SO2 Flux Research Articles

Understanding the SO2 Degassing Budget of Mt Etna's Paroxysms: First Clues From the December 2015 Sequence

The persistent open-vent activity of Mt. Etna volcano, in Sicily, is frequently punctuated by some of the most spectacular paroxysmal basaltic explosions in nature. Although magmatic gas is unquestionably the driver of these events, direct measurements of a paroxysm’s gas flux budget have remained challenging and limited in number, to date. A particularly violent paroxysmal sequence took place on Etna on December 2015, intermittently involving four of its summit craters, especially the Voragine (VOR) that had previously displayed no activity for several years. Here, we characterize the volcano’s SO2 degassing budget prior to, during and after this paroxysmal sequence, using ground-based (UV-Camera) and satellite (OMI) observations, complemented with thermal (thermal cameras and MODIS) measurements from both ground and space. We make use of the high spatial resolution of UV-cameras to resolve SO2 emissions from the erupting VOR crater for the first time, and to characterize temporal switches in degassing activity from VOR to the nearby New Southeast Crater (NSEC). Our data show that onset of paroxysmal activity on December 3-5 was marked by visible escalation in VOR SO2 fluxes (4700-8900 tons/day), in satellite-derived thermal emissions (2000 MW vs. ~2-11 MW July-November 2015 average), and in OMI-derived daily SO2 masses (5.4±0.7 to 10.0±1.3 kilotonnes, kt; 0.5 kt was the average in the pre-eruptive period). Switch in volcanic activity from VOR to NSEC on December 6 was detected by increasing SO2 fluxes at the NSEC crater (up to 3460±350 tons/day), and by decaying SO2 emissions at VOR, until activity termination on December 19. Taken together, our observations infer the total degassed SO2 mass for the entire VOR paroxysmal sequence at 21,000±2730 t, corresponding to complete degassing of ~1.9±0.3 Mm3 of magma, or significantly less than the measured erupted magma volumes (5.1-12 Mm3). From this mismatch, we propose that a sizeable fraction of the erupted magma during the paroxysms was stored and degassed in the volcano’s shallow plumbing system well before eruption.

Continuous monitoring of soil CO2 flux at Aso volcano, Japan: the influence of environmental parameters on diffuse degassing

Continuous measurements of soil CO2 flux are useful for understanding degassing processes and for monitoring volcanic activities. Recent studies at many volcanoes have revealed that soil CO2 flux variations are significantly influenced by environmental parameters as well as volcanic processes. In this study, we conducted continuous monitoring of soil CO2 flux in the flank of Nakadake cone, Aso volcano, Japan, from January 2016 to November 2017. The results of our observations during an active period before and after a large phreatomagmatic eruption on 8 October 2016 and during a calm period from 2017 showed variations in soil CO2 flux due to oscillations in environmental parameters. Excluding these variations from the raw time series by multivariate linear regression analysis, the time series of soil CO2 flux presented some anomalous peaks in both the active and calm periods. Careful comparison of the anomalous peaks with the environmental parameters revealed that most of the anomalous peaks were likely due to an increase in wind speed and/or a decrease in barometric pressure. However, the anomaly after the 8 October 2016 eruption was not completely explicable by the variations in the environmental parameters and coincided with increases in seismic amplitude and plume SO2 flux. This anomaly was possibly attributed to an increase in magmatic CO2 flux. These findings emphasized the importance of careful statistical treatment of the soil CO2 flux data after excluding the influences of the environmental parameters at each measurement site. These statistical treatments will contribute to a better understanding of the degassing processes and monitoring of volcanic activities, including phreatic or phreatomagmatic eruptions.

