In July of 2012, a volcano which was thought to be extinct produced a new eruption. This eruption
was truly massive, and represented the single largest eruption on the planet of the last 25
years. So, why didn't we hear about this deadly eruption in the news? The answer is that this
large eruption occurred about a kilometer beneath the ocean, so its effects were greatly reduced.
This video will discuss the volcano which produced this eruption, Mount
Havre, and mention what its future hazards are. The Havre Seamount volcano can be found several
hundred kilometers north-northeast of the north island of New Zealand in the Pacific Ocean.
Specifically, it is 73 kilometers southwest of a small volcanic island known as Cheesehead Island.
This submarine volcano is part of the greater Kermadec volcanic Arc, which contains more
than a dozen submarine volcanoes. A few of these volcanoes were large enough to reach the surface,
such as the famous White Island volcano. The reason why Mount Havre exists is due to
a destructive plate boundary. To the east of this volcano, the vast pacific plate is being subducted
underneath the indo australian plate. The oceanic crust from this collision then melts
and migrates upwards until it erupts on the ocean floor, creating a submarine volcano.
As much of the ocean floor still hasn't been explored, we didn't know that the
volcano even existed until 2002. As a result, there is limited information on
this volcano. I will make a hypothesis based on the data which we have on this volcano.
Sometime in the last 100,000 years, a new submarine volcano began forming in
the Pacific Ocean north of New Zealand. The early eruptions from this volcano were highly basaltic.
As a result, Mount Havre initially started to grow with the appearance of a shield volcano. However,
as the volcano continued to grow from the ocean floor, lavas began to contain more silica which
caused more explosive eruptions. Soon, both andesite and then dacite lavas erupted onto
the volcano which created a much steeper slope. Eventually, the Havre seamount volcano was only
250 meters beneath the surface of the ocean. Then, a supermassive eruption began at the
summit of this volcano. Several cubic kilometers of lava was ejected, which
caused the magma chamber to drain. This caused the volcano to collapse in a submarine landslide,
which created a 5 kilometer wide caldera. The eruption which had just occurred was likely
similar in size to the 1883 eruption of Krakatoa. Afterwards, a several thousand year long period
occurred with very infrequent eruptions. Then, in 2012, another large eruption began.
On July 17th, seismometers detected a large swarm of shallow moderate magnitude earthquakes
originating from the volcano. The eruption had begun. Beneath the ocean surface, a large magma
chamber erupted highly siliceous lavas known as rhyolite from several different vents, which ran
almost perpendicular to the nearby plate boundary. One or more of these vents erupted a special type
of volcanic rock known as pumice. As pumice is lightweight, it rose to the surface and formed
a 4 meter thick layer of loose rock known as a pumice raft. The formation of this pumice likely
marked the most explosive phase of the eruption. Above the surface, satellites detected a plume
of ash and vapor which rose above the ocean floor and went several kilometers into the atmosphere.
As the eruption continued, more and more pumice floated to the surface of the ocean.
After the eruption had ended on July 19th, this raft of pumice had spread out to more than
20,000 square kilometers. The massive eruption which had taken place was the largest on the
planet since 1991, when Mount Hudson in Chile erupted. For some additional context,
this eruption was 50% larger than the famous 1980 explosive eruption of Mount Saint Helens.
Although no additional eruptions have since been detected, this submarine volcano is now correctly
marked and monitored as an active volcano. I hope that you enjoyed this video.
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