Volcanic Gases Research Articles

Abundant Atmospheric Methane from Volcanism on Terrestrial Planets Is Unlikely and Strengthens the Case for Methane as a Biosignature

Abstract The disequilibrium combination of abundant methane and carbon dioxide has been proposed as a promising exoplanet biosignature that is readily detectable with upcoming telescopes such as the James Webb Space Telescope. However, few studies have explored the possibility of nonbiological CH4 and CO2 and related contextual clues. Here we investigate whether magmatic volcanic outgassing on terrestrial planets can produce atmospheric CH4 and CO2 with a thermodynamic model. Our model suggests that volcanoes are unlikely to produce CH4 fluxes comparable to biological fluxes. Improbable cases where volcanoes produce biological amounts of CH4 also produce ample carbon monoxide. We show, using a photochemical model, that high abiotic CH4 abundances produced by volcanoes would be accompanied by high CO abundances, which could be a detectable false-positive diagnostic. Overall, when considering known mechanisms for generating abiotic CH4 on terrestrial planets, we conclude that observations of atmospheric CH4 with CO2 are difficult to explain without the presence of biology when the CH4 abundance implies a surface flux comparable to modern Earth’s biological CH4 flux. A small or negligible CO abundance strengthens the CH4+CO2 biosignature because life readily consumes atmospheric CO, while reducing volcanic gases likely cause CO to build up in a planet’s atmosphere. Furthermore, the difficulty of volcanically generated CH4-rich atmospheres suitable for an origin of life may favor alternatives such as impact-induced reducing atmospheres.

Variation of volcanic gas composition at a poorly accessible volcano: Sakurajima, Japan

Volcanic gas compositions are estimated based on volcanic plume measurement with Multi-GAS at a frequently erupting Sakurajima volcano by application of airborne methods and automatic monitoring station on the flank during 2013–2019. The airborne measurements of CO2 and H2O concentrations often suffer from large fluctuation of background likely due to entrainment of the atmosphere derived from different altitude. By removing the background effect, a representative volcanic CO2/SO2 mole ratio is estimated as 0.4 ± 0.1 and we did not observe clear temporal variation. The volcanic H2O/SO2 ratios are estimated as 30–70 with a large uncertainty because of the strong atmospheric perturbation. The SO2/H2S ratios show quite a large variation ranging from 1 to 800. The large SO2/H2S ratios larger than 30 are observed during ash eruption and are suggested as a result of oxidation by atmosphere on hot ashes. The small ratios less than 10 are observed when frequency of explosions is low. Variation of the SO2/H2S ratios of the small values can be caused by variation of degassing pressure, however, the small variation of the CO2/SO2 ratio suggests a limited range of the pressure variation.

BVLOS UAS Operations in Highly-Turbulent Volcanic Plumes.

Long-range, high-altitude Unoccupied Aerial System (UAS) operations now enable in-situ measurements of volcanic gas chemistry at globally-significant active volcanoes. However, the extreme environments encountered within volcanic plumes present significant challenges for both air frame development and in-flight control. As part of a multi-disciplinary field deployment in May 2019, we flew fixed wing UAS Beyond Visual Line of Sight (BVLOS) over Manam volcano, Papua New Guinea, to measure real-time gas concentrations within the volcanic plume. By integrating aerial gas measurements with ground- and satellite-based sensors, our aim was to collect data that would constrain the emission rate of environmentally-important volcanic gases, such as carbon dioxide, whilst providing critical insight into the state of the subsurface volcanic system. Here, we present a detailed analysis of three BVLOS flights into the plume of Manam volcano and discuss the challenges involved in operating in highly turbulent volcanic plumes. Specifically, we report a detailed description of the system, including ground and air components, and flight plans. We present logged flight data for two successful flights to evaluate the aircraft performance under the atmospheric conditions experienced during plume traverses. Further, by reconstructing the sequence of events that led to the failure of the third flight, we identify a number of lessons learned and propose appropriate recommendations to reduce risk in future flight operations.

