Montserrat Volcano Observatory

Morning Report
Report for the period 8 pm 04 August
to 7 am 05 August 1997

Activity at the volcano overnight has remained at a very high level with a hybrid swarm and continued explosions and pyroclastic flow activity. A hybrid earthquake swarm this morning was followed by an explosive eruption and pyroclastic flows at 0445.

A vertical eruption column quickly rising to over 10,000 feet was observed from the MVO and an audible rumbling lasted for over 10 minutes. Lightning was observed in the eruption column. Fallout from the explosion reached Old Towne by 0450. This consisted of lithic clasts of up to 2cm. The fallout continued for around 15 minutes.

Pyroclastic flows followed closely after the eruption column. Incandescent material was observed at the head of the Gages valley, indicating that the route of the flows was down the Gages valley. The pyroclastic flow signals lasted for less than 10 minutes in duration and flows were thought to be smaller than those yesterday.

The hybrid earthquake swarm started at just after 0250 am, continued until after 5 am and consisted of 55 events. At the peak of the swarm the frequency of events was one every 40 seconds The swarm was shorter in duration than previous swarms and did not contain the same distribution of magnitudes.

At 0716 audible explosions were heard from the Plymouth area. Investigations into the origin of these explosions are being carried out.

The activity is still generally following a cyclical pattern in the tiltmeter with regular inflation and deflation of the volcano corresponding to the earthquake swarms on the inflationary part of the cycle. The explosion occurred as the cycle reached it's peak. However, pyroclastic flows have also occurred outside the most probable time period, and so at no time is it safe to enter the exclusion zone, including the Belham river valley. The risk of further explosive eruptions remains high and the present pattern of activity is expected to continue.

There is ash in the air in the west of Montserrat and therefore dust masks should always be worn in these areas. Drivers should also be considerate whilst driving in ashy conditions. The Belham River valley is very dangerous and should not be entered. Access to the exclusion zone is completely restricted, and people should stay completely away from all the flanks of the volcano. Everyone should continue to stay alert, and listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory