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We investigate the relationship between sulfur and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe 3+/ΣFe and major element compositions measured in olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have Fe 3+/ΣFe of 0.15-0.16, reflecting fO2 of ΔQFM 0.0 ± 0.3, which is indistinguishable from fO2 calculated from CO2/CO ratios in high-temperature gases. Masaya is more oxidized at ΔQFM +1.7 ± 0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (δ34S gas - 0.5‰; δ34Sscoria + 0.9‰) and Masaya (δ34Sgas + 4.8‰; δ34Sscoria + 7.4‰) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S6+/ΣS is 0.67 in Masaya melt inclusions. No change is observed in Fe3+/ΣFe or S 6+/ΣS with extent of S degassing at Erta Ale, indicating negligible effect on fO2, and further suggesting that H2S is the dominant gas species exsolved from the S2--rich melt (i.e., no redistribution of electrons). High SO2/H2S observed in Erta Ale gas emissions is due to gas re-equilibration at low pressure and fixed fO2. Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (+4.8‰) cannot be explained by fractionation effects but rather reflects recycling of high δ34S oxidized sulfur through the subduction zone. Key Points Oxygen fugacity is buffered during degassing of basalts Sulfur isotope fractionation is an equilibrium and kinetic process Sulfur isotopes of arc gases indicate contribution from subducted sulfate ©2013. American Geophysical Union. All Rights Reserved.

The exsolution, rise, expansion, and separation of volatiles from magma provide the driving force behind both effusive and explosive volcanic eruptions. The field of volcanic gas geochemistry therefore plays a key role in understanding volcanism. In this article, we summarize the most important findings of the past few decades and how these shape today’s understanding of volcanic degassing. We argue that the recent advent of automated, continuous geochemical monitoring at volcanoes now allows us to track activity from unrest to eruption, thus providing valuable insights into the behavior of volatiles throughout the entire sequence. In the next 10 years, the volcanological community stands to benefit from the expansion of geochemical monitoring networks to many more active volcanoes. This, along with technical advances in instrumentation and in particular the increasing role that unoccupied aircraft systems (UAS) and satellite-based observations are likely to play in collecting volcanic gas measurements, will provide a rich dataset for testing hypotheses and developing diagnostic tools for eruption forecasts. The use of consistent, well-documented analytical methods and ensuring free, public access to the collected data with few restrictions will be most beneficial to the advancement of volcanic gas science.

Aerial measurements using unoccupied aerial systems (UAS) transform our ability to measure and monitor volcanic plumes., Volcanic emissions are a critical pathway in Earth’s carbon cycle. Here, we show that aerial measurements of volcanic gases using unoccupied aerial systems (UAS) transform our ability to measure and monitor plumes remotely and to constrain global volatile fluxes from volcanoes. Combining multi-scale measurements from ground-based remote sensing, long-range aerial sampling, and satellites, we present comprehensive gas fluxes—3760 ± [600, 310] tons day−1 CO2 and 5150 ± [730, 340] tons day−1 SO2—for a strong yet previously uncharacterized volcanic emitter: Manam, Papua New Guinea. The CO2/ST ratio of 1.07 ± 0.06 suggests a modest slab sediment contribution to the sub-arc mantle. We find that aerial strategies reduce uncertainties associated with ground-based remote sensing of SO2 flux and enable near–real-time measurements of plume chemistry and carbon isotope composition. Our data emphasize the need to account for time averaging of temporal variability in volcanic gas emissions in global flux estimates.

