Monitoring active fumaroles through electrical and magnetic survey: an application to the Pisciarelli fumarolic field (Campi Flegrei, Italy).

The hydrothermal area of Pisciarelli, together with the adjacent Solfatara volcano, currently represents the most active structure of the Campi Flegrei caldera in terms of degassing and seismic activity and recently manifesting significant morphological variations, including the opening of new fumarolic vents and mud emission episodes as well as changes in the geochemical characteristics of the gases/fluids. 
To define the structural setting of the Pisciarelli fumarolic field, Electrical Resistivity (ERT) and Time-Domain Induced Polarization (TDIP) tomographies, Self-Potential (SP), Temperature (T), PH and Magnetic (Mag) mapping have been recently realized. 
The geophysical tomographies furnished a 3D model of the area, which reconstructs the Pisciarelli subsurface in its area of maximum degassing, containing the main fumarole (“soffione”) and the mud pool. The comparison of the 3D model with SP, T, PH and Mag maps acquired in the area revealed the occurrence of zones characterized by intense and complex faulting and fracturing processes, affected by fluid circulation, as well as identifying sectors of the subsurface where gases accumulate as also evidenced at the surface by the presence of fumaroles and intense hydrothermal rocks alteration. In particular, the 3D model evidenced an upwelling channel in which fluids stored in a more profound reservoir rise toward the surface. Such a structure seems to be surmounted by a clay-cap formation that could govern the circulation of fluids and the abundance of gases/vapours emitted by the soffione.
The conceptual model proposed for the Pisciarelli fumarolic field suggests plausible mechanisms for explaining, at the same time, the soffione activity and the role played by the deeper origin fluid/gas in the shallow fluid circulation system. In addition, the advance in the understanding of the Pisciarelli fumarolic field setting could also improve the strategy for monitoring the unrest processes in the area and evaluating the associated hazards.