On the evening of August 6th, 2008 two biologists were studying the surprisingly abundant wildlife
on a remote Aleutian island.
As their work continued, they began to feel increasily strong earthquakes.
Soon, these earthquakes were picked up by distant seismic stations, some located several
hundred miles away.
Throughout the night, the ground rumbled.
Then a 5.8 magnitude earthquake hit the island.
Suddenly, inside the cabin they began to smell a high amount of sulfur in the air.
Quickly grabbing their bags, they prepared to evacuate on a small skiff not worthy of
long distance travel.
However, on the radio, a message came in, a local fisherman was only 7 miles away, and
was coming to evacuate them.
Less than 30 minutes later, they looked back at the island and saw a massive explosion
take place.
A sustained plume of ash shot high into the atmosphere, reaching a height of 18 kilometers.
Lucky to escape with their lives, what had just occurred was a VEI = 4 or plinian eruption
from a volcano previously not thought worthy of being monitored due to a lack of activity.
The volcano in question is called Kasatochi, which we now know to be a highly dangerous
and active volcano.
This video will discuss this volcano and mention what its future hazards are.
The Kasatochi volcano can be found in the western part of the Aleutian island chain.
The closest settlement to this volcano, Adak, lies 55 miles to the west.
As we zoom in on this volcanic island, we can truly see how small it is.
With a large summit crater in the center, Kasatochi is only 5,700 feet wide and just
over 10,000 feet long.
I want to note that before its explosive eruption in 2008, the island was far smaller.
The reason why Kasatochi exists is due to a tectonic collision south of the island.
There, the Pacific Plate is being subducted underneath the North American Plate.
The melted crust from this collision then migrates upwards, before erupting on the surface
and forming a volcano.
Although we don't know exactly when Kasatochi began forming, it originated as a submarine
volcano on the northern section of a shallow submarine ridge.
As such, when this young volcano first erupted, it began only 250 feet beneath the ocean surface.
Over the span of several thousand years, numerous effusive and explosive eruptions built this
stratovolcano to a taller and taller height out of both basalt and andesite.
Eventually, Kasatochi reached the ocean surface, from which a highly explosive eruption occurred
due to the interaction of magma with shallow seawater.
After this eruptive sequence had finished, a small volcanic island with a central cone
and small platform built out of ash remained.
Due to the nature of deposits on Kasatochi, it is quite possible that all of the events
I just described occurred within the last 12,000 years.
After the volcano breached the surface, it continued to build in size.
For an unknown reason, subsequent eruptions built a more gentle slope to the south and
a steep slope to the north.
Eventually, Kasatochi grew in size to a height of 1030 feet or 314 meters above sea level.
In 1760, the faint glow of lava was witnessed on this island, likely from a small eruption.
Then, three times in the 19th century, minor eruptive activity was reported.
As such, the 2008 eruption was the largest eruption known to have originated from this
volcano.
The thick layers of ash this eruption deposited covered the cabin which the biologists were
staying in with more than 100 feet of ash.
This ash ended up expanding the island by up to 800 meters, although certain sections
saw less of an expansion.
Today, this volcano still emits various volcanic gasses via fumaroles in its summit crater.
When Kasatochi erupts again, it can pose a number of hazards.
Due to its location, the main hazard this volcano can pose is to air traffic as any
explosive eruption can make it impossible for aircraft to fly in the vicinity.
Such a disruption occurred during its highly explosive eruption in 2008.
Also, whenever Kasatochi erupts, it can generate pyroclastic flows and surges which can travel
across water, potentially up to 5 miles or 8 kilometers away.
Third, due to the shape of Kasatochi, it is quite possible that a future eruption will
blow out the north slope of the volcano.
This could generate a small tsunami which could effect the distant town of Adak.
As a result of these hazards, the US Geological survey designated Kasatochi as a high threat
volcano.
I hope that you enjoyed this video!
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