Volcanic activity monitoring by unique LIDAR based on a diode laser

For the first time, we monitored the Elbrus volcano activity detecting volcanic gases emanating through pores using an unique eye-safe LIDAR system. A highly sensitive eye-safe LIDAR system was developed for monitoring the fracture-emitted aerosol, which is transported by volcanic gases inside a hot tunnel near the Elbrus Mountain. The developed LIDAR is based on a diode laser (transmitter, 910 nm, 3 ns, <1 µJ cm−2) and a single-photon avalanche photodiode (detector). From August to October 2019, within the first months of the LIDAR monitoring, we have detected a two-fold decrease in the fracture-emitted aerosol emanation, while other parameters in the tunnel remained relatively stable (radon concentration, air temperature and humidity changed less than by 1%). A significant correlation between the LIDAR signal of volcanic aerosol and the Earth’s crust deformation measured by the laser strainmeter located nearby was found. Based on our preliminary experiments we consider the new LIDAR system as a sensitive, economical and robust instrument for Earth’s crust deformation and volcanic activity monitoring and eruption precursor observation.

First In-Situ Measurements of Plume Chemistry at Mount Garet Volcano, Island of Gaua (Vanuatu)

Recent volcanic gas compilations have urged the need to expand in-situ plume measurements to poorly studied, remote volcanic regions. Despite being recognized as one of the main volcanic epicenters on the planet, the Vanuatu arc remains poorly characterized for its subaerial emissions and their chemical imprints. Here, we report on the first plume chemistry data for Mount Garet, on the island of Gaua, one of the few persistent volatile emitters along the Vanuatu arc. Data were collected with a multi-component gas analyzer system (multi-GAS) during a field campaign in December 2018. The average volcanic gas chemistry is characterized by mean molar CO2/SO2, H2O/SO2, H2S/SO2 and H2/SO2 ratios of 0.87, 47.2, 0.13 and 0.01, respectively. Molar proportions in the gas plume are estimated at 95.9 ± 11.6, 1.8 ± 0.5, 2.0 ± 0.01, 0.26 ± 0.02 and 0.06 ± 0.01, for H2O, CO2, SO2, H2S and H2. Using the satellite-based 10-year (2005–2015) averaged SO2 flux of ~434 t d−1 for Mt. Garet, we estimate a total volatile output of about 6482 t d−1 (CO2 ~259 t d−1; H2O ~5758 t d−1; H2S ~30 t d−1; H2 ~0.5 t d−1). This may be representative of a quiescent, yet persistent degassing period at Mt. Garet; whilst, as indicated by SO2 flux reports for the 2009–2010 unrest, emissions can be much higher during eruptive episodes. Our estimated emission rates and gas composition for Mount Garet provide insightful information on volcanic gas signatures in the northernmost part of the Vanuatu Arc Segment. The apparent CO2-poor signature of high-temperature plume degassing at Mount Garet raises questions on the nature of sediments being subducted in this region of the arc and the possible role of the slab as the source of subaerial CO2. In order to better address the dynamics of along-arc volatile recycling, more volcanic gas surveys are needed focusing on northern Vanuatu volcanoes.

Reconciling the climate and ozone response to the 1257 CE Mount Samalas eruption

The 1257 CE eruption of Mount Samalas (Indonesia) is the source of the largest stratospheric injection of volcanic gases in the Common Era. Sulfur dioxide emissions produced sulfate aerosols that cooled Earth's climate with a range of impacts on society. The coemission of halogenated species has also been speculated to have led to wide-scale ozone depletion. Here we present simulations from HadGEM3-ES, a fully coupled Earth system model, with interactive atmospheric chemistry and a microphysical treatment of sulfate aerosol, used to assess the chemical and climate impacts from the injection of sulfur and halogen species into the stratosphere as a result of the Mt. Samalas eruption. While our model simulations support a surface air temperature response to the eruption of the order of -1°C, performing well against multiple reconstructions of surface temperature from tree-ring records, we find little evidence to support significant injections of halogens into the stratosphere. Including modest fractions of the halogen emissions reported from Mt. Samalas leads to significant impacts on the composition of the atmosphere and on surface temperature. As little as 20% of the halogen inventory from Mt. Samalas reaching the stratosphere would result in catastrophic ozone depletion, extending the surface cooling caused by the eruption. However, based on available proxy records of surface temperature changes, our model results support only very minor fractions (1%) of the halogen inventory reaching the stratosphere and suggest that further constraints are needed to fully resolve the issue.

