Soufriere volcano quiet, lahars remain a threat
The activity level has remained very quiet at La Soufrière for a week now, but a dangerous hazard associated with the volcano, mud flows, are carrying material down the valleys as the rains pour down.
“The volcano itself has been quiet, we had very few of the volcanic earthquakes that we were used to, no tremor is taking place; so, the volcano remains quiet which is good.” volcano seismologist Roderick Stewart of the University of the West Indies(UWI)-Seismic Research Centre(SRC), and Montserrat Volcano Observatory(MVO) said yesterday, April 29.
Since the last explosion on April 22, all reports have been almost silent on the seismic front, and there have been no further explosions.
Also, during the NBC program yesterday morning, the scientist noted that while they wouldn’t say as yet that the volcano is going to back to ‘sleep’; it is quietening down.
They continue to watch, “very carefully for any reversal of that”.
Stewart added: “I suspect we will be using the opportunity in the next few weeks to install some new equipment that’s replacing some of the stuff that was destroyed in the eruption, and watching closely to see if anything indicates a restart of activity, that’s really our major task in the coming months.”
While giving an update yesterday, the scientist informed that, “the big activity over the last 24 hours is, overnight we’ve had several lahars (or mud flows) on, I think, all the flanks of the volcano.”
Lahars are fast moving floods of water, rock, ash and debris which flow down the river valleys, while sometimes extending onto flatter ground. Because of the material they contain such as trees and rocks, they pose a significant danger. Persons may lose their lives if caught in one.
“..We suspect there are lahars in all the main drainage valleys and that these may have caused quite a lot of damage as they pass down from the volcano to the sea,” the scientist said.
The signals were dying down at the time of the program but could pick up again every time it rains.
Some sounds heard over Wednesday night/Thursday morning caused people to take to social media and ponder whether La Soufrière had exploded once again. However, this was not the case.
“…We heard noises here as well, at Belmont. It is actually the lahars going on, and thunder and lightning associated with the rain,” Stewart explained.
The lahar brings “trees down with it, and the amount of material that has been brought down, any time the lahar goes round the bend or goes over some topography, it will make thumping noises basically, and these can be heard quite a long way away.”
Professor Richard Robertson was in the field at the time that Stewart was speaking, and has relayed that by the river in Richmond a lot of trees have been brought down because the lahars are erosive.
In one place he said “the river bank has been moved back by about ten meters, that’s 30 feet, it’s eroded into the river bank,” Stewart said.
Robertson had also observed steam coming from the lahar in some areas, signifying that they were warm, from hot deposits around the volcano.
“…Another hazard that people should be aware of, sometimes on the road, you’ll see there’s flooding on the road, there’s some fastmoving water and it’s maybe only six inches deep,” Stewart noted, and people think they can drive through this.
“…but the water, because it’s got material in it, is incredibly powerful and can actually sweep vehicles away,” he said.
The scientists have been carrying out fieldwork over the duration of this week, and also took an observation flight on Monday, April 26, where they were able to get a look into the crater at that time.
Although this may be subject to change, Professor Robertson, speaking on NBC on Tuesday, gave an overview of what the crater looked like on Monday.
When persons ventured up Soufrière before this year’s explosive eruptions, they would would have seen a big open area inside the crater, with a dome in the middle, and another smaller dome next to the big dome that had been building since December.
Now, “…you will see no dome, what you will see is an open crater that goes down quite a ways down.
“…If you go up on the Windward side, you would look across and where you saw the dome growing before in 2020/2021, that’s kind of more or less, you can think of that as the epicenter,” Robertson revealed.
“…But you have a huge crater that goes out for a couple hundred meters in terms of width,” and, “it’s deeper now than the pre-exisitng crater floor.”
They also observed a lot of loose material on the crater, and two small pits, which were steaming.
Along the rims of one of the pits, was loose material or “tephra”, and the ash has built up so high on the side of the Larikai valley, that it reached the crater rim.
“…So in fact now you could walk all the way from the Windward side, all the way around, and you could essentially walk into the crater without actually going down a rope, because the material has built up so much,” the volcanologist explained.
Additionally, “there’s a part of it where you have a large mass of rock that sticks up – we call it a spine – it looks like a black pillar that’s up more towards the North Western side…”