Total CO2 output from Vulcano island (Aeolian Islands, Italy)

Total CO2 output from fumaroles, soil gas, bubbling gas discharges and water dissolved gases discharged from the island, was estimated for Vulcano island, Italy. The CO2 emission from fumaroles from the La Fossa summit crater was estimated from the SO2 crater output, while CO2 discharged through diffuse soil emission was quantified on the basis of 730 measurements of CO2 fluxes from the soil of the island, performed by using the accumulation chamber method. The results indicate an overall output of ≅500 t day 1 of CO2 from the island. The main contribution to the total CO2 output comes from the summit area of the La Fossa cone (453 t day 1), with 362 t day 1 from crater fumaroles and 91 t day 1 from crater soil degassing. The release of CO2 from peripheral areas is ≅20 t day 1 by soil degassing (Palizzi and Istmo areas mainly), an amount comparable to both the contribution of water dissolved CO2 (6 t day 1), as well as to seawater bubbling CO2 (4 t day 1 measured in the Istmo area). Presented data (September 2007) refer to a period of moderate solphataric activity, when the fumaroles temperature were 450°C and gas/water molar ratio of fumaroles was up to 0.16. The calculated total CO2 emission allows the estimation of the mass release and related thermal energy from the volcanic-hydrothermal system

HCl degassing from extremely acidic crater lakes: preliminary results from experimental determinations and implications for geochemical monitoring.

Crater lakes are monitored to detect volcanic unrest starting from the assumption that they behave as condensers for magmatic gases. A further assumption is that acidic gases such as HCl are conservative once dissolved in water. This is not true for extremely acidic crater lakes, whose H + activity is high enough to induce Cl2 hydrolysis and consequently HCl degassing. This study presents the results of experimental determinations at 40–458C demonstrating that HCl degassing from acidic water depends on pH and Cl2 concentration. HCl degassing starts at pH values c. 0.05–0.1 with a rate of 5–10 mg min21 l21, increasing up to c. 70 mg min21 l21 at pH,20.2. This implies that the rate of HCl removal from a crater lake with a volume of 104–105 m3 and a seawater-like Cl2 concentration ranges from 5 to 50 t h21. The estimated HCl/H2O ratio in the separated vapour phase (0.01–0.2) is coherent with HCl/H2O ratios of fumaroles. Our experiments imply that: (i) the presence of very acidic gas species in fumaroles can be associated with a liquid-dominated feeding system, and (ii) dissolved in extremely acidic crater lakes, Cl2 behaves as a non-conservative component.Published97-1064V. Dinamica dei processi pre-eruttiv

Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)

In this paper, fluid source(s) and processes controlling the chemical composition of volatile organic compounds (VOCs) in gas discharges from Mt. Etna and Vulcano Island(Sicily, Italy) were investigated. The main composition of the Etnean and Volcano gas emissions is produced by mixing, to various degrees, of magmatic and hydrothermal components. VOCs are dominated by alkanes, alkenes and aromatics, with minor, though significant, concentrations of O-, S- and Cl(F)-substituted compounds. The main mechanism for the production of alkanes is likely related to pyrolysis of organic-matterbearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alkene and aromatic compounds via catalytic reactions (dehydrogenation and dehydroaromatization, respectively). Nevertheless, an abiogenic origin for the light hydrocarbons cannot be ruled out. Oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions, typical of these volcanic-hydrothermal fluids, may explain the production of alcohols, esters, aldehydes, as well as O- and S-bearing heterocycles. By comparing the concentrations of hydrochlorofluorocarbons (HCFCs) in the fumarolic discharges with respect to those of background air, it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes. Finally, chlorofluorocarbon (CFC) abundances appear to be consistent with background air, although the strong air contamination that affects the Mt. Etna fumaroles may mask a possible geogenic contribution for these compounds. On the other hand, no CFCs were detected in the Vulcano gases, which are characterized by low air contribution. Nevertheless, a geogenic source for these compounds cannot be excluded on the basis of the present data

The crater lake of Ilamatepec (Santa Ana) volcano, El Salvador: insights into lake gas composition and implications for monitoring

We here present the first chemical characterization of the volcanic gas plume issuing from the Santa Ana crater lake, a hyper-acidic crater lake (pH of − 0.2 to 2.5) in north-western El Salvador. Our results, obtained during regular surveys in 2017 and 2018 using a Multi-GAS instrument, demonstrate a hydrous gas composition (H2O/SO2 ratios from 32 to 205) and SO2 as the main sulfur species (H2S/SO2 = 0.03–0.1). We also find that gas composition evolved during our investigated period, with the CO2/SO2 ratio decreasing by one order of magnitude from March 2017 (37.2 ± 9.7) to November 2018 (< 3). This compositional evolution toward more magmatic (SO2-rich) compositions is interpreted in the context of the long-term evolution of the volcano following its 2005 and 2007 eruptions. We find that, in spite of reduced (background-level) seismicity, the magmatic gas supply into the lake was one order of magnitude higher in March 2017 (total volatile flux: 20,200–30,200 t/day) than in the following periods (total volatile flux: 900–10,167 t/day). We propose that the elevated magmatic/hydrothermal transport in March 2017, combined with a 15% reduction in precipitation, caused the volume of the lake to decrease, ultimately reducing its sulfur absorbing and scrubbing capacity, and hence causing the gas plume CO2/SO2 ratio to decrease. The recently observed increases in temperature, acidity, and salinity of the lake are consistent with this hypothesis. We conclude that the installation of a continuous, fully-automated Multi-GAS is highly desirable to monitor any future change in lake plume chemistry, and hence the level of degassing activity

Escalating CO2 degassing at the Pisciarelli fumarolic system, and implications for the ongoing Campi Flegrei unrest

This short communication aims at providing an updated report on degassing activity and ground deformation variations observed during the ongoing (2012–2019) Campi Flegrei caldera unrest, with a particular focus on Pisciarelli, currently its most active fumarolic field. We show that the CO2 flux from the main Pisciarelli fumarolic vent (referred as “Soffione”) has increased by a factor > 3 since 2012, reaching in 2018–2019 levels (>600 tons/day) that are comparable to those typical of a medium-sized erupting arc volcano. A substantial widening of the degassing vents and bubbling pools, and a further increase in CO2 concentrations in ambient air (up to 6000 ppm), have also been detected since mid-2018. We interpret this escalating CO2 degassing activity using a multidisciplinary dataset that includes thermodynamically estimated pressures for the source hydrothermal system, seismic and ground deformation data. From this analysis, we show that degassing, deformation and seismicity have all reached in 2018–2019 levels never observed since the onset of the unrest in 2005, with an overall uplift of ~57 cm and ~448 seismic events in the last year. The calculated pressure of the Campi Flegrei hydrothermal system has reached ~44 bar and is rapidly increasing. Our results raise concern on the possible evolution of the Campi Flegrei unrest and reinforce the need for careful monitoring of the degassing activity at Pisciarelli, hopefully with the deployment of additional permanent gas monitoring units