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The Total Volatile (TV) flux from Mount Etna volcano has been characterised for the first time, by summing the simultaneously‐evaluated fluxes of the three main volcanogenic volatiles: H 2 O, CO 2 and SO 2 . SO 2 flux was determined by routine DOAS traverse measurements, while H 2 O and CO 2 were evaluated by scaling MultiGAS‐sensed H 2 O/SO 2 and CO 2 /SO 2 plume ratios to the UV‐sensed SO 2 flux. The time‐averaged TV flux from Etna is evaluated at ∼21,000 t·day −1 , with a large fraction accounted for by H 2 O (∼13,000 t·day −1 ). H 2 O dominates (≥70%) the volatile budget during syn‐eruptive degassing, while CO 2 and H 2 O contribute equally to the TV flux during passive degassing. The CO 2 flux was observed to be particularly high prior to the 2006 eruption, suggesting that this parameter is a good candidate for eruption prediction at basaltic volcanoes.

Marked increases of CO 2 , H 2 and He dissolved in thermal waters and changes in the dissolved carbon isotopic composition, were observed at Stromboli before the 28 December 2002 eruption and before a violent explosive paroxysm occurred on 5 April 2003. High anomalous CO 2 flux values were recorded at the crater rim since a week before the eruption onset. The first anomalies in the thermal waters (dissolved CO 2 amount) appeared some months before the eruption, when magma column rose at a very high level in the conduit. High peaks of dissolved H 2 and He were recorded a few days before the paroxysm. Carbon isotopic composition indicates a magmatic origin of the dissolved CO 2 whose increase, together with those of H 2 and He, is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas‐rich magma, whose fragments have been emitted during the explosion.

Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO 2 ‐rich gas (CO 2 /S total > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur‐rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8–10 km deep, whereas the shallow magmatic gas source is at ~3–5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H 2 S/SO 2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO 2 and H 2 S/SO 2 > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H 2 S/SO 2 < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high‐temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.

The fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide, due to the lack of suitable gas flux sensing techniques. In view of resumption of ground uplift (since 2005) and the associated variations in gas chemistry, Campi Flegrei, in southern Italy, is one of the restless calderas where gas flux observations are especially necessary. Here we report the first ever obtained estimate of the Campi Flegrei fumarolic gas output, based on a set of MultiGAS surveys (performed in 2012 and 2013) with an ad‐hoc‐designed measurement setup. We estimate that the current Campi Flegrei fumarolic sulphur (S) flux is low, on the order of 1.5–2.2 tons/day, suggesting substantial scrubbing of magmatic S by the hydrothermal system. However, the fumarolic carbon dioxide (CO 2 ) output is ∼460±160 tons/day (mean±SD), which is surprisingly high for a dormant volcano in the hydrothermal stage of activity, and results in a combined (fumaroles + soil) CO 2 output of ∼1560 tons/day. Assuming magma to be the predominant source, we propose that the current CO 2 output can be supplied by either (i) a large (0.6–4.6 km 3 ), deeply stored (>7 km) magmatic source with low CO 2 contents (0.05–0.1 wt%) or (ii) by a small to medium‐sized (∼0.01–0.1 km 3 ) but CO 2 ‐rich (2 wt%) magma, possibly stored at pressures of ∼100 to 120 MPa. Independent geophysical evidence (e.g., inferred from geodetic and gravity data) is needed to distinguish between these two possibilities.

Seismic, deformation, and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment. In spite of their wide use, there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques. Here we combine seismic (volcanic tremor and long‐period seismicity), deformation (GPS), and geochemical (volcanic gas plume CO 2 /SO 2 ratios) measurements in an attempt to interpret trends in the recent (2007–2008) activity of Etna volcano. We show that each eruptive episode occurring at the Southeast Crater (SEC) was preceded by a cyclic phase of increase‐decrease of plume CO 2 /SO 2 ratios and by inflation of the volcano's summit captured by the GPS network. These observations are interpreted as reflecting the persistent supply of CO 2 ‐rich gas bubbles (and eventually more primitive magmas) to a shallow (depth of 1–2.8 km asl) magma storage zone below the volcano's central craters (CCs). Overpressuring of the resident magma stored in the upper CCs' conduit triggers further magma ascent and finally eruption at SEC, a process which we capture as an abrupt increase in tremor amplitude, an upward (>2800 m asl) and eastward migration of the source location of seismic tremor, and a rapid contraction of the volcano's summit. Resumption of volcanic activity at SEC was also systematically anticipated by declining plume CO 2 /SO 2 ratios, consistent with magma degassing being diverted from the central conduit area (toward SEC).

