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We report in-plume carbon dioxide (CO 2) concentrations and carbon isotope ratios during the 2021 eruption of Tajogaite volcano, island of La Palma, Spain. CO 2 measurements inform our understanding of volcanic contributions to the global climate carbon cycle and the role of CO 2 in eruptions. Traditional ground-based methods of CO 2 collection are difficult and dangerous, and as a result only about 5 % of volcanoes have been directly surveyed. We demonstrate that unpiloted aerial system (UAS) surveys allow for fast and relatively safe measurements. Using CO 2 concentration profiles we estimate the total flux during several measurements in November 2021 to be 1.76±0.20×103 to 2.23±0.26×104 t d -1. Carbon isotope ratios of plume CO 2 indicate a deep magmatic source, consistent with the intensity of the eruption. Our work demonstrates the feasibility of UASs for CO 2 surveys during active volcanic eruptions, particularly for deriving rapid emission estimates. [ABSTRACT FROM AUTHOR]

We report in-plume carbon dioxide (CO2) concentrations and isotope ratios during an active eruption of the Tajogaite Volcano. CO2 measurements inform our understanding of volcanic contributions to the global climate carbon cycle, and the role of CO2 in eruptions. Traditional ground-based methods of CO2 collection are difficult and dangerous, as a result only 5% of volcanoes have been surveyed. We demonstrate that Unpiloted Aerial System (UAS) surveys allow for fast and relatively safe measurements. Using CO2 concentration profiles we estimate total flux to be 1.19x106 to 2.80x107 t day-1. Isotope ratios indicated a deep magmatic source, consistent with the intensity of the eruption. Our work demonstrates the feasibility of UASs for CO2 surveys during active volcanic eruptions, particularly in calculating plume characteristics. [ABSTRACT FROM AUTHOR]

East Africa hosts significant reserves of untapped geothermal energy. Exploration has focused on geologically young (<1 Ma) silicic calderas, yet there are many sites of geothermal potential where there is no clear link to an active volcano. The origin and architecture of these systems are poorly understood. Here, we combine remote sensing and field observations to investigate a fault‐controlled geothermal play located north of Lake Abaya in the Main Ethiopian Rift. Soil gas CO2 and temperature surveys were used to examine permeable pathways and showed elevated values along a ∼110 m high fault, which marks the western edge of the Abaya graben. Ground temperatures are particularly elevated where multiple intersecting faults form a wedged horst structure. This illustrates that both deep penetrating graben bounding faults and near‐surface fault intersections control the ascent of hydrothermal fluids and gases. Total CO2 emissions along the graben fault are ∼300 t d−1; a value comparable to the total CO2 emission from silicic caldera volcanoes. Fumarole gases show δ13C of −6.4‰ to −3.8‰ and air‐corrected 3He/4He values of 3.84–4.11 RA, indicating a magmatic source originating from an admixture of upper mantle and crustal helium. Although our model of the North Abaya geothermal system requires a deep intrusive heat source, we find no ground deformation evidence for volcanic unrest or recent volcanism along the graben fault. This represents a key advantage over the active silicic calderas that typically host these resources and suggests that fault‐controlled geothermal systems offer viable prospects for geothermal exploration. Key Points: First conceptual model of a fault‐controlled magmatic geothermal resource in the East African RiftFocus on North Abaya in the Main Ethiopian Rift and show that deep hydrothermal upflow is concentrated along a major graben bounding faultMagmatic CO2 emissions along this fault are ∼300 t d−1 and comparable to average values from the world's subaerial volcanoes [ABSTRACT FROM AUTHOR]

The phreatic eruption is one of the volcanic eruption styles triggered by the rapid vaporization of heated fluids at shallow depth without the involvement of juvenile magma (e.g., Stix and deMoor [23]). 10.1186/s40623-021-01468-3 5 Kataoka KS, Tsunematsu K, Matsumoto T. Crisis hazard assessment for snow-related lahars from an unforeseen new vent eruption: the 2018 eruption of Kusatsu-Shirane volcano, Japan. Papers on the Kusatsu-Shirane volcano Kusatsu-Shirane volcano is an active dacite-andesite Quaternary volcano located in Gunma Prefecture, Central Japan. After the onset of the 2010 phreatic eruption of the Turrialba volcano, the underlying geothermal system changed as seen from the significant increase in the fumarole output at the Turrialba volcano. [Extracted from the article]

