Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 09 August
to 16:00 10 August 1996

The level of activity at the Soufriere Hills volcano during the first part of this reporting period was at about the same level as during the previous reporting period but increased slightly from about 06:00 this morning, first with a series of volcano-tectonic earthquakes and then near-continuous occurrence of small- to large-sized rockfalls.

One hundred and fifty three (153) rockfalls were recorded. The largest of these which occurred at 07:33, 08:44, 09:23, 10:01, 10:37, 11:14 and 12:46 today were associated with small pyroclastic flows in the Upper reaches of the Tar River Valley. The largest flow seems to have travelled to just slightly beyond the Tar River Soufriere. These pyroclastic flows and other moderate-sized rockfalls generated ash clouds which were blown on the wind towards the west, possibly resulting in very light ashfalls in Plymouth and environs. The maximum height reached by the ash was about 5,000 ft above sea level. Seventy four (74) volcano-tectonic earthquakes which occurred in two bursts were recorded and these were again located at depths less than 2 km beneath the Crater region. One hundred and thirty seven (137) small hybrid earthquakes were recorded.

The dome was generally obscured by low clouds throughout most of the day. A few episodes of vigorous, near-continuous ashy steam emission from the volcano were noted.

EDM measurements made today on the eastern triangle showed shortenings of the slope distances Whites to Castle Peak and Long Ground to Castle Peak of 1 cm and 1.6 cm respectively. COSPEC measurements of the amount of SO2 in the volcanic plume were not made today but yesterday's measurements yielded an average value of 326 tonnes per day.

Dome growth at the Soufriere Hills volcano is still continuing. The current phase of activity has led to considerably increased hazards in some areas of the evacuated zone. 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