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Nisyros Island (Greece) is affected by widespread gas emissions from fumarolic fields located at the bottom of hydrothermal craters in the southern part of its caldera. This morphology and the current low gas fluxes make Nisyros an ideal site for testing the limits of physics-based gas dispersal models in confined and low-emission conditions. Here, we focused our attention on the local scale volcanic gas dispersion from the Stephanos hydrothermal crater. In April 2023, a 1-week survey was carried out to measure weather data, CO2 and H2S gas fluxes, air concentrations from portable gas stations, and chemical composition of fumarolic gases and to acquire thermal images of the crater floor. These data were used as inputs and boundary conditions for numerical simulations using a DISGAS-2.6.0 model in order to quantify the present-day volcanic degassing and its associated uncertainties, accounting for the meteorological variability. Model results are provided in terms of H2S probabilistic exceedance and persistence maps, showing gas concentrations within the crater that fall below the thresholds indicated for the occurrence of serious respiratory problems. Since DISGAS-2.6.0 does not account for chemical reactions, this study represents a good opportunity to discuss the methodological limits of simulating the dispersion of H2S which is challenging due to its rapid degradation and dilution in the atmosphere. In this regard, we also provided an empirical law of the H2S depletion in low-emission conditions that takes into account the uncertainties related to the field measurements. [ABSTRACT FROM AUTHOR]

This study systematically examines the origins and formation mechanisms of inorganic CO2 gas reservoirs located within the Dehui–Wangfu Fault in the southeastern uplift region of the Songliao Basin. The research aims to clarify the primary sources of inorganic CO2, along with its migration and accumulation processes. The identification of the Wanjinta gas reservoir within the Dehui–Wangfu Fault Zone, abundant in inorganic CO2, has sparked significant interest in the pivotal roles of volcanism and tectonic activity in gas generation and concentration. To analyze the release characteristics of CO2, this study conducted degassing experiments on volcanic and volcaniclastic rock samples from various boreholes within the fault trap. It evaluated CO2 release behaviors and controlling factors across varying temperatures (150 °C to 600 °C) and particle sizes (20, 40, and 100 µm). The findings indicated a negative correlation between CO2 release and particle size, with a notable transition at 300 °C—marking this temperature as critical for the release of adsorbed and lattice gases. Moreover, volcaniclastic rocks exhibited higher CO2 release compared to volcanic rocks, attributable to their larger specific surface area and higher porosity. At 600 °C, the decomposition of the rock crystal structure results in substantial gas escape. These observations suggest that the inorganic CO2 in this area derives not only from mantle sources but is also influenced by crustal components. Elevated temperatures prompted by tectonic activity and magmatic intrusion facilitated the degassing of the surrounding rocks, allowing released CO2 to migrate upwards through the fracture system and accumulate in the shallow crust, ultimately forming a gas reservoir. This study enhances the understanding of volcanic rock's roles in inorganic CO2 gas generation and migration, highlighting the fracture system's critical controlling influence on gas transport and aggregation. The findings indicate that inorganic CO2 gas reservoirs in the Dehui–Wangfu Fault Zone primarily originate from mantle sources with a mixture of crustal gases. This discovery offers new theoretical insights and practical guidance for the exploration and development of gas reservoirs in the Songliao Basin and similar regions. [ABSTRACT FROM AUTHOR]

The timing and duration of volatile generation from crystallizing magma reservoirs and fluid release across the magmatic‐hydrothermal interface depend on complex coupled interactions controlled by non‐linear, dynamic properties of magmas, rocks and fluids. Understanding these mechanisms is essential to explain the rare formation of economic porphyry copper deposits. For this study, we further developed a coupled numerical model that can simultaneously resolve magma and hydrothermal flow by introducing a description of fluid transport within the magma reservoir and volatile release to the host rock. Our simulations use realistic magma properties derived from published experimental and modeling studies and cover different magma compositions and water contents. We show that magma convection at melt‐dominated states leads to homogenization, which delays fluid release and promotes a rapid evolution toward a mush state. The onset of magmatic volatile release can be near‐explosive with a tube‐flow outburst event lasting <100 years for high initial water contents of >3.5 wt% H2O that could result in the formation of hydrothermal breccias and vein stockworks or trigger eruptions. This event can be followed by sustained fluid release at moderate rates by volatile flushing caused by magma convection. Subsequent fluid release from concentric tube rings by radial cooling of non‐convecting magma mush with a volume of ∼100 km3 at ∼5 km depth is limited to remaining water contents of ∼3.1 wt% H2O and lasts 50–100 kyr. Ore formation from hydrous magmas may thus involve distinct phases of volatile release. Plain Language Summary: High‐temperature fluids are expelled from water‐bearing magma bodies as they cool in the subsurface. These fluids can lead to the formation of ore deposits and geothermal resources and even trigger volcanic eruptions. In this study, we investigate how fluids are transported within a coupled magmatic‐hydrothermal system and how the magma composition, including the initial amount of water, and magma convection can affect the process of subsurface fluid flow. Using insights from experimental and numerical studies, we designed computer simulations to investigate the formation of porphyry copper deposits. We find that magma convection plays a critical role in the initial stage of cooling, creating a uniform mixture of magma and volatiles that stays in suspension during an "incubation" period. During cooling, magmas with high water contents exhibit near‐explosive outgassing events that can be both precursors to volcanic eruptions or a pre‐ore stage. Subsequently, as convection ceases, the magma body undergoes a transition from homogeneous uniform to radial cooling with more gradual fluid release over 50–100 kyr, leading to metal enrichment in porphyry copper deposits. Key Points: Coupled simulations of magma convection, crystallization, degassing and hydrothermal fluid flow reveal distinct stages of volatile releaseAfter a magma incubation phase with bubble suspension, hydrous magmas can experience a near‐explosive tube‐flow outburst from magma mushAfter crystal lock‐up, shifting from uniform to radial cooling leads to continuous outgassing, potentially forming porphyry Cu deposits [ABSTRACT FROM AUTHOR]

Changes in the emission rate of volcanic sulphur dioxide (SO 2 ) are crucial parameters for identifying volcanic unrest and forecasting the eruptive activity. Ground-based ultraviolet (UV) remote sensing provides a near continuous record of the SO 2 emission rate, with Differential Optical Absorption Spectroscopy (DOAS) being the preferred method for quantifying SO 2 absorption from recorded spectra. However, retrieving accurate column amounts of SO 2 using DOAS requires a complex fitting procedure that relies on user expertise for selecting suitable fit parameters and visually inspecting the fit results. We explore an alternative approach that exploits the well-defined spatial frequencies present in sky-scattered UV spectra. We use wavelet coherence to compare UV spectra recorded with calibration cells of known SO 2 concentration in the wavelength–spatial frequency plane. Our findings reveal that the Magnitude-Squared Wavelet Coherence (MSWC) is inversely proportional to the SO 2 concentration, suggesting that this relationship could be used to quantify volcanic SO 2 in natural spectra. To validate this approach, we analyze UV spectra recorded by scanning-DOAS instruments from the Network of Volcanic and Atmospheric Change (NOVAC) at Masaya volcano, Nicaragua, and Soufrière Hills volcano, Montserrat. We observe a favourable comparison between the MSWC values we calculate and the slant column densities (SCDs) of SO 2 obtained using the DOAS and iFit algorithms, respectively. We demonstrate the MSWC to be a robust indicator of SO 2 which may potentially serve as a proxy for differential SCDs of volcanic SO 2 . The straightforward computation of the wavelet coherence between spectra offers an efficient means to identify spectra which contain the signature of the volcanic plume and an objective approach to validate results obtained using traditional fitting routines. [ABSTRACT FROM AUTHOR]

Injecting volcanic gas into the air leads to an increase in carbon dioxide (CO2) levels compared with background concentrations and may establish gas hazard conditions. This study reports the results of five stable isotope (i.e., δ13C‐CO2 and δ18O‐CO2) surveys of airborne CO2 on Vulcano from August 2020 to November 2021. To measure CO2 in the air, a mobile laboratory was equipped with a laser‐based spectrophotometer that can selectively detect different CO2 isotopologues. Volcanic CO2 has a different isotopic signature than atmospheric CO2 and both δ13C‐CO2 and δ18O‐CO2 can help trace the injections of volcanic gases into the air. An isotopic mass balance model was developed for partitions CO2 between atmospheric background and volcanic CO2. The results of these studies show that volcanic CO2 emissions and atmospheric circulation deeply affected the concentration of CO2 in the air at Vulcano Porto. Studies of δ13C‐CO2 and δ18O‐CO2 provide an estimate of volcanic CO2 in the air. These results help identify spatially some points of interest for mitigating volcanic gas emission‐related hazards on Vulcano. Plain Language Summary: In volcanic areas, the concentration of CO2 in the air increases due to the dispersion of volcanic gases, as CO2 dominates among the local gas source components. Identifying variations in gas hazard due to changes in volcanic degassing is difficult when estimates of volcanic gases in air are based only on measurements of CO2 concentration. In this study, the effects of volcanic degassing on airborne CO2 are thoroughly evaluated by analyzing the isotopic composition of airborne CO2 during five onsite measurement surveys between August 2020 and November 2021. To quantify the contribution of volcanic CO2 to total CO2 in air, we developed a model based on the collected data using mass balance calculations. In 2021, a massive increase in volcanic degassing caused a clear increase of airborne CO2 concentration at Vulcano. We find that the effects of volcanic degassing depend on air turbulence, which changes throughout the day. The spatial variations in CO2 allow us to track the dispersion of volcanic gases in the air and their effects on gas hazards and atmospheric composition with unprecedented accuracy. Key Points: Spatial isotope monitoring enables the identification of the origin of CO2 in the airCalculating the stable isotope mass balances enables quantifying the volcanic CO2 in the total CO2 in the airSignificant changes in volcanic degassing increased air CO2 concentration and gas hazard on Vulcano—Italy—in 2021 [ABSTRACT FROM AUTHOR]

