Montserrat Volcano Observatory

Morning Report
Report for the period 4 pm 18 August
to 7 am 19 August 1997

Activity at the volcano remains at a high level with continuing hybrid swarms merging into continuous tremor and rockfalls. A hybrid swarm began at around 9.15 pm last evening and continued until around 0.35 am this morning. The hybrid swarm was rather less intense than previous swarms and did not develop into a period of sustained tremor as in the last few swarms. The swarm ended with some rock fall signals. Since then seismicity has been at a low level, but occasional rockfall signals have been recorded throughout the night. During this period near-continuous ash production was observed. Currently the summit of the dome is shrouded in cloud.

The recent hybrid earthquake swarms are thought to precede periods of more active dome growth in which rockfall activity is sometimes elevated. During the day or clear nights the hybrid swarms often culminate in vigorous gas plumes and occasionally minor explosions or ash emissions. The hybrid swarms are quite regular being spaced between 8 and 12 hours apart.

Further explosions may take place with little or no warning. These may be more intense and longer lasting than those already experienced. If explosions do occur, people should seek shelter under as strong a roof as possible and have a helmet or head protection available. After an explosion small rocks and ash can be expected to fall everywhere on the island. Ash and falling rocks make driving hazardous. Ash is present in the atmosphere and masks should be worn outdoors.

Pyroclastic flows are expected on all flanks of the volcano, and so at no time is it safe to enter the exclusion zone, including the Belham river valley. Access to the exclusion zone is completely restricted. The areas south of the Nantes River have been evacuated over night. Everyone should remain vigilant and continue to listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory