The Taal volcano in the Philippines is a fun geographic oddity of sorts.
Simply put, it contains an island within a lake within an island within a lake within
an island.
Another fun feature can be created through multiple very large explosive volcanic eruptions,
which like shown in the case of the Zavaritski Caldera volcano created a caldera within a
caldera within a caldera.
However, we can go a bit further with this, as shown by a little known Russian volcano
which produced the 9th largest explosive volcanic eruption of the 20th century.
What I am referring to is the Ksudach volcano.
It contains a caldera within a caldera within a caldera within a caldera within a caldera.
That is 5 layers.
And to make this all the more confusing, the youngest caldera which is this one formed
approximately 2200 years ago contains within it another vent.
There, a 1500 meter wide and 200 meter deep circular rim marks the explosion crater which
formed in this volcano's powerful 1907 eruption, which destroyed a preexisting small stratocone.
This eruption produced a sustained 22 kilometer or 72,200 foot high eruption column which
over the course of several hours emplaced 1.75 cubic kilometers of tephra.
Additionally, due to the open calderas to the north of this volcano, pyroclastic flows
escaped through this gap, going on to coat the surface in a layer of ignimbrite to a
distance of 12.8 kilometers or 8 miles.
Yet, as we can see by just how widespread these brownish tan colored deposits are which
mirror the appearance of Novarupta's Valley of 10,000 Smokes, this region has been repeatedly
inundated by longer reaching pyroclastic flows from far more voluminous explosive eruptions.
These pyroclastic flow deposited ignimbrites appears to have been also preferentially emplaced
to the southeast, suggesting that at one point a breached caldera section existed in that
direction.
Thus, Ksudach is one of the most frequently explosive volcanoes on the planet, as its
pyroclastic flows have reached up to 30 kilometers distant and during this volcano's lifespan
it has produced 4 VEI 6 eruptions, 4 VEI 5 eruptions, and 2 VEI 4 eruptions.
The reason this volcano is so explosive is due to its presumably large volume magma chamber,
high magma resupply rate, high gas content magma, and the high silica content lavas it
produces which sometimes include dacite or rhyolite.
The Ksudach volcano is located in the southern portion of Russia's Kamchatka peninsula where
it is 160 kilometers south-southwest of the city of Petropavlovsk-Kamchatsky.
Like many other volcanoes on the Kamchatka peninsula, Ksudach exists due to an offshore
tectonic plate collision where the Pacific Plate is subducting underneath the Okhotsk
Plate.
The melted material from this collision then migrates upwards until it occasionally reaches
the surface and erupts, forming a chain of volcanoes.
The exact age of the Ksudach volcano is unclear but it likely began erupting around 200,000
years ago.
Initially, it erupted at a high rate, which via vulcanian explosions produced overlapping
layers of lava and ash.
Over the timespan of 38,000 years, this primarily andesitic volcano was built into a 1500 meter
high gray colored stratovolcano.
However, at the end of this phase, eruptions became more silica rich and more explosive,
while also occurring at a lower frequency.
This allowed for a powerful explosive eruption to occur which destroyed the central part
of the volcano, causing it to collapse into a caldera in an event which ejected 10 cubic
kilometers of tephra and formed the first of what would be 6 calderas.
Dacite lava dome forming eruptions occurred within this caldera, eventually filling a
section of it.
Then, 40,000 years ago an eruption similar in magnitude to the 1883 eruption of Krakatau
occurred, forming the outer 9.5 kilometer wide caldera and depositing ignimbrite up
to 30 kilometers distant.
After this, 35,000 years ago a 6 kilometer wide caldera was formed via a VEI 6 eruption.
Inbetween each of these eruptions some smaller eruptions occurred, forming maars, small stratocones,
and lava domes.
The fourth caldera formed in 7806 BCE, representing an eruption of the same size as Ksudach's
1907 eruption.
The fifth caldera formed in two powerful eruptions in 5200 BCE and 4900 BCE.
Finally, the most recent caldera from this complex fomed in 240 CE, creating a 7 kilometer
long caldera which is filled with the two modern crater lakes.
Since then, several eruptions built the Stubel stratocone only for it to be destroyed in
its 1907 eruption.
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