We report here on the real‐time measurement of CO 2 and SO 2 concentrations in the near‐vent volcanic gas plume of Mount Etna, acquired by the use of a field portable gas analyzer during a series of periodic field surveys on the volcano's summit. During the investigated period (September 2004 to September 2005), the plume CO 2 /SO 2 ratio ranged from 1.9 to 10.8, with contrasting composition for Northeast and Voragine crater plumes. Scaling the above CO 2 /SO 2 ratios by UV spectroscopy determined SO 2 emission rates, we estimate CO 2 emission rates from the volcano in the range 0.9–67.5 kt d −1 (average, 9 kt d −1 ) . About 2 kt of CO 2 were emitted daily on average during quiescent passive degassing, whereas CO 2 emission rates from Etna's summit were 10–40 times larger during the 2004–2005 effusive event (with a cumulative CO 2 release of ∼3800 kt during the 6 months of the eruption). Such a syneruptive increase, ascribed to the replenishment of the shallow (<6 km) volcanic plumbing system by CO 2 ‐rich (0.25 wt %) more primitive magmas, supports the potential of CO 2 output rates as key parameters for volcanic hazard assessment.

Finding the geometry of aquifers in an active volcano is important for evaluating the hazards associated with phreato‐magmatic phenomena and incidentally to address the problem of water supply. A combination of electrical resistivity tomography (ERT), self‐potential, CO 2 , and temperature measurements provides insights about the location and pattern of ground water flow at Stromboli volcano. The measurements were conducted along a NE‐SW profile across the island from Scari to Ginostra, crossing the summit (Pizzo) area. ERT data (electrode spacing 20 m, depth of penetration of ∼200 m) shows the shallow architecture through the distribution of the resistivities. The hydrothermal system is characterized by low values of the resistivity (<50 Ω m) while the surrounding rocks are resistive (>2000 Ω m) except on the North‐East flank of the volcano where a cold aquifer is detected at a depth of ∼80 m (resistivity in the range 70–300 Ω m). CO 2 and temperature measurements corroborate the delineation of the hydrothermal body in the summit part of the volcano while a negative self‐potential anomaly underlines the position of the cold aquifer.

We applied the Multi‐GAS technique to measure compositions of the volcanic plumes continuously discharged from summit craters of Voragine, Northeast and Bocca Nuova at Mount Etna, in an attempt to estimate compositions of the source volcanic gases. The estimated CO 2 /SO 2 and H 2 O/CO 2 ratios of the volcanic gases show a large variation ranging from 0.6 to 30 and from 1 to 18, respectively. This variability overlaps with the compositional range of dissolved volatiles in melt inclusions and their coexisting bubbles in a magma chamber and can be caused by the low‐pressure degassing of a magma with variable bubble content ranging from 0.3 to 15 wt.%. The variable bubble content in the magma is likely a result of supply of deep‐derived CO 2 ‐rich gas phase to the chamber and subsequent bubble‐magma differentiation by bubble ascent in the magma chamber. In contrast, the variation of volcanic gas composition can also be caused by changes of degassing pressure (gas–magma separation pressure), ranging from 0 to 100 MPa, as a result of changes in the depth of the top of the convecting magma in volcanic conduits. Both mechanisms can cause similar compositional variations. However, the two mechanisms will result in contrasting correlations between the SO 2 emission rates and the gas compositions that can be examined by parallel observations of the emission rates and compositions in the future.

