There are features of the eruptions at La Soufrière that have been inexplicable, and while the scientists have established a pattern for now, they lean on the side of caution with such a dangerous volcano.
In terms of features of the eruption that have been striking, the size and extent of the eruptions is something that has taken their breath away, volcano-seismologist Roderick Stewart explained.
“This eruption has taken our breath away by the extent. The amount of ash affecting the whole island is something that wasn’t really expected, and it’s a different style of eruption to the 79’,” the scientist with the University of the West Indies (UWI)-Seismic Research Centre(SRC), and based at the Montserrat Volcano Observatory(MVO) said.
Geologist Professor Richard Robertson, with the UWI-SRC, who was still a student at the time of the eruption in 1979 and decided then to study volcanology, is now monitoring the volcano as an experienced volcanologist and lead scientist on the ground.
“It looked like it was moving into more frequent and smaller eruptions, so if it’s following that pattern,” the current eruption should have been a smaller one, Robertson told SEARCHLIGHT, “not a bigger one.
“This one is looking like it’s going to end up to be probably at least 1902 or bigger. It’s certainly bigger than 79’ and certainly, the initiation of it, when it went on for like two days of nonstop.”
Another instance where La Soufrière showed impressive actions was when it had a phenomenal dome growth rate on the night that the evacuations were ordered, just before it first exploded on April 9.
When the volcano did erupt, the ensuing explosions took out both the new 2020/2021 dome and older dome in the crater, “most of the ash that you see down to Barbados, that’s it fine grain stuff, so it’s not just big blocks, (the volcano) basically grind them to ash in the process of what it was doing, he said further” “I mean I knew it could do that, but to see it happen is something else.”.
During SEARCHLIGHT’s conversation with the scientists, on the topic of the future of the eruption, Professor Robertson noted: “there are things about this eruption that have been inexplicable thus far. So we have to figure it out. Because there are certain things that we are expecting to see that we didn’t quite see, or maybe we just haven’t the right model to explain what’s happening.”
On the other hand, “there are things that happened that was nice and easy to see.
“‘Rod’ will tell you that this was a textbook kind of, in terms of the seismic signals for volcanos erupting, but yet they have other elements of it that is puzzling,” Professor Robertson shared.
Stewart added, “there have been times when the seismicity doesn’t seem linked to the amount of (magma) that’s coming out, which is one of the fundamentals.” Stewart continued, “but these cycles that we’ve seen, we get seismic activity in the beginning, as it clears out, but then it seems to be open and it’s pushing ash out but not generating a seismic signal,” which is puzzling.
There is margin for error with the unpredictability of the volcano, and if something goes wrong, if people are in harm’s way they can be killed.
“…with this volcano, it’s a dangerous volcano, you have to err on the side of caution,” Robertson said.
While there has been a depressurization after the initial explosions, if the volcano swells again, the scientists should be able to tell.
However, there are possibilities. “If you think of a pipe”, (using this an analogy for the conduit where the magma is coming up), “if you have a pipe that’s sort of so strong that you can force things through without the pipe deforming, maybe that’s what it’s doing, which is the open vent. If it is that stuff can come from below and come straight up to the top, because it’s so open without doing anything else, without giving any seismic signals, without deforming the mountain, that’s the kind of fear you have; and if it does that, the kind of eruptions you can have, the beginning that you saw there is kind of what it will do.”
“It’s things like that that we think about all the time. You never know exactly what is happening,” Professor Robertson explained.