On May 22nd, 1956, the crew of a US Navy plane were flying between the islands Oahu and Kauai
when they observed an unusual sight.
A patch of brownish-yellow material was present in a section of the ocean, measuring more
than 1,000 feet across.
As they got closer, a strong sulfur odor was detected by the crew.
What had just occurred was a submarine volcanic eruption in an area thought to be void of
volcanic activity.
Although this eruption cannot be necessarily linked to the island of Oahu, it implies the
possibility that its volcano is not truly extinct but rather in a long term period of
dormancy.
Several young volcanic features exist on the island of Oahu, such as the Diamond Head tuff
cone.
This video will discuss the Oahu island volcano, and mention what it’s future hazards are
along with its odds of erupting once again.
The remote Hawaiian islands exist due to an underlying hotspot in the mantle.
This hotspot does not move, but the crust overlying it does.
Thus, over many millions of years, this hotspot constructed dozens of volcanoes, thus forming
the Hawaiian island chain.
Although the majority of molten rock is concentrated on the big island of Hawaii and its 4 volcanoes,
some material also manages to go into the Haleakala volcano on Maui.
On even rarer occasions, this magma can reach a bit further west such as Oahu.
The modern island of Oahu was constructed via eruptions from two large shield volcanoes.
Waianae built the western half on Oahu while Koolau built the eastern half of the island.
The Waianae volcano began forming 3.8 million years ago, when a large amount of magma erupted
onto the ocean floor.
Over a duration of approximately 100,000 years, numerous submarine eruptions built this volcano
until it reached the ocean’s surface.
From 3.8 to 2.2 million years ago, a large shield volcano with a curved rift zone constructed
the western half of the island of Oahu.
Beginning around 2.6 million years ago, a second volcano known as Koolau erupted.
This shield volcano was also constructed in a massive oblong edifice over the next 800,000
years.
Then, for 300,000 years this volcano lied dormant.
Suddenly, 1.5 million years ago, something caused the entire eastern half of the volcano,
cutting right through the eastern half of its caldera, to catastrophically collapse
into the ocean.
This landslide was one of the largest known to ever occur on the planet, and resulted
in 5,000 cubic kilometers of rock traveling up 230 kilometers to the north.
Debris from this landslide even created several large underwater mountains such as the seamount
shown on screen.
What remained of the island was a prominent ridge representing the western edge of the
prior collapse.
The remnants of the original caldera now lie in Kāneʻohe Bay which was once the center
of the volcano.
For the next 1 million years, the volcano lied dormant again.
Then, 500,000 years ago, a new more explosive phase of eruptions began.
These eruptions occurred along to the southeast coast of the modern island, constructing several
massive explosion craters known as tuff rings.
One of these tuff rings, known as Diamond Head, formed 400,000 years ago.
It formed when a large volume of magma intruded into the crust, which heated abundant groundwater
and caused it to flash to steam.
Eventually the steam became highly pressurized and a massive explosion occurred.
At least 30 similar eruptions occurred during this timespan, forming what is known as the
Honolulu volcanics.
The two youngest eruptions occurred 75,000 years ago, forming punchbowl Crater, and 40,000
years ago, forming Hanauma Bay.
Since then, no additional eruptions have occurred on the island.
If a future eruption was to occur, it would most likely originate in eastern Honolulu
or adjacent to Kaloko beach.
Luckily, additional eruptions are not truly certain.
The overall volcano during its latest phase of activity erupted once every 10,000 years
over the past 500,000 years.
Yet, it has been 40,000 years since the last eruption.
Any future eruption is likely to be highly explosive, creating pyroclastic flows and
requiring a 10 mile evacuation radius.
Overall, the odds of this volcano erupting each year is 1 in 40,000.
I hope that you enjoyed this video.
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