On May 21st of 2023, a new explosive eruption occurred at the Mount Etna volcano in Italy.
Beginning at 7:06 am local time, this explosive eruption ejected gas rich molten rock onto
the surface, creating a towering lava fountain.
This lava fountain likely towered to a height of at least 500 meters or 1,640 feet, all
the while releasing a significant plume of sustained ash emissions.
These ash emissions quickly rose to a height of 7,000 meters or 23,000 feet, creating a
30 kilometer or 18.6 mile wide ash plume even visible from orbit.
This marks about the radius of where widespread ash fell on the ground, which soon coated
nearly 1,000 square kilometers in 1 to 4 millimeters thick of material.
Even at a distance of several kilometers from the volcano, ejected pieces of lapili which
were up to 2.5 inches in diameter fell onto the ground.
Because of all of this activity, and the fact that airborne ash is potentially incredibly
damaging to aircraft, the regional Catania airport was temporarily closed to all aircraft.
What had just occurred, although spectacular, was not too unusual given the nature of Mount
Etna.
The 288 minute long eruption sequence represented a paroxysm, aka a relatively short yet violent
burst of activity.
The number of paroxysms which Etna produces can widely vary, ranging from none to more
than 50 in certain years.
These paroxysms generally infrequently interrupt long periods of low intensity eruptive activity.
Etna during the last century has been erupting in some form 83% of the time.
The paroxysm which occurred happened to end around 11:54 am local time on May 21st of
2023, being the first true paroxysm to occur at Etna in 15 months.
In total, I estimate that approximately 3.6 million cubic meters of tephra was ejected,
meaning the latest eruption would register in on the volcanic explosivity index as a
2.
It is quite likely that about ten times this amount of lava was ejected but the truth is
we really aren't sure of the nature of the eruption which just occurred.
The reason for this is that despite being within 20 miles of hundreds of thousands of
people who can see the volcano, during this entire eruption not only its summit but also
its flanks were shrouded in a dense layer of cloud cover and fog, being so heavy that
it even obscured any orange glow that would have been generated by any lava flows or lava
fountains.
Thus, the reconstruction of the latest paroxysm at Mount Etna was merely a hypothesis based
representation of what may have just occurred.
Ignoring two singular explosions which occurred on May 6th and May 14th of 2023, Mount Etna
had actually not produced an eruption until today's paroxysm for a little more than 3
months.
When a paroxysm occurs at Etna, marking heightened volcanic activity, a number of very different
things can happen, with 4 historically represented possibilities.
This ranges from strombolian or strombolian like eruptions, which involve low silica lava
with a high gas content, that create lava fountains which have been historically up
to 3,000 meters or 9,842 feet in height, being some of the tallest lava fountains in the
world.
It also includes vulcanian eruptions which produce more viscous lava that forms a temporary
cap above a magma conduit than then explodes, producing intense ash emissions and on occasion
pyroclastic flows.
Flank lava flows can also occur during paroxysms, which can originate at a near summit fissure
or a flank cinder cone which forms during such an eruption, although these are highly
infrequent occurrences.
The 4th type of paroxysm is a plinian eruption with a sustained eruption column that creates
pyroclastic flows which can travel beyond 5 kilometers distant, and deposit centimeters
to decimeters and sometimes more thick of ash.
Luckily, plinian eruptions are very rare, having only occurred at Etna 3 times in the
last 4,000 years with the last one occurring in 1787.
In the upcoming weeks, one of two things could happen.
First, more paroxysms might occur, generating additional spectacular lava fountains which
might actually be visible if the cloud layer clears.
After all, several recent paroxysms of this volcano generally occurred within 48 hours
of one another.
Or, there may be yet another temporary lull in eruptive activity, which could continue
for a few weeks to months.
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