what is the landslide type of the la conchita?

The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. Since that time, landslides frequently have inundated roads, railroads, cultivated land, and more recently, the La Conchita community (O'Tousa, 1995). 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)? The dominant mode of movement is lateral extension accompanied by shear or tensile fractures. Short-term stresses, such as those imposed by earthquakes and rainstorms, can likewise contribute to the activation of landslides. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. [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. After this point, a rain burst of 5-6 mm (0.2 to 0.25 in) in one hour has been observed to trigger abundant shallow landslides (seeLandslides in Santa Monica Mountains and Vicinity- Prof Paper 851). Many areas of coastal California are subject to cliff erosion and coastal landslides (see new research onEl Nio coastal hazardsin California). Language links are at the top of the page across from the title. 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. 1) (34.4 degrees north, 119.5 degrees west). Combination of two or more of the above types is known as a complex landslide. Historical accounts dating back to 1865 have reported landslides in the area around La Conchita as being a regular occurrence (Hemphill, 2001). Necessary cookies are absolutely essential for the website to function properly. 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. This is the only mitigation effort the town undertook. Recent Landslides in La Conchita, California Belong to a Much Larger 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. What type of slide is the La Conchita slide? Landslide Incidence and Susceptibility of the Southwestern - USGS 3C). 3F). 45. 10 and 11). The latter landslide killed 10 people, and destroyed or damaged dozens of houses. Course Hero is not sponsored or endorsed by any college or university. 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. 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. 3). 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. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. Earthflow: Earthflows have a characteristic "hourglass" shape (fig. 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. 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. Lateral spreading in fine-grained materials on shallow slopes is usually progressive. 7 What happened in the La Conchita landslide 2005? La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. Debris flows include <50% fines. Deep-seated landslides can be triggered by deep infiltration of rainfall, which can take weeks or months to occur. 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Please refer to the appropriate style manual or other sources if you have any questions. La Conchita Beach in Ventura, CA - California Beaches La Conchita (1995) La Conchita landslide, Ventura County. These recent landslides spilled over U.S. Highway 101 in the Ventura County community that is located 25 miles south of Santa Barbara. 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. In this report, empirical models are used to predict the probability and magnitude of debris-flow occurrence in response to a 10-year rainstorm for the 2013 Springs fire in Ventura County, California. Even modest rain storms during normal, non-El Nio years can trigger post-wildfire debris flows. Deep-seated landslides are generally greater than 3-5 m (10-15 ft) deep. It is likely that the new rainfall did not enter the deposits left behind after the 1995 landslide, but slid off it taking surface debris and few new materials with it. URL: https://pubs.usgs.gov/of/2005/1067/508of05-1067.html Since that time, other slides have occurred, covering at times cultivated land, roadways, and the community itself.[4]. 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. 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. 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. 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. Landslide | Definition, Types, Causes, & Facts | Britannica Unfortunately, we currently lack the understanding to accurately forecast what might happen in each possible rainfall scenario. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. Figure 1: Air photo of La Conchita, CA taken in 2002. Figure 3: Some major types of mass movements. 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. On March 10, a subsequent debris flow from a canyon to the northwest (see canyon on left part of figs. 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. The 11ha (28acre) community was first established in 1924 when subdivision created about 200 lots that mostly contain singlefamily residences. A .gov website belongs to an official government organization in the United States. 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). 2 When was the last landslide in La Conchita? The arcuate bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. A lock ( The largest single landslide in modern U. history whose origins were completely natural was the Gros Ventre slide in Wyoming . At Ventura (20 km [12 mi] southeast of La Conchita) seasonal antecedent rainfall from October 1, 2004 through January 10, 2005 totaled 493 mm (19.4 in) as compared to the mean value of 122 mm (4.8 in). La Conchita is a small Pacific coastal community that lies between Santa Barbara, CA and Ventura, CA. 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. 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. The materials may move by falling, toppling, sliding, spreading, or flowing. 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). Landslides in the United States occur in all 50 States. If the overlying material moves as a single, little-deformed mass, it is called a block slide. 3H). 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. However, you may visit "Cookie Settings" to provide a controlled consent. 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 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 (260330ft) wide. Deformation continued as the rainy season began, and by December 1994, several open cracks on the hillside were channeling surface runoff into the subsurface. Figure 1: Air photo of La Conchita, CA taken in 2002. Wildland fires are inevitable in the western United States. Updates? 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). 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 upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. What was the main cause of La Conchita landslide in 2005? The latter landslide killed 10 people, and destroyed or damaged dozens of houses. 