The chemistry of magmatic gases from Erta'Ale, Ethiopia

Abstract

The chemical composition of the gases emitted from a hornito close to the active lava lake of Erta'Ale, Ethiopia, as derived from chemical analyses on 18 samples collected on 23 January 1974, was found to be (in mol-%): H 2O: 79.4, CO 2: 10.4, total S: 7.36, HCl: 0.42, H 2: 1.49, N 2: 0.18, Ar: 0.001, CO: 0.46, and COS: 0.009. Thermodynamic considerations, based on the equilibria CO 2 + H 2 ⇌ CO + H 2 O and CO 2 + 3 H 2 + SO 2 ⇌ COS + 3 H 2 O show that the analytical values represent the equilibrium composition of a gas mixture at the measured temperature of around 1130°C under close to the surface pressure conditions. Comparison of the Erta'Ale gas emissions with those from other volcanoes suggests a close similarity in their chemical composition. This similarity is considered to be due to common processes governing the release of gaseous species from a magma.