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Escalating sulphur in the Campi Flegrei fumaroles marks a step change in caldera unrest.

Stefano Caliro1, Giovanni Chiodini2, Rosario Avino1, Antonio Carandente1, Emilio Cuoco1, Mauro Antonio Di Vito1, Carmine Minopoli1, Francesco Rufino1, Alessandro Santi1, Joao Lages3, Annarita Mangiacapra1, Brian Monteleone4, Lucia Pappalardo1, Zoltan Taracsák5, Cecilia Tramati3,6, Salvatrice Vizzini3,6, and Alessandro Aiuppa 3

  • Affiliations: 1Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy; 2Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Italy; 3Dipartimento di Scienze della Terra e del Mare, Università di Palermo, Italy; 4Department of Geology and Geophysics, Woods Hole Oceanographic Institute, United States of America; 5Department of Earth Sciences, University of Cambridge, United Kingdom; 6Consorzio Nazionale Interuniversitario per le Scienze del Mare, CoNISMa, Italy

  • Presentation type: Talk

  • Presentation time: Friday 14:30 - 14:45, Room S150

  • Programme No: 3.17.6

  • Theme 3 > Session 17

Abstract

The long-lived, inter-eruptive repose periods of active calderas worldwide are occasionally interrupted by phases of unrest, characterised by escalating seismicity, ground uplift, and intensifying gas emissions. The Campi Flegrei caldera, in the suburban metropolitan area of Napoli (Italy), has been restless since the 1950s, and yet the magmatic vs. hydrothermal nature of the unrest remains matter of debate. Here, we document a remarkable (factor >4) increase in H2S concentrations in the Solfatara fumaroles of Campi Flegrei since mid-2018. Isotopic results indicate an isotopically light (δ34S<0 vs. Vienna Canyon Diablo Troilite, VCDT) signature for this fumarolic H2S, consistent with the magmatic sulphur signature in the area (δ34S of ~ -1.7±1.1 ‰; as inferred from the isotope composition of sulphur in silicate melt inclusions in olivines). Using results of hydrothermal gas calculations and numerical models of magmatic degassing, we propose the escalating fumarolic H2S at Campi Flegrei to be sourced by mafic magma undergoing decompressional (ascent-driven) degassing in the 6-9 km depth range. We however cannot exclude some extent of sulphur remobilization from hydrothermal minerals due to magmatic gas-driven heating of the hydrothermal system and opening of new fractures during intense seismicity. Our results corroborate the magmatic origin of the ongoing Campi Flegrei unrest. Comparison with results elsewhere indicates escalating sulphur to be recurrent at reawakening hydrothermal volcanoes/calderas. At Campi Flegrei, any further compositional evolution of the fumaroles toward the magmatic gas range (increasing H2S, and appearance of  SO2 and HCl) should be carefully considered as a sign of increased eruption likelihood