Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán 04510, México, D. F., Mexico

Total CO2 output from soil gas and plume, discharged from the Stromboli Island, was estimated. The CO2 emission of the plume emitted from the active crater was estimated on the basis of the SO2 crater output and C/S ratio, while CO2 discharged through diffuse soil emission was quantified on the basis of 419 measurements of CO2 fluxes from the soil of the whole island, performed by using the accumulation chamber method. The results indicate an overall output of ≅416 t day−1 of CO2 from the island. The main contribution to the total CO2 output comes from the summit area (396 t day−1), with 370 t/day from the active crater and 26 t day−1 from the Pizzo sopra La Fossa soil degassing area. The release of CO2 from peripheral areas is ≅20 t day−1 by soil degassing (Scari area mainly). The result of the soil degassing survey confirms the persistence of the highest CO2 degassing areas located on the North-East crater side and Scari area.

In a volcanic area, the composition of air is influenced by the interaction between fluids generated from many different environments (magmatic, hydrothermal, meteoric, and marine). Any physical and chemical variation in one of these subsystems is able to modify the outgassing dynamic. The increase of natural gas hazard, related to the presence of unhealthy components in air, may depend on temporary changes both in the pressure and chemical gradients that generate transient fluxes of gases and can have many different causes. Sometimes, the content of unhealthy gases approaches unexpected limits, without clear warning. In this case, an altered composition of the air can be only revealed after accurate sampling procedures and laboratory analysis. The investigations presented here are a starting point to response to the demand for a new monitoring program in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy). Three multiparametric geochemical surveys were carried in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy) in 2011, 2014, and 2015. Carbon dioxide (CO2) and hydrogen sulfide (H2S) are the main undesired components, usually present at the local scale. Anomalous CO2 and H2S outputs from soil and submarine bubbling vents were identified; the thermal anomaly of the ground was mapped; atmospheric concentrations of CO2 and H2S were measured in the air 30 cm above the ground surface. Atmospheric concentrations above the suggested limits for the wellbeing of human health were retrieved in open areas where tourists stay and where CO2 can accumulate under absence of wind.

Stromboli volcano is characterized by a persistent strombolian activity thatwas interrupted by effusive eruptions in 1985, 2002–2003, 2007, and 2014. The considerable amount of soil CO2 flux data acquired by the continuous geochemical network installed in the summit and peripheral areas of Stromboli Island have allowed us to thoroughly investigate and to model the plumbing system. This study analyzed 16 years of soil CO2 fluxes from the summit area, which showed a wide range of values (from 2000 to 85,000 g m−2 day−1). A set of discontinuous pCO2 data (ranging from 0.1 to 0.35 atm) from a dedicated thermal well (COA) drilled in the Stromboli village has been taken into account for the peripheral degassing evaluation. One of the major accomplishments of this study is the confirmation of the previous formulated geochemical model based on of the soil CO2 fluxes database and the recent effusive eruptions. The analysis of soil summit degassing data recorded at the summit STR02 station throughout the monitoring period (2000–2015) revealed that the log(CO2 flux) values conformed to a polimodal distribution with different mean values of CO2 fluxes being recorded for each sub-period during the different effusive eruptions. The three selected periods (2000–2004, 2005–2010, and 2011–2015) were characterized by considerable increases in soil CO2 degassing coinciding with the periods of effusive eruptions, indicating volatiles overpressure and disequilibrium of the volcanic system. Moreover, the CO2 output evaluations based on soil CO2 fluxes and pCO2 values of thermal waters (COA), have showed a long increasing trend both in the summit and peripheral areas. From 2007 to 2014, culminating in the last effusive eruption (August–November 2014).

We have mapped the diffuse CO2 efflux from the Specchio di Venere Lake area using the accumulation chamber method. We calculated a CO2 emission of 43± 5 t day−1 for the area studied, accounting for both diffuse degassing from soil and bubbling through the lake.We also present data on the water composition of Specchio di Venere Lake, the Polla 3 spring, and Liuzza well. On the basis of water chemistry, two physical-chemical processes, evaporation and mineral precipitation of carbonate species, are invoked to explain the CO2 degassing for the lake area.

The composition of the gases released by El Chichón (Chiapas, Mexico) and Víti (Askja volcano, Iceland) volcanic lakes is examined by Multi-GAS for the first time. Our results demonstrate that H2S and SO2 are degassed by these pH 2–3 lakes. We find higher CO2/H2S and H2/H2S ratios in the lakes’ emissions (31–5,685 and 0.6–35, respectively) than in the fumarolic gases feeding the lakes (13–33 and 0.08–0.5, respectively), evidencing that only a fraction (0.2–5.4% at El Chichón) of the H2S(g) contributed by the subaquatic fumaroles ultimately reaches the atmosphere. At El Chichón, we estimate a H2S output from the crater lake of 0.02–0.06 t/day. Curiously, SO2 is also detected at trace levels in the gases released from both lakes (0.003–0.3 ppmv).We propose that H2S supplied into the lakes initiates a series of complex oxidation reactions, having sulfite as an intermediate product, and ultimately leading to SO2 production and degassing.