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 11ha (28acre) community was first established in 1924 when subdivision created about 200 lots that mostly contain singlefamily residences. The landslide area was approximately 350 m (1,150 ft) long and 80100 m (260330 ft) wide. Do they actually do gymnastics in Make It or Break It? But the mud stopped before reaching the homes, said county Geologist Jim O'Tousa. [5] The Ranch was found 50% negligent because it did not provide for adequate drainage of its orchards during torrential rains and settled the suit. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. 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. 13. Combination of two or more of the above types is known as a complex landslide. 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. Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). The project also helps to. Corrections? [3] Historical accounts support this. I estimate from viewing the video that high on the slope, the landslide was moving perhaps 10 m/s (30 ft/s). Several smaller, more recent slumps and earth flows also are visible, as is the 1995 slumpearth flow (terminology after Varnes, 1978). These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. The cookies is used to store the user consent for the cookies in the category "Necessary". The landslide destroyed 13 houses and severely damaged 23 others. La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. A classification system based on these parameters is shown in table 1. Answer-Based on the observation from the figure. Historical accounts dating back to 1865 have reported landslides in the area around La Conchita as being a regular occurrence (Hemphill, 2001). A complete prediction of the process would include assessments of where, when, and how big. 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. Law enforcement officers and media representatives were in the area, which facilitated capturing the moving landslide on video. 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). What was the type of landslide in recent 2005 La Conchita landslide? October 17, 2022. Official websites use .gov The landslides in the area around La Conchita have been a regular occurrence, according to the historical accounts dating back to 1865. 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. 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. The two formations are in fault contact along the active Red Mountain Fault, which extends across the slope face. 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. 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. Figure 1: Air photo of La Conchita, CA taken in 2002. 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 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. The landslide slumped as a coherent mass of material. 8 What year did the landslide happen in Ventura CA? Morton, D.M., 1971, Seismically triggered landslides above San Fernando Valley: California Geology, v. 24, no. These recent landslides spilled over U.S. Highway 101 in the Ventura County community that is located 25 miles south of Santa Barbara. 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. 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). 7 What happened in the La Conchita landslide 2005? People were evacuated and the houses nearest the slide were completely destroyed. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. A. Weathering affects rocks from the outside in, forming an outer weathered zone or rind. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. 10 and 11). This type of movement can subsequently cause the mass to fall or slide. 13, 60 p. National Oceanic and Atmospheric Administration, 1994b, Climatological dataCalifornia, OctoberDecember 1994: National Climatic Data Center, v. 98, nos. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others (figs. What kind of mitigation was done after the La Conchita landslide? On March 4, 1995, the hill behind La Conchita failed, moving tens of meters in minutes, and buried nine homes with no loss of life. 2) On figure 2, label the following: main scarp, head of slide, body of slide, toe of slide. 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. An unstable hillside The rain caused debris from an older landslide to fall about 150 feet. In the past two decades major landslides devastated the town of La Conchita, California. The materials may move by falling, toppling, sliding, spreading, or flowing. This cookie is set by GDPR Cookie Consent plugin. Please refer to the appropriate style manual or other sources if you have any questions. 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. This was not the first destructive landslide to damage this community, nor is it likely to be the last. The landslide scenarios sketched above potentially could impact any part of the La Conchita community. 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. This information provides tools to help make PDF files accessible. 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). It does not store any personal data. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. Questions or Assistance: USGS Web Contact 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? Large blocks of rock slide downhill. Colorado, and northern New Mexico) are complex in rock type and climate, and so the landslides there are also complex. 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. The 2005 landslide was a shallower remobilization of the very same material into a rapid, highly fluid debris flow that buried 10 people. This cookie is set by GDPR Cookie Consent plugin. Earthflow: Earthflows have a characteristic "hourglass" shape (fig. A week later, debris flow in the same location damaged five more houses. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). What year did the landslide happen in Ventura CA? The costliest landslide in U. history occurred in the Thistle, Utah area in April 1983. 45. 