Intercomparison of geochemical techniques at La Soufrière de Guadeloupe (FWI) volcano: their advantages and their limits over a long-standing unrest

Volcanic gas emissions from the main low-temperature fumaroles (around 100°C) of one of the most dangerous volcanoes in the Lesser Antilles, La Soufriere de Guadeloupe, are measured routinely using direct sampling with NaOH bottles (for H2O, CO2, H2Stot, H2, CH4, CO, N2, He, Ar, O2), with P2O5 bottles (for H2O, CO2, H2S, SO2, H) and MULTIGAS (for HO, CO HS, SO, H). This allows us to perform a study about an intercomparison of volcanic gas monitoring methologies. The results show some good overlap and similar temporal evolution between the dataset of the different methologies, which is of utmost of importance for monitoring purposes. However, there is no good agreement between the three methodologies for the same chemical ratio. The differences could be explained by a time- dependant diffusive phenomenon that affects the concentrations of sampled gases for two methods of the three (P2O5 bottles and MULTIGAS). P2O5-based analyses are affected because effusion on rapid decompression and fast sampling affects the gas volume in the pipeline connecting the vent outlet to the sampling. Although MULTIGAS is a continuous, flow-through, sampling method, results are likely affected because of the sampling architecture involving filter and pump. Moreover, sulphur reaction (precipitation of elemental S upon exit from the fumarole, conversion of H2S to SO2, chemical reaction with the P2O5 powder that release H2S) and water condensation can also explain some discrepancies.

Subsurface Resistivity Imaging of Nasudake (Chausudake) Volcano Determined from Time Domain Electromagnetic Survey (TDEM)

A time domain electromagnetic survey (TDEM method) was conducted to investigate the resistivity structure of the crater, fumarole, and hot spring area of the Nasudake (Chausudake) volcano. The findings of this survey are as follows: (1) Under the crater area, a thin low-resistivity layer (approximately 50 m) was found on the surface, and lens-shaped high-resistivity areas continued to a depth of 800 m below it. The lens-shaped high-resistivity areas are believed to correspond to a thermal volcanic gas region. (2) From the east-west direction survey line crossing the foot of the Nasudake, two or three horizontal resistivity layer structures, which are considered to be caused by the geological structure and surface water, were observed.

The Nature and Compositional Peculiarities of Volcanogenic Diamonds

Abstract —We have studied volcanogenic diamonds in the context of a discussion of their genesis, including some assumption on their artificial origin. The carbon isotope composition of diamonds collected from the eruption products of Tolbachik volcano (δ13CVPDB from –22 to –29‰) is within the range of the δ13CVPDB values of natural diamonds, including those from kimberlites. The δ15NAir values of the Tolbachik diamonds, measured for the first time (–2.58 and –2.32‰), correspond to δ15NAir of volcanic gases and differ from that of atmospheric nitrogen (δ15NAir = 0‰), which may be expected in synthetic diamonds. In the studied volcanogenic diamonds, as in synthetic ones, the nitrogen impurity is unaggregated. However, such an unaggregated form of nitrogen is specific to many natural diamonds (e.g., variety II diamonds, according to Orlov’s classification). Impurity elements (Cl, F, O, S, Si, Al, Ca, and Na) are locally concentrated in volcanogenic diamonds; they are a constituent of micro- and nanoinclusions in them. The high contents of F and Cl in the studied diamonds are correlated with the composition of volcanic gases; there is no reason to expect a similar correlation in synthetic diamonds. Moreover, the studied cube-octahedral Tolbachik diamonds have a number of accessory forms, some of which are not observed in synthetic diamonds. Their surfaces are frequently covered with films composed of Mg–Fe and Ca–Mg silicates, aluminosilicates, sulfates, metal alloys, and native Al. Mineral inclusions in the studied diamonds are Mn–Ni–Si alloys and silicides varying in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2, Mn5Si2, and pure Mn silicide MnSi. Summing up the obtained data, we conclude that volcanogenic diamonds form in a strongly reducing environment, in which silicides and native metals and their alloys are stable. The predominant cube-octahedral morphology of these diamonds and the unaggregated nitrogen impurity point to their short-term residence under high-temperature conditions. This makes them similar, to some extent, to synthetic diamonds. There are, however, clear differences as well. Volcanogenic diamonds are similar in compositional peculiarities, including isotope compositions, to natural diamonds that form under most unfavorable conditions, such as cuboids, balases, carbonado, and some diamonds of the eclogite paragenesis. They also resemble diamonds found in situ in harzburgite and chromitite of ophiolites. This suggests a specific mechanism of formation of both volcanogenic and ophiolitic diamonds in the oceanic lithosphere.

