In the last week, the number of erupting volcanoes within the nation of Japan jumped from 3 to
5.
This means that apart from the 9 actively erupting volcanoes in Indonesia, Japan has
the most erupting volcanoes of any country at the present.
There, on January 25th of 2023, the uninhabited island volcano of Nishinoshima erupted, ejecting
minor amounts of ash in an eruption which began after several weeks of heightened gas
emissions from the volcano.
The following day on January 26th of 2023, another primarily submarine volcano which
had not erupted since 1988 and is known as the Bayonnaise Rocks also erupted, producing
a distinctive blue hue in the ocean which is typical of submarine volcanic eruptions.
Although these two eruptions are unrelated, aka one did not cause the other to erupt,
they share a number of similar features.
For example, both have produced large or very large explosive eruptions in the past as evidenced
by their calderas.
While the caldera at the Nishinoshima volcano is approximately 1.5 kilometers wide, at the
Bayonnaise Rocks volcano the caldera is 9.6 kilometers wide.
The age of this larger caldera is unclear, but given the topography of the oceanfloor,
there likely was once an island which existed before it was destroyed in a catastrophic
eruption.
Assuming the caldera formed in a single eruption, it may have formed in a catastrophic high
end VEI 6 or low end VEI 7 explosive eruption, which likely caused a volcanic winter of sorts.
Since this presumably large eruption occurred, at least three post caldera vents formed.
Although the exact order in which they formed is unclear, this complex has created a series
of jagged rocks known as the Bayonnaise Rocks which barely scrape above sea level, the resurgent
cone of Takane Sho within the caldera, and the dacite composition lava dome known as
Myojinsho.
Just like during many other prior historical eruptions, Myojinsho has been the center of
eruptive activity, and is the vent which is erupting right now at a depth of more than
100 meters.
Despite being fairly remote and uninhabited, this volcano sadly caused one of Japan's deadliest
volcanic eruptions of the 20th century.
What happened?
A research ship passed in close proximity to the volcano which was still intermittently
erupting in 1952.
A powerful series of surtseyan eruptions then occurred, which sunk the ship with all crew
all board.
However, explosions from this volcano are not the only volcanic hazard it poses.
Ships can also be potentially sunk if they stray too close to the volcano even if it
is not actively erupting.
How?
Like many volcanoes, submarine volcanoes regularly produce large quantities of various gasses,
ranging from carbon dioxide, sulfur dioxide, and other materials.
These gasses are all less dense then water so they rise to the surface of the ocean.
While this process is occurring, the density of water which contains the rising gas is
lowered, which if ships pass over it can cause them to sink.
As a result of this eruption, the Japanese Meteorological Agency raised the alert level
of the Bayonnaise Rocks from white to orange.
In my opinion, I recommend keeping ships at least 10 kilometers or a little more than
6 miles away from the actively erupting vent aka Myonjinsho at the Bayonnaise Rocks volcano
to decrease the risk of a similar disaster occurring again.
With this being said, it is also logical to keep several kilometers away from the Bayonnaise
Rocks vent as that barely strays above sealevel and thus might be difficult for ships to spot.
To the south, the famed Nishinoshima volcano also erupted beginning on January 25th.
Although technically having an explosive component to it, the eruption was quite negligible as
it produced only minor amounts of ash.
Nishinoshima is a primarily submarine volcano whose island greatly expanded during the 21st
century through a combination of effusive and explosive eruptions.
Although both volcanoes have the potential to produce larger explosive eruptions, it
does not appear that either complex will produce a large explosive eruption given current observations.
I also recommend keeping at least a 10 kilometer exclusion zone around Nishinoshima.
Thanks for watching!
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