Analysis of magma flux and eruption intensity during the 2021 explosive activity at the Soufrière of St Vincent, West Indies

Seismic RSAM signals and eruption cloud height measurements were used to estimate peak intensities of 40 explosive events during the 8-22 April 2021 activity of the Soufrière volcano. We estimated magma supply rates and erupted volumes in each explosion, characterized uncertainty by stochastic modelling and identified four eruptive stages. Stage 1 included an intense period of 9.5 hours with 11 explosive events with peak eruption intensity between 2000 and 4000 m3/s and magma supply rate reaching 828 m3/s. 12 high intensity explosions (∼4000 m3/s) occurred in Stage 2 with average magma supply rate of 251 m3/s. Stage 3 involved declining intensity, magma supply rate and lengthening repose periods between explosions. Stage 4 involved 3 much weaker explosions. The total erupted volume of magma is estimated at 38.5 × 106 m3 (90% credible interval: [22.0 .. 61.9] × 106 m3) consistent with independent estimates from analysis of tephra deposits and volcano subsidence sourced at ∼6 km depth. The 150-fold increase in magma supply rate, from the preceding effusive phase to Stage 1 of the explosive phase, is attributed to replacement of very high viscosity degassed magma occupying the shallow conduit system with new lower viscosity volatile-rich magma from the magma chamber.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6558003