Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 19 August
to 16:00 20 August 1996

Activity at the Soufriere Hills volcano during this reporting period has continued at the slightly elevated level observed durimg the previous 24 hours. It is still dominated by near-continuous small- to moderate-sized rockfall and pyroclastic flow activity mainly from the eastern flank of growing lava dome.

One hundred and sixty one (161) rockfalls, 33 hybrid, 1 long-period and 30 volcano-tectonic earthquakes were recorded during this reporting period. Three episodes of near-continuous rockfall occurrence leading to small- to moderate-sized pyroclastic flows in the Tar River Valley were recorded: from 19:16 to 20:41 on 19 August and 05:25 to 06:46 and 14:45 to end of reporting period on 20 August. The longest flow which occurred at 20:00 on 19 August reached the new delta created by previous pyroclastic flows but did not enter the sea. Several of today's pyroclastic flows generated ash clouds with maximum heights between 5,000 ft and 12,000 ft. . Small to moderate amounts of ashfall from these flows occurred in several areas of western and central Montserrat, including Upper Gages, St. George's Hill, Cork Hill, Lees, Richmond Hill, Fox's Bay and Plymouth, because of the light and variable winds. Also, the near-continuous nature of the activity since yesterday seems to have resulted in a belt of very light ash extending from Montserrat to close to Puerto Rico, according to satellite imagery and aircraft reports. A single swarm of small volcano-tectonic and hybrid earthquakes occurred today from 11:50 to 13:16. These volcano-tectonic earthquakes were located at shallow depths beneath the crater region.

Visibility was good during most of the day. No significant changes in the dome shape were observed compared to yesterday. Near-continuous rockfalls were observed from the eastern and northeastern flanks, with most of the falls from the eastern dome being challenged through the deeply eroded gully 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