Residents of St Vincent may be required to remain at high alert for the long haul in case the effusive eruptions at La Soufriere, which may continue for more than a year, turn into explosive ones.
Geologist Professor Dr Richard Robertson of the University of the West Indies Seismic Research Centre (UWI-SRC) shared this information today, January 2, when he gave an update on the situation on NBC radio.
The Vincentian scientist forms part of a team that arrived from Trinidad and Tobago on December 31, working under a modified quarantine to provide scientific support.
They are supported by teams in Trinidad, Montserrat and here at the National Emergency Management Organization (NEMO).
“We really came here to augment the monitoring systems, to put in more stations, because once you’re at the stage of something happening, like it’s happening now at the volcano, it’s important to put in a lot more seismic stations,” Robertson explained.
The Volcano Hazard Alert Level at La Soufriere is now at orange, meaning eruptions may occur with less than 24 hours notice.
In an emergency news briefing on Tuesday, December 29, the public was informed of an ongoing effusive eruption taking place in the crater of the volcano. The public was also informed that there had been activity recorded since early November, sufficient to make the scientists a bit concerned.
The concern increased when, on December 22, the National Aeronautics and Space Administration (NASA) informed UWI-SRC of a hotspot located in the crater of La Soufriere.
Subsequently, the Soufriere monitoring unit of NEMO verified an emission of magma and the building of a dome-shaped black mass of rock, when they went to the crater on December 29.
“We’ve been collecting information. NEMO has been doing observation flights and we’ve been using that and we can now come up with estimates with how the dome is growing,” as well as the rate of growth, Robertson noted.
“What we can see is that the effusion, or the excretion of magma as it gets to the surface, becoming solid hard rock and the growth of the small dome, has continued. It seems that it started out at a particular rate and it’s slightly increased over the days since it started.”
The growth is still focused west of the 1979 dome, “it is essentially expanding a little bit further moving towards the west, it’s getting a little bigger.”
Robertson said that this activity is expected, and that once this type of eruption starts at Soufriere it can continue for weeks, months and “as is the case of 71’/72’ dome, it went on to a little bit over a year.”
The dome is pictured as a small black mass of rock in the crater. The scientist warned that while this dome grows, it’s possible that persons may start to see a glow. The black rock shown in the pictures is incandescent and it glows at night.
“As the dome gets bigger, it’s possible that you will see a little bit of that glow from surrounding areas, and again, that is expected,” Robertson reiterated.
The dome has also heated up slightly once more, as expected.
The team is continuing to install stations to monitor this growth and to monitor any indications that the effusive eruption is turning into a much more dangerous explosive eruption.
The Professor likened the excretion of magma in an effusive eruption to the squeezing of toothpaste out of a tube, and an explosive eruption to the opening of a bottle of Coca Cola after it has been vigorously shaken.
Eruptions that have been seen in Hawaii may show a classic example of an effusive eruption. “If you think of eruptions that you’ve seen at Hawaii of the long red lava flow, that’s an effusive eruption,” he described.
However, our lava can be seen as ‘sticky’ in comparison to Hawaii.
“It doesn’t flow out like what the Hawaiians have, what it does is it comes out in a blocky way,” he said.
“…because of the fact that the material properties of the magma itself is different, it comes out and it forms blocks of rock which then piles up as a dome,” Robertson further revealed.
Because our effusive eruption is taking place inside the crater, which is a “huge” crater, the current danger is kept inside of the crater.
“…as much as it stays within the confines of the crater, that’s probably a good thing because it then means the main dangers are to the top of the volcano and people visiting the volcano itself,” he said.
The public have been prohibited from visiting the volcano at this time.
An explosive eruption is caused by trapped gas which is not able to be released quietly. As it gets closer to the surface it expands, breaks up the magma, and shoots ash into the air. It collapses in on itself and comes down the mountain as “avalanches of basically ash and blocks of rock” called flows.
These avalanches are what will affect the areas surrounding the volcano. Ash may even reach Barbados and further afield.
While these current effusive eruptions are taking place, “we have to remain at a heightened state,” Robertson says, reiterating, “It can go from effusive to explosive in a very short time and we are very uncertain of how long that time is.”
He advised persons to listen to the authorities and reputable sources, as well as be prepared to move in the event that the eruption turns to an explosive one.
“The effusive part in Soufriere has often gone on for longer than the explosive part, so it may go on for a little while, so people need to sort of be prepared for a longer haul,” and continuing to be at a high level of alert.
“Don’t get complacent, don’t get overly panicky about the situation, but be prepared,” he said.
The professor cautioned persons not to go up the volcano, noting, “We do it under really very strict safety conditions.”
“Assist as much as you can in spreading good information rather than rumours, and if you do that I think that we should be able to weather the storm that we have to deal with currently,” Professor Robertson concluded.