Multiple lahars observed at St. Vincent, public advised to be vigilant and exercise caution

The National Emergency Management Organization (NEMO) of St. Vincent and the Grenadines is advising the public to be vigilant and exercise caution in areas close to valleys, rivers, streams, low-lying areas, and areas prone to flooding and landslides. Multiple lahars have already been observed on Monday, May 3.

The country's Meteorological Services says pockets of light to moderate showers are expected through early Tuesday morning (LT), May 4.

The stations at Jennings Valley, South Rivers, and Majorca recorded over 25 mm (1 inch) of rainfall over a 6 hour period on May 3, and soils are still saturated from the heavy rainfall event on Thursday, April 29, 2021.

More showers may result in flooding and landslides, NEMO said. 

There is also a heavy accumulation of volcanic ash especially in valleys close to the La Soufriere Volcano which can result in Lahars or mudflows in rainy conditions.

Residents are urged to be on the alert for possible impacts resulting from rain-soaked ash.

In addition, residents especially in the Yellow, Orange and Red Zones should avoid areas within the vicinity of rivers due to destructive mudflows (lahars).

Motorists are also asked to exercise caution on the roads due to slippery road conditions that can occur when ash mixes with rainwater.

NEMO said it will not be issuing passes for the Red Volcano Hazard Zones due to the potential dangers that mudflows pose.

Big and hazardous lahars in many valleys on #lasoufrière today. Here is one we witnessed in the Wallbou valley today. @uwiseismic @NEMOSVG pic.twitter.com/SWyv0uRFCZ

— Paul Cole (@PaulCole23) May 3, 2021

In 24 hours to 22:00 UTC on May 3, only a few long-period, hybrid and volcano-tectonic earthquakes were recorded and there was no further seismic tremor.

The seismic network recorded signals from multiple lahars for a period of about six hours starting around 09:00 LT (13:00 UTC).

These lahars most likely took place in the valleys around La Soufriere. The most intense lahars occurred between 11:00 and 12:00 LT (15:00 – 16:00 UTC).

Measurements of the sulfur dioxide flux at the volcano were carried out with the help of the coastguard off the west coast of St. Vincent on May 2. Measurements yielded an average SO₂ flux of 1 036 tons per day.

The volcano continues to be in a state of unrest. Explosions with accompanying ashfall, of similar or larger magnitude to those that have already occurred, can take place with little or no warning.

The volcano remains at Alert Level RED.

Geological summary

Soufrière St. Vincent is the northernmost and youngest volcano on St. Vincent Island. The NE rim of the 1.6 km (1 mile) wide summit crater is cut by a crater formed in 1812.

The crater itself lies on the SW margin of a larger 2.2 km (1.3 miles) wide Somma crater, which is breached widely to the SW as a result of slope failure.

Frequent explosive eruptions since about 4 300 years ago produced pyroclastic deposits of the Yellow Tephra Formation, which blanket much of the island.

The first historical eruption took place in 1718; it and the 1812 eruption produced major explosions.

Much of the northern end of the island was devastated by a major eruption in 1902 that coincided with the catastrophic Mont Pelée eruption on Martinique.

A lava dome was emplaced in the summit crater in 1971 during a strictly effusive eruption, forming an island in a lake that filled the crater prior to an eruption in 1979.

The lake was then largely ejected during a series of explosive eruptions, and the dome was replaced with another. (GVP)

Featured image credit: Paul Cole