Metal transport in volcanic plumes: A case study at White Island and Yasur volcanoes

Abstract

We report new data on trace metal emissions at White Island volcano (2015–2016), the first estimates from Yasur volcano (2016), and a brief review of global volcanic metal fluxes. Bi, Cd, Tl, Se, Sb, Te and Au are the most enriched metals and metalloids in the particulate phase of volcanic plumes. Observations of the particulate phase from the volcanic plumes of White Island, Yasur and Etna reveal abundant silicates and sulfates, sulfuric acid and more interestingly Zn oxide containing variable amounts of Cu. Thermodynamic speciation calculations show chloride species to be very important in terms of gaseous metal transport. Complexation with sulfur, in contrast, appears significant only in S-rich and Cl-poor gases, at high (>700 °C) temperature. Bromine, despite being a minor component of volcanic gases, is very efficient at complexing with metals, and especially with Cu, Pb, Bi, Zn and Cr. Metal emission rates in the study period at White Island are one to two orders of magnitude lower than reported previously, with ~6–10 kg/d of Cu, As, Se and Zn, and <2 kg/d of Pb, Bi, Tl, Sb, Te and Cd. Higher values were measured at Yasur volcano, ranging from ~175 kg/d of Cu, ~30 kg/d of As, Zn and Pb, and ~3 kg/d of Tl and Cd. Such fluxes of toxic metals are significant, representing a potential threat for local populations. We compare our new data to previously reported metal emissions from volcanoes worldwide, and show that high halogen emissions appear as the critical parameter controlling metal emissions, explaining the high metal fluxes measured at some intraplate volcanoes.