Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 20 August
to 16:00 21 August 1996

The main highlight of activity at the Soufriere Hills volcano during this reporting period was the near-continuous occurrence of pyroclastic flows in the Tar River Valley and associated ash clouds which were blown westward to northwestward on the wind during a three-hour period from mid-morning today. Small- to moderate-sized rockfalls and pyroclastic flows continued to dominate the activity at the Soufriere Hills volcano. Two distinct periods of increased rockfall and pyroclastic flow activity and one period of near-continuous small-sized rockfall occurrence were noted. During the first of these , from 14:45 to 17:49 on 20 August, the largest pyroclastic flow generated at 17:30 travelled a distance of about 1.5 km and produced an ash cloud which reached a maximum height of about 15,000 ft above sea level. The period of near-continuous, mainly small, rockfall occurrence started around midnight and ended around 04:00 this morning. From around 10:04 this morning, near-continuous rockfall occurrence led to a period from 10:40 to 13:50 during which several pulses of small- to moderate-sized pyroclastic flows were generated in the Tar River Valley. Several ash clouds up to a maximum height of 10,000 ft above sea level were produced and these were carried to the west and northwest by light and variable winds, resulting in significant ashfalls in St. George's Hill, Plymouth, Richmond Hill and Fox's Bay. Lighter ashfalls occurred in Cork Hill, Isle Bay and Old Towne. Since13:50, the nature of the activity has returned to one of intermittent low-amplitude with occasional rockfalls. Overall, 131 rockfalls, 2 long-period, 1 volcano-tectonic and 36 hybrid earthquakes were recorded.

Visibility during most of the day from the Observatory was poor. However, occasional views of the dome from the east revealed that most of the rockfalls and pyroclastic flows are channelized in the gully excavated just north of Castle Peak. Variable steam emission was observed from several areas of the dome.

EDM and COSPEC measurements were not made today.

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