Sawyer, G. M.

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 ofmajor,minor, trace and radioactive volatile species fromAmbrymvolcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H2O, CO2, SO2 and H2S in crater rim emissions, coupled with filter-pack determination of SO2, 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 (210Po/210Pb) and (210Bi/210Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO2/SO2 ratio (1.0 and 5.6–3.0, respectively) is attributed to deeper gasmelt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO2 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 duringmedium-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 H2O, CO2, HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO2, HF, HBr, Hg, 210Po and 210Pb, 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 feedingbasalt: this latter contains relativelymodest dissolved amounts ofH2O(≤1.3wt%), CO2 (~0.10 wt%), S (0.075 wt%) and Cl (0.05 wt%), and its degassing under prevalent closed-systemconditions 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 25m3 s−1, from a large (~ 0.5 km3)magma reservoir probably emplaced at ~3.8 km depth below the summit caldera according to both the H2O-CO2 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.

Over long periods of time (~Ma), we may consider the oceans, atmosphere and biosphere as a single exospheric reservoir for CO2. The geological carbon cycle describes the inputs to this exosphere from mantle degassing, metamorphism of subducted carbonates and outputs from weathering of aluminosilicate rocks (Walker et al. 1981). A feedback mechanism relates the weathering rate with the amount of CO2 in the atmosphere via the greenhouse effect (e.g., Wang et al. 1976). An increase in atmospheric CO2 concentrations induces higher temperatures, leading to higher rates of weathering, which draw down atmospheric CO2 concentrations (Berner 1991). Atmospheric CO2 concentrations are therefore stabilized over long timescales by this feedback mechanism (Zeebe and Caldeira 2008). This process may have played a role (Feulner et al. 2012) in stabilizing temperatures on Earth while solar radiation steadily increased due to stellar evolution (Bahcall et al. 2001). In this context the role of CO2 degassing from the Earth is clearly fundamental to the stability of the climate, and therefore to life on Earth. Notwithstanding this importance, the flux of CO2 from the Earth is poorly constrained. The uncertainty in our knowledge of this critical input into the geological carbon cycle led Berner and Lagasa (1989) to state that it is the most vexing problem facing us in understanding that cycle.

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 7–13 km 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.

Here we report results from a multidisciplinary field campaign at Villarrica volcano, Chile, in March 2009. A range of direct sampling and remote sensing techniqueswas employed to assess gas and aerosol emissions from the volcano, and extend the time series of measurements that have been made during recent years. Airborne traverses beneath the plume with an ultraviolet spectrometer yielded an average SO2 flux of 3.7 kg s−1. This value is similar to previous measurements made at Villarrica during periods of quiescent activity. The composition of the plume was measured at the crater rim using electrochemical sensors and, for the first time, open-path Fourier transforminfrared spectroscopy, yielding a composition of 90.5 mol% H2O, 5.7% CO2, 2.6%SO2, 0.9% HCl, 0.3% HF and b0.01% H2S. Comparison with previous gas measurements made between 2000 and 2004 shows a correlation between increased SO2/HCl ratios and periods of increased activity. Base-treated filter packs were also employed during our campaign, yielding molar ratios of HBr/SO2=1.1×10−4, HI/SO2=1.4×10−5 and HNO3/SO2=1.1×10−3 in the gas phase. Our data represent the most comprehensive gas inventory at Villarrica to date, and the first evaluation of HBr and HI emissions from a South American volcano. Sun photometry of the plume showed the near-source aerosol size distributions were bimodal with maxima at b0.1 and ~1 μm. These findings are consistent with results from analyses in 2003. Electron microscope analysis of particulatematter collected on filters showed an abundance of sphericalmicron-sized particles that are rich in Si, Mg and Al. Non-spherical, S-rich particles were also observed.

We report results from a multidisciplinary campaign carried out at Poás crater-lake (Costa Rica) on 17-18 March 2009. Thermal imagery of fumaroles on the north side of the dome and the lake surface revealed mean apparent temperatures of 25-40°C (maximum of 80°C), and 30-35°C (maximum of 48°C), respectively. Mean radiative heat output of the lake, uncorrected for downwelling flux, was estimated as ~230 MW. The mean SO2 flux emitted by the crater measured by walking-traverses was 76 tonnes day-1, with approximately equal contributions from both the dome and the lake and fumarole plumes. Gas measurements by active open-path FTIR spectroscopy indicated molar ratios of H2O/SO2 = 151 and CO2/SO2 = 1.56. HCl and HF were not detected in measured spectra but based on the detection limits of these species, we calculate SO2/HCl > 40, and SO2/HF > 200. Particles were sampled from the plume by air filtration. The filters were analysed using ion chromatography, which revealed an abundance of K+ and SO42-, with smaller amounts of Ca2+, Mg2+ and Cl-. We discuss here the implications of the results for degassing pathways through the shallow magmatic-hydrothermal system.

