Montserrat Volcano Observatory

Weekly Report
Report for the period 5 p.m. 25 June 1999
to 5 p.m. 2 July 1999

The level of activity at the volcano remained low this week, although there were four small collapse events producing pyroclastic flows on various flanks of the volcano.

The seismic networks recorded a total of 33 rockfall signals, 10 volcano-tectonic earthquakes and 1 long-period earthquake over the week.

Four collapse events occurred from the dome during the week. These were all during the night so that the direction of pyroclastic flows and drifting ash clouds was difficult to ascertain. Two events, one at 2:33 on Monday morning (28 June) and one at 1:54 this morning (Friday 2 July) produced ash clouds to 10,000 to 15,000 feet. Only one pyroclastic flow deposit could be seen from these events, and this travelled about half a mile down the Gages valley from the western flank of the dome.

Observations of the dome early in the week showed that the extremely unstable block on the northeast flank of the dome is still there and could generate a significant pyroclastic flow and ash cloud without warning when it collapses. No observations of the dome were possible later in the week.

No COSPEC measurements were taken during the week.

The campaign of GPS measurements of volcano deformation was completed week; the results will be processed during next week. The EDM (electronic distance meter) line between Chances Peak Steps and Lower Amersham was occupied again this week for the first time in 2 years. It showed 18 cm (7 inches) of shortening in that time, at an average rate of about 2mm per week.

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