Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 4 October
to 4 pm 5 October 1997

There have been three explosions in the last 24 hours separated by periods of relative quiescence. This brings the total number of explosions to 34 since the first one of this sequence on September 22.

The first explosion occurred at 6:27 pm yesterday evening (October 4). Pyroclastic flows entered the Gages Valley and Tuitt's Ghaut. Chance's Peak was showered with incandescent ballistic fragments. The eruption column was reported to have reached a height of 38,000 feet (11,500 metres or 11.5km). The second explosion occurred at 2:53 am this morning (October 5). This produced small pyroclastic flows in the Gages Valley and on the northern flank of the volcano. The ash column is estimated to have reached approximately 20-25,000 feet (6000-7600 metres or 6-7.6km). Ash from both these events was blown very slowly toward the north to north-west by light winds. No fall-out was reported for either of these events. Tremor associated with steam and ash venting occurred after both events.

The third explosion occurred at 10:42 am this morning (October 5). Pyroclastic flows were observed in Tuitt's Ghaut, Gages Valley and the White River. The ash column rose to above 10,000 feet (300 metres or 3km) and drifted northward. Low level ash from the pyroclastic flows was blown westward. Pulsatory steam and ash venting up to 3000-4000 feet (900-1200 metres) continued after the main explosion

There was very little seismic activity before the first two events and no precursory activity before the third event demonstrating how events like these can occur with little or no warning.

7 hybrids, 5 volcano-tectonic earthquakes, 4 long period earthquakes and 4 rockfall signals triggered the short-period seismic network over the reporting period. The dome was very clear today but there have been no major changes to it over the last few days. Yesterday's theodolite data were processed using data collected from Jack Boy Hill, Fleming's, Garibaldi Hill and the old observatory. The highest point on the dome is a large spine on the rim of the Galway's side of the explosion crater at 975 metres above sea level. There is a wall of pumice separating the explosion crater and the main part of the September 21st collapse scar. The lowest point on this pumice wall is 831 metres, so the September 21st collapse removed a thickness of at least 140 metres of rock from the top of the dome. The explosion crater is over 300 metres wide at the top of the volcano. The height of one of the three peaks on the northern crater wall has been reduced by over 30 metres due to erosion caused by pyroclastic flows this summer.

There is a good chance of more explosions and these could be larger than anything seen so far. The resulting pyroclastic flows could very easily reach the Belham valley and surges could travel up the valley sides for a considerable distance. All those remaining in the exclusion zone are urged to leave. If the sirens sound in this area at any time, people should move north immediately.

After an explosion fallout can occur anywhere on the island. People should shelter in a strong building and wait for the fallout to end. If you do have to move about then head protection should be worn. Falling ash and pumice reduces visibility and makes driving conditions extremely hazardous. Roads remain difficult and plenty of time should be allowed for any journey. The wearing of ash masks is recommended at all times. Everyone is advised to keep listening to Radio Montserrat for information on the activity.

Montserrat Volcano Observatory