Silicic volcanic eruptions commonly begin with the explosive ejection of pyroclastic material, before transitioning to gentler effusion-dominated activity. Well-exposed dissected silicic systems are scarce and poorly studied, hindering the advances in our understanding of the explosive–effusive transition needed to improve interpretations of volcanic unrest and hazard forecasting. The Mule Creek vent (New Mexico, USA) is a dissected silicic conduit that records the processes controlling conduit formation and evolution, and the role tuffisites (fractures filled with variably welded pyroclasts) play in conduit dynamics. Here, we use decimeter-scale photo-mapping of lithostratigraphic units and thin section analysis to differentiate and interpret three dominant emplacement styles during vent evolution. First, there was repeated deposition and erosion of pyroclastic material at the conduit walls, recorded by erosive surfaces in pyroclastic breccia and agglomerates at the conduit margins. Second, sub-vertical domains of dense melt-dominated magma were emplaced and preserved as glass-dominated vitrophyre and brecciated vitrophyre, with the textural hallmarks of assembly from welding of pyroclasts. Finally, the sub-horizontal fracturing of previously deposited lithologies produced laterally cross-cutting tuffisites. The vent deposits track the widening and then narrowing of the conduit through time and reflect progressive insulation and generally higher temperatures towards the conduit center as pyroclasts accumulate. Welding of pyroclastic fill and the formation of dense vitrophyres towards the conduit center lowers deposit porosity and effective wall permeability. This drives localized gas pressure increases and results in gas-driven fracturing, generating tuffisites, which act as transient outgassing pathways. The structure of the Mule Creek vent records an explosive–effusive transition, constraining the processes controlling conduit evolution and aiding our interpretation of volcanic unrest. [ABSTRACT FROM AUTHOR]

Identifying precursory phenomena is central to the short-range assessment and anticipation of volcanic hazards. The chemistry of gases, which may separate from magma at depth, is operationally monitored at many volcanoes worldwide to manage risk. However, owing to the complexity of volcanic degassing, decoding the message of gas geochemistry has proven challenging. Here, we report an approach to restoration of measured volcanic gas compositions that enables tracking of variations in the temperature and/or oxidation state of the source magma. We validate the approach with reference to independent estimates of melt oxidation state obtained by X-ray absorption near-edge structure (XANES) spectroscopy at the iron K-edge. We then apply the method to a global database of high temperature volcanic gases and to extended gas geochemical timeseries at Unzen, Aso, and Asama volcanoes, identifying hitherto unreported but significant changes in magma intensive parameters that preceded or accompanied changes in volcanic activity. Restoration of volcanic gas compositions offers a promising complement to monitoring strategies at active volcanoes, calling for more systematic operational surveillance of redox-sensitive gas species.

Volcanic SO 2 flux is a key indicator of magma influx into shallower portions of magmatic plumbing systems, and as such is central to volcano monitoring. However, observations have traditionally been challenged by a variety of technical and methodological caveats and limitations, to overcome which it is required an intercomparison of different observational techniques and, where possible, their integration. Here, we compare ∼9 years (2014 to 2022) of SO 2 flux records at Stromboli obtained through (i) a near-vent (∼500 m) UV Camera system and (ii) a network of DOAS spectrometers scanning the distal (∼2 km) bulk plume. We find a large (133 t/d on average) systematic offset between the SO 2 flux time-series streamed by the two observational techniques, with the flux from the scanning spectrometers being ∼200 % higher on average than UV Camera flux. We propose this mismatch to derive from a combination of (i) SO 2 flux underestimation by the UV Camera, as caused by incomplete coverage of the plume (due to topography of the crater area) and radiative transfer issues in the optically dense, near-vent plume, and (ii) SO 2 flux overestimation by the distal scanning spectrometers', caused by non-ideal (incomplete) atmospheric dilution of source-released gas puffs during atmospheric transport. Our analysis suggests this latter process to be dominant, imparting a positive wind speed dependence and a marked seasonality to the distal scanning spectrometers' fluxes, and causing them to significantly overestimate the source SO 2 fluxes. Finally, we propose a novel integrated SO 2 flux record, based on the combination of UV Camera-derived gas velocities and DOAS-derived SO 2 integrated column amounts (back-calculated at source using an experimentally derived plume dilution function). We expect this SO 2 flux time-series to be less affected by external factors (e.g., meteorological, illumination and volcano topography conditions) than using any of the two techniques alone and hence a better proxy of volcano behaviour. We recommend testing of the integrated UV Camera-scanning-DOAS method at other volcanoes to explore its utility for improved volcanic degassing characterization. • SO 2 daily flux records at Stromboli through a near-vent UV Camera system and a network of distal scanning-DOAS spectrometers. • We find the flux from the scanning spectrometers being ∼200% higher on average than UV Camera flux. • Fluxes mismatch derive from a combination of underestimation factors by UV Camera andflux overestimation by scanning-DOAS. • We propose a novel integrated SO 2 flux record, based on UV Camera-derived gas velocities and DOAS-derived SO 2 column amounts. [ABSTRACT FROM AUTHOR]

Volcanic plume composition is strongly influenced by both changes in magmatic systems and plume-atmosphere interactions. Understanding the degassing mechanisms controlling the type of volcanic activity implies deciphering the contributions of magmatic gases reaching the surface and their posterior chemical transformations in contact with the atmosphere. Remote sensing techniques based on direct solar absorption spectroscopy provide valuable information about most of the emitted magmatic gases but also on gas species formed and converted within the plumes. In this study, we explore the procedures, performances and benefits of combining two direct solar absorption techniques, high resolution Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet Differential Optical Absorption Spectroscopy (UV-DOAS), to observe the composition changes in the Popocatépetl’s plume with high temporal resolution. The SO2 vertical columns obtained from three instruments (DOAS, high resolution FTIR and Pandora) were found similar (median difference

One of the major problems in the volcanic surveillance is how data from several techniques can be correlated and used to discriminate between possible precursors of volcanic eruptions and changes related to non-eruptive processes. Gas chemical surveys and measurements of SO2 emission rates performed in the past (2006–2019) at Lastarria volcano in Northern Chile have revealed a persistent increment of magmatic sourced gas emissions since late November 2012, following a 13 years period of intense ground uplift. In this work, we provide new insights into the gas-chemical evolution of Lastarria’s fumarolic discharges obtained from direct sampling (2006–2019) and SO2 emission rates using UV camera and DOAS instruments (2018–2019) and link these to pre-existing information on ground deformation (1998–2016) in order to determine the origin of observed degassing and ground deformation processes. We revise the four mechanisms originally proposed as alternatives by Lopez et al. (Geosphere, 2018, 14 (3), 983–1007) to explain the changes observed in the fluid geochemistry and ground deformation between 2009 and 2012, in order to explain major changes in gas-geochemistry over an extended period between 1998 and 2019. We hypothesize that a continuous sequence of processes explains the evolution in the fluid geochemistry of fumarolic discharges. Two mechanisms are responsible of the changes in the gas composition during the studied period, corresponding to a 1) deep magma chamber (7–15 km depth) pressurized by volatile exsolution (1998–2020), which is responsible of the large-scale deformation; followed by 2) a crystallization-induced degassing (2001–2020) and pressurization of the hydrothermal system (2003-early November 2012), where the former process induced the changes in the gas composition from hydrothermal-dominated to magmatic-dominated, whereas the last produced the small-scale deformation at Lastarria volcano. The changes in the gas composition since late November 2012, which were strongly dominated by magmatic volatiles, produced two consecutive processes: 1) acidification (late November 2012–2020) and 2) depletion (2019–2020) of the hydrothermal system. In this work we have shown that a long-term surveillance of the chemistry of fluid discharges provides valuable insights into underlying magmatic/volcanic processes, and consequently, for forecasting future eruptions.

