GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.3 197 REACTIVATION DYNAMICS OF THE CAMPI FLEGREI VOLCANIC SYSTEM: INSIGHTS FROM THE BAIA–FONDI DI BAIA ERUPTION M. Pistolesi Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy The Phlegraean Fields are a vast area of volcanic origin located north-west of the city of Naples and centered in the Gulf of Pozzuoli, a few kilometers west of Vesuvius. Although the beginning of the eruptive history of the Phlegraean Fields is difficult to decipher, to date we know with confidence that the geological history of the caldera has been dominated by at least two major eruptive events: the Campanian Ignimbrite eruption (occurred about 39,000 years ago) and the eruption of the Neapolitan Yellow Tuff (occurred 15,000 years ago). The last eruption of Monte Nuovo occurred in 1538 and since then the activity in the Phlegraean Fields is characterized by phenomena of continuous deformation of the soil, modest seismic activity, variably intense fumarolic and hydrothermal activity. All these variations concur in testifying how the system is still active. In particular, since 2005 a new inflation phase has been underway and has exceeded 60 cm in the center of the caldera. Based on the eruptive history and available monitoring data, it was possible to outline the areas most exposed to the various dangerous phenomena. This information allowed the civil protection authorities to define a National Emergency Plan that was recently the subject of an exercise. The eruptive history and the current state of the system, together with the enormous exposure of the territory (over 400,000 people live inside the caldera) make the Phlegraean Fields one of the highest-risk volcanic areas in the world. The volcanic activity within the Phelgrean Fields caldera after the Neapolitan Yellow Tuff (NYT) eruption was characterized by a large number of eruptive events of variable style and intensity (e.g. Di Vito et al. , 1999; Orsi et al. , 2004; Isaia et al. , 2009; Smith et al. , 2011). About 70 eruptions occurred during this period, mainly clustered during three time intervals of activity (Epochs). Over the past few years tephro-stratigraphic, geochemical, geochronological, and isotopic studies were carried with the goal of developing a model of the general structure and evolution of the magmatic system (Di Renzo et al. , 2011 and references therein; Mormone et al. , 2011; Forni et al. , 2019) or have been specifically dedicated to the understanding of the active magma chamber system in large eruptions (Campanian Ignombrite and Neapolitan yellow tuff; Marianelli et al. , 2006, and references therein; Pabst et al. , 2007 and references therein) or of the dynamics of magmatic eruptions fed by magmas with different composition (Cannatelli et al. , 2007; Arienzo et al. , 2009; Mormone et al. , 2011; Di Vito et al. , 2011; Fourmentraux et al. , 2012). Due to the complexity of the eruptive activity, key eruptions which marked the unrest of the caldera at the onset of each eruptive Epoch generally suffer the lack of a detailed investigation. Such eruptions can provide fundamental insights on the modalities of reopening an eruptive epoch, as well as on the state of the magmatic system before the unrest (e.g., residence time, recharge events) and on the duration of expected unrest preceding an eruption (timing of magma ascent). The Baia-Fondi di Baia eruption, in particular, represents the opening activity of Epoch II. A detailed physical volcanological and geochemical investigation of the eruption allowed to define specific eruptive scenarios related to the reactivation of the caldera as well as magma ascent and dynamics during pre and syn-eruptive conditions. The eruption has been selected based on the completeness of tephra eruption sequence, availability of outcrops and suitability of erupted products for the investigation. The eruption is one of the sporadic events that have occurred in the western sector of the caldera and dates back to 9525–9696 BP, after a 1000-year- long period of quiescence. Although relatively small in terms of erupted volume with respect to most of the events of the past 15 ka, the Baia-Fondi di Baia eruption was characterized by a complex series of events, which have led to different interpretations in the literature. A detailed stratigraphic study coupled with sedimentological, physical, textural, and