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© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2volatilized from ten sediment samples acquired by NASA's Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in34S. Measured values of Δ34S range from - 47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods.

Although pH measurements of hot spring water are taken in conventional geothermal resource research, previous studies have seldom created pH distribution maps of stream and spring waters for an entire geothermal field as a technique for geothermal exploration. In this study, a pH distribution map was created by measuring stream and spring water pH at 75 sites in the Mutsu Hiuchi Dake geothermal field, Japan. Areas of abnormally high pH were detected in midstream sections of the Ohaka and Koaka rivers; these matched the location of the Mutsu Hiuchi Dake East Slope Fault, which is believed to have formed a geothermal reservoir. The abnormally high pH zone is attributed to the trapping of rising volcanic gases in a mature geothermal reservoir with neutral geothermal water. This causes the gas to dissolve and prevents it from reaching the surface. Thus, the mapping of stream water pH distribution in a geothermal field could provide a new and effective method for estimating the locations of geothermal reservoirs. As the proposed method does not require laboratory analysis, and is more temporally and economically efficient than conventional methods, it might help to promote geothermal development in inaccessible and remote regions.

In their recent study, Pering et al. (2017) presented a novel method for measuring volcanic water vapor fluxes. Their method is based on imaging volcanic gas and aerosol plumes using a camera sensitive to the near-infrared (NIR) absorption of water vapor. The imaging data are empirically calibrated by comparison with in situ water measurements made within the plumes. Though the presented method may give reasonable results over short time scales, the authors fail to recognize the sensitivity of the technique to light scattering on aerosols within the plume. In fact, the signals measured by Pering et al. are not related to the absorption of NIR radiation by water vapor within the plume. Instead, the measured signals are most likely caused by a change in the effective light path of the detected radiation through the atmospheric background water vapor column. Therefore, their method is actually based on establishing an empirical relationship between in-plume scattering efficiency and plume water content. Since this relationship is sensitive to plume aerosol abundance and numerous environmental factors, the method will only yield accurate results if it is calibrated very frequently using other measurement techniques.

Interactions with volcanic gases in eruption plumes produce soluble salt deposits on the surface of volcanic ash. While it has been postulated that saturation-driven precipitation of salts following the dissolution of ash surfaces by condensed acidic liquids is a primary mechanism of salt formation during an eruption, it is only recently that this mechanism has been subjected to detailed study. Here we spray water and HCl droplets into a suspension of salt-doped synthetic glass or volcanic ash particles, and produce aggregates. Deposition of acidic liquid droplets on ash particles promotes dissolution of existing salts and leaches cations from the underlying material surface. The flow of liquid, due to capillary forces, will be directed to particle-particle contact points where subsequent precipitation of salts will cement the aggregate. Our data suggest that volcanically-relevant loads of surface salts can be produced by acid condensation in eruptive settings. Several minor and trace elements mobilised by surface dissolution are biologically relevant; geographic areas with aggregation-mediated ash fallout could be “hotspots” for the post-deposition release of these elements. The role of liquids in re-distributing surface salts and cementing ash aggregates also offers further insight into the mechanisms which preserve well-structured aggregates in some ash deposits.

The role of volatiles in magma dynamics and eruption style is fundamental. Magmatic volatiles partition between melt, crystal, and vapor phases and, in so doing, change magma properties. This has consequences for magma buoyancy and phase equilibria. An exsolved vapor phase, which may be distributed unevenly through reservoirs, contains sulfur and metals that are either transported into the atmosphere or into ore deposits. This article reviews the controls on volatile solubility and the methods to reconstruct the volatile budget of magmas, focusing particularly on the exsolved vapor phase to explore the role of volatiles on magma dynamics and on eruption style.

The composition of volcanic gases discharged from Miyakejima volcano has been monitored during the intensive degassing activity that began after the eruption in 2000. During the 15 years from 2000 to 2015, Miyakejima volcano discharged 25.5 Mt of SO2, which required degassing of 3 km3 of basaltic magma. The SO2 emission rate peaked at 50 kt/day at the end of 2000 and quickly decreased to 5 kt/day by 2003. During the early degassing period, the volcanic gas composition was constant with the CO2/SO2 = 0.8 (mol ratio), H2O/SO2 = 35, HCl/SO2 = 0.08, and SO2/H2S = 15. The SO2 emission rate decreased gradually to 0.5 kt/day by 2012, and the gas composition also changed gradually to CO2/SO2 = 1.5, H2O/SO2 = 150, HCl/SO2 = 0.15, and SO2/H2S = 6. The compositional changes are not likely caused by changes in degassing pressure or volatile heterogeneity of a magma chamber but are likely attributed to an increase of hydrothermal scrubbing caused by large decrease of the volcanic gas emission rate, suggesting a supply of gases with constant composition during the 15 years. The intensive degassing was modeled based on degassing of a convecting magma conduit. The gradual SO2 emission rate that decrease without changes in volcanic gas composition is attributed to a reduction of diameter of the convecting magma conduit.

International audience; Stable isotopes of carbon and oxygen in volcanic gases are key tracers of volatile transfer between Earth's interior and atmosphere. Although important, these data are available for few volcanoes because they have traditionally been difficult to obtain and are usually measured on gas samples collected from fumaroles. We present new field measurements of bulk plume composition and stable isotopes (δ13CCO2 and δ18OH2O+CO2) carried out at three northern Chilean volcanoes using MultiGAS and isotope ratio infrared spectroscopy. Carbon and oxygen in magmatic gas plumes of Lastarria and Isluga volcanoes have δ13C in CO2 of +0.76‰ to +0.77‰ (VPDB), similar to slab carbonate; and δ18O in the H2O + CO2 system ranging from +12.2‰ to +20.7‰ (VSMOW), suggesting significant contributions from altered slab pore water and carbonate. The hydrothermal plume at Tacora has lower δ13CCO2 of -3.2‰ and δ18OH2O+CO2 of +7.0‰, reflecting various scrubbing, kinetic fractionation, and contamination processes. We show the isotopic characterization of volcanic gases in the field to be a practical complement to traditional sampling methods, with the potential to remove sampling bias that is a risk when only a few samples from accessible fumaroles are used to characterize a given volcano's volatile output. Our results indicate that there is a previously unrecognized, relatively heavy isotopic signature to bulk volcanic gas plumes in the Central Andes, which can be attributed to a strong influence from components of the subducting slab, but may also reflect some local crustal contamination. The techniques we describe open new avenues for quantifying the roles that subduction zones and arc volcanoes play in the global carbon cycle.

We use the chemical and isotopic composition of volcanic gases and steam condensate, in situ measurements of plume composition and remote measurements of SO2 flux to constrain volatile sources and characterize subvolcanic conditions at three persistently degassing and seismically active volcanoes within the Katmai Volcanic Cluster (KVC), Alaska: Mount Martin, Mount Mageik and Trident. In situ plume measurements of gas composition were collected at all three volcanoes using MultiGAS instruments to calculate gas ratios (e.g. CO2/H2S, SO2/H2S and H2O/H2S), and remote measurements of SO2 column density were collected from Mount Martin and Mount Mageik by ultraviolet spectrometer systems to calculate SO2 fluxes. Fumaroles were directly sampled for chemical and isotopic composition from Mount Mageik and Trident. Mid Ocean Ridge Basalt (MORB)-like 3He/4He ratios (~ 7.2–7.6 Rc/RA) within Mount Mageik and Trident's fumarole emissions and a moderate SO2 flux (~ 75 t/d) from Mount Martin, combined with gas compositions dominated by H2O, CO2 and H2S from all three volcanoes, indicate magma degassing and active hydrothermal systems in the subsurface of these volcanoes. Mount Martin's gas emissions have the lowest CO2/H2S ratio (~ 2–4) and highest SO2 flux compared to the other KVC volcanoes, indicative of shallow magma degassing. Geothermometry techniques applied to Mount Mageik and Trident's fumarolic gas compositions suggest that their hydrothermal reservoirs are located at depths of ~ 0.2 and 4 km below the surface, respectively. Observations of an unusually reducing gas composition at Trident and organic material in the near-surface soils suggest that thermal decomposition of sediments may be influencing gas composition. When the measured gas compositions from Mount Mageik and Trident are compared with previous samples collected in the late 1990's, relatively stable magmatic-hydrothermal conditions are inferred for Mount Mageik, while gradual degassing of residual magma and contamination by shallow crustal fluids is inferred for Trident. The isotopic composition of volcanic gases emitted from Mount Mageik and Trident reflect mixing of subducted slab, mantle and crustal volatile sources, with organic sediment and carbonate being the predominant sources. Considering the close proximity of the target volcanoes in comparison with the depth to the subducted slab we speculate that Aleutian Arc volatiles are fed by a relatively homogeneous subducted fluid and that much of the apparent variability in volatile provenance can be explained by shallow crustal volatile sources and/or processes.

