Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 11 September
to 4 pm 12 September 1997

Volcanic activity has been fairly low during this reporting period. There was a two-hour episode of vigorous ash venting from the summit of the volcano starting at noon.

The summit of the volcano was shrouded in cloud for much of the day. A period of heightened activity on the dome started at around noon today with a small pyroclastic flow into Mosquito Ghaut, travelling halfway across Farrell's Plain. This was followed, from 12:40 until 2:00 pm, by a number of pulses of vigorous ash-venting from the summit. There were no pyroclastic flows during the ash-venting episode, although any rockfall activity would have been obscured by the clouds. At times the ash was ejected forcefully upwards, although the top of the plume was always less than 10,000 ft above sea level. The plume was blown over Plymouth. The last of the ash-venting pulses, starting at 1:58 pm, was the best observed. There was vigorous ash venting from both the summit of the dome and the north side of the summit. This carried on for about a minute, generating moderately-convecting clouds of ash. This was followed by much more gentle venting of ash and steam.

Seismic activity was dominated by signals from rockfalls; 21 were recorded on the broad-band system, and only one each of the hybrid, long-period and VT earthquakes. The majority of the rockfall signals were recording during the ash-venting episode.

The dome is very large and unstable and further collapses are likely. These may take place with little or no warning and need not necessarily be preceded by hybrid earthquake swarms. The pyroclastic flows generated by a large collapse could reach the Belham Bridge or further and fill the Belham Valley with material. This would then allow flows to impact upon the Old Towne and Friths areas and the associated surges could get to Salem. The southern part of Montserrat is extremely dangerous and all areas south of the Nantes River should be evacuated.

If an explosion occurs, small rocks and ash can fall anywhere on the island. People should seek shelter under a strong roof as soon as possible. Helmets or other head protection should be used and it should be remembered that ash and falling rocks make driving hazardous. People are urged to wear their dust masks if there is ash in the air, particularly near roads or if walking through vegetation.

Montserrat Volcano Observatory