An experimental study of SO2 reactions with silicate glasses and supercooled melts in the system anorthite–diopside–albite at high temperature

Sulfur dioxide [SO2(g)] is the most abundant sulfur-bearing volcanic gas species on Earth. From its magmatic origin at depth to expulsion at the surface via either persistent degassing or large explosive volcanic eruptions, SO2(g) interacts with silicate materials at elevated temperatures. Similar high-temperature reactions also occur in the volcanic systems and the atmospheres of Venus, the Galilean moon Io, and in Mars’ past, as well in industrial flue-gas processing. We present an experimental investigation of the reaction between SO2(g), glasses and supercooled melts in the system anorthite–diopside–albite (CaAl2Si2O8–CaMgSi2O6–NaAlSi3O8). The samples were exposed to SO2(g) at 600–800 °C for experimental durations of 10 min to 24 h. The reactions resulted in the formation of sulfate coatings and modified the near-surface composition of the silicate samples. The predominant sulfate reaction product is CaSO4, with hydrated MgSO4 or Na2SO4 also observed in some experiments. In the anorthite–diopside system, the reaction extent strongly depends on the temperature relative to the glass transition temperature (Tg). Above Tg, in reactions with supercooled melts, the reaction forms up to 20 times more sulfate. The overall rate of sulfate formation is controlled by the diffusive flux of Ca, Mg and Na from the increasingly depleted silicate to the surface where the reaction with SO2(g) occurs. The sulfate-forming reaction results in a volume increase relative to the unreacted silicate. When this reaction occurs in the subvolcanic environment it causes an increased molar volume that may close veins, reducing the permeability and decrease the SO2(g) flux at the surface. An increase in the SO2(g) flux would then result in the opening of new veins, which may be accompanied by seismic activity. Additionally, the change in molar volume may itself trigger seismicity. The strong preferential uptake of Ca into the sulfate reaction product results in a Si- and Al-enriched silicate. In the sulfate, the Ca component may be mobilized by secondary processes such as through the interaction with meteoric fluids. We recommend that the products of such gas–solid reactions should be the object of remote and robotic investigations of planetary environments with volcanic histories such as on Mars, Io, Venus and Mercury.

Petrological characteristics and volatile content of magma of the 1979, 1989, and 2014 eruptions of Nakadake, Aso volcano, Japan

Petrological observations and chemical analyses of melt inclusions in scoria were used to investigate the magma ascent and eruption processes of the 1979, 1989, and 2014 eruptions of Nakadake, Aso volcano, Japan. Major elements and sulfur contents of the melt inclusions were determined using an electron probe microanalyzer, and their water and CO2 contents were determined using secondary ion mass spectrometry. Five scoria specimens from the 2014 eruptions had an andesite composition identical to the scoria from the 1979 and 1989 eruptions. Thermometry using the chemical composition of the groundmass and the rims of the phenocrysts indicated that the temperature of the 2014 magma was 1042–1092 °C. Melt inclusions in plagioclases, clinopyroxenes, and olivines in the 2014 scoria had an andesite composition similar to that of the groundmass. The volatile content of the melt inclusions was 0.6–0.8 wt% H2O, 0.003–0.017 wt% CO2, and 0.008–0.036 wt% S. The variation in CO2 and S content of the melt inclusions was not correlated with the K2O content, suggesting that the magma degassed as pressure decreased. Melt inclusions in plagioclases, clinopyroxenes, and olivines from the 1979 and 1989 scoria had similar major elements and volatile content to the 2014 eruption specimens. The similarity in chemical composition of both the whole-rock and melt inclusions among all samples suggests that the magmas of these eruptions were derived from the same magma chamber. The gas saturation pressure estimated from the H2O and CO2 contents of the 1979, 1989, and 2014 scoria ranged from 18 to 118 MPa, corresponding to depths of 1–4 km. Comparison of this depth with geophysical observations suggests that the inclusion entrapments occurred in the upper part of the magma chamber and/or a conduit. By combining the melt inclusion analysis with volcanic gas observations, we estimated the bulk volatile content of the magma. Based on the bulk sulfur content of the magma and the SO2 flux between January 2014 and December 2017, the amount of degassed magma over that period was estimated to be the equivalent of 1–3 km3 of dense rock. The estimated volume was more than 600 times larger than that of products erupted during the same period. This suggests that magma degassing occurred at several depths in the magma chamber due to magma convection in a conduit.