The La Fossa volcano on the Island of Vulcano, Italy, showed signs of more energetic fumarolic–solfataric activity during 2021. Several increases in volcanic gas emissions and seismicity, namely, "crisis," punctuated the passive degassing at Vulcano that had ensued after the last 1888–1890 vulcanian eruption. Most of the gases (i.e., up to 90%) were emitted at the crater cone while the diffuse degassing of CO2 at Vulcano Porto accounted for more than 10% of the volcanic emissions. Two anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi and Faraglione) showed notable changes in the gas output during the volcanic crisis. In these zones, increases of soil CO2 flux (φCO2) had several practical implications other than of volcanological interest, owing to the risk related to people's exposure to volcanic gas emissions. The results of this study reveal variations of the average φCO2 from 74 g m−2 d−1 during September 2021 to 370 g m−2 d−1 in November 2021, which were 27% and 538% higher than the statistical background since 1988 (φCO2 ≈ 58 g m−2 d−1), respectively. These observations helped in volcanic surveillance at Vulcano. The soil CO2 partitioning determined using both φCO2 and carbon isotope measurements, helped track changes in the volcanic CO2 output from 9.97 · 104 to 101.15 · 104 kg d−1. Estimates for volcanic CO2 suggest that the instability of a magmatic body caused a transition from background fumarolic–solfataric activity toward an unrest event after September 2021. Plain Language Summary: A noticeable increase in volcanic outgassing occurred at Vulcano, Italy, in 2021. Although the volcano has not achieved critical conditions to produce an eruption, the soil CO2 emissions have prevented access into some zones of the island, due to the volcanic risk known as the gas hazard. Specialized instruments such as fluxmeters and spectrophotometers were used to measure the soil CO2 flux and the carbon isotopes of CO2 during four soil gas surveys. To understand why the volcanic system evolved toward a period of unrest, we modeled our measurements using mass balance calculations. We find that the CO2 increase, almost 10 times its baseline, was most likely due to the instability of a magmatic body within the mantle to crustal boundary known as the Moho discontinuity. Because of this magmatic instability, the volcanic CO2 emissions resumed in some zones of the island where volcanic activity had been dormant for decades. The resumption of volcanic degassing in a short period had not been recorded before at Vulcano, and it is important to understand its cause because future changes in magmatic activity might produce larger CO2 emissions that will have the added risk of gas hazards as well as that of an explosion. Key Points: Diffuse degassing surveys help track transition toward volcanic unrest periodsCarbon isotope composition allows quantification of the volcanic CO2 emitted by soilsSignificant changes in volcanic outgassing state caused increases in soil CO2 emissions and gas hazard at Vulcano—Italy—during 2021 [ABSTRACT FROM AUTHOR]

Improving volcanic gas monitoring techniques is central to better understanding open-vent, persistently degassing volcanoes. SO2 cameras are increasingly used in volcanic gas studies, but observations are commonly limited to one single camera alone viewing the volcanic plume from a specific viewing direction. Here, we report on high frequency (0.5 Hz) systematic measurements of the SO2 flux at Stromboli, covering a 1-year long observation period (June 2017-June 2018), obtained from two permanent SO2 cameras using the same automated algorithm, but imaging the plume from two different viewing directions. Our aim is to experimentally validate the robustness of automatic SO2 camera for volcano monitoring and to demonstrate the advantage of using two co-exposed SO2 camera stations to better capturing degassing dynamics at open-vent volcanoes. The SO2 flux time-series derived from the two SO2 camera stations exhibit good match, demonstrating the robustness of the automatic SO2 camera method. Our high-temporal resolution SO2 records resolve individual Strombolian explosions as transient, repetitive gas bursts produced by the sudden release of over pressurized gas pockets and scoriae. Calculations show that explosive degassing activity accounts for ∼10% of the total SO2 emission budget (dominated by passive degassing) during mild regular open-vent activity. We show that the temporal variations of the explosive SO2 flux go in tandem with changes in total SO2 flux and VLP seismicity, implicating some commonality in the source processes controlling passive degassing and explosive activity. We exploited the spatial resolution of SO2 camera to discriminate degassing at two distinct regions of the crater area, and to minimize biases due by the station position respect to the target plume. We find that the SO2 fluxes from southwest-central (SWCC) and northeast (NEC) crater areas oscillate coherently but those from the NEC are more sensitive to the changes in the volcanic intensity. We interpret this as due to preferential gas/magma channeling into the structurally weaker north-eastern portion of the crater terrace in response to increasing supply rate of buoyant, bubble-rich magma in the shallow plumbing system.

The Sturtian glaciation of the Cryogenian represents a unique, global, protracted icehouse climatic event in Earth's history. The Snowball Earth hypothesis predicts that the termination of the Sturtian glaciation was globally synchronous and rapid. Long-term, volcanic degassing has been suggested to trigger the end of the Sturtian glaciation, but whether intense volcanism bracketing the termination of the glaciation on several cratons played a pivotal role in ending the glaciation has not yet been resolved. Here, we report a high-precision, U-Pb zircon, chemical-abrasion, isotope-dilution, thermal-ionization mass-spectrometry date of 661.86 ± 1.06 Ma for a tuff layer of the basal Datangpo Formation in South China, which is a manganese-rich, carbonaceous shale sequence deposited during deglaciation in the aftermath of the Sturtian glaciation. This volcanic age is consistent with a previously published date of 660.98 ± 0.31 Ma for the Datangpo Formation, but statistically different within analytical uncertainties from the date of 658.80 ± 0.54 Ma for a tuff layer in the same region of South China, indicating a series of volcanic eruptions, bracketing the end of the Sturtian glaciation, that lasted over 1.5 to 4.7 Ma. Taken together with ages for globally stratigraphically correlative units, it suggests that volcanism occurred at the end of the Sturtian glaciation and in its aftermath as a series of discrete events that lasted for at least 3.4 to 5.1 Ma. Widespread Fe-Mn-rich deposits in the glacial aftermath are also consistent with extensive submarine mafic volcanism during the Sturtian glaciation and its aftermath. Combined submarine mafic and subaerial felsic volcanism at the end of the Sturtian glaciation and in its immediate aftermath and a ca. 715–615 Ma gap in the record of Large Igneous Provinces argue for the contemporaneous arc and mid-ocean ridge magmatism as a trigger for the termination of the Sturtian glaciation. Our findings highlight feedbacks among the Cryogenian extreme climatic changes and global volcanic events as well as seawater Fe and Mn cycles. [ABSTRACT FROM AUTHOR]

The different flow regimes of two‐phase gas‐in‐liquid flow—as it occurs in the shallow conduit of basaltic volcanoes—are characterized by distinct frequency‐size distributions of the liquid and gaseous slugs. Assuming that the ascent of gaseous bubbles is indicated by seismic events, we explore the possibility of inferring the flow regime from the frequency distributions of magnitudes and interevent times. Our data set consists of 20,000 volcanic seismic events recorded in early March 2012 at Villarrica Volcano (Chile), which are commonly attributed to Strombolian activity. One crucial factor is the completeness of the catalog in terms of detectable amplitudes, which we assess using a stochastic simulation of the network output based on statistical properties of the ambient seismicity. Magnitudes, at which we consider the catalog complete, show an exponential occurrence. Yet, the simulation approach indicates that low magnitude events occur indeed more sparsely than expected for an exponential distribution, and that the magnitude distribution does not obey the Gutenberg‐Richter law. Interevent times are log‐normally distributed, which implies a preferred recurrence interval. The distributions are consistent with a slug flow regime. They correlate weakly with the preceding magnitude, suggesting that slugs coalesce while ascending. Plain Language Summary: A common type of volcanic seismic events at Villarrica is thought to result from gas bubbles, which ascend through the liquid magma in the conduit and produce mild volcanic explosions at the surface. We investigated the statistical occurrence of the time between these events and of their size. In contrast to normal earthquakes, the events recur more periodically and the number of smaller events does not increase exponentially, hence confirming their different nature. Laboratory experiments showed that bubbles flowing in a liquid develop characteristic patterns of size and distance between them, which depend on the gas supply rate and the flow ability of the liquid. We qualitatively compared the statistical distributions of event sizes to bubble sizes and the time between the events to the distance between gas bubbles. The result suggests a flow pattern where the gas bubbles span the entire width of the conduit and are several times longer than wide. Such batches of gas are known to produce the typical volcanic activity of Villarrica. Key Points: Seismic transient events are commonly seen as ascending gas slugs but other mechanisms, for example, brittle failure, are conceivableAmplitudes and time between events are approximately log‐normally distributed and thus different from tectonic earthquakesComparison with slug size distributions in gas‐in‐liquid flow suggests a sustained slug flow regime [ABSTRACT FROM AUTHOR]

