Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 16 August
to 16:00 17 August 1996

The level and nature of activity at the Soufriere Hills volcano during this reporting period was similar to that observed during the past several days. Activity continues to be dominated by small- to moderate -sized rockfalls and a few small pyroclastic flows from the eastern flank of the growing lava dome.

One hundred and eighteen (118) rockfalls, 35 hybrid and 13 volcano-tectonic earthquakes were recorded during this reporting period. The largest rockfalls occurred at 09:57, 11:50, 12:06 and 12:14 today, with the events of 11:50 and 12:14 being associated with small pyroclastic flows none of which travelled beyond the Tar River Soufriere. The largest rockfalls were also associated with small ash clouds and that for the event of 12:14 attained a height of 6,000 ft. A swarm of small volcano-tectonic earthquakes was recorded between 01:00 and 02:25 this morning. These VTs were located at depths of less than 2 km beneath English's Crater. One episode of flash flooding in Fort Ghaut was recorded by the Gages seismic station in the form of a moderate-amplitude broadband tremor from 03:24 to 03:45 today. A few episodes of intermittent low-amplitude broadband tremor were also recorded at the stations closest to the Crater.

Visibility was good during parts of the day. Vigorous steaming was observed from most of the dome. Several areas of the eastern part of the dome appear very unstable and the observed rockfalls generally originated from this area. The eroded gully channelling material from the upper flanks of the eastern dome into the upper reaches of the Tar River valley is almost full with debris.

COSPEC measurements were not made today because of problems with the instrument. EDM measurements were made on the eastern triangle late yesterday and today. Yesterday's results show a shortening of 11mm for the Whites to Castle Peak line since 14 August while today's measurements indicated no change in the line length. Today's measurement for the Long Ground to Castle Peak line showed no change compared to yesterday's. The highest point on the dome was measured from Chance's Peak yesterday and yielded a value of about 3161 ft .

Further rockfalls and pyroclastic flows will occur but all indications are that these 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