La Soufrière Volcano Erupts, Alert Level At Orange

Small satellite dome in the crater of the La Soufrière Volcano as fresh magma made its way to the surface of the volcano on December 29th, 2020. (Kemron Alexander/Soufriere Monitoring Unit)

Present La Soufrière Alert Level:ORANGEThere is a highly elevated level of seismic and/or fumarolic activity or other unusual activity. An eruption may begin with less than twenty-four hours' notice.

On December 29th, 2020, the La Soufrière Volcano on the island of St. Vincent erupted. While no evacuation orders are in effect, the alert level for the volcano was raised to orange level.

How did we get here?

According to the University of the West Indies Seismic Research Centre‘s Director, Dr. Erouscilla Joseph, beginning in early November, there was an increase in the background level of seismicity at the La Soufrière Volcano.

La Soufrière in the Southern Windward Islands, well northwest of Trinidad and Tobago.
La Soufrière in the Southern Windward Islands, well northwest of Trinidad and Tobago.

While the increase in seismic events were no cause for concern to the public, the SRC was providing updates to the Vincentian government. Professor Richard Robertson of the SRC also noted that this “increase” means that the Centre was recording 1 to 2 volcanic-tectonic earthquakes a day, with some days recording no quakes at all.

The largest recorded earthquake registered at a magnitude 3.3 on the Richter Scale on December 16th. A team from the Soufrière Monitoring Unit visited the summit on the 16th and noted there were marginal changes in the small lake on the eastern crater floor of the volcano.

The last seismic events were recorded on December 23rd, with a peak of 8 earthquakes recorded in one day. Still, Joseph reiterated that this was not highly unusual for the area. Then, there was a period of seismic quiet.

NASA FIRMS Showing the La Soufrière eruption hotspot over the last four days.
NASA FIRMS Showing the La Soufrière eruption hotspot over the last four days.

At 1:20 PM on December 27th, 2020, a UWI SRC staff member was made aware of a hotspot being detected on a NASA satellite used to track wildfires globally. The hotspot, near the center of the crater, was detected by NASA’s MODIS and VIIRS satellites used for Fire Information for Resource Management System.

The hotspot persisted over the last 4 days (December 27th through December 30th). Upon routine, visible inspection by the Soufrière Monitoring Unit, the team confirmed the hotspot in the crater, with satellite imagery on the 29th of December showing an extension of the hotspot.

As the team was preparing to make another visible inspection, reports came in from Rose Hall, St. Vincent of greyish-white emissions above La Soufrière’s crater.

Small plume of steam above the crater of La Soufrière on December 29th, 2020
Small plume of steam above the crater of La Soufrière on December 29th, 2020

The La Soufrière Monitoring Unit visited the site on December 29th and reported the presence of the satellite dome, with a strong gas emission. The crater lake was virtually gone, due to the intense heat causing the water to evaporate.

The Safeguards

La Soufrière Volcano. Top: 23rd July 2017. Middle: 27th December 2020. Bottom: 29th December 2020. (Jason Viera/Kent Thomas)
La Soufrière Volcano. Top: 23rd July 2017. Middle: 27th December 2020. Bottom: 29th December 2020. (Jason Viera/Kent Thomas)

An effusive eruption was then confirmed, ending the 40-year lull in eruptive activity at the volcano. This eruption, according to the Seismic Research Centre, is similar to that of 1971-1972.

What is an effusive eruption?

Effusive eruptions occur when molten rock (lava) reaches the Earth’s surface and erupts passively. The products of these eruptions are lava flows and lava domes. They generally occur when the gas content of the magma is low.

The mass of newly formed rock remains confined to the crater of La Soufrière. However, sulfur-rich gas is coming out of the rock, which can make it difficult to breathe. Hence, Vincentians are advised to stay away from the volcano rim and crater.

There should be no unofficial people visiting the dome to avoid any possible hazards from the emissions or the rapid change in activity. All recreational activities to the volcano are now suspended. Do not visit the crater.

Though the magma has already made its way to the surface, changes in the magma composition below the ground can cause seismic events, some of which may be felt over the next several weeks to months.

Image showing the new, satellite dome developing within the crater of La Soufrière. (Jason Viera/Kent Thomas)
Image showing the new, satellite dome developing within the crater of La Soufrière. (Jason Viera/Kent Thomas)

There are no evacuation orders in effect as of Wednesday 30th December 2020 but those living near the crater of the volcano should be on alert.

The volcano alert level has risen to Orange Level. See what that means here.

Present La Soufrière Alert Level:ORANGEThere is a highly elevated level of seismic and/or fumarolic activity or other unusual activity. An eruption may begin with less than twenty-four hours' notice.

What’s next?

The Seismic Research Centre will be sending a team of three people to St. Vincent later today with additional monitoring equipment to collect more data.

This data will be integral in determining whether this effusive eruption may turn into an explosive event or gradually subside as an effusive event. It will not be an immediate determination, as the SRC will need to collect data over the next several weeks to even months. At this time, there is no way to tell if the event will become a large, explosive eruption.

Based on history, La Soufrière erupts every 100 years, +/- 30 years, with the last eruption recorded in 1979. There is also no reliable precident for determining the pattern of this eruptive event. The last eruption events began with an effusive event in 1971-1972, then years later in 1979, the eruption became explosive and immediately subsided with an effusive eruption. There is no way, at this time, scientists can predict which way this eruption may go until there is more data.

Is La Soufrière Linked To Other Volcanoes in the Lesser Antilles?

The short answer is no. The process of subduction across the Lesser Antilles is the region islands north of T&T (with the exception of Barbados) are volcanic islands, but that’s where the link stops. Seismicity associated with different volcanoes is not linked. Hence, an eruption of La Soufrière does not mean an eruption of Kick’em Jenny or any other Lesser Antilles volcano is imminent. If one occurs, it will likely be an unlucky coincidence.

The SRC is responsible for monitoring all seismic and all volcanological hazards across the English-speaking islands of the Eastern Caribbean. Presently, the ongoing seismic unrest in Dominica is returning to background levels. There are occasional volcanic-tectonic quakes in St. Lucia.

Is there any threat to T&T?

There is no threat to T&T and the remainder of the Lesser Antilles, with the obvious exception being St. Vincent.

Facebook Comments