What caused the Conchita landslide?
The 1995 landslide apparently occurred as a result of an extraordinarily wet year. Mean seasonal rainfall at Ojai (20 km [12 mi] northeast of La Conchita) from October 1 through March 3 (the day before the landslide occurred) is 390 mm (15.37 in) (National Oceanic and Atmospheric Administration, 1994a, 1995a).
What factors cause landslides at La Conchita California?
"The question is not if but when the next landslide will impact the community of La Conchita. A combination of factors makes future landslides inevitable. These are: active faulting and folding; rapid tectonic uplift; very weak rocks; steep topography; and, the presence of springs."
What triggered both the 1995 and 2005 mass movements in La Conchita California?
CASE STUDY 1: Slumping in La Conchita in both 1995 and 2005, heavy rain was the likely trigger of mass movements though the timing in both cases was different.
What was a major factor in the deaths that occurred in La Conchita CA in 2005?
landslideOn January 10, 2005, a major landslide occurred in La Conchita. The 2005 landslide killed 10 people, and destroyed or damaged dozens of houses. The landslide recurred on part of a previous landslide in 1995.
Why does California have so many landslides?
Landslides in California occur mainly due to intense rainfall but occasionally are triggered by earthquakes. Landslides are common in Southern California, the San Francisco Bay Area and other parts of Northern California, and the Sierra Nevada.
What type of mass movement is La Conchita slide?
In La Conchita, there was a landslide and earthflow in the spring of 1995 (see figure 1). People were evacuated and the houses nearest the slide were completely destroyed. This is a typical type of landslide.
What mitigation took place after the La Conchita slide?
retaining wallAfter the 1995 landslide, the town of La Conchita built a retaining wall at the foot of the hill. This is the only mitigation effort the town undertook.
Can you build in La Conchita?
But there are regulatory hurdles to any development on the coast, and the La Conchita property's history and geology would make it even harder to build on. Any development plan would have to include work to terrace and stabilize the hillside, Murray said.
Which of the following are common triggers of landslides choose all the possible triggers?
Mass-wasting events often have a trigger: something changes that causes a landslide to occur at a specific time. It could be rapid snowmelt, intense rainfall, earthquake shaking, volcanic eruption, storm waves, rapid-stream erosion, or human activities, such as grading a new road.
How many people died in La Conchita slide?
10 peopleOn January 10, 2005, a major landslide occurred in the town of La Conchita, California. The landslide killed 10 people, and destroyed or damaged dozens of houses.
When was the La Conchita mudslide?
January 10, 2005By Randall W. Jibson 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. This was not the first destructive landslide to damage this community, nor is it likely to be the last.
What causes debris flow?
Debris flows can be triggered by intense rainfall or snowmelt, by dam-break or glacial outburst floods, or by landsliding that may or may not be associated with intense rain or earthquakes.
What mitigation took place after the La Conchita slide?
retaining wallAfter the 1995 landslide, the town of La Conchita built a retaining wall at the foot of the hill. This is the only mitigation effort the town undertook.
What is the greatest mass wasting hazard to guests in Yosemite National Park?
al., 2012b). Since the melting of the Tioga ice sheet, landslides currently cause the greatest change in landform at Yosemite National Park. Landslides, rapid downslope movements of rock or soil, are result from unstable slopes.
Which of the following are common triggers of landslides choose all the possible triggers?
Mass-wasting events often have a trigger: something changes that causes a landslide to occur at a specific time. It could be rapid snowmelt, intense rainfall, earthquake shaking, volcanic eruption, storm waves, rapid-stream erosion, or human activities, such as grading a new road.
What are some clues that a proposed home site may be susceptible to landslide activity?
Landslide warning signsSprings, seeps or saturated ground in areas that are not usually wet.New cracks or unusual bulges in the ground, street or sidewalks.Soil moving away from foundations, or the tilting or cracking of concrete floors and foundations.Sunken or down-dropped road beds.More items...•
When did the La Conchita landslide happen?
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. This was not the first destructive landslide to damage this community, nor is it likely to be the last.
What are the landslides above La Conchita?
The bluff above La Conchita has produced a variety of landslides over an extended period of time. Figure 3 shows LIDAR and false–color infrared images of the bluff above La Conchita and the surrounding area, and several sizes, types, and ages of landslides are visible. The arcuate bench at the top of the bluff is the head of a very large prehistoric landslide that affected the entire bluff. Several smaller, more recent slumps and earth flows also are visible, as is the 1995 slump—earth flow (terminology after Varnes, 1978). Similar combinations of large ancient landslides and smaller, recently active landslides also are present in areas southwest of the 1995 and 2005 landslides. In addition, large and small ravines that incise the bluff have produced debris flows recently and in the past.
How much rain did the 1995 La Conchita landslide cause?
The 1995 landslide apparently occurred as a result of an extraordinarily wet year. Mean seasonal rainfall at Ojai (20 km [12 mi] northeast of La Conchita) from October 1 through March 3 (the day before the landslide occurred) is 390 mm (15.37 in) (National Oceanic and Atmospheric Administration, 1994a, 1995a). In 1994—95, about twice as much rain—761 mm (29.96 in)—fell during that period (National Oceanic and Atmospheric Administration, 1994b, 1995b). Figure 4 shows the rainfall distribution during the 1994—1995 rainy season. 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). February 1995 produced only about one–third of the normal rainfall, but a modest storm on March 2—3 produced 21 mm (0.81 in) of rain. The La Conchita landslide then occurred on March 4.
What is the rock that forms the bluff above La Conchita?
The bluff above La Conchita consists of poorly indurated marine sediment of the Monterey and Pico Formations. The upper part of the slope consists of interlayered siliceous shale, siltstone, and sandstone of the Middle to Upper Miocene Monterey Formation. The lower part of the slope is siltstone, sandstone, and mudstone of the Pliocene Pico Formation (O'Tousa, 1995). 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 two formations are in fault contact along the active Red Mountain Fault, which extends across the slope face.
What is the scarp in the photograph of La Conchita?
Oblique false–color infrared photograph of La Conchita taken in 2002. The arcuate bench near the top of the bluff in the center of the photograph is the main scarp of an ancient landslide that involved the entire bluff. The 1995 landslide is visible in the right center of the photograph.
How much rain did the 2005 landslide cause?
The 2005 landslide occurred at the end of a 15–day period that produced record and near–record amounts of rainfall in many areas of southern California. 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). 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). Although rainfall intensities were not extreme, moderate– to high–intensity rainfall persisted for more than 2 weeks, and the landslide occurred at the culmination of this 15–day high–rainfall period (fig. 7).
Where is landsliding occurring?
Historical accounts and geologic evidence show that landsliding of a variety of types and scales has been occurring at and near La Conchita for many thousands of years, and on a relatively frequent basis, up until the present. There is no reason to believe this pattern of landsliding will stop.
How much soil was deposited on the road during the La Conchita landslide?
In the La Conchita landslide, seven to eight feet of soil from the hillside was deposited on public road.
When did the Vista Del Rincon landslide happen?
At the time of the landslide (March 4, 1995), emergency measures and debris removal were eligible for FEMA funding according to FEMA Landslide Policy No. 4511.300 A, EX. An existing landslide complex had failed in a localized area covering 300-feet of Vista Del Rincon (VDR) Drive and posed a threat to public safety and improved property. However, over the 17 months following the slide (up to August 1996), the County, rather than taking action, contested the scope and funding of each DSR, and proposed large scale regional studies and stabilization measures in an attempt to address the entire landslide complex. As a result, the County failed to take any substantive action in the 17 months after the slide, prompting FEMA to deobligate all funding in August 1996.
What happened in 1995?
Heavy rains of January 1995 led to a March 4, 1995, landslide in the LaConchita Ranch Community in Ventura County (County), California, covering 300 feet of Vista Del Rincon (VDR) Drive with 7-8 feet of mud and debris. Nine private residences were damaged and three were destroyed as a result of the slide. 75 other residences were evacuated after the slide. The slide stabilized after covering the road with earth, rock and debris, with this material making up the new toe of the slope. Engineering and geotechnical studies of the area (USGS, Geologists, Engineers) from both before and after the slide indicate the hillside was a component of a pre-existing, historically active landslide complex encompassing the entire area. In studying the slide area, geologists determined the local landslide failure was accelerated by the rains from the January storm. Initial DSR's written for stabilization were later voided and replaced by damage survey report (DSR) 11440 which was prepared on January 11, 1996, in the amount of $69,000, for the installation of landslide slope drainage and associated engineering. This DSR was amended by FEMA in March 1996, changing the scope of the DSR to provide $45,000 exclusively for a "Geotechnical Investigation Estimate." This funding was for a limited geotechnical study of the localized slide that was resting on the road, and to determine methods for removing debris from the road without triggering further sliding. As of March 1996, the County had not undertaken any emergency measures or debris removal activities on the road.
How long did the 1995 landslide last?
By not taking action, the County has allowed the landslide to cover a road and become stable (in the context of immediate threat) for over 28 months.
How long after the 1995 landslide was the landslide considered an emergency?
The landslide, which occurred on March 4, 1995, was initially eligible for emergency measures within 6 - 12 months after the disaster. 2. No. The localized landslide which occurred was initially eligible for emergency stabilization (within up to 12 months) but is no longer eligible, 17 months after the disaster.
Is a landslide a component of a large, pre-existing landslide?
Review of documentation submitted shows that the landslide was a component of a large, pre-existing landslide complex. According to the Federal Emergency Management Agency (FEMA) landslide policy No. 4511.300 A.EX, funding for permanent restoration of pre-existing landslide complexes is not eligible. FEMA will fund only emergency (Category B) work within 6 months of the disaster (12 months with an approved extension). Since no action was taken within 17 months of the disaster, I am denying the appeal as detailed in the enclosed appeal analysis.
Is permanent restoration eligible for landslide?
Also, permanent restoration is not eligible, because the slide was part of a large pre-existing, regional landslide complex, making only emergency measures and debris removal eligible per FEMA policy 4511.300.A.EX, and only if completed within allowable time frames. Rationale:
How many people died in the California landslide?
The landslide, which occurred about 130 km northwest of Los Angeles, California, mobilized over 40,000 cubic yards of wet debris into a large scale debris flow (commonly referred to in the media as a mudslide) that flowed into a residential community at the foot of the slope, killing 10 persons and damaging or destroying 36 residences.
What happened in California in 2004?
In late 2004 and early 2005, an intense series of rainstorms impacted southern California, causing flooding and innumerable landslides throughout the region. The January 10, 2005 La Conchita landslide was the deadliest single event triggered by the 2004-2005 storm sequence. The landslide, which occurred about 130 km northwest of Los Angeles, California, mobilized over 40,000 cubic yards of wet debris into a large scale debris flow (commonly referred to in the media as a mudslide) that flowed into a residential community at the foot of the slope, killing 10 persons and damaging or destroying 36 residences. Ten years earlier, in March 1995, a large rotational landslide had occurred in the same area following a period of heavy rainfall. This event damaged or destroyed seven residences, destroyed an access road that traversed the slope, and covered a major street in the community, Vista Del Rincon Avenue, with up to about 20 ft of debris. In 2000, the County of Ventura constructed a temporary soldier pile wall consisting of steel H-piles and wood lagging along the northern margin of Vista del Rincon Avenue to allow the removal of debris from the street. The wall was 270 feet long and stood between 5 and 23.5 feet above the road. Litigation triggered by the 2005 debris flow focused in part on the role played by the temporary wall in affecting the path taken by the flow as it entered the community.
Introduction
Setting of La Conchita
Landslide History
1995 La Conchita Landslide
2005 La Conchita Landslide
- The 2005 La Conchita landslide occurred at about 12:30 p.m. on January 10. 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). The landsl...
Comparison of 1995 and 2005 Landslides
Continuing Hazards at La Conchita
Conclusion
References