The 2005 landslide occurred on part of a previous landslide that occurred in 1995. The catastrophic movement of the 2005 landslide damaged or destroyed 36 houses and killed 10 people. The 2005 landslide pushed many of the houses off their foundations and into each other at the toe of the landslide (figs. 3F). Contact between the flowing mass and the underlying material can be distinct, or the contact can be one of diffuse shear. Landslides in La Conchita - ArcGIS StoryMaps The cookies is used to store the user consent for the cookies in the category "Necessary". However, this still leaves some troubling questions unanswered. The rising groundwater level within the 1995 deposit would thus have resulted from deeper recharge from rainfall infiltration upslope. The landslide occurred on part of a previous landslide that occurred in 1995. Often the initial failure is a slump, but in some materials movement occurs for no apparent reason. The main mass that failed is on the southeastern margin of the larger ancient landslide that encompasses the entire front of the bluff (see fig. Chapter 12 Flashcards | Quizlet What was the type of landslide in recent 2005 La Conchita landslide? After covering the road with 7-8 feet of debris, the slide stabilized. This website uses cookies to improve your experience while you navigate through the website. The landslide killed 10 people, and destroyed or damaged dozens of houses. In both 1889 and 1909, the Southern Pacific rail line running along the coast was inundated. The costliest landslide in U. history occurred in the Thistle, Utah area in April 1983. PDF Falling Into the Pacific: California Landslides and Land Use Controls Ultimately, the County prevailed against the plaintiffs on all claims. Explain why. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. 7). The bluff above La Conchita has produced a variety of landslides over an extended period of time. 2 and 3) damaged five additional houses in the northwestern part of La Conchita. Many readers will be familiar with the La Conchita landslide in California. As discussed above, the 1995 landslide was relatively deep and primarily moved as a coherent slumpearth flow. 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. 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. 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. 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. 10.5: Landslide Types and Processes is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts. The slope material liquefies and runs out, forming a bowl or depression at the head. Types of landslides Factors contribute to landslides Landslide in Utah. What type of slide is the La Conchita slide? - Heimduo 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). The materials may move by falling, toppling, sliding, spreading, or flowing. 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. On March 10, a subsequent debris flow from a canyon to the northwest (see canyon on left part of figs. What happened in the La Conchita landslide 2005? An unstable hillside The rain caused debris from an older landslide to fall about 150 feet. Articles from Britannica Encyclopedias for elementary and high school students. What about the remaining 1995 deposit? 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. Future earthquakes, of course, also could trigger landsliding in the area (Harp and Jibson, 1995, 1996). Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). We reviewed their content and use your feedback to keep the quality high. Landslides can also be activated by processes that weaken the shear strength of a slopes material. 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? La Conchita is located on the southern California coastline midway between Ventura and Santa Barbara (fig. The cookie is used to store the user consent for the cookies in the category "Performance". Fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards. The worst of these was the tragic slide on January 10, 2005 when a huge rain-caused side killed 10 residents. Debris avalanche: This is a variety of very rapid to extremely rapid debris flow (fig. 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 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.. The town is located on a narrow coastal plain, with a steep . Evacuation order lifted at La Conchita, but officials warn area is However, dry flows of granular material are also possible. Various processes that weaken the shear strength of a slope may also activate landslides. La Conchita landslides - Wikipedia Prudence would certainly dictate, however, that we anticipate renewed landslide activity during or after future periods of prolonged and(or) intense rainfall. Below are publications associated with this project. January 10, 2005 A lock () or https:// means youve safely connected to the .gov website. 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). National Oceanic and Atmospheric Administration, 1995a, Climatological data annual summaryCalifornia 1995: National Climatic Data Center, v. 99, no. The already loosened sediment from the 1995 landslide made the 2005 event a lot more catastrophic. Some materials with a loose, open sediment fabric will weaken if they are mechanically disturbed or flooded with water. The landslide recurred on part of a previous landslide in 1995.La Conchita, California. There were 10 confirmed fatalities, unfortunately. Publications. This is the only mitigation effort the town undertook. Earthflow: Earthflows have a characteristic hourglass shape (fig. . Landslides are a type of "mass wasting" which denotes any down slope movement of soil and rock under the direct influence of gravity. 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). Three years after the 2005 landslide, the owners of an avocado ranch agreed to turn over all 700 acres (280ha) of their land and other assets to settle the suit. These cookies will be stored in your browser only with your consent. The judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible. The bluff above La Conchita consists of poorly indurated marine sediment of the Monterey and Pico Formations. 2023 California Landslide Response The bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. Debris flows include <50% fines. 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). 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. Why did the landslide material not mobilize into a rapid debris flow in 1995? During the winter season in California, beaches typically erode thereby allowing waves to reach further inland and to inundate the bottoms of coastal cliffs. https://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html, Combination or two or more principal types of movement. Although landslides are primarily associated with mountainous regions, they can also occur in areas of generally low relief. Fires that denude slopes of vegetation intensify the susceptibility of slopes to debris flows. The neighborhood of La Conchita has suffered from large landslides in the recent past that have wiped out homes and even killed people. 1 What type of slide is the La Conchita slide? The 2005 landslide occurred at the culmination of an extremely wet 2week period (fig. LockA locked padlock The following summary of the 1995 La Conchita landslide is extracted from O'Tousa (1995) and Anderson (Robert Anderson, RJR Engineering, 2005, personal commun.). 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. The landslide entered the La Conchita neighborhood destroying 13 houses and severely damaging 23 others (figs. The volume of material moved by the landslide was 2.8 cubic kilometers (0.67 mi 3) . About USGS/ Science Topics/ Maps, Products & Publications/ Education/Publication: FAQ. Analysis of the 1995 and 2005 La Conchita, CA Landslides - NASA/ADS 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. [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. 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. In 1995, after an exceptionally wet winter, the landslide moved tens of meters (tens of yards) damaging nine houses. Many areas of coastal California are subject to cliff erosion and coastal landslides (see new research onEl Nio coastal hazardsin California). Photo by R.L. 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. 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. 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). 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. Reported landslides began in 1865. 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. 3I). This was not the first destructive landslide to damage this community, nor is it likely to be the last. You'll get a detailed solution from a subject matter expert that helps you learn core concepts.
