Montserrat Volcano Observatory

Morning Report
Report for the period 4 pm 06 August
to 7 am 07 August 1997

Activity at the volcano has remained at a high level overnight with another vertical explosion and pyroclastic flow generation in the valleys which radiate from the volcano. A hybrid earthquake swarm was recorded overnight with this continuing to define a cyclical pattern of activity which has been experienced during the past 7 days.

56 hybrids, 3 long period earthquakes and 5 rockfalls were recorded during the period. Most of the hybrids occurred during a swarm which began at 11:23 pm last night and ended by about 1:26 am this morning. The swarm was less intense than the one recorded early yesterday afternoon. A vertical explosion occurred at 34 minutes past midnight and this ejected an eruption column which rapidly rose to in excess of 10,000 ft. Immediately following the start of the eruption incandescent debris was observed to fallback onto the northern and western flanks of the volcano feeding pyroclastic flows which descended the Gages valley, Mosquito Ghaut and possibly Tuitts Ghaut. The event saturated the seismic drum recorders for about 2.5 minutes and was followed by a period of low frequency tremor which lasted for about 80 minutes.

Following the early morning rainfall, the dome cleared for about 20 minutes today and allowed the first views to be obtained of the summit since the current phase of elevated activity began one week ago. A bowl-shaped crater with a lower edge facing towards Gages mountain is now present at the top of the dome. Static photographs were taken so as to allow future calculations of the volume of the dome and the amount of material removed during the last few days.

The activity is currently still following a cyclical pattern with a hybrid earthquake swarm followed by an explosion with collapse of the column in all directions. However, this pattern may not continue and people should not become complacent. All parts of the exclusion zone are now extremely dangerous and at risk from sudden pyroclastic flows or ballistic projectiles from explosive eruptions. Pyroclastic flows have travelled into the head waters of the Belham River valley, and there is a potential for further flows in this direction. People should not attempt to enter any part of the exclusion zone. During the current activity, the central zone should be evacuated. Parts of the northern zone may expect to get ashfall or small rocks, and people should stay inside during an eruption. People should stay alert and listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory