Soufriere monitoring soon to return to pre-eruption mode
SEISMOLOGIST RODERICK STEWART is monitoring data at the (Belmont) Observatory. (File photo)
October 22, 2021
Soufriere monitoring soon to return to pre-eruption mode

AS SCIENTISTS working with the Seismic Research Centre(SRC) are on their final rotation, the monitoring arrangements for the volcano will soon continue as it was prior to the eruption, strengthened by a near impenetrable front of instrumentation on- island and around the volcano summit.

“..With the amount of instrumentation on this volcano, and the continuous monitoring, it is very unlikely that we would miss anything, because now we have gas, seismic, and ground deformation vs one seismic station that was there before (prior to the eruption),” Director of the University of the West Indies(UWI) SRC, Dr Erouscilla Joseph noted last Friday, October 15.

Instrumentation remaining for monitoring includes eight continuous ground deformation stations, eight seismic stations, and a tilt meter, and these now form part of the permanent monitoring network for St Vincent and the Grenadines(SVG).

Seismologist Roderick Stewart, who has been instrumental in setting up the systems to monitor the seismic signals from the volcano, and who was one of the team on island during the explosive phase of the volcano in April, is currently joined by technician Raquel Syers on SVG for the current rotation.

After their rotation is completed, “we transition to what would be our regular way of monitoring prior to the eruption where we monitor from Seismic.”

Joseph explained that “It would just mean that the (Belmont) Observatory is not manned 24 hours, but there is on-island monitoring by the Soufrière Monitoring Unit(SMU).”

Director of the National Emergency Management Organisation(NEMO), Michelle Forbes, said on Wednesday, October 20, that “it will be a mixture of the monitoring physically on site – and the monitoring on site is really sometimes to look at the volcano itself because you can see the summit of the volcano – and then you can also monitor remotely using the computer and and the displays.”

“We moved quickly in January to ensure that we have that capacity so we can have that Obs[observation] room where you can see all the seismic signals coming in to the observatory and you can actually see what is happening and that also is tied to your phone, you can log in and see at every site that we have monitoring the volcano,” she added.

Further additions to the local monitoring scene are said to be in motion with the advertisement for the position of a resident geologist.

Applications for this post closed last week, and are in the hands of the Service Commissions Department, “so we will get to know in a few weeks, how many persons would have applied and so on as they go through the process.”

Therefore, NEMO is contemplating “…A geoscientist/geophysicist who will be in charge of the Soufrière Monitoring Unit(SMU),” Forbes noted, as well as an engineer who will be in charge of monitoring all the seismic stations.

These persons will join Kemron Alexander, Asroy Price and Leanka Henry, the latter being a young geologist who is measuring the gas on a weekly basis.

La Soufrière is in a post eruption phase of activity since the last explosion recorded on April 22, and is expected to continue to decline in activity.

The scientists have been analysing the events that occurred with the monitoring that took place, and Dr Joseph summarised briefly last week, what they believes was happening beneath the surface in April.

“…We do not know the timeline for when there might have been a fresh batch of magma that came up. That wasn’t detected by the instrument. That could have happened months before we saw any kind of surface activity,” she explained.

At a depth somewhere below six kilometres, “there would have been a pulse of molten magma that wanted to come up to the surface. As this magma would have tried to come up, it would have met with resistance,” in the form of the 1979 dome and solidified material in the conduit.

“…this magma couldn’t easily find a way to the surface so eventually pressure built up, and then it started to push the old stuff out, but you still had that dome there,” so it went to the side and formed a new dome, she said.

“ After a while when it started to degas, and it started to extrude, the pressure built up more and more, that the effusive eruption then was able to transition to an explosive eruption.”

The ensuing explosions, “excavated deeper down into the crater than what was previously seen so the deposits that would have been making up the crater floor from prior eruptions, 1972 and a lot of the older eruptions, a lot of that would have been blasted out too.”

Currently, what has been shown in pictures is a bulge, “because the main area where the conduit was, that’s now cooled, and there’s still hot rock in there so that will bulge in the middle, where there’re cracks and gases escaping.”