This paper provides new data on sulfur, halogens, and minor and trace metal contents in airborne particulate matter from the Mt. Etna volcanic plume. Aerosol samples were collected by conventional filtration techniques before and during the summer 2001 eruption, in order to investigate relations between plume chemistry and volcano dynamics. Data analysis reveals that abundances of trace metals in the plume result from mixing of erosive and volatile components. The former is responsible for the contents of rare earth elements (REE), Ca, Ba, Sr, Ti, Sc, Y, Hf and Th; the latter contributes significantly to the abundance of Cs, Rb, Na and K, probably transported in the plume as metal halides, and Cd, Pb, Zn, Ge, Te, Mo, Re, Se, Sb, Sn, In, Bi, Tl, Cu and Au, associated with sulfur in plume particles. Enrichment factors show that plume particulate matter from the Monti Carcarazzi vent, which opened on the southern flank of the volcano in July 2001, is typically depleted in volatile trace elements with respect to the output from the summit crater, suggesting the secondary nature of the outpouring lavas. The decreasing trend observed throughout the eruption in the enrichment factors of most trace metals probably indicates a small-volume batch of magma with limited feed from depth.

The flow of ground water in a buried permeable paleo‐channel can be observed at the ground surface through its self‐potential signature. We apply this method to delineate the Saint‐Ferréol paleo‐channel of the Rhone River located in Camargue, in the South East of France. Negative potentials, ∼−30 mV (reference taken outside the paleo‐channel), are associated with ground water flow in this major sand‐filled channel (500 m wide). Electrical resistivity is primarily controls by the salinity of the pore water. Electrical resistivity tomography and in situ sampling show the salinity of the water inside the paleo‐channel is ten times smaller by comparison with the pore water of the surrounding sediments. Combining electrical resistivity surveys, self‐potential data, and a minimum of drilling information, a 3‐D reconstruction of the architecture of the paleo‐channel is obtained showing the usefulness of this methodology for geomorphological reconstructions in this type of coastal environment.

Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth's history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth's volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

Abstract This work presents a new database of SO 2 and CO 2 fluxes from the Southern Central American Volcanic Arc (SCAVA) for the period 2015–2016. We report ∼300 SO 2 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 SO 2 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 CO 2 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 Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of Copahue, a very active volcano on the Argentina‐Chile border. Our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in March 2013, when the crater hosted an active fumarole field, and in March 2014, when an acidic volcanic lake covered the fumarole field. In the latter campaign, we found that 566 to 1373 t d −1 of SO 2 were being emitted from the lake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, was converted into flux of other volcanic species (H 2 O ~ 10989 t d −1 , CO 2 ~ 638 t d −1 , HCl ~ 66 t d −1 , H 2 ~ 3.3 t d −1 , and HBr ~ 0.05 t d −1 ). These levels of degassing, comparable to those seen at many open‐vent degassing arc volcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue's unusual degassing regime was also confirmed by the chemical composition of the plume that, although issuing from a hot (65°C) lake, preserves a close‐to‐magmatic signature. EQ3/6 models of gas‐water‐rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H 2 O flux (10,988 t d −1 ) suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likely common to many degassing volcanic lakes worldwide.

Soil radon emissions have been proved as a useful tool for predicting earthquakes and volcanic eruptions and furthermore aided in determining the location of active faults. Continuous radon monitoring was carried out near Southeast Crater of Mt. Etna in September–November 1998, during a period of frequent eruptive episodes at that crater. Radon anomalies were detected when eruptive episodes and the accompanying volcanic tremor became increasingly intense: no anomalies in radon activity were observed during the first five, and weaker, eruptive episodes, whereas significant spikes in radon activity preceded the latter five episodes by ≥46 hours. This probably reflects increased gas leakage through fractures intersecting the shallow plumbing system, as gas pressure in the Southeast Crater conduit became higher with time. Radon monitoring thus might serve to better understand eruptive mechanisms and possible precursors, making further studies in this field a promising perspective.

