In the 1909 slide, a train was buried. Shear stresses can be built up within a slope by a number of processes. [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. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. B. Weathering attacks corners from three sides and so these are preferentially removed. The two formations are in fault contact along the active Red Mountain Fault, which extends across the slope face. Landslide Preparedness | U.S. Geological Survey Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. 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. 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). Subsequently, residents formed the La Conchita Community Organization (LCCO) to coordinate with government officials to determine the best way to protect the community. 3H). On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. Some move slowly, while others can move rapidly with little notice. Failure is usually triggered by rapid ground motion, such as that experienced during an earthquake, but can also be artificially induced. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. The lower part of the slope is siltstone, sandstone, and mudstone of the Pliocene Pico Formation (O'Tousa, 1995). The already loosened sediment from the 1995 landslide made the 2005 event a lot more catastrophic. During and just after storms, existing coastal landslides may become reactivated and seemingly stable coastal cliffs may erode and fail rapidly. Landslides in the United States occur in all 50 States. 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. This dynamic tectonic environment has created a spectacular landscape of rugged mountains and steep-walled valleys that compose much of the regions scenic beauty. Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. The 2005 landslide involved few new materials and seems to have been a continuation of the original 1995 landslide. Accessibility StatementFor more information contact us atinfo@libretexts.org. Shallow landslides can occur at any time during the winter, but are more likely happen when the ground is nearly saturated. A type of landslide in which the distribution of particle velocities resembles that of a viscous fluid is called a flow. Of primary interest to the general public and various Governmental entities is the current state of hazard at La Conchita. The materials may move by falling, toppling, sliding, spreading, or flowing. The town is located on a narrow coastal plain, with a steep . 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? LaConchita Community Landslide | FEMA.gov 1012. ) or https:// means youve safely connected to the .gov website. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. Casualties in the United States are primarily caused by rockfalls, rock slides, and debris flows. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. Landslide. Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting (fig. Rainfall and Landslides in Southern California Active - USGS Or will it remain metastable? Historical accounts dating back to 1865 have reported landslides in the area around La Conchita as being a regular occurrence (Hemphill, 2001). A lock () or https:// means youve safely connected to the .gov website. The slide covered 300 feet of Vista Del Rincon (VDR) Drive. In some instances, for example in many newspaper reports, mudflows and debris flows are commonly referred to as mudslides.. La Conchita Beach in Ventura, CA - California Beaches People were evacuated and the houses nearest the slide were completely destroyed. 4 What type of mass wasting took place in La Conchita? Click the image to open a larger version in a new window. Once the smoke clears from a wildfire, the danger is not over!! This is a typical type of landslide. You also have the option to opt-out of these cookies. "[1], La Conchita is a small community located on the southern California coastline between Ventura and Santa Barbara. 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. 7). This information provides tools to help make PDF files accessible. Lesson All About Landslides: Land on the Run - TeachEngineering.org An official website of the United States government. Figure 1: Air photo of La Conchita, CA taken in 2002. Legal. Week 14 Lecture on Landslides - Landslides When gravity - Studocu Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 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 entrance to La Conchita is from the northbound lanes of Hwy 101. Module 7, Page 7 - Physical Geography 3F). 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. 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. Shallow landsides are generally less than (3-5 m) (10-15 ft) in depth and can transform into rapidly moving debris flows. The bluff above La Conchita consists of poorly indurated marine sediment of the Monterey and Pico Formations. This cookie is set by GDPR Cookie Consent plugin. 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. British Geological Survey - What is a landslide? Official websites use .gov The materials may move by falling, toppling, sliding, spreading, or flowing. What was the main cause of La Conchita landslide in 2005? 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. Figure 1: Air photo of La Conchita, CA taken in 2002. Debris avalanche: This is a variety of very rapid to extremely rapid debris flow (fig. This report has not been reviewed for stratigraphic nomenclature. [1] The USGS report stated that "no part of the community can be considered safe from landslides. 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. Landslides in La Conchita - ArcGIS StoryMaps The 2005 landslide occurred at the culmination of an extremely wet 2week period (fig. What experience do you need to become a teacher? The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows. 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. Wofford, Michael, 2005, Ventura, California weather conditions. Actually there have been several sizes, types, and ages of landslides. This cookie is set by GDPR Cookie Consent plugin. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. The most important fluidizing agent is water, but trapped air is sometimes involved. 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). Other hazards, such as flash floods and debris flows, now become the focus. What was the type of landslide in recent 2005 La Conchita landslide? 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. It is often triggered by heavy rainfall. Maps displaying where shallow landslides are most likely to occur are based on observation of previous landslide activity, topographic slope, and information on the bedrock material (seePreliminary soil-slip susceptibility maps, southwestern California-Open-File Report 2003-17). 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). Colorado, and northern New Mexico) are complex in rock type and climate, and so the landslides there are also complex. These tools and the accessible reader may be obtained free from Adobe at Adobe Access. Landslide | Definition, Types, Causes, & Facts | Britannica It does not store any personal data. [2] The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080ft) long, and 30 meters (98ft) deep. 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. Figure 4 shows the rainfall distribution during the 19941995 rainy season. This cookie is set by GDPR Cookie Consent plugin. Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. 4, p. 2224. These cookies ensure basic functionalities and security features of the website, anonymously. The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. 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. January 10, 2005 By clicking Accept All, you consent to the use of ALL the cookies. Saturated soil (soil filled with water) flows down a slope. These types of landslides take weeks, even months, to happen. 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. 13, 52 p. National Oceanic and Atmospheric Administration, 1995b, Climatological dataCalifornia, JanuaryMarch 1995: National Climatic Data Center, v. 99, no. A .gov website belongs to an official government organization in the United States. The La Conchita landslide then occurred on March 4. The 2005 landslide mobilized the south flank of a larger landslide that occurred in March 1995, and destroyed 9 homes. 3I). The 2005 event in La Conchita was a deep-seated landslide, which is characterized as 10-15 ft. deep. Future earthquakes, of course, also could trigger landsliding in the area (Harp and Jibson, 1995, 1996). While shallow, that. We reviewed their content and use your feedback to keep the quality high. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. Share sensitive information only on official, secure websites. Geol 1014 Chapter 10 Flashcards | Quizlet [2] The County of Ventura immediately declared the whole community a Geological Hazard Area, imposing building restrictions on the community to restrict new construction. 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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