Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 22 December
to 16:00 23 December 1996
The current alert level is ORANGE

Renewed growth of the October 1 dome appears to be continuing and deformation of the pre-September dome and Galway's Wall is also ongoing. There are dangers of pyroclastic flows into the Tar River valley and of a 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.

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 throughout this reporting period, although visual observations during the day have been hampered by poor weather. A total of 37 rockfall signals triggered the seismic network during the reporting period; the larger of these signals were probably generated by small pyroclastic flows which produced ash clouds. These ash clouds drifted westwards from the volcano and some light ash was deposited in Plymouth and surrounding areas.

Heavy rain in the middle of this afternoon caused mudflows (also known as lahars) in Fort Ghaut, and probably also in White River (towards O'Garra's). The seismic signals from these lahars lasted about 30 minutes. Observations of Fort Ghaut at this time revealed a flow of muddy water carrying rocks up to half a metre across into the sea, with peak flow continuing for approximately 20 minutes. Noises from the vicinity of English's Crater suggested that some steam jetting and rockfall activity may also have been occurring at this time. A helicopter inspection of the Galway's Wall is under way to see whether the heavy rain has prompted any rock avalanches from it.

Seismic activity has continued at a relatively high level today, with hybrid events dominating the records. The current swarm peaked at about midnight last night at a rate of 2 per minute and has diminished in rate of occurrence and amplitude since then. 107 hybrids triggered the networks during the reporting period. Hybrid events have in the past been associated with more rapid dome growth, but the lack of visual observations make this difficult to prove for this swarm to date. However, increased ash production and pyroclastic flow generation in the Tar River valley is to be expected if dome growth rate has indeed increased. In addition to the hybrid events, 5 long-period earthquakes were recorded.

No EDM or GPS surveys were undertaken today. Micro-gravity surveys continue on the western flank of the volcano. Water samples and SO2 tubes were collected today as part of the ongoing environmental monitoring programme undertaken by MVO.

Montserrat Volcano Observatory