Rainfall At La Soufrière Producing Lahars, Increased Steaming

Multiple areas of venting and a possible lava spine at the La Soufrière Volcano. A lava spine is a volcanic feature of solid lava squeezed out from a vent that grows upwards forming a tall feature. It can range from tens to hundreds of meters in height and width once it remains stable. It was noted that tephra, materials of all types and sizes that are erupted from a volcano and deposited from the air onto surrounding areas, has filled the crater so that it now reaches the top of the southwestern part of the summit. This can make it easier for pyroclastic density currents PDCs to get out of the summit crater. (Roderick Stewart, MVO/UWI-SRC)

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), seismic activity at La Soufrière, St Vincent has remained low since the tremor associated with the explosion and ash venting around noon on 22nd April.

The SRC added that in the last 24 hours, only a few long-period, hybrid and volcano-tectonic earthquakes were recorded and there was no further tremor.

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. 

The UWI SRC also noted signals from several lahars (mudflows) were recorded between 9:00 AM and 10:00 AM today, during and after a period of rainfall. A lahar is a rapidly flowing dense mixture of rock debris, ash, and water. They have the consistency of wet concrete as they flow and can happen during and after eruptions.

Further, the SRC added following the rainfall, large amounts of steam could be seen billowing up from a valley south of the summit which would have been generated when the runoff encountered buried volcanic deposits that were still hot.

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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