On June 6th, 1912, the largest volcanic eruption of the 20th century began.
As a volcano dramatically exploded in remote Alaska, pyroclastic flows raced across the
landscape, burying everything in a vast amount of superheated rock.
These pyroclastic flows were unusually energetic, travelling beyond 19 miles or 30 kilometers
distant.
As the powerful eruption continued for a period of 72 hours, particles of ash carried high
into the atmosphere were deposited as far away as Seattle in Washington State.
For several decades, the eruption just described was believed to have originated from the Katmai
volcano.
After all, the caldera you see on its edifice formed during the eruption, and it was covered
in volcanic ash.
Yet, further research revealed that Katmai, despite being active did not produce the aforementioned
eruption, despite the formation of a large caldera on the same date.
So, how was this possible?
Which volcano produced the major eruption?
This video will answer these two questions and discuss this active stratovolcano.
Mount Katmai can be found in southwest Alaska where it is 67 miles east southeast of the
town of King Salmon.
It is one of a number of several closely spaced volcanoes which are located in the scenic
Katmai National Park.
Mount Katmai began forming 70,000 years ago, when a volume of andesite magma erupted onto
the surface.
This initial eruption was unusually explosive, as the magma feeding the eruption contained
an abundance of combustible gas.
As a result, energetic vulcanian explosions occurred, ejecting bombs of lava in a several
mile radius which occurred alongside pyroclastic flows.
By the end of the eruption, a small gray volcanic cone had been constructed.
Additional eruptions later continued to build this volcanic cone, which started on a raised
ridge at an initial height of 770 meters or 2526 feet.
After tens of thousands of years of eruptions, two large volcanic cones, separated by a distance
of 1 mile had been constructed.
The peak to the south was 7500 feet tall while the peak to the north had a height of 7360
feet.
Over time, the underlying magma chamber below Katmai became more silica rich, which in turn
caused the nature of eruptions to change.
Instead of producing frequent andesitic eruptions, Katmai would now produce infrequent large
explosive eruptions, in a manner similar to Mount Pinatubo in the Philippines or El Chichon
in Mexico.
One such massive eruption occurred 22,500 years ago, which ejected 35 cubic kilometers
of ash and volcanic rock.
Much of this ash fell on Kodiak island to the east.
This massive eruption buried some areas in as much as 50 meters or 164 feet of superheated
rock.
After a long period of dormancy, another explosive eruption occurred 16,000 years ago, but was
an order of magnitude smaller.
This eruption likely had a volcanic explosivity index of a 5, and ejected several meters of
dacite composition ash in a several mile radius.
Then, Katmai became dormant once again.
Finally, on June 6th 1912, a large volcanic eruption began.
10 kilometers to the west of Mount Katmai, the first eruption from a new volcano emerged
on the valley floor.
Over the span of 72 hours, this new volcano known as Novarupta ejected 31 cubic kilometers
worth of volcanic rock.
This rock buried a vast area in superheated ash which would take decades to cool and is
now known as the valley of 10,000 smokes.
Strangely, this new volcano used a massive amount of magma directly from Katmai's magma
chamber.
Thus, although Katmai did not initially erupt, a caldera collapse occurred as its magma was
drained away.
Its towering 7500 foot tall peak dropped to a height of 6700 feet, while the newly formed
caldera was 4000 feet deep.
This collapse also triggered a minor explosive lava dome forming eruption within the newly
formed caldera, which constructed two small lava domes.
By July 21st, the eruption had ended and this volcano has never erupted since.
Mount Katmai is one of those volcanoes that if it were to erupt again would solely be
through a major explosive eruption.
Although no nearby settlements are in the direct path of any pyroclastic flows if it
were to erupt again, any tourists in this remote national park would be placed in danger.
As a result of these hazards the US Geological Survey designated Katmai as a high threat
volcano.
I hope that you enjoyed this video.
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