Abstract Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing and, on geological time scales, constitute an important source of volatiles to the Earth's atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO 2 , which requires proximal sampling of a concentrated plume) for those volcanoes where the near‐vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at Volcán Villarrica, Chile. We compare UAS‐derived gas time series to simultaneous crater rim multi‐GAS data and UV camera imagery to investigate early plume evolution. SO 2 concentrations measured in the young proximal plume exhibit periodic variations that are well correlated with the concentrations of other species. By combining molar gas ratios (CO 2 /SO 2 = 1.48–1.68, H 2 O/SO 2 = 67–75, and H 2 O/CO 2 = 45–51) with the SO 2 flux (142 ± 17 t/day) from UV camera images, we derive CO 2 and H 2 O fluxes of ~150 t/day and ~2,850 t/day, respectively. We observe good agreement between time‐averaged molar gas ratios obtained from simultaneous UAS‐ and ground‐based multi‐GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short‐term periodic structure that reflects active degassing through discrete, audible gas exhalations.

The chemical and isotopic compositions of the precipitation at Stromboli Island, Italy, were investigated between October 2003 and October 2005. We employed a rain gauge network designed to cover the range in exposures and elevations of the volcanic edifice. The hydrogen and oxygen isotopic ratios vary greatly on a seasonal basis and correlate with air temperature. Deuterium excess values show a positive correlation with altitude. No direct contribution of volcanogenic H or O is evident in the isotopic composition of the rainwater. The chemical composition of the rainwater is principally controlled by the sea aerosol contribution at the coastal sites, whereas it is significantly influenced by volcanic activity near the summit vents. Interaction with volcanic acid gases is indicated by the pH, which is usually 1–2 units lower near the craters than at the coastal sites. The S/Cl, Cl/F, and S/F molar ratios in rainwater 1.5 km from the craters are consistent with those measured in the volcanic plume using other methods (diffusive tubes and Fourier transform infrared spectroscopy). Rising of undegassed magmas changes these molar ratios because of the differential degassing of sulphur, chlorine, and fluorine from the magma. We therefore propose that the chemical composition of precipitation, within 1.5 km of the craters, provides additional information that is useful for monitoring volcanic activity at Stromboli Island. Moreover, this paper presents estimates of the fluxes of F, Cl, S, Na, K, Ca, and Mg to the soil that could be useful for geochemical studies on groundwater.

We present unprecedented data of real-time measurements of the concentration and isotope composition of CO2 in air and in fumarole-plume gases collected in 2013 during two campaigns at Mount Etna volcano, which were made using a laser-based isotope ratio infrared spectrometer. We performed approximately 360 measurements/h, which allowed calculation of the δ13C values of volcanic CO2 the fumarole gases of Torre del Filosofo (2900-m-above sea level) range from -3.24-±-0.06‰ to -3.71-±-0.09‰, comparable to isotope ratio mass spectrometry (IRMS) measurements of discrete samples collected on the same dates. Plume gases sampled more than 1-km from the craters show a δ13C-=2.2-±-0.4‰, in agreement with the crater fumarole gases analyzed by IRMS. Measurements performed along ∼17-km driving track from Catania to Mount Etna show more negative δ 13C values when passing through populated centers due to anthropogenic-derived CO2 inputs (e.g., car exhaust) the reported results demonstrate that this technique may represent an important advancement for volcanic and environmental monitoring. Key Points Real-time data of CO 2 content and δ13C in atmospheric/volcanic gases This study opens new perspective for the community for volcanic surveillance

We report results on the measured high 3 He/ 4 He isotope ratio in western Sicily, interpreted together with the heat data. The study of this sector of the Europe‐Africa interaction is crucial to a better understanding of the tectonics and the geodynamical evolution of the central Mediterranean area. The estimated mantle‐derived helium fluxes in the investigated areas are up to 2–3 orders of magnitude greater than those of a stable continental area. The highest flux, found in the southernmost area near the Sicily Channel, where recent eruptions of the Ferdinandea Island occurred 20 miles out to sea off Sciacca, has been associated with a clear excess of heat flow. Our results indicate that there is an accumulation of magma below the continental crust of western Sicily that is possibly intruding and out‐gassing through roughly N‐S trending deep fault systems linked to the mantle, that have an extensional component. Although the identification of these faults is not sufficiently constrained by our data, they could possibly be linked to the pre‐existing faults that originated during the Mesozoic extensional‐transtensional tectonic phases.

