Montserrat Volcano Observatory

Weekly Report
Report for the period 5 p.m. 14 May 1999
to 5 p.m. 21 May 1999

The level of activity at the volcano has been lower this week when compared with the previous week.

A total of 125 rockfall signals, 1 long period, and 23 volcano-tectonic earthquakes were recorded over the last week. The signals were evenly distributed throughout the week.

Two periods of increased activity occurred during the period. The first of these was on 18 May, and was a small magnitude ash venting episode that produced only a minor ash cloud.

An explosion occurred on 20 May. This began at 17.42 local time and lasted for about 10 minutes. A plume of ash quickly rose to about 15,000 feet and drifted to the north-west, depositing ash mostly south of the Belham river. No pyroclastic flows occurred with this event, although it was accompanied by a deep rumbling noise.

Correlation spectrometer measurements have been re-started this week. Values for the sulphur dioxide flux on 18, 19, 20 and 21 May were 126, 171, 151, and 272 tonnes per day respectively. These values are low relative to the fluxes during the peak activity, when levels reached over 2000 tonnes per day.

GPS occupations have occurred at Whites, Tar River, and the new site south of Tar River in conjunction with the permanent sites at Whites Yard, Hermitage, Harris and South Soufriere Hills. Recent occupations show that these sites are either not moving or continue to move at slow rates on the same trends as previously.

Residents of Montserrat are advised to keep listening to ZJB Radio Montserrat for information in case of any changes in the state of the volcano.

Montserrat Volcano Observatory