Texto completo del documento Identification of unambiguous signals of volcanic unrest is crucial in hazard assessment. Processes leading to phreatic and phreatomagmatic eruptions remain poorly understood, inhibiting effective eruption forecasting. Our 5‐year gas record from Poás volcano, combined with geophysical data, reveals systematic behavior associated with hydrothermal‐magmatic eruptions. Three eruptive episodes are covered, each with distinct geochemical and geophysical characteristics. Periods with larger eruptions tend to be associated with stronger excursions in monitoring data, particularly in SO2/CO2 and SO2 flux. The explosive 2017 phreatomagmatic eruption was the largest eruption at Poás since 1953 and was preceded by dramatic changes in gas and geophysical parameters. The use of drones played a crucial role in gas monitoring during this eruptive period. Hydrothermal sealing and volatile accumulation, followed by top‐down reactivation of a shallow previously emplaced magma body upon seal failure, are proposed as important processes leading to and contributing to the explosivity of the 2017 eruption. La identificación de señales inequívocas de agitación volcánica es crucial para la evaluación de riesgos. Los procesos que conducen a las erupciones freáticas y freatomagmáticas siguen siendo poco conocidos, lo que impide la previsión eficaz de las erupciones. Nuestro registro de gas de 5 años del volcán Poás, combinado con datos geofísicos revela un comportamiento sistemático asociado a las erupciones hidrotermales-magmáticas. Se han cubierto tres episodios eruptivos eruptivos, cada uno con características geoquímicas y geofísicas distintas. Los periodos con mayores erupciones tienden a estar asociados con excursiones más fuertes en los datos de monitoreo, particularmente en el flujo de SO2/CO2 y SO2. El erupción freatomagmática explosiva de 2017 fue la mayor erupción en el Poás desde 1953 y fue precedida por cambios dramáticos en los parámetros gaseosos y geofísicos. El uso de drones jugó un papel crucial en la monitorización de gases de gas durante este período eruptivo. El sellado hidrotermal y la acumulación de volátiles, seguidos de de un cuerpo magmático poco profundo previamente emplazado al fallar el sellado, se proponen como procesos importantes que condujeron y contribuyeron a la explosividad de la erupción de 2017. Universidad Nacional, Costa Rica Observatorio Vulcanológico y Sismológico de Costa Rica

OVSICORI Understanding the trigger mechanisms of phreatic eruptions is key to mitigating the effects of these hazardous but poorly forecastable volcanic events. It has recently been established that high-rate volcanic gas observations are potentially very suitable to identifying the source processes driving phreatic eruptions, and to eventually detecting precursory changes prior to individual phreatic blasts. In February-May 2017, we deployed a Multi-GAS instrument to continuously monitor gas concentrations in the crater lake plume of Rincón de la Vieja, a remote and poorly monitored active volcano in Costa Rica, site of frequent phreatic/phreatomagmatic eruptions. Forty-two phreatic/phreatomagmatic eruptions were seismically recorded during our investigated period, 9 of which were also recorded for gas by the Multi-GAS. To the best of our knowledge, these represent the first instrumentally measured gas compositions during individual phreatic/phreatomagmatic explosions at an active volcano. Our results show that during background quiescent degassing the Rincón de la Vieja crater lake plume was characterized by high CO2/SO2 ratios of 64±59 and H2S/SO2 ratios of 0.57±0.20. This composition is interpreted as reflecting hydrothermal (re)processing of magma-sourced gas in the sub-limnic environment. Phreatic blasts were recorded by the Multi-GAS as brief (1–2min long) pulses of elevated gas mixing ratios (up to ∼52 ppmv SO2 and >3,000 ppmv CO2), or more than an order of magnitude higher than during background degassing (∼1 ppmv SO2 and ∼450 ppmv CO2). During the phreatic eruption(s), the H2S/SO2 ratio was systematically lower (3000 ppmv de CO2), o más de un orden de magnitud superior que durante la desgasificación de fondo ( ∼1 ppmv SO2 y ∼450 ppmv CO2). Durante la(s) erupción(es) freática(s), la relación H2S/SO2 fue sistemáticamente más baja (

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.

