When people think of geologic hazards in California, they tend to not think
about volcanoes. Yet, alongside earthquakes, volcanoes also pose a major threat in the state.
California has 9 active volcanoes which have erupted in the last 10,000 years,
and an additional 3 volcanoes are not currently active but could erupt in the future. This video
will focus on the volcano responsible for the most recent eruption in the state of California,
Lassen Peak. The photo shown on screen displays one of its eruptions in 1917.
Lassen Peak is part of a large volcanic complex which is the southernmost volcano
in the Cascade range. It can be found in the northern third of California, and is 10.5
miles north-northeast of the town of Mineral. I need to distinguish between Lassen Peak and
Lassen Volcanic center. Lassen peak is an individual lava dome volcano which
is responsible for the most recent eruption. Lassen volcanic center
encompasses all of the volcanoes in the region. Within the last 825,000 years, there have been
hundreds of explosive eruptions from various vents in the Lassen Volcanic center. These eruptions
came from numerous vents over a region of 200 square miles. These vents produced several types
of volcanoes from differing compositions of lava. It produced a large stratovolcano which has now
eroded away, several cinder cones, and a series of large lava domes. Of these, Lassen Peak is
not a stratovolcano but rather a large lava dome. For the vast majority of the last 25,000 years,
there was no volcanic activity in the region. This changed with a series of 6
eruptions in 3 different areas of lassen volcanic center, which all occured in the last 1500 years.
The first series of eruptions formed a new series of lava domes, which are referred to as Chaos
Crags. The eruptions which formed these occured between 800 and 980 AD, with a potential more
recent 1650 eruption. The second recent eruption occured in a different region of the volcanic
center. It formed a large cinder cone in 1666. Of all of the recent eruptions from this region,
the most famous one occured at lassen peak. After thousands of years of dormancy,
Lassen Peak erupted on May 30th, 1914. The initial eruption occurred when magma close to the surface
caused nearby ice and groundwater to flash to steam and explode. For about a year, several small
explosions continued to occur at Lassen Peak. Then, in May of 1915, lava began oozing from a
vent on the surface. This lava contained a high amount of silicion and as a result did not move
very quickly. The slow build up of lava caused pressure to build beneath the surface. Then,
on May 19th, a large steam explosion fragmented the still hot lava that had filled Lassen’s summit
crater during the previous week. This blasted out a new crater at the volcano’s summit.
This created a large and dangerous mudflow of volcanic materials, which is known as a lahar.
This lahar rushed 7 miles down Lost Creek, where it released huge volumes of water, flooding
the lower Hat Creek Valley. The avalanche, lahars, and floods produced by this explosion
uprooted and carried away 100-foot-tall trees with ease and destroyed six ranch houses.
Three days later, the volcano erupted again, but this time in the largest explosion of the series.
This explosion sent a cloud of ash high into the air, which reached upwards of 30,000 ft.
Additionally, the eruption created a high-speed avalanche of hot ash, pumice, rock fragments,
and gas, called a pyroclastic flow. Overall, the eruptions in May of 1915 destroyed a 3 square
miles area, which was subsequently referred to as the devestated area. Lassen Peak continued to
erupt in much smaller explosions until June 29th, 1917 when the eruption ended. The overall size
of this eruption series was quite large, but was about 140 times smaller in terms of explosiveness
than the 1980 eruption of mount saint helens. Today, Lassen Peak sleeps again, but active
steam vents, hot springs, and bubbling mudpots are still found within Lassen Volcanic National Park.
As a result of this volcano still being geologically active, it was rated as a
"very high threat" volcano in California. It was rated as a high threat volcano due
to volcano's explosive nature, and deadly lahars which is has produced. A future eruption could
endanger the nearby towns of Burney, Mineral, or Chester. A future eruption is certain,
but we do not know when it will occur. The next eruption from this volcanic center could occur
hundreds or even thousands of years in the future. I hope that you enjoyed this video! If you would
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