On January 15th, 2022 the Hunga-Honga Hunga Ha'apai volcano violently exploded in a blast
equivalent in energy to the detonation of 6 megatons of TNT.
During the initial seconds of the explosion, a large area in the center of the island slid
into the sea in a massive landslide, generating a destructive tsunami, with initial wave heights
of up to 15 meters or 49 feet.
This tsunami would go on to hit the entire Pacific Ocean, causing damage as far away
as Peru.
The powerful shockwave created by the eruption was so loud that it was heard more than 5800
miles distant in the city of Fairbanks in Alaska.
Several of my viewers even sent me emails reporting that they heard the blast in northern
Yukon.
After the tallest eruption plume in recorded history cleared, reaching 58 kilometers or
190,000 feet in height, what remained was a fraction of the former volcano.
What used to be one large island was now two distinct small islands, representing the core
of two ancient vents.
In the days after the eruption, preliminary data suggested that about half a cubic kilometer
of material was ejected in a VEI 4 event.
This figure was largely estimated by both the amount of ash which fell compared to known
historical eruptions and by measuring the amount of sulfur dioxide which was released.
It is now three months later, and since then, several scientific papers have been published
which have made differing but more thorough claims about the size of the eruption which
occurred.
One of these papers recently made the rounds on various scientific publications, with a
claim that the eruption had a volcanic explosivity index of a 6.
For context, the volcanic explosivity index is a scale that goes from 0 to 8.
With a small exception on the lower end of the scale, each increase in number indicates
that an eruption is 10 times larger.
For example, the 1980 eruption of Mount Saint Helens ejected 1 cubic kilometer of material,
and thus was rated on the scale as a 5.
The 1991 eruption of Pinatubo ejected 13 cubic kilometers of volcanic rock, and since it
was slightly more than ten times larger than the aforementioned eruption, was rated as
a 6.
Eruptions that rate higher than a 5 are rare, as one such eruption only occurs an average
of every 12 years.
Eruptions designated a VEI 6 are even rarer, as they occur about once every 75 years.
Thus, the claim that the eruption of Hunga Tonga Hunga Ha'apai is a 6 must initially
be taken with skepticism, as such eruptions are absurdly rare.
This claim was made in a paper written by Poli and Shapiro, which proposed a novel method
to estimate the size of Hunga Tonga's eruption.
The paper used recorded seismic waves from the eruption to determine the amount of energy
expended as well as eruption duration and the velocity at which material which was ejected.
With a few assumptions, this data suggested that 10 cubic kilometers of material were
erupted, indicating a volcanic explosivity index of a 6.
Their method is promising, but there are some problems with their extrapolation for this
volcano.
While the main eruption duration was measured in the paper at 100 minutes, the authors assumed
that volcanic material was ejected at the same velocity during the entire duration.
Observations of the eruption showed that continuous eruptive activity only lasted for 10 minutes,
after which only smaller scale eruptive activity occurred interspersed by lengthy periods of
where next to nothing erupted.
This model thus overestimates the volume of ejecta by as much as a factor of 10.
While this method is definitely intriguing, it makes assumptions of constant velocity
ejecta over the entire eruption duration which simplified the math but doesn't reflect the
reality of what was witnessed.
Their model needs to take into account the rather burpy nature of eruptions and be fine
tuned by applying it to more eruptions with already known VEIs to better predict the size
of future eruptions.
In conclusion, observations still point towards the eruption being a mid end VEI 4.
But, this is science and more data may yet prove me wrong.
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