Seismic activity at La Soufriere declining further

SEISMIC ACTIVITY at La Soufriere volcano remains low and has been on a steady decline since the last explosive eruption on April 22.

Head of the University of the West Indies (UWI) Seismic Research Centre (UWI-SRC) Dr. Erouscilla “Pat” Joseph said the monitoring team at the Belmont observatory in North Leeward has been recording less than 10 seismic events per day, sometimes even one or two events.

Dr. Joseph said when the clouds permit, people can see degassing of the plume, primarily sulphur- dioxide, which is on average 480 tonnes per day. Gas measurements are measured by a boat that visits the west coast twice a week.

“So we are in a kind of steadily declining type of activity associated with a post eruption. However if there is new magmatic input, which is a very small possibility, then with fresh magma influx we can see a change in the system,” Dr. Joseph explained.

She gave the information on VC3’s Round Table Talk episode 67 which addressed the latest developments at La Soufriere.

Dr. Joseph stressed that at this point, the types of hazards that must be monitored are associated with the deposits that are on the flanks of the volcano which can cause lahars when there is heavy rainfall, and send them down into the valleys on the flanks of the volcano.

About two weeks ago, Dr. Adam Stinton, a Volcanologist attached to the UWI–SRC visited St. Vincent and flew over the volcano in a helicopter with a camera attached to its base.

He told persons listening to the Eyeing La Soufriere program on NBC Radio on Wednesday June 30 that the volcano currently has no lava dome and continues to show a decline in seismic activity.

In volcanology, a lava dome is a circular moundshaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dr. Stinton said the fly overs allowed them to map the new crater and from that, they were able to observe that the summit has no lava dome inside the new crater.

“There are some interesting features to be seen in the new crater, for example, there has been some sort of collapse of a spine being seen and that feature is not a new feature.

“It is a pre-existing feature that has been exhumed by the effects of the explosion, and it is actually a conduit that fed the 1979 lava dome and it’s essentially standing tall as a very prominent mass of lava that dates back to the 1970s,” Dr.Stinton said.

Dr. Stinton added that a bulge exists in the centre of the floor of the new crater and this sits over what they think is the conduit that fed the explosions, and potentially also the conduit that fed the new lava dome that began growing in December last year before the eruptive explosions.

“…but there is no evidence of a lava dome, there is no evidence of any significant changes inside the new crater and any changes that are occurring are a result of erosion of the slopes of the inner walls of the crater caused simply by the loose material slumping down into the crater or being washed down by rainfall,” Dr. Stinton said.

He however noted that in his experience, you do not have to have a lava dome to lead to an explosive eruption.

Giving some measurements, Dr. Stinton said the new crater has dimensions of between 800 to 1000 meters in diameter, “fairly sizeable”, and is up to about 200 meters deep.

“…and it has excavated down below the level of the floor of the old summit crater and it is still possible to see remnants of the 1979 lava dome in the north eastern and eastern sectors of the rim of the new crater and there is no new lava dome so we have no dome growth at all in this new crater,” Dr. Stinton further stressed.