Surface deformation and volcanic activity at Campi Flegrei caldera (Italy) over the last 5000 years

Campi Flegrei caldera (Italy) has experienced repeated unrest episodes over historical and instrumental times, with the latest Monte Nuovo eruption in 1538 CE, making eruption forecasting particularly challenging. This contribution integrates long-term records of surface deformation with modern geodetic observations to interpret the short- and long-term dynamics of the caldera over the last 5000 years. A revised dataset of 32 elevation points integrates onshore borehole stratigraphy and offshore abrasion platforms, and provides documentation of the uplift due to the resurgence in the centre of the caldera 5 ka. Also, historical, archaeological, and bathymetric data constrain elevation changes at 20 coastal sites since Roman times, allowing reconstruction of pre-, syn-, and post-eruptive deformation associated with the Monte Nuovo eruption. Then, GNSS and InSAR measurements documenting the unrest since 2005 are combined with 3D finite element modelling to infer the geometry, depth, and volume changes of the active plumbing system. Results over these different time periods consistently indicate an active two-source plumbing system at Campi Flegrei, comprising a shallow deformation source at ~4–5 km depth beneath Pozzuoli and a deeper magmatic reservoir at ~8 km depth. Similar deformation patterns and source configurations characterize both historical eruptive phases and the current unrest. Petrological constraints suggest that magma ascent to depths shallower than ~8 km is the primary driver of unrest, even when an eruption does not occur. These findings provide a coherent framework for linking centuries-scale caldera dynamics with present-day observations. They suggest that the magmatic system at Campi Flegrei has been stable over the last 5000 years, thereby improving our understanding of unrest processes at this caldera.