Some additional context
The Monte Nuovo eruptionIn this article on volcanocafe there is some more information about the build-up to the last eruption here taking place in 1538. It's worth to note that this also took place when the neighbouring and more famous Vesuvius volcano was in a quiet phase.
During this time, the dragon of Campi Flegrei had not fully fallen asleep, or perhaps she had restless dreams. At times, a new eruption or explosion would leave its mark on the caldera. These eruptions were very much smaller than the big ones (most were VEI3 or 4) but they left the caldera pockmarked with cones and craters. There have been some 70 eruptions in the caldera since the Neapolitan collapse. These were monogenetic, meaning each came from a separate magma intrusion in a new location. At first, the eruptions occurred mainly close to the caldera rim. Many of these earlier eruptions happened below sea level. Around 8000 years ago the caldera went quiet. About 6000 years ago eruptions resumed with 20 eruptions over a period of 2500 years. The new eruptions occurred mainly around an uplifted block within the caldera. And 3500 years ago the caldera went quiet again. There is only one eruption known after this: Monte Nuovo.
More recent history
Prelude to the eruption
Often the signs of an impending eruption are recognized very easily – but only in hindsight. Volcanic 20:20 foresight only comes after the fact. So it was here. The old records show indications that something had been brewing but these signs could not have been recognized as such at the time.
Recent studies indicate that slow re-emergence of land lost after the Roman period started after 1250. Around 1300, new buildings (churches, actually) appear at Pozzuoli in a place which previously was submerged. The inflation was probably ‘only’ a few meters. This period may also be when the old market square with the Roman pillars resurfaced. It was the first indication of a change at Campi Flegrei since the deflation had begun a millennium earlier.
The first direct sign of re-activation started in 1470. Between 1470 and 1472 there was an earthquake swarm, strong enough that damage to buildings in Pozzuoli is recorded. More gas was emitted by nearby Solfatara, sufficient to kill trees. After 1472, it appears things quieted down again, although a few earthquakes continued to be strong enough to cause damage.
Around 1500, another slow change was becoming obvious: the land was rising. This was clear because the shoreline was receding. New land became available for people to use. That did not go unnoticed by people in need of new houses because of the damage done to the old ones. A declaration in 1503 was made that the new land belonged to the University of Pozzuoli. Another declaration regarding ownership of new land was issued in 1511, so apparently the sea was still withdrawing further. Between 1250 and 1536, the promontory at Pozzuoli had risen by 14 meters. The coast further west had inflated by 5-8 meters.
In between these declarations, there were strong earthquakes in 1505 and 1508, causing significant damage in Pozzuoli. Again, it quieted down apart from a damaging earthquake in 1520.
Crisis
Things suddenly turned for the worse in September 1536 when the earthquakes became much more frequent and more severe. In February 1537, reports state that many houses in Pozzuoli had been damaged, some severely so. People began to leave the town. At the same time Solfatara became smellier.
On April 20, 1538, an earthquake was felt in Naples strong enough to cause fear. Activity continued for the next months, and the earthquakes became progressively stronger and more frequent over the summer. This peaked on September 14, only to restart on September 20. By September 22, people began to sleep outdoors, away from the ruined houses. The shaking continued and became near continuous by September 27. In distant Naples, 5 to 10 events were felt per day. Even for the Neapolitans, this got a bit much.
-> The eventual eruption started on 29 september.
For the remainder, just check the article.
Given the unrest in 1970s and 1980s already, i think that could be quite comparable to the unrest in 1470s. And we see noticeable inflation as well, especially long term.
I do not think we are currently in a stage much closer to an eruption, because there would have to be more escalation. But what is clear is that the more unrest increases the more it will point or sign towards an eruption getting closer. And these seismic crisises are already part of a new phase of unrest. It could point towards an eruption (not supereruption but just eruption) that won't happen tomorrow but perhaps sometime this century. Though given its past, usually it'll give its warning signs and i suspect the damaging earthquakes leading to the eruption would already lead to evacuations prior to an eruption occuring.
