Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 23 September
to 4 pm 24 September 1997

Activity has been high during the last 24 hours with a total of three explosive events. Pyroclastic flows generated during these events travelled down Tuitt's Ghaut, Mosquito Ghaut and Gages Valley.

A swarm of hybrid earthquakes began yesterday afternoon at 3.30pm and continued throughout the night until 8.16am this morning. It was not an intense swarm but some individual events were quite large. The first explosion occurred in the middle of the hybrid swarm at half past midnight, and generated pyroclastic flows which travelled into Gages Valley and the upper parts of Tyers Ghaut. The ash cloud from this event reached at least 10,000ft and ash was blown over Plymouth. At 10.54 am this morning another explosion occurred. Collapse of the vertical ash column generated pumice flows which travelled into Tuitt's Ghaut and probably Gages Valley and material also came down chutes on the dome above the Tar River valley. The flows in Tuitt's Ghaut reached the Paradise River. Ash from this event was blown over much of the western part of Montserrat as far north as Cudgoehead, the ash cloud reached at least 20,000ft. The third explosion occurred at 5.16pm and pumice flows were again observed in Gages Valley and on Farrell's plain.

Each explosion was followed by an episode of volcanic tremor which lasted for several hours. Observations suggest that the tremor is associated with vigorous pulse-like ash venting. The tremor slowly decreases in amplitude with time but appears to decrease more rapidly after explosions which have been preceded by a hybrid swarm.

Observations of the dome today show that there is a well-defined horse-shoe shaped crater at the summit which has formed during the explosions of the last few days. The crater opens out to the north above Tuitt's Ghaut and the ash venting is clearly coming from within the crater.

Scientists are anticipating further explosions and these may be larger than before. If the wind direction changes then clasts could fall on Salem and areas further north. Pyroclastic flows and surges from the explosions are very mobile and threaten all of those areas in the exclusion zone. Pyroclastic flows can also occur between explosions, and these could be large enough to reach to the Belham Bridge or beyond. These flows move extremely fast and you cannot get out of their way.

The volcano is in a highly dangerous state and everyone still in the exclusion zone is encouraged to move north as quickly as possible. Those remaining in that area do so at great risk. If the sirens sound, move north and to higher ground immediately, taking a hard hat or cushion for protection from falling clasts.

Montserrat Volcano Observatory