The chemical composition of Icelandic rain and snow is dominated by marine aerosols, however human and volcanic activity can also affect these compositions. The six month long 2014–15 Barðarbunga volcanic eruption was the largest in Iceland for more than 200 years and it released into the atmosphere an average of 60 kt/day SO2, 30 kt/day CO2, 500 t/day HCl and 280 t/day HF. To study the effect of this eruption on the winter precipitation, snow cores were collected from the Vatnajokull glacier and the highlands northeast of the glacier. In addition to 29 bulk snow cores from that precipitated from September 2014 until March 2015, two cores were sampled in 21 and 44 increments to quantify the spatial and time evolution of the chemical composition of the snow. The pH and chemical compositions of melted snow samples indicate that snow has been affected by the volcanic gases emitted during the Barðarbunga eruption. The pH of the melted bulk snow cores ranged from 4.41 to 5.64 with an average value of 5.01. This is four times greater H+ activity than pure water saturated with the atmospheric CO2. The highest concentrations of volatiles in the snow cores were found close to the eruption site as predicted from CALPUFF SO2 gas dispersion quality model. The anion concentrations (SO4, Cl, and F) were higher and the pH was lower compared to equivalent snow samples collected during 1997–2006 from the unpolluted Icelandic Langjokull glacier. Higher SO4 and Cl concentrations in the snow compared with the unpolluted rainwater of marine origin confirm the addition of a non–seawater SO4 and Cl. The δ34S isotopic composition confirms that the sulphur addition is of volcanic aerosol origin. The chemical evolution of the snow with depth reflects changes in the lava effusion and gas emission rates. Those rates were the highest at the early stage of the eruption. Snow that fell during that time, represented by samples from the deepest part of the snow cores, had the lowest pH and highest concentrations of SO4, F, Cl and metals, compared with snow that fell later in the winter. Also the Al concentration, did exceed World Health Organisation drinking water standard of 3.7 μmol/kg in the lower part of the snow core closest to the eruption site. Collected snow represents the precipitation that fell during the eruption period. Nevertheless, only minor environmental impacts are evident in the snow due to its interaction with the volcanic aerosol gases. In addition, the microbial communities identified in the snow that fell during the eruption were similar to those found in snow from other parts of the Arctic, confirming an insignificant impact of this eruption on the snow microecology.

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.

A series of experimental simulations of the genetic mechanism of banded iron formations has been conducted using a suite of self-designed glassware to model the hypergene circulation of surface water. The simulation process involved two parts: in the first part, the weathering and leaching of basalt by strongly acidic meteoric water during early Precambrian volcanism would have resulted in amorphous silica precipitation and strongly acidic ore-bearing solutions (pH 2 -saturated meteoric water without contamination of other volcanic gases would increase the pH value of the solution. When the pH increased to 1.25–5.50, ferric hydroxides and amorphous silica would alternately precipitate owing to periodic heating and continuous addition of high-pH basalt-leaching solutions. This is a possible explanation of the genetic mechanism of the Algoma-type banded iron formations.

The injection of carbon dioxide (CO2) captured at large point sources into deep saline aquifers can significantly reduce anthropogenic CO2 emissions from fossil fuels. Dissolution of the injected CO2 into the formation brine is a trapping mechanism that helps to ensure the long-term security of geological CO2 storage. We use thermochronology to estimate the timing of CO2 emplacement at Bravo Dome, a large natural CO2 field at a depth of 700 m in New Mexico. Together with estimates of the total mass loss from the field we present, to our knowledge, the first constraints on the magnitude, mechanisms, and rates of CO2 dissolution on millennial timescales. Apatite (U-Th)/He thermochronology records heating of the Bravo Dome reservoir due to the emplacement of hot volcanic gases 1.2-1.5 Ma. The CO2 accumulation is therefore significantly older than previous estimates of 10 ka, which demonstrates that safe long-term geological CO2 storage is possible. Integrating geophysical and geochemical data, we estimate that 1.3 Gt CO2 are currently stored at Bravo Dome, but that only 22% of the emplaced CO2 has dissolved into the brine over 1.2 My. Roughly 40% of the dissolution occurred during the emplacement. The CO2 dissolved after emplacement exceeds the amount expected from diffusion and provides field evidence for convective dissolution with a rate of 0.1 g/(m(2)y). The similarity between Bravo Dome and major US saline aquifers suggests that significant amounts of CO2 are likely to dissolve during injection at US storage sites, but that convective dissolution is unlikely to trap all injected CO2 on the 10-ky timescale typically considered for storage projects.

Repetitive explosions of silicic volcanoes are thought to be triggered by volcanic gases in the shallow parts of the conduit. To trap the volcanic gases in the conduit, the lava dome or plug must be impermeable. However, silicic magma undergoes brittle fracturing during ascent because its viscosity increases via dehydration and groundmass crystallization. Since fractured magma has high permeability, the reduction of permeability is a key process that allows gases to accumulate, leading to an explosion. We performed uniaxial compression experiments on rhyolite fragments at temperatures of 700–900 °C to investigate the permeability reduction of fractured rhyolite. Experimental results show that permeability is controlled by porosity, and permeability reduction can be caused by compaction of fractured magma. Based on the observed relationship between permeability and porosity, we calculate the time scale of permeability reduction, i.e., the transition from permeable to impermeable magma. The calculated time scale (∼100–1000 s) is much shorter than the eruption repose (∼1–10 h) observed at Sakurajima volcano, Japan. This result implies that an impermeable lava dome and plug formed during the eruption repose. In contrast, the repose time (20–40 min) of Santiaguito volcano, Guatemala, is shorter than the time scale of permeability reduction (>∼10 h); this indicates that gases could not have accumulated before volcanic explosions and that other mechanisms could control eruption cyclicity.

Gases and aerosols from the 2012–13 effusive eruption of Tolbachik basaltic volcano, Kamchatka, were sampled in February and May, 2013, from a lava tube window located 300 m from the eruptive crater; temperature at the sampling point was 1060–1070 °C. The chemical and isotopic compositions of the sampled gases (92.4% H 2 O, 3.5% CO 2 , 2.3% SO 2 on average; δD from − 25.0 to − 38.6‰) correspond to a typical volcanic arc gas without dilution by meteoric or hydrothermal water. Halogen contents in the gases (1.37% HCl, 0.5% HF) were higher than average arc values. The total amount of analyzed metallic and metalloid (trace) elements in the gas exceeded 665 ppm. Six most abundant trace elements, K (250 ppm), Na (220 ppm), Si (74 ppm), Br (48 ppm), Cu (21 ppm) and Fe (12 ppm), accounted for 95% of the total content of trace elements in the gas. The gases contained 24 ppb Re, 12 ppb Ag, 4.9 ppb Au and 0.45 ppb Pt. Refractory rock-forming elements (Mg, Al, Ca) and some other elements such as Ba and Th were transported mainly in the form of silicate microspheres and altered rock particles. The concentrations of metals in the eruptive Tolbachik gases are higher than the corresponding concentrations in high-temperature fumaroles worldwide, although the mutual ratios of the elements are approximately the same. The gas/magma partition coefficients of eleven elements exceed unity, including the non-metals F, S, Cl, Br, As, Se and Te and the rare metals Cd, Re, Tl and Bi. Despite the relatively low concentrations of trace elements in the volcanic gases at the highest temperatures, superficial magma degassing provides information on the sources and sinks of metals.

Ecological observation of surviving organisms and their interactions during and after volcanic activity provides an indispensable opportunity to study how organisms respond to environmental devastation. Eurya japonica satisfies the criteria as a facilitator plant species in recovering forest on the volcanic Miyake Island, which erupted in 2000, because this species is more resistant to volcanic gases than other tree species on the island. We examined the effects of volcanic disturbance on reproductive success of E. japonica and compared the visitation frequencies of pollinator insects and frugivorous birds at nine sites showing different degrees of disturbance. The leaf health was strongly decreased by frequent volcanic gas exposure, whereas flower bud formation was not suppressed. The fruit abortion rate did not differ among sites, whereas the fruit set rate significantly decreased with increasing volcanic damage. The frequencies of pollinator and frugivorous bird visits were higher in heavily damaged areas. These results indicate that the pollination and seed-dispersal system of E. japonica was potentially maintained under volcanic disturbance, though the final reproductive success decreased.

