Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 15 August
to 4 pm 16 August 1997

Activity at the volcano has remained at a high level and, following the pattern of the last few days, is still dominated by hybrid earthquake swarms and dome growth.

223 hybrid earthquakes and 20 rockfalls triggered on the broadband seismic network over the last 24 hours. No volcano-tectonic earthquakes or long period events were recorded. The hybrids occurred in three swarms. The first hybrid swarm began at 2:22 pm yesterday afternoon and lasted until about 7:15 pm yesterday evening. A further hybrid swarm started at 10:16 pm and continued until 3:26 am this morning. This swarm was composed of 80 hybrid earthquakes. A third hybrid swarm started at 6:16 am and continued until 9:07 am. 95 hybrid earthquakes were recorded during this swarm. Short periods of continuous tremor occurred during the peaks of these hybrid swarms. Between the swarms the predominant seismic signals were due to small pyroclastic flows and rockfalls. The recent hybrid earthquake swarms are thought to be associated with extrusion of new dome material. The high levels of seismic activity suggest that extrusion rates are rapid.

EDM measurements were made today on the Waterworks to Lees Yard lines. It is now possible to recognise a slow trend of shortening on this line. Regular measurements will be made in order to monitor the changes of this line. Wind blown ash made measurements impossible from MVO to Lees Yard.

Ash clouds have been observed intermittently throughout the day as the result of rockfalls and small pyroclastic flows from the growing dome. Periods of enhanced steam emission has also been observed during periods of high seismicity.

The small explosions which occurred on Monday and Tuesday demonstrate the potential for explosive eruptions. Further explosions are possible and these may be more intense and longer lived 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 a strong roof as soon as possible. After an explosive event, small rocks and ash can be expected to fall anywhere on the island. Ash and falling rocks can make driving hazardous. Ash is present in the atmosphere and dust masks should be worn outdoors.

All ghauts on the volcano are now filled with hot pyroclastic flow deposits. It is expected that as the current elevated level of activity continues, further pyroclastic flows could occur on all flanks of the volcano. This makes all of the exclusion zone extremely dangerous. Pyroclastic flows could reach into the Belham river valley. Access to the exclusion zone is completely restricted, and people should stay away from the flanks of the volcano. The Government of Montserrat today advised that people living south of Nantes River should temporarily leave this area in the light of the recent increase in volcanic activity. People should remain vigilant and continue to listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory