La Conchita Landslide – Nearly 4 Years Later
This past weekend, while traveling home to San Francisco and driving up California Highway 101, we passed the small town of La Conchita. I quickly pulled out my camera and snapped a few shots of the slide to compare with past photos (this is a perfect example of what we geologists love to often do: “Drive-by-geology”). Vegetation covers most of the material that mobilized in the 2005 slide, while the escarpment is rather bare.
While searching for some more information and photos from the La Conchita slide, I found this *incredible* video of the slide!
Here are a few photos as well. If you look at this aerial photo below, you can see the remnants of an old landslide to the left of the active slide, in the form of a scarp and a bench. It’s only a matter of time before that part of the hillside begins to fall as well!
More information about the La Conchita slide from a study conducted in 2005:
“The slope that failed in 1995 and 2005 is a holocene paleosea cliff and is near the seaward edge of an ancient landslide that has produced prehistoric and historic slides, slumps, debris and mud flows,” said Gurrola. “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.”
Keller and Gurrola explained that the triggering mechanism for debris flows and mud flows appears to be prolonged, intense precipitation. The larger, complex slides may increase in activity months or even years after wet years and infiltration of rainwater to the subsurface environment. An earthquake could also trigger a slide.
“Landslides similar or larger than the 1995 and 2005 events may occur next year or in coming decades, during or shortly after intense rain,” said Gurrola. “People tend to have short memories when it comes to geologic hazards such as landslides. If people continue to live in La Conchita, more lives will be lost in the future and this is unacceptable.”
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