The noble gas isotope composition of the mantle can provide unique insights into the origin and evolution of volatile elements on Earth. Xenon isotopes combine primordial signatures with contributions from extinct and extant radionuclides, therefore offering the potential to set constraints on both the nature of Earth's planetary precursor(s) and the timing of their contributions. However, measuring the Xe isotope composition of mantle-derived samples to sufficiently high-precision has proven difficult due to (i) large occurrence of a modern-like atmospheric component in the mantle, and (ii) contribution from shallow and post-eruptive atmospheric contamination. Mantle-derived samples therefore exhibit only small deviations from the modern atmospheric composition, making the identification and deconvolution of mantle-derived Xe signals challenging. Here, we use the Giggenbach sampling method to concentrate magmatic noble gases from the Eifel volcanic area (Germany) into glass bottles in order to conduct high-precision analyses of Ne, Ar and Xe isotopes. The three samples collected from Victoriaquelle and Schwefelquelle wells (South East Eifel) show variable contributions from atmospheric contamination, with the least contaminated sample reaching 40Ar/36Ar ∼8,300. Our data indicate that the mantle beneath the Eifel volcanic area, and by extension the Central European Volcanic Province, resembles the convective upper mantle reservoir with limited evidence for an OIB-like deep plume source contribution. It has a geochemical signature that is similar (e.g. in Ne isotopic composition, 40Ar/36Ar, 129Xe/130Xe and 129Xe/136Xe) to the mantle source of the so-called popping rocks (thought to best represent the upper mantle), with an additional source of 238U-derived Xe and low 3He/4He that we attribute to the influence of an ancient subducted component (HIMU). A dichotomy exists between the main sources of fissiogenic xenon isotopes measured in popping rocks and Eifel gas, which appear to be mainly derived from 244Pu and 238U, respectively. According to their respective ratios of 244Pu- to 238U-derived Xe, the mantle sources for Eifel volcanism and popping rocks would have experienced extensive and limited degassing, respectively. In this regard, high Pu–Xe/(Pu+U)–Xe may no longer be considered as being indicative of a mantle deep origin, therefore calling for the geochemical differences between plume and MORB sources to be redefined, with the possibility that volatile signatures within the solid Earth may be more heterogeneously distributed than previously thought.

The complexity of volcano-hosted hydrothermal systems is such that thorough characterisation requires extensive and interdisciplinary work. We use here an integrated multidisciplinary approach, combining geological investigations with hydrogeochemical and soil degassing prospecting, and resistivity surveys, to provide a comprehensive characterisation of the shallow structure of the south-western Ischia’s hydrothermal system. We show that the investigated area is characterised by a structural setting that, although very complex, can be schematised in three sectors, namely the extra caldera sector (ECS), caldera floor sector (CFS), and resurgent caldera sector (RCS). This contrasted structural setting governs fluid circulation. Geochemical prospecting shows, in fact, that the caldera floor sector, a structural and topographic low, is the area where CO2-rich (>40 cm3/l) hydrothermally mature (log Mg/Na ratios <-3) waters, of prevalently meteoric origin (δ18O <-5.5 ‰), preferentially flow and accumulate. This pervasive hydrothermal circulation within the caldera floor sector, being also the source of significant CO2 soil degassing (>150 g∙m-2∙day-1), is clearly captured by electrical resistivity tomography (ERT) and transient electromagnetic (TEM) surveys as an highly conductive (resistivity <3 Ω•m) layer from depths of ~100 m, and therefore within the Mount Epomeo Green Tuff (MEGT) formation. Our observations indicate, instead, that less-thermalised fluids prevail in the extra caldera and resurgent caldera sectors, where highly conductive seawater-like (Total Dissolved Solid, TDS >10,000 mg/l) and poorly conductive meteoric-derived (TDS <4,000 mg/l) waters are observed, respectively. We finally integrate our observations to build a general model for fluid circulation in the shallowest (<0.5 km) part of Ischia's hydrothermal system.