In this review paper a set of chemical (H2O, CO2, S, HCl, HF) and water isotopic (dD, d 18 O) data is compiled for 26 subduction zone volcanoes and 3 volcanoes of other tectonic settings. To the arc-volcano dataset we added new data on high-temperature gas vents from three Kamchat- kan volcanoes (Gorely, Bezymianny and Tolbachik) and also published data on the chemical com- position of volcanic plumes obtained by remote instrumental techniques (Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR), Differential Optical Absorption Spectroscopy (DOAS) MultiGas) for volcanoes of different tectonic settings. Three typical cases of the persist- ent volcanic degassing in terms of dD, d 18 O of the volcanic vapour and its HCl content are dis- cussed in detail: (1) Kudryavy type with a clear two-end-member mixing behaviour; (2) degassing of active or cooling lava domes with fractionation of both water isotopes and Cl content; and (3) degassing of small volcanic islands with a complex admixing of meteorics and sea- water. We show that independently of the complexity of the shallow processes which affect volcano degassing, the highest temperature volcanic gases are characterized by dD values and HCl concentrations close to 225‰ V-SMOW and 0.5- 1.0 mol%, respectively. These values are the same for any volcanic arc (except maybe Mediterranean volcanoes) and are the result of seawater recycling at subduction zones on the global scale. In contrast to volcanic fluids of non- arc settings, the arc-magmatic fluid has uniformity not only in water isotopic composition and Cl content but also in the total composition (H- C-O- S- Cl- F).

The mephitis of Maschito, known since historical times as Lago Fetente (Smelly Lake) -although the lake is now dry-, is located 20 km from the Mt. Vulture volcanic edifice (Southern Italy). It is placed along the same regional tectonic discontinuity where some maars are located, close to the boundary between the foredeep and the Apulian foreland. About 300 m2 of surface is lacking in flora, while dead animals are frequently found all around it. The smelly exhalations are mainly composed of CO2 (∼98%), and, in lesser amounts, of H2S, N2, CH4 and other hydrocarbons. He, Ne and Ar occur in trace amounts. The CO2 isotopic composition is in the range of that of the main active Italian volcanic gases. The helium isotopic ratio (4.7 Ra) fits with the values measured in Mt. Vulture volcano and particularly with the olivine and pyroxene fluid inclusions of mantle xenoliths ejected during its last volcanic activity (140,000 years). The 40Ar/36Ar isotopic ratio of ∼320 supports some minor non-atmospheric contributions. The C/3He ratio (2.9 × 109) is in the typical range of magma released fluids, while δ C ( CH 4 ) 13 and δ D ( CH 4 ) values fall in the field of thermogenic methane. The amount of CO2 released is about 3200 tons/year. The flux of mantle-derived helium (>7 × 1010 atoms m−2 s−1) is at least three orders of magnitude higher than that of a stable continental crust. This study strongly supports the possibility that Maschito manifestations are fed by a geothermal system, which is powered by a degassing melt, bearing in mind that the Maschito gas emissions fall along the same fault system of the Monticchio maars, which formed during Mt. Vulture volcano's last activity.

The mass and heat budget of volcanic gases released from magma is critical to understanding a number of volcanic activities, including the ease with which magma can ascend. Due to its elevated temperature and salinity, the crustal electrical conductivity in a groundwater flow system increases through the addition of hydrothermal fluids which are produced by mixing of volcanic gases with meteoric-origin water. Therefore, the spatial extent of high electrical conductivity regions within groundwater flow systems may be used to evaluate the mass flux of volcanic gases to the systems. The present study attempts to estimate the mass flux of volcanic gases beneath the Unzen volcanic area in Southwest Japan, by developing a simple flow model of hydrothermal fluids and applying this model to the electrical conductivity structure of the area. The estimated mass flux of volcanic gases (10 4.8 ± 0.3 t/yr) yields results for CO 2 flux (10 3.1 ± 0.3 t/yr) and magma input rate (10 0.1 ± 0.3 million m 3 /yr) that are consistent with those estimated by geochemical and geodetic observations. This suggests that volcanic gases are steadily released from magma into the overlying groundwater flow system beneath the area, and that effective degassing may be one of the factors controlling the relatively effusive style of recent volcanism at Unzen volcano.

This study performed the first assessment of the volcanic gas output from the Central Volcanic Zone (CVZ) of northern Chile. We present the fluxes and compositions of volcanic gases (H2O, CO2, H2, HCl, HF, and HBr) from five of the most actively degassing volcanoes in this region—Lascar, Lastarria, Putana, Ollague, and San Pedro—obtained during field campaigns in 2012 and 2013. The inferred gas plume compositions for Lascar and Lastarria (CO2/Stot = 0.9–2.2; Stot/HCl = 1.4–3.4) are similar to those obtained in the Southern Volcanic Zone of Chile, suggesting uniform magmatic gas fingerprint throughout the Chilean arc. Combining these compositions with our own UV spectroscopy measurements of the SO2 output (summing to ~1800 t d−1 for the CVZ), we calculate a cumulative CO2 output of 1743–1988 t d−1 and a total volatiles output of >20,200 t d−1.

The adsorption of pure sulfur dioxide gas on volcanic ashes has been studied from 0.1 mbar to 1 bar and from −80 to +150 °C. Finely ground synthetic glasses of andesitic, dacitic, and rhyolitic composition served as proxies for fresh natural ash surfaces. Powders from two natural obsidian samples were also studied and yielded results broadly similar to the synthetic model systems. SO2 adsorption on ash is partially irreversible; it appears that the first layer of SO2 molecules absorbed on the surface cannot be removed. The pressure and temperature dependence of adsorption can be described by the equation ln c = A T −1 + B ln P + C, where c is the surface concentration of adsorbed SO2 in mg/m2, T is temperature in Kelvin, and P is the partial pressure of SO2 in mbar. A multiple regression analysis of the experimental data yielded A = 1645, B = 0.29, C = −7.43 for andesite, A = 2140, B = 0.29, C = −9.32 for dacite, and A = 910, B = 0.21, C = −4.48 for rhyolite. These data imply that adsorption strongly decreases with temperature, but only slowly decreases with decreasing partial pressure of SO2. Therefore, adsorption primarily occurs in the cool and diluted parts of the volcanic plume. Model calculations show that most of the SO2 may be removed from the plume, if the initial SO2 concentration in the volcanic gases is low and the surface area of the ash is high. For high initial SO2 concentrations, the fraction of SO2 that is lost by adsorption decreases, since the amount of SO2 in the gas phase is proportional to the SO2 partial pressure P , while adsorption is proportional only to P 0.2 – P 0.3. Adsorption of SO2 on ash particles may therefore be one reason why the climatic impact of explosive volcanic eruptions does not always scale with total sulfur yield.

This paper reports the analysis of the distribution of hydrocarbon and other gases in Mendeleev and Golovnin volcanoes and other occurrences of Kunashir Island. It was shown that, in addition to methane, the solfatara gases and gases dissolved in thermal waters contain ethane, propane, and butane. The volume concentration of methane in gas samples was no higher than 0.4 vol %. Carbon isotopes were analyzed in methane, ethane, and carbon dioxide in free and dissolved states. The hydrocarbon gases of Kunashir I. are of the thermogenic and metamorphogenic types, and their distribution depends on the position of springs relative to the eruptive centers of the volcanoes. Thermogenic gases are probably products of the high-temperature transformation of sedimentary organic matter buried during the formation of volcanic edifices. General gas geochemical characteristics are presented for Kuril volcanoes, and it was found that hydrocarbon generation in the sediments of the Kuril Basin increases toward volcanic edifices.