This project was supported by Centro de Investigación en Ciencias Geológicas of Universidad de Costa Rica (830-B7-A00) and the Costa Rican Department of Science and Technology (MICITT) fund FI-160B-14 to Andrés Ulloa Carmiol. The caves of the Irazú volcano (Costa Rica), became accessible after the partial collapse of the NW sector of the Irazú volcano in 1994, offering the opportunity to investigate active minerogenetic processes in volcanic cave environments. We performed a detailed mineralogical and geochemical study of speleothems in the caves Cueva los Minerales and Cueva Los Mucolitos, both located in the northwest foothills of the main crater. Mineralogical analyses included X-ray diffraction (XRD) and Raman spectroscopy, while geochemical characterization used Energy Dispersive X-ray spectroscopy (EDX) coupled to Scanning Electron Microscopy (SEM). In addition, measurements of environmental parameters in the caves, cave drip water and compilation of geochemical analyses of the Irazú volcanic lake (~150 m above the cave level) and fumarole analyses were conducted between 1991 and 2014. We identified forty-eight different mineral phases, mostly rare hydrated sulfates of the alunite, halotrichite, copiapite, kieserite and rozenite groups, thirteen of which are described here as cave minerals for the first time. This includes the first occurrence in cave environments of aplowite, bieberite, boyleite, dietrichite, ferricopiapite, ferrinatrite, lausenite, lishizhenite, magnesiocopiapite, marinellite, pentahydrite, szomolnokite, and wupatkiite. The presence of other new cave minerals such as tolbachite, mercallite, rhomboclase, cyanochroite, and retgersite, is likely but could not be confirmed by various mineralogical techniques. Uplifting of sulfurous gases, water seepage from the Irazú volcanic lake and hydrothermal interactions with the volcanic host rock are responsible for such extreme mineralogical diversity. These findings make the caves of the Irazú volcano a world-type- reference locality for investigations on the formation and assemblage of sulfate minerals and the biogeochemical cycle of sulfur, with potential implications for Astrobiology and Planetary science. Publisher PDF

Obtaining accurate estimates of the CO2 output from arc volcanism requires a precise understanding of the potential along-arc variations in volcanic gas chemistry, and ultimately of the magmatic gas signature of each individual arc segment. In an attempt to more fully constrain the magmatic gas signature of the Central America Volcanic Arc (CAVA), we present here the results of a volcanic gas survey performed during March and April 2013 at five degassing volcanoes within the Costa Rica-Nicaragua volcanic segment (CNVS). Observations of the volcanic gas plume made with a multicomponent gas analyzer system (Multi-GAS) have allowed characterization of the CO2/SO2-ratio signature of the plumes at Pads (0.30 +/- 0.06, mean +/- SD), Rincon de la Vieja (27.0 +/- 15.3), and Turrialba (2.2 +/- 0.8) in Costa Rica, and at Telica (3.0 +/- 0.9) and San Cristobal (4.2 +/- 1.3) in Nicaragua (all ratios on molar basis). By scaling these plume compositions to simultaneously measured SO2 fluxes, we estimate that the CO2 outputs at CNVS volcanoes range from low (25.5 +/- 11.0 tons/day at Pods) to moderate (918 to 1270 tons/day at Turrialba). These results add a new information to the still fragmentary volcanic CO2 output data set, and allow estimating the total CO2 output from the CNVS at 2835 1364 tons/day. Our novel results, with previously available information about gas emissions in Central America, are suggestive of distinct volcanic gas CO2/S-T (= SO2 + H2S)-ratio signature for magmatic volatiles in Nicaragua (similar to 3) relative to Costa Rica (similar to 0.5-1.0). We also provide additional evidence for the earlier theory relating the CO2-richer signature of Nicaragua volcanism to increased contributions from slab-derived fluids, relative to more-MORB-like volcanism in Costa Rica. The sizeable along-arc variations in magmatic gas chemistry that the present study has suggested indicate that additional gas observations are urgently needed to more-precisely confine the volcanic CO2 from the CAVA, and from global arc volcanism.