To the north of mainland New Zealand are a chain of several islands which stretch for
several hundred kilometers called the Kermadec Islands.
These islands are all volcanic in origin, of which the most famous example is White
Island.
As seen via the 2019 eruption of White Island, many of these volcanoes are still highly active.
However, one volcano stands apart in this island chain due to the impressive size of
its eruptions.
One of its recent eruptions was 15 times larger than the 1886 eruption of Tarawera.
The volcano I am referring to is called Raoul, which encompasses all of an unusually shaped
island.
This video will discuss this volcano, and mention what its future hazards are.
Raoul island and stratovolcano are located at the northernmost edge of the Kermadec Island
chain.
Specifically, this volcano is 1080 kilometers north-northeast of the city of Whakatane.
The Raoul stratovolcano began forming approximately 1 million years ago, when a volume of magma
erupted on the ocean floor at a depth of 1280 meters or 4200 feet.
Due to the initial depth of this stratovolcano, its early eruptions were largely effusive,
causing layer after layer of lava to pile on top of one another.
Over the next several hundred thousand years, this submarine volcano climbed higher and
higher.
Eventually, the volcano became shallow enough that explosive eruptions could occur, causing
small volumes of ash to become emplaced on its edifice.
Finally, sometime in the last 200,000 years, this towering volcano reached the ocean surface.
Over time, this island continued to expand in height and width, as layers of a gray lava
called basaltic andesite erupted out of the volcano.
By 10,000 years ago, almost the entirety of Raoul island had formed, containing an area
of approximately 45 square kilometers.
At the time, the tallest peak on the island was Moumoukai, which stood at approximately
800 meters above sea level.
However, the volcano was undergoing an unusually long period of dormancy.
The reason for this was that at depth, a large volume magma chamber was continuing to grow
in size.
Then, in 2000 BC, the resulting pressure became too great, and the volcano exploded in a massive
eruption.
Pyroclastic flows then raced across the entire island, before traveling into the Pacific
Ocean.
Due to the large volume of material which had erupted, the center of this volcano then
collapsed downwards, forming a 3500 meter wide caldera.
However, this eruption had not released all of the pressure built by Raoul's large magma
chamber.
As a result, in 250 BC, an even larger volcanic eruption occurred.
At the time of this eruption, Raoul island had a completely different appearance, with
its original coastline shown on screen.
Although it is not known where the eruption began, its effects were immense.
Pyroclastic flows raced across the Pacific Ocean, likely traveling more than 20 kilometers.
As a 45 kilometer high ash cloud towered into the atmosphere, the underlying magma chamber
neared on empty.
Then, due to the large volume of magma erupted, totaling about 12 cubic kilometers of molten
rock, the volcano collapsed downwards and into the sea.
This collapse created an even larger 6500 by 4000 meter wide caldera, and lead to the
modern C shaped hole in the west of Raoul island.
Since then, at least a dozen eruptions have occurred, the vast majority of which did not
eject any lava.
These eruptions were largely phreatic, resulting from the interaction of magma with groundwater,
which causes it to flash to steam and explode.
Three such eruptions which occurred in 550 AD, 700 AD, and 1630 led to the creation of
the area now overlaid by Green Lake.
However, other eruptions have occurred from separate areas within this caldera, along
with a series of submarine vents in the Denham Caldera.
Two eruptions from the larger of these calderas created short lived volcanic islands in 1815
and 1870.
Since then, 4 eruptions have occurred.
Two of these eruptions occurred at a submarine vent 7 kilometers to the northeast of the
island, while the rest occurred from green lake crater.
The last of these eruptions occurred in 2006.
Although no eruptions have occurred since then, the frequency of eruptions on this island
indicates that more eruptions will occur in the future.
As a result of the unpredictable nature of this volcano, I suggest that people be completely
banned from visiting this island when even a low level of residual earthquake activity
is detected.
Otherwise, people's lives could once again be put at risk.
I hope that you enjoyed this video!
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