Source Modelling from Ground Deformation and Gravity Changes at the Campi Flegrei Caldera, Italy

The deformation history of the Campi Flegrei caldera during the last decades consists of two large uplift events in 1970–1972 and 1982–1984, with ~3.5 m cumulative uplift, occurring at a rate of ~1 m/yr. Both events were accompanied by seismic activity, gravity changes and compositional variations of volcanic gases but no eruption took place. During the following decades, the area has been slowly subsiding but minor uplift episodes (~a few cm), seismic swarms and changes in degassing activity took place, showing that the area persisted in a near-critical state. Since November 2005, ground deformation resumed, although at a slower rate, totalling a displacement of ~0.77 m (February 2021). In this chapter, we present a retrospective analysis of ground deformation leading to a critical re-evaluation of the 1982–1984 uplift and of the following deflation, employing the most updated modelling techniques. Deformation and gravity data provide important constraints on depth, volume, mass density and dislocation mechanisms accompanying magma emplacement processes. The correct evaluation of these parameters is strongly conditioned by simplifying assumptions built in the different inversion procedures: in particular, the inferred source depth ranges from 5.5 km to less than 3 km and the intrusion density ranges from values pertinent to aqueous fluids to typical magmatic values. This review depicts the salient phases of the deformation history of this densely populated and high-risk volcanic area, helping to address debated issues, such as the role of the magmatic system, and their interaction with the shallower hydrothermal system. In spite of the mentioned difficulties, the following conclusion may be considered as firmly established: during 1982–1984 a magmatic intrusion took place, and the subsequent complex deformation history (1985–2010) was mainly controlled by the exsolution of volatiles with magmatic origin and their interaction with a shallow hydrothermal system. However, data collected after 2011 were modelled in terms of a deep inflating source of deformation, possibly resulting from a resumed magmatic recharge at depth.