Many large volcanic eruptions are well known, such as the 1980 eruption of Mount Saint Helens
which destroyed part of its summit.
In 1991, a different eruption an order of magnitude larger caused a medium sized volcano
to completely collapse.
A third eruption in 1883 at Krakatoa was 3x the size of the aforementioned eruption of
Pinatubo and caused an entire volcanic island to collapsed into the ocean, generating a
massive tsunami.
With this being said, there is a much larger eruption which occurred in the last 10,000
years in Japan.
It generated more than 100 kilometer long pyroclastic flows which raced across a vast
swath of ocean, before reaching southern Kyushu.
This eruption which occurred in 5284 BC left the southern half of the island uninhabitable
for several hundred years.
The volcano which produced this catastrophic eruption has erupted quite recently, and is
known as the Kikai caldera.
This video will discuss this volcano, its massive eruption, and mention what its future
hazards are.
The Kikai volcano can be found in southern Japan south of Mainland Kyushu.
Specifically, it is 94 kilometers south of the city of Kagoshima.
The islands you are looking at is only a small fraction of the overall volcano, which is
mostly submerged.
Note the visible caldera rim on these islands.
Zooming outwards, the true extent of this volcano is a 20 kilometer long and 17 kilometer
wide section which represents the outer reach of two overlapping calderas.
The Kikai volcano began forming approximately 700,000 years ago, when a volume of low silica
basaltic magma erupted onto the ocean floor.
Beginning at a depth of 200 meters, a submarine volcanic cone began growing due to numerous
effusive and explosive eruptions.
Eventually, this cone reached the surface, forming an island known as Satsuma Iojima.
During the next several tens of thousands of years, intermittent lava dome building
eruptions built the north section of this island.
Later, a second submarine volcanic cone reached the surface, forming the beginnings of Takeshima
island to the east.
The first caldera forming eruptions occurred 580,000 years ago, which caused more than
100 square kilometers of ground to subside by more than 50 meters into the crust.
Two subsequent larger caldera forming eruptions occurred 140,000 years ago and then again
95,000 years ago.
By 10,000 years ago, these two islands had a similar shape to their appearance today
but had a more symmetrical structure.
Then, in 5284 BC, the composition of lava changed as the volcano began erupting several
large rhyolite lava domes.
Eventually, a large amount of pressure began to build underneath these domes, which built
up over time.
Then, the pressure was released simultaneously at more than a dozen vents.
As a 50 kilometer high plume of ash towered into the atmosphere, an immense amount of
volcanic rock was released in all directions.
This generated deadly pyroclastic flows which raced across the ocean in all directions,
making its way towards several nearby islands.
All life on these islands was wiped out, after which the flows continued.
Reaching the southern end of Kyushu, several areas of human habitation were wiped out more
than 100 kilometers away from the eruption source.
Then, due to the immense amount of released volcanic rock, a 20 by 17 kilometer section
of ground collapsed downwards forming a massive caldera.
This created a towering tsunami which then swept over much of Japan's coastline.
What had just occurred was the second largest eruption on the planet of the last 10,000
years.
In total, 153 cubic kilometers of volcanic rock was ejected, and the eruption was assigned
a volcanic explosivity index rating as a 7.
The only larger eruption during this timespan was the 6440 BC eruption of Kurile Lake in
Russia.
Since then, eruptions have been confined to Satsuma Iojima.
Subsequent eruptions primarily occurred at two volcanic cones.
Inamura dake, the older of the two cones, has not erupted since 1090 BC.
On the other hand, the Iwo-dake cone has erupted via frequent vulcanian style eruptions as
recently as late 2020.
One other notable eruption occurred from 1934 to 1935, which formed a small island 2 kilometers
to the east the aforementioned volcanic cone.
I hope that you enjoyed this video!
If you would like to request a specific topic, please leave a comment below.
Additionally, if you would like to support this channel, consider becoming a patron on
patreon.