Japan contains more than 100 active volcanoes, which include Mount Fuji,
Mount Aso, and Mount Ontake. However, none of these volcanoes are as active as Sakurajima.
This volcano has produced a dozen distinct eruptions in the last 100 years,
the most recent of which continues today. This video will discuss this active volcano,
and mention what its future hazards are. The Sakurajima volcano can be found in the far
south of the Japanese archipelago. Specifically, it is 10 kilometers east of Kagoshima.
From satellite, you can see a number of eruptive features on this volcano. However,
if we zoom outwards, you will note a large bay. This large bay is actually the caldera
of a recent supervolcano known as the Aira Caldera. This caldera formed 29,000 years ago,
in an massive eruption 70 times larger than the 1991 eruption of Mount Pinatubo.
The Sakurajima volcano began forming 26,000 years ago, at the southern edge of this 20 kilometer
wide caldera. During the next 2,000 years, three highly explosive eruptions took place.
These eruptions deposited ash which fell largely outside the summit of the new volcano. Afterwards,
Sakurajima became dormant for 13,000 years. Then, 12,800 years ago, an eruption similar in
size to the 1883 eruption of Krakatau took place, which caused ash to fall hundreds of kilometers
away. This eruption did not take place on the peninsula which we typically associate Sakurakima
with. Rather, it took place to the northeast, and created a new 8 kilometer wide caldera.
Over the next seven thousand years, numerous eruptions took place which built up the Kitadake
cone. The tallest point of modern day Sakurajima was formed by this period of volcanic activity.
4500 years ago, the main vent of the volcano shifted about a kilometer to the south. The new
vent was called Minamidake, and has since produced the vast majority of the volcano's eruptions.
Record's of Sakurajima's eruptions began to be written down during the beginning of the 8th
century. One of the eruptions around this time was unusual as it did not take place on the
main summit. This explosive eruption in 764 AD formed a tuff cone 2.5 kilometers to the east.
The largest eruption which occurred in recorded history as the volcano occurred from
1471 to 1476. During this eruption, large pyroclastic flows raced down the mountain,
ash fell more than 50 kilometers away, and 770 million cubic meters of lava was erupted.
These lava flows greatly expanded the island. You might note that throughout this video,
I had been referring to the Sakurajima volcano as being on an island. That was,
until the 1914 eruption. This eruption produced so much lava that it expanded the
island by more than a kilometer, which finally connected it to the mainland.
From 1955 onwards, the eruption style at the volcano changed. Instead of there being a long
interval between eruptions, eruptions became much more frequent and were generally much smaller.
Today, Sakurajima is currently erupting. Every 4 to 24 hours, the volcano produces an explosion.
These explosions may be accompanied by lava bombs, lahars, or pyroclastic flows.
So, what hazards does this volcano pose in the future?
As scientists, we are relatively certain that a major eruption will take place in the
next 25 years. We just cannot say exactly when in this span of time it will occur.
This future major eruption will likely rate as a 4 on the volcanic explosivity index, and could be
quite similar to the eruption in 1914 or 1780. When this next eruption occurs, anyone within 7
or 8 kilometers would need to be evacuated due to the threat of ashfall and pyroclastic flows.
Until this major eruption occurs, Sakurajima still poses several hazards from its frequent
smaller eruptions. When an explosion takes place, you do not want to be in a riverbed or valley
which is connected to the mountain, especially if the volcano has a lot of snow on its summit.
Any eruption could melt a significant amount of this snowfall and generate a lahar.
These small eruptions can also produce fast moving pyroclastic flows, but these rarely
travel more than 2 kilometers from an eruptive vent. A more likely future hazard is posed by
the threat of slow moving lava flows. I hope that you enjoyed this video. If
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