On March 8th 2023, the alert level was raised at a volcano within the United States which
has produced two voluminous flank collapse landslides which destroyed much of an existing
volcanic cone during its lifetime and has also not erupted in more than 100 years.
Although such a repeat landslide is in my opinion out of the question for the moment,
the volcano I am talking about is in danger of possibly producing a volcanic eruption
as it is producing its most activity since it last erupted in 1914.
Although, a new eruption is not guaranteed.
This is occurring at the volcano known as Tanaga, which is the westernmost of two active
volcanoes on Tanaga Island in the Aleutian Island chain.
It has become the fifth volcano to be at a yellow alert level in Alaska at the same time,
with the other volcanoes at this level currently being the massive caldera volcano Aniakchak,
Trident Volcano in Katmai National Park, Semisopochnoi with its large caldera, and Takawangha which
is on the same island Tanaga is!
In addition to these 5 volcanoes, 1 volcano aka Great Sitkin is erupting in Alaska, a
magmatic intrusion is ongoing underneath the Edgecumbe volcano northwest of Sitka on Kruzof
Island, and three volcanoes in Katmai National park are producing an elevated rate of earthquakes.
If you think this is a lot to keep track of, you are not alone.
Thus, to help my audience understand the intensity of the volcanic unrest in my opinion at each
of these 9 volcanoes in Alaska which are not erupting but are showing signs of unrest,
I have rated them on an opinion based 0 to 10 volcanic unrest intensity scale.
I am placing Tanaga in the middle of the pack in Alaska at a similar albeit less intense
earthquake swarm occurred approximately 18 years ago in 2005, which suggests that quake
swarms of a similar magnitude recur at about once every 15 or so years.
This is in comparison to Trident which probably has a magmatic intrusion ongoing underneath
its edifice and is much more likely to unexpectedly erupt than its counterparts, although each
item on the aforementioned list could very well all end up not erupting.
The Tanaga volcano is located in the far western section of the Aleutian Island chain, where
it is 65 miles west of the city of Adak.
Since Takawangha and Tanaga are both simultaneously at a raised alert level on the same island
where their centers are a mere 5 miles apart, there might be some related igneous intrusion
at depth.
The earthquake swarm at the Takawangha volcano began on November 17th on the eastern section
of the volcano at depths of 2 to 4 miles below sea level and although it has waned slightly
over time, it is still at a raised alert level for its 111th consecutive day.
On the other hand, the earthquake swarm at Tanaga began on March 7th 2023 at 1:30 pm
local time in Alaska, largely occurring at 2 to 8 miles depth underneath the center of
the Tanaga volcanic cone.
Over the next several hours earthquake frequency slowly increased until at 8:45 pm 2 to 3 earthquakes
were occurring every minute, the largest of which was a magnitude 2.5.
In my opinion, this is probably occurring due to some form of a deep magmatic intrusion
which is causing changes in the hydrothermal systems of 2 closely spaced volcanoes, causing
groundwater to move and expand.
Thus, while a magmatic eruption does not seem imminently likely, a possible phreatic eruption
caused by the flashing of water to steam, building in pressure, and an eventual explosion
occurring does seem possible especially at Tanaga.
As a brief overview, Tanaga is a volcanic complex with five separate peaks consisting
of various volcanic cones and lava domes which have been intermittently active during the
125,000 year lifespan of this volcano.
Two large collapse scars are visible which were generated by lateral eruptions 120,000
years ago that destroyed an ancestral volcanic cone and 3,000 years ago which destroyed the
Sajaka One volcanic cone.
The Sajaka Two volcanic cone was completely built by semi frequent eruptions of about
once a century since then via both blocky flows of basalt and andesite lava, hence its
red and gray coloration.
Recent eruptions have occurred at both the Sajaka Two and Tanaga Cones, and based on
the current location of seismicity if an eruption was to occur it appears most likely to begin
at the Tanaga Cone.
Although such an eruption would likely have an explosive component to it, the island the
volcano is on is unpopulated, and in my opinion, the only effect an eruption` might bring to
the city of Adak is a light dusting of ashfall.
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