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The Volcanic Explanation
For The 24 Hour Period Ending 4 PM On Thursday July 31, 1997
A Presentation Of The Government Information Services
In Conjunction With The MVO.

The alert level system has been revised by zones.

The volcano has been very active since about 3 am today (Thursday). with ashclouds reaching 20,000 feet.

133 rockfalls, 35 long-period events 14 of which triggered rockfalls and one hybrid earthquake were recorded. The Lees Yard station has had continuous high amplitude tremor shown on the seismometers since about 3 am. It was thought that pyroclastic flows caused these, but Helicopter views of the sides of the volcano during the late morning and early evening showed very few new deposits. Tuitts Ghaut had a few small flows about 2 km from the dome and Gages Valley also had some new deposits as far as Gages village. Tar River, Mosquito Ghaut, and Galways Wall did not show any new deposits. Long-period earthquakes have increased. The Soufriere Hills Volcano has had major pyroclastic flows following such increases.

Early in the morning many of the ashclouds which reached 15,000 feet drifted to the north and northwest, but later in the day they moved to the west. Seismic signals from the broadband network confirmed the reports of small explosive sounds from the volcano.

Between 12:30 pm and 2:30 pm the Lees Yard seismometer recorded near maximum amplitude signals with only one moderate pyroclastic flow. Pulses of ash plumes were seen every few minutes and seem to come from near the top of Galways Wall but did not seem to be connected to pyroclastic flows.

Pyroclastic flows and ash eruptions have not necessarily been associated with an increase in seismicity. Anyone entering the exclusion zone is at great risk. 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.

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