In the recent history of the planet, a number of great civilizations and empires have risen
and fallen.
Given enough time, a long term famine or period of low crop yields often leads to war and
civil unrest.
However, many of these periods of unusual weather can be directly attributed to unusually
large volcanic eruptions.
One example is the 1783 eruption of Laki in Iceland, which is considered to be one of
the eventual causes of the French Revolution as it caused widespread crop failures.
However, there is another famous civilization in Europe which underwent a significant change
due to a volcanic eruption, the Roman Republic.
The volcano which helped trigger its eventual collapse can be found on the opposite side
of the planet, and is called Okmok.
The eruption which caused this collapse was truly massive, as it takes an impressive amount
of energy to create the massive 10 kilometer wide caldera shown on screen.
The Okmok volcano is located in the central portion of the Aleutian island chain, where
it makes up the northern half of the island it is based on, Unmak island.
This vast shield volcano began forming 2.1 million years ago, when magma at depth reached
the ocean floor, and began erupting a large volume of basaltic lava.
Over the subsequent period of several hundred thousand years, this volcano reached the ocean
surface, as the waters surrounding this volcano were only a few hundred feet deep.
As the years progressed, the Okmok volcano became larger and larger as voluminous eruptions
of basalt lava added to its edifice.
However, eventually the composition of the magma changed, as silica leached into the
underlying magma chamber.
This caused the volcano to produce more explosive eruptions as it now produced both basaltic
andesite and andesite.
By 70,000 years ago, the Okmok volcano had grown to 27 miles in length and 17 miles in
width.
Eventually, activity largely stopped, as a large volume of magma began to build beneath
its edifice.
Over time, this magma chamber continued to grow in size, along with a large volume of
highly combustible volcanic gasses.
Then, 12,000 years ago, the pressure in the magma chamber became too great, and was released
via a massive eruption.
As a plume of ash shot more than 100,000 ft into the sky, pyroclastic flows raced across
the surrounding landscape.
Some of these pyroclastic flows crossed the entirety of the island, reaching the Pacific
Ocean, and traveling more than 25 kilometers.
Then, due to the large volume of material erupted, totaling about 50 cubic kilometers
of molten rock, the volcano collapsed downwards thus forming a 9.5 kilometer wide caldera.
The remnants of this caldera can be easily seen today, as it represents the upper layer
of two overlapping calderas.
The second caldera formed in 43 BC, when a similarly sized eruption occurred.
This eruption was slightly less explosive than the prior one, as less glacial ice was
present on the island at the time of its eruption.
Regardless, this eruption also formed a massive 10 kilometer wide caldera.
The effects this eruption would have on the planet would be catastrophic.
Across Europe, average temperatures plummeted by 10 degrees Fahrenheit or 6 degrees Celsius.
Across much of the world, including the Roman Republic and Egypt, crops failed, as an unusually
wet decade of weather began.
By the time this decade had ended, almost every major civilization on the planet had
been weakened by warfare caused by a lack of food.
Since this last caldera forming eruption, eruptions from Okmok have been confined to
its caldera floor.
The last major eruption in 2008 was assigned a volcanic explosivity index of 4, as it created
a new 2500 foot wide crater within the caldera.
On average, Okmok produces an eruption about once every 7 to 8 years.
Despite the history of large and destructive eruptions from Okmok, the closest settlement
is more than 40 miles away.
As a result, this volcano only poses two potential hazards.
During eruptions, large volumes of ash are frequently ejected up to 50,000 feet into
the atmosphere.
When this ash falls back to the ground, it can cause long term blackout conditions and
if heavy enough can cause structures to collapse.
Additionally, any explosive eruption puts nearby airplanes at risk, as ash can damage
their engines.
With all of this being said, you would not want to be anywhere within 20 miles of this
volcano in the event it does have another major eruption.
As a result of these hazards, the US geological survey designated Okmok as a high threat volcano.
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