The largest landslide in modern U.S. history (in terms of volume) was most likely one that occurred just last year in Bingham Canyon outside of Salt Lake City, Utah on April 10, 2013. It had a slide mass of 55 million cubic meters (compared to an estimated 10 million cubic meters during the Oso, Washington event). Fortunately, no one was injured or killed during the Utah slide.
In California, landslides impact the terrain often [see image of landslide susceptibility below]. These are
generally related to precipitation patterns, in particular if there has been
previous months of drought conditions. In 1982, a series of landslides near San
Francisco killed 33 people and closed the Golden Gate Bridge. A total of 18,000
different landslides took place in the San Francisco Bay Area following a very
heavy rain storm (data collected by aerial surveillance in the days following
the event). Two fast-moving fronts carrying extremely heavy rain passed through
in a 36-hour period, during which the area received an amount of rain equal to
half its average annual precipitation.
Another famous
unstable area is La Conchita. A mudslide of 400,000 tons of mud in 2005 killed
10 people. This should not be surprising as the exact same place suffered
another hill collapse in 1995, destroying 9 homes [see topo map below]. I that
first occasion, the landslide consisted of 600,000 tons of mud and silt slid
600 feet down a cliff face.
The obvious approach is study well the
soil in where we put homes and also learn from previous occurrences,
understanding that areas that are unstable will continue being so (La Conchita is not alone; Oso area had been
unstable before the 2014 event).
Detailed geologic reports have been made in the past of these places,
but the personnel that has the power to act have not followed up/ignored them
or have not read them. Gravity always wins. We know better?
After
the 2005 disaster, there
was an attempt of a $50-million grading project. There were also calls for the county to buy up all the homes through eminent
domain and never allow anyone to live there again. It was an idea that came and
went, as was the grading project.
This is the USGS page with information
on how to identify landslides and what to do if one happens.
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