Scientists Observe Volcanic-Tectonic Earthquakes As La Soufrière Erupts

March 19th 2021. View of the dome from the top of the Windward trail. Photo credit: MVO, Thomas Christopher.

View of the La Soufrière Volcano dome from the top of the Windward trail taken on March 19th. 2021. (MVO, Dr. Thomas Christopher)

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.

The National Emergency Management Organization and the University of the West Indies Seismic Research Centre (UWI SRC) have noted a change in the behavior of the La Soufrière Volcano.

Monitoring scientists at the Belmont Observatory led by scientists from the UWI SRC have noted a change in seismic activity associated with the ongoing eruption of the La Soufrière Volcano.  Up until 23rd March 2021, the seismic activity had been dominated by very small low-frequency events which were associated with the ongoing extrusion of the lava dome.  These were almost always only recorded at the seismic station closest to the dome.

Starting at approximately 10:30 local time (14:30 UTC) on 23rd March 2021, the monitoring network recorded a swarm of small low-frequency seismic events which lasted for about 45 minutes.  These events were different from previous activity in that they were also recorded on other stations.  These events were probably associated with magma movement beneath the dome, although the earthquakes’ depth cannot be determined.  This is the first time that such a swarm has been seen since the seismic network was upgraded in early 2021.

Starting at 16:53 local time (20:53 UTC) on 23rd March 2021, the monitoring network started recording volcano-tectonic (VT) earthquakes. These earthquakes are normally associated with underground fractures of the rock mass and are commonly generated by magma pushing through an unyielding rock mass.  The volcano-tectonic earthquakes were located beneath the volcano, at depths down to 10 km below the summit.  The largest of these had a magnitude of 2.6.  Some of them have been reported felt by people living in communities close to the volcano such as Fancy Owia and Sandy Bay.  

At the present time, the volcano-tectonic earthquakes continue, with the numbers of events fluctuating.  The very small dome-extrusion events also continue.

The National Emergency Management Organisation (NEMO) wishes to inform the public that earthquakes associated with the La Soufrière Volcano’s ongoing eruption continue to occur from time to time; some of the largest ones may be felt.  The alert level remains at Orange, and no evacuation order or notice has been given.  However, NEMO is encouraging residents, especially person living in communities close to the volcano (i.e., the Red and Orange Volcanic Hazard zone), to heighten their preparedness if it becomes necessary to evacuate at short notice.

The La Soufrière Volcano continues to be closely monitored by a locally based team consisting of scientists from the Soufriere Monitoring Unit (SMU), The UWI Seismic Research Centre (SRC), and the Montserrat Volcano Observatory (MVO).  This team works closely with an extended group based at the SRC (Trinidad) and MVO (Montserrat).  The Team Lead at this time is Vincentian Professor Richard Robertson. The monitoring network uses various techniques to monitor the volcano that is constantly being improved and upgraded.

There is NO ‘explosive’ eruption at the La Soufrière volcano at this time. La Soufrière continues to have effusive eruptions as hot magma reaches the surface at extreme temperatures. This appears in the night as fire or a bright red glow above the crater. As the dome gets higher and closer to the crater’s rim, this phenomenon will continue to be visible on clear nights.

The alert level remains at Orange. The volcano continues to exude magma on the surface and steam can still be observed from the Belmont Observatory. Persons living in areas close to the volcano should expect strong sulfur smells for several days to weeks, depending on changes in wind direction.

The NEMO is reminding the public that no evacuation order or notice has been issued. NEMO continues to appeal to the public to desist from visiting the La Soufrière Volcano and especially going into the crater since doing so is extremely dangerous.

The @uwiseismic and NEMO continue to advise access to the #LaSoufriere Volcano is strictly prohibited at this time….

Posted by Trinidad and Tobago Weather Center on Thursday, January 14, 2021

According to the SRC, the new volcanic dome is extremely dangerous for those in close proximity as it can explode at any time without warning. People have been killed in this way. This warning comes as images from a birthday photoshoot surfaced on social media.

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)

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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