Total (fumarolic+diffuse soil) CO sub(2) output from Furnas volcano

• Published in: Earth, planets, and space planets, and space, 2015-12, Vol.67 (1), p.1-12
• Main Authors: Pedone, M, Viveiros, F, Aiuppa, A, Giudice, G, Grassa, F, Gagliano, AL, Francofonte, V, Ferreira, T
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Degassing; Flux; Fumaroles; Soil (material); Springs; Villages; Volcanoes
• ISSN: 1880-5981
• DOI: 10.1186/s40623-015-0345-5

Furnas volcano, in Sao Miguel island (Azores), being the surface expression of rising hydrothermal steam, is the site of intense carbon dioxide (CO sub(2)) release by diffuse degassing and fumaroles. While the diffusive CO sub(2) output has long (since the early 1990s) been characterized by soil CO sub(2) surveys, no information is presently available on the fumarolic CO sub(2) output. Here, we performed (in August 2014) a study in which soil CO sub(2) degassing survey was combined for the first time with the measurement of the fumarolic CO sub(2) flux. The results were achieved by using a GasFinder 2.0 tunable diode laser. Our measurements were performed in two degassing sites at Furnas volcano (Furnas Lake and Furnas Village), with the aim of quantifying the total (fumarolic+soil diffuse) CO sub(2) output. We show that, within the main degassing (fumarolic) areas, the soil CO sub(2) flux contribution (9.2 t day super(-1)) represents a minor (~15 %) fraction of the total CO sub(2) output (59 t day super(-1)), which is dominated by the fumaroles (~50 t day super(-1)). The same fumaroles contribute to ~0.25 t day super(-1) of H sub(2)S, based on a fumarole CO sub(2)/H sub(2)S ratio of 150 to 353 (measured with a portable Multi-GAS). However, we also find that the soil CO sub(2) contribution from a more distal wider degassing structure dominates the total Furnas volcano CO sub(2) budget, which we evaluate (summing up the CO sub(2) flux contributions for degassing soils, fumarolic emissions and springs) at ~1030 t day super(-1).