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This short communication aims at providing an updated report on degassing activity and ground deformation variations observed during the ongoing (2012–2019) Campi Flegrei caldera unrest, with a particular focus on Pisciarelli, currently its most active fumarolic field. We show that the CO2 flux from the main Pisciarelli fumarolic vent (referred as “Soffione”) has increased by a factor > 3 since 2012, reaching in 2018–2019 levels (>600 tons/day) that are comparable to those typical of a medium-sized erupting arc volcano. A substantial widening of the degassing vents and bubbling pools, and a further increase in CO2 concentrations in ambient air (up to 6000 ppm), have also been detected since mid-2018. We interpret this escalating CO2 degassing activity using a multidisciplinary dataset that includes thermodynamically estimated pressures for the source hydrothermal system, seismic and ground deformation data. From this analysis, we show that degassing, deformation and seismicity have all reached in 2018–2019 levels never observed since the onset of the unrest in 2005, with an overall uplift of ~57 cm and ~448 seismic events in the last year. The calculated pressure of the Campi Flegrei hydrothermal system has reached ~44 bar and is rapidly increasing. Our results raise concern on the possible evolution of the Campi Flegrei unrest and reinforce the need for careful monitoring of the degassing activity at Pisciarelli, hopefully with the deployment of additional permanent gas monitoring units.

Obtaining accurate estimates of the CO2 output from arc volcanism requires a precise understanding of the potential along-arc variations in volcanic gas chemistry, and ultimately of the magmatic gas signature of each individual arc segment. In an attempt to more fully constrain the magmatic gas signature of the Central America Volcanic Arc (CAVA), we present here the results of a volcanic gas survey performed during March and April 2013 at five degassing volcanoes within the Costa Rica-Nicaragua volcanic segment (CNVS). Observations of the volcanic gas plume made with a multicomponent gas analyzer system (Multi-GAS) have allowed characterization of the CO2/SO2-ratio signature of the plumes at Pads (0.30 +/- 0.06, mean +/- SD), Rincon de la Vieja (27.0 +/- 15.3), and Turrialba (2.2 +/- 0.8) in Costa Rica, and at Telica (3.0 +/- 0.9) and San Cristobal (4.2 +/- 1.3) in Nicaragua (all ratios on molar basis). By scaling these plume compositions to simultaneously measured SO2 fluxes, we estimate that the CO2 outputs at CNVS volcanoes range from low (25.5 +/- 11.0 tons/day at Pods) to moderate (918 to 1270 tons/day at Turrialba). These results add a new information to the still fragmentary volcanic CO2 output data set, and allow estimating the total CO2 output from the CNVS at 2835 1364 tons/day. Our novel results, with previously available information about gas emissions in Central America, are suggestive of distinct volcanic gas CO2/S-T (= SO2 + H2S)-ratio signature for magmatic volatiles in Nicaragua (similar to 3) relative to Costa Rica (similar to 0.5-1.0). We also provide additional evidence for the earlier theory relating the CO2-richer signature of Nicaragua volcanism to increased contributions from slab-derived fluids, relative to more-MORB-like volcanism in Costa Rica. The sizeable along-arc variations in magmatic gas chemistry that the present study has suggested indicate that additional gas observations are urgently needed to more-precisely confine the volcanic CO2 from the CAVA, and from global arc volcanism.

