Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 1 August
to 4 pm 2 August 1997

Activity at the volcano has remained at an elevated level today. There have been several periods of intense rockfalls and pyroclastic flow activity and two hybrid swarms. Weakly convecting ash plumes have been produced throughout the period depositing ash on areas to the west of the volcano.

65 rockfalls, 11 long period events and 124 hybrids were recorded during the day. No volcano-tectonic earthquakes were recorded. 6 of the long period events triggered rockfalls. Most of the hybrid earthquakes occurred in two swarms.

The first of the two hybrid earthquake swarms began at 4:17 pm yesterday evening and ended at 6:04 pm. It consisted of 16 events. This was followed by a period of high amplitude tremor and pyroclastic flow activity from about 6:44 pm until 8:00 pm. At this time glowing from behind St. George's Hill was seen periodically. This was most likely due to pyroclastic flows in the Gages valley. A small mudflow signal also occurred last night at about 1:10 am. This emphasises that there is still a potential hazard from re-mobilisation of fresh pyroclastic flows deposits by heavy rain and all ghauts on the flanks of the volcano could be affected.

A further hybrid earthquake swarm began at 4:42 am this morning and continued until about 10:50 am. This was a more intense swarm than the previous swarms this week and contained some very large hybrid events. The intensity of the swarm gradually increased to a peak at about 9 am, at which point there were about 3 events per minute and continuous moderate tremor between events. The activity then decreased and was followed by a moderate pyroclastic flow over Gages at 10:25 am.

The activity is following a cyclical pattern in the tiltmeter with regular inflation and deflation of the volcano corresponding to the earthquake swarms and continuous pyroclastic flows respectively. However, large 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. This type of activity is similar to that observed towards the end of June and the beginning of July, and it is possible that major pyroclastic flows like those of 25 June may occur.

An observation flight this afternoon showed that there no major new deposits in any of the ghauts around the volcano except for Gages valley. Here, the newest deposits went as far as just below Gages Lower Soufriere. A limited view of a small amphitheatre above Gages wall was obtained; this was probably formed as a result of the recent pyroclastic flow events. During this flight, short stops were made to collect samples from and make measurements on the pyroclastic flow deposits of 25 June. These will help our understanding of the formation of these deposits, and thus on the mechanisms that produce pyroclastic flows.

EDM measurements are being made today on the Waterworks to Lees Yard and Garibaldi Hill to MVO lines. The field party was still working at the time of reporting and results from these measurements will be reported later in the week.

The Gages valley is now filled in and flows and surges will overspill the valley anywhere along its length. Under no circumstances should people be in this area. The Belham River valley is very dangerous and should not be entered at all. Access to the exclusion zone is completely restricted, and people should stay completely away from any of the flanks of the volcano. Everyone should continue to stay alert, and listen to Radio Montserrat for any announcements. The new ash is still 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.

Ms. Costanza Bonadonna of Bristol University arrived on Montserrat today for a month long tour of duty to the MVO.

Montserrat Volcano Observatory