sections. 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 cookie is used to store the user consent for the cookies in the category "Analytics". The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting (fig. Also, the video shows dust in the air as the landslide flowed downslope. What caused the Los Angeles landslide in 1995? On January 10, 2005, a major landslide occurred in La Conchita. "[1], La Conchita is a small community located on the southern California coastline between Ventura and Santa Barbara. 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. 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. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as mudslides.. 3E). The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. In the past two decades major landslides devastated the town of La Conchita, California. 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 entrance to La Conchita is from the northbound lanes of Hwy 101. 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. Landslide Incidence and Susceptibility of the Southwestern - USGS The latter landslide killed 10 people, and destroyed or damaged dozens of houses. January 10, 2005 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. 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). 3F). 2 and 3) damaged five additional houses in the northwestern part of La Conchita. The lush, green vegetation visible in the southeastern (lower right in photograph) part of the 1995 deposit clearly indicates that drainage on and within the 1995 landslide deposit concentrated water in the part of the mass that failed in 2005. Or will it remain metastable? [2] The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080ft) long, and 30 meters (98ft) deep. Some, but not all, of the major winter storms that have caused landslide fatalities and property damage in southern California have occurred during El Nio (1997-98 info) conditions. A complete prediction of the process would include assessments of where, when, and how big. This was not the first destructive landslide to damage this community, nor is it likely to be the last. 5 What was different about the 2005 slide at La Conchita compared to the 1995 slide in the same place? Deep-seated landslides can be triggered by deep infiltration of rainfall, which can take weeks or months to occur. 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. The 2005 landslide mobilized the south flank of a larger landslide that occurred in March 1995, and destroyed 9 homes. Bits of rock fall off the cliff face, usually due to freeze-thaw weathering. These reports and maps can be used as examples of what may occur during the upcoming 2015-2016 El Nio season if heavy precipitation occurs. La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. 1 What type of slide is the La Conchita slide? A slide happens when a section of soil or rock suddenly gives way and moves down a slope. Answer-Based on the observation from the figure. Necessary cookies are absolutely essential for the website to function properly. LaConchita Community Landslide | FEMA.gov This slower rate also is suggested by eyewitnesses who stated that some residents were able to outrun the advancing flow, which would not have been possible at the higher upslope velocity. 3C). 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. Deep-seated landslides are generally greater than 3-5 m (10-15 ft) deep. Earlier that morning, debris flows from canyons northwest of La Conchita reached Highway 101. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. The arcuate bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. The landslide, a complex slumpearth flow, destroyed or severely damaged nine houses. There were 10 confirmed fatalities. After the 1995 landslide, the town of La Conchita built a retaining wall at the foot of the hill. Future earthquakes, of course, also could trigger landsliding in the area (Harp and Jibson, 1995, 1996). The most important fluidizing agent is water, but trapped air is sometimes involved. Rockslides and other types of slides involve the displacement of material along one or more discrete shearing surfaces. If the overlying material moves as a single, little-deformed mass, it is called a block slide. The materials may move by falling, toppling, sliding, spreading, or flowing. Some move slowly, while others can move rapidly with little notice. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. 1B, p. S319S332. 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. Geol 1014 Chapter 10 Flashcards | Quizlet 3I). 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. Shallow landslides can occur at any time during the winter, but are more likely happen when the ground is nearly saturated. landslide, also called landslip, the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). 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. Prudence would certainly dictate, however, that we anticipate renewed landslide activity during or after future periods of prolonged and(or) intense rainfall. [3] Historical accounts support this. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). The difference between slides and flows is gradational, with variations in fluid content, mobility, and type of movement, and composite slide movement and flow movement are common. Landslide Types and Processes - USGS The materials may move by falling, toppling, sliding, spreading, or flowing. Below are other science projects associated with this project. 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. 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. Since only about 15 percent of the 1995 deposit remobilized in 2005, could the remainder also mobilize into a rapid debris flow, or is it more likely to remobilize as a deep slump? Our editors will review what youve submitted and determine whether to revise the article. Areas recently burned by wildfires are particularly susceptible to flash floods and debris flows during rainstorms. Module 7, Page 7 - Physical Geography ) or https:// means youve safely connected to the .gov website. 2023 California Landslide Response Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. 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 occurred on part of a previous landslide that occurred in 1995. British Geological Survey - What is a landslide? Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors. An official website of the United States government. At the time of our visit (January 14, 2005) water was still issuing from the base of the main landslide scarp and was ponding at several locations on the 2005 deposit (fig. This cookie is set by GDPR Cookie Consent plugin. The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to improve resiliency of communities to natural disasters including earthquakes, tsunamis, wildfires, landslides, floods and coastal erosion. A week later, debris flow in the same location damaged five more houses. If people continue to live in La Conchita, more lives will . A large section of the hillside slid down and buried several homes after receiving almost 30 inches of rain that winter. 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 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. 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). Of primary interest to the general public and various Governmental entities is the current state of hazard at La Conchita. 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. The slope material liquefies and runs out, forming a bowl or depression at the head. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. 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. 4, p. 2224. La Conchita landslides - Wikipedia You'll get a detailed solution from a subject matter expert that helps you learn core concepts. 9). Earthflow: Earthflows have a characteristic hourglass shape (fig. 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.