With this short communication we address the principal issues raised by Delmelle et al. (2014) in relation to the work of Bagnato et al. (2013) concerning the 2010 eruption of Eyjafjallajokull, Iceland. The principal conclusions of the work of Bagnato et al. (2013) include the observation that protracted gas-aerosol interaction in the plume promotes selective leaching of cation species from ash, with alkalis and Ca (and, among trace elements, Zn and Cu) being more rapidly re-mobilized (and transferred to soluble surface salts) relative to more inert elements (Mg, Ti). They also observed that adsorption onto ash surfaces is a major atmospheric sink of volcanic acidic gases, with 282 tons of elemental sulfur and 605–691 tons of halogens being daily ground deposited via ash over Iceland in early May 2010. Acidic gas adsorption onto ash increases almost linearly with plume aging (e.g., upon increasing in-plume residence times of ash and gases), and is seen to proceed at about 3 time faster rates for HF than for SO2 and HCl. However, Delmelle et al. (2014) criticized our strategies for data acquisition, processing and interpretation. They also raised some objections concerning several key topics explored by Bagnato et al. (2013) , with a special focus on the discussion of rates of interaction between ash particles and gases in a volcanic cloud, and the consequent formation of soluble salts on ash surfaces. They also considered incorrect the estimate of depositional fluxes and volatile budget for the Eyjafjallajokull eruption. While we appreciate the in-depth analysis of Delmelle et al. (2014) , we show that most of their criticisms derive from a partial and sometimes incorrect understanding of the work of Bagnato et al. (2013) , which overall led to unsupported conclusions and misleading analysis of the original results. Here, we present a detailed response to the comments of Delmelle et al. (2014) , accompanied by additional explicative material. The principal conclusions presented in Bagnato et al. (2013) are given additional support by this complementary note.

The Eyjafjallajökull volcanic eruption in 2010 released considerable amounts of ash into the high troposphere-low stratosphere, leading to unprecedented disruption of air traffic over Europe. The role of such fine-grained tephra in adsorbing, and therefore rapidly scavenging, volcanogenic volatile elements such as sulphur and halogens, is explored here. We report on results (major to trace element chemistry) of leaching experiments carried out on 20 volcanic ash samples, taken from the deposits of the main phases of the eruption (March–April 2010), or directly while falling (5–9 May 2010). Ash leachate solutions from Eyjafjallajökull are dominated – among cations – by Ca and Na, and display nearly equal S:Cl:F abundances (mean S/Cl and S/F molar ratios of 0.95 and 0.34, respectively). Abundances of major elements on surface minerals from freshly fallen ash are found to increase linearly upon increasing distance from the eruptive vents (a proxy for in-plume residence times). This allows for the formation rates of sulphur- and halogen-bearing surface salts to be quantified (3 × 10−9 to 2 × 10−8 mol m2 s−1), and for the averaged rate of in-plume ash-dissolution to be estimated (1.5 × 10−8 mol m−2 s−1; this sourcing the majority of cation species to soluble surface salts). These fast in-plume heterogeneous reactions are the cause of large volatile depositions: we estimate that 282 tons of elemental S, 605 tons of Cl, and 691 tons of F were daily ground deposited via ash over Iceland in early May 2010. Since fluorine is ∼3 times more rapidly processed in the plume than S and halogens (e.g., F is extremely reactive both in gas and aerosol forms and it is rapidly adsorbed onto ash), ash leachate compositions are in no way representative of S:Cl:F proportions in volcanic gases, and consequently of limited use in eruption monitoring.

There have been limited studies to date targeting mercury emissions from volcanic fumarolic systems, and no mercury flux data exist for soil or fumarolic emissions at Santorini volcanic complex, Greece. We present results from the first geochemical survey of Hg and major volatile (CO2, H2S, H2O and H-2) concentrations and fluxes in the fumarolic gases released by the volcanic/hydrothermal system of Nea Kameni islet; the active volcanic center of Santorini. These data were obtained using a portable mercury spectrometer (Lumex 915+) for gaseous elemental mercury (GEM) determination, and a Multi-component Gas Analyzer System (Multi-GAS) for major volatiles. Gaseous Elemental Mercury (GEM) concentrations in the fumarole atmospheric plumes were systematically above background levels (similar to 4 ng GEM m(-3)), ranging from similar to 4.5 to 121 ng GEM m(-3). Variability in the measured mercury concentrations may result from changes in atmospheric conditions and/or unsteady gas release from the fumaroles. We estimate an average GEM/CO2 mass ratio in the fumarolic gases of Nea Kameni of approximately 10(-9), which falls in the range of values obtained at other low-T (100 degrees C) volcanic/hydrothermal systems (similar to 10(-8)); our measured GEM/H2S mass ratio (10(-5)) also lies within the accepted representative range (10(-4) to 10(-6)) of non-explosive volcanic degassing. Our estimated mercury flux from Nea Kameni's fumarolic field (2.56 x 10(-7) t yr(-1)), while making up a marginal contribution to the global volcanic non-eruptive GEM emissions from closed-conduit degassing volcanoes, represents the first available assessment of mercury emissions at Santorini volcano, and will contribute to the evaluation of future episodes of unrest at this renowned volcanic complex.

