Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 26 February
to 16:00 27 February 1997
The current alert level is AMBER

Activity at the volcano has continued at a low level over the last 24 hours. Another earthquake swarm occurred today. Visibility has been variable throughout the day, but some good views of the dome were obtained in the afternoon. Observations seem to indicate that the height of south-east part of the January dome has increased markedly.

The seismic activity at the volcano was again dominated by a swarm of volcano-tectonic and hybrid earthquakes between 3:27 am and 11:21 am today. This swarm was more intense than the one which ended early yesterday afternoon. A total of 29 volcano-tectonic and 62 hybrid events were recorded during the reporting period, and most of these occurred during the swarm. The volcano-tectonic events were located at depths of 1 to 4 km below the crater. 23 small to moderate sized rockfall signals were also recorded by the seismic network. One regional earthquake was also recorded by the seismic network at 4:20 am. Medium amplitude tremor on several stations began at approximately 4.00 pm yesterday afternoon, peaked at around 5.00 pm and had ended by 5.30 pm yesterday. Low amplitude tremor has been recorded on the Gages seismic station from midnight until mid morning and then recurred between noon and 4.00 pm.

The summit of the volcano was visible for a short period this afternoon and good views of the dome were obtained from the helicopter and from Whites. Observations indicate that the dome within the January scar has grown upwards by at least 30 m since 18 February, and there is now a small summit spine on top of the January dome. The south-east flank of the dome has been modified by avalanching and two large blocks formerly on the talus slope have now disappeared. Small rockfalls and pyroclastic flows continue to come off the north and south-east flanks of the dome, and one small pyroclastic flow from the north flank gave rise to some ash over Plymouth at 3.15 pm. Galway's Wall has deteriorated only slightly since it was last seen on February 18.

EDM measurements were made today on the northern triangle between St George's Hill, Windy Hill and Farrells. The Farrells-Windy Hill line shortened by 7 mm and the Farrells-St George's Hill line lengthened by 5 mm since they were last measured on 13 February.

The volcano remains active and potentially dangerous. The dome is currently larger than ever before, and so further dome collapses and pyroclastic flows are expected. These will probably follow the recent pattern, but a change in the activity could occur at any time. People entering Zone C are reminded to remain alert at all times, and spend the minimum possible time in the evacuated zone. The ash levels in Plymouth are hazardous, especially during dry, windy weather, and so it is essential to wear masks in areas affected by ash. The Tar River Valley and the upper Galway's area are very dangerous and should not be entered at any time.

Montserrat Volcano Observatory