No explosion at La Soufriere Tuesday night — expert

There was no explosion at La Soufriere last night (Tuesday), contrary to a message circulated via WhatsApp.

“As with the last few days and weeks, activity overnight has been quiet,” geologist Adam Stinton, who leads the team of scientists monitoring the volcano, said on NBC Radio on Wednesday.

“There has been no eruption. I understand that there was a message on WhatsApp last night suggesting that there had been [an explosion]. I categorically can say there was no eruption last night,” Stinton said.

La Soufriere erupted explosively on April 9, after four months of effusive eruption, but the volcano has remained largely quiet since the last explosion on April 22.

“Activity has remained low, we have only had a few seismic events overnight and the volcano could just continue this sort of low level sort of unrest with the steaming visible and the gas output from the volcano,” Stinton said.

Over the past few days, persons in communities from which the volcano is visible have reported heavy steaming from the crater.

Stinton has said that the magma inside the volcano is gas-rich, and, on Wednesday, he was asked whether the explosions could continue as a result of pressure in the volcano, should a new dome form.

“Yes, that is one possibility. If there was a dome or if there is a dome present at the surface of the volcano then, yes, it would act a little bit like a cork in a bottle, trapping the gas inside,” Stinton said.
He continued:

“But also, as we saw during the growth of the new lava dome, before the explosion started in April, a certain amount of gas is able to escape from the magma through the lava dome. The dome itself contains gas within the lava that came out and some of that is able to escape.”

He compared this to the volcano in Montserrat, which has a very large lava dome but gas is still able to vent through that dome.

“It follows certain fixed pathways through the lava dome. So just because there might be a lava dome at the surface doesn’t’ necessarily mean that there will be a build up of pressure but it is certainly something that could happen,” Stinton said of Montserrat’s Soufriere Hills Volcano.

Contrasting the current seismic activity at La Soufriere to wha was occurring before the effusive eruption last December, Stinton said:

“The seismic activity, I think we are getting right now, I think, as I said, very low numbers. And I think it is slightly different to what was occurring once the dome was growing, and, I think, even prior to the onset of dome growth last year. And it is probably related to the steaming and the gas venting that we have occurring at the moment.

“With this persistent steaming and gas venting that we have, it does generate a little bit of a seismic signal and it shows up slightly different to the extrusion of lava and the fracturing of rocks underground as the magma pressure builds up in the system below the ground. So what we are seeing now is slightly different and it is likely related to the steaming and gas venting that’s occurring at the moment.”

He was asked to comment on whether the warning signs of any further explosive eruption would be the same as in April, given the current observation of the heat signatures close to top of the volcano.

Stinton said that given that his team believes that there is a batch of magma close to the surface, that is potentially giving off this thermal anomaly, “if there is going to be a change in the activity, we will almost certainly pick up a change in seismicity, which actually might relate to more magma entering the system or pressure build up within the system.

“So just because we potentially got this batch of magma sitting close to the surface doesn’t necessarily mean we won’t see something different happening that might signal a change in the system.”

He said that material generally enters the volcanic system from kilometers below the surface and then works its way up.

“… and it will often give off seismic signal that suggests that those processes are happening,” Stinton said.

He said that the team made a series of traverses via the Coast Guard, on Tuesday, to measure the sulphur dioxide levels being emitted by the volcano.

“I do not have the results from those traverses yet but hopefully they should be available either later today or tomorrow,” Stinton said.

The vgeologist said that before the explosive eruption, there were eight monitoring station around the volcano, but four of them are no long online.

He said that one of them is offline, potentially due to damage as it was located at the crater rim. The others three are due to power and communication issues on the windward side of the St. Vincent.

Stinton said that his team has checked the instruments in Fancy and Owia and they are functional, but are not generating any information because of power and communication at the moment.

“Those are being investigated and worked on, hopefully,” Stinton said, adding that the team is still able to monitor the volcano, despite the lower number of instruments that in the past.

He said that a colleague has arrived from Trinidad and will be working to enforce the monitoring network by installing more seismometers as soon as he complete his COVID-19 quarantine.

The team will also install tiltmetres, which would look for swelling in the volcano to see if there is a build up of pressure.

“And also, one of his priorities is hoping to install a seismic instrument close to the summit of the volcano,” Stinton said of his colleague.

“But, obviously, that is going to require quite a bit of planning on our behalf and also it is going to require helicopter support in order for us to do that…

“Everything is pretty quiet at the moment, there was no unusual activity overnight, the volcano is just continuing its normal activity as it has done for the last few weeks at the moment,” Stinton said.