what is the landslide type of the la conchita?

The latter landslide killed 10 people, and destroyed or damaged dozens of houses. Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually. 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. These types of landslides take weeks, even months, to happen. In 1995, the community experienced a major slide, which damaged and destroyed a significant portion of the community. 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. Types of mass movement Flows are a mixture of water, rock and sediment. 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. 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. The landslide killed 10 people, and destroyed or damaged dozens of houses. Thus, it appears that the landslide mobilized on a saturated layer deep in the 1995 deposit but that much of the material above this saturated zone was dry or nearly so. These recent landslides spilled over U.S. Highway 101 in the Ventura County community that is located 25 miles south of Santa Barbara. 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). Near a Slope? 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). Subsequently, residents formed the La Conchita Community Organization (LCCO) to coordinate with government officials to determine the best way to protect the community. 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). The various types of landslides can be differentiated by the kinds of material involved and the mode of movement. National Oceanic and Atmospheric Administration, 1994a, Climatological data annual summaryCalifornia 1994: National Climatic Data Center, v. 98, no. The judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible. The landslide occurred after a 15-day period of unprecedented records of rainfall in Southern California. The USGS has a long history of research to identify landslide hazards in southern California (seeSouthern California LandslidesAn Overview- Fact Sheet 2005-3107). The landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. The bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. A week later, debris flow in the same location damaged five more houses. Our editors will review what youve submitted and determine whether to revise the article. The slope material liquefies and runs out, forming a bowl or depression at the head. This report has not been reviewed for stratigraphic nomenclature. On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. Eyewitness accounts indicate, however, that similar to 2005, dust was in the air and much of the deposit included relatively dry material. 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. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. The timing of the two landslides with respect to the triggering storms is of primary interest. Course Hero is not sponsored or endorsed by any college or university. The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows. Surface cracks in the upper part of the slope were noted as far back as the summer of 1994. In southern California, at least 25 cm (10 in) of rainfall during the winter is needed to nearly saturate the ground. Actually there have been several sizes, types, and ages of landslides. 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. The 2005 landslide occurred on part of a previous landslide that occurred in 1995. While this preliminary report does not represent a detailed evaluation of those hazards, a few reasonable observations can be made. Deep-seated landslides are generally greater than 3-5 m (10-15 ft) deep. An unstable hillside The rain caused debris from an older landslide to fall about 150 feet. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others. Combination of two or more of the above types is known as a complex landslide. 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. 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. 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. 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. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. 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. 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. October 17, 2022. Some, but not all, of the major winter storms that have caused landslide fatalities and property damage in southern California have occurred duringEl Nio(1997-98 info) conditions. The 2005 landslide pushed many of the houses off their foundations and into each other at the toe of the landslide (figs. https://www.britannica.com/science/landslide, Geology.com - Landslide Hazard Information. 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. Photo taken March 8, 1995. Photo by R.L. 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. Landslides pose a recurrent hazard to humans in most parts of the world, especially in regions that have experienced rapid population and economic growth. The bluff above La Conchita consists of poorly indurated marine sediment of the Monterey and Pico Formations. There were 10 confirmed fatalities. landslide, also called landslip, the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). Short-term stresses imposed by earthquakes and rainstorms can likewise contribute to the activation of landslides. Types of landslides Factors contribute to landslides Landslide in Utah. 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). (See avalanche.) Steep, recently burned areas in southern California are especially susceptible to debris flows (seeSouthern CaliforniaWildfires and Debris Flows- Fact Sheet 2001-3106). 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. 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? Some move slowly, while others can move rapidly with little notice. Although many types of mass movements are included in the general term landslide, the more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. Parise, Mario, and Jibson, R.W., 2000, A seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the January 17, 1994 Northridge, California, earthquake: Engineering Geology, v. 58, p. 251270. [2] The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080ft) long, and 30 meters (98ft) deep. The worst of these was the tragic slide on January 10, 2005 when a huge rain-caused side killed 10 residents. 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). A type of landslide in which the distribution of particle velocities resembles that of a viscous fluid is called a flow. An official website of the United States government. 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). Publications. 1). Short-term stresses, such as those imposed by earthquakes and rainstorms, can likewise contribute to the activation of landslides. 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. URL: https://pubs.usgs.gov/of/2005/1067/508of05-1067.html The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions. In 1994-1995, the seasonal rainfall at Ojai (20 kilometers (12 miles) northeast of La Conchita) from October 1 through March 3 (the day before the landslide occurred) was 761 millimeters (29.96inches), approximately twice the normal amount. 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. [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. YUARA SLUMP EARTHFLOW DEBRIS SLIDE ROCKFALL SCARP ORIGINAL LAND SURFACE -SLIP PLANE. The 2005 landslide occurred at the culmination of an extremely wet 2week period (fig. The arcuate bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. What was the type of landslide in recent 2005 La Conchita landslide? 45. This area has experienced two massive landslides in the past decade: March 4, 1995, and January 10, 2005. Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). Earthflow: Earthflows have a characteristic "hourglass" shape (fig. The 1995 slide was 120 m (400 ft) wide, 330 m (1100 ft) long, and covered approximately 4 ha (10 acres). The 2005 La Conchita landslide occurred at about 12:30 p.m. on January 10. Photo by Pam Irvine, CGS. Figure 3. The 1995 landslide had a horizontal length, vertical length, and depth of 120 x 330 x 30 m and covered approximately 10 acres with a volume of 1.3x106 m3. Photo by R.L. 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). After the 1995 landslide, the town of La Conchita built a retaining wall at the foot of the hill. They write new content and verify and edit content received from contributors. The two major types of slides are rotational slides and translational slides. Answer-Based on the observation from the figure. Morton, D.M., 1971, Seismically triggered landslides above San Fernando Valley: California Geology, v. 24, no. The materials may move by falling, toppling, sliding, spreading, or flowing. The already loosened sediment from the 1995 landslide made the 2005 event a lot more catastrophic. 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. 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. There were 10 confirmed fatalities. 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. Figure 1. Rotation of a mass of rock, debris, or earth outward from a steep slope face is called toppling. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. The 1995 landslide was a deep, coherent slumpearth flow that deformed plastically and moved slowly enough that people could get out of its way. and more. The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. Some are triggered by earthquakes, but more frequently landslides are caused by intense and/or prolonged rainfall. People were evacuated and the houses nearest the slide were completely destroyed. This was a wholesale remobilization of a significant portion of the 1995 deposit.

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