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. La Conchita, coastal area of southern California. 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. The historic slides are part of the larger Rincon Mountain slide, which "started many thousands of years ago and will continue generating slides in the future. Photo by R.L. The landslide destroyed 13 houses and severely damaged 23 others. NOAA uses this information to provide early warning for debris flows in areas affected by the fire. Some materials with a loose, open sediment fabric will weaken if they are mechanically disturbed or flooded with water. What happened at La Conchita in 1995 and 2005? The bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. Saturated soil (soil filled with water) flows down a slope. Landslide Types and Processes - USGS Analytical cookies are used to understand how visitors interact with the website. This was not the first destructive landslide to damage this community, nor is it likely to be the last. 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. 8.4: Examples of Landslides - Geosciences LibreTexts During and just after storms, existing coastal landslides may become reactivated and seemingly stable coastal cliffs may erode and fail rapidly. Questions or Assistance: USGS Web Contact 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). After covering the road with 7-8 feet of debris, the slide stabilized. What was the type of landslide in recent 2005 La Conchita landslide? They write new content and verify and edit content received from contributors. 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 following summary of the 1995 La Conchita landslide is extracted from O'Tousa (1995) and Anderson (Robert Anderson, RJR Engineering, 2005, personal commun.). 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. Let us know if you have suggestions to improve this article (requires login). In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). Know the Signs of a Deep-Seated Landslide A slide happens when a section of soil or rock suddenly gives way and moves down a slope. Rotation of a mass of rock, debris, or earth outward from a steep slope face is called toppling. These tools and the accessible reader may be obtained free from Adobe at Adobe Access. In addition, an accessible version of Acrobat Reader 6.0, which contains support for screen readers, is available. The La Conchita landslide then occurred on March 4. The entrance to La Conchita is from the northbound lanes of Hwy 101. Schuster, U.S. Geological Survey. 2023 California Landslide Response Eyewitnesses also reported seeing material failing from the main scarp and lateral margins of the landslide as a result of removal of lateral support. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). [2] The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. 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. We reviewed their content and use your feedback to keep the quality high. 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. They move very quickly. 7). 1012. 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. Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. 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. Coherent blocks of material subside into the weaker substrate, and the slow downslope movement frequently extends long distances as a result of the retrogressive extension from the zone of origin, such as an eroding riverbank or coastline. 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. An official website of the United States government. What experience do you need to become a teacher? What about the remaining 1995 deposit? 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. They can be deadly, however, and can cost billions of dollars to clean up. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. 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. 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. 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. 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. 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. While this preliminary report does not represent a detailed evaluation of those hazards, a few reasonable observations can be made. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. 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. This was not the first destructive landslide to damage this community, nor is it likely to be the last. This cookie is set by GDPR Cookie Consent plugin. Below are other science projects associated with this project. 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 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). 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. A lock () or https:// means youve safely connected to the .gov website. I estimate from viewing the video that high on the slope, the landslide was moving perhaps 10 m/s (30 ft/s). 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. 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. Other hazards, such as flash floods and debris flows, now become the focus. The 2005 landslide mobilized the south flank of a larger landslide that occurred in March 1995, and destroyed 9 homes. 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. 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. Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. In the past two decades major landslides devastated the town of La Conchita, California. Landslides are a type of "mass wasting" which denotes any down slope movement of soil and rock under the direct influence of gravity. 3D). Official websites use .gov Explain why. On January 10, 2005, a major landslide occurred in La Conchita. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. Incipient movement of the upper part of the slide was reported as early as the summer of 1994, when surface cracks were observed in the upper part of the slope (O'Tousa, 1995). 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. 1 it is A) La Conchita, California The community of La Conchita in Ventura County, California experiences frequent landslides. In the 1909 slide, a train was buried. 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. Or will it remain metastable? Geol 1014 Chapter 10 Flashcards | Quizlet The two formations are in fault contact along the active Red Mountain Fault, which extends across the slope face. Several smaller landslides occurred between the summer of 1994 and March 1995, when the large slide occurred. C. Preferential weathering along fractures can cause blocks to become rounded. 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.