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