Montserrat Volcano Observatory

Weekly Report
Report for the period 5 p.m. 9 April 1999
to 5 p.m. 16 April 1999

Activity at the volcano has been at about the same level as last week.

A total of 162 rockfall signals and 51 volcano-tectonic earthquakes were recorded over the last week. The signals were generally evenly distributed through the week, but there was an increase in volcano-tectonic earthquakes on 13 April with a total of 27 events.

There was a total of 7 ash venting or small explosive events in the last week. The largest event occurred in the early morning of 14 April. This event produced a convecting ash cloud to about 15,000 feet with accompanying thunder. Sandy ash fell over most of the island. Later in the day, a new small pyroclastic flow deposit down Tar River from this event was observed, together with minor deposits in the top of Tuitt's Ghaut and White River.

Most of the other events this week produced low level ash clouds.

Observations over the weekend and early in the week showed that fumarolic activity was very vigorous in the dome above Tar River, and some steaming was seen on the northern flanks of the dome. On 10 April, the Tar River vents were emitting a very ash rich plume but, by 12 April, the main constituent of the plume was steam.

Correlation spectrometer measurements of sulphur dioxide emissions were made on 15 April and gave a value of 240 tonnes per day. This is lower than most recent measurements.

Electronic distance measurements were made on the network in Long Ground. Currently the results show no consistent trends in the movement of the area.

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