3B). What are various methods available for deploying a Windows application? On January 14, 2005, at the invitation of the California Geological Survey, I visited La Conchita with James O'Tousa, contract geologist for Ventura County, and Pamela Irvine, Janis Hernandez, and Terry Jones, all from the California Geological Survey. Lateral spreads are distinctive because they usually occur on very gentle slopes or flat terrain (fig. Debris flows include <50% fines. Landslides can also be activated by processes that weaken the shear strength of a slopes material. The La Conchita landslide then occurred on March 4. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The landslide killed 10 people, and destroyed or damaged dozens of houses. 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. The cookie is used to store the user consent for the cookies in the category "Other. 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. 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. 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. Many readers will be familiar with the La Conchita landslide in California. 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. 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. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. The term "landslide" encompasses events such as rock falls, topples, slides, spreads, and flows. 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)? In particular, the extraordinary rainfall of January 1995 probably was the principal contributing factor to the elevated groundwater levels and, hence the landslide movement. The slope material liquefies and runs out, forming a bowl or depression at the head. There were 10 confirmed fatalities. In 2005, an additional landslide occurred at the end of a 15day period of near-record rainfall levels. The 2005 landslide killed 10 people, and destroyed or damaged dozens of houses. 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). Movement is caused by shear stress sufficient to produce permanent deformation, but too small to produce shear failure. . 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. The judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible. 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. Bits of rock fall off the cliff face, usually due to freeze-thaw weathering. 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. On January 10, 2005, a major landslide occurred in 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. In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). Even modest rain storms during normal, non-El Nio years can trigger post-wildfire debris flows. 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. About USGS/ Science Topics/ Maps, Products & Publications/ Education/Publication: FAQ. 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. Click the image to open a larger version in a new window. These schematics illustrate the major types of landslide movement. 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. 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. The 2005 landslide mobilized the south flank of a larger landslide that occurred in March 1995, and destroyed 9 homes. However, this still leaves some troubling questions unanswered. Course Hero is not sponsored or endorsed by any college or university. Although there are multiple types of causes of landslides, the three that cause most of the damaging landslides around the world are these: Original content from Kimberly Schulte (Columbia Basin College) and supplemented by Lumen Learning. 1). 3G). 3I). The 2005 landslide occurred on part of a previous landslide that occurred in 1995. 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. 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. The timing of the two landslides with respect to the triggering storms is of primary interest. Rotational slip. This is a typical type of landslide. [2] The landslide occurred after a 15-day period of unprecedented records of rainfall in 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. Since that time, other slides have occurred, covering at times cultivated land, roadways, and the community itself.[4]. Landslide. La Conchita, CA. Subsequently, residents formed the La Conchita Community Organization (LCCO) to coordinate with government officials to determine the best way to protect the community. 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. 3D). 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. The neighborhood of La Conchita has suffered from large landslides in the recent past that have wiped out homes and even killed people. From December 27, 2004, through January 10, 2005, the nearby city of Ventura received 378 millimeters (14.9 inches) of rainfall, only slightly less than its mean annual total of 390 millimeters (15.4 inches). In 2008, family members of those killed and or who suffered loss of property in the 2005 La Conchita Landslide filed a lawsuit against the La Conchita Ranch Co., located at the top of slope. These cookies will be stored in your browser only with your consent. Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. La Conchita (1995) La Conchita landslide, Ventura County. Earthflow: Earthflows have a characteristic hourglass shape (fig. Similar combinations of large ancient landslides and smaller, recently active landslides also are present in areas southwest of the 1995 and 2005 landslides. These types of landslides take weeks, even months, to happen. Analytical cookies are used to understand how visitors interact with the website. There is no reason to believe this pattern of landsliding will stop. January 10, 2005 On January 10, 2005, the southeastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. Schuster, U.S. Geological Survey. People were evacuated and the houses nearest the slide were completely destroyed. A) La Conchita, California The community of La Conchita in Ventura County, California experiences frequent landslides. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments. 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). The bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. These cookies ensure basic functionalities and security features of the website, anonymously. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually.
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