Montserrat Volcano Observatory

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

Activity at the Soufriere Hills volcano during this reporting period has continued at about the same relatively high level as during the previous 24 hours.

Activity continues to be dominated by small- to moderate-sized rock avalanches from the flanks of the growing lava dome. Ninety four (94) rockfalls were recorded. About seven (7) very small pyroclastic flows were observed in the upper reaches of the northern part of the Tar River valley. None of these flows reached the Tar River Soufriere about 800m away from the dome. These small pyroclastic flows and the larger rockfalls were associated with small ash clouds which were blown on the wind towards the west, over the Upper Gages, Amersham and Plymouth areas.

Approximately 82 small volcano-tectonic earthquakes were recorded. These events were mainly located beneath the volcano at depths less than about 3 km. Some of these earthquakes were reported felt by people in the Bramble and Bethel areas during the period 01:00 to 03:00 today morning. One hundred and fourteen (114) hybrid and 105 long-period earthquakes were also recorded. The hybrid events were small while a few of the long-period earthquakes were of moderate size. Intermittent low- to moderate-amplitude broadband tremor occurred and was well-recorded at the nearest stations to the crater.

Visibility was variable throughout the observation period, with very brief intervals when the mid and lower parts of the dome were not under cloud cover. Observations from several points on the ground and from the helicopter indicated that most of the significant rockfall activity was concentrated on the eastern and northeastern flanks of the dome. Many large blocks have been carved out by the rockfall erosion channels on the eastern and northeastern flanks and these look very unstable. Rockfalls may also be occurring on the western flank of the dome, towards Chances Peak. Smaller additional deposits were observed in the upper reaches of the northern part of the Tar River valley. The emission of steam was observed from several areas of the dome, with that from behind the old Castle Peak spine being very vigorous. No new material was observed in the upper part of Fort Ghaut. The lowest points of both Farrell's and Galway's walls are about 10m above the debris in the moat.

Gravity, GPS and COSPEC measurements were made today but the data are still being processed. No EDM measurements were made.

The increase in earthquake activity during this reporting period does not signal an escalation of activity at the Soufriere Hills volcano. More rockfall activity from the eastern and northeastern parts of the dome and pyroclastic flows in the Tar River Valley area should be expected within the next few days. These will obviously be associated with ash clouds which will be blown on the wind.

The Soufriere Hills Volcano is still considered to be highly dangerous to people and property on it's eastern and upper western flanks. Visits to the evacuated zone must be kept to a minimum. The Tar River and Long Ground areas to the east and upper Fort Ghaut, Gages Village and Upper Amersham areas to the west are all extremely dangerous. All access roads to these areas remain closed and people should not enter these areas under any circumstances. If they do, they put themselves and others at direct risk of serious injury or death.

Montserrat Volcano Observatory