A plethora of in-situ bulk chemical and mineralogical analyses, remote sensing data, and geochemical models suggest that the Martian crust is sulfur(S)-rich, exceeding the S content of terrestrial basalts by almost an order of magnitude. The main source of crustal S on Mars is the volcanic exhalation of SO2 and H2S gases. Volcanic ash, expelled along with gases, may be a sink for up to 30% of the exhaled S gas species. We analyze the elemental composition of the Martian shallow sub-surface using the Mars Odyssey Gamma Ray Spectrometer to find areas that are simultaneously enriched in constituents of major volcanic gases such as S, Cl, and H2O. A large sedimentary deposit of likely pyroclastic origin called the Medusae Fossae Formation (MFF) is located within this region of possibly extensive alteration by volcanic gases. Based on reasonable terrestrial analog estimates that the MFF scavenged, at maximum, 30% of the exhaled S gas species, we find that a significant amount of S (>1017 kg) would have been delivered to the atmosphere over the time it took for the MFF to be deposited on Mars. The mass of the S emitted from the MFF-forming event(s) is up to 8 orders of magnitude higher than the mass of S emitted from the largest Quaternary volcanic eruption on Earth. Thus, volcanic degassing from the MFF forming events could have significantly affected surface geological processes, climate evolution, and habitability of Mars.

Continuous geochemical monitoring of thermal waters at Tokachidake volcano has been conducted for more than three decades to detect changes in its volcanic activity. Based on the geochemical data from 1986 to 2013, the origin and temporal changes of the thermal waters were discussed in our previous study. Here, we supplement the previous dataset with the geochemical data from 2014 to 2018 and comprehensively discuss the results of geochemical and geophysical monitoring to reveal the interactions between deep magmatic fluids, volcanic gases, and shallow aquifers. Thermal waters, discharging in the Tokachidake spa area, are formed by the interaction of volcanic gas and a shallow aquifer, and show the Cl change which have a significant correlation with the change in the volcanic plume height. This suggests a parallel volcanic gas input from the magma to the shallow aquifer and fumarole. Both changes are caused by a variation in the volcanic gas release rate from the magma. Around the 1988–1989 magmatic eruption, thermal waters in the Fukiage spa area showed remarkable thermal and chemical changes due to the interaction with the magmatic fluid (NaCl-type thermal water). Based on the chemical and isotopic compositions of the thermal waters, we calculated the Cl concentration and temperature of the NaCl-type thermal water as being approximately 20,000 mg/L and ∼280 °C, respectively. Our calculation of the supply rate of the NaCl-type thermal water indicates that large amounts of the NaCl-type thermal water are in continuous supply when volcanic activity increases prior to a magmatic eruption. In this area, the recent monitoring results reveal that the changes in the Cl concentration and seismic activity show a relatively good correlation, indicating that at least some of the volcanic earthquakes are related to the migration of the NaCl-type thermal water. Thus, when volcanic activity increases before a future magmatic eruption, chemical changes in the thermal waters in the Fukiage spa area should be apparent and the changes are likely to occur together with seismic activity. Our results propose that it is possible to interpret the present state of an active volcano more precisely through a comprehensive discussion of geochemical data from the thermal waters along with the other observations.

An ocean bottom seismometer (OBS) network was deployed for 1 month at Deception Island volcano, Antarctica, in early 2005. Although only two volcano-tectonic and three long-period events were observed, the three OBSs located > 2 km apart inside the caldera detected over 3900 events that could not be attributed to known volcanic or hydrothermal sources. These events are found on one instrument at a time and occur in three types. Type 1 events resemble impulsive signals from biological organisms while type 2 and type 3 events resemble long-period seismicity. The largest number of events was observed in a region of volcanic resurgence and hydrothermal venting. All three types occur together suggesting a common cause and they show evidence for a diurnal distribution. The events are most likely to be due to aquatic animals striking the sensors, but a geological source is also possible. In the first case, these signals indicate the presence of a biological community confined to the caldera. In the second case, they imply widespread hydrothermal activity in Port Foster. Future OBS experiments should bury the seismometers, include a hydrophone, deploy instruments side-by-side, or include a video camera to distinguish between biological and geological events.

Discharge of volcanic gases in the marine environment can lead to local perturbations in ocean acidity, with consequences for biological communities and the potential for hazards related to depressurization and release of gases at the surface. Numerous hydrothermal vents in the crater of Kolumbo submarine volcano (Aegean Sea) are discharging virtually pure gaseous CO 2 together with clear fluids at temperatures up to 220 °C. Acoustic imaging of the ascending bubbles suggests that the gas is being dissolved into seawater within ∼10 m above the crater floor (500 m below sea level). Dissolution of the gas likely causes local increases in water density that result in sequestration of CO 2 within the enclosed crater, and the accumulation of acidic seawater. Lack of macrofauna at the Kolumbo hydrothermal vents, occurrence of carbonate-poor sediment in the crater, and pH values as low as 5.0 in recovered water samples point to acidic conditions within the crater. Buildup of CO 2 -rich water in the bowl-shaped crater of Kolumbo may be producing conditions analogous to some African volcanic lakes (Lake Monoun and Lake Nyos, Cameroon) where overturn of gas-rich bottom waters led to abrupt releases of CO 2 at the surface. A minimum estimate of 2.0 × 10 5 m 3 (STP) of excess CO 2 may currently exist in the bottom 10 m of the Kolumbo crater.

With the aim of detailing the interaction between volcanic emissions and water harvesting by Roof Water Catchment Systems (RWCSs), the present work illustrates the results of a study carried out at Stromboli Island, a small but densely populated active volcanic area in the South of Italy. Concentrations of major and trace elements determined in RWCS waters and sediments revealed clear clues of a contamination with gases and suspended particles of volcanic origin, even if the values of those contaminants considered by the World Health Organization as dangerous for human health are always below the Maximum Admitted Concentration (MAC). In particular, cistern water showed a composition similar to local coastal rainwater, with dissolved ions related not only to sea aerosol but also to volcanic gases and ash leaching, with a secondary enrichment in Ca ions due to the interaction with the limewashed surfaces of both roofs and cistern walls. The simulation of the potential increase in dissolved chemical species due to volcanic ash deposition on the water catchment surfaces indicates the possible exceedance of the MAC for several species. The symptoms of fluorosis affecting elderly people who were young at the time of the 1930–40 volcanic crisis is a clue of a possible volcanogenic fluorine contamination. On the other way, the simulation of the digestion process on solid volcanogenic particulate ingested with drinking water highlighted a potential dramatic increase (orders of magnitudes) of dangerous element concentrations in stomach fluids above their MACs. Despite the evidence of potential health risks induced by volcanic activity, no anamnesic evidence of related pathologies has been found among Stromboli population. This apparent discrepancy is solved taking into account the positive feedback among the good practice in maintaining clean conditions in the harvested waters and the prevalent fallout of volcanogenic ashes away from the main inhabited areas, favoured by the morphological setting of the island and its wind regime.

At Merapi volcano, Indonesia, explosive eruptions lasting several months result from injections of reduced mafic magmas and are interspersed by periods of lava dome growth and collapse, quiescent degassing, assimilation of wall rock and fractional crystallization lasting a few years. Silicate melt inclusions and volcanic gases were analyzed to study processes of magmatic volatile exsolution and volcanic degassing during periods of quiescent degassing at Merapi. Volcanic gases were sampled at Merapi in 1994 during a phase of quiescent degassing and in 2006 at the end of a dome-growth and collapse explosive eruption. Silicate melt inclusions were collected and analyzed from lavas and scorias for their major element and volatile components. Solubility relationships between H 2 O and CO 2 in melt inclusions demonstrate that melt was being trapped beneath Merapi to depths reaching 19 km. Host amphibole geobarometry indicates crystallization pressures reaching up to 26 km. Hence there is evidence of deep pooling and crystallization of magma beneath Merapi at appreciable depths. Using a mass balance model of magmatic volatile exsolution, we demonstrate that the magma degassing from 19 km to the surface approaches closed-system behavior. Compared to the bulk magmatic volatiles analyzed in melt inclusions, volcanic gases had similar amounts of CO 2 , were enriched in H 2 O and S and depleted in Cl and F. We thus propose that the magmatic volatile phase was initially exsolved from the magma as a supercritical fluid and that it subsequently exsolved into a H 2 O–Cl–F-rich brine and CO 2 –S-rich vapor. According to the H 2 O–NaCl model, brine-vapor exsolution occurred at ~ 5 km in depth for a 5 wt.% NaCl, 900 °C to 1000 °C fluid, although the presence of H 2 S, SO 2 and CO 2 may cause the supercritical fluid to unmix at greater depths. Magma at shallower depths exsolved a brine and a vapor directly from the melt. The volcanic gases at Merapi thus represent the vapor fraction of a magmatic volatile phase, as brine ponded below the surface. We further suggest that carbon dioxide liberated by the magmatic assimilation of limestone, as proposed by other studies, fluxed the melt thereby promoting CO 2 enrichment of the melt and H 2 O degassing. Finally, we propose that Merapi volcanic gases are enriched in sulfur compared to the modeled volatile phase composition because deep, reduced mafic magma supplies sulfur to the shallow magmatic plumbing system.

