Government Information Service

The Volcanic Explanation
For The 24 Hour Period Ending 4 PM On Monday July 21, 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 (Monday) was slightly higher than yesterday (Sunday). Rockfalls were the main type of seismic signals recorded. Again overcast conditions for most of the day prevented viewing of the dome.

58 rockfalls, none of which were of high amplitude or long duration, 4 long-period, and one volcano-tectonic earthquakes were recorded. There were no hybrid earthquakes. A rockfall was triggered by one of the long-period earthquakes. Low amplitude tremor was recorded on the St. George's Hill seismometer, throughout the day. The Chances Peak tiltmeter is not operational at this time..

No clear views of the dome were possible due to low cloud cover for most of the day. Temperature measurements were taken from today from the end of the June 25 flow in Trant's. After almost one month the temperature of the deposit at a depth of 2 m (approximately 6.5 ft) was still 640 degrees centigrade (approximately 1,184 degrees Fahrenheit). This clearly shows that the ash and debris on the edges of the volcano are extremely dangerous and no one should go near the deposits.

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. A reminder to wear your ash mask if there is ash in the air.

Government Information Service