Mount Etna and the 1971 eruption - Oxygen and sulphur fugacities of magmatic gases directly measured in active vents of Mount Etna

Abstract

Solid-electrolyte sensors were used to measure the oxygen and sulphur fugacities of magmatic gases in vents located at an elevation of about 3170 m on the northeast flank of the NE crater of Mt Etna in July 1970. The temperature of the gas ranged from 773 to 1057 °C. The least-squares fit of 13 measured lgfo2 values yielded the relation: lg/o2 (atm) = 2.175- 15110/T (K), which gives values of 0.9 to 2.2 lgfo2 units higher than those obtained in the Makaopuhi lava lake, Hawaii, within the temperature range measured, the difference increasing with decreasing temperature. Laboratory study of a water-quenched sample of the Etna lava and calculations of gas equilibria indicate that the difference is due partly to the intrinsically higher f 02 of the Etna magma and partly to the mixing of air with the Etna gases. The measured j^2 value was 10-2 4 atm at 860 °C.