Origins and Early Evolution of the Atmosphere and the Oceans

My journey in science began with the study of volcanic gases, sparking an interest in the origin, and ultimate fate, of the volatile elements in the interior of our planet. How did these elements, so crucial to life and our surface environment, come to be sequestered within the deepest regions of the Earth, and what can they tell us about the processes occurring there? My approach has been to establish geochemical links between the noble gases, physical tracers par excellence, with major volatile elements of environmental importance, such as water, carbon and nitrogen, in mantle-derived rocks and gases. From these analyses we have learned that the Earth is relatively depleted in volatile elements when compared to its potential cosmochemical ancestors (e.g., ~2 ppm nitrogen compared to several hundreds of ppm in primitive meteorites) and that natural fluxes of carbon are two orders of magnitude lower than those emitted by current anthropogenic activity. Further insights into the origin of terrestrial volatiles have come from space missions that documented the composition of the proto-solar nebula and the outer solar system. The consensus behind the origin of the atmosphere and the oceans is evolving constantly, although recently a general picture has started to emerge. At the dawn of the solar system, the volatile-forming elements (H, C, N, noble gases) that form the majority of our atmosphere and oceans were trapped in solid dusty phases (mostly in ice beyond the snowline and organics everywhere). These phases condensed from the proto-solar nebula gas, and/or were inherited from the interstellar medium. These accreted together within the next few million years to form the first planetesimals, some of which underwent differentiation very early on. The isotopic signatures of volatiles were also fixed very early and may even have preceded the first episodes of condensation and accretion. Throughout the accretion of the Earth, volatile elements were delivered by material from both the inner (dry, volatile-poor) and outer (volatile-rich) solar system. This delivery was concomitant with the metals and silicates that form the bulk of the planet. The contribution of bodies that formed in the far outer solar system, a region now populated by comets, is likely to have been very limited. In that sense, volatile elements were contributed continuously throughout Earth’s accretion from inner solar system reservoirs, which also provided the silicates and metal building blocks of the inner planets. Following accretion, it likely took a few hundred million years for the Earth’s atmosphere and oceans to stabilise. Luckily, we have been able to access a compositional record of the early atmosphere and oceans through the analysis of palaeo-atmospheric fluids trapped in Archean hydrothermal quartz. From these analyses, it appears that the surface reservoirs of the Earth evolved due to interactions between the early Sun and the top of the atmosphere, as well as the development of an early biosphere that progressively altered its chemistry.

Studi pengaruh erupsi abu vulkanik gunung agung terhadap hasil pengukuran partikel tersuspensi

Mount Agung with an altitude of 3.142 meters above sea level is located in Karangasem. This mountain is one of the active volcanoes in Indonesia. Some dangerous impacts caused by the eruption of Mount Agung are acid rain, earthquakes, lava/lava flow, landslides/mudflow, smoke from lava, pyroclastic, rain of volcanic ash, and rocks and also volcanic gas. One of them which is Rain of volcanic ash can cause blisters on the skin and eyes as well as respiratory irritation. For long-term effects can cause silicosis (lung disease resulting from dust) and chronic lung disease. This study was conducted to determine the Mount Agung volcanic ash eruption effect on the results of SPM concentration measurements at the Jembrana Climatology Station using comparative data and sample data obtained from SPM, VONA concentration measurement data, and the HYSPLIT Volcanic Ash (NOAA) models.

