Kingstown – The lead scientist monitoring the La Soufriere volcano here, Professor Richard Robertson, says an increase in earthquakes at the site could suggest that an explosive eruption could happen soon.
La Soufriere has been erupting effusively since late December, and a new dome has formed alongside the one left inside the crater after the 1979 eruption of the volcano.
The National Emergency Management Organisation (NEMO) Wednesday warned residents of communities near to the volcano to heighten their preparedness in the event that it becomes necessary for them to evacuate at short notice.
NEMO said that scientists at the Belmont Observatory, have noted a change in seismic activity associated with the ongoing eruption of the volcano.
Robertson said that the scientists had always indicated that the volcano could continue effusing material for a long time, it could stop effusing material, or it could erupt effusively.
“And one of the things that will drive it to go explosive is fresh material coming in; new material to give it energy,” Robertson said, adding that the earthquakes which began on Tuesday could indicate that fresh magma is trying to make its way to the surface.
“So this is the first indication that maybe this is happening. We have to track it to see if it is really indicative of that,” he further explained.
He said that the material that has oozed out of the volcano since December could have been there since the eruption of April 1979. However, this week’s events suggest that new material could be making its way to the surface.
“This magma is deeper down, is trying to get to the surface, it’s trying to find a pathway through and, in doing that, it is causing vibrations in the ground, which our instruments are detecting,” Robertson said.
Since the effusive eruption began, scientists have installed additional monitoring equipment across the country and Robertson said that the information generated this week shows that the equipment is functioning as intended.
“That is what they are set up there to do. They are set up there precisely to tell us if something like that is trying to come through and we are then about to track it . . . ,” he explained.
“So, in a sense, it’s probably not a good thing that is happening because it tells us that this eruption could go to a stage where we all really don’t want it to get to, but also, it tells us that the instrumentation that we put in is working . . . .”
Robertson led the team that was initially deployed from the Trinidad-based Seismic Research Centre (SRC) of the St Augustine campus of the University of the West Indies (UWI) after the effusive eruption began.
He has since returned here after leaving in January and noted that the new dome that resulted from the ongoing effusive eruption is probably twice as large as it was in January.
“At the end of January it was bobbing around four to five million cubic metres. Now, it’s 13.1 [million cubic metres] last time we checked,” Robertson said.
“Last time, it was kind of something that we could still say, call a dome, but right now, it looks more like a — almost like a lava flow in a sense because it’s extended so much.”
In January, the dome measured between 100 and 200 metres across, but it is now 900 metres long.
“So it stretches from around the Larikai gap all the way to the place where the fumarole is on the pre-existing dome,” Robertson said.
The scientist said that eruption continues to be effusive but there have been some slight changes since Tuesday.
“We have now started to feel what we call proper earthquakes,” he said, adding that up until Tuesday, most of the earthquake activity from the volcano was really related to the dome building itself up — which scientists call dome emplacement events.
“So you have magma coming out and oozing out and as it oozes out, its solid rock, because it is solid rock, is moving, it has gas and so on, all of those general seismic signals,” he said, noting that these signals don’t travel very far and were only captured by stations very close to the volcano.
“But early Tuesday we had a small swarm of events and late yesterday evening we started to have proper earthquakes, what we call volcanic tectonic earthquakes, which are earthquakes associated with more rock breaking and magna trying to get through from below the ground, not something at the surface.”
Robertson said that these types of earthquakes tend to have a little bit more energy and larger in magnitude and detected by more volcano monitoring stations.
“And because they have more energy, because they are bigger, it’s possible that they are being felt, and we have reports that they have been felt by people on the volcano itself,” he said, referring to communities located on the slope of the volcano.
While speaking on the programme, Robertson said the monitoring station recorded the biggest event since the increased activity started.
“We have to keep tracking it to see if the signature of the signal will change as it tries to get further up. The number of events might change; the magnitude might change.
“There is a possibility that it will get to the surface, it will add to what is there now and because of the fact that it is fresher, it would change the way in which the material is erupting, so it could change it from being effusive to being something that is a bit more energetic,” Robertson added. (CMC)
