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

Mather, T.A. and Witt, M.L.I. and Pyle, D.M. and Quayle, B.M. and Aiuppa, A. and Bagnato, E. and Martin, R. S. and Sims, K.W.W. and Edmonds, M. and Sutton, A.J. and Ilyinskaya, E. (2012) Halogens and trace metal emissions from the ongoing 2008 summit eruption of Kīlauea volcano, Hawai`i. Geochimica et Cosmochimica Acta, 83. pp. 292-323. DOI 10.1016/j.gca.2011.11.029

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Abstract

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.

Item Type: Article
Uncontrolled Keywords: 2012AREP; IA63;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Geochimica et Cosmochimica Acta
Volume: 83
Page Range: pp. 292-323
Identification Number: 10.1016/j.gca.2011.11.029
Depositing User: Sarah Humbert
Date Deposited: 16 Mar 2012 08:53
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2407

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