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Selective decoupling of soil degassing species and heat flux at surface-sealed hydrothermal systems

Sophie Pailot-Bonnétat 1, Victoria Rafflin1,2, Lydie Gailler1, Giancarlo Tamburello3, Guillaume Boudoire1,4, Andrew J.L. Harris1

  • Affiliations: 1.   Laboratoire Magmas et Volcans, Université Clermont Auvergne, Clermont-Ferrand, France 2.   Now at Department of Earth Sciences, Royal Holloway, University of London, Egham, UK 3.   Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy 4.   Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy

  • Presentation type: Talk [Invited]

  • Presentation time: Tuesday 09:45 - 10:00, Room R280

  • Programme No: 3.15.9

  • Theme 3 > Session 15

Abstract

Volcanic hydrothermal systems are characterized by enhanced heat and gas fluxes. At "steaming ground", vapor is transferred through permeable soils to be diffusively discharged. However, presence of impermeable crusts seals the surface, allowing heat transfer by conduction but trapping gas and steam beneath the surface, decoupling heat and gas emission. Area and intensity of emission are thus dependent on near surface permeability. To investigate the near-surface dynamics of fluid circulation and advection at Vulcano (Aeolian Islands, Italy), we conducted a multiparametric experiment aimed at mapping the spatial distribution of heat and gas emission, and understanding how soil properties influence these pathways. This involved the deployment of an integrated array of thermocouples, CO2 accumulation chambers, multigas and electrical resistivity tomography for periodic surveys during 2020--2024. We find two sealed heat-pipes associated with thermal ground: at the Fossa crater and at Baia di Levante. We map an annular convection cell, with steam fluxes of 300 kg s-1 during unrest. Ascending gas cannot pass through the impermeable crust but are channelized towards fumaroles. However, soil CO2 degassing is found beyond the heat-pipes, implying that CO2 scrubbing occurs at a small scale at the crater and the Faraglione area. Permeabilities are ~10-15 m² around the pipe, and ~10-10 m² within it, with values as low as 10-3 m² in localized areas of steaming ground. Our study highlights how a multidisciplinary approach can map the uppermost portion of a heat-pipe, infer pathways of vapor, fluid and heat flow, and quantify mass fluxes through the system.