Carbonic nanostructures in subsurface rocks: problem review Part II. Graphene, carbonic nanotubes, nanofibers

The paper reviews the publications on the search and exploration of carbonic nanotubes and other nanocarbonic structures in subsurface rocks. It is shown that the graphenes and carbonic nanotubes (CNT) exist in the composition of various magmatic and sedimentary rocks. They are formed in the graphite globules of volcanic rocks, as well as in the sediments, where the pressure, the particles of metallic catalysts, the tension stresses and time factors in million years compensate the absence of high temperatures. Experimental laboratory modeling of natural processes has been carried out and the reality of formation of carbonic nanostructures during the pyrolysis of volcanic gases on the lava catalysts, mechanical activation and processing of amorphous carbon or bituminous coal shown. Principal possibility of realization of technology of CNT mass production via pyrolysis of hydrocarbon crude material in the presence of different catalytically-active natural minerals has been reviewed and proven. The analysis of the aspects following the activity of mud volcanoes shows that there are all suppositions for the formation of carbonic nanostructures: the pressure bump of deep rocks out of the hot eruptive centre, methane as carbonic crude, catalytically-active breccias containing transition metals and their oxides, the process of methane burning in the medium poor of oxygen. However, it is not yet absolutely clear. As a working hypothesis we propose a model of formation of these structures due to the mud volcanism activity in the reactions of methane flow, the catalysts in which natural minerals exist. In such processes as a result of intensive methane flow, there occur negative pressure values and cavitation effects in the presence of which local temperature and pressure increase efficient for formation of adamantine and nanosize carbonic structures take place. In case if this mechanism is real, the studies point to a perspective of obtaining valuable products in conditions of natural geological processes. There are no messages or publications yet on the exploration of carbonic nanostructures in the rocks of mud volcanoes.

The BrIdge voLcanic LIdar—BILLI: A Review of Data Collection and Processing Techniques in the Italian Most Hazardous Volcanic Areas

Volcanologists have demonstrated that carbon dioxide (CO2) fluxes are precursors of volcanic eruptions. Controlling volcanic gases and, in particular, the CO2 flux, is technically challenging, but we can retrieve useful information from magmatic/geological process studies for the mitigation of volcanic hazards including air traffic security. Existing techniques used to probe volcanic gas fluxes have severe limitations such as the requirement of near-vent in situ measurements, which is unsafe for operators and deleterious for equipment. In order to overcome these limitations, a novel range-resolved DIAL-Lidar (Differential Absorption Light Detection and Ranging) has been developed as part of the ERC (European Research Council) Project “BRIDGE”, for sensitive, remote, and safe real-time CO2 observations. Here, we report on data collection, processing techniques, and the most significant findings of the experimental campaigns carried out at the most hazardous volcanic areas in Italy: Pozzuoli Solfatara (Phlegraen Fields), Stromboli, and Mt. Etna. The BrIdge voLcanic LIdar—BILLI has successfully obtained accurate measurements of in-plume CO2 concentration and flux. In addition, wind velocity has also been retrieved. It has been shown that the measurements of CO2 concentration performed by BILLI are comparable to those carried out by volcanologists with other standard techniques, heralding a new era in the observation of long-term volcanic gases.

Thin section and X-ray computed tomography for characterizing volcanic reservoirs in Chagan Sag, Yin-E Basin, China

We have synthesized macroscopic data (cores) and microscopic data (thin sections and computed tomography images) to characterize volcanic oil and gas reservoir spaces in the Chagan Sag, Yin-E Basin, China. We also have assessed the controlling factors affecting the formation of these reservoirs. Primary pores significantly improve the reservoir quality because they enable the formation of secondary pores (dissolution pores) by allowing migration, alteration, and filling by inorganic and organic fluids. Consequently, the development of secondary pores modifies the permeability of the volcanic rocks. The formation of volcanic reservoirs is influenced by lithology, diagenic minerals, faults, and fractures. The size and abundance of pores, especially gas pores, varies with the lithology. Gas pores are consistently larger and more abundant in basalts than in andesites and tuffs. Moreover, the carbonates and chlorites readily dissolve in the vesicles and fractures, thus resulting in the formation of secondary pores. However, quartzes are not susceptible to dissolution in this study area. Further, faults and fractures are necessary for the formation of reservoir spaces and for oil and gas migration. The tomographic images provide 3D distributions of fractures, vesicles, and matrix dissolution pores. The results suggest that fractures connecting isolated gas pores provide favorable spaces for oil accumulation.

