La Soufrière Scientific Update: Different Types Of Earthquakes Being Recorded

Drone footage of the Dry Wallibou filled with sediment lahars. Heavy rainfall in the days after would rework the La Soufrière Volcano‘s emitted sediment. (Paul Cole, University of Plymouth)

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. In the last 24 hours, seismic activity was limited to a few long-period, hybrid and volcano-tectonic earthquakes.

Volcano-tectonic (VT) earthquakes represent the brittle failure of rock – similar to that of tectonic quakes that occur along tectonic faultsLong-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 SRC also added when the cloud is high enough, there is persistent steaming observable from the observatory. Thermal anomalies indicating high temperatures inside the new crater continue to be detected by the NASA FIRMS alert system. These have been persistent since the 22nd April explosion.

Gas measurements on May 18 yielded an average sulphur dioxide flux of 633 tons per day.

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)

The alert level is orange. The volcano continues to be in a state of unrest. Escalation in activity can still take place with little or no warning. Caution should be taken in crossing river valleys on the volcano due to the increased risk of lahars (mudflows) during periods of rainfall on the volcano.

For more information on coping and handling volcanic ash, the UWI SRC is directing people to the International Volcanic Hazard Health Network for volcanic ash resources.

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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