Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 21 August
to 16:00 22 August 1996

Activity at the Soufriere Hills volcano during this reporting period was variable but generally lower than that observed during the previous 24 hours. Small- to moderate-sized rockfalls and small pyroclastic flows in the Tar River Valley and their associated ash clouds continue to dominate the activity.

One hundred and eighteen (118) rockfalls, 20 volcano-tectonic, 1 long-period and 34 hybrid earthquakes were recorded. There were two episodes of near-continuous generation of rockfalls and/or small pyroclastic flows: from 21:12 to 23:11 on 21 August and from 06:41 to 07:03 today. The largest pyroclastic flows occurred at 17:59 on 21 August and 06:54 on 22 August. The flow front for the former reached the new delta and produced an ash cloud which rose to about 8,000 ft above sea level while the latter travelled just past the Tar River Estate house and was also associated with an ash cloud 8,000 ft high. The ash clouds for both of these events were blown westward on the wind, resulting in ashfall in Plymouth and environs. Most of the volcano-tectonic earthquakes occurred in a single sequence from 18:09 to 19:30 on 21 August and these were generally located at shallow depths beneath English's Crater. Intermittent low-amplitude broadband tremor was recorded at the seismic stations closest to the Crater throughout the reporting period.

Very good views of the lower and middle sections of the dome were obtainable from the ground in the east and from the air. The pyroclastic flows of yesterday were produced by the loss of material from the lower section of the new dome which had grown in the collapse structure produced by events of 29 and 31 July. The gully just north of Castle Peak through which the majority of the flows and rockfalls are channelized is now deeper and wider. Variable steam emission was observed from several areas of the dome.

EDM measurements were made on the northern triangle: St. George's Hill - Farrell's - Windy Hill , but the data is still being processed. No COSPEC measurements were made today because of the poorly developed plume.

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