On February 22nd of 2023, the alert level was raised at a volcano within the United
States which has produced two of the most powerful volcanic eruptions in all of North
America since the end of the last ice age.
The volcano I am referring to is known as Aniakchak, and looking at its edifice from
satellite you can see that something catastrophic once occurred here.
Whereas there used to be a 7,000 foot high glacier covered stratovolcano there is now
only a massive 6 mile wide wide and slightly more than 2,000 foot deep hole in the ground
referred to as a caldera.
Ever since its two caldera forming eruptions occurred, eruptions within it have been infrequent
but when they do occur have been for the most part highly explosive.
For example, Aniakchak's last eruption occurred around 100 years ago in 1931 and was about
1 third the size of the 1980 eruption of Mount Saint Helens.
Or, its last verified eruption before 1931 occurred in 1531 and was a bit more than twice
the size of its 1931 eruption.
My point is that simply while this volcano has produced smaller eruptions, if its current
period of unrest did result in an eruption, an eruption of a highly explosive magnitude
aka that of a VEI 4 or perhaps higher would be surprisingly likely, meaning an event larger
than what Mount Redoubt produced between 1989 and 1990 would be expected.
With this being said, let us discuss why the alert level was raised at Aniakchak in the
first place.
After all, this was the first time its alert level had been raised since it last erupted
in 1931, so volcanic unrest episodes at this complex could be best distinguished as rare.
The primary reason for this sudden change in alert level via an increase from green
to yellow was numerous earthquakes which were suspected to be volcanic in origin.
Intermittent weak earthquake swarms had been occurring underneath the Aniakchak complex
at a rate of less than once a month since January of 2022.
However, these quakes did not occur in larger than clusters of 5 and occurred at depths
of greater than 10 kilometers or 6 miles with the entire volcano averaging approximately
4 earthquakes a month.
Then, in late October 2022 the number of earthquakes notably increased while also occurring at
around 5 kilometers depth.
Over the next few months more minor swarms occurred which got slightly shallower and
shallower until we reached January 31st of 2023.
On that date, the number of daily earthquakes jumped to more than the number which would
typically occur in a 3 month timespan.
This high rate has continued until the present aka February 24th 2023 and is still ongoing
as of the writing of this video.
Not only are these earthquakes occurring at high rates, including a larger magnitude 3.7
event event on February 17th but they are also occurring at incredibly shallow depths
of less than 5 kilometers or 3 miles.
While a number of events could be causing this unrest, here is my opinion on what might
be occurring.
Like many volcanoes between eruptions, Aniakchak has been most likely receiving a steady yearly
influx of molten rock into its presumably large volume complex magma chamber.
This has slowly been filling one or more of its magma chambers with background seismicity
occurring due to the influx of material.
However, over the past year one of these magma chambers might have become increasingly become
close to full and higher and higher pressurized.
This pressure continued to grow until a notable effect occurred on January 31st 2023 when
dike propagation may have begun at a low intensity as a minor amount of rock at the top of the
magma chamber fractured and small amounts of molten rock intruded into it, creating
the recent earthquake swarms.
On a scale of 0 to 10 on what this volcanic unrest exactly means and how unusual it is,
I have assigned Aniakchak's unrest as of February 23rd of 2023 as a 5 and I want to note that
this does not mean a 50% chance of an eruption as the scale is subjective.
And, thus ends my opinion which could be proven wrong later on.
The good news is that for now other signs of unrest which might be expected with a very
shallow magmatic intrusion have not been detected.
This includes increased gas emissions, ground deformation aka uplift, and elevated geothermal
feature temperatures such as at hot springs and fumaroles which so far have remained largely
unchanged.
If one or more of these things suddenly did change, then we might actually receive confirmation
that a magmatic intrusion is underway, as for now we do not have this confirmation as
magma might not even be involved at all in the current activity which could be best classified
as only minor volcanic unrest.
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