Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 2 August
to 8 pm 3 August 1997

The cyclical pattern of activity at the volcano with hybrid earthquakes and tiltmeter cycles has continued during the period. An intense period of activity which began at about 6:00 pm today, generated pyroclastic flows which reached the sea in Plymouth and caused destruction of several buildings along Fort Ghaut.

48 rockfalls, 14 long period events and 135 hybrids were recorded during the day. No volcano-tectonic earthquakes were recorded. Most of the hybrid earthquakes occurred in two swarms.

The first of the two hybrid earthquake swarms began at 9:18 pm yesterday evening and ended at 2:48 am this morning. This was followed by a short period of pyroclastic flow activity for about 10 minutes at about 3:20 am. This was most likely due to pyroclastic flows in the Gages valley. A further hybrid earthquake swarm began at 1:28 pm this afternoon and continued up to 5:00 pm. This was a more intense swarm than the previous swarm and contained some very large hybrid events. The events increased in frequency during the latter parts of the swarm and went into near continuous tremor at 5:17 pm. At 6:00 pm the first major pyroclastic flow occurred in the Gages valley. Further pyroclastic flows were generated which produced flows and surges down the Gages valley and surges onto St George's Hill. This period of pyroclastic flow activity lasted until about 8:30 pm and resulted in strongly convecting ash plumes which extended up to above 15,000 feet. Heavy, wet ashfalls were experienced in Isles Bay, Ole Towne, Salem and other areas to the west of the volcano.

A late afternoon helicopter flight during the period of heightened activity confirmed that all the flows were confined to the Gages valley. The flows which extended into Plymouth had reached the sea at Port Plymouth and ignited buildings along the entire stretch of Fort Ghaut. New flows had extended onto the northern flank of the Gages valley and had caused fires in Gages village area.

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.

EDM measurements were made today on the Waterworks to Lees Yard and Garibaldi Hill-MVO-Lees Yard triangle. The results from these measurements will be reported later in the week.

The Gages valley is now filled with hot pyroclastic flow deposits and under no circumstances should people venture into this area. It is expected that as the current elevated level of activity continues further pyroclastic flows would occur in the Gages valley. This makes Plymouth extremely dangerous. The Belham River valley is also 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.

Montserrat Volcano Observatory