The state of California has several volcanoes which are classified as active. Of these,
the most recent volcanic eruption occurred from Lassen Peak in 1917. However, Lassen Peak is not
the only volcano within California which could erupt in the near future. In southern California,
there is a volcanic field just to the east of a portion of US Route 395. What I am referring to
is the Coso Volcanic Field. Although this field is currently dormant, it is still geologically active
as it contains both hot springs and a number of active fumaroles. At some point in the future,
this area will produce another eruption. This video will discuss this unique volcanic field,
and mention what its future hazards are. For this video, we are defining a dormant
volcano as any volcano or volcanic field which has not erupted in the last 10,000 years, but is
likely to erupt again at some point in the future. The Coso Volcanic field can be found in the
southern third of the state. Specifically, it is 20 miles north-northwest of the town
of Ridgecrest, and just to the east of part of US Route 395.
This volcanic field is quite large, and covers an area of approximately 150 square
miles (or 400 square kilometers). It features dozens of geologically recent eruptive vents
which created both cinder cones and lava domes. The Coso Volcanic field began forming about 6
million years ago. This marked the beginning of first of three different phases of activity
in this field (6.0 to 5.3 million years ago). These early eruptions primarily produced low
silica basalt lava flows and cinder cones, but also created a number of lava domes.
The second eruptive period is responsible for the vast majority of magma which has been erupted
by this volcanic field. From 4 to 2.5 million years ago, this period erupted 7.2 cubic miles
of lava. This represents 85% of the total volume of lava produced over the geologic history of this
field. As time progressed, the amount of silica in the lava increased alongside the explosiveness of
eruptions. The lava produced from this region transitioned from mainly basalt to dacite,
and then from dacite to rhyolite. One location that produced a large number of rhyolite
explosive eruptions during this period was the area surrounding the south Haiwee reservoir.
The third eruptive period lasted from 1.1 to 0.04 million years ago. This phase of activity
created 38 lava domes, and 14 basaltic centers. One of the eruptions from this period created
the red hill cinder cone. It formed through a series of strombolian style eruptions which
produced downhill flowing lava flows and ash which mainly fell close to the eruptive vent.
The most recent volcanic eruption from this field created Sugarloaf Mountain.
This mountain is a 9000 by 4500 foot lava dome, which formed through eruptions very
high silica and slow moving lava produced about 41,000 years ago.
It has been claimed that the red hill cinder cone erupted 10,000 years ago, or even sometime
within the last 600 years. However, I could not find any scientific literature to support
either assertion. If we were to just go off of appearances, this cinder cone looks much
older than 10,000 years old. As a result, I rate these series of recent eruption claims as false.
So, what is the hazard posed by this volcanic field?
Although the coso volcanic field has been quiet for the last 41,000 years,
it will almost certainly erupt again. However, it might be a rather long time before the next
eruption. If we look at the eruption frequency of the last 1.1 million years, a new lava flow formed
an average of once every 20,000 years. If a future eruption was to occur,
it would either produce a basaltic cinder cone or rhyolite lava dome.
Both of these formations are created by explosive eruptions. Any future eruption would produce both
slow moving lava flows and plumes of ash. As a result of these hazards, in the most
recent volcano hazard assessment from the US geological survey, the coso volcanic field was
assigned a moderate risk designation. I hope that you enjoyed this video. If
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