On March 9th 2023, the alert level was simultaneously raised at 2 volcanoes which are a mere 5 miles
apart from one another in Alaska.
This occurred at both the Tanaga and Takawangha volcanoes, as their alert levels were increased
from yellow to orange due to a swarm of 464 earthquakes in the last week which have seemingly
got progressively shallower over time.
These earthquakes have since March 7th increased in abundance, magnitude, and decreased in
depth until many of them occurred right beneath the summit Tanaga Cone.
And on March 8th, harmonic tremor was also possibly detected underneath Tanaga, which
means a volcanic eruption is now possibly imminent at its edifice and due to a level
of uncertainty an eruption could also possibly occur at Takawangha.
To understand why the possible detection of harmonic tremor is so important, I present
this quote from a U.S. Geological Survey webpage; "Harmonic tremor, or volcanic tremor, is the
name for the continuous, rhythmic seismic energy associated with underground magma movement."
Supporting this assertion that magma is involved is that there appears to be ground deformation
centered 2.5 miles south of Tanaga volcano's highest point, which has seemingly pushed
up a section of ground by about an inch.
While seemingly insignificant, numbers in this range tend to not occur unless magma
is directly involved.
While no one lives on Tanaga island, two things could be reasonably effected if an explosive
volcanic eruption were to occur at one or more of these volcanoes.
These are northern Pacific air traffic which could be temporarily grounded over a region
over a wide swath of the Aleutians or more depending on an eruption size, and the city
of Adak.
Before I explain what Adak could experience, I will outline my personal opinion based hypothesis
about what is occurring underneath the Tanaga and Takawangha volcanoes.`
An elevated rate of earthquakes began occurring at the Takawangha volcano all the way back
in November of 2022, but I do not believe this was the start of the magmatic intrusion.
Rather, in my opinion a magmatic intrusion had probably been ongoing for at least a week
beforehand but was intruding at such a slow rate that it stayed within the so-called ductile
region of the crust where earthquakes are incredibly rare and infrequent as it can largely
absorb strain placed into it.
Thus, when the intrusion paused going upwards, material kept flowing into it, causing it
to branch off into a path of least resistance via what is termed a sill.
This sill then reached the magma chamber of Takawangha and began slowly refilling it,
which created the first detectable increase in earthquakes in November of 2022.
After only minimal earthquakes for a few months, a new greater input of magma occurred on March
7th 2023 which finally caused magma to flow into Tanaga's magma chamber.
This generated hundreds of earthquakes, and in addition may have generated another sill
intrusion which may be heating a section of Takawangha's water table underneath a highly
hydrothermally altered region.
In other words, while the Tanaga cone of Tanaga could produce a magmatic eruption, the western
section of the Takawangha volcano or the valley between the two volcanoes could be the eventual
site of a phreatic eruption.
Due to this uncertainty is why the alert levels were raised at both volcanoes.
The small city of Adak is located 65 miles east of the Tanaga volcano, and in all likelihood
if an explosive eruption was to occur from one or both of the aforementioned volcanoes
the only effects it might give the small city are a light dusting of ash since it would
be most likely to blow to the east.
With this being said, there is a theoretically possible but highly unlikely worst case scenario
to be aware of.
The area I have outlined on screen is highly hydrothermally altered and prone to minor
edifice collapse as shown by one landslide the area already produced possibly at some
point during the last 20,000 years.
If a phreatic eruption occurred in this area there is a chance it could create another
large landslide.
During a highly unlikely worst case scenario, part of this landslide could reach the ocean,
generating a minor tsunami.
However, if you live in Adak, in my opinion, I would not worry about this occurring as
it represents a highly unlikely worst case scenario which will not happen.
Just like I could theoretically get struck by a meteorite today, a lot of highly unlikely
events would have to occur first before the generation of a tsunami could occur due to
a volcanic landslide.
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