what is the landslide type of the la conchita?

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. 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. [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. 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). 4). 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. This type of movement can subsequently cause the mass to fall or slide. 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. "[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. An official website of the United States government. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. The worst of these was the tragic slide on January 10, 2005 when a huge rain-caused side killed 10 residents. A slide happens when a section of soil or rock suddenly gives way and moves down a slope. 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. Week 14 Lecture on Landslides - Landslides When gravity - Studocu The most important fluidizing agent is water, but trapped air is sometimes involved. 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. 13. Mudflow. 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. 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. 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 2005 event in La Conchita was a deep-seated landslide, which is characterized as 10-15 ft. deep. 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). Get a Britannica Premium subscription and gain access to exclusive content. 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. 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. Rotational slip. October 17, 2022. Landslide Hazards at La Conchita, California - USGS A type of landslide in which the distribution of particle velocities resembles that of a viscous fluid is called a flow. These types of landslides take weeks, even months, to happen. When was the last landslide in La Conchita? Deformation continued as the rainy season began, and by December 1994, several open cracks on the hillside were channeling surface runoff into the subsurface. A .gov website belongs to an official government organization in the United States. La Conchita lies on a narrow coastal strip about 250 m (800 ft) wide between the shoreline and a 180m (600ft) high bluff having a slope of about 35; above the top of the bluff is a gently rising terrace surface covered by avocado and citrus orchards (fig. 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. Rockfall. Since that time, other slides have occurred, covering at times cultivated land, roadways, and the community itself.[4]. The landslide killed 10 people, and destroyed or damaged dozens of houses. However, you may visit "Cookie Settings" to provide a controlled consent. The La Conchita landslides that occurred in 1995 and 2005 form only a small percent of a much larger landslide complex, according to the geologists. 1). The La Conchita area has experienced, and will likely continue to experience, a rather bewildering variety of landslide hazards. 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). Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. 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. The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. Triggered by earthquake shock or torrential rain in mountainous relief with steep gradients, a huge volume of avalanching rock or debris (of up to millions of metric tons) can reach a velocity of more than 50 metres (160 feet) per second and leave a long trail of destruction. 1012. National Oceanic and Atmospheric Administration, 1995a, Climatological data annual summaryCalifornia 1995: National Climatic Data Center, v. 99, no. 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. La Conchita Beach in Ventura, CA - California Beaches 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. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. Casualties in the United States are primarily caused by rockfalls, rock slides, and debris flows. 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. Falls are strongly influenced by gravity, mechanical weathering, and the presence of interstitial water. Chapter 12 Flashcards | Quizlet Separation occurs along discontinuities such as fractures, joints, and bedding planes, and movement occurs by free-fall, bouncing, and rolling. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as mudslides.. 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. The La Conchita landslide then occurred on March 4. The slope material liquefies and runs out, forming a bowl or depression at the head. 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. Rainfall and Landslides in Southern California Active - USGS The bluff above La Conchita has produced a variety of landslides over an extended period of time. It is often triggered by heavy rainfall. They move very quickly. This cookie is set by GDPR Cookie Consent plugin. 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. 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. 1B, p. S319S332. The materials may move by falling, toppling, sliding, spreading, or flowing. O'Tousa, James, 1995, La Conchita landslide, Ventura County, California: Association of Engineering Geologists AEG News, v. 38, no. What was different about the 2005 slide at La Conchita compared to the 1995 slide in the same place? 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). [3] Historical accounts support this. 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. Little or no newly failed material was involved in the landslide; rather, it consisted of a remobilization of the southeastern portion of the 1995 landslide deposit, involving about 200,000 m3 (250,000 yd3) (James O'Tousa, RJR Engineering, personal commun., 2005). A. Weathering affects rocks from the outside in, forming an outer weathered zone or rind. 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. Legal. Page Last Modified: Sat Jan 12 21:11 EDT 2013. and more. [2] The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080ft) long, and 30 meters (98ft) deep. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. Types of landslides Factors contribute to landslides Landslide in Utah. What mitigation took place after the La Conchita slide? Figure 2. In the 1909 slide, a train was buried. 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. 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. On January 10, 2005, a major landslide occurred in La Conchita. Similar combinations of large ancient landslides and smaller, recently active landslides also are present in areas southwest of the 1995 and 2005 landslides. The cookie is used to store the user consent for the cookies in the category "Performance". 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. Corrections? (See avalanche.) Geol 1014 Chapter 10 Flashcards | Quizlet What was the type of landslide in recent 2005 La Conchita landslide? 45. This mode of movement would most likely be relatively slow (compared to 2005) but still could pose serious hazards to property and, perhaps, life. Heavy rains of January 1995 led to a March 4, 1995, landslide in the La Conchita Community of Ventura County (County), California. 1 What type of slide is the La Conchita slide? Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. What year did the landslide happen in Ventura CA? This cookie is set by GDPR Cookie Consent plugin. In 2003, only three children lived in town; today, there are more than 30, said Mike Bell, chairman of the La Conchita Community Organization, formed after the 2005 landslide to address safety . Shallow landsides are generally less than (3-5 m) (10-15 ft) in depth and can transform into rapidly moving debris flows. 