La Soufrière Updates #73-#74: Earthquake Occurrence Increases At Volcano

The La Soufrière Volcano eruption on April 16th, 2021 (Professor Richard Robertson, UWI SRC)

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 National Emergency Management Organization (NEMO), in their 73rd update at 7:00 PM Tuesday 20th April 2021, stated seismic activity at the La Soufrière Volcano continued the pattern established after the explosive activity on April 18th. Small long-period and hybrid earthquakes continued to be recorded. The network also recorded a few rockfalls and volcano-tectonic earthquakes. They added no seismic tremor has been recorded in the last 12 hours.

According to NEMO, measurements of sulphur dioxide flux at La Soufriere volcano were again undertaken along the west coast today with the assistance of the coastguard. Several traverses were done by boat and yielded an average SO2 flux of 350 tons per day.

In their 74th update, issued at 6:00 PM Wednesday 21st April 2021, NEMO maintained seismic activity at the La Soufrière Volcano continued the pattern established after the explosive activity on April 18th. However, small long-period and hybrid earthquakes continued to be recorded, with their rate of occurrence increasing gradually over the last 24 hours. The network also recorded a few rockfalls and volcano-tectonic earthquakes. Still, no seismic tremor has been recorded in the last 24 hours.

Long-period (LP) earthquakes are caused by cracks resonating as magma and gases move toward the surface. Volcano-tectonic (VT) earthquakes represent the brittle failure of rock – similar to that of tectonic quakes. However, volcano-tectonic earthquakes can occur due to “normal” tectonic forces, changing stresses caused by moving magma, and the movement of fluids through pre-existing cracks. 

Hybrid earthquakes are somewhat a mixture between a VT and an LP. 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. They have also sometimes been precursors to major dome collapses, or switches in the direction of lava extrusion

In both updates, NEMO advised since the initial depressurization noted immediately following the April 9 explosive phase, the continuous GPS network has recorded a decrease in the overall rates of horizontal and vertical movement.

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. Its pattern of seismic activity over the last few days is typical of the growth and destruction of lava domes. 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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