Eddy flux measurements of sulfur dioxide deposition to the sea surface

Abstract. Deposition to the sea surface is a major atmospheric loss pathway for many important trace gases, such as sulfur dioxide (SO2). The air–sea transfer of SO2 is controlled entirely on the atmospheric side of the air–sea interface due to high effective solubility and other physical–chemical properties. There have been few direct field measurements of such fluxes due to the challenges associated with making fast-response measurements of highly soluble trace gases at very low ambient levels. In this study, we report direct eddy covariance air–sea flux measurements of SO2, sensible heat, water vapor, and momentum. The measurements were made over shallow coastal waters from the Scripps Pier, La Jolla, CA, using negative ion chemical ionization mass spectrometry as the SO2 sensor. The observed transfer velocities for SO2, sensible heat, water vapor, and momentum and their wind speed dependences indicate that SO2 fluxes can be reliably measured using this approach. As expected, the transfer velocities for SO2, sensible heat, and water vapor are lower than that for momentum, demonstrating the contribution of molecular diffusion to the overall air-side resistance to gas transfer. Furthermore, transfer velocities of SO2 were lower than those of sensible heat and water vapor when observed simultaneously. This result is attributed to diffusive resistance in the interfacial layer of the air–sea interface.

Breathing and Coughing: The Extraordinarily High Degassing of Popocatépetl Volcano Investigated With an SO2 Camera

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, Popocatepetl volcano has produced more than fifty 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 Popocatepetl 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 minutes, 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.

Renewed Explosive Phreatomagmatic Activity at Poás Volcano, Costa Rica in April 2017

Phreatic and phreatomagmatic eruptions at volcanoes often present no short term precursory activity, making them a challenge to forecast. Poas volcano, Costa Rica, exhibits cyclic activity with phreatic and some phreatomagmatic eruptions separated by times of quiescence. The latest phreatomagmatic stage began in March 2017 with increases in crater lake temperatures, SO2 flux, and the rate of seismicity, as well as accelerated ground inflation near the active crater. On 23 April 2017 at 04:12 UTC, a large phreatomagmatic eruption occurred at Poas, sending blocks up to 1 m in length to distances greater than 1 km. Hindsight analysis revealed a precursory seismic sequence from 25 March to 22 April of similar seismic events (in terms of their frequency and waveform characteristics). Fourteen families of similar seismic events (containing >10 events per family) were identified during this precursory sequence, totaling over 1300 events. An acceleration within the dominant family of LF (low frequency) waveforms was identified, suggesting that a forecast for the onset of the eruption may have been possible using the Failure Forecast Method (FFM). However, no confidence could be placed in the forecast generated, reiterating that not all accelerating trends are suitable for analysis using the FFM, in particular in conjunction with a least-squares linear regression. Our residual analysis further supports the concept that using a least-squares linear regression analysis is not appropriate with this dataset, and allows us to eliminate commonly used forecasting parameters for this scenario. However, the identification of different families of similar seismicity allows us to determine that magmatic fluid on its way to the surface initially became stalled beneath a chilled margin or hydrothermal seal, before catastrophically failing in a large phreatomagmatic eruption. Additionally, we note that 24 hours prior to the large phreatomagmatic eruption, all LF families became inactive, which could have been falsely interpreted in real time as the waning of activity. Our results suggest that identifying families of seismicity offers unique opportunities to better understand ongoing processes at depth, and to challenge conventional forecasting techniques.