We report measurements of Hg, SO2, and halogens (HCl, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gaseous SO2 and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO2 and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m-3. Hg/SO2 mass ratios measured with the real-time instruments ranged from 1.1 × 10-7 to 3.5 × 10-5 (mean 2 × 10-5). Total gaseous mercury (TGM) concentrations measured by gold trap ranged from 100 to 225 ng m-3. Reactive gaseous mercury accounted for 1% of TGM, while particulate mercury was 5% of the TGM. Field measurements of Masaya's SO2 flux, combined with the Hg/SO2 ratio, indicate a Hg flux from Masaya of 7.2 Mg a-1. At Masaya's low temperature famaroles, Hg/CO2 mass ratios were consistently around 2 × 10-8, lower than observed in the main vent (Hg/C02 ∼ 10-7). Low-temperature fumarole Hg fluxes from Masaya are insignificant (∼150 g a-1). Ratios of S, C and halogen species were also measured at Masaya and Telica volcanoes. CO2/ SO2 ratios at Masaya ranged from 2.8 to 3.9, comparable to previously published values. At Masaya molar Br/SO2 was 3 × 10-4 and I/SO2 was 2 × 10-5, suggesting fluxes of 0.2-0.5 Mg HBr d-1 and 0.02-0.05 Mg HI d-1. At Telica the Br/SO2 ratio was also 3 × 10-4 and the I/SO2 ratio was 5.8 × 10-5, with corresponding fluxes of 0.2 Mg HBr d-1 and 0.06 Mg HI d-1. Gases at both volcanoes are enriched in I relative to Br and Cl, compared to gases from volcanoes elsewhere. Copyright 2008 by the American Geophysical Union.

Volcanic plume samples taken in 2008 and 2009 from the Halemàumàu eruption at Kīlauea provide new insights into Kīlauea's degassing behaviour. The Cl, F and S gas systematics are consistent with syn-eruptive East Rift Zone measurements suggesting that the new Halemàumàu activity is fed by a convecting magma reservoir shallower than the main summit storage area. Comparison with degassing models suggests that plume halogen and S composition is controlled by very shallow (77%) as gaseous elemental mercury at the point of emission. Sulphate is an important aerosol component (modal particle diameter ∼0.44μm). Aerosol halide ion concentrations are low compared to other systems, consistent with the lower proportion of gaseous hydrogen halides. Plume concentrations of many metallic elements (Rb, Cs, Be, B, Cr, Ni, Cu, Mo, Cd, W, Re, Ge, As, In, Sn, Sb, Te, Tl, Pb, Mg, Sr, Sc, Ti, V, Mn, Fe, Co, Y, Zr, Hf, Ta, Al, P, Ga, Th, U, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm) are elevated above background air. There is considerable variability in metal to SO 2 ratios but our ratios (generally at the lower end of the range previously measured at Kīlauea) support assertions that Kīlauea's emissions are metal-poor compared to other volcanic settings. Our aerosol Re and Cd measurements are complementary to degassing trends observed in Hawaiian rock suites although measured aerosol metal/S ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry. Plume enrichment factors with respect to Hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed (i.e., lithophile elements having lower volatility and chalcophile elements having higher volatility). The proportion of metal associated with the largest particle size mode collected (>2.5μm) and that bound to silicate is significantly higher for lithophiles than chalcophiles. Many metals show higher solubility in pH 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility. Nonetheless, many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form. Preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog. However, metal levels in grass samples showed no clear enrichment downwind of the active vents. © 2011 Elsevier Ltd.

