Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 8 December
to 16:00 9 December 1996
The current alert level is ORANGE

Another intense swarm of volcano-tectonic earthquakes started today. The events are very similar to those in the previous swarm. They are located at shallow depths beneath the crater and some are large enough to be felt at locations close to the volcano. There is more evidence of deformation of the Galway's Wall, with measureable movements across one of the cracks on Chances Peak. The condition of the volcano has not improved and Galways Wall is still liable to a sudden collapse. A major collapse of the wall could trigger a lateral blast which could affect a large part of southern Montserrat. There is a small possibility that a vertical eruption column would be generated. Residents of Montserrat should know the alert procedures and be prepared to follow them. The revised risk map is still in operation and there is no access to Zone A/B. Access to zone C/D is restricted to short visits for essential purposes.

A total of 31 VT earthquakes were recorded in this reporting period. The first earthquake in the swarm occurred at 09:27 this morning and the number of events has increased slowly since. The rate of activity at the end of the reporting period was 8 per hour, only slightly less than the average rate during the previous swarm. The locations and magnitudes of the events are similar to those in the previous swarm. They are located at shallow depths beneath the crater and the some of the large events were felt strongly by MVO staff on Chances Peak. There was one landslide from the Galway's Wall that was large enough to be detected by the seismic network. Three dome rockfalls were also recorded.

Helicopter inspections of the Galway's Wall and the crater area were hampered by poor visibility. Movements on two of the cracks on Chances Peak were measured today, measuring between nails that had been hammered into trees on either side of the cracks. The crack nearer Chances Peak shows no significant movements. The crack near to Galways Wall has opened by 33 cm (about a foot) since it was last measured on 4 December. The Galways side of the crack has moved outwards by about 7 cm (2.5 inches). These measurements, the largest rate of ground deformation ever detected on the volcano, are consistent with the Galways Wall being pushed outwards.

A tiltmeter was installed on Chance's Peak today. This should be able to provide real-time information on deformation in the Galway's Wall/Chances Peak area. However, the instrument needs some time to settle before it gives any useful data. The television camera on Perches Mountain was removed so that it canl be installed at the Galway's Wall observation post. This will reduce the need for MVO staff to visit a very dangerous area and give safe, continuous observations of the wall when conditions are favourable.

EDM measurements were made today on stations on the western side of the volcano. The lines show no significant changes since they were last measured on 7 November.

GPS measurements were made on the network which includes stations in the north of Montserrat. The data has not yet been processed.

Montserrat Volcano Observatory