Coupling Between Magmatic Degassing and Volcanic Tremor in Basaltic Volcanism

Magmatic degassing, typically measured as SO2 flux, plays a key role in controlling volcanic eruption style and is one of the key parameters used by volcano observatories to assess volcanic unrest and detect eruption precursors. Volcanic tremor, the integrated amplitude of seismic energy release over a range of frequencies, is also a key parameter in volcano monitoring. A connection between volcanic degassing and tremor has been inferred through correlations between the signals which are often, but not always, observed during periods of unrest or eruption. However, data are often equivocal and our understanding of the physical processes, which couple degassing with tremor are still evolving. New insights into degassing-tremor coupling can be made by investigation of the long-term relationship between degassing and tremor, focussing on the frequency-dependence of tremor and passive degassing behaviour. In this study, we examine how long-term SO2 emission rates and volcanic tremor on Mt. Etna, track rapid variability in eruptive dynamics. Correlations between SO2 flux and tremor are explored in both quiescent and eruptive periods, comparing the two parameters at both long and short time-scales (<< 1 day) for ~2 years. Our analysis reveals that over month-long timescales passive degassing of SO2 and tremor tend to be well-correlated, but these correlations are lost over shorter timescales. This reflects a coupling process between passive degassing and tremor, produced by a combination of gas flow through permeable magma and the convective flow of magma within the conduit. Short-term correlations are lost because variations in the continuous degassing process are relatively small compared with the overall degassing rate and fall below measurement noise..During eruptive periods strong correlations are observed between degassing and tremor, with a greater contribution of higher frequency signal in tremor, controlled by eruptive style. These observations suggest that in sin-eruptive periods the tremor source is dominated by the coupling between the eruption column and the ground through infrasonic waves, rather than conduit processes. Our results demonstrate the importance of high quality long-term observations and offer new insights into the physical mechanisms which couple degassing and volcanic tremor at active volcanoes.

Experimental Investigation and Numerical analysis of SO2 Removal Using Polypropylene Membrane Contactor

In this study, polypropylene membrane contactor is designed for SO2 absorption of simulated flue gas. Water and the aqueous solution of Na2SO3 are used as an absorbent. Absorption performance of the longitudinal module is compared to novel transversal membrane contactor module. The result shows that the transversal configuration of hollow fiber module significantly enhances absorption performance over conventional longitudinal configuration. Absorption flux of SO2 in aqueous Na2SO2 is 1.8 times higher than water at optimum Na2SO3 concentration and gas flow rate. According to performance stability test, polypropylene hollow fiber membrane is successfully operated for 15 hours maintaining average absorption flux of 20 x 10−5 mol.m−2.s−1. Numerical simulation shows good agreement with physical absorption data.

Dynamic measurement of liquid‐phase mass transfer coefficient and significance on the SO2 absorption rate

AbstractLiquid‐phase mass transfer coefficient is important for characterization of gas–liquid reactors and relevant to the modelling of gas absorption rate. Both direct and indirect methods have been used to obtain this coefficient. However, these methods have not been compared on the same basis. Liquid‐phase mass transfer coefficients were measured in three ways—(a) CO2 absorption into water, (b) SO2 absorption into 1 kmol m−3 of HCl, and (c) O2 absorption into Na2SO3—and then normalized to the coefficient for SO2. Based on transient experiments, the normalized values for liquid‐phase mass transfer coefficient obtained from three methods are in turn of . The fluxes of SO2 predicted from three methods were further compared with the experimental values measured in SO2‐NaOH system. The fluxes predicted from agreed well with the experimental values, whereas those from and were significantly lower or higher. Therefore, the liquid‐phase mass transfer coefficient is preferably obtained from the targeted gas. Modelling on the flux of SO2 demonstrates the transition of controlling regions against pH. At pH above 4, the gas side resistance is larger than the liquid side, whereas at pH below 4, the gas side resistance is smaller than the liquid side.

