Description: The Campi Flegrei caldera is a large volcanic complex lying in the Campanian Plain, Southern Italy. During its history the caldera experienced episodes of bradyseism and intense swarm seismicity. The mechanism leading to unrest episodes is still debated, and great efforts are ongoing to improve the knowledge of this structure and its evolution due to the high volcanic risk in such a densely populated area. Here we present a resistivity model from a two‐dimensional inversion of audiomagnetotelluric data acquired along an approximately 5.6‐km long profile crosscutting the Solfatara‐Pisciarelli district and the Agnano plain. The resistivity model shows (1) very low resistivity values confined in the first 500 m of depth both in correspondence of the Solfatara‐Pisciarelli districts and the Agnano depression; (2) a resistive plume that extends underneath the Solfatara crater down to 2,000‐ to 3,000‐m depth, and (3) an adjoining relative conductive unit eastward. We discuss the resistivity structures in a multidisciplinary framework integrating inedited geochemical and seismological observations with existing surface geology and subsurface information. The Solfatara‐Pisciarelli district and the Agnano plain, both being expression of intense hydrothermal activity, show different characteristics. Below the Solfatara‐Pisciarelli area, the shallow conductive zone is interpreted as a faulted clay cap that overlies a highly active vapor‐dominated reservoir characterized by a convective mechanism. Conversely, below the Agnano plain, a liquid phase seems to prevail in the reservoir. The spatiotemporal variations of seismicity imply a combined action of preexisting tectonic lineaments and fluid interaction between the gas/steam reservoir and the outflow zone.

Description: Published

Description: 5336-5356

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Within a general volcanic unrest in the densely urbanized area of Campi Flegrei caldera (Italy) an increase in the activity of Pisciarelli hydrothermal area is occurring. The seismic amplitude of Pisciarelli fumarolic tremor is a proxy for the fluid emission rate of the entire Solfatara‐Pisciarelli hydrothermal system. The long‐term analysis indicates a significant increase, by a factor of ~3 of the fumarolic tremor amplitude since May 2017. This increment matches with the trend of geochemical and seismic parameters observed in Campi Flegrei, therefore highlighting that Pisciarelli is a key site to monitor the volcanic unrest underway in this high‐risk caldera. The analysis of data from three closely spaced seismic stations provided new clues about the source mechanism of the tremor. Analyzing the fumarolic tremor amplitude we could also identify an episode of enlargement of the emission area close to the main fumarole of Pisciarelli. We propose a monitoring system based on the fumarolic tremor analysis, which provides real‐time information on the Pisciarelli hydrothermal activity and therefore on the current unrest in Campi Flegrei caldera.

Description: Published

Description: 5544-5555

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: 〈jats:p〉Hydrothermal explosions occur through the sudden expansion of fluids at or near boiling condition with little or no precursors, making any kind of forecast difficult. Here, we investigate the processes occurring within hydrothermal systems in a potential critical state for explosions through a new methodology based on mass balances of thermal water solutes. The usage of this method reveals that the pore water samples of the Paleochori Bay (Milos, Greece; 〈20 m depth below sea level), chosen as a case study, are binary mixtures of a geothermal component and seawater, from which steam is either added through condensation of underlying, ascending vapors or separates through boiling. This new method enables us to quantify and map both the fraction of the original geothermal liquid in each pore water sample and that of the vapor supplied or separated from the solutions. Furthermore, the method allows us to compute the composition of the geothermal endmember. The map of the fraction of supplied vapor shows that decompressional boiling of ascending liquids predominantly focuses in the central part of the Paleochori Bay. Both the estimated composition and temperature (324°C) of the geothermal liquid endmember overlap those measured in geothermal well fluids at or near-boiling condition, except SO〈jats:sub〉4〈/jats:sub〉 and SiO〈jats:sub〉2〈/jats:sub〉. The lower SiO〈jats:sub〉2〈/jats:sub〉 and higher SO〈jats:sub〉4〈/jats:sub〉 content in the pore waters may be ascribed to the current production of an impermeable cap, which enables underlying fluids to accumulate and pressure to buildup. The evidence of liquid at or near boiling conditions and self-sealing processes in the Paleochori Bay suggests that decompressional boiling during abrupt pressure drawdowns might have caused hydrothermal explosions at Milos in historical times, whose occurrence is testified by several hydrothermal craters. Finally, our work shows that similar conditions favoring explosions still affect the hydrothermal system of Milos. The new methodology described in this work can find useful applications in the study of submerged hydrothermal systems and in understanding the physicochemical conditions that favor hydrothermal explosions.〈/jats:p〉

Description: Published

Description: 1254547

Description: OSA5: Energia e georisorse

Description: JCR Journal