Government Information Service

The Volcanic Explanation
For The 24 Hour Period Ending 4 PM On Saturday August 02, 1997
A Presentation Of The Government Information Services
In Conjunction With The MVO.

The alert level system has been revised by zones.

The Soufriere Hills Volcano activity has again remained at a high level today (Saturday), with intense rockfalls, pyroclastic flows, hybrid swarms and ash being deposited to the west.

65 rockfalls, 11 long-period events (6 of which triggered rockfalls) and 124 hybrids were recorded. There were no volcano-tectonic earthquakes. The first of the 2 swarms of hybrid earthquakes had 16 events and started at 4:17 pm yesterday (Friday) and lasted about 2 hours. High amplitude tremor and pyroclastic flows occurred for about 2 hours after this. During this time pyroclastic flows in the Gages Valley seemed to cause the glowing seen behind St. George's Hill. At about 1:00 am a small mudflow signal was recorded. This emphasises that all the ghauts on all sides of the volcano have the potential of being the site of fresh pyroclastic flows being re-mobilized by heavy rain.

The 2nd hybrid earthquake swarm began at 4:42 am until 10:50 am. This was more intense than earlier in the week and peaked at 9 am when the frequency was about 3 per minute. Continuous moderate tremor continued between events. After a decrease in activity there was a pyroclastic flow at 10:25 over Gages.

The cyclical pattern in the tiltmeter is continuing to follow the earthquake swarms, but large pyroclastic flows could occur without any warning. The activity is similar to that of late June and early July and pyroclastic flows similar to June 25 could occur. The only new deposits are in Gages Valley, they went to just below Gages Lower Soufriere. The small amphitheatre above Galways Wall was viewed and seems to be the result of recent pyroclastic flows. During the observation flight measurements and samples were collected of the pyroclastic flow deposits from the June 25 event. This will help in understanding the mechanisms that produce pyroclastic flows and their formation.

EDM measurements were made today between Waterworks to Lees Yard and Garibaldi Hill to MVO. Results will be reported later in the week.

Gages Valley is filled in and flows and surges will overspill any place in the valley and no one should be in the area. No entry is allowed into the exclusion zone. Residents in the northern or central zones should stay alert and listen to ZJB which will remain on the air all night. Activity may increase without any warning.

Dust masks should be worn where there is still ash. Drivers should drive slowly in ashy areas.

Ms. Costanza Bonadonna of Bristol University arrived for a month long tour of duty to the MVO.

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