Abstract

Real-time Seismic Amplitude Measurement signals and eruption cloud height measurements were used to estimate peak intensities of 40 explosive events during the 8-22 April 2021 activity of La Soufriere 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 m(3) s(-1) and magma supply rate reaching 828 m(3) s(-1). Twelve high-intensity explosions (c. 4000 m(3) s(-1)) occurred in Stage 2 with average magma supply rate of 251 m(3) s(-1). Stage 3 involved both declining intensity and magma supply rate and lengthening repose periods between explosions. Stage 4 involved three much weaker explosions. The total erupted volume of magma is estimated at 38.5 x 10(6) m(3) (90% credible interval: [22.0.. 61.9] x 10(6) m(3)) consistent with independent estimates from analysis of tephra deposits and volcano subsidence sourced at c. 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, lowerviscosity, volatile-rich magma from the magma chamber.