We report the first combined measurements of the composition and flux of gas emitted from Nyiragongo volcano by ground-based remote-sensing techniques. Ultraviolet spectroscopic measurements made in May/June 2005 and January 2006 indicate average SO2 emission rates of 38 kg s−1 and 23 kg s−1, respectively. Open-path Fourier transform infrared spectroscopic measurements obtained in May/June 2005, January 2006, and June 2007 indicate average molar proportions of 70, 24, 4.6, 0.87, 0.26, 0.11, and 0.0016% for H2O, CO2, SO2, CO, HCl, HF, and OCS, respectively. The composition of the plume was remarkably similar in 2005, 2006, and 2007, with little temporal variation in proportions of CO2, SO2, and CO, in particular, on the scale of seconds or days or even between the three field campaigns that span a period of 24 months. This stability persisted despite a wide range of degassing behaviors on the surface of the summit crater's lava lake (including discrete strombolian bursts and lava fountains) and variations in the SO2 emission rate. We explain these observations by a regime of steady state degassing in which bubbles nucleate and ascend in chemical equilibrium with the convecting magma. Short-term (seconds to minutes) temporal fluctuations in the SO2–HCl–HF composition were observed, and these are attributed to shallow degassing processes.

In January 2002, Nyiragongo volcano erupted 14–34 × 106 m3 of lava from fractures on its southern flanks. The nearby city of Goma was inundated by two lava flows, which caused substantial socioeconomic disruption and forced the mass exodus of the population, leaving nearly 120,000 people homeless. Field observations showed marked differences between the lava erupted from the northern portion of the fracture system and that later erupted from the southern part. These observations are confirmed by new 238U and 232Th series radioactive disequilibria data, which show the presence of three different phases during the eruption. The lavas first erupted (T1) were probably supplied by a residual magma batch from the lava lake activity during 1994–1995. These lavas were followed by a fresh batch erupted from fissure vents as well as later (May–June 2002) from the central crater (T2). Both lava batches reached the surface via the volcano's central plumbing system, even though a separate flank reservoir may also have been involved in addition to the main reservoir. The final phase (T3) is related to an independent magmatic reservoir located much closer (or even beneath) the city of Goma. Data from the January 2002 eruption, and for similar activity in January 1977, suggest that the eruptive style of the volcano is likely to change in the future, trending toward more common occurrence of flank eruptions. If so, this would pose a significant escalation of volcanic hazards facing Goma and environs, thus requiring the implementation of different volcano-monitoring strategies to better anticipate where and when future eruptions might take place.

Ground-based thermal imaging is becoming an increasingly important tool for volcano surveillance, however the impact of volcanic plumes on quantitative measurements of surface temperature has not been previously evaluated. Here we use a radiative transfer model to simulate gas (primarily H2O and SO2) and aerosol absorptions over the path between a thermal camera and a heat source on Stromboli volcano, Italy. A FTIR spectrometer was used to quantify path amounts of gases likely to be encountered when making thermal measurements of the active craters. We find that when using a camera sensitive from 7.5 to 13 mm, underestimates of 400 K may be produced when viewing a source with an actual temperature of 1200 K. Cameras that operate between 3 and 5 mm are somewhat less susceptible to these errors.

We report on the first period of the 2002 Etna eruption started on 27th October and ended on 5th November, occurring 15 months after the end of the 2001 eruption. Volcanological and geochemical data are presented in order to characterize the complex intrusion mechanism that contemporaneously involved the NE and S flanks of the volcano. Preliminary data outline that two distinct magma intrusions fed the eruptive fissures. Strong fire fountain activity mainly from the S fissure, produced copious ash fall in eastern Sicily, causing prolonged closure of Catania and Reggio Calabria airports. Lava emitted from the NE fissure formed a 6.2 km long lava flow field that destroyed the tourist facilities of Piano Provenzana area and part of Linguaglossa pine forest.