The state of Alaska has more active volcanoes than other area of the United States.
It contains 86 active volcanoes, a number of which have erupted quite recently.
One of these, redoubt volcano, produced a large eruption from 1989 to 1990.
However, this eruption was not even 1000 times smaller than a 1912 eruption from another
volcano in Alaska.
The volcano in question is Novarupta, which was responsible for the largest volcanic eruption
in the world of the 20th century.
This video will discuss this volcano, and mention what its future hazards are.
For this video, we are defining an active volcano as any volcano or volcanic field which
has erupted in the last 10,000 years.
Although 10,000 years may seem like a long timeframe, this is the definition used by
the global volcanism program.
The Novarupta volcano can be found in a remote southern portion of Alaska.
Specifically, it can be found 275 miles southwest of Anchorage, or 63 miles southeast of the
town of King Salmon.
Novarupta is part of the Aleutian volcanic arc, which is a curving chain of volcanoes
extending from southcentral Alaska to the far western end of the Aleutian Islands.
This chain of volcanoes exist due to subduction of the pacific plate underneath the north
american plate.
Before its eruption in 1912, the Novarupta volcano simply did not exist.
Today, it is covered by a summit lava dome and thus could be technically classified as
either a lava dome volcano, or a caldera volcano.
Lava domes form when viscous lava builds in a central location due to its slow movement
speed.
This eventually forms a rough looking shape which resembles the upper half of a sphere.
The 1912 eruption of Novarupta technically took place at two volcanoes.
Let me explain.
Within 10 miles of Novarupta, there are 5 other active volcanoes.
One of these volcanoes which is 6 miles east-northeast is a stratovolcano known as Mount Katmai.
Underneath Mount Katmai was a large magma chamber.
During the 1912 eruption of Novarupta, this magma chamber was largely emptied.
As a result, much of Mount Katmai collapsed and formed a 2.5 or 4 kilometer wide caldera.
Today, this caldera is largely filled with a crater lake.
The fact that the source of the major eruption was not immediately adjacent to the caldera
is highly unusual.
As a result, when scientists first observed the aftermath of the eruption, they assumed
that it occurred from Mount Katmai and not novarupta.
The eruption of Novarupta began on June 6th, 1902, and continued well into October.
The size of this eruption is massive, and on the 0 to 8 volcanic explosivity index,
this eruption was classified as a 6.
During the course of this eruption, the Novarupta volcano emitted about 30 cubic kilometers
or 7.2 cubic miles of tephra.
It deposited ash over a vast area, and reached as far away as Juneau, Vancouver, and Seattle.
It created large pyroclastic flows and lahars which traveled more than 12.5 miles or 20
kilometers away.
This event is considered the largest volcanic eruption of the entire 20th century, and today
remains the largest eruption since the 1883 eruption of Krakatoa.
Another way of providing some context, is that the 1912 eruption of Novarupta was about
30 times the size of the 1980 explosive eruption of Mount Saint Helens.
Today, the aftermath of this eruption can be viewed in the Valley of 10,000 smokes and
within the Katmati National Park and preserve.
This area is home to the world's largest brown bear population, of which it has 2200.
So, what is the hazard posed by Novarupta, and will it erupt again?
The novarupta volcano is not likely to erupt for sometime, although it likely will erupt
again.
If a future eruption was to occur, it would most likely be several orders of magnitude
smaller than its 1912 eruption.
As a result of these hazards, in the most recent volcano hazard assessment from the
US geological survey, the novarupta volcano was assigned a high risk designation.
I hope that you enjoyed this video.
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