Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 18 August
to 16:00 19 August 1996

Activity at the Soufriere Hills volcano during the first part of this reporting period was again at about the same level as that observed during the past several days. From about 08:00 this morning, the level of activity increased slightly. However, the nature of the activity remained essentially the same, being characterised by the occurrence of small- to moderate -sized rockfalls and small pyroclastic flows from the eastern flank of the growing lava dome.

One hundred and three (103) rockfalls, 22 hybrid, 1 long-period and 32 volcano-tectonic earthquakes were recorded during this reporting period. Three episodes of near-continuous rockfall occurrence leading to small pyroclastic flows in the Tar River Valley were observed: from 08:15 to 10:28, 13:51 to 14:30 and 14:59 to 16:01. The longest flow reached as far as the Tar River Estate house. The resulting ash clouds were blown by very light and variable winds towards the northern part of the island during the early part of the day and towards the western part of the island during the afternoon and early evening. This resulted in light ashfalls in most of central Montserrat, including St. George's Hill, Cork Hill, Salem, Old Towne, Isle Bay, and as far north as Brades. The ashfalls in the Amersham, Parsons, Plymouth, Richmond Hill and Kinsale areas were much heavier. The highest height attained by an ash cloud during this period was 7,000 ft. The volcano-tectonic earthquakes occurred as part of a VT and hybrid swarm from 06:30 to 08:05 today and were located at depths less than 2 km beneath English's Crater. A few episodes of intermittent low-amplitude broadband tremor were also recorded at the stations closest to the Crater.

Visibility was excellent during most of the day. Near-continuous rockfalls were observed from the eastern and northeastern flanks, with most of the falls from the eastern dome being challenged through the eroded gully just north of Castle Peak. Variable steam emission was observed from several areas of the dome.

EDM measurements were made today on the southern triangle. Yesterday's measurements on the eastern triangle showed lengthening of the Whites to Castle Peak and Long Ground to Castle Peak lines by 4mm and 1 mm respectively. Today's results for the southern triangle reveal ed shortenings for the lines Galways to Chances Peak and Ogarras to Chances Peak of 1.6 cm and 1.2 cm respectively compared to measurements made on 26 May.

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