Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 09 October
to 16:00 10 October 1996
The current alert level is AMBER

The new dome in English's' Crater continues to grow rapidly, and it is now higher than Castle Peak. Good views of the dome were obtained this morning. The level of seismic activity has remained low, although the style of activity has changed slightly.

Only 8 rockfall events were recorded by the seismic network, about the same level as yesterday. Some of these events were observed by MVO staff working in the east. Six small long-period earthquakes were recorded. These have been rare during recent weeks, and are thought to be caused by magma movement. There was a moderately large long-period earthquake at 14:04 this afternoon. This earthquake was accompanied by the largest rockfall of the day, which occurred on the north face of the scar and resulted in a small ash cloud visible from the west. There has been only a low level of tremor today. A flash flood in Fort Ghaut this morning was recorded by the Gages seismic station between 0411 and 0422.

Visibility has been excellent during much of today. Good views of the crater area were possible from Whites, Roches Mountain and the helicopter. The new dome has grown higher than the top of Castle Peak, and now mostly fills the floor of the scar caused by the 17/18 September explosion. It should be emphasised that this scar is a huge feature, comprising about 25% of the volume of the dome complex, and the scar is now about one-quarter filled by the new dome. The dome is a chocolate-brown colour, has an even surface, and nearly rounded conical shape. Vigorous steaming was observed from all round the base of the dome.

Many rockfalls have been observed from the dome during the day. These were mostly small, and seemed to involve only the surface material of the dome, with no large blocks falling. These rockfalls have resulted in low-amplitude seismic signals. A helicopter survey of the dome complex has been carried out this afternoon, although the results will not be available for some days.

EDM measurements were made today on the Long Ground, Whites and Castle Peak triangle. The Whites to Castle Peak line has lengthened by 6 mm since it was last measured two days ago. This line is currently not showing any consistent trend. The Long Ground to Castle Peak line was measured for the first time since the new reflector was installed on 2 October. Any changes in the line length cannot be determined until further measurements are made.

Installation of all the new broadband seismic stations has now been completed. There are still some problems in transmitting some of the data to the Observatory by telephone, but all the other signals are being received successfully. Three of the stations were visited today for fine tuning and checking.

Drs Hiroshi Shimizu and Setsuya Nakada of Japan left Montserrat today after a short visit to share their experience of the Unzen volcano with MVO scientists. Professor Steve Sparks also left today to return to the UK. He will be back in Montserrat in a few weeks.

The continued rapid growth of the October 1 dome means that pyroclastic flows may occur during the next few days. The volcano remains highly active, and pyroclastic flows could trigger another explosive eruption with very little warning. Everyone who enters the evacuated zone must remain alert and be ready to move at short notice. Individuals who go beyond the Long Ground area into the Tar River valley are risking death. The new alert system and evacuation procedures will be formally launched at a press conference tomorrow. Details of the new procedures would be also be published in newspaper tomorrow, and all residents are asked to ensure they are familiar with these plans.

Montserrat Volcano Observatory