The highly scenic state of Alaska is geologically well known for its many active and potentially
active volcanoes.
This includes well known volcanoes which have erupted since the end of the last ice age
such as Mount Redoubt and the Hayes volcano.
It also includes the world's smallest volcano known as Buzzard Creek, while also including
the volcano which produced the largest explosive volcanic eruption of the 20th century; Novarupta.
Yet, you might notice that none of the volcanoes I just mentioned are located in the Alaskan
Panhandle.
And it is true that this area is not as volcanically active as other parts of Alaska.
Yet, as shown by Mount Edgecumbe's ongoing magmatic intrusion and the fact that it last
erupted 800 years ago, this section of the state can produce volcanic eruptions.
Yet, the Alaska Panhandle also has three other potentially active volcanoes per the U.S.
Geological Survey which are largely forgotten by the public.
One of these forgotten volcanoes is located 14 miles east-northeast of the city of Ketchikan,
being known as Behm Canal-Rudyerd Bay.
Unlike, Mount Edgecumbe, this volcanic complex does not consist of a towering stratovolcano
or a large caldera.
Rather, it consists of a series of small volume scattered lava flows which contrast in color
with the surrounding landscape, with at least one of these flows having erupted at some
point during the last 10,000 years.
Here, you can find occasional layers of black ash, recent lava flow samples, and occasional
basaltic columns in the shapes of hexagons.
But, there are also three larger noticeable eruptive centers across this 352 square mile
volcanic field.
For example, the highly vertical vent known as New Eddystone Rock formed during a single
eruption 14,000 years ago when the sea level was much lower.
Or, adjacent to Princess Bay there is a cinder cone which erupted incredibly slow moving
up to 500 foot tall viscous lava flows of a likely andesite or trachyandesite composition.
However, the most prominent and debatably spectacular vent in this forgotten volcanic
complex is a near vertical 1200 foot tall tuff cone known as Painted Peak.
You might be wondering why this volcano exists in the first place as to the offshore of this
section of the Alaskan Panhandle, there is a plate boundary but it is not creating any
subduction.
Instead, the plate boundary forms a strike slip boundary somewhat similar to the San
Andreas Fault.
Yet, this plate boundary is not the cause of the Behm Canal volcano.
Instead, Behm Canal is part of a chain of volcanoes 700 miles in length which exist
for a different reason, being known as the Northern Cordiellan Volcanic Province.
Here, the crust is at a slow rate spreading apart to the east and west.
This allows for material in the mantle to intrude into the crust and erupt via a path
of least resistance, forming a chain of volcanoes, with the last eruption in this province occurred
during 1904 where a lava flow from the Iskut Unuk River Cones crossed the international
border from Canada into Alaska.
It is thus no coincidence that many of the lava flows produced by this volcanic field
are located along low points or areas `adjacent to or on regional fault lines.
Although the age of the scattered vents are largely unclear, it is pretty safe to say
that they all formed in the last 50,000 years.
Painted Peak perhaps formed 30,000 years ago based on my own estimate when a body of intruding
magma interacted with an abundant shallow water table, causing it to flash to steam
and produce repeated explosions.
This created an abundance of ash deposits in the shape of a ring.
These explosions repeated for perhaps several months until the tuff cone had grown to a
height of more than 1,000 feet and was breached to the southeast.
Later, the Princess Bay Cone erupted in a slightly explosive manner alongside New Eddystone
Rock approximately 14,000 years ago.
Then between 12,000 and 8,000 years ago a series of eruptions were triggered by the
fast melting of previously thick regional glaciers which caused the crust to rebound
and for magma to intrude into weak points.
Although the date of the last eruption in Behm Canal is unclear, it produced a viscous
lava flow on the eastern end of Lake Grace.
If this volcano does erupt again, which for now seems unlikely for the next 1,000 years
since the complex appears to erupt cyclically at the end of glacial periods, the site of
the initial vent will largely determine how explosive the eruption will be.
A vent erupting into a body of water will produce an explosive eruption while an eruption
on land will most liklely be purely effusive like witnessed at the Fagradalsfjall volcano
in Iceland during 2021 and 2022.
However, in my opinion no one lives in a close enough proximity to the volcanic field to
be heavily effected by any future eruption, if one were to ever occur.
As a result of these hazards, the U.S. Geological Survey designated Behm Canal-Rudyerd Bay as
a very low threat volcano.
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