A satellite study of the volcanic plumes produced during the April 2021 eruption of La Soufrière, St Vincent

The April 2021 explosive eruption of La Soufrière, St Vincent, produced plumes of ash and SO2 which were observed with multiple satellite instruments. In this project these were studied with the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite (GOES) and the Infrared Atmospheric Sounding Interferometer (IASI) onboard the three MetOp satellites. The high temporal resolution of the ABI instrument (1-10 minutes) was used to identify the approximate start and end times of each eruptive event during the 14-day eruption. There were a minimum of 35 explosive events which have been divided into four phases. The first was an initial explosive event, which was followed by a sustained event lasting over nine hours. The eruption then entered a pulsatory phase which consisted of 25 explosive events in a 65.3 hour period. Finally, there was a waning sequence of events. Over the final two phases, the duration of each event and the repose time between them was shown to increase. The IASI instrument has sensitivity to sulfur dioxide (SO2) which can be exploited to flag pixels containing SO2 and then to quantify the amount and height. Using IASI data, the SO2 plume was tracked as it was transported around the globe between –45 and 45° N. The retrievals showed a complex structure to the plume which may reflect the multiple explosive events that occurred. Most of the SO2 was shown to be in the upper troposphere and lower stratosphere. A peak SO2 mass loading of 0.31 ± 0.09 Tg occurred on 13 April a few days after the eruption began. The total mass values were converted into fluxes, with the highest fluxes occurring in the first few days of the eruption. In total it is estimated that the eruption emitted 0.63 ± 0.5 Tg of SO2. A number of similarities between the 1979 and 2021 eruptions of La Soufrière were observed in this study. These include the sequence of events with both eruptions including a pulsatory phase and the plume heights. These similarities highlight the value of these studies for better understanding eruptive events.