Passive degassing, or volatile release from persistent, non-eruptive volcanic activity, may have contributed significantly to the Martian ice budget over the planet's history by providing a pathway for volatile species, such as water vapor, to outgas from the interior into the atmosphere and accumulate on the surface. Passive degassing from Martian volcanoes can result in ice accumulations in unusual locations (e.g., outside of the typical cold traps like the Tharsis Rise and polar ice caps). Such locally derived water could cover the volcanic source in an ice-rich veneer that may later serve as a source of ice for subsequent interactions between impactors or lava. Using the Laboratoire de Météorologie Dynamique Generic Planetary Climate Model, we model the spatial distribution of ice that results from passive degassing from five major Martian volcanic centers, Cerberus Fossae, Apollinaris Mons, Elysium Mons, Hadriacus Mons, and Pityusa Patera, and assess the sensitivity of these results to a range of volcanic, atmospheric, orbital, environmental, and numerical parameters. Previous studies have placed estimates on the amount of water released from volcanic outgassing (e.g., Carr, 1987; Craddock and Greeley, 2009; Grott et al., 2011; Carr and Head, 2015), but this is the first study to track the water released from specific volcanoes and to determine the spatial distribution of resulting ice deposits. We find that volcanic variables, such as mass flux and duration of degassing, primarily drive the thickness of volcanogenic ice fields –– higher mass fluxes create the thickest ice deposits (up to ∼210 mm around the volcanic center for a mass flux 106 kg s−1) and durations of >6 months are required for ice to reach near-global distributions. Ice accumulation around the degassing source is maximized if the latitude of passive degassing occurs near the south pole (i.e., Pityusa Patera) due to its exposure to circulation patterns that promote ice deposition in that region. Changes in the season, dust visible optical depth, and eccentricity can also impact the thickness of ice, with ice accumulation around the volcanic source being maximized in the spring, with higher dust visible optical depths, and when the eccentricity is low, due to more favorable temperatures and atmospheric circulation. Variances in the obliquity can also influence ice fields by modulating which latitudes receive more surface ice accumulation. The amount of activated cloud condensation nuclei (CCN) in the atmosphere has a lesser impact on the thickness and spatial distribution of ice fields than other parameters, with lower amounts of CCN leading to narrower, but slightly thicker deposits compared to higher amounts of CCN. The mean surface pressure and longitude of perihelion both affect the timing of ice fields. The surface pressure influences how long water lingers in the atmosphere before depositing to the surface, while the longitude of perihelion controls the time of year in which the thickest ice deposits accumulate around the degassing source. Ice fields are highly sensitive to the model resolution. Higher model resolutions allow for a more detailed representation of physical processes, such as cloud formation and ice deposition, while lower resolution model runs provide a more approximate guide to the representation of these processes and may underestimate surface ice thicknesses around the degassing source. The thickest deposits of ice form around the source of passive degassing, but later migrates and restabilizes in cold traps after degassing has ceased, unless it is protected against sublimation by the deposition of dust or pyroclastic material. Assuming the ice is protected, recurrent episodes of passive degassing could have facilitated the gradual accumulation of ice deposits several meters thick over time. [ABSTRACT FROM AUTHOR]

The opening of magmatic hydraulic fractures is an integral part of magma ascent, the triggering of volcano seismicity, and defusing the explosivity of ongoing eruptions via outgassing magmatic volatiles. If filled with pyroclastic particles, these fractures can be recorded as tuffisites. Tuffisites are therefore thought to play a key role in both initiating eruptions and controlling their dynamics, and yet their genesis remains poorly understood. Here we characterise the processes, pressures and timescales involved in tuffisite evolution within the country rock through analysis of the sedimentary facies and structures of a large sub-horizontal tuffisite vein, 0.9 m thick and minimum 40 m in length, at the dissected Húsafell volcano, western Iceland. The vein occurs where a propagating rhyolitic sheet intrusion stalled at a depth of ∼500 m beneath a relatively strong layer of welded ignimbrite. Laminations, cross-stratification, channels, and internal injections indicate erosion and deposition in multiple fluid pulses, controlled by fluctuations in local fluid pressure and changes in fluid-particle concentration. The field evidence suggests that this tuffisite was emplaced by as many as twenty pulses, depositing sedimentary units with varying characteristics. Assuming that each sedimentary unit (∼0.1 m thick and minimum 40 m in length) is emplaced by a single fluid pulse, we estimate fluid overpressures of ∼1.9–3.3 MPa would be required to emplace each unit. The Húsafell tuffisite records the repeated injection of an ash-laden fluid within an extensive subhorizontal fracture, and may therefore represent the fossil record of a low-frequency seismic swarm associated with fracture propagation and reactivation. The particles within the tuffisite cool and compact through time, causing the rheology of the tuffisite fill to evolve and influencing the nature of the structures being formed as new material is injected during subsequent fluid pulses. As this new material is emplaced, the deformation style of the surrounding tuffisite is strongly dependent on its evolving rheology, which will also control the evolution of pressure and the system permeability. Interpreting tuffisites as the fossil record of fluid-driven hydrofracture opening and evolution can place new constraints on the cycles of pressurisation and outgassing that accompany the opening of magmatic pathways, key to improving interpretations of volcanic unrest and hazard forecasting.

The solubility of CO2 in hydrous basaltic andesite was examined in fO2-controlled experiments at a temperature of 1125 °C and pressures between 310-1200 MPa. Concentrations of dissolved H2O and CO2 in experimental glasses were determined by ion microprobe calibrated on a subset of run glasses analyzed by high-temperature vacuum manometry. Assuming that the solubility of H2O in mafic melt is relatively well known, estimates of XfluidH2O and Рfluidн2о in the saturating fluid were modeled, and by difference, values for ΧfluidCO2 and PfluidCO2 were obtained (XC02 ~0.5-0.9); fCO2 could be then calculated from the fluid composition, temperature, and pressure. Dissolved H2O over a range of 2.3-5.5 wt% had no unequivocal influence on the dissolution of CO2 at the pressures and fluid compositions examined. For these H2O concentrations, dissolved CO2 increases with fCO2 following an empirical power-law relation: dissolved CO2 (ppmw) = 14.9+4−3.5.5[fCO2(MPa)]0.7±0.03. The highest-pressure results plot farthest from this equation but are within its 1 standard-error uncertainty envelope. We compare our experimental data with three recent CO2-H2O solubility models: Papale et al. (2006); Iacono-Marziano et al. (2012); and Ghiorso and Gualda (2015). The Papale et al. (2006) and Iacono-Marizano et al. (2012) models give similar results, both over-predicting the solubility of CO2 in a melt of the Pavlof basaltic andesite composition across the fCO2 range, whereas the Ghiorso and Gualda (2015) model under-predicts CO2 solubility. All three solubility models would indicate a strong enhancement of CO2 solubility with increasing dissolved H2O not apparent in our results. We also examine our results in the context of previous high-pressure CO2 solubility experiments on basaltic melts. Dissolved CO2 correlates positively with mole fraction (Na+K+Ca)/Al across a compositional spectrum of trachybasalt-alkali basalt-tholeiite-icelandite-basaltic andesite. Shortcomings of current solubility models for a widespread arc magma type indicate that our understanding of degassing in the deep crust and uppermost mantle remains semi-quantitative. Experimental studies systematically varying concentrations of melt components (Mg, Ca, Na, K, Al, Si) may be necessary to identify solubility reactions, quantify their equilibrium constants, and thereby build an accurate and generally applicable solubility model. [ABSTRACT FROM AUTHOR]

Abstract Understanding magma storage and differentiation in the East African Rift underpins our understanding of volcanism in continental rift settings. Here, we present the geochemistry of melt inclusions erupted in Main Ethiopian Rift transitional basalts, trachytes, and peralkaline rhyolites, produced by fractional crystallization. Basalts stored on‐ and off‐axis are saturated in an exsolved volatile phase at up to 18 km in the upper crust. Much of the CO2 outgassed from the magmas is likely lost through diffuse degassing. Observed CO2 fluxes require the intrusion of up to 0.14 km3 of basalt beneath the rift each year. On‐axis peralkaline rhyolites are stored shallowly, at ~4–8 km depth. In the Daly Gap, magmas saturate in sulfide and an exsolved volatile phase, which promotes magma rise to shallower levels in the crust. Here, magmas undergo further protracted fractional crystallization and degassing, leading to the formation of a substantial exsolved volatile phase, which may accumulate in a gas‐rich cap. The exsolved volatile phase is rich in sulfur and halogens: their projected loadings into the atmosphere during explosive peralkaline eruptions in the MER are predicted to be substantially higher than their metaluminous counterparts in other settings. The high fraction of exsolved volatiles in the stored magmas enhances their compressibility and must be considered when interpreting ground displacements thought to be caused by magma intrusion at depth; otherwise, intruding volumes will be underestimated. Pockets of exsolved volatiles may be present at the roof zones of magma reservoirs, which may be resolvable using geophysical techniques.

