In Central Alaska is a dangerous and mysterious volcano.
So mysterious in fact, that scientists didn't even know it existed until 1975.
This volcano, known as Hayes or the Hayes Volcano, is the second closest volcano to
Anchorage.
If you ever worked in construction around Anchorage, you have probably encountered the
aftermath of its large eruptions.
The Hayes volcano is responsible for the thickest layers of ash deposited around the city in
the last 5,000 years.
This video will discuss this volcano, and mention what its future hazards are.
The Hayes Volcano can be found in south central Alaska, where it is 90 miles west-northwest
of Anchorage and 24 miles north of another active volcano, Mount Spurr.
This volcano is covered by numerous thick glaciers, and due to its remoteness, we really
do not know much about this volcano.
As a result, much of what I say will be based on limited information and could end up being
wrong.
The earliest potential record of an eruption from the Hayes volcano is quite interesting.
Two dozen miles to the northeast, geologists found a layer of ash which contained high
silica rhyolite.
This is quite interesting, as this rare rock type often is created during or after the
formation of a caldera.
Since the layer of ash in question was not very thick, we can assume that by 10,000 years
ago, Mount Hayes already was the site of a large caldera.
Although no detailed geologic maps have been made of this volcano, via satellite you can
make out a faint circular depression which could be this caldera.
It measures 4 miles long by 4.5 miles wide, and appears to be at least 30,000 years old.
The next source of eruptions from Hayes likely originated in the center of the caldera, at
a circular region which is called a resurgent dome.
Resurgent domes form when the center of a large caldera is uplifted in the aftermath
of a massive eruption.
Since the center represents a regional weak point, lavas erupt onto the surface and build
a series of overlapping lava domes.
At Hayes, several thousand years of lava dome building eruptions constructed an edifice
which towered to at least 3000 feet higher than the base of the caldera rim.
By 3800 years ago, the lava dome complex had grown so large and steep, that it became structurally
unstable.
Eventually, a large section of this volcano collapsed due to gravity, which generated
a long distance pyroclastic flow.
This pyroclastic flow raced to the northeast at about 100 miles per hour, and traveled
more than 17 miles before it stopped.
Due to the pressure released by this collapse, a large plume of ash was ejected 8 miles into
the atmosphere.
Ash subsequently fell across much of central Alaska.
In total, an inch of ash fell on Anchorage, while a half inch of ash fell on Homer and
Kenai.
What had just occurred was a pelee-style eruption, which was about twice the size of the 1980
eruption from Mount Saint Helens.
Over the next 300 years, five similarly large eruptions took place.
One of these was 8 times the size of the aforementioned Mount Saint Helens eruption, and deposited
a total of 2 cubic miles of ash in a several hundred mile radius.
Several smaller eruptions also occurred during this timeframe, likely indicating largely
effusive eruptions that were a precursor to dome collapses.
The most recent eruption from Mount Hayes occurred about 800 years ago in 1200 AD.
Since then, no additional activity has been detected.
Although the volcano now appears to be quiet, it will erupt again.
When Hayes erupts once again, the primary hazard posed by this volcano would be due
to its ash cloud.
This ash cloud could make air travel impossible across much of Alaska and western Canada.
Additionally, depending on the prevailing winds at the time of an eruption, ash could
fall on towns as far away as Fairbanks or Kodiak.
With this being said, only one town would be in significant danger during a future eruption;
Skwentna.
Much of this town is located less than 20 feet above the nearby Skwentna river, which
is largely fed by melting ice from the glaciers at Mount Hayes.
Thus, if a large eruption occurred, much of the overlying glacier at the volcano could
melt, and send floodwaters towards the town.
Overall, the odds of an eruption from the Hayes Volcano is about 1 in 1000 each year.
I hope that you enjoyed this video.
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