Landslides impact California’s terrain often. 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. In that occasion, the landslide consisted of 600,000 tons of mud and silt slid
600 feet down a cliff face (see topo map in the figure. Note all houses are built donwlope of a very steep slope...).
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.
There is a USGS
page with information on how to identify landslides and what to do if one
happens: http://landslides.usgs.gov/learn/prepare.php
