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The Solfatara eruption of Campi Flegrei (Italy): combining field, textural and geochemical data to understand the dynamics of small-volume volcanic events at active calderas

Andrea Todde 1, Bianca Scateni2, Roberto Isaia3, Marija Voloschina1, Paola Marianelli1, Antonella Bertagnini4, Raffaello Cioni5, Marco Pistolesi1

  • Affiliations: 1Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy; 2Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Roma, Rome, Italy; 3Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli, Osservatorio Vesuviano, Naples, Italy; 4Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, Italy; 5Dipartimento di Scienze della Terra, Università di Firenze, Florence, Italy 

  • Presentation type: Talk

  • Presentation time: Friday 09:30 - 09:45, Room R290

  • Programme No: 3.10.5

  • Theme 3 > Session 10

Abstract

The 4.3 ka Solfatara eruption (Campi Flegrei, Italy) provides valuable insights into the eruption mechanisms and scenarios of small-volume explosive volcanic events at active calderas that host long-lived hydrothermal systems. In this study, we present results from the stratigraphic analysis of the Solfatara tephra deposits, alongside a detailed characterization of the physical, textural and chemical properties of the erupted juvenile products. The Solfatara deposit sequence is divided into two stratigraphic units, each corresponding to a distinct eruptive phase. Unit 1 predominantly consists of bedded ash deposits that exhibit clear signs of hydrothermal alteration. In contrast, Unit 2 is characterized by massive to cross-bedded ash deposits and by massive lapilli-bearing layers. The ash deposit extends up to approximately 10 km NE of the crater. Proximal outcrops include lithic-rich breccia deposits and ballistic shower beds, abundant in Unit 2. Component and textural analyses reveal that Unit 1 contains only 10--20% of dense to moderately vesicular juvenile glass, with the rest of the particles being hydrothermally altered lithics. In Unit 2, juvenile content ranges from 30% to >50%, with predominantly vesicular textures. The juvenile material has a homogeneous phonolitic-trachytic composition in both units, indicating that the eruption originated from a common magma batch. Overall, our findings suggest that Unit 1 formed during low-energy explosions primarily driven by fluid expansion within the hydrothermal system, with some contribution from the ascending magma. In contrast, Unit 2 formed during a phase characterized by multiple, transient events, including explosion breccia events, mainly driven by magma fragmentation.