Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 16 February
to 16:00 17 February 1997
The alert level has been reduced to AMBER.

Activity at the volcano has continued at a low level. There were two small swarms of earthquakes during the day together with a few rockfalls. The visibility was excellent for most of the day. A dome survey was successfully completed and excellent views were obtained of the summit area and Galway's wall.

Seismic activity has been dominated by the occurrence of two volcano-tectonic earthquake swarms, the first of which was a continuation of the swarm which started yesterday morning and finished at 4.59 pm yesterday evening. The second swarm occurred between 10.41 am and 2:20 pm today. A total of 32 volcano-tectonic earthquakes were recorded, all of which occurred during the swarms (6 during the end of yesterday's swarm and 26 during today's swarm). These were located at less than 3 km depth beneath the crater. One of these events at 12.42 pm was reported felt at Bramble airport. Only one hybrid event and no long period events were recorded by the network during the period. Sixteen rockfall signals were recorded; no major ash clouds were associated with any of these events.

Visibility was very good for most of the day, and excellent views were obtained from Whites and the helicopter. Observations indicated relative quiescence of the dome with one small pyroclastic flow and several small rockfalls seen from Whites. The active south-eastern face of the dome appeared to have inflated slightly over the last few days. Galway's Wall continues to degrade slowly, with one further small pyroclastic flow deposit, to approximately 1 km from the wall, since 15 February.

A full dome survey was completed in the morning. The data are currently being processed. Measurements on recent pyroclastic flow deposits on the new fan were also made briefly.

The Chance's Peak reflector was cleaned and, subsequently, total station measurements were made on the southern triangle today. The Chance's Peak-O'Garra's line has shortened by only 14 mm since it was last measured on Dec 2 1996.

Despite the low level of activity and the reduction in alert level, more pyroclastic flows are expected from the steep eastern face of the dome and over Galway's Wall. Thus the Tar River Valley and the upper Galway's area are very dangerous. Any collapses are likely to be gradual, and produce small or moderate pyroclastic flows. However, a larger and more prolonged collapse can not be ruled out. Residents are reminded to remain alert and responsible at all times, carry ash masks and spend the minimum possible time in the evacuated zone. It is advisable to have access to a battery operated radio in case of electricity power cuts. Ash levels in Plymouth are hazardous, especially during dry, windy weather: it is essential to wear masks in affected areas. Access is now allowed to zone C during daytime only (from dawn on Tuesday). Zone E, which includes Cork Hill and the airport, remains safe at this time. People are also advised to be aware that flash floods which could destroy bridges across Fort Ghaut and other ghauts, and therefore to make their way north in cases of very heavy rain.

Late Note: There was an episode of volcanic tremor and pyroclastic flows from about 6 pm to 6:40 pm tonight. This episode was similar to previous occurrences in the last few weeks, and resulted in ash fall in the Plymouth area. This type of activity is expected to continue during the next few days, and so visitors to zone C should be prepared for ash fall.

Montserrat Volcano Observatory