The control of magma crystallinity on the fluctuations in gas composition at open vent basaltic volcanoes

Basaltic open vent volcanoes are major global sources of volcanic gases. Many of these volcanoes outgas via intermittent Strombolian-type explosions separated by periods of passive degassing. The gas emitted during the explosions has high molar CO2/SO2 and SO2/HCl ratios, while during the passive degassing these ratios are lower. We present new laboratory experiments in a model volcanic conduit, which suggest that these differences in gas geochemistry are a consequence of gas migration through crystal-rich magma. We show that gas may flow along channels through the particle-laden liquid and, at a critical depth, the gas may displace an overlying crystal-rich plug en masse, producing a growing slug of gas. Owing to the friction on the walls of the conduit, this plug becomes progressively sheared and weakened until gas enriched in the least soluble volatiles breaks through, causing an explosion at the surface. When the gas slug bursts, liquid is drawn up in its wake, which exsolves the more soluble volatile components, which then vent passively at the surface until the next explosive slug-bursting event.

Productivity Improvement by Reperforation of Multistage-Fractured Wells in High-Pressure/High-Temperature Tight Gas Reservoirs: A Case History

SummaryProductivity of multistage-fractured gas wells is possibly degraded by conductivity impairments and non-Darcy flow during long-term production. Such degradations are pronounced by flow convergence to short perforated intervals, while it is challenging to identify degraded stages for remediation. Moreover, remedial actions can be expensive under a high-pressure/high-temperature (HP/HT) environment. A field case demonstrates successful application of reperforation as a cost-effective way to mitigate the flow convergence by prioritizing targets with multirate production-logging (PL) results.This work presents theoretical investigations using numerical simulations and field execution of reperforation for a well with six-stage fracturing treatments in a HP/HT volcanic gas reservoir onshore Japan. Apparent conductivity reduction was suspected during more than 15 years of production, and it was pronounced by non-Darcy flow effects associated with flow convergence to short perforated intervals. Multirate PL was used to identify impaired stages by quantifying the inflow-performance relationship (IPR) of each stage under transient flow-after-flow (FAF) testing. The impaired stages were reperforated, adding perforation intervals with wireline-conveyed perforators. Pressure-buildup (PBU) tests before and after the job and post-job PL were used to validate productivity improvements.Target zones for reperforations were identified and prioritized with results of the multirate PL conducted. The stage IPRs were drawn, and relatively large non-Darcy effects were identified in three stages by shapes of the IPRs and/or decreasing inflow contributions as the surface rate increased. Also, a temperature log showed steep temperature change at the bottom of the fourth stage; the fracture might propagate below the perforated interval. Ranges of production increment were estimated using a numerical model calibrated against the estimated stage IPRs. The estimated increment was in the range of 15 to 30% with the planned reperforation program, while its magnitude depended on the connection between new perforations and existing fractures. Afterward, the reperforation job was performed and the gas rate was confirmed to be increased by 26% with the same wellhead pressure after 1 month of production. The post-job PL was conducted 3 months after the reperforation. The well IPR was improved, implying reduction of the non-Darcy effects. Results of PBU tests also indicated reduction of skin factor. The stage IPRs were redrawn with the post-job PL, and they suggested clear improvements in two stages where screenout occurred during fracturing treatments and a stage where significant non-Darcy effect was suspected.The workflow and strategy in this paper can be applied for productivity restoration in a cost-effective way to multistage-fractured gas wells with short perforated intervals and impaired apparent conductivity during long-term production. Especially, the interpreted results suggested effectiveness of the proposed approach for productivity improvement in stages where screenout occurs during fracturing treatments. Moreover, lessons learned on the importance of careful test designs for PL were discussed because they are keys for success.

Radon Activity in Volcanic Gases of Mt. Etna by Passive Dosimetry

AbstractRadon (222Rn) activity in air was measured for about 6 months at the summit of Mt. Etna Central Crater (Sicily) by integrative radon dosimetry at two different heights above ground level (5 cm and 1 m). This technique for air radon monitoring proved operational in the harsh volcanic environment of Mt. Etna summit with a 94% recovery rate of dosimeters. In the southeast sector exposed to the main gas plume, mean radon activity in free air (height 1 m) is significantly higher than the local background and the ground level activity (height 5 cm). The results strongly suggest that the plume is enriched in radon by ≈550 Bq/m3, which has never been evidenced before. Radon activities also reflect soil degassing occurring in the proximity of the crater, with increased ground level activities in zones of enhanced soil fracturing and degassing. Radon measurements also revealed a hot spot in front of the Voragine vent with extraordinary high levels of air activities (26 kBq/m3 at ground level and 8 kBq/m3 in free air). The temporal variation of radon activity was investigated by replacing a few stations half way through the exposure period. The only significant increase was associated with the site located under the main gas plume and correlated with eruptive unrest within the crater. Finally, air radon levels higher than the recommended threshold of 300 Bq/m3 were detected in several zones on the rim and could generate a nonnegligible radiologic dose for workers on the volcano.