We present methods for autonomous collaborative surveying of volcanic CO2 emissions using aerial robots. CO2 is a useful predictor of volcanic eruptions and an influential greenhouse gas. However, current CO2 mapping methods are hazardous and inefficient, as a result, only a small fraction of CO2 emitting volcanoes have been surveyed. We develop algorithms and a platform to measure volcanic CO2 emissions. The Dragonfly Unpiloted Aerial Vehicle (UAV) platform is capable of long-duration CO2 collection flights in harsh environments. We implement two survey algorithms on teams of Dragonfly robots and demonstrate that they effectively map gas emissions and locate the highest gas concentrations. Our experiments culminate in a successful field test of collaborative rasterization and gradient descent algorithms in a challenging real-world environment at the edge of the Valles Caldera supervolcano. Both algorithms treat multiple flocking UAVs as a distributed flexible instrument. Simultaneous sensing in multiple UAVs gives scientists greater confidence in estimates of gas concentrations and the locations of sources of those emissions. These methods are also applicable to a range of other airborne concentration mapping tasks, such as pipeline leak detection and contaminant localization. [ABSTRACT FROM AUTHOR]

A multi-rotor drone has been adapted for studies of volcanic gas plumes. This adaptation includes improved capacity for high-altitude and long-range, real-time SO2 concentration monitoring, long-range manual control, remotely activated bag sampling and plume speed measurement capability. The drone is capable of acting as a stable platform for various instrument configurations, including multi-component gas analysis system (MultiGAS) instruments for in situ measurements of SO2 , H2S , and CO2 concentrations in the gas plume and portable differential optical absorption spectrometer (MobileDOAS) instruments for spectroscopic measurement of total SO2 emission rate, remotely controlled gas sampling in bags and sampling with gas denuders for posterior analysis on the ground of isotopic composition and halogens. The platform we present was field-tested during three campaigns in Papua New Guinea: in 2016 at Tavurvur, Bagana and Ulawun volcanoes, in 2018 at Tavurvur and Langila volcanoes and in 2019 at Tavurvur and Manam volcanoes, as well as in Mt. Etna in Italy in 2017. This paper describes the drone platform and the multiple payloads, the various measurement strategies and an algorithm to correct for different response times of MultiGAS sensors. Specifically, we emphasize the need for an adaptive flight path, together with live data transmission of a plume tracer (such as SO2 concentration) to the ground station, to ensure optimal plume interception when operating beyond the visual line of sight. We present results from a comprehensive plume characterization obtained during a field deployment at Manam volcano in May 2019. The Papua New Guinea region, and particularly Manam volcano, has not been extensively studied for volcanic gases due to its remote location, inaccessible summit region and high level of volcanic activity. We demonstrate that the combination of a multi-rotor drone with modular payloads is a versatile solution to obtain the flux and composition of volcanic plumes, even for the case of a highly active volcano with a high-altitude plume such as Manam. Drone-based measurements offer a valuable solution to volcano research and monitoring applications and provide an alternative and complementary method to ground-based and direct sampling of volcanic gases. [ABSTRACT FROM AUTHOR]

