Government Information Service

The Volcanic Explanation
For The 24 Hour Period Ending 4 PM On Wednesday July 16, 1997
A Presentation Of The Government Information Services
In Conjunction With The MVO.

The alert level system has been revised by zones.

The level of activity at the Soufriere Hills Volcano was about the same level as yesterday (Tuesday) and was dominated by rockfall signals.

Due to overcast conditions all day no clear views of the dome were possible. A GPS field team reported fresh rockfalls on the eastern face of the dome. There were some rockfalls in Tuitts and Mosquito Ghaut about 500 m from the dome. After the heavy rains this morning steam was seen in the Belham Valley at about 9:30 am. This occurred in a steep sided part of the valley below Molyneux, probably due to the interaction of rainwater with hot pyroclastic deposits.

There were 35 rockfall signals and one long-period earthquake. The early morning thunder storm generated 3 very high frequency events which were recorded on the seismic stations. The morning rainfall caused increased steaming which slightly increased the level of tremor on St. George's Hill.

The EDM line between Waterworks and Lees Yard has not shown any changes since 8 July when it was set up. A GPS survey of the entire volcano was completed using the helicopter. This survey included the stations at Long Ground, Whites, Harris, Windy Hill, St. George's Hill and Lees Yard. The results will be announced when the data has been processed.

The tiltmeter at Chances Peak showed a slight increase in amplitude during the past 24 hours. There was also a very low amplitude peak with a continuation in the long term trend.

The recent pyroclastic flows and ash eruptions have not been associated with an increase in seismicity or tiltmeter readings. Anyone entering the exclusion zone is at great risk. Further pyroclastic flows are most likely to occur in Mosquito Ghaut and Gages Valley but pyroclastic flows could also occur in Tuitts, Tar River Valley and White River. There has been no warning of the pyroclastic flows in Gages Valley and this makes Plymouth very dangerous. Belham River Valley could be the sight of pyroclastic surges or hot mudflows. These mudflows are at or near boiling point and travel very fast and may go further than pyroclastic surges.

Government Information Service