Campi Flegrei News

 

Volcanic unrest continues at the volcano, characterised by continuing uplift, seismic swarms involving quakes felt by the local population, and intense degassing from various fumaroles and through diffuse ground emissions. Some of these phenomena have increased in intensity over the past weeks. However, it is believed that chances of an eruption in a near future are still very low, but the situation should be monitored very closely.
The observatory in Naples (OV-INGV) published a detailed article based on its latest monitoring data, evaluating the situation. It is reported that ground deformation, centered around the area of Pozzuoli, not only continues but its rate has increased in recent weeks: Between August 14 and 20, 2023, the average value of the uplift rate in the area of maximum deformation was about 15 mm/month, OV-INGV writes. Since the current episode of uplift started in 2005, the slow ground uplift has reached 111 centimeters in the Rione Terra area in total.

In addition to the increase of rate of ground deformation, seismic activity has been more intense recently. In particular, seismic swarms have been occurring more frequently. In the week 14-20 August 2023, 3 earthquake swarms occurred with a total of 203 quakes detected above magnitude 0.0 and up to a magnitude 3.6 event during the night 17-18 August, which was felt widely in the area of Solfatara, Pisciarelli, and Accademia. Most hypocenters of the quakes were east of Pozzuoli town and at shallow depths between 3-0 km below the ground.

A well-known phenomenon
Ground movements over years or decades are a typical feature of the Campi Flegrei and known since antiquity. Since Roman times, the areas has been characterised by gentle subsidence at a mean rate of about 170 cm a century, interrupted occasionally by intervals of comparably rapid uplift during 600-700 AD, the 100 years preceding the only historic eruption in 1538, and the current period that began in 1950. The latter so far involved three episodes: 1950-52, 1969-72, and 1982-84, when many inhabitants of the area, especially those in the historic center of Pozzuoli, were forced to abandon their homes.
During these 3 episodes in the last century, ground uplift was up to ten times more intense, on the order of 0.1–1 m per year, and totalled almost 4 meters by the end of the 1980s. This was followed by two decades of slow deflation until the trend reversed again in 2005 and entered the current phase of uplift, with (so far) significantly lower rates of 0.01-0.1 m / year.

The cause of the uplift
According to OV-INGV, the likely cause of the seismic swarms and uplift “may be due to strong gas uplift and increased pressurisation of the deep hydrothermal system: the rocks are being stressed, fracturing and generating earthquakes. Another possibility is that small batches of magma fed by the deep magmatic system, are being injected into the subsurface about 3-4 km deep.”
The source of the fluids (volcanic gasses, watery solutions) is believed to be a vast magma storage (“magma chamber”) under the Phlegrean Fields and Gulf of Naples at depths below 6-8 km. “The amount of gas released is considerable: in the Solfatara-Pisciarelli area, more than 3,000 tons of CO2 per day is released, much of it resulting from deep magmatic outgassing and the interaction of magma with carbonate rocks.”

Evaluation of the situation
“At present, the probability of a volcanic eruption is relatively low, since there is no evidence of magma rising to the surface. Moreover, the crustal volume uplifted at the moment is much less than 1 cubic km in size: consider, for reference, that some eruptions in the past were preceded by rapid and concentrated ground uplifts of a few tens of meters. Seismic, geochemical, ground deformation, surface and in well thermal variations, and gravimetric variations do not, at present, provide indications that magma is rising to the surface. However, the volcano has its unstoppable natural evolution and, sooner or later, it will erupt again. The INGV-OV's attention is utmost in the collection, study and interpretation of data, and any changes are and will always be discussed and communicated promptly to the Civil Protection Department at its various levels.”


Will there be an eruption?
The Campi Flegrei is a very active volcano, and it is not a question whether it will erupt, but when. The last eruption occurred in 1538 and was the only historic eruption. It probably had followed a repose an interval of 3000 years. It is therefore not feasible to use statistics on past behaviour, but it is possible to compare the current situation with what is known from back then. Prior to the eruption in 1538, gradual uplift occurred over approx. 100 years, before it finally escalated to several meters of rapid movements during the very last days immediately before the eruption. As well, seismic activity was noticed at increasing rates and intensity during the years, months, and days before the eruption started.If the current phase of unrest is a precursor to an event similar to 1538, it seems not to be very close, at least.
On the other hand, too little is known about the behaviour of large caldera volcanoes. Phases of ground uplift are typical precursors of volcanic activity, but also part of their natural behaviour during repose times, and even if magma intrusions are causing them at depth, most of the times, they are not followed by an eruption:magma often rises and then stalls and starts cooling; in such cases, ground deformation typically fades out eventually, or even reverses, reflecting a new stable situation of the system underground.
Other scenarios discussed by scientists involve that the proceeding uplift might lead to ruptures of the upper crust in the area, allowing sudden, massive releases of fluids, potentially but not necessarily involving magma, but more likely pressurised batches gasses and water, which could generate sudden steam-driven (phreatic) explosions with little warning. How likely and when this might be is matter of debate, but the most active areas of fumarolic activity in the Solfatara-Pisciarelli zone are best to be avoided.