Karymskii Volcano typically shows explosive activity with great variations in the frequency and energy of explosions. This is demonstrated here for three time segments of the volcano’s activity (1970–1973, 1976–1980, and 1996–2000). We examine various types of seismic and acoustic emission as controlled by crater morphology and the character of activity. The explosion funnels migrated over the crater area, and the 1976 effusive-explosive eruption occurred at two centers of lava flow effusion; this is here explained by the fact that magma as it was moving along the conduit was stratified to form a set of vertical filaments. The shape of shock waves in air recorded in August 2011 favors the hypothesis that the leading explosive mechanism during that period was a fragmentation wave that was produced in a gas-charged, viscous, porous magma during decompression. One notices that the shape of some shock waves in air recorded in 2011 indicates the occurrence of air blasts above the crater. The air blasts may have been caused by combustible volcanic gases such as carbon monoxide and hydrogen (CO and H2), which entered the atmosphere in sufficient amounts.

Persistent degassing of closed-conduit explosive volcanoes may be used to inspect and monitor magmatic processes. After interaction with shallow hydrothermal fluids, volcanic gases collected at surface can differ substantially from those exsolved from magma. We report here on an innovative approach to identify and separate the contribution of variable magmatic components from fumarolic gases, by processing the 30-year-long geochemical dataset from the Campi Flegrei caldera, Southern Italy. The geochemical record shows periodic variations, which are well correlated with geophysical signals. Such variations are interpreted as due to the time-varying interplay of two magma degassing sources, each differing in size, depth, composition, and cooling/crystallization histories. Similar multiple degassing sources are common at explosive volcanoes, with frequent ascent and intrusion of small magma batches. Our innovative method permits the identification of those magma batches, which contributes to the interpretation of unrest signals, forecasting and assessment of volcanic hazards.

One of the main goals of the Hyperspectral and Infrared Imager (HyspIRI) mission is to provide global observations of surface attributes at local and landscape spatial scales (tens of meters to hundreds of kilometers) to map volcanic gases and surface temperatures, which are identified as indicators of impending volcanic hazards, as well as plume ejecta which pose risks to aircraft and people and property downwind. Our project has created precursor HyspIRI data sets for volcanological analyses, using existing data over Mt. Etna, Italy. We have identified 28 EO-1 Hyperion data acquisitions, and 12 near-coincident ASTER data acquisitions, covering six eruptive periods between 2001 and 2010. These data sets provide us with 30 m hyperspectral VSWIR data and 90 m multispectral TIR data (satellite). They allowed us to examine temporal sequences of several Etnaean eruptions. We addressed the following critical questions, directly related to understanding eruption hazards: 1) What do changes in SO2 emissions tell us about a volcano's activity? How well do these measurements compare with ground-based COSPEC measurements? 2) How do we use measurements of lava flow temperature and volume to predict advances of the flow front? 3) What do changes in lava lake temperatures and energy emissions tell us about possible eruptive behavior?

Reviewing the results from different authors on the ice crust and supposing the presence of an internal ocean inside Europa, chaos terrains and various lenticulae features might be in connection with submarine geothermal centers while pull-apart terrains and other linear features are probably in connection with tidal processes. Ranking the surface features according to the possibility how much are they connected to deep submarine processes, the above mentioned first group is more important than tidal related linear features. Surveying the size and height of blocks at the example terrain of Conamara Chaos we found that the thickness of the ice crust during its formation could be around 2 km at the rafts and 0.5 km at the matrix in agreement with some other authors’ estimated values. Calculating the hydrostatic pressure at the bottom of the approximately 25 km thick ice crust 10 000–20 000 kPa was estimated, and at the bottom of a 100 km deep ocean at the order of 150 000 kPa was found. At such pressure and assumed temperature, volcanic gases became dissolved in the water—although clathrates might also form, and could be released later as gas bubbles. This process was enhanced during the formation of chaos terrains if the ice crust thickness is only 2 km at the active phase and the pressure is around 2400–3100 kPa at its base, or inside a subsurface brine lens still roughly 100 times smaller than at the bottom of the ocean. Calthrate decomposition and bubble formation might be the most intensive at chaos regions and bubbles may be trapped between ice grains ( McCord et al., 1999 ) or inside clathrate structure ( Prieto-Ballesteros et al., 2004 ). Using terrestrial analog observations we conclude that trapped bubbles might be detectable remotely by the difference in the infrared and visual albedo, and by other scattering properties. The rationality of such observations is the highest at those units of the chaos regions’ low level matrix, where the smallest linear structures are present suggesting the strongest disruption, but they are not covered by debris aprons. The possibility of the detection of gas bubbles or other material floating upward in the warm rising plume is of high interest at chaos terrains, and development of detecting methods for the next Europa mission is useful.

The Eyjafjallajökull volcanic eruption in 2010 released considerable amounts of ash into the high troposphere-low stratosphere, leading to unprecedented disruption of air traffic over Europe. The role of such fine-grained tephra in adsorbing, and therefore rapidly scavenging, volcanogenic volatile elements such as sulphur and halogens, is explored here. We report on results (major to trace element chemistry) of leaching experiments carried out on 20 volcanic ash samples, taken from the deposits of the main phases of the eruption (March–April 2010), or directly while falling (5–9 May 2010). Ash leachate solutions from Eyjafjallajökull are dominated – among cations – by Ca and Na, and display nearly equal S:Cl:F abundances (mean S/Cl and S/F molar ratios of 0.95 and 0.34, respectively). Abundances of major elements on surface minerals from freshly fallen ash are found to increase linearly upon increasing distance from the eruptive vents (a proxy for in-plume residence times). This allows for the formation rates of sulphur- and halogen-bearing surface salts to be quantified (3 × 10−9 to 2 × 10−8 mol m2 s−1), and for the averaged rate of in-plume ash-dissolution to be estimated (1.5 × 10−8 mol m−2 s−1; this sourcing the majority of cation species to soluble surface salts). These fast in-plume heterogeneous reactions are the cause of large volatile depositions: we estimate that 282 tons of elemental S, 605 tons of Cl, and 691 tons of F were daily ground deposited via ash over Iceland in early May 2010. Since fluorine is ∼3 times more rapidly processed in the plume than S and halogens (e.g., F is extremely reactive both in gas and aerosol forms and it is rapidly adsorbed onto ash), ash leachate compositions are in no way representative of S:Cl:F proportions in volcanic gases, and consequently of limited use in eruption monitoring.

We analyzed crater SO 2 fluxes from Mt Etna, together with soil CO 2 effluxes from the volcano's flanks, in the period from 2001 to 2005. Between the 2001 and 2002–2003 eruptions, persistently low values of both parameters suggest that no new gas-rich magma was accumulating at shallow depth ( 2 sin-eruptive fluxes during the two eruptions indicated sudden decompression of an un-degassed magma rising along newly-formed eccentric conduits. In November 2003, soil CO 2 data indicate migration of gas-rich magma from deep (> 10 km) to shallow ( 2 fluxes. A similar behavior was observed also during and after the following 2004–2005 eruption. This degassing style matches a period of increased structural instability of the volcanic edifice caused by acceleration of spreading that affected both its eastern and southern flanks. Spreading could have triggered progressively deeper depressurization in the central conduit, inducing release of the more soluble gas (SO 2 ) first, and then of CO 2 , contrary to what was observed before the 2001 eruption. This suggests that the edifice has depressurized, promoting ascent of fresh-magma and increasing permeability favouring release of CO 2 flux. By integrating geochemical and structural data, previous degassing models developed at Mt. Etna have been updated to advance the understanding of eruptive events that occurred in recent years.