The injection of gas and pyroclastic material from volcanic vents into the atmosphere is a prolific source of acoustic waves. Infrasound arrays offer efficient, cost-effective, and near real-time solutions to track the rate and intensity of surface activity at volcanoes. Here, we present a simple framework for the analysis of acoustic array data, based on least-squares beamforming, that allows to evaluate the direction and speed of propagation of acoustic waves between source and array. The algorithms include a new and computationally efficient approach for quantitative assessment of the uncertainty on array measurements based on error propagation theory. We apply the algorithms to new data collected by two 6-element infrasound arrays deployed at Mt. Etna during the period July–August 2019. Our results demonstrate that the use of two infrasound arrays allowed detecting and tracking acoustic sources from multiple craters and active vents associated with degassing and ash-rich explosions, vigorous and frequent Strombolian activity, opening of new eruptive fractures and emplacement of lava flows. Finally, we discuss the potential use of metrics based on infrasound array analyses to inform eruption monitoring operations and early warning at volcanoes characterized by episodic intensification of activity.

Highly periodic, repetitive long‐period (LP) earthquakes, known as "drumbeats," have been observed at a range of volcanoes, typically during the ascent of degassed magma. Accelerating rates of drumbeats have been reported before explosions and potentially offer forecasts of future activity. However, the broader phenomenology of drumbeats is poorly understood. Here we describe an episode of over 900 LP earthquakes recorded in November 2015 at Tungurahua Volcano, Ecuador, that we believe are associated with a failed explosion. Rates of LP drumbeats accelerated for 10 hr, consistent with an inverse Omori's law. Before any explosion occurred, seismicity decreased following Omori's law, over a further 6 days. Despite earthquake rates decelerating, amplitudes, spectral peaks, Q values, and periodicity remain constant, suggesting there is little change in the source process with time. We argue that the decelerating seismicity is a result of progressive reduction of gas flux, unable to provide sufficient overpressure for explosion. Plain Language Summary: When a volcano is erupting, small earthquakes from the volcano can be used to infer what internal processes may be occurring. Earthquakes that are very similar to one another and repeat at consistent intervals are known as drumbeat earthquakes. These are of interest in volcanic systems as it implies the earthquakes are generated by a single, repeating source. Previous studies of drumbeat earthquakes at Tungurahua Volcano, Ecuador, have described these earthquakes occurring closer together in time and accelerating up to an explosion. In this case, we identify a sequence of drumbeats where the rate accelerates and, without any explosion, decelerates again. We suggest these earthquakes are generated by gas flux which is slowing down. This gas originates beneath a plug at the top of the conduit. We use statistical models to estimate when the volcano may have exploded if the earthquakes had continued to accelerate and quantify the subsequent deceleration in earthquake rate. Key Points: An episode of accelerating and decelerating long‐period (LP) drumbeat earthquakes is identified at Tungurahua volcano, EcuadorBayesian gamma point process analysis constrains mirrored sequences of Omori law accelerating and decelerating seismicityWaveforms examined by cross correlation and Q factor reveal a gas‐driven, repeating, single source, which failed to culminate in an eruption [ABSTRACT FROM AUTHOR]

Understanding magma storage and differentiation in the East African Rift underpins our understanding of volcanism in continental rift settings. Here, we present the geochemistry of melt inclusions erupted in Main Ethiopian Rift transitional basalts, trachytes, and peralkaline rhyolites, produced by fractional crystallization. Basalts stored on‐ and off‐axis are saturated in an exsolved volatile phase at up to 18 km in the upper crust. Much of the CO2 outgassed from the magmas is likely lost through diffuse degassing. Observed CO2 fluxes require the intrusion of up to 0.14 km3 of basalt beneath the rift each year. On‐axis peralkaline rhyolites are stored shallowly, at ~4–8 km depth. In the Daly Gap, magmas saturate in sulfide and an exsolved volatile phase, which promotes magma rise to shallower levels in the crust. Here, magmas undergo further protracted fractional crystallization and degassing, leading to the formation of a substantial exsolved volatile phase, which may accumulate in a gas‐rich cap. The exsolved volatile phase is rich in sulfur and halogens: their projected loadings into the atmosphere during explosive peralkaline eruptions in the MER are predicted to be substantially higher than their metaluminous counterparts in other settings. The high fraction of exsolved volatiles in the stored magmas enhances their compressibility and must be considered when interpreting ground displacements thought to be caused by magma intrusion at depth; otherwise, intruding volumes will be underestimated. Pockets of exsolved volatiles may be present at the roof zones of magma reservoirs, which may be resolvable using geophysical techniques. Key Points: Alkali basalts are stored both on‐ and off‐axis at depths >15 km in the crust; on‐axis peralkaline rhyolites are stored at between ~4–8 km depthSaturation of mafic magmas in a sulfide and exsolved volatile phase in the Daly Gap promotes buoyancy and rise of magmas to shallower reservoirs, where protracted fractional crystallization and degassing occursCaldera‐forming, explosive eruptions in the MER may give rise to large emissions of SO2 and halogens, which may have significant environmental impacts [ABSTRACT FROM AUTHOR]

CO2 flux measurements are often used to monitor volcanic systems, understand the cause of volcanic unrest, and map sub-surface structures. Currently, such measurements are incomplete at Tarawera (New Zealand), which erupted with little warning in 1886 and produced a ∼17 km long fissure. We combine new soil CO2 flux and C isotope measurements of Tarawera with previous data from Rotomahana and Waimangu (regions also along the 1886 fissure) to fingerprint the CO2 source, understand the current pathways for degassing, quantify the CO2 released along the entire fissure, and provide a baseline survey. The total CO2 emissions from the fissure are 1227 t⋅d–1 (742–3398 t⋅d–1 90 % confidence interval), similar to other regions in the Taupō Volcanic Zone. The CO2 flux from Waimangu and Rotomahana is far higher than from Tarawera (>549 vs. ∼4 t⋅d–1 CO2), likely influenced by a shallow silicic body at depth and Okataina caldera rim faults increasing permeability at the southern end of the fissure. Highly localized regions of elevated CO2 flux occur along the fissure and are likely caused by cross-cutting faults that focus the flow. One of these areas occurs on Tarawera, which is emitting ∼1 t⋅d–1 CO2 with a δ13CO2 of −5.5 ± 0.5 ‰, and comparison with previous observations shows that activity is declining over time. This region highlights the spatial and temporal complexity of degassing pathways at volcanoes and that sub-surface structures exert a primary control on the magnitude of CO2 flux in comparison to the surface mechanism (i.e., CO2 released through the soil or lake surface).

A new type of instrument for in-situ detection of volcanic sulfur dioxide is presented on the basis of non-dispersive UV absorption spectroscopy. It is a promising alternative to presently used compact and low-cost SO2 monitoring techniques, over which it has a series of advantages, including an inherent calibration, fast response times (< 2 s to reach 90 % of the applied concentration), a measurement range spanning about 5 orders of magnitude and small, well-known cross sensitivities to other gases. Compactness, cost-efficiency and detection limit (< 1 ppm, few ppb under favorable conditions) are comparable to other presently used in-situ instruments. Our instrument prototype has been extensively tested in comparison studies with established methods. In autumn 2015, diverse volcanic applications were investigated such as fumarole sampling, proximal plume measurements and airborne measurements several kilometers downwind from the vent on Mt. Etna and White Island. General capabilities and limitations of the measurement principle are discussed, considering different instrument configurations and future applications.

Iodine (I) and xenon (Xe) are two key elements that trace Earth's differentiation (e.g. atmosphere formation) and dynamics (e.g. volcanism and recycling at subduction zones). Iodine and Xe abundances are linked through the decay of the extinct 129I that produced 129Xe, which is today depleted in the Earth's atmosphere compared to the composition of the solar system (i.e. chondrites). Iodine and Xe cycles and storage in the deep Earth are almost unknown, which is in large part due to the fact that their behaviour in magmas and fluids, key agents of mass transfer through planetary envelopes, are poorly known. Here, the solubility of Xe and I in melts is measured under high pressure (P) and temperature (T) conditions using large volume presses, and Xe and I behaviour in melts and fluids is monitored in situ under high P-T conditions using resistive heating diamond anvil cells combined with synchrotron x-ray fluorescence (XRF) and Raman spectroscopy. Xenon, I and H (H 2 O) contents were measured in quenched glasses by particle x-ray Emission (PIXE) and Elastic Recoil Detection Analysis (ERDA). Solubility, speciation and degassing processes are investigated for two different compositions: haplogranitic melt (HPG analogue for crustal melts) and basaltic melts (MORB and IAB). Experimentally measured solubilities for both elements are much higher than their natural abundances in terrestrial magmas. Xenon solubility at 3.5 GPa reaches 4.00 wt.% in HPG and 0.40 wt.% in basalts. Iodine solubility is 0.46 wt.% at 0.4 GPa on average in HPG, and reaches 1.42 wt.% in basalts at 2 GPa. The in situ Raman spectroscopic study shows that I forms I-I bonds in hydrous high P fluids/melts unlike Xe that was previously shown to oxidize in high P melts. The XRF monitoring of I and Xe partitioning between aqueous fluids and silicate melts during decompression (i.e. water degassing) shows that Xe degassing is strongly P-T dependent and can be retained in the melt at deep crust conditions, while I is totally washed out from the silicate melt by the aqueous phase. Xenon and I degassing processes are based on different mechanisms, which implies that the atmospheric isotopic signature of Xe cannot be inherited from a process involving volcanic water degassing. Instead, 129Xe depletion may originate from a separation of both elements at depth, by deep fluids, a proposition that agrees with a deep storage of Xe in minerals. • I and Xe fully degas during volcanic processes but follow different mechanisms. • Iodine and xenon exhibit very high solubility in magmas despite their low abundances. • In high pressure melts I is incorporated as polyiodides, Xe is oxidized. • Xe and I may be stored in high pressure melts/fluids and/or minerals. • The depletion of the atmosphere in 129Xe cannot be caused by volcanic degassing. [ABSTRACT FROM AUTHOR]

