Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 31 May
to 16:00 01 June 1996

Volcanic activity at the Soufriere Hills volcano continued at a relatively high level for most of the day, with rock falls occurring throughout the day and small pyroclastic flows in the upper parts of the Tar River valley.

Seismicity has been dominated by the occurrence of small hybrid events and moderate-sized rockfall signals. There were 115 rockfall signals today with a slight reduction in the frequency and size after about 11:30 on 01 June. The largest rockfall signals occurred at 15:36 and 20:03 on 31 May and 04:10 and 06:00 on 01 June. Ash plumes which ascended up to about 4-6000 ft were associated with most of the larger rockfall signals. The 06:00 event on 01 June produced a small pyroclastic flow in the upper Tar River.

Five long-period events were recorded by the seismic network today. There were 329 of the small, repetitive hybrid events which reappeared on 30 May on seismic stations closest to the volcano. The rate of these events increased overnight to about two per minute but have reduced during the day to about one every two minutes. These events are too small to be felt and have in the past been associated with increased periods of dome growth. One regional earthquake was recorded by the seismic network at 20:25 on 31 May. This event was located about 120 km east of Montserrat and had a magnitude of 3.6.

Viewing conditions at the volcano was variable throughout the day with only brief glimpses being obtained of the dome. Several ash plumes from rockfalls on the north-eastern, eastern and southern part of the dome were observed throughout the day. No clear views were obtained of the active areas of the dome. Measurement made with the EDM instrument to the top of the dome yesterday gave a height of 3101 ft above sea level. No measurements were possible today.

No EDM or GPS measurements were made today due to low cloud cover and technical problems respectively.

FTIR measurements were attempted today between St Georges Hill and Amersham but were unsuccessful due to poor signal strength. COSPEC measurements of gas concentrations in the volcanic plume was undertaken along the coastal road from Kinsale to Cork Hill. Analysis of the results indicate a sulphur dioxide flux of about 52 tonnes per day; these are consistent with similar low levels obtained over the past few weeks.

The continued occurrence of pyroclastic flows in the Tar River Valley demonstrate the very dangerous nature of the current volcanic activity at the Soufriere Hills volcano. The MVO urges that visits to the evacuated zone are kept to a minimum. The Tar River, Long Ground and Whites areas are extremely dangerous and should not be entered under any circumstances.

Montserrat Volcano Observatory