Satellite measurements of plumes from the 2021 eruption of La Soufrière, St Vincent

Abstract. Satellite instruments play a valuable role in detecting, monitoring and characterising emissions of ash and gas into the atmosphere during volcanic eruptions. Plumes of ash and sulfur dioxide (SO2) from the April 2021 eruption of La Soufrière volcano on St Vincent in the Eastern Caribbean were observed by a multiple satellite instruments. This study looks at these plumes with two satellite instruments: the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite (GOES), and the Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp platforms. Using true and false colour images, and brightness temperature difference images produced from the ABI data, a minimum of 32 eruptive events were identified. The ABI images were used to determine the approximate start and end times and character of each event. In this way the eruption has been divided into four phases: (1) an initial explosive event, (2) a sustained event lasting over nine hours, (3) a pulsatory phase with 23 explosive events in a 54 hour period and (4) a waning sequence of explosive events. The IASI instrument was used to study the dispersion of SO2 from this eruption. The results showed a highly complex structure to the plume, in terms of the column amounts and height, which is likely linked to the multiple explosive events. The SO2 is shown to have largely been emitted between 13 and 19 km. This was primarily in the upper troposphere and around the height of the tropopause, but with some emission into the stratosphere. The SO2 was transported around the globe with parts of the plume reaching as far as 45° S and 45° N. The largest SO2 atmospheric burden measured with IASI was 0.31±0.09 Tg, recorded on the 13 April 2021 (descending orbits). The SO2 masses were converted into fluxes. The SO2 flux was shown to peak on 10 April and then shown to decrease over time. By summing the IASI SO2 flux results, it is estimated that a total of 0.57±0.44 Tg of SO2 was emitted to the atmosphere. However, due to the limitations associated with the retrieval this should be considered a minimum estimate of the total mass of SO2 emitted. An average e-folding time of 7.09±5.70 days was computed based on the IASI SO2 results: similar to other tropical eruptions of this magnitude. There are a number of similarities between the 1979 and 2021 eruptions at La Soufrière. For example, both eruptions consisted of a series of explosive events with varied heights including some emission into the stratosphere. The similarities between the 1979 and 2021 highlight the importance of studying these eruptions to be prepared for future activity.