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. You also have the option to opt-out of these cookies. B. Weathering attacks corners from three sides and so these are preferentially removed. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). The ZIP Code is 93001, and the community is inside area code 805 . 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). 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). Ultimately, the County prevailed against the plaintiffs on all claims. Accessibility StatementFor more information contact us atinfo@libretexts.org. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. 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. Landslide Types and Processes - USGS Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. Landslides are a type of "mass wasting" which denotes any down slope movement of soil and rock under the direct influence of gravity. Figure 4 shows the rainfall distribution during the 19941995 rainy season. The lower part of the slope is siltstone, sandstone, and mudstone of the Pliocene Pico Formation (O'Tousa, 1995). 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. Agenda What is a landslide? Answer-Based on the observation from the figure. 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. 3H). 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. A translational slide is sometimes called a mud slide when it occurs along gently sloping, discrete shear planes in fine-grained rocks (such as fissured clays) and the displaced mass is fluidized by an increase in pore water pressure. Module 7, Page 7 - Physical Geography What kind of mitigation was done after the La Conchita landslide? 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 landslide destroyed 13 houses and severely damaged 23 others. Recent Landslides in La Conchita, California Belong to a Much Larger Omissions? . 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. 13, 60 p. National Oceanic and Atmospheric Administration, 1994b, Climatological dataCalifornia, OctoberDecember 1994: National Climatic Data Center, v. 98, nos. The town of La Conchita, California, experienced major landslides in 1995 and 2005. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. Debris flows include <50% fines. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The slope material liquefies and runs out, forming a bowl or depression at the head. 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. People were evacuated and the houses nearest the slide were completely destroyed. 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. 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. These cookies will be stored in your browser only with your consent. It does not store any personal data. LockA locked padlock As such, the maps offer a partial answer to one part of the three parts necessary to predict the soil-slip/debris-flow process. 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. This was not the first destructive landslide to damage this community, nor is it likely to be the last. 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). Early Warning System for Southern California. 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. There is a good web site where you can read and see pictures about the slide in La Conchita: By reading it I can tell you that the bluff above La Conchita has produced a variety of landslides over an extended period of time. This area has experienced two massive landslides in the past decade: March 4, 1995, and January 10, 2005. 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). Creep: Creep is the imperceptibly slow, steady, downward movement of slope-forming soil or rock. Landslides can also be activated by processes that weaken the shear strength of a slopes material. In the past two decades major landslides devastated the town of La Conchita, California. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. 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. NOAA uses this information to provide early warning for debris flows in areas affected by the fire. 4 What type of mass wasting took place in La Conchita? . From December 27, 2004 through January 10, 2005, Ventura received 378 mm (14.9 in) of rainfall, only slightly less than its mean annual total of 390 mm (15.4 in) (Wofford, 2005; National Oceanic and Atmospheric Administration, 1994a, 1995a). These tools and the accessible reader may be obtained free from Adobe at Adobe Access. Eyewitnesses also reported seeing material failing from the main scarp and lateral margins of the landslide as a result of removal of lateral support. Wofford, Michael, 2005, Ventura, California weather conditions. 3I). Different landslide scenarios are more or less likely to occur as a result of different specific rainfall conditions, and no part of the community can be considered safe from landslides. Short-term stresses imposed by earthquakes and rainstorms can likewise contribute to the activation of landslides. [2] The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. 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. The most common types of landslides are described as follows and are illustrated in figure 3. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. 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. Future earthquakes, of course, also could trigger landsliding in the area (Harp and Jibson, 1995, 1996). Landslides in the United States occur in all 50 States. Landslide Incidence and Susceptibility of the Southwestern - USGS Law enforcement officers and media representatives were in the area, which facilitated capturing the moving landslide on video. 3I). 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? 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. 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). We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. 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 slide covered 300 feet of Vista Del Rincon (VDR) Drive. The USGS has conducted hazard assessments forpost-wildfire debris flowsfor four recent fires in southern CA, as well as numerous fires across the Western U.S. including central and northern California. The project also helps to. 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. While this preliminary report does not represent a detailed evaluation of those hazards, a few reasonable observations can be made. If people continue to live in La Conchita, more lives will . Surface cracks in the upper part of the slope were noted as far back as the summer of 1994. Bits of rock fall off the cliff face, usually due to freeze-thaw weathering. 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. 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. The latter landslide killed 10 people, and destroyed or damaged dozens of houses. 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. 5 What was different about the 2005 slide at La Conchita compared to the 1995 slide in the same place? In particular, the extraordinary rainfall of January 1995 probably was the principal contributing factor to the elevated groundwater levels and, hence the landslide movement. Eyewitness accounts indicate, however, that similar to 2005, dust was in the air and much of the deposit included relatively dry material. What type of mass wasting took place in La Conchita? La Conchita landslides - Wikipedia 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. 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.

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