Volatile emissions and magma storage conditions for the 2021 explosive eruption at La Soufrière volcano, St Vincent, from melt inclusions

Abstract

The VEI 4 eruption of La Soufrière Volcano underwent a dramatic transition in style from initial lava dome effusion in December 2020 to hazardous explosive activity in April 2021. Understanding the magmatic processes underpinning such transitions is critical. We provide the first comprehensive dataset of the compositions and volatile contents of melt inclusions from the 2021 explosive activity, including the first measurements of pre-eruptive total CO₂ at La Soufrière and estimates of magmatic temperature. We use the petrological method to quantify volatile fluxes to the atmosphere of 5.40 ± 0.60 Mt H₂O, 0.37 ± 0.04 Mt CO₂, 0.13 ± 0.01 Mt SO₂, and 0.33 ± 0.04 Mt HCl. Modelling of volatile saturation pressures indicates final magma storage depths of 2.4–8.9 km (mean 6.4 km) throughout four phases of explosive activity after migration of magma in the lower storage region within the transcrustal mush system. Inferred depths are consistent with recorded seismicity and deformation before and during the explosions.