Long-term eruptive trends from space-based thermal and SO2 emissions: a comparative analysis of Stromboli, Batu Tara and Tinakula volcanoes

Batu Tara (Indonesia) and Tinakula (Solomon Island) are two poorly known volcanoes with morphologies and short-term eruptive activity similar to Stromboli (Italy). However, quantitative information about their long-term eruptive behaviour is limited, making the comparisons with Stromboli descriptive and based on short periods of observations. Here, we use over a decade of satellite data to measure and compare the radiant flux (2000–2017) and the SO2 mass (2004–2017) of all three volcanoes. The combined analysis of volcanic radiant power (from MODIS data) and SO2 flux (from OMI data) reveals different long-term eruptive trends and contrasting ratios of SO2/VRP. These data indicate that the eruptive mechanisms operating at each volcano are quite different. The persistent open-vent activity of Stromboli volcano is episodically interrupted by flank eruptions that drain degassed magma stored in the very shallow portion of the central conduit. In contrast, a long-lasting exponential decay of both VRP and SO2 flux observed at Batu Tara is consistent with the eruption of undegassed magma from a deep, closed magma chamber, whilst Tinakula displays multiple year-long eruptive phases, characterised by evolving gas/thermal ratios and an eruptive intensity increasing with time. Magma budget calculations for the latter volcano are consistent with eruption from a volatile-zoned magma chamber, coupled with periods of gas/magma accumulations at depth. Our results suggest that the combined analysis of satellite thermal/gas data provides a valuable tool for decrypting the long-term volcanic dynamics that could remain hidden over shorter timescales.

Using Drones and Miniaturized Instrumentation to Study Degassing at Turrialba and Masaya Volcanoes, Central America

AbstractGas measurements using unmanned aerial vehicles, or drones, were undertaken at Turrialba volcano, Costa Rica, and Masaya volcano, Nicaragua, in 2016 and 2017. These two volcanoes are the largest time‐integrated sources of gas in the Central American Volcanic Arc, and both systems are currently extremely active with potential for sudden destabilization. We employed a series of miniaturized drone‐mounted instrumentation including a mini‐DOAS, two MultiGAS instruments, and an optical particle counter, supplemented by ground‐based measurements. Payloads were typically 1–1.5 kg and flight times were 10–15 min. The measurements were both accurate and precise due to the inherent sensitivity of the instrumentation and the high gas concentrations, which the drones were able to sample. The quality of data obtained by our drones was comparable to that obtained by our ground‐based measurements. At Turrialba in April 2017, we measured an average SO2 flux of 1,380 ± 280 T/day, CO2/SO2 of 6.5, and H2O/SO2 of 27.8. Using these values, we calculated a CO2 flux of 6,170 T/day and an H2O flux of 10,790 T/day. At Masaya in May 2017, the average SO2 flux was 1,560 ± 180 T/day, with CO2/SO2 of 3.9 and H2O/SO2 of 62.3, giving a mean CO2 flux of 4,150 T/day and mean H2O flux of 27,330 T/day. The elevated carbon and water fluxes and ratios are indicative of underlying magmas that are enriched in these components, resulting in the high levels of activity observed.

Satellite and Ground Remote Sensing Techniques to Trace the Hidden Growth of a Lava Flow Field: The 2014–2015 Effusive Eruption at Fogo Volcano (Cape Verde)

Fogo volcano erupted in 2014–2015 producing an extensive lava flow field in the summit caldera that destroyed two villages, Portela and Bangaeira. The eruption started with powerful explosive activity, lava fountains, and a substantial ash column accompanying the opening of an eruptive fissure. Lava flows spreading from the base of the eruptive fissure produced three arterial lava flows. By a week after the start of the eruption, a master lava tube had already developed within the eruptive fissure and along the arterial flow. In this paper, we analyze the emplacement processes based on observations carried out directly on the lava flow field, remote sensing measurements carried out with a thermal camera, SO2 fluxes, and satellite images, to unravel the key factors leading to the development of lava tubes. These were responsible for the rapid expansion of lava for the ~7.9 km length of the flow field, as well as the destruction of the Portela and Bangaeira villages. The key factors leading to the development of tubes were the low topography and the steady magma supply rate along the arterial lava flow. Comparing time-averaged discharge rates (TADR) obtained from satellite and Supply Rate (SR) derived from SO2 flux data, we estimate the amount and timing of the lava flow field endogenous growth, with the aim of developing a tool that could be used for hazard assessment and risk mitigation at this and other volcanoes.

