White Island volcano, New Zealand: carbon dioxide and sulfur dioxide emission rates and melt inclusion studies

Abstract

CO 2 and SO 2 emission rates are reported for the volcanic gas plume from White Island, the most active volcano in New Zealand. SO 2 emission rates were measured 16 times by correlation spectrometer (COSPEC) from 1986 to 1999 and range from 171 to 900 Mg day −1. We estimate the average SO 2 emission rate was 430±70 Mg day −1 between 1983 and 1999. CO 2 emission rates of 2570 and 2650 Mg day −1 were determined in January 1998 by aircraft directly in the plume using a CO 2 analyzer and a ladder survey technique. Using the average SO 2 emission rate and a CO 2/S weight ratio of 3.6 previously reported for fumarole samples collected from the crater floor, an indirect estimate of the CO 2 is 1550 Mg day −1. A soil gas survey of CO 2 emissions from the crater floor gave an emission rate of 8.7 Mg day −1. Soil gases contribute less than 1% of the total CO 2 emitted from this volcano and show that the magmatic degassing of the underlying andesite magma is mostly isolated to the active crater and associated fumaroles. Volatile elements (H 2O, Cl, F, S) were measured in melt inclusions trapped in plagioclase and clinopyroxene crystals. The low H 2O contents (0.6±0.2 wt.%) of melt inclusions suggest that crystal formation occurs at pressures of 35 to 70 bars. The Cl contents of melt inclusions (0.10–0.18 wt.%) are higher than that of matrix glass (0.11 wt.%), suggesting Cl was lost from the magma between the time of crystallization and eruption. Therefore, Cl degassing also occurred in part at shallow depths in the magmatic system. The low SO 2 contents of both melt inclusions and matrix glass implies that it exsolves at depths greater than 300 m. CO 2 is insoluble in andesitic magma and probably was degassing with SO 2 at depths >300 m within the magmatic system.