Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 20 August
to 4 pm 21 August 1997

Activity at the volcano is at a somewhat reduced level of seismic activity, but rock fall activity has become slightly elevated. The cyclic pattern of hybrid swarms has begun to break down and the intensity and length of the swarms have declined. Over the last 24 hours one swarm with 72 hybrids has been recorded starting at 9.53 pm and finishing at 1.15 am.

72 hybrid earthquakes, 1 volcano-tectonic earthquake, 2 long period earthquakes and 71 rockfalls triggered the broadband seismic network over the last 24 hours. Two (2) regional earthquakes occurred at 6.43 pm yesterday evening and 9:42 am this morning. The hybrids mainly occurred in a swarm between 9.53 pm and 1.15 am last night. There have been intermittent rock fall activity which generates minor ash plumes above the volcano. There have no major ash emissions today. Viewed over a period of about 9 days (from 12th August) the intensity of the swarms approximately spaced at 10 to 12 hour intervals has increased and decreased defining a longer time-scale fluctuation in activity.

The volcano has remained in cloud all day and no visual observations have been possible.

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. The enhanced pyroclastic flow activity indicates increasingly instability of the dome and further pyroclastic flow activity is anticipated.

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. People should remain vigilant and continue to listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory