In the last two weeks, the activity at a volcano best known for being somewhat of a Russian
equivalent of Mount Saint Helens began intensifying its eruptive activity.
As the primary lava dome of the erupting Bezymianny volcano grew larger and larger due to an influx
of new molten rock in the lava dome core, it became increasingly unstable.
This resulted in periodic small collapses of the dome, creating an ever increasing number
of pyroclastic flows and ash emissions.
Then, on April 7th 2023 at around 5:38 pm local time, a far more powerful explosion
occurred.
As a plume of ash shot high into the atmosphere, superheated and energetic gas currents were
released from the lava dome as it underwent a small scale collapse in what is known as
a pyroclastic flow.
These pyroclastic flows traveled at least 5 kilometers to the east-southeast based on
the continuing thermal signatures the superheated deposits gave off as they cooled.
The associated cloud of ash rose to a height of 12.8 kilometers or 42,000 feet while drifting
to the east-southeast.
The vast majority of this eruption was over within 15 minutes as eruptive activity drastically
dropped thereafter, producing far smaller and intermittent explosions.
What had just occurred was the largest volcanic eruption Bezymianny had produced since May
28th of 2022, when a similar sequence generated an approximately 15 kilometer high eruption
plume.
Both of these eruptive sequences would best be classified as Merapi type vulcanian eruptions,
where a partial lava dome collapse occurs, causing highly pressurized gas to be released
and fall back to the ground as a superheated pyroclastic flow with all of this occurring
in association with a vulcanian explosion.
This vulcanian eruption left behind a discernable layer of ash visible from satellite which
covered an area of several thousand square kilometers and caused the associated eruption
plume to drift at least 2,000 kilometers to the east.
As a result, the alert level of Bezymianny was raised from orange to red by KVERT.
However, less than 24 hours later it was lowered back from red to orange as the highly explosive
paroxysm ended, shifting back to moderately explosive activity.
For context, the Bezymianny volcano is located in east central Kamchatka where it is 350
kilometers north northeast of Petropavlovsk Kamchatskiy.
Bezymianny is located in a highly volcanically active section of Kamchatka where in about
the same area as New York City are 5 active volcanoes 4 of which have produced historical
eruptions in addition to 2 dormant volcanoes.
Bezymianny is the smallest and youngest volcano of this group, as its modern volcanic cone
only began forming 5,000 years ago.
Before 1955, Bezymianny was incorrectly thought to be an extinct volcano.
This is how it received its name, which roughly translates to "unnamed", indicating the very
low threat local scientists once thought this volcano posed.
Then, after around 1000 years of dormancy, the volcano awoke on October 22nd of 1955.
Over the next several months, a large body of magma intruded into its southeastern flank,
destabilizing the entire edifice.
Then, on March 30th, 1956, 0.5 cubic kilometers of the volcano dramatically collapsed to the
southeast, sending a massive landslide and pyroclastic flows up to 23 kilometers distant.
The associated eruption plume subsequently rose to a height of 45 kilometers, representing
the peak of this VEI 5 eruption.
This plinian eruption was essentially what Mount Saint Helens would produce 24 years
later albeit with some minor differences.
Bezymianny's 1956 eruption and collapse thus left behind a large horseshoe shaped collapse
scar in addition to causing the volcano to lose 185 meters in height.
Since this major eruption in 1956, Bezymianny has continued to almost continuously erupt
albeit with some pauses some of which lasted more than a year.
Most of its eruptive activity during this timespan has consisted of vulcanian explosions
and small lava dome collapses.
These both occurred from its ever growing lava dome which has largely filled in a section
of the existing collapse scar.
However, since material from this lava dome will continue to be funneled downslope in
the direction of the collapse scar, it is prone to producing more large ash plumes from
small to moderate volume lava dome collapses.
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