SO2 emissions, plume heights and magmatic processes inferred from satellite data: The 2015 Calbuco eruptions

Quantifying time-series of sulfur dioxide (SO2) emissions during explosive eruptions provides insight into volcanic processes, assists in volcanic hazard mitigation, and permits quantification of the climatic impact of major eruptions. While volcanic SO2 is routinely detected from space during eruptions, the retrieval of plume injection height and SO2 flux time-series remains challenging. Here we present a new numerical method based on forward- and backward-trajectory analysis which enable such time-series to be determined.Using this method applied to GOME-2 satellite imagery we investigate the SO2 emissions from two sub-Plinian eruptions of Calbuco, Chile, produced in April 2015. Our results show a mean injection height of 15 km for the two eruptions, with overshooting tops reaching 20 km. We calculate a total of 0.295 ± 0.045 Tg of SO2 emitted, with 0.140 ± 0.033 Tg produced by the first eruption and 0.155 ± 0.031 Tg by the second one. Using standard models we convert plume heights to mass eruption rates (MER). Comparing gas flux and MER we discover quite different volcanic processes driving the two eruptions, with the first eruption producing an SO2 flux three times higher than the second one, while they both had similar MERs. We propose that this difference reflects different exsolved volatile contents before the onset of the two eruptions, with the first eruption richer in pre-exsolved gas than the second one. This hypothesis is supported by melt inclusion measurements of sulfur concentrations in plagioclase phenocrysts and groundmass glass of tephra samples through electron microprobe analysis. Combining the satellite and petrological analysis, we propose that the overpressure caused by the pre-exsolved volatile phase (not only SO2, but also probably H2O and CO2) may have triggered the eruption.These results demonstrate that our new methodology produces constraints on SO2 flux and plume height time-series permitting new insights into sub-surface processes using satellite SO2 data.

Plumetrack: Flux calculation software for UV cameras

Ultraviolet (UV) cameras are increasingly employed to map and measure SO2 abundances in volcanic emissions to the atmosphere. The main purpose of this is to estimate mass fluxes of SO2, which requires estimation of the transport velocity of the plume. In this paper, we present Plumetrack, open-source Python based software for computing SO2 fluxes from calibrated UV camera images. Designed to be the final component in UV camera processing toolchains, Plumetrack provides functionality for velocity estimation using optical-flow, flux calculation and error estimates. It can be used interactively via a graphical user interface or for batch processing via a commandline interface. We discuss the features and implementation details of Plumetrack, describe in detail a new flux calculation algorithm and demonstrate its performance on a set of synthetic UV camera images. The new algorithm is found to out perform the established flux calculation method, especially for highly spatiotemporally variable plumes. Furthermore, we show that the Plumetrack software may be successfully used with data from other imaging systems such as standard video cameras.

Gas Emissions From Volcanoes of the Kuril Island Arc (NW Pacific): Geochemistry and Fluxes

AbstractThe Kuril Island arc extending for about 1,200 km from Kamchatka Peninsula to Hokkaido Island is a typical active subduction zone with ∼40 historically active subaerial volcanoes, some of which are persistently degassing. Seven Kurilian volcanoes (Ebeko, Sinarka, Kuntomintar, Chirinkotan, Pallas, Berg, and Kudryavy) on six islands (Paramushir, Shiashkotan, Chirinkotan, Ketoy, Urup, and Iturup) emit into the atmosphere &gt; 90% of the total fumarolic gas of the arc. During the field campaigns in 2015–2017 direct sampling of fumaroles, MultiGas measurements of the fumarolic plumes and DOAS remote determinations of the SO2 flux were conducted on these volcanoes. Maximal temperatures of the fumaroles in 2015–2016 were 510°C (Ebeko), 440°C (Sinarka), 260°C (Kuntomintar), 720°C (Pallas), and 820°C (Kudryavy). The total SO2 flux (in metric tons per day) from fumarolic fields of the studied volcanoes was measured as ∼1,800 ± 300 t/d, and the CO2 flux is estimated as 1,250 ± 400 t/d. Geochemical characteristics of the sampled gases include δD and δ18O of fumarolic condensates, δ13C of CO2, δ34S of the total sulfur, ratios 3He/4He and 40Ar/36Ar, concentrations of the major gas species, and trace elements in the volcanic gas condensates. The mole ratios C/S are generally &lt;1. All volcanoes of the arc, except the southernmost Mendeleev and Golovnin volcanoes on Kunashir Island, emit gases with 3He/4He values of &gt;7RA (where RA is the atmospheric 3He/4He). The highest 3He/4He ratios of 8.3RA were measured in fumaroles of the Pallas volcano (Ketoy Island) in the middle of the arc.

Unrest at the Nevados de Chillán volcanic complex: a failed or yet to unfold magmatic eruption?

Resuming erupting activity at volcanoes that have been long quiescent poses a significant challenge to hazard assessment, as it require assessment of whether the change in activity is an isolated event or the beginning of a new eruptive sequence. Such inception is often poorly characterised as quiescent volcanoes tend to be poorly equipped and not extensively monitored, especially with respect to gas geochemistry. Here, we report gas composition and flux measurements from a newly opened vent at the very onset of eruptive activity at the Nevados de Chillán volcanic complex (Chile) in January-February 2016. The molar proportions of H2O, CO2, SO2, H2S and H2 gases are found to be 98.4, 0.97, 0.11, 0.01 and 0.5 mol% respectively. The mean SO2 flux recorded in early February 2016 during periods of eruptive discharge amounts to 0.4-0.6 kg s-1. Our results indicate that the new vent opening was propelled by magmatic gases, triggering repeated eruptions. Ash particles ejected by the first blast of 8 January are dominated by lithic fragments of dacitic composition. By contrast the ash ejected in a subsequent eruption contains both lithic fragments of dense dacite, and a fresher, sparsely vesicular material of basaltic andesite composition. By October 2017 the ejected ash is back to being dominated by the dense dacitic lithic material. Together with the seismic and deformation record, these observations point to the explosive activity resulting from a small intrusion of basaltic to andesitic magma at shallow level. The fate of this magma, whether stalling or eventually triggering a magmatic eruption, remains to be seen, but current observations suggest the former is most likely.

Implementation of electrochemical, optical and denuder-based sensors and sampling techniques on UAV for volcanic gas measurements: examples from Masaya, Turrialba and Stromboli volcanoes

Abstract. Volcanoes are a natural source of several reactive gases (e.g., sulfur and halogen containing species) and nonreactive gases (e.g., carbon dioxide) to the atmosphere. The relative abundance of carbon and sulfur in volcanic gas as well as the total sulfur dioxide emission rate from a volcanic vent are established parameters in current volcano-monitoring strategies, and they oftentimes allow insights into subsurface processes. However, chemical reactions involving halogens are thought to have local to regional impact on the atmospheric chemistry around passively degassing volcanoes. In this study we demonstrate the successful deployment of a multirotor UAV (quadcopter) system with custom-made lightweight payloads for the compositional analysis and gas flux estimation of volcanic plumes. The various applications and their potential are presented and discussed in example studies at three volcanoes encompassing flight heights of 450 to 3300 m and various states of volcanic activity. Field applications were performed at Stromboli volcano (Italy), Turrialba volcano (Costa Rica) and Masaya volcano (Nicaragua). Two in situ gas-measuring systems adapted for autonomous airborne measurements, based on electrochemical and optical detection principles, as well as an airborne sampling unit, are introduced. We show volcanic gas composition results including abundances of CO2, SO2 and halogen species. The new instrumental setups were compared with established instruments during ground-based measurements at Masaya volcano, which resulted in CO2 ∕ SO2 ratios of 3.6 ± 0.4. For total SO2 flux estimations a small differential optical absorption spectroscopy (DOAS) system measured SO2 column amounts on transversal flights below the plume at Turrialba volcano, giving 1776 ± 1108 T d−1 and 1616 ± 1007 T d−1 of SO2 during two traverses. At Stromboli volcano, elevated CO2 ∕ SO2 ratios were observed at spatial and temporal proximity to explosions by airborne in situ measurements. Reactive bromine to sulfur ratios of 0.19 × 10−4 to 9.8 × 10−4 were measured in situ in the plume of Stromboli volcano, downwind of the vent.

