|Present La Soufrière Alert Level:||ORANGE||There 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.|
La Soufrière (or Soufrière Saint Vincent) is the sole active volcano on the island of St Vincent. This is one of the many volcanoes in the Lesser Antilles named Soufrière, which translates into “sulfur outlet” in French.
La Soufrière has had a number of violent eruptions in the past, namely in 1812, 1902, and 1979. As of 2020, nearly 40 years of quiet was ended as a new dome began to form inside the crater on December 29th.
St. Vincent is located between latitude 13°N and 13° 30’N and longitude 61°W and 61° 30’ W, about 100 miles west of Barbados, 68 miles north of Grenada and about 306 km north of Trinidad.
The island is roughly oval and has an area of 344 km2. It is approximately 29 km long, and 17.5 km wide and is located within the southern part of the Lesser Antilles island arc. The island consists of a central axial range of mountains starting from La Soufrière (1,234 m) in the north to Mount St. Andrew (736 m) in the south.
This range of volcanic mountains divides the island almost equally between a gently sloping eastern or windward side and a deeply dissected and rugged western or leeward side. The north-south trending stratovolcanic centers that make up the island’s backbone show a northward migration in age from 3 Ma, near the south of the island, to 0.6 Ma – Recent at the Soufrière Volcano.
La Soufrière is the highest peak on Saint Vincent and the highest point in the country of Saint Vincent and the Grenadines. Soufrière is a stratovolcano with a crater lake and is the island’s youngest and northernmost volcano.
The youngest volcanic center on St. Vincent is the La Soufrière Volcano, which occupies the northernmost third of the island. This is considered to be the only volcano that is likely to erupt in the future. No detailed geological map of the volcano exists, although the principal formations have been identified by several geoscientists over the years, including Trinidad and Tobago’s Prime Minister, Dr. Keith Rowley, and former UWI Seismic Research Centre’s head, professor Richard Robertson.
The volcanic edifice consists of an older strato-cone or Somma (2.5 km diameter), which forms a steep arcuate ridge to the north, and a younger pyroclastic cone, which has been the source of historical (post-1700) eruptions, nestled within this crater. The older stratovolcano is thought to have been active during the late Pleistocene (~700 ka). The main crater of the Soufrière Volcano is about 1.6 km in diameter and is 300-600 m in depth. Located immediately to the northeast is the 1812 crater, an oval-shaped depression (~450 m diameter and 60 m depth), from which the volcano erupted once (April 27 to June 6, 1812).
Monitoring La Soufrière
According to the University of the West Indies Seismic Research Centre, before the twentieth century the potentially destructive capacity of this volcano was not fully realized. No monitoring system was in place and scientific knowledge of the system was very limited.
Seismological studies at the Soufrière volcano began in 1953 with the establishment of the Seismic Research Unit and since then has evolved to its present state.
Presently, monitoring of the Soufrière volcano is carried out by the Seismic Research Centre assisted by a small local unit (called the Soufrière Monitoring Unit) that operates from the Ministry of Agriculture in Kingstown, St. Vincent and the Grenadines.
The monitoring network consists of five seismic stations, eight GPS stations, and several dry tilt sites. Seismic data are transmitted from field sites to the Belmont Observatory, operated by the Soufrière Monitoring Unit. The data are then accessed from Trinidad via the internet. Regular observation is made at the volcano summit, and measurements are taken of lake and fumarole temperature. Observed changes in the state of the volcano noted.
At any given time, the alert level reflects the status of the La Soufrière Volcano. According to the University of the West Indies Seismic Research Centre, the alert levels for volcanoes in the Commonwealth Caribbean are set by a committee which consists of the professional, scientific staff of the Seismic Research Centre, with consultation with other scientists with special knowledge of this region. Governments responsible for the volcano in question are consulted before the alert level is changed, but this may not always be possible as alert levels may change rapidly.
This alert level system can be found in detail here.
The Integrated Volcanic Hazard Zones for the La Soufrière Volcano was developed for designing an emergency plan for effective management of the Soufrière Volcano. Zones were assigned based on the projected effect of an explosive eruption, with some consideration of a long-term and large-scale explosive eruption.
Details on the Integrated Volcanic Hazard Zones can be found here.
According to the Volcanic Hazard Atlas of the Lesser Antilles, during the past 4000 years, the volcano has had an average of one explosive eruption every 100 years.
More recently (during the past 250 years) the Soufrière Volcano has displayed two distinct types of eruptions.
Type 1: Explosive Eruptions
These are the typical “St. Vincent style” eruptions. They are highly explosive eruptions usually preceded by frequent, strong earthquakes. Rapid rates of magma production result in the ejection of large volumes of new material. This type of activity is exemplified by the 1902-03 and 1979 eruptions.
Type 2: Non-explosive or Effusive Eruptions
This type of eruption is effusive and may be unaccompanied by earthquakes. It involves the extrusion of a viscous lava dome and results in the production of smaller volumes of new material than type 1 eruptions. This type of eruption is exemplified by the 1971-1972 eruption.
A cyclical pattern of eruptive activity during the past 250 years with alternating eruptions of Type 1 and Type 2 has been observed at the volcano.
As of December 2020, La Soufrière is undergoing an effusive eruption with a new dome building within the crater.
Geothermal activity associated with the Soufrière Volcano is confined to the crater and the base of the volcano’s southern flank. Two groups of high-temperature fumaroles are present near the base of the southern part of the andesitic dome that occupies the north-western portion of the summit crater.
The fumaroles emit steam and gases and have reduced in vigor since their first manifestation immediately following dome emplacement at the final stages of the 1979 eruption.
Along the northern streambed of the Wallibou River at an elevation of 280 m (approximately 1 km from the Trinity waterfalls), a group of lukewarm springs (37°C) is present.
The La Soufrière Volcano poses many hazards to the island of St. Vincent. Following the effects of past eruptions in the last 300 years and the geological record, scientists have discovered which hazards are most common.
Pyroclastic flows and surges, mudflows, ashfall, and projectiles are the most hazardous events expected compared to lava flows, atmospheric phenomena, earthquakes, and phreatic explosions. Secondary effects such as landslides and events of more remote possibility such as directed blasts and structural collapse are also possible. Future eruptions are likely to be explosive or effusive similar to those experienced in the historical past.
Information was adapted from the Volcanic Hazard Atlas of the Lesser Antilles (UWI SRC).
The U.W.I. Seismic Research Centre is the official source of information for earthquakes and volcanoes in the English-speaking Eastern Caribbean. The SRC is the scientific monitoring agency that supports various local disaster management agencies of the Eastern Caribbean. This includes the monitoring of the La Soufrière Volcano.
The Seismic Research Centre (SRC) updates the National Emergency Management Organization (NEMO) of St. Vincent and the Grenadines which is then responsible for adjusting the alert level of La Soufrière based on the SRC’s information. NEMO is then responsible for coordinating evacuations across the hazard zones based on the alert level and volcanic hazard.