Download California`s Natural Hazards

California’s Natural Hazards
California’s geology has unique natural hazards
that goes along with its natural beauty.
California is in danger of earthquakes, which
could cause liquefaction, seismic shaking,
landslides, and tsunamis.
There are volcanic hazards and the potential for
mudflows and flooding due to storms.
Hundreds of earthquakes happen each day in California.
Most of them are so small they can’t be felt, but those
above a magnitude 5 can be dangerous.
Tsunamis, which are shifts in the ocean floor that
send sea waves in all directions, can grow to
enormous sizes as it nears the shore.
Earthquakes at subduction zones all around the Pacific
Ocean can cause tsunamis. In Northern California
where the Juan de Fuca plate is sinking under the North
American Plate is a place that could generate tsunamis.
Scientists have evidence that in the past 200 years,
more than a dozen locally generated tsunamis have
struck California coastlines.
In 1964 a major earthquake in Alaska produced a
tsunami that struck Crescent City hours later, killing 12
people.
Crescent City,
California
Seismic shaking or the amount of ground shaking that
occurs during a quake can cause damage to structures.
The more consolidated or solid the ground the better the
structure can absorb the seismic waves.
The modified Mercali Scale describes the effects of
seismic shaking. It measures how strong the
earthquake was felt and how much damage it did, in
other words its intensity.
Liquefaction is another natural hazard that is caused by
seismic shaking. As the unconsolidated soil shakes the
water in the pores of the soil shake out toward the
bottom.
This leaves air pockets which causes the soil to
sometimes sink under the weight of structures that are
above it.
Earthquakes often cause loose rock and soil on slopes
to move. This is called a landslide. Most landslides
occur on steep slopes where sediment is loose or rock is
fractured.
California has volcanic hazards as well. Natural hazards
from volcanic eruptions include volcanic ash,
pyroclastic flows, lava flows and volcanic gasses.
The Cascade Range which extends from Washington
down to Northern California has several composite
(Stratovolcanos) volcanoes.
In California we have Black Butte, Mt. Shasta, Lassen
Peak, and Medicine Lake Volcano. Only Mt. Shasta and
Lassen Peak are classified as active.
Volcanic fields, such as the Long Valley Caldera near
Mammoth Lakes, has current active volcanism. In 1980
the town of Mammoth Lakes was evacuated because
scientists believed an eruption was about to happen.
The last natural hazards California has to endure are
mudflows and flooding due to storms. Mudflows
happen most often when fires burn hillsides and the
topsoil is exposed and when heavy rains fall the
mudflows come down.
In Northern California flooding happens in the river delta
areas in the Central Valley due to more water than the
rivers can hold.