The famed Mount Fuji in Japan is widely considered to be one of the world's most symmetrical
active volcanoes.
Yet, Mount Fuji has a major problem that prevents it from being perfectly symmetrical, with
the culprit being its most recent eruption.
As between December of 1707 and February of 1808, a series of powerful explosion carved
out two gaping craters on its southeast flank, the largest of which measures 1500 meters
long, 1000 meters wide, and 125 meters deep.
Because of this VEI 5 eruption which occurred more than 300 years ago, Fuji cannot be considered
the world's most symmetrical volcano.
Yet, in Russia, there is a volcano that few know about outside of Russia, a volcano with
a near perfect snow covered symmetrical profile.
This volcano is known as Klyuchevskoy, with this stratovolcano rising to a truly impressive
height of 4,755 meters or 15,600 feet above sea level.
With a base at only 229 meters or 750 feet above sea level, you might have guessed that
Klyuchevskoy could have only grown to such an impressive height over many hundreds of
thousands of years.
Yet, what if I were to tell you that this 15 kilometer wide volcano and every single
one of its flank vents all completely formed in the last 7,000 years?
While this might seem like an absurd claim, it is in fact true.
As, for every second during this volcano's lifespan, it has on average, including times
when it is not erupting along with times it is erupting, emitted lava at a rate of 1.22
cubic meters per second.
For context, this rate is absurdly high, meaning that Klyuchevskoy during this 7,000 year long
period Klyuchevskoy had erupted at a higher rate than the combination of Mount Merapi
in Indonesia, Mount Etna in Italy, and Mount Stromboli in Italy.
As a result, Klyuchevskoy has been near continuously erupting through its entire lifespan, and
is even erupting right now, at least as of the writing of this video.
In the last 80 years, this volcano hasn't gone longer than a 24 month period without
some form of an eruption occurring, and some of these eruptions last for several years,
although most last for only 2 to 3 months.
So, what exactly is the secret to why Klyuchevskoy is so tall and symmetrical?
The answer involves three factors.
The most important of these factors involves the eruption of basaltic lava and occasional
basaltic andesite lava, as both of these lava varieties have a fairly low viscosity.
This allows the flows to quickly run down the volcano without stalling in place unlike
what often occurs in several hundred foot high blocky andesite lava flows at a standard
stratovolcano.
Because of how fluid the lava is, it can quickly divert to areas of lower topography if there
is an obstruction of higher elevation on its slope, allowing for molten rock to fill the
voids and create a fairly symmetrical volcanic cone.
You might ask, "but wait, shield volcanoes like Mauna Loa also primarily erupt basalt.
So, why is Klyuchevskoy a stratovolcano?"
The answer comes down to gas content.
Mauna Loa erupts basaltic lava with an incredibly low gas content, while Klyuchevskoy erupts
basalt with a fairly moderate gas content.
Because of this, much of Klyuchevskoy is constructed from ashfall and pyroclastic flow deposits,
allowing for steep near 45 degree sloped topography to form.
Second, Klyuchevskoy's eruptions are almost always strombolian in nature, involving intermittent
ejection of bombs of lava in a several hundred meter radius from a vent, often occurring
at its summit alongside lava flows, but sometimes instead occurring at flank cinder cones.
Vulcanian eruptions with pyroclastic flows have also occurred, along with sub-plinian
and plinian eruptions, but current records show that these never exceeded a moderate
VEI 4 rating.
This lack of voluminous explosive eruptions has prevented Klyuchevskoy from producing
a caldera collapse and partially helped prevent a major flank collapse from occurring.
And third, the subduction of the Pacific Plate underneath the Okhotsk Plate has for 300,000
years kept this specific region of Kamchatka volcanically active, with 7` volcanoes forming
during this timespan, 4 of which are still active.
Among this volcanic cluster, the highest rate of magma intruding into the crust simply goes
underneath the Klyuchevskoy volcano.
Interestingly, Klyuchevskoy has produced dozens of cinder cones during its 7,000 year lifespan,
but all of these have seemingly occurred in a 120 degree arc ranging from southeast to
north-northeast.
One of these cinder cones in 1938 produced a lava flow from a vent 21 kilometers northeast
of Klyuchevskoy's summit, sending a lava flow to within 6 kilometers of the town of Klyuchi.
In all likelihood, Klyuchevskoy will probably continue to erupt at a high rate in the next
few decades, contnuing to grow in height, with its latest eruption having begun in June
of 2023, and with more than 60 distinct eruptions occurring in the last century.
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