A major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. These results contrast with an earlier model study and allow us to explain recent measurements of Hg speciation at the crater rim of Etna without invoking rapid (

Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H 2 O, CO 2 , SO 2 and H 2 S in crater rim emissions, coupled with filter-pack determination of SO 2 , halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content (~ 93 mol%), similar S/Cl, Cl/F, Br/Cl molar ratios, similar ( 210 Po/ 210 Pb) and ( 210 Bi/ 210 Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO 2 /SO 2 ratio (1.0 and 5.6–3.0, respectively) is attributed to deeper gas-melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO 2 plume flux (90 kg s − 1 or 7800 tons d − 1 ) demonstrates a prevalent degassing contribution (~ 65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H 2 O, CO 2 , HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO 2 , HF, HBr, Hg, 210 Po and 210 Pb, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest dissolved amounts of H 2 O (≤ 1.3 wt%), CO 2 (~ 0.10 wt%), S (0.075 wt%) and Cl (0.05 wt%), and its degassing under prevalent closed-system conditions well reproduces the composition of emitted volcanic gases. Instead, we show that the gas discharge is sustained by a very high basalt supply rate of 25 m 3 s − 1 , from a large (~ 0.5 km 3 ) magma reservoir probably emplaced at ~ 3.8 km depth below the summit caldera according to both the H 2 O-CO 2 content of bubble-free melt inclusions and preliminary seismic data. Radioactive disequilibria in the volcanic gases constrain that this reservoir may be entirely renewed in about 240 days. The comparatively low magma extrusion rate requires extensive convective overturn of the basaltic magma column and recycling of the unerupted (denser) degassed magma in the plumbing system, in agreement with textural features of erupted products. Finally, our results suggest that the Indian MORB-type mantle source of Ambrym basalts is modestly enriched in slab-derived water and other volatiles, in agreement with the prevalent volcanoclastic nature of subducted sediments and their lower subduction rate under the central Vanuatu arc due to its collision with the D'Entrecasteaux Ridge.

There have been limited studies to date targeting gaseous elemental mercury (GEM) flux from soil emission in enriched volcanic substrates and its relation with CO 2 release and tectonic structures. In order to evaluate and understand the processes of soil–air exchanges involved at Solfatara of Pozzuoli volcano, the most active zone of Campi Flegrei caldera (Italy), an intensive field measurement survey has been achieved in September 2013 by using high-time resolution techniques. Soil–air exchange fluxes of GEM and CO 2 have been measured simultaneously at 116 points, widely distributed within the crater. Quantification of gas flux has been assessed by using field accumulation chamber method in conjunction with a Lumex®-RA 915 + portable mercury vapor analyzer and a LICOR for CO 2 determination, respectively. The spatial distribution of GEM and CO 2 emissions correlated quite closely with the hydrothermal and geological features of the studied area. The highest GEM fluxes (from 4.04 to 5.9 × 10 − 5 g m − 2 d − 1 ) were encountered close to the southern part of the crater interested by an intense fumarolic activity and along the SE–SW tectonic fracture (1.26 × 10 − 6 –6.91 × 10 − 5 g GEM m − 2 d − 1 ). Conversely, the lowest values have been detected all along the western rim of the crater, characterized by a weak gas flux and a lush vegetation on a very sealed clay soil, which likely inhibited mercury emission (range: 1.5 × 10 − 7 –7.18 × 10 − 6 g GEM m − 2 d − 1 ). Results indicate that the GEM exchange between soil and air inside the Solfatara crater is about 2–3 orders of magnitude stronger than that in the background areas (10 − 8 –10 − 7 g m − 2 d − 1 ). CO 2 soil diffuse degassing exhibited an analogous spatial pattern to the GEM fluxes, with emission rates ranging from about 15 to ~ 20,000 g CO 2 m − 2 d − 1 , from the outermost western zones to the south-eastern sector of the crater. The observed significant correlation between GEM and CO 2 suggested that in volcanic system GEM volatilizes from substrate in a similar manner to the release of CO 2 . The quantitative estimation of the total amount of CO 2 and GEM released from the Solfatara crater gave values of about 304 ± 13 and 3.7 ± 0.2 × 10 − 6 t d − 1 , respectively. Finally, based on our dataset and previous work, we propose that an average GEM/CO 2 molar ratio of ~ 2 × 10 − 8 ( n = 9) is best representative of hydrothermal degassing. Taking into account the uncertainty in global hydrothermal CO 2 emissions from sub-aerial environments (~ 10 12 Mol yr − 1 ), we infer a global volcanic GEM flux from hydrothermal environments of ~ about 8.5 t yr − 1 . Although this value has to be considered as a lower limit for the global emission of GEM from these sources, we suggest that on a local scale hydrothermal activity can be regarded as a significant source of GEM than previously recognized to the atmospheric pool.

