Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 17 December
to 16:00 18 December 1996
The current alert level is ORANGE

There was a moderate level of activity at the volcano during the last 24 hours. The December 11 dome continues to grow and generate rockfalls into the upper Tar River valley. There were some small ash clouds that drifted to the west. The dome growth means that the Tar River and Long Ground areas are increasingly at risk from pyroclastic flows. Deformation of the Galway's Wall has slowed over the last few days but sudden failure of the wall could still occur which would have serious consequences for the rest of zone A/B. Nobody should be in this zone. Zone E remains safe at this time.

Visibility was generally poor today. There was a helicopter inspection this morning of the lower flanks of the new dome and of Galway's Wall. Neither showed much activity. There was a moderate-sized rockfall to the south of Castle Peak at 1:27 pm generating a small convective ash cloud which was blown to the west and south west on the wind. Another small ash cloud was observed at 3:03 pm.

The level of seismicity was low during this period, and was dominated by rockfalls from the growing dome. There were 17 dome rockfalls, a similar level to yesterday. The size of the rockfalls was slightly smaller than yesterday. Only two small, long-period earthquakes were recorded today, a decrease from yesterday. No volcano-tectonic earthquakes were recorded.

EDM measurements were made today on the lines on the east and north of the volcano. The lines to Castle Peak show only 3 mm of shortening since they were last measured on 10 December. There have been no significant changes on the lines on the north of the volcano since they were last measured on 5 November.

A continuous-recording gravity meter was deployed at Whites today, close to the permanent GPS station. In the event of any significant swelling of the volcano, this will help us understand the nature of the source of the swelling.

Montserrat Volcano Observatory