La Soufrière Scientific Update: Multiple Lahars Recorded

Damage at the Rabacca Dry River Bridge as ash from the La Soufrière Volcano eruption is remobilized by heavy rainfall on St. Vincent. (April 29th 2021)


Present La Soufrière Alert Level:YELLOWThe La Soufrière Volcano is restless. Seismicity and/or fumarolic activity are above the historical level at the volcano, or other unusual activity has been observed. This unusual activity will be specified at the time that the alert level is raised. This is level two of four.

According to the latest scientific advisory from the University of the West Indies Seismic Research Centre (UWI SRC), multiple lahars have been recorded at seismic stations monitoring the La Soufrière Volcano, St Vincent.

The SRC explained that the seismic stations recorded signals from multiple lahars during a 12-hour period starting at 9:00 PM on the 28th April. Lahars seem to have taken place in all the valleys that drain from La Soufrière and caused considerable erosion and damage. Lahars are fast moving, dense mixture of rocks, ash and vegetation and water originating from a volcano.

The scientific advisory also added that some of these mudflows were hot lahars which were visibly steaming, having passed through hot volcanic deposits. In addition. many trees were brought down by the lahars that floating logs are a hazard to small craft near shore.

Seismic activity at La Soufrière has remained low since the tremor associated with the explosion and ash venting on the 22nd of April 2021. In the last 24 hours, only a few long-period, hybrid and volcano-tectonic earthquakes have been recorded and there was no further tremor. The volcano continues to be in a state of unrest.

Volcano-tectonic (VT) earthquakes represent the brittle failure of rock – similar to that of tectonic quakes that occur along tectonic faults. Long-period (LP) earthquakes are caused by cracks resonating as magma and gases move toward the surface. As the name suggests, a hybrid earthquake is somewhat a mixture between a VT and an LP. They tend to have impulsive starts but also contain a significant amount of low-frequency signals. They are thought to represent magma making its way to the surface at shallow depths and are often associated with periods of rapid dome growth. 

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)

According to the UWI SRC, the volcano continues to erupt. Explosions with accompanying ashfall, similar to or larger, can occur with little or no warning impacting St Vincent and neighboring islands.

The alert level remains red. The National Emergency Operations Center continues to be fully functional operating on a twenty-four-hour, around-the-clock basis. NEMO will continue to provide regular updates as they continue to monitor the Volcano.

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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