On January 15th, 2022 at 4:28 pm local time, the Hunga-Honga Hunga Ha'apai volcano in the
nation of Tonga produced its most powerful explosion ever recorded.
This explosion sent a sustained plume of ash to a height of 30 kilometers or 98,000 feet
into the atmosphere.
As this explosion triggered a magnitude 5.8 earthquake, one of the largest landslides
in recorded history occurred.
As much of the volcano's edifice slid into the ocean, it generated an energetic tsunami,
which went on to cause damage to locations as far away as Japan, California, and Peru.
Meanwhile, residents as far away as Alaska heard the associated explosion, as confirmed
by the national weather service.
Now that the eruption appears to be over or at least decreased for the moment, we can
take a look at what the island on which this volcano is based now looks like.
Although ash particles may be obscuring radar telemetry, it appears that more than 95% of
the original 4 kilometer or 2.5 mile wide island from January 13th has been destroyed.
Not only was all of the central edifice of ash which connected two more sturdy islands
destroyed, but the majority of the northeast and parts of the western island are also gone.
Thus, the vent which produced the January 15th eruption is no longer above sea level,
and the Hunga Tonga volcano is now almost completely a true submarine volcano.
I can with confidence say that this event was the single largest volcanic eruption of
the last decade.
However, since a volcanic explosivity index rating which measures the eruption's size
won't be definitively made for several weeks at a minimum, it has led to a large degree
of speculation.
Many news websites and experts are suggesting a wide range of eruption sizes, ranging from
VEI 4 to VEI 6.
Based on the available evidence, I think that the eruption was a mid end VEI 4, and I will
explain why.
When looking at a volcanic eruption, there are several useful factors which can help
to approximate an eruption's size.
These include the thickness of ash which fell at a specific distance, the amount of sulfur
dioxide released into the atmosphere, and the peak height of the eruption plume.
The reason many people are making high estimates is they look at the 30 kilometer eruption
column height, compare it to historical eruptions, and place the volcano in the VEI 5 to 6 range.
However, those people are forgetting the geologic setting of this volcano.
Hunga Tonga is a primarily submarine volcano, and the abundance of ocean water at shallow
depths greatly amplified the size of the explosion, making the eruption plume be far larger than
if the same eruption had occurred in the middle of a desert.
Using a mathematical formula, we get a figure suggesting a large VEI 4 or small 5 eruption.
Now let's look at the amount of sulfur dioxide released by the eruption.
Sulfur dioxide is released during all volcanic eruptions, and the amount of erupted magma
whether through flows of lava or fine ash is closely aligned with the amount of gas
measured.
Using NASA satellites, the amount of sulfur dioxide released by the eruption totals 400,000
metric tons.
While this is a large number, it is only a fraction of sulfur dioxide comparatively released
by recent VEI 5 or 6 eruptions.
Comparing the figure of 400,000 tons to recent smaller volume VEI 4 eruptions such as Calbuco
in 2015-2016 and La Soufriere in 2021, you can note that there's a near perfect match.
Thus, I estimate that the eruption ejected around 0.35 cubic kilometers of volcanic rock.
While the immediate eruption is seemingly over, there is a warning sign of more events
to come.
Several scientists noted that in the geologic history of Hunga Tonga, the volcano produced
a caldera forming eruptive sequence every 1,000 years.
These sequences did not contain a single eruption, but rather several over a closely spaced period.
Thus, more similarly sized eruptions and tsunamis are likely over the next decade.
As a final note, the edifice of Hunga Tonga is still unstable, so more tsunamis may occur
over the next several days to weeks.
Thanks for watching.
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