The Magmatic Gas Signature of Pacaya Volcano, With Implications for the Volcanic CO2 Flux From Guatemala

AbstractPacaya volcano in Guatemala is one of the most active volcanoes of the Central American Volcanic Arc (CAVA). However, its magmatic gas signature and volatile output have received little attention to date. Here, we present novel volcanic gas information from in‐situ (Multi‐GAS) and remote (UV camera) plume observations in January 2016. We find in‐plume H2O/SO2 and CO2/SO2 ratios of 2‐20 and 0.6‐10.5, and an end‐member magmatic gas signature of 80.5 mol. % H2O, 10.4 mol. % CO2, and 9.0 mol. % SO2. The SO2 flux is evaluated at 885 ± 550 tons/d. This, combined with co‐acquired volcanic plume composition, leads to H2O and CO2 fluxes of 2,230 ± 1,390 and 700 ± 440, and a total volatile flux of ∼3,800 tons/d. We use these results in tandem with previous SO2 flux budgets for Fuego and Santiaguito to estimate the total volcanic CO2 flux from Guatemala at ∼1,160 ± 600 tons/day. This calculation is based upon CO2/total S (St) ratios for Fuego (1.5 ± 0.75) and Santiaguito (1.4 ± 0.75) inferred from a gas (CO2/St ratio) versus trace‐element (Ba/La ratio) CAVA relationship. The H2O‐poor and low CO2/St ratio (∼1.0‐1.5) signature of Pacaya gas suggests dominant mantle‐wedge derivation of the emitted volatiles. This is consistent with 3He/4He ratios in olivine hosted fluid inclusions (FIs), which range between 8.4 and 9.0 Ra (being Ra the atmospheric 3He/4He ratio) at the upper limit of MORB range (8 ± 1 Ra). These values are the highest ever measured in CAVA and among the highest ever recorded in arc volcanoes worldwide, indicating negligible 4He contributions from the crust/slab.

Tracking Formation of a Lava Lake From Ground and Space: Masaya Volcano (Nicaragua), 2014–2017

AbstractA vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented‐long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO2 rich, as testified by high CO2/SO2 ratios (mean: 12.2 ± 6.3) and low H2O/CO2 ratios (mean: 2.3 ± 1.3). The volcanic CO2 flux also peaked in November 2015 (mean: 81.3 ± 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO2 degassing as sourced by degassing of a volatile‐rich fast‐overturning (3.6–5.2 m3 s−1) magma, supplying CO2‐rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (&lt;1 km) Masaya magma reservoir, leading to upward migration of vesicular (buoyant) resident magma, and ultimately to (re)formation of the lava lake. At onset of lava lake activity on 11 December 2015 (constrained by satellite‐based MODIS thermal observations), the gas emissions transitioned to more SO2‐rich composition, and the SO2 flux increased by a factor ∼40% (11.4 ± 5.2 kg/s) relative to background degassing (8.0 kg/s), confirming faster than normal (4.4 versus ∼3 m3 s−1) shallow magma convection. Based on thermal energy records, we estimate that only ∼0.8 of the 4.4 m3 s−1 of magma actually reached the surface to manifest into a convecting lava lake, suggesting inefficient transport of magma in the near‐surface plumbing system.