Features of basaltic melt-hydrogen interaction at hydrogen pressure 10–100 MPa and temperature 1100–1250 °C

New experimental data on interaction of basaltic melt with hydrogen at high temperature (1100–1250 °C) and hydrogen pressure (10–100 MPa) have been obtained to gain insight into the possible role of hydrogen in the processes occurring in basaltic melts in the earth's crust under reducing conditions (f(O2) = 10−13–10−15). The experiments were carried out in a unique in house built internally heated pressure vessel (IHPV). This apparatus is equipped with an internal device, which allows long-term experiments under hydrogen pressure at high temperatures without losing hydrogen. Two types of experiments were carried out: 1 - kinetic experiments with isobaric quenching, 2 - crystallization experiments with subsequent isobaric quenching. It was found that, despite the high reducing potential of the H2 - basaltic melt system, the hydrogen oxidation reactions and the Fe oxides reduction in the melt are not complete. Initially homogeneous basaltic melts become heterogeneous. H2O is formed in the fluid phase (initially consisted of pure hydrogen); H2O (0.34–0.9 wt%) also dissolves in the basaltic melts, and small metal blobs with an emulsion-like texture are formed in the melts at temperature significantly lower than the melting temperature of the metal phase (Fe). The texture and dimensions of the metal segregations resemble those reported from natural magmatic rocks. Some new features of the crystallization process of basaltic melt under very reducing conditions are also discussed. The assemblage of subliquidus minerals (olivine + clinopyroxene + plagioclase) formed in the crystallization experiment at T = 1100 °C, P(H2) = 10 MPa with run duration 2 h, and their chemical compositions match closely those described in natural lavas (e.g. Kamchatka volcanoes). This result can be considered as an experimental confirmation of the participation of hydrogen in the magmatic process, which also corroborates with the composition of volcanic gases.

Mantle degassing related to changing redox and thermal conditions during the Precambrian supercontinent cycle

The C-O-H cycling of the early shallow Earth is suggested to be closely related to mantle degassing and speciation processes. These processes are influenced by the mantle’s thermal and redox states, which have changed significantly in different mantle reservoirs during Earth’s protracted history. However, the link between speciation of C-O-H magmatic volatiles and the temporal changes of the mantle’s thermal and redox states in different mantle reservoirs remains elusive. We test this link through chemical equilibrium modeling of C-O-H magmatic volatiles to assess its influences on shallow C-O-H cycling and the oxidization history of the shallow Earth. We find that a rapid oxidization of Archean mantle related to recycling of oceanic crust, core-mantle material exchange, or evolution of primitive mantle redox heterogeneities can strongly reduce the fraction of reducing compositions (e.g., H2 and CH4) in volcanic gases, which then consumed less photosynthetic oxygen, leading to a net increase of atmospheric oxygen and triggering the Great Oxidation Event (GOE) at 2.4–2.3 Ga. After the GOE, mantle degassing at rifts, mid ocean ridges, and plumes became more oxidizing and thus triggered later atmospheric oxidation synchronous with supercontinent breakup. Our results support that the oxidation of the atmosphere in the Precambrian was influenced by mantle oxidation, upwelling and/or degassing, especially during the GOE.

Equilibrium compositions in gas phase systems

A new method of calculation of equilibrium compositions of single-phase multicomponent systems in a wide range of temperatures, pressures, and elemental compositions is proposed. It is based on the minimization of the integral characteristic of the slope of the thermodynamic potential surface in the space of coordinates of chemical reactions. The proposed algorithm is applied to the definition of area of the thermodynamic stability of freons in volcanic gases and to the construction of the equilibrium profiles of the height distribution of sulphur-containing components of Venusian atmosphere.