A technique for measuring two-dimensional (2-D) plumes of volcanic gases with thermal emission spectroscopy was described in Part 1 by Stremme et al. (2012a). In that paper the instrumental aspects as well as retrieval strategies for obtaining the slant column images of SO2 and SiF4, as well as animations of particular events observed at the Popocatépetl volcano, were presented. This work focuses on the procedures for determining the propagation speed of the gases and estimating an emission rate from the given image sequences. A 2-D column density distribution of a volcanic gas, available as time-consecutive frames, provides information of a projected wind field and the average velocity at which the volcanic plume is propagating. This information is valuable since the largest uncertainties when calculating emission rates of the gases using remote sensing techniques arise from propagation velocities which are often inadequately assumed. The presented reconstruction method solves the equation of continuity as an ill-posed problem using mainly a Tikhonov-like regularisation. It is observed from the available data sets that if the main direction of propagation is perpendicular to the line-of-sight, the algorithm works well for SO2, which has the strongest signals, and also for SiF4 in some favourable cases. Due to the similarity of the algorithm used here with the reconstruction methods used for profile retrievals based on optimal estimation theory, diagnostic tools like the averaging kernels can be calculated in an analogous manner and the information can be quantified as degrees of freedom. Thus, it is shown that the combination of wind field and column distribution of the gas plume can provide the emission rate of the volcano both during day and night.

Adsorbent-trapped volcanic gases, sublimates and condensates from active vents of the La Fossa crater on the island of Vulcano (Aeolian Islands, Italy) as well as ambient and industrial air were quantitatively analyzed by Short-Path Thermal Desorption–Solid Phase Microextraction–Cryotrapping–Gas Chromatography/Mass Spectrometry (SPTD–SPME–CF–GC–MS). Among the over 200 detected and quantified compounds are alkanes, alkenes, arenes, phenols, aldehydes, carboxylic acids, esters, ketones, nitriles, PAHs and their halogenated, methylated and sulfonated derivatives, as well as various heterocyclic compounds including thiophenes and furans. Most compounds are found at concentrations well above laboratory, ambient air, adsorbent and field blank levels. For some analytes (e.g., CFC-11, CH 2 Cl 2 , CH 3 Br), concentrations are up to several orders of magnitude greater than even mid-latitudinal industrial urban air maxima. Air or laboratory contamination is negligible or absent on the basis of noble gas measurements and their isotopic ratios. The organic compounds are interpreted as the product of abiogenic gas-phase radical reactions. On the basis of isomer abundances, n -alkane distributions and substitution patterns the compounds are thought to have formed by high-temperature (e.g., 900 °C) alkyl free radical reactions and halide electrophilic substitution on arenes, alkanes and alkenes. The apparent abiogenic organic chemistry of volcanic gases may give insights into metal transport processes during the formation and alteration of hydrothermal ore deposits, into the natural volcanic source strength of ozone-depleting atmospheric trace gases (i.e., halocarbons), into possibly sensitive trace gas redox pairs as potential early indicators of subsurface changes on volcanoes in the state of imminent unrest, and into the possible hydrothermal origin of early life on Earth, as indicated by the presence of simple amino acids, nitriles, and alkanoic acids.

Carbon is a major element in the Earth’s system and plays an important role in many geochemical processes including metamorphism, volcanism, oceanic systems and atmospheric evolution. Knowledge and understanding of chemical speciation, mineral solubility and reactivity involving carbon are very important in order to qualitatively and quantitatively understand these processes. Indeed, dissolved inorganic carbon is among the major components of natural geothermal fluids. It originates from various sources including magmatic degassing, rock dissolution and organic matter degradation (e.g., Giggenbach 1992; Giggenbach et al. 1993; Simmons and Cristenson 1994; Sanoa and Marty 1995). Dissolved CO2 is the most common form of dissolved inorganic carbon in these systems, though other forms exist like CH4 and CO but usually in much lower concentrations than CO2 (e.g., Chiodini and Marini 1998; Stefansson and Arnorsson 2002). The concentrations of dissolved inorganic carbon (DIC) in geothermal fluids from active geothermal systems throughout the world are shown in Figure 1a together with the pH of the fluids. In general, the DIC concentration increases in geothermal fluids with increasing temperature from a few mmol per kg up to half a mole per kg of fluid. This increase is accompanied by a decrease in the fluid pH (Fig. 1b). Higher concentrations (not shown) are observed in fumarole fluids discharging volcanic gases (e.g., Chiodini et al. 1996). At Earth’s surface, CO2 also degasses through the soils in active geothermal systems (e.g., Chiodini et al. 1998). The chemistry and transport of DIC in natural geothermal systems is influenced by many processes including magma degassing, water-rock interaction and partitioning of CO2 between liquid and vapor phases upon boiling and phase separation. It has been concluded that the concentration of DIC and all other major elements besides incompatible elements such as Cl are …

In recent years, methane and other light hydrocarbons with an apparently abiotic origin have been identified in an increasing number of geologic fluids on Earth. These compounds have been found in a variety of geologic settings, including seafloor hydrothermal systems, fracture networks in crystalline rocks from continental and oceanic crust, volcanic gases, and gas seeps from serpentinized rocks (e.g., Abrajano et al. 1990; Kelley 1996; Sherwood Lollar 2002, 2008; Fiebig et al. 2007, 2009; Proskurowski et al. 2008; Taran et al. 2010b). Understanding the origin of these compounds has significant implications for range of topics that includes the global carbon cycle, the distribution of life in the deep subsurface (Gold 1992), and the origin of life (Martin et al. 2008). There are even claims that abiotic sources are major contributors to global hydrocarbon reservoirs (Gold 1993; Glasby 2006; Kutcherov and Krayushkin 2010; Sephton and Hazen 2013). While most experts are highly skeptical of such broad claims, it seems possible that at least some petroleum and gas reservoirs could contain hydrocarbons with an abiotic origin. Conceptually, there are two potential major sources of abiotic hydrocarbons to fluids in Earth’s crust. First, abiotic hydrocarbons could migrate to the crust from deeper sources within Earth, through processes such as convective transport, grain boundary diffusion, or release of magmatic volatiles. Second, abiotic hydrocarbons could form in situ within the crust through reduction of inorganic carbon sources. Potential substrates for carbon reduction include CO2 and CO in circulating fluids, and carbon-bearing solids such as carbonate minerals and graphite. In either case, the ultimate source of the inorganic carbon may be primordial (i.e., from the mantle) or recycled from Earth’s surface. This paper summarizes some of the recent laboratory experimental studies conducted to investigate potential …

The ability to image and quantify SO2 path-concentrations in volcanic plumes, either by day or by night, is beneficial to volcanologists. Gas emission rates are affected by the chemical equilibria in rising magmas and a better understanding of this relationship would be useful for short-term eruption prediction. A newly developed remote sensing long-wave thermal InfraRed (IR) imaging hyperspectral sensor – the Thermal Hyperspectral Imager (THI) – was built and tested. The system employs a Sagnac interferometer and an uncooled microbolometer in rapid scanning configuration to collect hyperspectral images of volcanic plumes. Each pixel in the resulting image yields a spectrum with 50 samples between 8 and 14 μm. Images are spectrally and radiometrically calibrated using an IR source with a narrow band filter and two blackbodies. In this paper, the sensitivity of the instrument for the purpose of quantifying SO2 using well constrained laboratory experiments is evaluated, and initial field results from Kīlauea volcano, Hawai’i, are presented. The sensitivity of THI was determined using gas cells filled with known concentrations of SO2 and using NIST-traceable blackbodies to simulate a range of realistic background conditions. Measurements made by THI were then benchmarked against a high spectral resolution off-the-shelf Michelson FTIR instrument. Theoretical thermal IR spectral radiances were computed with MODTRAN5 for the same optical conditions, to evaluate how well the (known) concentration of SO2 in the gas cells could be retrieved from the resulting THI spectra. Finally, THI was recently field-tested at Kīlauea to evaluate its ability to image the concentration of SO2 in a real volcanic plume. A path-concentration of 7150 ppm m was retrieved from measurements made near the Halema’uma’u vent.