Carbon dioxide is one of the most abundant volatile components in magmas after H 2 O along with S and Cl, which are of great importance to the extraction of trace metals into magmatic-hydrothermal fluids and ore minerals. Yet the effect of CO 2 on the partition coefficients of chlorine between water-rich fluid and melt (i.e. the ratio of mass Cl concentrations in the corresponding phase; [ D Cl fluid/melt ]) is still poorly constrained. We conducted a set of experiments to constrain the effect of CO 2 on D Cl fluid/melt by equilibrating felsic silicate melts with aqueous NaCl-bearing fluids while varying the concentration of CO 2 at pressures between 120 and 300 MPa and temperatures of 850 and 1000 °C. The starting melt was synthetized as a glass in the ternary albite-quartz-Al 2 O 3 system to ensure the only significant metal chloride species in the equilibrium fluid phase was NaCl. The results demonstrate that D Cl fluid/melt values increase with the concentration of Cl in the fluid phase and the silicate melt. The addition of CO 2 into aqueous metal chloride-bearing fluids induces a pronounced drop in D Cl fluid/melt , the extent of which is only weakly affected by pressure, temperature and fluid salinity, at least at relatively low Cl concentrations (<12 wt% NaCl equivalent). The values of D Cl fluid/melt drop by approximately a factor of 3 in response to the addition of 20–25 mol% CO 2 to the fluid phase due to the decreased ability of the fluid to hydrate NaCl ion pairs. A new empirical equation describing wt%-based D Cl fluid/melt is derived: l n [ D C l f l u i d / m e l t ] = 1.419 ± 0.048 ∗ l n P + 0.912 ± 0.031 ∗ l n C C l f l u i d + 1.434 ± 0.260 + 4547 ± 443 T - 4.026 ± 0.155 ∗ X C O 2 - 9.790 ± 0.440 which expresses D Cl fluid/melt as a function of pressure (in MPa), temperature (in Kelvins), and the equilibrium concentration of Cl (in wt%) and CO 2 (as molar fraction) in the fluid. The average absolute percentage error of the model predictions relative to the experimental data is 7.3%. The equation contains only monotonous functions to allow moderate extrapolation outside the range of the calibration dataset as long as the fluid remains in the single-phase field (e.g. pressure above 100 MPa and up to 500 MPa or even higher). Our model equation represents a reasonable approximation for granitoid magma evolution in the upper and middle crust. The presence of CO 2 suppresses fluid salinity at a given chloride content of a granitoid melt, which will also hinder the extraction of chloride-complexed ore metals (e.g. Cu, Pb, Zn, Mo, and Ag) into magmatic fluids, reducing the likelihood of base-metal ore formation (e.g. porphyry copper deposits) from such fluids in the uppermost crust. On the other hand, the highly volatile components, CO 2 , H 2 S and SO 2 , are enriched in magmatic fluids exsolving early during the ascent of hydrous magmas. Chloride suppression by CO 2 and enrichment of fluids in sulfur species near the SO 2 /H 2 S predominance boundary favors extraction of sulfide-complexed metals, notably Au as Au(HS)0, Au(HS) 2 −, NaAu(HS) 2 0 or Au(HS)S 3 − into low-salinity magmatic fluids. Such fluids resemble those forming mid-crustal lode gold deposits that are typically poor in base metals. Our experimental results may therefore be taken as indirect support for a magmatic component in fluids forming orogenic lode gold deposits. [ABSTRACT FROM AUTHOR]

The chemistry of gases measured in ice caves and from warm geothermal ground at Erebus volcano, Antarctica, shows that gas emissions are dominated by air, with varying amounts of added volcanic CO 2. This suggests widespread circulation of air through the volcanic edifice, as well as spatially or temporally varying contributions from magmatic degassing. The resulting gases are further modified by two processes. The first is CO 2 dissolution in water, resulting in fractionation from magmatic δ 13C-CO 2 values, which are estimated to be around −4‰, to heavier values, up to −1‰. Assuming all magmatic CO 2 is dissolved in neutral water as HCO 3 −, this requires hydrothermal temperatures of over 120 °C. However, other phases such as calcite may be present, implying even higher temperatures, while lower water pH values could result in similar isotope ratios at much lower temperatures, such as 60 °C at pH of 5.3. A large proportion of magmatic CO 2 must be lost to this hydrothermal system or to mixing with air. The hydrothermal influence is localized to certain areas on the volcano, which may be associated with high velocity zones identified in previous studies by seismic tomography. Two sites with stronger magmatic signatures, by contrast, are above low velocity zones representing possible shallow magma storage. The second modification is the removal of oxygen from both deeply-sourced and air-derived gases. This is likely due to prevailing conditions in the subsurface, as it is independent of the original source of the gases and of hydrothermal modifications, and thus may affect sites with magmatic, air-like, or hydrothermal signatures. Unlabelled Image • Fumarolic degassing on Erebus volcano reflects complex subsurface processes. • Large proportions of air are entrained into the volcanic edifice. • Carbon isotope ratios indicate localized hydrothermal systems at varying temperatures. • Oxygen is removed from some samples, potentially due to subsurface redox interactions. [ABSTRACT FROM AUTHOR]

The oxidation state of volcanic gas emissions influences the composition of the exosphere and planetary habitability. It is widely considered to be associated with the oxidation state of the melt from which volatiles exsolve. Here, we present a global synthesis of volcanic gas measurements. We define the mean oxidation state of volcanic gas emissions on Earth today and show that, globally, gas oxidation state, relative to rock buffers, is a strong function of emission temperature, increasing by several orders of magnitude as temperature decreases. The trend is independent of melt composition and geodynamic setting. This observation may explain why the mean oxidation state of volcanic gas emissions on Earth has apparently increased since the Archean, without a corresponding shift in melt oxidation state. We argue that progressive cooling of the mantle and the cessation of komatiite generation should have been accompanied by a substantial increase of the oxidation state of volcanic gases around the onset of the Great Oxidation Event. This may have accelerated or facilitated the transition to an oxygen-rich atmosphere. Overall, our data, along with previous work, show that there are no single nor simple relationships between mantle-, magma- and volcanic gas-redox states. • The oxidation state of volcanic gases is correlated with emission temperature. • It is independent of geodynamic setting and melt composition. • Closed-system re-equilibration of volcanic gases dictates their oxidation state. • Dichotomy between melt and volcanic gases f O 2 in the early earth is reconciled. • Shift in volcanic gases oxidation state must have occurred near the GOE time. [ABSTRACT FROM AUTHOR]

Abstract We present analyses of phyllosilicates, volcanic glass, and a series of experiments and observations on the δ18O of water extracted by rapid thermal pyrolysis at 1450 °C using the TCEA (Thermal Conversion Elemental Analyzer). The study includes the same hydrous glasses that were previously analyzed for their δD values of extracted water (Seligman et al., 2016). We utilize natural phyllosilicates (where water is present as OH– only), natural magmatic and experimentally quenched glasses, (in which water occurs as H 2 O m and OH−), and glasses that underwent low-temperature secondary hydration by meteoric water (almost completely as H 2 O m). Our study documents that: 1) thermal extraction and simultaneous pyrolysis of H 2 O t into CO and H 2 produces little or no exchange (<1‰) in δ18O between hydrogen-bound and silica-bound oxygen; 2) water extracted from different natural phyllosilicates have 103lnα silicate-OH (~δ18O silicate – δ18O OH) values ranging from −3 to 6‰, which is in agreement with previous results using partial fluorination, Density-Functional Theory, and the increment method; 3) water extracted from eruptively or experimentally quenched hydrous magmatic glasses have 103lnα silicate-H2Ot values that decrease with increasing quench temperature from 10‰ (900 °C) to 3‰ (1100 °C); 4) during progressive volcanic degassing, the δ18O of remaining water in glass decrease as the departing H 2 O m is more positive in δ18O, especially at lower temperature; this oxygen isotope trend correlates with δD as the departing H 2 O m is also more positive in δD than the remaining magmatic water. 5) the δ18O of water extracted from glass hydrated at low-temperature by secondary water yields isotopically negative δ18O values that are closer to the δ18O values of local meteoric water than values appropriate for low temperature silicate-water 18O/16O equilibrium; this suggests that upon hydration water simply dissolves into glass as H 2 O; 6) subsequently, secondarily hydrated glasses appear to show an increase in δ18O values that trend towards equilibrium with continued secondary hydration, with time, and at higher temperatures. This research demonstrates that the δ18O of extracted water, despite its 1–2 per mil- analytical precision, provides an isotopic tool for investigations of first order trends of both magmatic degassing, and of secondary hydration by meteoric waters. The trends described here aids hydrogen isotopic variations in the same processeses and combined use of both O and H isotopic variation of water in glass to help fingerprint sources of meteoric water, extent and stages of alteration of glass, and magmatic degassing. Highlights • Water-in-glass δ18O analyses help understanding magmatic degassing and secondary hydration. • Rapid thermal extraction by TCEA carries no or little exchange of water with host glass. • Meteoric water is added in glass as H 2 O with negative (meteoric) δ18O with small exchange with glass. • A mass balance method to resolve δ18O in OH and H 2 O m of water in glass is described. • The δ18O of extracted water from phyllosilicates are comparable to previous and theoretical calculations. [ABSTRACT FROM AUTHOR]

