The recent highly explosive eruption of Hunga Tonga Hunga Ha'apai has brought additional
attention to other volcanoes in the nation of Tonga.
One of these other volcanoes is in fact erupting right now, and has been erupting ever since
October 2nd of 2015.
Despite the low intensity of the current eruption, this volcano, known as Tofua, hasn't always
produced such small eruptions.
Tofua has in fact produced two geologically recent eruptions an order of magnitude larger
than what the Hunga Tonga volcano produced.
This video will discuss this lush island volcano, and discuss just how recently its last major
explosive eruption occurred.
The Tofua stratovolcano is located in central western Tonga, where it is 156 kilometers
north of the island of Tongatapu.
The island adjacent to it, named Kao, is also a volcano, but it has not erupted in historical
times.
The most prominent feature of Tofua it its 5.5 kilometer or 3.4 mile wide caldera, which
formed through not one but two closely spaced supermassive eruptions.
The Tofua and Kao volcanoes exist for the same reason as the Hunga Tonga Hunga Ha'apai
volcano.
To the east of the island chain, the Pacific Plate is colliding with the Indo Australian
plate, which is driving the Pacific Plate downwards.
The subducted crust from this plate then melts and migrates upwards, until it erupts through
the ocean floor, forming the Tofua volcanic arc.
Although the exact age of Tofua is unknown, it can be estimated that this volcano began
erupting approximately 50,000 years ago, when a volume of basaltic andesite composition
lava erupted onto the ocean floor.
This began at a depth of approximately 1200 meters or 3900 feet.
Over a period of tens of thousands of years, Tofua's central volcanic cone grew higher
and higher.
Then, it finally broke the surface, erupting in an explosive manner.
A plateau of ash was subsequently constructed, after which lava erupted, building a sturdy
island.
Through numerous strombolian style eruptions, the peak of Tofua grew to a height of approximately
1220 meters above sea level.
Meanwhile, at depth, a batch of magma which did not erupt leached material from the surrounding
crust, which changed its composition to dacite.
A few small yet highly explosive eruptions occurred due to this small batch of magma,
building a small dacite lava dome.
Then, eruptions seemingly paused, as a large batch of magma expanded underneath the island.
Finally, in 1040, a massive eruption began on the surface.
As pyroclastic flows raced across the island, a 35 kilometer high eruption plume shot into
the atmosphere.
As all vegetation and plant life on the island was burned and buried in ash, the eruption
continued.
Then, due to the large volume of material which erupted, a 5.5 kilometer wide section
of the island collapsed downwards like a sinkhole, forming a large caldera.
In total, 15 cubic kilometers of volcanic rock was ejected.
After 70 years of only minor activity, another major eruption occurred, which deepened the
overall caldera.
This second eruption was also rated as a 6 on the volcanic explosivity index, releasing
13 cubic kilometers of volcanic rock.
Everything seen within Tofua's caldera formed after this eruption, including its 4 volcanic
cones.
The vegetated tuff ring is the oldest, while the youngest vent is known as Lofia.
Lofia contains a spatter cone, which has been continuously erupting for more than 6 years.
On the eastern rim of the caldera, a prominent fissure vent can be spotted, where several
vents simultaneously released lava which cascaded down a cliff into the caldera lake.
Although Tofua is still a dangerous volcano, it is unlikely to produce a major explosive
eruption for the foreseeable future.
With this being said, a small explosive eruption which begins in its central crater lake could
spell disaster for anyone on the island.
Such an eruption would produce pyroclastic flows and hurl boulders of rock which could
reach any part of the island.
Luckily, the vast majority of eruptions have been confined to its northern caldera rim.
However, some small lava flows have occurred outside its caldera to the north and east,
which is likely to repeat in the future.
I hope that you enjoyed this video!
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