Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 27 November
to 16:00 28 November 1996
The alert level was upgraded from AMBER to ORANGE early this morning.

The situation at the volcano has been stable during the day today, following a period of high activity during the early hours of the morning. There have been no major changes to the Galways Wall during the last 24 hours, although heavy rain overnight has cleared much of the loose material from the face of the wall. The volcano is in a highly dangerous state, and further avalanches from the Galways Wall could happen at any time. A major collapse of the wall could expose hot, gas-rich magma from the lower sections of the dome, and trigger a lateral blast. This has the potential to cause major damage to St Patrick's and the surrounding areas, and could also lead to the development of a vertical eruption column.

High seismic activity between 01:39 and 03:00 this morning was recorded by the entire seismometer network, with signals being especially strong at Long Ground, St Patrick's and Gages stations. These signals were due to a series of debris flows in White River, pyroclastic flows and debris flows in the Tar River valley and mudflows in Fort Ghaut. Further, similar activity occurred between 5 and 6 am, although this was at a lower intensity.

The debris flows in White River were caused by mobilisation of rock at the base of the Galway's Wall and also by small avalanches from the wall. The debris flows occurred during a period of heavy rain and were close to destroying the bridge at O'Garra's. A small delta has been built at the end of White River. Observations of the Galway's Wall during the day suggest that much of the loose material on the surface of the wall has been washed off, and this explains why there have been few avalanches during today. However, there are still many cracks on the wall and it is still being pushed from behind by the lava dome within the crater so that scientists are still strongly of the opinion that the whole wall or parts of it could collapse at any time with very little or no warning.

Pyroclastic flows within the Tar River valley were caused by small collapses from the northeastern and southeastern flanks of the lava dome. These flows were contained within the canyon but travelled over one kilometre from the dome. The debris flows in the valley were caused by remobilisation of old pyroclastic flow material, some of which was still very hot, leading to areas of vigorous steaming. Re-opening of a steam vent on the eastern side of Castle Peak was also noted; this vent first appeared in October last year.

VT earthquakes continued during the reporting period, although most of the 17 triggered events occurred before midnight yesterday and the swarm which started 3 days ago appears to have come to an end. Five signals indicating rockfalls from the dome were recorded as well as 3 long-period events.

EDM measurements were made on the eastern triangle today. These indicate continued outward movement of the Castle Peak reflector at a rate of about 6 mm per day, which has been the established trend since the middle of July.

Scientists are extremely concerned about the stability of the Galway's Wall and the possibility of a lateral explosion if the wall should undergo catastrophic collapse. This could then lead rapidly to a vertical explosion such as happened on 17/18 September. All citizens of Montserrat are urged to follow the alert procedures and stay vigilant and prepared at this time of heightened danger.

Montserrat Volcano Observatory