Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 20 September
to 16:00 21 September 1996

Activity at the Soufriere Hills volcano throughout the reporting period has continued at a low level. Rockfalls continue to be the most dominant seismic signals recorded by stations around the volcano today.

Ninety-eight rockfalls were recorded during the reporting period. The largest event occurred at 01:51 on 21 September. One long period event and a single regional earthquake were recorded by the seismic network. No volcano-tectonic or hybrid events were recorded. Low amplitude broadband tremor was continuous throughout the reporting period.

Visibility was generally poor for most of the day but some brief views were obtained of the dome. Several unstable blocks were observed on the northern face of the lava dome by scientists working in the field at Windy Hill today; these are expected to produce further rockfalls in the next few days. Results from mapping of the pumice deposits which were produced by last Tuesday's activity indicate a roughly even distribution of these rock fragments on the flanks of the volcano. Pumice clasts of up to 95 grams were deposited at 3km from the volcano; at 6km this had fallen to about 3.5 grams.

EDM measurements were carried out today on the western triangle between St Georges Hill, Windy Hill and Farrells. Both line lengths to the Farrells reflector site lengthened between 16 September and 21 September. The changes observed were 4mm and 9mm respectively on line lengths between St Georges Hill - Farrells and Windy Hill - Farrells. A GPS survey was initiated today on a new network of stations which involves a modification of the old configuration. The new arrangement now provides scientists coverage of the entire island and involves a rationalization of the pre-existing network.

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 stabilizes. 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 subject 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