On January 15th, 2022, at 5:14 pm local time, the Hunga Tonga Hunga Ha'apai volcano exploded
in the nation of Tonga in what was the largest volcanic eruption of the 21st century.
This eruption obliterated the existing island, causing a 4 kilometer wide section of ground
to drop by 750 meters or 2,460 feet.
Although the exact size of the eruption which occurred on that day is still unclear, it
was somewhere between 6.5 to 14.7 times larger than the 1980 eruption of Mount Saint Helens.
Due to the sheer size and unusualness of this eruption, it produced a number of highly unusual
phenomena in the short and long term.
Short term, the sound of the initial explosions was confirmed to have been heard as far away
as Fairbanks in Alaska and central Yukon; a whopping 6,089 miles or 9,800 kilometers
distant.
However, it may have been even heard at an even greater distance as several of my viewers
reported hearing the eruption in Lexington Kentucky.
Another unusual effect was that this eruption had an unusually white water vapor rich and
ash poor eruption column that reached the highest level ever recorded, an impressive
58 kilometers or 190,000 feet into the atmosphere, even reaching the layer of the mesosphere.
Of the slightly more than 90 million US dollars in damage which the eruption caused, almost
all of it was caused by the volcano's deadly tsunami.
It struck almost the entire Pacific Ocean basin, with wave heights of up 15 meters or
49 feet, with the highest waves closest to the eruption site.
Most importantly, as per M. Heirdarzadeh & others in an article in Ocean Engineering, the tsunami
began with an initial wave height of 90 meters or 295 feet, and was 12 kilometers wide.
Additionally, this paper confirmed that there was not 1 but 2 tsunamis created by different
causes.
The first tsunami was smaller with wave heights under 2 meters propagated outwards at just
under the speed of sound.
This smaller tsunami was unusual in that it even caused measurable waves in the Caribbean
and in other ocean basins away from the Pacific, and arrived before the main larger tsunami
hit the western coast of Mexico.
How was this possible?
The simple answer is that this smaller tsunami was a so-called meteo-tsunami.
In other words, significant displacement whether it be through a landslide, earthquake, or
pyroclastic flows was not the cause.
Rather, it was caused directly by the atmospheric shockwave that originated from a blast equivalent
in energy to the simultaneous detonation of tens million tons of TNT.
As this shockwave raced around the planet, it caused a prominent short term spike in
atmospheric pressure.
As this pressure spike raced across the ocean, it temporarily pushed water down.
After the shockwave moved beyond, the ocean rebounded slightly, forming a discernable
wave.
A similar phenomena occurred during the 1883 eruption of Krakatoa, which is the only known
recent documented volcanic eruption which was comparable to Hunga Tonga's eruption.
Just like Krakatoa, the tsunami at Hunga Tonga Hunga Ha'apai was not caused primarily by
a landslide.
Rather, it was generated when part of the massive eruption column collapsed downwards,
creating pyroclastic flows.
As these pyroclastic flows raced outwards, travelling at least 15 kilometers, part of
the gas and material contained in them fell into the water, displacing it and generating
a tsunami.
The same authors who estimated the initial tsunami height also estimated the approximate
volume of water which was displaced; 6.6 cubic kilometers.
Although the tsunami created by this catastrophic eruption was indeed massive, it just barely
missed the margin required to be considered as a megatsunami.
Megatsunamis have wave heights of 100 meters or more.
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