Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 23 December
to 16:00 24 December 1996
Christmas Eve
The current alert level is ORANGE

Growth of the October 1 dome appears to be continuing, with a number of rockfalls and small pyroclastic flows generated. Seismic activity is at a high level, with 8 hour cycles of tremor continuing to increase in their intensity. There are real dangers of bigger pyroclastic flows into the Tar River valley and of sudden collapses from the Galway's Wall. Both could have serious consequences for much of the evacuated area, although it is more likely that any activity would be confined to the Tar River and White River valleys respectively at the present time. Depending on wind direction, there may be some ash fall in any area to the west or northwest of the volcano.

Zone A/B remains a no-go area. Access is allowed by the authorities to zone C/D for essential purposes and for people with a means of rapid exit only. Zones E, F and G have normal occupation.

The rockfall activity from the October 1 dome continued today, although visual observations during the day were limited by low cloud. A total of 15 rockfall signals triggered the seismic network during the reporting period; this is a reduction from yesterday. Some of the bigger rockfalls and small pyroclastic flows generated ash plumes which drifted west from the volcano.

Seismic activity has reached a higher level again today, with hybrid events and continuous tremor dominating the records. Although only 17 individual hybrid events were recorded during the reporting period, the peak levels of seismic activity as recorded by energy release were higher today than yesterday; these peaks are occurring at regular, 8 hour intervals and are caused mainly by high amplitude tremor. This type of seismicity is very similar to that recorded prior to partial dome collapses in late July through to September, and may lead to similar events this time, with associated pyroclastic flow activity and possibility of explosive events. In addition to the hybrid events, 5 long-period earthquakes were recorded.

No EDM surveys were undertaken today due to low cloud shrouding the targets high on the flanks of the volcano. Micro-gravity surveys continue on the western flank of the volcano and a continuous gravity station is in place at Whites.

One of the most important seismic stations in the network was sabotaged during the week and this caused problems with data acquisition. Fortunately on this occasion, it did not impact seriously on the monitoring operations. However, MVO does depend on the honesty of the public in not tampering with vital field equipment which is generally unsecured for ease of maintenance.

Montserrat Volcano Observatory