La Soufrière Update #57, #58: Scientists Informed of Pyroclastic Flow, Lahars

Lahar at the Rabacca Dry River Bridge on April 11th, 2021

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 57th update at 1:15 PM April 2021, advised that scientists informed of possible pyroclastic flow on the eastern side of the island due to La Soufrière‘s eruption.

The University of the West Indies Seismic Research Center (UWI SRC) in their scientific updates also advised that heightened seismic activity was still ongoing.

According to the 9:00 AM update, “In the last twelve hours episodes of tremor normally lasting up to 20 minutes have continued to be recorded. The intervals between the tremors have been between 1.5 to 3 hours. Based on visual observations and satellite imagery, the intervals are associated with periods of explosive activity or enhanced venting.”

In their later 6:00 PM update, the gaps in the seismic tremors have increased. “The seismic network recorded short episodes of high-amplitude seismic tremor, each lasting around 20 minutes and with gaps between them from one to six hours.” UWI SRC also stated that seismic tremors’ background level between the episodes has been increasing slowly since about 10:30 AM.

The SRC has also reported volcanic lightning and accompanying thunder during explosive activity or enhanced venting. Heavy ashfall was also reported at the Belmont Observatory throughout the previous night.

Scientists also noted that steaming in the upper parts of the Rabacca valley was observed at about midday. Investigation of the cause of this phenomenon was being investigated. According to the UWI SRC Director, Dr. Erouscilla Joseph, this steaming was associated with a Lahar. Joseph explained rainfall remobilized hot volcanic material from La Soufrière, causing steaming to occur at the Rabacca Dry River bridge.

Ashfall was also reported in most areas of the island overnight and in neighboring islands: the Grenadines, Barbados, and Saint Lucia. The UWI SRC is advising that explosions and accompanying ashfall of similar or larger magnitude are likely to continue to occur over the next few days impacting St. Vincent and neighboring islands.

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)

In NEMO’s 58th update, issued at 9:00 PM April 11th, 2021, advised that eighty-four (84) shelters with more than 3,718 occupants are now fully operational. This does not include those who have sought shelter with family and friends. Evacuation of persons who had previously remained behind in their communities continued.

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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