Government Information Service

The Volcanic Explanation
For The 24 Hour Period Ending 4 PM On Saturday July 19, 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 today (Saturday) was at the same level as yesterday and was again dominated by rockfall signals, with an increase in ash production.

The viewing conditions were very poor in the morning due to heavy rain overnight and throughout the day. Some views of the dome were possible later in the day and there is a spine with 3 peaks above Galways Wall. This part of the dome has not been visible for several weeks and it is not clear when this was formed. Pyroclastic flow deposits were seen at a distance of about 500 m away from the dome in Gages, Galway's and Mosquito Ghaut. Several small pyroclastic flows from the northern flank of the dome with ash clouds occurred during the day. These ash clouds rose to less than 10,000 ft and were followed by strong steam emission.

27 rockfalls were recorded and none were of high amplitude or long duration. No long-period, volcano-tectonic, or hybrid earthquakes were recorded. A mudflow possibly in Fort Ghaut or Aymers Ghaut caused moderate amplitude tremor on the St. Patrick's Windy Hill and St. George's Hill seismometer for about 30 minutes very early this morning. Thunder caused several high frequency signals early this morning. The Chances Peak tiltmeter is not showing any cyclical behaviour but the long term deflationary trend continues. The broad band seismometers at Roche's Yard, Bethel and Galway's Estate were reviewed today (Saturday) during a reconnaissance flight.

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