LA SOUFRIÈRE BULLETIN #52
1. Seismic activity at La Soufrière, St Vincent changed significantly today when the seismic station closest to the summit began recording low-level seismic tremors on April 8.
2. Six separate episodes, or bands, of tremors, starting at 3 am were recorded with intervals of about two and a half hours between them. The tremor episodes have slowly increased in magnitude.
3. A tremor is a continuous seismic signal that is usually associated with the movement of magma to the surface.
4. The seismic network also recorded five long-period earthquakes during the second and fourth bands of tremor. Long-period earthquakes are also usually associated with the movement of magma.
5. There were also two brief swarms of small volcano-tectonic (VT) earthquakes, both taking place between bands of tremor. These were located at depths up to 5 kilometres below the summit of La Soufrière, which is consistent with the depths of the two VT swarms on 23-26 March and on April 5.
6. Elevated and continuous periods of gas venting from the summit of the volcano, coinciding with the bands of tremor were observed. At times there was a well-defined plume.
7. Visual observations made from the Observatory at Belmont during the early evening indicate that the dome height increased significantly during the day. The glow from the dome was visible from Belmont.
8. The volcano has entered a heightened period of activity indicative of a fresh batch of magma either near to, or approaching the surface. The possibility for the activity to move to an explosive phase has increased significantly. Given the current data, it’s not possible to say exactly what the time scale would be.