Can the La Soufrière Eruption Turn Explosive?

Plume of steam and volcanic gases emanate from the new La Soufrière volcanic dome. (UWI SRC/Richard Robertson)

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.

It has been the question on most Vincentians’ minds – can the ongoing effusive eruption turn explosive?

Since December 27th, 2020, an effusive eruption was confirmed within the crater of the La Soufrière Volcano, with a new satellite dome forming that continues to grow in size.

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

Effusive vs explosive eruption explained by the UWI SRC. (UWI SRC/NEMO)
Effusive vs explosive eruption explained by the UWI SRC. (UWI SRC/NEMO)

In an explosive eruption, magma is still involved, except with more trapped gases. As the gas-rich magma reaches to the surface, it explodes instead of oozing quietly. The, now lava, fragments and explodes into the air, creating volcanic ash. The ash is then pelted high into the air or collapses onto the flanks of the volcano as pyroclastic flows – which usually is very hot, travel far and fast and are dangerous to properly and livelihoods.

How quickly can the ongoing effusive eruption turn explosive?

According to Professor and Geologist at the University of the West Indies Seismic Research Center (UWI SRC), Richard Robertson, there is still a lot of uncertainty and a lot of things scientists still don’t quite understand.

Robertson has been part of a three-person team from the UWI SRC, supplementing the local Soufriere Monitoring Unit with additional personnel and monitoring equipment for the La Soufrière volcano.

“One of the reasons we’re putting all of this monitoring equipment close to the volcano, we want to be able to detect any changes that would signify moving from the effusive stage to something different. We think we can detect changes if we look at it closely. One of the things we are looking for is changes in patterns.”

Robertson explained that if the volcano switches to an explosive phase, there would need to have a certain type of gas-rich magma come in. With the right monitoring in place, it can be detected.

Will there be sufficient evacuation time?

Robertson explained that the scientists attached to monitoring La Soufrière are trying to give as much time as possible, more than 24 to 48 hours, even longer than that.

However, he explained that with the dynamic nature of volcanoes, that lead time may not always be the case. “There is a possibility we may not have a lot of time. Prepare for the worst which may be an explosive eruption but hope for the best with the effusion continuing and dying out after a while. If you do that, and when it happens, you can take the necessary actions.”

In an earlier interview, Robertson explained communities will not be evacuated unless they are under direct threat, usually until an explosive eruption occurs. “When it [La Soufrière] goes explosive, the material goes into the atmosphere and produces a lot of ash. One of the main dangers is the volume of ash that goes up in a column of air, then collapses on itself. It also goes down the valley slopes and reaches further out along the northern flanks of the volcano. This is where people live, at the lower flanks close to the coastline. It can only get there if it [La Soufrière] goes explosive.” He reiterated that presently, it is effusive and impacts are confined to the crater rim and the crater floor.

Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)
Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)

The National Emergency Management Organisation reminds the public that no evacuation order or notice has been issued. NEMO continues to appeal to the public to desist from visiting the La Soufrière Volcano until the scientists advise that it is safe.

Official information will originate from St. Vincent and the Grenadines National Emergency Management Organization and the University of the West Indies Seismic Research Center.

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