A multi-copter drone has been adapted for studies of volcanic gas plumes. This adaptation includes improved capacity for high altitude and long range, real-time SO2 concentration monitoring, long range manual control, remotely-activated bag sampling, and plume speed measurement capability. The drone is capable of acting as a stable platform for various instrument configurations including: MultiGAS instruments for in-situ measurements of SO2, H2S, CO2 and H2O concentrations in the gas plume, MobileDOAS instruments for spectroscopic measurement of total SO2 emission rate, remotely-controlled gas sampling in bags and sampling with gas denuders for posterior analysis on the ground of isotopic composition and halogens. The platform we present has been field-tested during three campaigns in Papua New Guinea: in 2016 at Tavurvur, Bagana and Ulawun volcanoes, in 2018 at Tavurvur and Langila volcanoes and in 2019 at Tavurvur and Manam volcanoes; as well as in Mt. Etna in Italy in 2017. This paper describes the drone platform and the multiple payloads, the various measurement strategies, an algorithm to correct for different time-responses of MultiGAS sensors. Specifically, we emphasise the need for an adaptive flight path, together with live data transmission of a plume tracer (such as SO2 concentration) to the ground station, to ensure optimal plume interception when operating beyond visual line of sight. We present results from a comprehensive plume characterization obtained during a field deployment at Manam volcano in May 2019. The Papua New Guinea region, and particularly Manam volcano, has not been extensively studied for volcanic gases due to its remote location, inaccessible summit region and high level of volcanic activity. We demonstrate that the combination of a multi-rotor with modular payloads is a versatile solution to obtain the flux and composition of volcanic plumes, even for the case of a highly active volcano with a high-altitude plume such as Manam. Drone-based measurements offer a valuable solution to volcano research and monitoring applications, and provide an alternative and complementary method to ground-based and direct sampling of volcanic gases. [ABSTRACT FROM AUTHOR]

Quantifying the global volcanic CO2 output from subaerial volcanism is key for a better understanding of rates and mechanisms of carbon cycling in and out of our planet and their consequences for the long‐term evolution of Earth's climate over geological timescales. Although having been the focus of intense research since the early 1990s, and in spite of recent progress, the global volcanic CO2 output remains inaccurately known. Here we review past developments and recent progress and examine limits and caveats of our current understanding and challenges for future research. We show that CO2 flux measurements are today only available for ~100 volcanoes (cumulative measured flux, 44 Tg CO2/year), implying that extrapolation is required to account for the emissions of the several hundred degassing volcanoes worldwide. Recent extrapolation attempts converge to indicate that persistent degassing through active crater fumaroles and plumes releases ~53–88 Tg CO2/year, about half of which is released from the 125 most actively degassing subaerial volcanoes (36.4 ± 2.4 Tg CO2/year from strong volcanic gas emitters, Svge). The global CO2 output sustained by diffuse degassing via soils, volcanic lakes, and volcanic aquifers is even less well characterized but could be as high as 83 to 93 Tg CO2/year, rivaling that from the far more manifest crater emissions. Extrapolating these current fluxes to the past geological history of the planet is challenging and will require a new generation of models linking subduction parameters to magma and volatile (CO2) fluxes. Key Points: Progress in determining subaerial volcanic CO2 flux has been significantChallenges remain with regard to extrapolations through time and global coverage of measurements and with regard to diffuse tectonic degassing and dynamic nature of volcanic degassingVolcanic and tectonic contributions are <2% of current anthropogenic contributions [ABSTRACT FROM AUTHOR]

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

Abstract: High-temperature (1084°C) fumarolic emissions from a spatter cone at the Erta Ale north pit crater granted a rare opportunity to collect Giggenbach bottles, condensates, and sublimates from the fumarolic gases of a rift/plume volcano in the immediate proximity of degassing lava. These results represent the highest-temperature gases sampled directly for trace elements and the first high-T fumarolic samples for a rift/plume volcano. Sixty-seven metals and metalloids were measured quantitatively by ICP-AES and ICP-MS in liquid gas condensates and solid sublimates. The total amount of trace elements in the gas (without Si) exceeded 170ppm. The ten most abundant elements transported in nonsilicate modes were Na (61ppm), Fe (41ppm), K (32ppm), Br (12.4ppm), Cd (3.0ppm), Se (2.3ppm), Cu (2.0ppm), Zn (2.0ppm), Te (1.7ppm), and As (1.2ppm). The gases contained 27ppb Re, 1.5ppb Au, 0.5ppb Pt, and 0.27ppb Os. Rh- and Pd-containing phases were observed in solid sublimates. The only metal not detected by all analytical methods was ruthenium. Chalcophile elements (Cd, Cu, Zn, Se, Te, As) were transported primarily in the gaseous form. Alkali metals were emitted, at least partially, as liquid micron-size sulfate droplets, whereas alkali earths, aluminum, and REE had a high affinity to silicate aerosol in the form of basaltic microspheres. The silicate aerosol content was evaluated at 59ppm on average but varied within a 7.5-fold range during sampling. Because of the extremely high temperature, refractory elements Ca, Ba, Ta, U, and LREE showed evidence of transport in the form of gaseous species. The SO2 flux in January 2011 was evaluated at 91±24t/d for the entire volcano, including ~31t/d from the north crater and ~60t/d from the lava lake. The daily output of trace elements from both Erta Ale craters (without Si) was estimated at 53kg/d, including 20kg of Na, 13.5kg of Fe, 10.5kg of K, 4.5kg of chalcophile elements, 9g of Re, 0.5g of Au, and 0.17g of Pt. The trace element pattern of Erta Ale fumarolic gases do not possess any distinct geochemical specialization and resemble TE patterns from fumarolic emissions of studied arc and plume volcanoes. [Copyright &y& Elsevier]