Mt. Etna is a major natural source of Hg to the Mediterranean region. Total mercury concentrations, [Hg] tot, in Castanea sativa (sweet chestnut) leaves sampled 7-13km from Etna's vents (during six campaigns in 2005-2011) were determined using atomic absorption spectroscopy. [Hg] tot in C. sativa was greatest on Etna's SE flank reflecting Hg deposition from the typically overhead volcanic plume. [Hg] tot also showed Hg accumulation over the growing season, increasing with leaf age and recent eruptive activity. [Hg] tot in C. sativa was not controlled by [Hg] tot in soils, which instead was greatest on Etna's NW flank, and was correlated with the proportion of organic matter in the soil (% Org). An elevated [Hg] tot/% Org ratio in soils on Etna's SE flank is indicative of increased Hg deposition. This ratio was also found to decrease with local soil pH, suggesting that Hg deposited to the low pH and organic-poor soils on Etna's SE flank may not be retained but will instead be released to groundwater or re-emitted to the atmosphere. These results show that the deposition of volcanic Hg has clear impacts and confirm that Etna is an important source of Hg to the local environment. © 2012 Elsevier B.V.

[1] Many volcanoes show a change in chemical composition of the gas phase prior to periods of eruptive activity. Fine-grained tephra erupted from active vents and transported through volcanic plumes can adsorb, and therefore rapidly scavenge, volatile elements such as sulfur, halogens, and metal species in the form of soluble salts adhering to ash surfaces. Analysis of such water-soluble surface materials is a suitable supplement for remote monitoring of volcanic gases at inaccessible volcanoes. In this work, ash samples of the 2004 to 2009 eruptive activity of Stromboli volcano were sampled, leached, and analyzed for major and trace elements. Data analysis and interpretation was focused on determining the relationship between chemical composition of water-soluble components adhering to volcanic ash and the volcano's activity state. First results show significant temporal variations in ash leachate compositions, reflecting changes in the eruptive style of the volcano. In particular, we reveal that ash leachates S/F and Mg/Na ratios showed marked increases prior to a large-scale explosion on 15 March 2007.

This study reports on the first quantitative assessment of the geochemical cycling of volcanogenic elements, from their atmospheric release to their deposition back to the ground. Etna’s emissions and atmospheric depositions were characterised for more than 2 years, providing data on major and trace element abundance in both volcanic aerosols and bulk depositions. Volcanic aerosols were collected from 2004 to 2007, at the summit vents by conventional filtration techniques. Precipitation was collected, from 2006 to 2007, in five rain gauges, at various altitudes around the summit craters. Analytical results for volcanic aerosols showed that the dominant anions were S, Cl, and F, and that the most abundant metals were K, Ca, Mg, Al, Fe, and Ti (1.5–50 μg m−3). Minor and trace element concentrations ranged from about 0.001 to 1 μg m−3. From such analysis, we derived an aerosol mass flux ranging from 3000 to 8000 t a−1. Most analysed elements had higher concentrations close to the emission vent, confirming the prevailing volcanic contribution to bulk deposition. Calculated deposition rates were integrated over the whole Etna area, to provide a first estimate of the total deposition fluxes for several major and trace elements. These calculated deposition fluxes ranged from 20 to 80 t a−1 (Al, Fe, Si) to 0.01–0.1 t a−1 (Bi, Cs, Sc, Th, Tl, and U). Comparison between volcanic emissions and atmospheric deposition showed that the amount of trace elements scavenged from the plume in the surrounding of the volcano ranged from 0.1% to 1% for volatile elements such as As, Bi, Cd, Cs, Cu, Tl, and from 1% to 5% for refractory elements such as Al, Ba, Co, Fe, Ti, Th, U, and V. Consequently, more than 90% of volcanogenic trace elements were dispersed further away, and may cause a regional scale impact. Such a large difference between deposition and emission fluxes at Mt. Etna pointed to relatively high stability and long residence time of aerosols in the plume.