Adjacent to the city of Naples in Italy is the famous Vesuvius volcano, which is well
known for its large and deadly explosive eruptions.
However, since 1944 this volcano has been quiet.
In contrast, worrying signs are beginning to show at another nearby volcano which is
just as dangerous.
What I am referring to is the supervolcano known as Campi Flegrei, whose most prominent
feature are its two large calderas.
Since 2011, this supervolcano has been on a state of heightened volcanic alert, characterized
by a yellow alert level.
The main two features of this heightened state of unrest have been abundant earthquakes and
dramatically increased levels of ground uplift.
Of the two, ground uplift is the most significant, as it indicates the intrusion of magma underground
which pushes up overlying soil.
This occurs in a manner similar to a mole digging underground in a grass yard.
Since 2011, a very shallow intrusion of magma at a depth of approximately 3 kilometers has
pushed up the ground underlying the Pozzuoli site by 85 centimeters or 33 inches.
Along with other effects, this uplift has caused several regional docks to completely
dry out during low tide as they are now too far above sea level.
If this uplift were to continue at its present rate, a dangerous threshold would be reached
around mid May of 2022.
This threshold might seem insignificant to the average person, but it marks the maximum
directly measured uplift of the local ground in the 20th century.
The last time the soil was uplifted this much was in 1984, which led to the evacuation of
40,000 residents in the Terra district due to the threat of houses potentially collapsing
and a possible volcanic eruption.
Thus, if the ground uplift continues at its present rate, which in all likelihood it will,
evacuations will become increasingly likely by May or June.
Of course, the overall situation is different than it was in 1984, and the decision to evacuate
or remain will be left up to the good scientists at INGV.
Regardless, the aforementioned threshold happens to mark what the minimum level of uplift is
required to produce a volcanic eruption.
For example, the last time before the 20th century that the Campi Flegrei volcano was
uplifted beyond this threshold was in 1538, which led to the formation of the Monte Nuevo
cinder cone.
Of course, some context is needed.
While the uplift beyond typical caldera levels is about 3.5 meters right now, in 1538 it
was 17 meters above normal.
Thus, this uplift could theoretically continue for several hundred more years at its present
rate before an eruption becomes a near certainty.
Although an eruption is not imminent and in all likelihood won't occur anytime soon, the
possibility of a surprise volcanic eruption occurring is becoming increasingly likely
as the uplift continues.
Based on the current center of volcanic activity, the next eruption is most likely to occur
at a site within a 1500 meter radius of the Solfatara volcanic crater.
Assuming that the next eruption occurs at Solfatara itself, it would be most likely
to cause what is known as a "phreatic eruption".
Phreatic eruptions are caused by underlying magma heating overlying groundwater, which
causes the water to flash to steam, build in pressure, and explode upwards.
While this type of eruption does not eject any magma, it is still just as dangerous as
an eruption that does, as it produces pyroclastic flows.
If a small phreatic eruption were to occur, much like what happened at this very crater
in 1198, a potentially several kilometer long pyroclastic flow could be generated, incinerating
everything in its path.
This is an issue as thousands of residents live not only in close proximity to the crater
but also physically live on the crater rim.
Phreatic eruptions as a whole are almost completely impossible to predict based on our current
knowledge of volcanology, but generally occur in heightened states of unrest, much like
what is ongoing at Campi Flegrei right now.
Two recent examples of deadly phreatic eruptions which occurred without warning are the 2014
eruption of Mount Ontake in Japan and the 2019 eruption of White Island in New Zealand.
In summary, we are entering a dangerous period of activity which has a low albeit statistically
possible chance of a volcanic eruption in the next several years.
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