Abstract: This study presents volatile, trace, and major element compositions of silicate glasses (nepheline-hosted melt inclusions and matrix glass) from the 2007–2008 explosive eruption at Oldoinyo Lengai volcano, Tanzania. The bulk compositions of the heterogeneous ash erupted in 2007–2008 are consistent with physical mixing between juvenile nephelinite magma and natrocarbonatite emplaced during the preceding ∼25 years of effusive carbonatite eruption. The melt inclusions and matrix glasses span a wide range of silica-undersaturated compositions, from ∼46wt% SiO2 and (Na+K)/Al∼3 in the least evolved melt inclusions to 38wt% SiO2 and (Na+K)/Al up to 12 in the matrix glass. The depletion in SiO2 between melt inclusions and matrix glass is accompanied by strong enrichment in all of the incompatible trace elements measured (Ba, Nb, La, Ce, Sr, Zr, Y), which is consistent with fractional crystallization of a bulk mineral assemblage with SiO2 higher than that of the melt inclusions but inconsistent with silicate melt evolution by assimilation of carbonatite. The melt inclusions are volatile-rich with 2.7wt% to 8.7wt% CO2 and 0.7wt% to 10.1wt% H2O, indicating that Oldoinyo Lengai is a hydrous system. This is contrary to the long-held assumption that Oldoinyo Lengai is relatively anhydrous, which is based on the observation that natrocarbonatite lavas are water-poor. We argue that natrocarbonatites are derived from hydrous carbonate liquid that degas H2O at low pressure. The silicate glass data show that H2O concentration is negatively correlated with incompatible element enrichment, which we attribute to crystallization of the melt in response to decompression degassing of H2O. The eruptive cycle at Oldoinyo Lengai reflects changes in bulk silicate magma viscosity due to extensive H2O-driven crystallization and explosive eruptions occur when volatiles (i.e. H2O>CO2 gas, and carbonate liquid) cannot separate from the crystal-rich nephelinite magma. Melt H2O content decreases as a function of pressure; however CO2 concentration in the melt inclusions is buffered by the presence of immiscible carbonate liquid. CO2 content increases with melt evolution parameters (e.g. increasing (Na+K)/Al) due to enhanced solubility with alkali enrichment and SiO2 depletion in the melt. The matrix glasses and evolved melt inclusions, on the other hand, experienced low pressure (<50MPa) CO2 degassing and were not buffered by a coexisting carbonate liquid. Whereas the melt inclusions are the most CO2-rich yet identified, their CO2/Nb ratios are without exception lower than that in MORB, indicating that a volatile-rich mantle source is not required for Oldoinyo Lengai. [Copyright &y& Elsevier]

Examines vent processes at Karymsky volcano, Kamchatka, Russia by measuring sulphur dioxide (SO[sub 2]) emissions using a correlation spectrometer. SO[sub 2] variations in Karymsky's plume; Frequency of eruption occurrence; Number of cycles.

Examines the relationship between fumarole gas composition and eruptive activity at Galeras Volcano, Colombia. Correlation of temporal changes in gas compositions with eruptive activity; Fumarole sampling; Effects of long-term degassing of the magma body.

Infers the degassing history during the episode of long-period events preceding the March 23, 1993 eruption of the Galeras volcano in Colombia. Monitoring of sulphur dioxide flux and long-period seismicity; Interpretation of the movement of gases from the magma body to the surface.

Abstract: In this introduction, recent progress in the study of the evolution, transfer and release of magmas and volcanic gases is briefly reviewed, based on discussions at the MAG2007 international conference held in Taipei, Taiwan, in April 2007. The meeting pooled the diverse expertise of igneous and volcanic gas geochemists. This special issue, which presents six case studies covering a range of topics from variations in mantle source compositions to the nature of volcanic degassing, reflects that diversity. [Copyright &y& Elsevier]

Our understanding of the role of volcanoes in the global sulfur cycle and how volcanic gas emissions can be used to monitor volcanoes is limited by the complex interactions between hydrothermal systems and volcanic sulfur emissions. Hydrothermal systems influence the amount and speciation of volcanogenic sulfur, which is ultimately released to the surface and atmosphere via a range of physicochemical processes. To understand the effect of the hydrothermal system on surface emissions, we model the magmatic-hydrothermal systems at Whakaari/White Island, Aotearoa New Zealand, and Etna, Italy. We quantify the magmatic sulfur inputs using mass balance and MELTS modeling (thermodynamic model of crystallization); model the effects of degassing using Sulfur_X (an empirical model of melt-gas equilibria); and model the influence of the hydrothermal system using CHIM-XPT and EQ3/6 (thermodynamic and kinetic models of gas+water±rock reactions), which we compare to measured plume and fumarole compositions. We find that the sulfur inputs can broadly equal sulfur outputs over long timescales. However, the hydrothermal system can modulate the total mass of sulfur released and its H 2 S/SO 2 ratio on shorter timescales, especially as the system evolves from water- to gas-dominated through the development of dry, gas-dominated pathways. • We modeled sulfur in the magmatic-hydrothermal systems of Whakaari and Etna. • We compared MELTS, Sulfur_X, EQ3/6, and CHIM-XPT results to plume and fumarole data. • The sulfur inputs can broadly equal sulfur outputs over long timescales. • The hydrothermal system can modulate the composition on shorter timescales. [ABSTRACT FROM AUTHOR]

Magma movement, fault structures and hydrothermal systems influence volatile emissions at rift volcanoes. Longonot is a Quaternary caldera volcano located in the southern Kenyan Rift, where regional extension controls recent shallow magma ascent. Here we report the results of a soil carbon dioxide (CO 2 ) survey in the vicinity of Longonot volcano, as well as fumarolic gas compositions and carbon isotope data. The total non-biogenic CO 2 degassing is estimated at < 300 kg d − 1 , and is largely controlled by crater faults and fractures close to the summit. Thus, recent volcanic structures, rather than regional tectonics, control fluid pathways and degassing. Fumarolic gases are characterised by a narrow range in carbon isotope ratios (δ 13 C), from − 4.7‰ to − 6.4‰ (vs. PDB) suggesting a magmatic origin with minor contributions from biogenic CO 2 . Comparison with other degassing measurements in the East African Rift shows that records of historical eruptions or unrest do not correspond directly to the magnitude of CO 2 flux from volcanic centres, which may instead reflect the current size and characteristics of the subsurface magma reservoir. Interestingly, the integrated CO 2 flux from faulted rift basins is reported to be an order of magnitude higher than that from any of the volcanic centres for which CO 2 surveys have so far been reported. [ABSTRACT FROM AUTHOR]

Abstract: We present the chemical and isotope (He–C–N) characterization of active fumaroles and hydrothermal gases and waters from the summits and flanks of 19 volcanic centers along the western Sunda arc, Indonesia. Samples were collected over two field expeditions (1991 and 2010) and cover 13 volcanic centers in Sumatra, 5 in Java and one in Bali. In addition, we present data from three geothermal sites in Sumatra associated with active fault systems in-between volcanic centers (IBVC). The overall aim is to resolve volatiles associated with the sub-arc mantle (subducting slab and mantle wedge) from inputs derived from the over-riding arc crust. The western Sunda arc is a prime locality to assess controls on volatile provenance at subduction zones due to changes in composition and thickness of over-riding crust and variations in sediment input rates along the strike of the arc. The dry gas chemistry of the majority of volcanic samples is dominated by CO2 with inert gas variations (He–Ar–N2) typical of subduction zone gases. However, there is a strong crustal control on the He–CO2 isotope and relative abundance systematics on a number of volcanic centers: this effect is most clearly observed at flank localities and in water phase samples. Filtering the entire database for modifications due to air contamination, degassing-induced fractionation (C-isotopes and CO2/3He ratios) and crustal contamination associated with volatile transport within shallow-level hydrothermal systems allows recognition of the magmatic volatile signature of individual volcanoes along the arc. Helium isotopes at all but two volcanic centers (Talang and Dempo on Sumatra) range from 5.3 RA to 8.1 RA (RA =air 3He/4He) pointing to the mantle wedge as the principal source of He but with a small input of crustal (radiogenic) He at some localities. Samples from Java and Bali span an even more limited range (6.6 to 7.9 RA) implying a relatively smaller input of crustal He. Carbon isotope and CO2/3He ratios vary from −1.4‰ to −6.4‰ and 4.38 to 150 (×109), respectively, with higher and more variable values to the north of Sumatra. This latitudinal effect is not apparent in air-corrected N-isotope values (δ15NC =−3.91 to +5.92‰) or various elemental ratios such as N2/Ar and N2/He. The three IBVC sites, all located in Sumatra, have significantly lower 3He/4He ratios (<3.6 RA) with CO2/3He values both higher and lower than volcanic centers. Their δ13C, δ15NC and gas ratios overlap with the volcanic centers. The elemental and isotopic characteristics of carbon and helium have been modified at IBVC sites due to crustal processes. However, based upon relationships between CH4 and 3He as well as co-variations between He–C–N isotopes, the over-riding crust and associated sediments add minimal volatiles to volcanic centers throughout the western Sunda arc. In turn, subducted sediment, particularly the Nicobar Fan which supplies Himalayan-derived sediment to the slab off Sumatra, exerts a strong control on the magmatic CO2 characteristics although it is less influential for N2. In spite of large sections of incoming sedimentary material being off-scraped during subduction, our data suggest that a significant fraction must enter the trench, enhancing fluid/melt production in the mantle wedge. We propose that subduction-related source contamination plays the dominant role over thick/old crustal basement in supplying the major volatile output budget of the western Sunda arc. [ABSTRACT FROM AUTHOR]

Abstract: Four of the nine potentially active volcanoes on the island of Dominica in the Lesser Antilles volcanic island arc have associated active volcanic-hydrothermal systems. Between 2000 and 2006 the gas and thermal waters from these systems were investigated to geochemically characterise the fluids, gain insight into the temperature and equilibrium state of the underlying reservoirs, and evaluate the feasibility of monitoring geothermal features as a volcano surveillance tool in Dominica. The geothermal gases are typical of those found in arc-type settings, with N2 excess and low amounts of He and Ar. The dry gas is dominated by CO2 (ranging from 492 to 993mmol/mol), and has a hydrothermal signature with hydrogen sulphide as the main sulphurous gas. The waters are predominantly acid-sulphate (SO4 =100–4200mg/L, pH≤4), and likely formed as a result of dilution of acidic gases in near surface oxygenated groundwater. Enrichment in both δ18O and δD with respect to the global meteoric water line (GMWL) confirms that the waters are of primarily meteoric origin, but have been affected by evaporation processes. Quartz geothermometers gave equilibrium temperatures of 83°C–203°C. These temperatures contrast with the higher equilibrium temperature ranges (170°C–350°C) obtained for the gases using the H2/Ar*–CH4/CO2 gas ratios plot, suggesting that the quartz geothermometers are affected by non-attainment of equilibrium. This may be a result of precipitation of the dissolved silica and/or dilution by relatively cold shallow aquifers of the thermal fluids. Generally, no significant variations in fluid gas chemistry of the hydrothermal systems were observed during the study period, and we propose that there were no changes in the state of volcanic activity in this period. One exception to this occurred in a feature known as the Boiling Lake, which underwent a month-long period of significant compositional, temperature and water level fluctuations ascribed to a drastic decrease of hydrothermal input related to a perturbation in the lake (probably seismically induced). This geochemical study is part of an ongoing monitoring programme of Dominica geothermal systems, aimed at establishing long-term geochemical observations for the purpose of volcano monitoring. [Copyright &y& Elsevier]

Abstract: The first historical eruption of Anatahan volcano began on May 10, 2003. Samples of tephra from early in the eruption were analyzed for major and trace elements, and Sr, Nd, Pb, Hf, and O isotopic compositions. The compositions of these tephras are compared with those of prehistoric samples of basalt and andesite, also newly reported here. The May 2003 eruptives are medium-K andesites with 59–63 wt.% SiO2, and are otherwise homogeneous (varying less than 3% 2σ about the mean for 45 elements). Small, but systematic, chemical differences exist between dark (scoria) and light (pumice) fragments, which indicate fewer mafic and oxide phenocrysts in, and less degassing for, the pumice than scoria. The May 2003 magmas are nearly identical to other prehistoric eruptives from Anatahan. Nonetheless, Anatahan has erupted a wide range of compositions in the past, from basalt to dacite (49–66 wt.% SiO2). The large proportion of lavas with silicic compositions at Anatahan (>59 wt.% SiO2) is unique within the active Mariana Islands, which otherwise erupt a narrow range of basalts and basaltic andesites. The silicic compositions raise the question of whether they formed via crystal fractionation or crustal assimilation. The lack of 87Sr/86Sr variation with silica content, the MORB-like δ 18O, and the incompatible behavior of Zr rule out assimilation of old crust, altered crust, or zircon-saturated crustal melts, respectively. Instead, the constancy of isotopic and trace element ratios, and the systematic variations in REE patterns are consistent with evolution by crystal fractionation of similar parental magmas. Thus, Anatahan is a type example of an island-arc volcano that erupts comagmatic basalts to dacites, with no evidence for crustal assimilation. The parental magmas to Anatahan lie at the low 143Nd/144Nd, Ba/La, and Sm/La end of the spectrum of magmas erupted in the Marianas arc, consistent with 1–3 wt.% addition of subducted sediment to the mantle source, or roughly one third of the sedimentary column. The high Th/La in Anatahan magmas is consistent with shallow loss of the top ∼50 m of the sedimentary column during subduction. [Copyright &y& Elsevier]

Abstract: Ground-based and aircraft correlation spectrometer (COSPEC) measurements at the principal active volcanoes in Guatemala (Pacaya, Santiaguito, Fuego, and Tacaná) and El Salvador (Santa Ana and San Miguel) were carried out at intervals during the period 1999–2002, as part of an attempt to measure baseline SO2 emissions of potentially dangerous volcanoes and to better understand their eruption mechanisms. We discuss some of the uncertainties involved in interpreting intermittent gas data, together with possible improvements. Other problems pertaining to current monitoring of SO2 and implications for future studies are also discussed. Santa Ana volcano is proposed to be a venting hydrothermal system, while Santiaguito, Fuego, Pacaya, and San Miguel all exhibit open-vent characteristics. Data for Tacaná volcano are presented, but are not enough to make descriptions of its characteristics and activity. Pacaya is emitting high fluxes of SO2 (>1000 tonnes/day), while the other vents are much lower emitters (20–300 tonnes/day in general). SO2 emissions at Pacaya suggest a large circulating and convecting high level chamber. The most recent emission rates at Fuego were measured during its current active phase (since January 2002). Average SO2 emission rates during 1999–2002 are: 1350 tonnes/day for Pacaya, 340 tonnes/day for Fuego, 120 tonnes/day for Santiaguito, 260 tonnes/day for San Miguel, 140 tonnes/day for Santa Ana, and 30 tonnes/day for Tacaná. These volcanoes account for about 6% to 12% of the estimated annual global volcanic output of SO2. [Copyright &y& Elsevier]