If you head west from the city of Naples you will begin to see large craters, altered regions,
and calderas in the ground, representing vents of the Campi Flegrei volcano.
Over the last few days, several news outlets have produced articles with titles that suggest
that this “supervolcano could erupt for the first time since 1538” or that it “might
be creeping towards an eruption”.
However, the wording like this is ripe for being misinterpreted and being grossly taken
out of context.
Thus, I will explain how significant or insignificant the current eruption hazard is at this volcano.
Campi Flegrei is not a towering stratovolcano like Mount Vesuvius, but rather could best
be described as a series of overlapping calderas, which also contains a series of large and
deep explosion craters.
The edifice of Campi Flegrei is dominated by two large calderas that measure 12.6 and
14.5 kilometers wide, having formed in very large explosive eruptions 14,900 and 39,850
years ago which ejected 79 and 320 cubic kilometers of tephra respectively.
Eruptions of this scale were truly catastrophic when they occurred, being far larger than
the eruption that destroyed Pompeii from Mount Vesuvius in 79 CE.
Luckily, the vast majority of eruptions from this volcano in the last 10,000 years have
been 2 to 4 orders of magnitude smaller than the caldera forming eruptions just described,
with smaller eruptions occurring about once every 500 years on average.
Campi Flegrei today has a fairly large and complex magma chamber which is divided into
two sections.
There is a deeper and larger section at a depth of 8 kilometers which in the last 73
years has been feeding a smaller magma chamber that is a sill at a depth of 3.6 kilometers.
This sill is not perfectly flat as it contains a bulge in its center.
As this sill continues to expand, so does the sill's bulge, which causes overlying ground
to be uplifted by about the same amount as the bulge's thickness.
In the last 10,000 years, sections of the Campi Flegrei caldera have been uplifted or
have subsided by as much as 30 meters or 98 feet, and the mechanism just described appears
to be the cause.`
Overall, there appear to be 4 phases which the volcano undergoes before it erupts which
are displayed in this chart.
I have overlaid what years each stage leading up to Campi Flegrei's last eruption in 1538
fell into, along with where I think the volcano stands in as of 2023.
My justification for placing Campi Flegrei in the higher unrest tier which last time
it entered this phase lasted for 136 years is due to the average rate of peak uplift
it is experiencing, totaling an average of about 6.2 centimeters a year since 1950, when
the volcano stopped its long term subsidence that followed its 1538 eruption.
Due to how long term this uplift is which is centered a bit south of the Solfatara site,
despite the fact that it is occurring in spikes in activity followed by longer minor subsidence
periods, we are pretty confident that a body of magma exists which measures about 3,600
meters wide, 6 meters thick, and contains 40.7 million cubic meters of molten rock.
As it stands right now, if this were to somehow all find a pathway to the surface, it could
generate in a worst case scenario a large VEI 3 or very small end VEI 4 explosive eruption.
However, in my opinion such an eruption cannot occur yet because a crucial factor is missing.
Preceding almost every eruption of Campi Flegrei in the past, the ground repeatedly ruptured
above the magma chamber, providing already shallow magma a path of least resistance towards
the surface.
This occurred during 1536 when magma migrated to the west away from the sill where it pooled
for 24 months and then erupted.
We have not yet reached this stage, although a scientific paper referenced in this video's
description suggests that we might be getting close to a period when the volcano could rupture.
This could either one rupture the crust but magma does not intrude into it due to being
at the wrong location, two rupture the crust and magma intrudes into it which leads to
an explosive volcanic eruption, or three ruptures the crust but fluids seals it before magma
reaches it.
In my opinion, I find the third possibility to be the most likely.
It is not known when exactly the crust overlying Campi Flegrei's relatively shallow sill will
rupture, but the chance of it rupturing is seemingly at its highest since 1950, as the
rock is about 3 times weaker in 2023 than it was in 1984.
So in summary, Campi Flegrei in my opinion does not appear to be in danger of imminently
erupting, but is at its highest chance of producing a ground rupture since 1950.
We do not know when such a rupture will occur, but when it does, if a very specific albeit
unlikely set of circumstances occur, an eruption could follow.
Thus, a volcanic eruption is overall unlikely but is now theoretically possible, but only
once a rupture occurs which has not yet happened at Campi Flegrei.
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