The Carboniferous Donghe sandstone reservoir is the most important target in the Tabei Uplift of the Tarim Basin, which contains a range of hydrocarbon types, including bitumen, heavy oil, condensate oil, light oil, crude oil, and hydrocarbon gas, and has high contents of CO2 and N2. The origin of multiple phase hydrocarbons from Carboniferous reservoir rocks in the Donghetang area, Western Tabei Uplift, is documented in this paper based on integral analysis of the geochemistry, pyrolysis, and carbon isotopes of the bulk composition and light composition hydrocarbons. Oil-source correlations determined that the paleoreservoir hydrocarbons that formed from Permian to Triassic derived from the Lower Ordovician (O1) source rocks and that those of the present-day reservoir that formed in the Neogene derived from Middle-Upper Ordovician (O2-3) source rocks. During the uplift episode lasting from Permian to Triassic, the hydrocarbons in the entire paleoreservoir underwent water washing, biodegradation, and bacterial sulfate reduction (BSR), resulting in residual bitumen, heavy oil, H2S, and pyrites in the paleoreservoir. The high CO2 and N2 contents originated from volcanic degassing due to volcanic activity from Permian to Early Triassic. The present-day reservoirs underwent gas washing and evaporative fractionation due to natural gas charging that originated from oil cracking and kerogen degradation in the deeper reservoirs; this resulted in fractionation and formed condensate oil and light oil with a high wax content in the residual crude oil. Based on this research, it was concluded that the diverse hydrocarbon phases in the Donghetang area were primarily attributed to water washing, biodegradation, BSR, volcanic degassing, gas washing, and evaporative fractionation. [ABSTRACT FROM AUTHOR]

SO2 cameras are able to measure rapid changes in volcanic emission rate but require accurate calibrations and corrections to convert optical depth images into slant column densities. We conducted a test at Masaya volcano of two SO2 camera calibration approaches, calibration cells and co-located spectrometer, and corrected both calibrations for light dilution, a process caused by light scattering between the plume and camera. We demonstrate an advancement on the image-based correction that allows the retrieval of the scattering efficiency across a 2D area of an SO2 camera image. When appropriately corrected for the dilution, we show that our two calibration approaches produce final calculated emission rates that agree with simultaneously measured traverse flux data and each other but highlight that the observed distribution of gas within the image is different. We demonstrate that traverses and SO2 camera techniques, when used together, generate better plume speed estimates for traverses and improved knowledge of wind direction for the camera, producing more reliable emission rates. We suggest combining traverses and the SO2 camera should be adopted where possible.

We present the first in-situ partitioning data for bromine between a natural basaltic melt and a coexisting fluid. For this study hydrothermal diamond anvil cell experiments at pressures up to 1.7 GPa were conducted. We combined laser heating to melt the basalt glass with external heating to lower the temperature gradient in the cell and to initiate circulation for the aqueous fluid. Bromine concentrations were measured in-situ with X-ray fluorescence in the basaltic melts, glasses, and in the fluid. From the results we calculated partition coefficients of DBr fluid/melt = 1.19 to 3.92 in the range of 0.4 to 1 GPa for aqueous fluids. Experiments with neon as the surrounding fluid (DBr fluid/melt = 0.38 ± 0.01 at 1.1 GPa) suggest that Br-release from a basalt into volatiles that have no bonding affinity with Br is weak. This should be the case for dry intra-plate volcanic eruptions. From the experimentally gained partition coefficients and from global Br concentration values in melt inclusions of arc magmas, we calculated an annual global Br flux of 23.5–72.9 × 109 g/y. • We find DBr fluid /melt = 1.19 to 3.92 for experimental Br degassing from basalt magma into aqueous fluids. • D <1 under almost dry conditions propose only little Br degassing for dry intra-plate volcanism relative to volcanic arcs. • An annual global Br flux of 23.5–72.9 × 109 g/y into the atmosphere was calculated. [ABSTRACT FROM AUTHOR]

Awu is a remote and little known active volcano of Indonesia located in the northern part of Molucca Sea. It is the northernmost active volcano of the Sangihe arc with 18 eruptions in less than 4 centuries, causing a cumulative death toll of 11,048. Two of these eruptions were classified with a Volcanic Explosivity Index (VEI) of 4. Since 2004, a lava dome has occupied the centre of Awu crater, channelling the fumarolic gas output along the crater wall. A combined Differential Optical Absorption Spectroscopy (DOAS) and Multi-component Gas Analyzer System (Multi-GAS) study highlight a relatively small SO2 flux (13 t/d) sustained by mixed magmatic–hydrothermal emissions made-up of 82 mol.% H2O, 15 mol.% CO2, 2.55 mol.% total S (ST) and 0.02 mol.% H2. The CO2 emission budget, as observed during a short observation period in 2015, corresponds to a daily contribution to the atmosphere of 2600 t/d, representing 1% of the global CO2 emission budget from volcanoes. The gas CO2/ST ratio of 3.7 to 7.9 is at the upper limit of the Indonesian gas range, which is ascribed to (i) some extent of S loss during hydrothermal processing, and perhaps (ii) a C-rich signature of the feeding magmatic gas phase. The source of this high CO2 signature and flux is yet to be fully understood; however, given the peculiar geodynamic context of the region, dominated by the arc-to-arc collision, this may result from either the prolonged heating of the slab and consequent production of carbon-rich fluids, or the recycling of crustal carbon.

UV cameras have been used for over a decade in order to remotely sense SO2 emission rates from active volcanoes, and to thereby enhance our understanding of processes related to active and passive degassing. Whilst SO2 column density retrievals can be more accurate/sophisticated using alternative techniques (e.g., Differential Optical Absorption Spectrometer (DOAS), Correlation Spectrometer (COSPEC)), due to their higher spectral resolutions, UV cameras provide the advantage of high time-resolution emission rates, a much greater spatial resolution, and the ability to simultaneously retrieve plume speeds. Nevertheless, the relatively high costs have limited their uptake to a limited number of research groups and volcanic observatories across the planet. One recent intervention in this regard has been the introduction of the PiCam UV camera, which has considerably lowered instrumental cost. Here we present the first data obtained with the PiCam system from seven persistently degassing volcanoes in northern Chile, demonstrating robust field operation in challenging conditions and over an extended period of time, hence adding credence to the potential of these units for more widespread dissemination to the international volcanic gas measurement community. Small and weak plumes, as well as strongly degassing plumes were measured at distances ranging 0.6–10.8 km from the sources, resulting in a wide range of SO2 emission rates, varying from 3.8 ± 1.8 to 361 ± 31.6 td−1. Our acquired data are discussed with reference to previously reported emission rates from other ground-based remotely sensed techniques at the same volcanoes, in particular considering: resolution of single plume emissions in multi-plume volcanoes, light dilution, plume geometry, seasonal effects, and the applied plume speed measurement methodology. The main internal/external factors that influence positive/negative PiCam measurements include camera shake, light dilution, and the performance of the OpenCV and control points post processing methods. A simple reprocessing method is presented in order to correct the camera shake. Finally, volcanoes were separated into two distinct groups: low and moderate SO2 emission rates systems. These groups correlate positively with their volcanological characteristics, especially with the fluid compositions from fumaroles.