We report measurements of Hg, SO2, and halogens (HCl, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gaseous SO2 and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO2 and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m-3. Hg/SO2 mass ratios measured with the real-time instruments ranged from 1.1 × 10-7 to 3.5 × 10-5 (mean 2 × 10-5). Total gaseous mercury (TGM) concentrations measured by gold trap ranged from 100 to 225 ng m-3. Reactive gaseous mercury accounted for 1% of TGM, while particulate mercury was 5% of the TGM. Field measurements of Masaya's SO2 flux, combined with the Hg/SO2 ratio, indicate a Hg flux from Masaya of 7.2 Mg a-1. At Masaya's low temperature famaroles, Hg/CO2 mass ratios were consistently around 2 × 10-8, lower than observed in the main vent (Hg/C02 ∼ 10-7). Low-temperature fumarole Hg fluxes from Masaya are insignificant (∼150 g a-1). Ratios of S, C and halogen species were also measured at Masaya and Telica volcanoes. CO2/ SO2 ratios at Masaya ranged from 2.8 to 3.9, comparable to previously published values. At Masaya molar Br/SO2 was 3 × 10-4 and I/SO2 was 2 × 10-5, suggesting fluxes of 0.2-0.5 Mg HBr d-1 and 0.02-0.05 Mg HI d-1. At Telica the Br/SO2 ratio was also 3 × 10-4 and the I/SO2 ratio was 5.8 × 10-5, with corresponding fluxes of 0.2 Mg HBr d-1 and 0.06 Mg HI d-1. Gases at both volcanoes are enriched in I relative to Br and Cl, compared to gases from volcanoes elsewhere. Copyright 2008 by the American Geophysical Union.

Submarine volcanism represents ~80% of the volcanic activity on Earth and is an important source of mantle-derived gases. These gases are of basic importance for the comprehension of mantle characteristics in areas where subaerial volcanism is missing or strongly modified by the presence of crustal/atmospheric components. Though, the study of submarine volcanism remains a challenge due to their hazardousness and sea-depth. Here, we report 3He/4He measurements in CO2–dominated gases discharged at 500 m below sea level from the high-temperature (~220 °C) hydrothermal system of the Kolumbo submarine volcano (Greece), located 7 km northeast off Santorini Island in the central part of the Hellenic Volcanic Arc (HVA). We highlight that the mantle below Kolumbo and Santorini has a 3He/4He signature of at least 7.0 Ra (being Ra the 3He/4He ratio of atmospheric He equal to 1.39×10−6), 3 Ra units higher than actually known for gases-rocks from Santorini. This ratio is also the highest measured across the HVA and is indicative of the direct degassing of a Mid-Ocean-Ridge-Basalts (MORB)-like mantle through lithospheric faults. We finally highlight that the degassing of high-temperature fluids with a MORB-like 3He/4He ratio corroborates a vigorous outgassing of mantle-derived volatiles with potential hazard at the Kolumbo submarine volcano.

International audience; Understanding the interaction between volcanic gases and ash is important 8 to derive gas compositions from ash leachates and to constrain the environmental 9 impact of eruptions. Volcanic HCl could potentially damage the ozone layer, but it is 10 unclear what fraction of HCl actually reaches the stratosphere. The adsorption of HCl 11 on volcanic ash was therefore studied from-76 to + 150 ˚C to simulate the behavior 12 of HCl in the dilute parts of a volcanic plume. Finely ground synthetic glasses of 13 andesitic, dacitic, and rhyolitic composition as well as a natural obsidian from 14 Vulcano (Italy) served as proxies for fresh natural ash. HCl adsorption is an 15 irreversible process and appears to increase with the total alkali content of the glass. 16 Adsorption kinetics follow a first order law with rate constants of 2.13. 10-6 s-1 to 17 1.80. 10-4 s-1 in the temperature range investigated. For dacitic composition, the 18 temperature and pressure dependence of adsorption can be described by the equation 19 ln c = 1.26 + 0.27 ln p-715.3/T, where c is the surface concentration of adsorbed HCl 20 in mg/m 2 , T is temperature in Kelvin, and p is the partial pressure of HCl in mbar. A 21 comparison of this model with a large data set for the composition of volcanic ash 22 suggests that adsorption of HCl from the gas phase at relatively low temperatures can 23 quantitatively account for the majority of the observed Cl concentrations. The model 24 implies that adsorption of HCl on ash increases with temperature, probably because of 25 2 the increasing number of accessible adsorption sites. This temperature dependence is 26 opposite to that observed for SO 2 , so that HCl and SO 2 are fractionated by the 27 adsorption process and the fractionation factor changes by four orders of magnitude 28 over a temperature range of 250 K. The assumption of equal adsorption of different 29 species is therefore not appropriate for deriving volcanic gas compositions from 30 analyses of adsorbates on ash. However, with the experimental data provided here, the 31 gas compositions in equilibrium with the ash surfaces can be calculated. In particular, 32 for dacitic composition, the molar ratio of S/Cl adsorbed to the ash surface is related 33 to the molar S/Cl ratio in the gas phase according to the equation ln (S/Cl) adsorbed = 34 2855 T-1 + 0.28 ln (S/Cl) gas-11.14. Our data also show that adsorption on ash will 35 significantly reduce the fraction of HCl reaching the stratosphere, only if the initial 36 HCl content in the volcanic gas is low (< 1 mole %). For higher initial HCl 37 concentrations, adsorption on ash has only a minor effect. While HCl scavenging by 38 hydrometeors may remove a considerable fraction of HCl from the eruption column, 39 recent models suggest that this process is much less efficient than previously thought. 40 Our experimental data therefore support the idea that the HCl loading from major 41 explosive eruptions may indeed cause severe depletions of stratospheric ozone. 42 43

At Mount Etna, the present-day active volcano is an open conduit structure characterized by continuous eruptive activity. Such conditions have been thought unique in the evolution of the Etnean volcano as well as in the Mediterranean region. However, a review study of available geophysical data and models, combined with geological records, petrographic and geochemical considerations, has led us to consider that a large area of about 28 km2 located in Val Calanna, on the eastern side of Valle del Bove, can be interpreted as the site of an old open conduit volcano. A dyke swarm outcrops in the area, whose deep alteration and fumarolization can be attributed to the sustained passage of volcanic gases over long periods. Radiometric dating yields an age of about 129 ka. This finding sheds new light on the evolution of Mount Etna volcano, indicating that the tectonic conditions leading to an open conduit volcano must also have been active in the past.

Large earthquakes sometimes activate volcanoes both in the near field as well as in the far field. One possible explanation is that shaking may increase the mobility of the volcanic gases stored in magma reservoirs and conduits. Here experimentally and theoretically we investigate how sloshing, the oscillatory motion of fluids contained in a shaking tank, may affect the presence and stability of bubbles and foams, with important implications for magma conduits and reservoirs. We adopt this concept from engineering: severe earthquakes are known to induce sloshing and damage petroleum tanks. Sloshing occurs in a partially filled tank or a fully filled tank with density-stratified fluids. These conditions are met at open summit conduits or at sealed magma reservoirs where a bubbly magma layer overlays a newly injected denser magma layer. We conducted sloshing experiments by shaking a rectangular tank partially filled with liquids, bubbly fluids (foams) and fully filled with density-stratified fluids; i.e., a foam layer overlying a liquid layer. In experiments with foams, we find that foam collapse occurs for oscillations near the resonance frequency of the fluid layer. Low viscosity and large bubble size favor foam collapse during sloshing. In the layered case, the collapsed foam mixes with the underlying liquid layer. Based on scaling considerations, we constrain the conditions for the occurrence of foam collapse in natural magma reservoirs. We find that seismic waves with lower frequencies < 1 Hz, usually excited by large earthquakes, can resonate with magma reservoirs whose width is > 0.5 m. Strong ground motion > 0.1 m s− 1 can excite sloshing with sufficient amplitude to collapse a magma foam in an open conduit or a foam overlying basaltic magma in a closed magma reservoir. The gas released from the collapsed foam may infiltrate the rock or diffuse through pores, enhancing heat transfer, or may generate a gas slug to cause a magmatic eruption. The overturn in the magma reservoir provides new nucleation sites which may help to prepare a following/delayed eruption. Mt. Fuji erupted 49 days after the large Hoei earthquake (1707) both dacitic and basaltic magmas. The eruption might have been triggered by magma mixing through sloshing.

Large explosive eruptions inject volcanic gases and fine ash to stratospheric altitudes, contributing to global cooling at the Earth’s surface and occasionally to ozone depletion. The modelling of the climate response to these strong injections of volatiles commonly relies on ice-core records of volcanic sulphate aerosols. Here we use an independent geochemical approach which demonstrates that the great 1257 eruption of Samalas (Lombok, Indonesia) released enough sulphur and halogen gases into the stratosphere to produce the reported global cooling during the second half of the 13th century, as well as potential substantial ozone destruction. Major, trace and volatile element compositions of eruptive products recording the magmatic differentiation processes leading to the 1257 eruption indicate that Mt Samalas released 158 ± 12 Tg of sulphur dioxide, 227 ± 18 Tg of chlorine and a maximum of 1.3 ± 0.3 Tg of bromine. These emissions stand as the greatest volcanogenic gas injection of the Common Era. Our findings not only provide robust constraints for the modelling of the combined impact of sulphur and halogens on stratosphere chemistry of the largest eruption of the last millennium, but also develop a methodology to better quantify the degassing budgets of explosive eruptions of all magnitudes.

