On January 15th, 2022, the Hunga-Honga Hunga Ha'apai volcano in the nation of Tonga produced
its most powerful eruption ever recorded.
As the volcano exploded with a force equivalent to the detonation of 6 million tons of TNT,
a sustained eruption column was sent high into the atmosphere.
Soon, small fragments of rock termed lapilli rained down across sections of the nation
of Tonga including Tongatapu.
Meanwhile, the explosion generated a tsunami wave which would go on to cause destruction
across the Pacific Ocean.
While individual tsunami waves lasted for as long as thirty minutes, by the time the
first wave hit, the explosive eruption had already ended.
Originally, us scientists had thought that the distinct eruption had lasted for around
55 minutes.
In reality, the eruption lasted around 10 minutes, during which the volcano ejected
0.5 cubic kilometers of rock.
This is very strange as eruptions with sustained columns, termed plinian eruptions, typically
last on the timeframe of many hours.
As an example, the largest eruption of the 20th century, the Novarupta eruption of 1912
in Alaska lasted for 60 hours.
Therefore, what was witnessed at Hunga Tonga Hunga Ha'apai marked the shortest duration
plinian eruption ever recorded.
An interesting fact is that if you take into account the rate of ejected material per hour,
and compare it to other recent large volume eruptions, the Hunga Tonga eruption would
be the most energetic since the 1883 eruption of Krakatoa.
As so much material was ejected in a short timeframe, it explains why the eruption plume
was unusually tall despite the eruption's small size.
Speaking of the eruption plume, recent data suggests that the top of the mushroom cloud
reached around 35 kilometers in height.
However, at its center, a very small section of the plume reached perhaps as high as 55
kilometers in height which is more than halfway into space.
It was even witnessed from on board the international space station.
Of course, this impressive height has not yet been confirmed, and would represent the
highest eruption plume ever measured.
All that we are certain of is that a section of the eruption plume reached higher than
35 kilometers in height, hence the shadow visible on the main portion of the plume top.
Regardless, even the figure of a 35 kilometer plume is unusual, as typically only eruptions
which are two orders of magnitude larger reach this height.
This brings me to my next point.
There has been a bit of discussion around the volcanology community about calling the
January 15th eruption a brand new eruption type.
I happen to agree with this idea.
While we are unsure what to call it, names are typically designated off of the first
volcano documented to produce such an eruption.
For example, the 1963 to 1967 island forming eruption of Surtsey in Iceland was used as
the basis to describe so called "Surtseyan eruptions" which describe shallow island forming
eruptions which often result in peripheral islands.
Before January 14th, this eruption type was the dominant type of activity witnessed at
Hunga Tonga Hunga Ha'apai.
While later activity was initially described as plinian due to its sustained eruption column,
this isn't a good description of the eruption as it was too brief.
Another possibility could be a so called phreatoplinian eruption; that is a very wet plinian eruption
with an unusually high eruption column.
While this initially seems like a good match, comparing it to two known historical examples,
those eruptions each lasted at least 6 hours.
Thus, the Hunga Tonga eruption was clearly different, and I suggest the new term be called
a "Ha'apaian" eruption.
This eruption type would describe a very brief eruption with a sustained eruption column
that occurs from a vent beneath a body of water.
Such an eruption would be triggered by water seeping into the underlying magma conduit,
flashing to steam, and producing a very large albeit brief eruption.
Eruption columns generated via this eruption type would be generally higher than 30 kilometers
and composed primarily of water vapor instead of ash dominant plumes which typically have
an ominous gray color.
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