Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 122, Issue 11, Pages 8749-8768Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2017JB014389
Keywords
electrical resistivity tomography; hydrothermal system; Solfatara volcano; Campi Flegrei caldera; fumarole
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Funding
- Rhone-Alpes region [CPER07_13 CIRA]
- OSUG@2020 labex [ANR10 LABX56]
- Equip@Meso project of the programme Investissements d'Avenir [ANR-10-EQPX-29-01]
- Med-Suv project
- European Union [FP7 ENV.2012.6.4-2, 308665]
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The Solfatara volcano is the main degassing area of the Campi Flegrei caldera, characterized by 60years of unrest. Assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood. In this study, we decipher the complex structure of the shallow Solfatara hydrothermal system by performing the first 3-D, high-resolution, electrical resistivity tomography of the volcano. The 3-D resistivity model was obtained from the inversion of 43,432 resistance measurements performed on an area of 0.68km(2). The proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model, a high-resolution infrared surface temperature image, and 1,136 soil CO2 flux measurements. In addition, we realized 27 soil cation exchange capacity and pH measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity. Hence, we show that the resistivity changes are mainly controlled by fluid content and temperature. The high-resolution tomograms identify for the first time the structure of the gas-dominated reservoir at 60m depth that feeds the Bocca Grande fumarole through a 10m thick channel. In addition, the resistivity model reveals a channel-like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the Fangaia area within a buried fault. The model delineates the emplacement of the main geological structures: Mount Olibano, Solfatara cryptodome, and tephra deposits. It also reveals the anatomy of the hydrothermal system, especially two liquid-dominated plumes, the Fangaia mud pool and the Pisciarelli fumarole, respectively.
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