AS Geography: The California hotspot

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Dan Grist
Examine the reasons why California is considered to be a multiple
hazard hotspot.
California is considered to be a multiple hazard hotspot due to its wide disaster portfolio and
it being situated in an area where both geophysical and hydrometerological hazards are
common. Around 3.5 million poor, vulnerable people are
living in hazardous conditions.
Firstly California is situated on the San Andreas Fault.
This is a conservative plate margin where the pacific
plate is sliding past the North American plate; the pacific
plate is moving 6 times faster. Sometimes the two
plates lock together which causes a rise in tension, and
when this pressure is released it causes seismic waves.
Both LA and San Francisco are sat on the boundary and
are therefore very vulnerable to shallow focus quakes.
These quakes also create a high risk of liquefaction.
On the 17th October 1989 an earthquake of 7.1 on the Richter scale struck, the epicentre
being Loma Prieta in the Santa Cruz Mountains. 63 people died and 13,757 were injured
(most were killed due to the collapse of the Nimitz highway) 1018 homes and 366
businesses were destroyed; the damage cost $6 billion. An aftershock with a magnitude of
5.2 struck the region 37 minutes after the main quake.
When both geophysical and hydrometerological hazards interact, landslides often occur. This
is mainly due to the deep ravines in the Sierra Nevada Mountains and its loose sandy soil.
Floods, which mainly occur in El Nino years, usually trigger dangerous landslides and
Another hydrometerological hazard, which is exacerbated by the background context hazard
of global warming, is eustatic sea level rise. As well as high energy waves, this erodes
Californian beaches; removing sand and eroding cliffs.
The San Francisco bay area is particularly at risk due to
its dense coastal population of 37 million people.
California suffers from both El Nino and la Nina years,
which is part of a cycle of approximately 7 years; this is
because it is situated on the eastern side of the Pacific
Ocean. Each of these years creates several distinctive
threats. In El Nino years, air currents move eastwards
across the pacific ­ bringing over moist air which creates
landslides and flash floods. On the other hand, La Nina
years occur when the current reverses. During this time

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Dan Grist
California will suffer from the warm and dry Santa Ana wind from the Arizona desert which
will bring drought and the threat of wild fires. Wildfires e.g. in summer 2004 and 2007 are
becoming a greater risk due sprawling suburbanisation (the edge of La is moving into the
Sierra Nevada Mountains.)
Another geophysical hazard is the tsunami risk. This secondary hazard to earthquakes is very
prone to the pacific basin.…read more


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