Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 18 September
to 16:00 19 September 1996

Activity at the Soufriere Hills volcano during this reporting period has continued at a relatively low level compared to yesterday. Rockfalls and volcano-tectonic earthquakes continue to be the most dominant seismic signals.

Seventy eight small- to moderate-sized rockfalls were recorded during the reporting period. The largest rockfalls were recorded at 23:03 on 18 September and 04:39 on 19 September. Twenty-two volcano-tectonic events were also recorded during the period; none of these occurred in swarms. The VT events were all located at shallow depths beneath English's Crater (above 2 km). Twelve hybrid events and no long period events were recorded during the reporting period. Low amplitude broadband tremor was recorded for most of the period under review.

Visibility was generally poor for most of the day but some good views were obtained of the large scar feature which has developed at English's Crater. The scar is a massive, u-shaped feature with an open end which extends down into the Tar River valley. This new collapse or blast feature extends along the boundary between Castle Peak and the new dome, towards the point at which the old 18 July vent was located. Approximately 25% of the new dome and some parts of Castle Peak has been removed. Clear views of the scar feature during an evening flight allowed observation of the internal structure of the new dome and indicated a number of cracks on the sides of the scar. Small rockfalls from the unstable sides of the scar were observed by scientists from Whites. Emission of steam and other volcanic gases was observed from the base of the scar.

No EDM measurements were carried out today. The GPS survey which was started yesterday on the large net which covers the entire volcano was completed today; the data from this survey is currently being processed. Field surveys of the distribution and dimensions of the air-borne particles were undertaken today; these would be used to produce maps of the lithic and ash distribution which resulted from the 17-18 September event.

MVO scientists are expecting more rockfalls and possibly pyroclastic flows to occur during the next few days as the unstable sides of the new scar feature at English's Crater stabilises. All indications are that the rockfalls and pyroclastic flows will be confined to the Tar River valley area. Areas affected by associated ashfalls will depend on the direction and strength of the wind at the time. Dust masks should be worn at all times in ashy environments, and drivers should exercise caution and consideration for other road users.

The extensive damage which occurred in the Long Ground area on Tuesday night further demonstrates the extreme danger which individuals suject themselves to if they venture into these areas. The Tar River and Long Ground areas are now extremely hazardous and we urge individuals who persist in ignoring this advice to think very seriously before making trips to these potentially deadly zones.

Montserrat Volcano Observatory