How do lava domes release volcanic gases? Studying this problem is crucial to understand, and potentially anticipate, the generation of the sudden and dangerous explosive eruptions that frequently accompany dome extrusions. Since its awakening in 1994, Popocatépetl volcano has produced more than 50 lava domes and has been consistently among the strongest permanent emitters of volcanic gases. In this work, we have characterized the passive and explosive degassing between 2013 and 2016 at a high time resolution using an SO2 camera, to achieve a better understanding of the conduit processes. Our 4-year average SO2 flux is 45 kg/s, in line with the long-term average of the whole current eruptive period. We show that Popocatépetl volcano is essentially an open system and that passive degassing, i.e., degassing with no associated emission of lava or ash, dominates >95% of the time. This passive degassing is continuous and sustained, whether the crater contains a lava dome or not. It shows most of the time a strong periodic component, with a pseudo-period of ~5 min, and amplitudes of 30 to 60% of the average value. We could distinguish two types of explosions based on their SO2 flux patterns. The first type (E1) occurs in the middle of the normal passive degassing and is followed by a rapid return of the SO2 flux down to its pre-explosive level. The second type (E2), which corresponds to the strongest events, is anticipated by a rapid decrease of the SO2 flux to abnormally low values and is followed by a return to its normal values. The E2 explosions are probably caused by the accumulation of gas below a rapidly compacting permeable dome. We suggest that transient episodes of gravitational compaction of the usually permeable dome and the upper conduit is the only mechanism that is fast enough to explain the sharp decrease of the SO2 flux that anticipates the E2 explosions. Our model is potentially applicable to a large number of andesitic volcanoes that undergo passive degassing interspersed with short-lived explosions.

Primitive olivine-hosted melt inclusions provide information concerning the pre-eruptive volatile contents of silicate melts, but compositional changes associated with post-entrapment processes (PEP) sometimes complicate their interpretation. In particular, crystallization of the host phase along the wall of the melt inclusion and diffusion of H + through the host promote CO 2 and potentially S or other volatiles to exsolve from the melt into a separate fluid phase. Experimental rehomogenization and analysis of MI, or a combination of Raman spectroscopy, numerical modeling, and mass balance calculations are potentially effective methods to account for PEP and restore the original volatile contents of melt inclusions. In order to compare these different approaches, we studied melt inclusions from a suite of samples from Klyuchevskoy volcano (Kamchatka Arc) for which volatile compositions have been determined using experimental rehydration, Raman spectroscopy, and numerical modeling. The maximum CO 2 contents of melt inclusions are in agreement (~3600–4000 ppm), regardless of the method used to correct for CO 2 in the bubble, but significantly more uncertainty is observed using mass balance calculations. This uncertainty is largely due to the lack of precision associated with the petrographic method of determining bubble volumes and may also be related to the presence of daughter minerals at the glass-bubble interface. [ABSTRACT FROM AUTHOR]

The diffusivity of S in a hydrous dacitic melt (4.5–6.0 wt.% H 2 O) has been investigated in the temperature ( T ) and pressure ( P ) range of 950 °C to 1100 °C and 200 to 250 MPa, respectively. Three series of experiments were conducted at relatively low oxygen fugacity ( fO 2 ) conditions [0.8 log units below fayalite-magnetite-quartz equilibrium (FMQ −0.8); referred to as “low fO 2 ”] and high fO 2 conditions (FMQ +2.5; referred to as “high fO 2 ”) to determine if the diffusivity of S is affected by its oxidation state and speciation. Sulfur concentration profiles were measured by electron microprobe and the diffusion coefficient ( D ) was calculated by fitting these profiles. Sulfur diffusion is approximately one order of magnitude faster when S is dominantly present as sulfide species (low fO 2 ) in comparison to the sulfate dominated experiments (high fO 2 ). The following Arrhenian equations were obtained for high and low fO 2 conditions at 200 MPa: high fO 2 : D = 10 - 5.92 ± 0.86 ∗ exp - 137.3 ± 21.5 kJ / mol RT low fO 2 : D = 10 - 5.18 ± 1.39 ∗ exp - 125.7 ± 34.4 kJ / mol RT where D is the average diffusion coefficient in m 2 s −1 , R is the gas constant in 8.3144 J mol −1 K −1 and T is the temperature in K. Our results demonstrate for the first time in natural melts that S diffusion is strongly sensitive to fO 2 . Our S diffusivities under low fO 2 conditions are only slightly slower of those found for H 2 O, suggesting that S can be rather efficiently purged from reduced dacitic melts during volcanic eruptions. However, for more oxidized systems (e.g. subduction zones), S diffusion will be much slower and will hinder equilibrium syn-eruptive degassing during rapid decompression. Therefore, we conclude that the “excess S” measured during many explosive volcanic eruptions in arcs is dominantly derived from S-rich bubble accumulation in the eruptible portion of the magma reservoir. [ABSTRACT FROM AUTHOR]

Bubble nucleation and growth control the explosivity of volcanic eruptions, and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products. These samples, however, only provide a view of the final state, from which the initial conditions of a time-evolving magmatic system are then inferred. The interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites, an uncertainty that can obscure their nucleation location – either homogeneously within the melt or heterogeneously at the interface between crystals and melts. We present results of a series of dynamic, real-time 4D X-ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas. Experimentally synthesized andesitic glasses with 0.25–0.5 wt% H 2 O and seed silicate crystals were heated at 1 atm to induce bubble nucleation and track bubble growth and movement. In contrast to previous studies on natural and experimentally produced samples, we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals, that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated. The rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues, influencing subsequent permeability development and effusive vs. explosive transition in volcanic eruptions. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a new database of SO2 and CO2 fluxes from the Southern Central American Volcanic Arc (SCAVA) for the period 2015–2016. We report ∼300 SO2 flux measurements from 10 volcanoes and gas ratios from 11 volcanoes in Costa Rica and Nicaragua representing the most extensive available assessment of this ∼500 km arc segment. The SO2 flux from SCAVA is estimated at 6,240 ± 1,150 T/d, about a factor of three higher than previous estimations (1972–2013). We attribute this increase in part to our more complete assessment of the arc. Another consideration in interpreting the difference is the context of increased volcanic activity, as there were more eruptions in 2015–2016 than in any period since ∼1980. A potential explanation for increased degassing and volcanic activity is a change in crustal stress regime (from compression to extension, opening volcanic conduits) following two large (Mw > 7) earthquakes in the region in 2012. The CO2 flux from the arc is estimated at 22,500 ± 4,900 T/d, which is equal to or greater than estimates of C input into the SCAVA subduction zone. Time‐series data sets for arc degassing need to be improved in temporal and spatial coverage to robustly constrain volatile budgets and tectonic controls. Arc volatile budgets are strongly influenced by short‐lived degassing events and arc systems likely display significant short‐term variations in volatile output, calling for expansion of nascent geochemical monitoring networks to achieve spatial and temporal coverage similar to traditional geophysical networks. [ABSTRACT FROM AUTHOR]

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO 2 flux of 15.3 ± 2.3 kg s − 1 (1325-ton day − 1 ) at Sabancaya and of 11.4 ± 3.9 kg s − 1 (988-ton day − 1 ) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H 2 O, CO 2 , SO 2 , H 2 S and H 2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H 2 O, CO 2 , SO 2 and H 2 S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27, 1.2 and 0.01 kg s − 1 of H 2 O, CO 2 , SO 2 , H 2 S and H 2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO 2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes. [ABSTRACT FROM AUTHOR]

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO2). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO2 may influence the fO2 at Earth’s surface. However, degassing can impact magmatic fO2 before or during eruption, potentially obscuring relationships between the fO2 of the solid Earth and of emitted gases and their impact on surface fO2. We show that low-pressure degassing resulted in reduction of the fO2 of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the upper mantle sources of Hawaiian magmas have higher fO2 than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO2 than modern magmas. Estimates of fO2 of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere. [ABSTRACT FROM AUTHOR]

Although the impacts of large volcanic eruptions on the global environment have been frequently studied, the impacts of lower tropospheric emissions from persistently degassing volcanoes remain poorly understood. Gas emissions from persistent degassing exceed those from sporadic eruptive activity, and can have significant long-term (years to decades) effects on local and regional scales, both on humans and the environment. Here, we exploit a variety of high temporal and high spatial resolution satellite-based time series and complementary ground-based measurements of element deposition and surveys of species richness, to enable a comprehensive spatio-temporal assessment of sulfur dioxide (SO 2 ) emissions and their associated impacts on vegetation at Turrialba volcano (Costa Rica) from 2000 to 2013. We observe increased emissions of SO 2 coincident with a decline in vegetation health downwind of the vents, in accordance with the prevalent wind direction at Turrialba. We also find that satellite-derived vegetation indices at various spatial resolutions are able to accurately define the vegetation kill zone, the extent of which is independently confirmed by ground-based sampling, and monitor its expansion over time. In addition, ecological impacts in terms of vegetation composition and diversity and physiological damage to vegetation, all spatially correspond to fumigation by Turrialba’s plume. This study shows that analyzing and relating satellite observations to conditions and impacts on the ground can provide an increased understanding of volcanic degassing, its impacts in terms of the long-term vegetation response and the potential of satellite-based monitoring to inform hazard management strategies related to land use. [ABSTRACT FROM AUTHOR]