Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 04 August
to 16:00 05 August 1996

The level of activity at the Soufriere Hills volcano during the past 24 hours has been slightly lower than that observed during the previous 24 hours. However, the style of the activity, which is characterised mainly by the occurrence of rockfalls and near-periodic, low frequency tremor episodes, continues.

Four (4 ) episodes of high-amplitude, near-periodic, relatively low frequency, near-harmonic, tremor lasting about 60 minutes were recorded during this reporting period. All the tremor episodes were preceded by small hybrid and volcano-tectonic earthquakes and followed by small hybrid earthquakes. These episodes of VTs and/or repetitive hybrid earthquakes and tremor are probably associated with magma migration from shallow depths to the surface as the process of dome growth at the Soufriere Hills volcano continues. Given the significant amounts of steam that seem to be pumped out during the times of large tremor amplitude, the interaction of the magma with the volcano's groundwater system may also be involved.

Sixty four (64) small- to moderate-sized rockfalls were recorded, with the largest occurring at 16:13 and 21:24 on 04 August and 05:28 and 07:50 on 05 August. The event of 16:13 on 04 August produced a small ash cloud which was seen drifting westwards over Upper Gages. Approximately 373 distinct small hybrid earthquakes and 71 small volcano-tectonic (VT) earthquakes were recorded. The VTs were generally located at shallow depths beneath the crater region. Three small long-period events were also recorded.

Visibility was generally very poor throughout the day.

GPS measurements were made on the eastern flank of the volcano but the data is still being analysed. No EDM or COSPEC measurements were made today because of low cloud cover on the volcano and episodic rainfall.

The ashfalls due to the pyroclastic flows on 29 and 31 July have not been completely washed away by the recent rains and continue to make driving hazardous. Please exercise some care when driving and remember to wear dust masks while cleaning ash in the home or outside.

While the current phase of activity at the Soufriere Hills volcano continues, hazards in some areas of the evacuated zone have increased significantly. In particular, we expect significant-sized pyroclastic flows to occur more frequently in the Tar River Valley area. These will obviously be associated with ash clouds which will be blown on the wind, with areas affected by ashfall being determined by the wind direction and strength at that time. The Tar River Valley and surrounding areas are now extremely hazardous, and should not be entered under any circumstances. If activity continues, there is a risk that flows or ash surges may come over Farrells' Wall and the upper reaches of some of the ghauts closest to the Tar River Valley. People are, therefore, advised not to work these areas. We also urge individuals who continue to ignore this advice to think very seriously before making trips to these highly hazardous zones.

Montserrat Volcano Observatory