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Coso Volcanic Field
inyo county, california
overview
Coso volcanic field is located in Inyo
County, California.
Latitude: 36.03° N
Longitude: 117.82° W
Elevation: 2,400 (m) 7,874 (f)
Composition: basalt to rhyolite
Most recent eruption: 40,000 years ago
Nearby towns: Olancha, Pearsonville
Threat Potential: Moderate (source)
A volcano is a rupture in the crust of a planetarymass object, such as Earth, that allows hot lava,
volcanic ash, and gases to escape from a magma
chamber below the surface.Earth’s volcanoes
occur because its crust is broken into 17 major,
rigid tectonic plates that float on a hotter, softer
layer in its mantle. Therefore, on Earth, volcanoes
are generally found where tectonic plates are
diverging or converging. (source)
structure
The Coso volcanic field covers
approximately roughly 150 square miles,
and is home to one of the largest producers
of geothermal power in the U.S., with an
output sufficient to supply the needs of
270,000 homes.
The geothermal resource fuels the many
hot springs, steam vents, and boiling mud
pots near the center of the Coso Volcanic
Field. About 40 eruptions in the last quarter
million years produced a field of steep-sided
lava domes, red hills of volcanic cinder, and
rough-surfaced lava flows. The most recent
eruption occurred about 40,000 years ago
forming the Volcano Peak basaltic cinder
cone and lava flow.
Geophysical and geochemical studies
detect a zone of partially molten rock
(magma) underlying the center of the
Coso Volcanic Field. Small to moderate
earthquakes, some due to the geothermal
resource are common. The U.S. Navy
monitors earthquake and geothermal activity
within the Coso Volcanic Field. (source)
Geologic history
Volcanism began in the Coso Range approximately
6 million years ago, and the earliest basaltic
lava flows are tilted, indicating that the start
of volcanism in the area preceded the onset
of faulting associated with Basin and Range
extension.
Three periods of volcanic activity have occurred
within the Coso Range. Basalt was the primary
magma type erupted during the oldest episode,
which started 6 million years ago. The most
volcanically active period occurred during the
Pliocene between about 4 and 2.5 million years
ago producing 30 km3 (7.2 mi3) of the total 35
km3 (8.4 mi3) erupted material found in the Coso
Range. Volcanic rocks age dated to this time
period include basalt, andesite, dacite, rhyodacite
and high-silica rhyolite. The third period of activity
occurred during the Pleistocene between about
1.1 and 0.04 million years ago.
The region is most well known for the 38 highsilica rhyolite domes and lava flows that erupted
during this time period. These well-known domes
were accompanied by the eruption of 14 basaltic
centers. (source)
Geothermal power
Commercial power development began in the
1980s. Located within the Naval Air Weapons
Station China Lake Station near Ridgecrest,
California, power plants at the Coso Geothermal
was operated by Caithness Energy, LLC (Reno,
Nevada) and sold in 2006.
It currently produces 270 MW from four
geothermal power plants. More than 100 wells
have been drilled throughout the field, with
production depths from 2,000 to 12,000 feet (610
to 3,700 m), and temperatures from 200° to 350
°C. Coso began generating electricity in 1987.
Since then, improvements have resulted in more
efficient use of the resource. (source)
Geothermal power is considered to be a
sustainable, renewable source of energy because
the heat extraction is small compared with
the Earth’s heat content. The greenhouse gas
emissions of geothermal electric stations are on
average 45 grams of carbon dioxide per kilowatthour of electricity, or less than 5 percent of
that of conventional coal-fired plants. However,
fluids drawn from the deep earth carry a mixture
of gases, notably carbon dioxide, hydrogen
sulfide, methane, and ammonia. These pollutants
contribute to global warming, acid rain, and
noxious smells if released. (source)
basic geology
The Coso volcanic field is composed largely
of basalt and rhyolite. These are igneous rocks
that were formed through the cooling and
solidification of magma or lava.
Igneous rock may form with or without
crystallization, either below the surface as
intrusive (plutonic) rocks or on the surface as
extrusive (volcanic) rocks. This magma can
be derived from partial melts of existing rocks
in either a planet’s mantle or crust. Typically,
the melting is caused by one or more of
three processes: an increase in temperature,
a decrease in pressure, or a change in
composition.
A cinder cone is a steep conical hill of loose
pyroclastic fragments, such as either volcanic
clinkers, cinders, volcanic ash, or scoria that
has been built around a volcanic vent. The Red
Cinder Hill is an eroded cinder cone.
Top right: molten basalt
Middle: hardened basalt
Bottom: hardened rhyolite
(source)
why I’m interested
I think this site is interesting because it
is not what I would expect a volcano to
look like. In my imagination, volcanos look
more like JRR Tolkein’s Mount Doom.
I am interested in this divide between
expectations and the imaginary vs reality.
Though this volcano has been dormant a
long time, there is still magma bubbling
miles below your feet. It’s quiet, but not
dead. This site is interesting geologically
because it is one of many sites that reflects
how tectonically active California has been
and continues to be. It also reflects the ways
in which people harnassed this geology and
exploited it for basalt mining, geothermal
power, and military testing.
My mom is a geologist and she has been
feeding me little tidbits of knowledge about
rocks my whole life. She has instilled in
me an appreciation for what these ancient
landforms can teach us.