Two approaches to the challenging aim of forecasting impending eruptions are searching for empirical precursors and developing suitable interpretative models. Here we present high-resolution time series of 3He/4He ratios measured in gases emitted from peripheral vents around Mount Etna volcano (Italy), which revealed variations with strong correlations over both time and a broad spatial scale. The main eruptive episodes are preceded by increases in 3He/4He, making this ratio a unique tracer for monitoring volcanic activity. These features strongly reflect pressurization beneath the volcano due to deep magma influx. We propose a pioneering model that relates the changes in 3He/4He to the time-dependent outflow of volatiles from a magmatic chamber subjected to evolution of its internal pressure due to magma injection. At Mount Etna, the model makes it possible to estimate in near real time key parameters such as the rate of magma input and volume change in deep chamber preceding eruptions, and to compare them with geodetic estimations. This represents an unprecedented use of 3He/4He to obtain quantitative information on the physics of magmatic systems. Volcanoes showing changes of 3He/4He ratio in discharged gases due to unrest episodes are widespread in the world, and therefore we envisage extensive future applications of this approach.

Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H 2 O, CO 2 , SO 2 and H 2 S in crater rim emissions, coupled with filter-pack determination of SO 2 , halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content (~ 93 mol%), similar S/Cl, Cl/F, Br/Cl molar ratios, similar ( 210 Po/ 210 Pb) and ( 210 Bi/ 210 Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO 2 /SO 2 ratio (1.0 and 5.6–3.0, respectively) is attributed to deeper gas-melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO 2 plume flux (90 kg s − 1 or 7800 tons d − 1 ) demonstrates a prevalent degassing contribution (~ 65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H 2 O, CO 2 , HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO 2 , HF, HBr, Hg, 210 Po and 210 Pb, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest dissolved amounts of H 2 O (≤ 1.3 wt%), CO 2 (~ 0.10 wt%), S (0.075 wt%) and Cl (0.05 wt%), and its degassing under prevalent closed-system conditions well reproduces the composition of emitted volcanic gases. Instead, we show that the gas discharge is sustained by a very high basalt supply rate of 25 m 3 s − 1 , from a large (~ 0.5 km 3 ) magma reservoir probably emplaced at ~ 3.8 km depth below the summit caldera according to both the H 2 O-CO 2 content of bubble-free melt inclusions and preliminary seismic data. Radioactive disequilibria in the volcanic gases constrain that this reservoir may be entirely renewed in about 240 days. The comparatively low magma extrusion rate requires extensive convective overturn of the basaltic magma column and recycling of the unerupted (denser) degassed magma in the plumbing system, in agreement with textural features of erupted products. Finally, our results suggest that the Indian MORB-type mantle source of Ambrym basalts is modestly enriched in slab-derived water and other volatiles, in agreement with the prevalent volcanoclastic nature of subducted sediments and their lower subduction rate under the central Vanuatu arc due to its collision with the D'Entrecasteaux Ridge.

We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low He-3/He-4 ratios in thermal fluids of Epi (4.0 +/- 0.1 R-a), Efate (4.5 +/- 0.1 R-a) and Pentecost (5.3 +/- 0.5 R-a) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display He-3/He-4 and C/He-3 ratios typical of subduction-related volcanic arcs: He-3/He-4 ratios range from 6.4 +/- 0.5 Ra in southernmost Tanna and 7.23 +/- 0.09 R-a in northernmost Vanua Lava to typical MORE values in the central islands of Gaua (7.68 +/- 0.06 R-a), Ambrym (7.6 +/- 0.8 R-a) and Ambae (7 2 R-a in groundwaters, 7.9 +/- 1.4 R-a in olivine phenocrysts, and 8.0 +/- 0.1 Ra in summit fumaroles of Aoba volcano). On Ambrym, however, we discover that hydrothermal manifestations separated by only 10-15 km on both sides of a major E-W transverse fault zone crossing the island are fed by two distinct helium sources, with different 3He/4He signatures: while fluids in southwest Ambrym (Baiap and Sesivi areas) have typical arc ratios (7.6 +/- 0.8 R-a), fluids on the northwest coast (Buama Bay area) display both higher He-3/He-4 ratios (9.8 +/- 02 R-a in waters to 10.21 +/- 0.08 R-a in bubbling gases) and lower C/He-3 ratios that evidence a hotspot influence. We thus infer that the influx of Indian MORB mantle beneath the central Vanuatu arc, from which Ambrym magmas originate, also involves a He-3-rich hotspot component, possibly linked to a westward influx of Samoan hotspot material or another yet unknown local source. This duality in magmatic He source at Ambrym fits with the bimodal composition and geochemistry of the erupted basalts, implying two distinct magma sources and feeding systems. More broadly, the wide He isotopic variations detected along the Vanuatu arc further verify the complex tectonic and magmatic framework of this intra-oceanic island arc.

The monitoring methods for volcanic gases are divided into remote sensing and direct gas sampling approaches. In the remote sensing approach, COSPEC and Li-COR are used to measure and , respectively, with FT-IR for detection of a range of volcanic gases. However, the remote sensing approach is not applicable to Mt. Baegdu, where the atmospheric contents of volcanic gases are very low as a result of the strong interaction of volcanic gases with the nearby surface water and groundwater. On the other hand, the direct gas sampling approach involves the collection of volcanic gases from volcanic vents or fumaroles and the subsequent laboratory analysis, thus making it possible to measure even very low levels of volcanic gases. The direct sampling approach can be subdivided into the evacuated bottle method and the flow-through bottle method. In applying both methods, sampling bottles typically contain reaction media to trap specific volcanic gases. For example, NaOH solution(Giggenbach bottle), solution, and acid condensates have been experimented for volcanic gas sampling. Once taken from vents and fumaroles, the samples of volcanic gases are pretreated and subsequently analyzed for volcanic gases using GC, IC, HPLC, titrimetry, TOC-IC, or ICP-MS. Recently, there has been the increasing number of evidences on the potential volcanic activity of Mt. Baegdu. However, little technical development has been made for the sampling and analysis of volcanic gases in Korea. In the present work, we reviewed various volcanic gas monitoring methods, and provided the detailed information on the monitoring methods applied to Mt. Baegdu.

March 20, 2010, in southern Iceland, the Eyjafjallajokull volcano began to erupt after almost 200 years of silence. Three weeks later, on April 14, a 500-m long fissure opened in the ice cap covering the volcano, ejecting molten lava and huge amounts of steam, volcanic ash, and toxic gases into the atmosphere. This produced a giant ash cloud, which disrupted air traffic across Europe for several days. This paper presents a description of the eruption and gives a brief review of the composition of volcanic lava and gases, as well as examples of the adverse effects of volcanic ash on humans and livestock in many Icelandic farms.

Volcanic air pollution, known as vog (volcanic smog) has recently become a major issue in the Hawaiian islands. Vog is caused when volcanic gases react with oxygen and water vapor. It consists of a mixture of gases and aerosols, which include sulfur dioxide and other sulfates. The source of the volcanic gases is the continuing eruption of Mount Kilauea. This paper studies predicting vog using statistical methods. The data sets include time series for SO2 and SO4, over locations spanning the west, south and southeast coasts of Hawaii, and the city of Hilo. The forecasting models include regressions and neural networks, and a frequency domain algorithm. The most typical pattern for the SO2 data is for the frequency domain method to yield the most accurate forecasts over the first few hours, and at the 24 h horizon. The neural net places second. For the SO4 data, the results are less consistent. At two sites, the neural net generally yields the most accurate forecasts, except at the 1 and 24 h horizons, where the frequency domain technique wins narrowly. At one site, the neural net and the frequency domain algorithm yield comparable errors over the first 5 h, after which the neural net dominates. At the remaining site, the frequency domain method is more accurate over the first 4 h, after which the neural net achieves smaller errors. For all the series, the average errors are well within one standard deviation of the actual data at all the horizons. However, the errors also show irregular outliers. In essence, the models capture the central tendency of the data, but are less effective in predicting the extreme events.