Montserrat Volcano Observatory

Weekly Report
Report for the period 5 p.m. 4 June 1999
to 5 p.m. 11 June 1999

The level of activity at the volcano was at a higher level this week than over the previous reporting period.

A total of 136 rockfall signals, 9 long period, and 27 volcano-tectonic earthquakes were recorded over the last week.

The main event of the week occurred on 5 June at 5:45 p.m. when a portion of the dome on the north-eastern flank above Tuitt^s Ghaut collapsed. About 1.5 million cubic metres were eroded from the dome, and formed pyroclastic flows that travelled down Tuitt^s Ghaut to about 1.5 km from the dome, White^s Ghaut to about 2 km from the dome and Tar River to the sea. Surge clouds singed vegetation in Paradise Estate, Hermitage and on the northern side of the Tar River towards Long Ground. An ash cloud to an estimated 12,000 feet travelled west and north-west, depositing up to 1 cm of ash in Salem and Old Towne. A smaller pyroclastic flow in the same direction occurred later in the evening.

A small ash venting episode on 7 June at 11:30 p.m. deposited light ashfall as far north as St. Peter^s, and a further pyroclastic flow on 11 June at 12:30 a.m. travelled down Tuitt^s Ghaut to about 1 km from the dome, and down Tar River onto the new delta. Ashfall from this latter event was deposited in the north-west of Montserrat from Woodlands to Cork Hill.

Heavy rain on 9 June in the afternoon produced mudflows down all flanks of the volcano, and deposited new material in the Belham valley.

Correlation spectrometer measurements have continued this week. Values for the sulphur dioxide flux on 5, 6 and 8 June were 200, 230 and 420 tonnes per day respectively. These are generally low values, but tend to be higher immediately after ash venting episodes. Attempts were made to make measurements at other times, but ashy conditions or an unusual wind direction prevented collection of good data.

GPS results for the past two months, have shown an increase in the rate of movement of some sites. The increase occurred around early April 99. For example, the distance from Harris to Hermitage has shortened by 2.4 cm in 2 months. This is comparable to the rate of movement from October to December 1998.

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