Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 02 August
to 16:00 03 August 1996

Both the level and style of activity at the Soufriere Hills volcano during this reporting period were about the same as those observed during the previous 24 hours.

Five (5 ) periods of sustained, high-amplitude, low-frequency, near-harmonic tremor, lasting about 60 to 90 minutes, were recorded at intervals of about 3 to 4 hours. Two of these episodes of maximum-amplitude tremor were preceded by small VTs and small, near-repetitive hybrid earthquakes while the other three were preceded by just small near-repetitive hybrid events. All five periods of peak amplitude tremor decayed first into smaller hybrid events and then background. During the day time, large steam plumes mixed with small quantities of ash were observed to be associated with the times when the tremor level was very high. 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.

Fifty eight (58) small- to moderate-sized rockfalls were recorded and a few of these produced visible small ash clouds. Approximately 340 distinct small hybrid earthquakes and 43 small volcano-tectonic (VT) earthquakes were recorded. The VTs were generally located at shallow depths beneath the crater region.

Visibility was generally poor throughout most of the day but periodic partial cloud clearances from the dome revealed that it was steaming vigorously from several areas.

EDM measurements were made today on the eastern triangle. Yesterday's (02 August) results showed a shortening of 1.2 cm since 30 July for both the Long Ground and Whites lines to Castle Peak. Today' s results revealed that the Whites to Castle Peak and Long Ground to Castle Peak lines shortened by 2 mm and 9 mm respectively. COSPEC measurements of the amount of SO2 in the volcanic plume were also made but the results are still awaited. No GPS measurements were made today.

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