On June 17th of 2023, the number of earthquakes centered underneath a populated volcanic island
south of the island of Kyushu began to increase to abnormal levels.
The island in question goes by the name of Kuchinoerabujima, which also is the name of
its volcano which has erupted on 16 separate occasions since 1841.
Eruptions from this volcano in the last 20,000 years have been universally explosive, with
some abnormally large events that registered in on the volcanic explosivity index as a
4, causing as much as 4 meters thick of ash and pyroclastic flow deposits to fall on sections
of the island.
One such VEI 4 eruption in 1933 to early 1934 wiped out a village on the island, causing
one third of the island's populations to be casualties.
Luckily, the vast majority of eruptions Kuchinoerabujima produces are 2 orders of magnitude less explosive
than its 1933 to 1934 eruption, sending thick plumes of ash to a height of 2 to 8 kilometers
into the sky, alongside ejecting bombs of lava, and often generating small to moderate
length pyroclastic flows.
While earthquake levels at presumably shallow depths of less than a kilometer began increasing
on June 17th, by June 26th, a total of 100 volcano tectonic earthquakes had occurred.
Since the rate of earthquakes kept increasing, Kuchinoerabujima's alert level was raised
from 1 to 2 at 4:40 am local time on June 26th.
Yet, only 38 hours later, its alert level was raised again from 2 to 3, translating
to an increase from yellow to orange, which is now the same alert level as the currently
erupting Sakurajima volcano.
This second increase was triggered by 50 earthquakes occurring in the last 24 hours, with the possibility
that this rate might further increase.
Alongside this, a 100 meter high white gas plume began rising above one of the three
main craters on the island, known as Shindake Crater.
This is an important development, as it suggests a change in the volcano's shallow hydrothermal
system, which is located at a mere depth of 100 meters.
If this is experiencing increased heat and thus producing more gas, it could indicate
a sufficient pressure and temperature exists for water to flash to steam and explode, creating
the potential for a phreatic volcanic eruption to occur.
Beneath this hydrothermal system, is a shallow storage area magma can pool at during and
before an eruption at a depth of around 400 to 700 meters.
Thus, if volcano tectonic earthquakes are highly clustered at those depths, it suggests
that magma is on the move.
But, the exact depths of these quakes has not yet been published.
As a result of this uncertainty combined with the increased number of earthquakes, a 2 kilometer
exclusion zone has been declared in all directions surrounding the volcano.
Although there are not yet signs of an imminent eruption right now, phreatic eruptions are
incredibly difficult, sometimes impossible to predict so there is a chance that a new
volcanic eruption could occur with little or no warning.
The two kilometer exclusion zone represents the approximate maximum radius an unexpected
volcanic explosion could throw bombs of molten lava or ballistic blocks given a small to
medium sized event.
If a hypothetical small to medium sized eruption were to occur, the western flank of the Shindake
crater would be most at risk.
As, while pyroclastic flows can theoretically go in any direction, they tend to travel downhill
and are funneled into low points in regional topography.
Shindake's crater has a 30 meter or 98 foot high rim on its eastern side but its western
side has a breached crater rim which is lower than the center of the crater where a hypothetical
eruption would be most likely to begin.
Longer pyroclastic flows would be most likely to travel along one or more of the two drainages,
but could theoretically traverse higher spots to the west or even go beyond the eastern
crater rim, heading towards a drainage to the east.
Typical eruptions at Kuchinoerabujima are phreatomagmatic or vulcanian, with both commonly
ejecting bombs of lava and creating an orange glow of andesite lava at the active crater.
While half of this volcano's historical eruptions last less than 24 hours, its eruptions have
been documented as lasting up to approximately 4 months in length.
While Kuchinoerabujima during its 500,000 year lifespan has created a multitude of volcanic
craters, only 1 has produced every single eruption in the last 150 years, Shindake Crater.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below.
Additionally, I would like to thank this channel's patrons on Patreon and channel members on
YouTube!