When people think of the term supervolcano, they tend to think of the Yellowstone caldera
in wyoming. However, yellowstone is not the only active supervolcano on the planet. In Indonesia
is another supervolcano known as Toba which is responsible for the largest explosive eruption
on the planet in the last 25 million years. This video will discuss this large supervolcano in
detail, and mention what its future hazards are. The Lake Toba supervolcano can be found in the
northwest portion of the island of Sumatra in Indonesia. Specifically,
it is 35 kilometers southeast of another volcano often in the news, Mount Sinabung.
Before Toba began erupting, volcanic activity had been ongoing in the region for several million
years. This volcanic activity was due to two tectonic plates colliding southwest of Sumatra,
where the Indo Australian plate was being subducted underneath the Eurasian plate.
The melted crust then migrated upwards, but instead of erupting on the surface, it collected
in the crust. Over hundreds of thousands of years, the magma chamber continued to expand until it had
a volume of several hundred cubic kilometers. Then, 1.2 million years ago, something caused a
portion of this magma chamber to shoot upwards towards the surface which caused an eruption.
During this eruption, large amounts of lava and ash were ejected from an area that was
filled with low relief mountains. Over the next several days, pyroclastic flows
and lava repeatedly traveled outwards into the surrounding jungle. Eventually, this eruption
had sufficiently drained a section of the larger magma chamber which caused the overlying rock to
collapse and form a 6.5 kilometer wide caldera. Over the next 350,000 years, magma began building
in a different area 65 kilometers southeast of the previous eruption. Then, 820,000 years ago,
the first true supereruption at Toba occurred. Over the course of this massive eruption, dozens
of vents erupted about 1,200 cubic kilometers of both lava and ash. This caused a 24 by 58
kilometer section of Sumatra to collapse and fill the space left by a previously full magma chamber.
Over the next 340,000 years, lava began building once again at the site of Toba's first
large eruption. Then, 501,000 years ago, the existing 6.5 kilometer wide caldera
was expanded into a 10 kilometer wide caldera via a third massive eruption.
The magnitude of this event was likely similar in size to the 1815 eruption of Mount Tambora.
After this eruption ended, magma once again began collecting and building in pressure beneath the
surface. However, this time, the entire magma chamber began expanding and building in pressure.
Then, 74,000 years ago, the largest explosive eruption in the last 25 million years began. As
the eruption continued, a series of kilometer high pyroclastic flows traveled outward from
a series of vents at speeds of more than 150 kilometers per hour. These pyroclastic flows
likely traveled more than 200 kilometers in every direction before they stopped, wiping
out all plant and animal life along the way. This eruption created a vast cloud of ash which
traveled 80 kilometers high into the atmosphere. Soon, a dusting of ash fell in eastern europe,
africa, and the middle east. Over the next several days, much of India was covered with
a meter of ash. Closer to the eruption, in Malaysia, a large section of the country was
covered with 9 meters of ash. Finally, a 100 kilometer long and 35 kilometer wide section
of the earth's crust collapsed into the ground to form the largest caldera currently known on land.
For the next decade, temperatures around the world were 5 to 10 degrees Celsius colder than normal,
as this eruption had caused a volcanic winter. The cooling caused by this
eruption lingered for more than a millennia. After this eruption, magma began pushing upwards
at the center of the caldera, forming what is known as a resurgent dome. During this process,
small amounts of magma traveled upwards along a series of regional faults and erupted onto the
surface. The first of these eruptions occurred on the northeast coast of Samosir island,
and formed a 3 kilometer wide lava dome. Over the next 5000 years, 3 additional
lava domes formed along the island's east coast. The next series of eruptions took place along a
different fault 24 kilometers to the south. Between 63,000 and 54,000 years ago, 4 more
lava domes were built. Since then, no additional eruptions have occurred. However, Toba is still
geologically active, as indicated by the number of fumaroles still `emitting volcanic gasses.
As a result, we must consider the possibility of another non caldera forming eruption in the near
future. Based on the positioning of regional faults, I have mapped out area which is most
likely to be the site of future volcanic activity. If another lava dome eruption was to occur,
it would require a regional evacuation of at least 10 kilometers in every direction due to
the threat of both pyroclastic flows and bombs of lava. Overall, the odds of a new eruption at Toba
are quite low at about 1 in 25,000 each year. I hope that you enjoyed this video.
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