Sweet chestnut (Castanea sativa) leaves as a bio-indicator of volcanic gas, aerosol and ash deposition onto the flanks of Mt Etna in 2005-2007

Sweet chestnutleaves (Castanea sativa) collected from the flanks of Mt Etna volcano in 2005–2007 were analysed by inductively-coupled plasma mass spectrometry to investigate the spatial and temporal variability of element concentrations. The aim of this work was to determine whether these leaves are a bio-indicator for volcanic gas, aerosol and ash deposition and to gain new insights into the environmental effects of quiescent and eruptive volcanic plumes. Results show a positive correlation between sample variability in the concentration of elements in Castanea sativa and enrichment factors of elements in the plume. The spatial and temporal variability of chalcophilic elements (As, Cd, Cu, Mo, Tl, Zn) is consistent with prevailing winds transporting eruptive plumes to the south-east of the summit, resulting in enhanced plume deposition onto the flanks of the volcano. Similar spatial and temporal variability was found for the halide-forming elements (Cs, K, Rb) and intermediate elements (Al, Co, Mn). The spatial variability of chalcophilic, intermediate and halide-forming elements during quiescent periods was diminished (relative to eruptive periods) and could not be explained by plume deposition. In contrast, the concentrations of lithophilic elements (Ba, Ca, Mg, Sr) did not show any clear spatial variability even during eruptive periods. Comparisons between enrichment factors for elements in Castanea sativa and literature values for enrichment factors of the volcanic plume, groundwater and lichen were made. Whilst Castanea sativa offers insights into the spatial and temporal variability of deposition, the species may not be a bio-indicator for plume composition due to biological fractionation

Bioindication of volcanic mercury (Hg) deposition around Mt. Etna (Sicily)

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 environmen

Halogens and trace metal emissions from the ongoing 2008 summit eruption of Kīlauea volcano, Hawai`i

Volcanic plume samples taken in 2008 and 2009 from the Halema`uma`u 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 Halema`uma`u 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 (<3 m depth) decompression degassing and progressive loss of volatiles at the surface. Compared to most other global volcanoes, Kīlauea’s gases are depleted in Cl with respect to S. Similarly, our Br/S and I/S ratio measurements in Halema`uma`u’s plume are lower than those measured at arc volcanoes, consistent with contributions from the subducting slab accounting for a significant proportion of the heavier halogens in arc emissions. Analyses of Hg in Halema`uma`u’s plume were inconclusive but suggest a flux of at least 0.6 kg day−1 from this new vent, predominantly (>77%) as gaseous elemental mercury at the point of emission. Sulphate is an important aerosol component (modal particle diameter ∼0.44 μm). 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 SO2 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 (>2.5 μm) 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

(33)S MAS NMR of a disordered sulfur-doped silicate: signal enhancement via RAPT, QCPMG and adiabatic pulses

Three different signal enhancement techniques have been applied to (33)S magic-angle spinning nuclear magnetic resonance (MAS NMR) of a disordered silicate containing 1.15 wt% (33)S. Partial saturation of the satellite transitions was achieved using a rotor-assisted population transfer (RAPT) pulse sequence, resulting in a signal enhancement of 1.63, albeit with a slight distortion of the line shape due to selective excitation. Adiabatic inversion of the satellite transitions by various amplitude-and frequency-modulated pulse shapes (such as hyperbolic secant and wideband uniform-rate smooth truncation) was also attempted, resulting in a signal enhancement of up to 1.85, with no apparent line shape distortion. Quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) and RAPT-QCPMG sequences were also used, both of which yielded spikelet spectra that accurately reflected the MAS line shape with a greatly improved signal-to-noise ratio. It is hoped that this study demonstrates that (33)S solid-state MAS NMR is now feasible even on disordered, low-sulfur-content systems

Magma storage, transport and degassing during the 2008–10 summit eruption at Kīlauea Volcano, Hawai‘i

The 2008–current summit eruption at Kīlauea Volcano, Hawai‘i offers a unique opportunity to test models of degassing and magma plumbing and to improve our understanding of the volatile budget. The aim of this work was to test the hypothesis that gases emitted from a summit lava lake will be rich in carbon dioxide (CO2) and similar to those measured during the persistent lava lake activity in the early 20th century at Kīlauea Volcano (Gerlach and Graeber, 1985). We measured the sulfur dioxide (SO2) and CO2 concentrations in the gas plume from Halema‘uma‘u using electrochemical and non-dispersive infrared sensors during April 2009. We also analysed olivine-hosted melt inclusions from tephra erupted in 2008 and 2010 for major, trace and volatile elements. The gas and melt data are both consistent with the equilibration of a relatively evolved magma batch at depths of 1.2–2.0 km beneath Halema‘uma‘u prior to the current degassing activity. The differences in the volatile concentrations between the melt inclusions and matrix glasses are consistent with the observed gas composition. The degassing of sulfur and halogen gases from the melt requires low pressures and hence we invoke convection to bring the magma close to the surface to degas, before sinking back into the conduit. The fluxes of gases (900 and 80 t/d SO2 and CO2 respectively) are used to estimate magma fluxes (1.2–3.4 m3/s) to the surface for April 2009. The observation of minimal loss of hydrogen from the melt inclusions implies a rapid rise rate (less than a few hours), which constrains the conduit radius to 1–2 m. The inferred conduit radius is much narrower than the lava lake at the surface, implying a flared geometry. The melt inclusion data suggest that there is a progressive decrease in melt volatile concentrations with time during 2008–2010, consistent with convection, degassing and mixing in a closed, or semi-closed magma system. The degassing regime of the current summit lava lake activity is not similar to that observed in the early 20th century; instead the gases are extensively depleted in CO