Montserrat Volcano Observatory

Morning Update
Report for the period 16:00 03 August
to 07:00 04 August 1996

The level of activity at the Soufriere Hills volcano overnight was slightly higher than during the preceding reporting period although the pattern was relatively similar. Three periods of sustained, large-amplitude, low-frequency, near-harmonic tremor associated with small hybrid earthquakes and/or small volcano-tectonic earthquakes occurred. During one of these vigorous tremor episodes at around 05:00 this morning, ash clouds were observed which rose to about 10,000 ft above sea level. These ash clouds were most probably due to pyroclastic flows in the Tar River Valley caused by collapses of the over steepened flanks of the lava dome. The ash clouds were blown on the wind towards the west, possibly causing ashfalls in the Plymouth, Richmond Hill and Fox's Bay areas. These episodes of VTs and/or repetitive hybrid earthquakes and harmonic 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.

Several small- to large-sized rockfalls also occurred and some of these were associated with small ash clouds. The largest rockfalls occurred at 00:09 and 05:31 this morning. The rockfall at 05:31 was associated with an ash cloud with an estimated height of about 10,000 ft above sea level. The ash was observed drifting westwards over the Richmond Hill and Fox's Bay areas. This large rockfall may have been associated with a small pyroclastic flow.

Visibility was very poor during the early morning period, with the cloud level very low.

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