Lahars at Rabacca. Heavy rain, added to ash on hillsides can result in lahars, a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water.  
June 11, 2021
SVG will be under threat of Lahars for long time – Scientists

The threat of lahars now looms over parts of mainland St. Vincent and this will be so for a very long time.  

Scientists say that heavy rain, added to ash on hillsides can result in lahars, a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water.  

The material flows down from a volcano, typically along a river valley, and are now more possible with the Atlantic Hurricane Season in progress. 

But despite this fact, the Seismic Research Unit of the University of the West Indies (SRC-UWI), the body responsible for monitoring the Soufriere volcano, does not at this point have equipment or a system in place to monitor what could be potentially deadly flows.  

This point was addressed on Monday by head of the SRC-UWI monitoring team Lloyd Lynch, during NBC Radio’s “Eyeing La Soufriere”, programme. 

Lynch said that as a result of this extremely destructive natural event, a system to monitor lahars should be put in place as soon as possible.  

“It was busy weekend for lahars,” he said, referring to last weekend when a tropical wave dumped rain on the country.  

“The question was asked, how soon do I think we could put together a proper lahar monitoring system, and I don’t really know the answer, and I have been involved in monitoring for many years.  

“I know there are many well intentioned people around who can get a system in place, but you have to be mindful that we live in a society where there can be a lot of impediments…,” Lynch commented.  

The scientist said that while the seismicity of La Soufriere continues to show a declining trend, secondary hazards like lahars now pose a serious threat.  

“We have at the moment a two man team on the ground. Our primary focus is to bolster the monitoring network, so our emphasis is on preparing the monitoring equipment,” Lynch said when asked about lahar monitoring.

“We don’t have a person who is specifically trained in that region (lahar monitoring) and whose remit is to, you know, map or look at the lahar deposit at the moment,” he added.

He said that on Saturday, the team attempted to travel to Richmond to deal with some monitoring equipment, but got stuck in the mud and had to abort the task. 

He stressed that with this higher level of lahar inundation, it is important that some measure or assessment be undertaken, “because we are getting deeper into the hurricane season and a lot more rainfall is expected, and with heavy rainfall, you will get more lahars, so we need to undertake some sort of lahar mapping or lahar hazard mapping so to speak.”  

He added further that it is very difficult to say how soon lahar equipment can be sourced, because they have just begun to discuss lahars, and it is not a program that has been in place before.  

“In 1979, I don’t recall there was a lahar monitoring network after the eruption, so it is something that we are new to and as I say, it’s not as simple as just buying some instruments and put them near the volcano,” Lynch pointed out.  

He said that a lahar early warning system comprises of monitoring which requires cameras to confirm the actual flows, as well as acoustic flow monitors which are basically narrow band seismic instruments used to monitor the vibration of the flows.  

“When the flows come down, they cause a lot of vibrations and these instruments can detect the vibrations,” explained Lynch who added that weather stations are also needed to gauge how much precipitation has occurred so you can have an idea of the size of flows to be expected.  

Lynch also noted that monitoring also has a communication component which involves the medium, and equipment that will be used to get the information out to the at risk community. This can mean sirens, or a common alert protocol, which is a system that is used to interrupt broadcasts on radios and television. 

“You have also the hazard and impact component and this involves mapping the pyroclastic flows deposit to get an idea where the loose material is located and its potential to be mobilised and washed down in the lahars,” Lynch said.

Monitoring, according to Lynch, also involves mapping of the population centres, those that are at risk, and mapping of past deposits to get an idea of what future deposits would be like.  

The monitoring system is also made of up of preparedness components as Lynch said it makes no sense to monitor and issue a warning if the at risk population is not prepared to take the necessary action to evade the hazard.  

“So the preparedness components involves things like outreach and education to give the at risk community  more information about the hazard and what action they need to take.  

“It gives information about the warning system. If you are using a siren, what the certain sequences of wails, what it means.. 

“It involves drills and so on, so basically a warning system is fairly complex and to get a warning system up and running very soon requires a lot of planning, a lot of investment and therefore it is hard for me to say how soon this could be done,” Lynch stressed.  

He noted that over the weekend, they received about 11 lahar signals on both the eastern and western sides of the volcano but it was difficult to pinpoint which valleys they occurred in.  

Over the weekend, Lahars were reported in Sandy Bay, and Lynch said the weekend brought more precipitation on the western side of the island, so they saw more signals at the Wallilabou station than at the Bamboo Range station.  

“It is not a matter of just putting a few instruments on the slope of the volcano, that alone won’t cut it…,” Lynch noted while advising that a system like this needs all the people who are working on all the components to work in concert for it to work properly.  

Prime Minister Dr. Ralph Gonsalves, calling into the program from Cuba said hazard mapping, which is on element of the what Lynch was speaking about has already been done.  

He said the Central Water and Sewage Authority (CWSA ) and the National Emergency Management Organization (NEMO) have done hazard mapping, and there is also a detailed hydrology assessment of all the water systems.  

“…but in view of the fact that we need to have a better warning system in relation to the lahars, we have to put that in a capital project…” Gonsalves said while adding these things have a cost attached to them.  

“…the instrumentation you are talking about, in addition to updating work on the hazard mapping, plus matters connected to the hydrology system… we should get a capital project to see what is the total overall cost… the recommendation is one we would embrace,” Gonsalves told Lynch. 

The PM said setting up a lahar monitoring system is important as volcanologist Richie Richardson of the UWI-SRC has indicated that the country is going to have lahars, not only in this rainy season, but into the next rainy season and beyond.  

Dr. Gonsalves also stressed that we are not looking to set up a system of this nature “with a blank slate” ,as the professionals have a broad idea from the physical planning standpoint where we should not build back, “because we will see with our eyes what is happening.”