The state of California has several volcanoes which are classified as active.
Of these, the most recent volcanic eruption occured from Lassen Peak in 1917.
However, Lassen Peak is not the only volcano within california which could erupt in the
near future.
In northern california, there is a much more active volcano which is rated as the most
dangerous volcano within the state.
The volcano I am referring to is Mount Shasta, which has erupted more than 20 times in the
last 10,000 years.
For this video, we are defining an active volcano as any volcano or volcanic field which
has erupted in the last 10,000 years.
Within California, the vast majority of active volcanoes within the state are lava domes,
such as Lassen Peak or Mammoth Mountain.
These volcanoes tend to have steep slopes and look roughly like the upper half of a
sphere.
Mount Shasta is unique among the active volcanoes within California, as it is not a lava dome.
Rather, it is a stratovolcano, as indicated by its steep slopes and massive size.
Stratovolcanoes contain alternating layers of both cooled lava, and ash.
Mount Shasta has a very long geologic and eruptive history.
About 360,000 years ago, a different stratovolcano stood where Mount Shasta is today.
In an instant, a the volcano experienced a catastrophic collapse which destroyed this
mountain.
The exact mechanism is unclear but odds are that an eruption far greater than the explosive
eruption of mount saint helens took place.
This collapsed mountain formed the base from which the future mount shasta grew.
The modern Mount Shasta did start growing until 250,000 years ago.
Since then, the volcano has grown to be the tallest active volcano within California.
Today, it measures is 14,180 ft or 4,322 meters tall.
To understand why the volcano is so tall, it is easiest to think of the geology of the
mountain as not one volcano, but rather 4 overlapping cone shaped volcanoes.
At various points in the geologic history of the mountain, lava erupted from a different
dominant cone in the mountain.
On screen is a graphic which shows which portion of Mount Shasta was formed by one of the 4
lava cones.
Of these cones, two of them are rather notable.
The most explosive of the 21 eruptions in the last 10,000 years occured at the cone
known as Shastina.
The Shastina cone is quite distinguishable in photos of the mountain, as it forms quite
a distinctive peak on the western side of the mountain.
This area last erupted about 9500 years ago.
The second notable cone is not on the volcano's summit.
About 9400 years ago, an eruption series created an entirely different lava dome 8.5 miles
west of Mount Shasta's center.
This lava dome complex is known as Black Butte, and can be found between the towns of Mount
Shasta and Weed.
The presence of this lava dome indicates that not all eruptions occur at its summit, and
can present a much wider regional hazard.
(pause 5 seconds) So, what is the hazard posed by Mount Shasta?
To answer this question, we must first look at how often this volcano erupts.
During the last 10,000 years, Mount Shasta has erupted an average of every 800 years.
The last eruption from this volcano was in 1250 AD, but this doesn't neccessarily mean
we are overdue.
Research indicates that the volcano erupts episodically with ten or more eruptions occurring
in short (500-2,000 year) time periods separated by long intervals (3,000-5,000 years) with
few or no eruptions.
As of 2020, the volcano is rather quiet.
The only obvious sign of this volcano's active status is the fumaroles which can be found
around its summit.
If Mount Shasta was to erupt again, it would most likely produce an explosive eruption.
Such an eruption would produce pyroclastic flows, lava bombs, and deadly lahars.
A lahar is almost certain due to the frequent presence of snow on its summit.
A future eruption would melt of this snow and the sheer mass of melting water would
carry anything in its path with it.
Evidence of previous lahar flows have been found up to 30 miles away from the center
of the volcano.
Any future eruption would put thousands of people at risk.
As a result of this hazard, the US geological survey designated Mount Shasta as a very high
threat volcano.
This is the highest risk category.
Within california, Mount Shasta is rated at the highest risk volcano within the state.
I hope that you enjoyed this video.
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