La Soufrière Update: No Lahars Observed In St. Vincent

Still of a flash flood within the Richmond River, following heavy rainfall higher in the river basin. According to the UWI SRC, this is not a lahar associated with the La Soufrière Volcano. (Gerald Johnson)

Present La Soufrière Alert Level:ORANGEThere is a highly elevated level of seismic and/or fumarolic activity or other unusual activity. An eruption may begin with less than twenty-four hours’ notice.

The UWI Seismic Research Centre is advising the public that no lahar has occurred in St. Vincent, associated with the La Soufrière Volcano. This comes as a video circulated on social media over the last week, showing a torrent of mud and water within the Richmond River of St. Vincent.

No lahars have been observed in SVG. The videos circulating show a flooding event in Richmond. Helicopter surveillance…

Posted by UWI Seismic Research Centre on Saturday, January 23, 2021

According to the UWI SRC, “Helicopter surveillance showed a landslip higher up the river and heavy rainfall resulted in the material coming down.”

Professor Richard Robertson of the UWI SRC, in an interview with UWI SRC’s Education and Outreach Manager, Stacey Edwards, explained that this flash flood was nothing unusual.

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“What happened is that something that normally happens. It happens from time to time at all the river systems in St Vincent.” Robertson elaborated that this was likely a sediment-rich flash flood. “When you have heavy rain in the maintains, often you would say locally “the river come down,” which means it gets muddy, there is a lot more sediment in it, and it flows much faster. It may have been associated with some landslides that happened higher up and brought the material down.”

According to Robertson, lahars are the remobilization of volcanic material, often associated with an active eruption or recent eruption. Lahars have the consistency, viscosity, and approximate density of wet concrete: fluid when moving, solid at rest.

Lahars vary in size and speed. Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second. Large lahars hundreds of meters wide and tens of meters deep can flow several tens of meters per second, much too fast for people to outrun.

On steep slopes, lahar speeds can exceed 200 KM/H or 120 MPH. With the potential to flow distances of more than 300 kilometers, a lahar can cause catastrophic destruction in its path.

Professor Robertson emphasized that lahars are usually associated with recent [explosive] activity. “Rain would not have caused that lahar, even though it was the remobilization of volcanic material, it wasn’t from a recent eruption.”

This clarification is important because calling the flash flood a lahar, Robertson explained that it would have “given the impression that the current eruption, which has its hazards confined to the crater rim and the crater itself, that the hazards had somehow gotten outside and it hasn’t.”

There is NO ‘explosive’ eruption at the La Soufrière volcano at this time. La Soufrière continues to have effusive eruptions, as hot magma reaches the surface at extreme temperatures. This appears in the night as fire or a bright red glow above the crater. As the dome gets higher and closer to the crater’s rim, this phenomenon will continue to be visible on clear nights.

The alert level remains at Orange. The volcano continues to exude magma on the surface and steam can still be observed from the Belmont Observatory. Persons living in areas close to the volcano should expect strong sulfur smells for several days to weeks, depending on changes in wind direction.

The NEMO is reminding the public that no evacuation order or notice has been issued. NEMO continues to appeal to the public to desist from visiting the La Soufrière Volcano and especially going into the crater since doing so is extremely dangerous.

The @uwiseismic and NEMO continue to advise access to the #LaSoufriere Volcano is strictly prohibited at this time….

Posted by Trinidad and Tobago Weather Center on Thursday, January 14, 2021

According to the SRC, the new volcanic dome is extremely dangerous for those in close proximity as it can explode at any time without warning. People have been killed in this way. This warning comes as images from a birthday photoshoot surfaced on social media.

Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)
Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)

Official information will originate from St. Vincent and the Grenadines National Emergency Management Organization and the University of the West Indies Seismic Research Center.

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