Alaska contains 86 active volcanoes.
Among these, there are a surprisingly high number of volcanoes which have produced eruptions
between 10 and 50 times the size of the 1980 eruption of Mount Saint Helens.
The most recent of these occurred in 1912, when the newly formed Novarupta volcano erupted
31 cubic kilometers of volcanic rock, depositing ash as far away as Seattle.
This eruption formed a large caldera at the adjacent Mount Katmai volcano, which it shares
a joint magma chamber with.
Further to the southwest, are two volcanoes with even larger calderas.
One of these is the highly active Veniaminof volcano, which contains a 5 mile wide ice
filled caldera.
To the east, is the more massive Aniakchak caldera, which measures 6 miles wide.
Yet, due to the size of eruptions from these two volcanoes, another large caldera between
these two volcanoes is largely forgotten about.
Between these is a third volcano, simply referred to as Black Peak.
This video will discuss this volcano, the massive eruption which formed its large caldera,
and mention what its future hazards are.
Black Peak is located in southwest mainland Alaska, where it is 250 miles south-southwest
of the closest major city, Kodiak.
The reason why this volcano is called black peak relates to the appearance of one of its
youngest vents.
It truly has a dark black coloration to it, as this represents volumes of andesite lava
and ash mixed together.
The outer edifice of Black Peak represents a distinct older volcano, which once stood
in its place around 2.5 million years ago.
It also contains small amounts of rock associated with the early stages of the modern volcano.
The most prominent feature of this volcano is its large caldera, which measures 3.5 kilometers
or 2.2 miles wide, and 1500 feet deep.
It originated in 1900 BC, when a massive explosive eruption occurred.
Before it occurred, the existing central edifice, which probably looked similar to Lassen Peak
in California, consisted of a group of overlapping lava domes.
The edifice acted as a sort of pressure plug which temporarily contained a large volume
of magma which had just reached the surface.
Eventually, the pressure became too great, and one of the mile wide lava domes exploded
into a cloud of fragments.
Thus began the eruption, causing a towering plume of ash to travel more than 40 kilometers
or 131,000 feet into the atmosphere.
Soon, pyroclastic flows raced across the landscape, traveling up to 15 miles before they stopped.
Then, due to the vast amount of volcanic rock released, sections of the shallow underlying
magma chamber became empty.
This caused the overlying rock to collapse downwards by 1500 feet, forming a large caldera.
After the erupted ended, some areas had been buried by more than 100 meters or 330 feet
of ash.
What had just occurred was one of Alaska's largest eruptions in the last 10,000 years.
In total, 30 cubic kilometers of volcanic rock had been ejected, meaning this eruption
was rated on the volcanic explosivity index as a 6.
Everything dark colored within the caldera formed after this eruption, meaning that dozens
of undated eruptions have occurred since.
These eruptions constructed overlapping domes of both andesite and dacite lavas, which have
a high viscosity.
The most recent eruption from Black Peak occurred sometime between 500 and 1,000 years ago,
which resulted in a series of pyroclastic flows from partial lava dome collapses.
The two lakes within the caldera represent low points of the overall volcano, where snowfall
water has pooled.
One of these lakes, known as Purple Lake, is geothermally active.
It shows signs of a repeated rare volcanic hazard known as a limnic eruption.
This occurs when carbon dioxide in saturated water is released into the surrounding landscape,
by the order of hundreds of thousands to millions of tons of material.
This coats the ground in a 50 meter thick cloud which suffocates anything alive.
Luckily, no one lives immediately adjacent to the volcano.
However, three towns are close enough that a limnic eruption could cause a thick layer
of carbon dioxide to travel to their location.
Otherwise, Black Peak only poses a risk to aircraft if it was to ever erupt again due
to its uniformly explosive eruptions.
As a result of these hazards, the US Geological Survey designated Black Peak as a moderate
threat volcano.
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