Volcanic gases emitted during mild Strombolian activity of Villarrica volcano, Chile

The composition of volcanic gas emitted during mild Strombolian activity at the summit of Villarrica volcano ( Chile) was estimated based on plume measurements at the rim of the summit crater about 100 m downwind of the vent, by application of a Portable Multi-Sensor System, Alkaline Filter Pack and Gas Detection Tubes. Comparison of the measured volcanic gas composition with volatile contents in a gas-rich melt inclusion indicates that the gas separation from magma occurs at low pressure. The measured H2O/CO2 and CO2/SO2 ratios of the gas were constant for about two hours during the measurements in spite of intermittent lava spattering from the vent, indicating that the gas emitted with the spattering lava has the same composition as the continuously emitted volcanic gas. This implies the lava spattering is not driven by bubbles supplied at depth but caused by bursting of bubbles formed under equilibrium with the magma.