Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 29 August
to 16:00 30 August 1996

Activity at the Soufriere Hills volcano during this reporting period continued at a slightly higher level than that observed during the previous reporting period. The occurrence of small- to moderate-sized rockfalls from the flanks of the growing lava dome, together with two swarms of volcano-tectonic earthquakes were the main features for the period.

Fifty five (55) rockfalls, 24 hybrid, 2 long-period and 146 volcano-tectonic earthquakes were recorded. From 16:00 yesterday 29 August to 00:30 today, the continuous low-amplitude broadband tremor that had been recorded on most of the seismic stations since the later part of the previous reporting period continued. Occurring within this tremor from 18:30 to 23:15 on 29 August was a swarm of small volcano-tectonic earthquakes. Near-continuous small- to moderate-sized rockfall and possible small pyroclastic flow occurrence was recorded between 22:00 on 29 August and 00:30 on 30 August. The level of seismic activity decreased considerably after 00:30 but again picked up from 06:30 to 10:17 with a sequence of small hybrid and volcano-tectonic earthquakes. The VT and hybrid earthquake sequence was immediately followed by low-amplitude broadband tremor with occasional small- to moderate-sized rockfalls till the end of the reporting period. The volcano-tectonic earthquakes were located at depths less than 2 km beneath English's Crater and point to the continuous movement of magma from shallow depths to the surface as the process of dome growth at the Soufriere Hills volcano continues.

Visibility during most of the day was very poor but brief glimpses of parts of the dome were obtained from Bramble Airport Control Tower in the early morning. These glimpses suggested that two extruded features (possibly spines) may exist in the central part of the eastern dome. Light ash associated with some of the larger rockfalls and/or small pyroclastic flows was occasionally seen drifting towards the south or southeast at about 3,500 ft above sea level.

COSPEC and EDM measurements were not made today because of instrumental problems and the low cloud cover respectively.

Further rockfalls and pyroclastic flows will occur but all indications at the moment are that the pyroclastic flows will be confined to the Tar River Valley area. However, areas affected by associated ashfalls will obviously depend on the direction and strength of the wind at the time. People in areas affected by ash falls should exercise great care when driving. Dust masks should be worn in ashy environments.

The Tar River Valley and surrounding areas are now extremely hazardous, and should not be entered under any circumstances. We urge individuals who continue to ignore this advice to think very seriously before making trips to these highly hazardous zones.

Montserrat Volcano Observatory