La Soufriere 2021: Recharge, remobilisation or complete renewal of a magmatic system

Volcanic eruptions that form lava domes pose a significant hazard, as they tend to last for extended periods of time (often weeks to months) and can often switch quickly from slow effusion to violent explosion. The start of a new lava dome eruption offers a rare opportunity to carry out a rapid study to understand where the new lavas came from; and to test ideas about how the eruption will progress.

On December 27, 2020, a new lava dome eruption began in the summit crater of the Eastern Caribbean volcano of La Soufriere, on the island of St Vincent, after a short period of unusual seismic activity. The new lava dome has been growing steadily, erupting on to the floor of the summit crater, next to an old lava dome that erupted in 1979. Scientists at the University of the West Indies Seismic Research Centre (SRC) have been monitoring events, and collected some new lava samples on January 16, 2021.

St Vincent had two previous lava-dome eruptions in the 1970s. In 1971-2, a lava-dome formed in the summit crater, which at that time was flooded. After 3-4 months of slow dome growth the eruption ended, and there was no explosive activity.

Scientists collected one lava dome sample at the time, and a piece of this is now held in the Smithsonian Institution in the USA. In 1979, a new eruption began with a series of violent explosions, and then switched to a steady lava-dome eruption for the next 5 months.

Our rapid-response study of the newly-erupting lavas on St Vincent will answer the question of where the new magma has come from. There are several possibilities that we anticipate, and our observations will allow us to work out which possibility is the most likely: - Is this a new batch of magma, which has just risen up into the volcano? And if so, can we understand why?

- Is this a batch of magma that was left over from an earlier eruption, which has been disturbed, and has begun to erupt as a result? And if so, can we understand how the system was disturbed?

In both cases, our findings will feed directly into the continuing investigations by the scientific team in charge of the volcano response, and will help to develop and firm up ideas about what will happen next in the eruption.