The vast state of Alaska contains 86 active volcanoes, of which three are erupting right
now.
While many of these volcanoes, such as Mount Redoubt are well known, others are not.
One of these lesser known volcanoes lied completely undiscovered until 1979.
Yet, the volcano in question produced a large eruption nearly identical to the 1980 eruption
of Mount Saint Helens approximately 2800 years ago.
The volcano I am referring to is known as Yantarni, which is a fascinating low prominence
volcano.
The Yantarni volcano can be found in southwest Alaska on the sparsely populated Alaskan peninsula
where it is 40 miles or 65 kilometers south of the town of Pilot Point.
If I turn off overlays of the volcano, it becomes quite easy to see why it was unknown
to science until its discovery in 1979 since it does not greatly stand out in the overall
landscape.
Also, it is located between two larger volcanoes; Aniakchak to the west and Chiginagak to the
northeast.
In total, this volcano contains a meager 3.5 cubic kilometers of material, a third of which
was produced in a single eruption.
Its summit consists of a small stratocone which is breached to the east upon which a
2500 foot wide lava dome is present.
The Yantarni volcano began forming 460,000 years ago when a volume of basaltic andesite
lava erupted onto the surface at the site of a high angle fault.
This fault was the site of prior volcanic activity several million years ago, and thus
represented a path of least resistance for fresh molten rock.
At the time, the glacially carved valleys were already present, so the freshly erupted
lava began depositing on the western edge of an already elevated slope.
However, since this lava was rather viscous it did not quickly travel downslope.
Rather, it remained there and slowly began building a small volcanic cone.
This cone was built due to intermittent ejections of ash which occurred through vulcanian explosions,
occasionally generating short distance pyroclastic flows.
Over the span of several years, low level eruptive activity built a 330 foot or 100
meter tall volcanic cone.
Then, the volcano became dormant for 50,000 years.
When it erupted again, the lava it produced was slightly more viscous as it contained
a higher silica content.
Once again, several small scale eruptions increased the overall height of the volcanic
cone, building it to its modern height.
Over the next 400,000 years, the record of eruptive activity is unclear.
Small scale effusive eruptions likely continued intermittently, but more importantly, a body
of magma underlying the volcano began altering the rocks on its eastern flank, causing the
area to change to yellow and white colors.
Fumaroles continued deforming the edifice, until a critical point was reached.
Then, in 800 BC, a new intrusion of magma occurred underneath the east flank of Yantarni.
This pushed the ground upwards, forming a prominent bulge.
This bulge eventually burst, leading to a massive landslide.
As the eastern half of the volcano collapsed, it was funneled at high speeds into the adjacent
glacial valley, traveling up to 4 kilometers distant.
Pyroclastic flows excellerated at several hundred miles per hour out of this blast,
incinerating everything up to 5 miles or 8 kilometers distant.
As large amounts of ash were ejected high into the atmosphere, the day seemingly turned
to night due to the immense amount of falling material.
After this explosive phase ended, a lava dome was built in the site of the new U-shaped
collapse scar, forming Yantarni's modern summit.
In total, 1 cubic kilometer of volcanic rock was ejected in an eruption which was assigned
a volcanic explosivity index of 5.
Since then, no additional volcanic activity has occurred.
In all likelihood, it will be tens of thousands of years before this volcano erupts again.
The vast majority of its eruptions are primarily effusive, resulting in short distance lava
flows.
Since no one lives adjacent to this volcano, no structures are in direct danger.
However, a less likely explosive eruption could disrupt regional air traffic, if it
were to erupt again.
As a result of these hazards, the US Geological Survey designated Yantarni as a moderate threat
volcano.
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