Bequia and the Grenadines: La Soufrière volcano St. Vincent

Soufrière in state of effusive eruption

The volcano in the north of St. Vincent has entered a state of effusive eruption since the 27th of December 2020. This was first noticed through satellite imagery used for tracking high temperatures (fires). In this case, the high temperature was caused by magma reaching the surface.

An effusive eruption means that magma (molten rock) reaches the surface producing a lava flow or dome. This generally occurs when there is a relatively low amount of gas. In an explosive eruption, pressurized gases are trapped within the magma, causing it to break apart violently.

The alert level is orange at the moment; no evacuation orders have been issued.

An extensive array of monitoring equipment has been put in place around the volcano, which should be sufficient for the scientists staffing it to notify the disaster management authorities on time.

Signals could include changes in gas chemistry, changes in the mountain shape, or volcanic earthquakes.

The new dome is hot: in the beginning, a red glow was observed. This turned out to be burning vegetation. Some of the smoke you see in the pictures is steam boiling the groundwater in the crater. From the 1st of February, sulfur dioxide gas was detected in the eruption. The scientific team thinks this is because the groundwater in which the SO2 was previously dissolving is now drying up.

The old dome is 130 meters high, the new one on 21st March is 105 meters high. Before the last explosive eruption of 1979, there was also a dome growth associated with an effusive eruption which started in 1971.

Starting at approximately 10:30 local time (14:30 UTC) on the 23rd of March 2021, the monitoring network recorded a swarm of small low-frequency seismic events, which lasted for about 45 minutes. These events were different from previous activity in that they were also recorded on other stations.

Starting at 16:53 local time (20:53 UTC) on 23 March 2021, the monitoring network started recording volcano-tectonic (VT) earthquakes. These earthquakes are normally associated with underground fractures of the rock mass and are commonly generated by magma pushing through an unyielding rock mass. The volcano-tectonic earthquakes were located beneath the volcano, at depths down to 10 km below the summit. The largest of these had a magnitude of 2.6. Some of them have been reported felt by people living in communities close to the volcano, such as Fancy Owia and Sandy Bay. It stopped again on the 26th.

The lead scientist monitoring the volcano, professor Robertson, says these volcano-tectonic earthquakes are associated with magma trying to push its way through, whereas the small tremors observed daily around the crater are associated with the growth of the dome.

Update 5th April 2021: A new swarm of Volcano-Tectonic (VT) earthquakes began at the

La Soufrière Volcano at 6:38 am today. They occurred at a depth of about 6km. The largest so far had a magnitude of 3.9 and was felt by residents living in the volcano's vicinity.

I include pictures, most taken by the monitoring scientists except the first one, of the development of the new dome. Please click to enlarge.