Montserrat Volcano Observatory

Morning Report
Report for the period 4 pm 14 August
to 7 am 15 August 1997

Activity at the volcano has remained at a high level with continuing hybrid swarms and pyroclastic flows. A hybrid swarm began at 7:19 pm last night and lasted until about midnight. The intensity of the swarm gradually increased to a peak at just before midnight. A large amplitude, long duration signal at 11:05 pm was probably a pyroclastic flow down the north flank of the volcano.

Following the end of the swarm the predominant seismic signals were due to small pyroclastic flows and rockfalls.

A further hybrid swarm started at about 5:30 am and is still continuing at the time of reporting. Some of the events in this swarm are large volcanic earthquakes. A particularly large amplitude signal was recorded at 6:08 am and saturated on all drums for 30 seconds. A detonation was heard from the volcano at this time, and it was followed by a pyroclastic flow down Gages valley and a gently rising ash column.

The recent hybrid earthquake swarms are thought to be associated with rapid extrusion of new dome material. It appears that small explosions are also taking place as new magma increases the pressure within the dome.

Further explosions may take place with little or no warning. These may be more intense and longer lasting than those already experienced. If explosions do occur, the central zone should be evacuated immediately and people in the northern zone should seek shelter under as strong a roof as possible. After an explosion small rocks and ash can be expected to fall everywhere on the island. Ash and falling rocks make driving hazardous. Ash is present in the atmosphere and masks should be worn outdoors.

Pyroclastic flows are expected on all flanks of the volcano, and so at no time is it safe to enter the exclusion zone, including the Belham river valley. Access to the exclusion zone is completely restricted. The central zone is evacuated over night and people should not return to their homes until advised to do so. Everyone should remain vigilant and continue to listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory