Thermal features and heat budget of Campi Flegrei unrest caldera from fast, high-resolution airborne mapping

Campi Flegrei caldera (CFc; Southern Italy) is the archetype for volcanic risk occurring within a highly anthropized area. CFc was mostly shaped by the collapse following the Neapolitan Yellow Tuff eruption (NYT) ~15 ky BP, which generated about 50 km³ of volcanic products mainly deposited via huge pyroclastic flows. More than 50 eruptions from several volcanic centers were generated within the caldera after the NYT, with last eruption occurring in 1538 (Monte Nuovo eruption). Since the 1950s, CFc experiences a long-term unrest in the Pozzuoli area. After the 1969-72 and 1982-84 episode, uplift started again in 2004, raising serious concern to population and authorities also because of the recurrent seismic activity and the persistence of fumarolic emissions fed by the underlying hydrothermal system.

In this context, thermal monitoring of the caldera is a strategic issue for volcanic forecasting, considering that several areas are prone to the opening of volcanic vents. The large size of the onshore portion of the CFc (90 km²), the difficulties to access several anomalous sites and the huge degree of anthropization make the direct assessment of ground-thermal anomalies and the realization of periodic measurement campaigns very difficult, time-consuming and unsafe.

Here we report on a detailed airborne thermal mapping from a flight made on 15 April 2022 at ~6.30 am (local time). Thermal acquisition was performed with a wide-array broadband thermal sensor in conjunction with optical imagery in Red-Green-Blue bands via a 150 MP camera. The sensor platform and the aircraft ¾  including logistic facilities, agreements with military airports and authorizations to fly ¾  are a strategic asset of the BENECON. The high resolution of thermal mapping (instrumental accuracy: 0.05 °C on temperature; pixel size: 0.45m x 0.45m) in conjunction with real-time acquisition of optical images allows a straightforward discrimination of natural ground anomalies from thermal emissions and spots due to anthropic activities. Ground thermal anomalies related to volcanic-hydrothermal activity and associated with the caldera unrest are concentrated in the well-known Solfatara and Pisciarelli sites, whereas minor features are detected on the relief bordering the western side of Agnano plain, inside the Astroni crater and on the southern flank of Monte Nuovo, in line with results from existing ground surveys. At Solfatara and Pisciarelli, the shape of measured thermal anomalies matches that of CO₂ fluxes interpolated from literature data. The consistency between heat fluxes computed from airborne-detected ground temperatures and soil CO₂ fluxes (e.g., in the order of 100 MW for the Solfatara crater) confirms that steam condensation from hydrothermal activity is presently the dominant engine responsible for endogenous heat release at CFc.

The fast execution of the airborne survey, the rapid data processing and post-processing and the capability of detecting the most subtle anomaly prompt for periodic surveys of the CFc thermal flux aimed at 1) the tracking of existing anomalies 2) the rapid detection of new thermal features and 3) the building of time-series. Integration with optical and, in perspective, hyperspectral VNIR images foster an unprecedented capability to monitor the ongoing volcanic unrest.