Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 5 September
to 4 pm 6 September 1997

Volcanic activity remained relatively low during the reporting period. Seismic activity was dominated by rockfall signals as the dome continues to grow.

During the reporting period 83 rockfalls, 3 hybrid earthquakes, 41 long-period earthquakes and 3 volcano-tectonic earthquake triggered the broadband seismic network. These counts are consistent with recent activity, except for the increase in long-period earthquake activity. Small peaks in the seismic activity still appear to be regularly spaced, with the current interval about 10 hours.

There were some excellent viewing conditions during the night when the dome was seen clearly from the Observatory. Rockfall activity was taking place over much of the north and west flanks of the dome. The activity appeared to be more concentrated above Gages Valley and Mosquito Ghaut. Small rockfall activity was almost continuous and shows that the dome continues to grow at a fast rate, underlining the potential dangers from it.

The dome was also seen clearly around noon today and, with the wind from the West, it was possible to see the western parts of the dome clearly. There has been growth of the western parts of the dome since last it was seen clearly on 29 August, with an increase in height of more than 20 m. The highest point of the dome, which is in the eastern part, has not changed significantly although there is an expansion of the growth area to the north-east and north-west.

The size of the dome coupled with the high extrusion rate suggests that large collapses could occur at any time in the near future, possibly without warning. Both Mosquito Ghaut and the Upper Gages Valley have been filled by pyroclastic flow deposits, so topography will have little constraint on flows down the northern or western flanks of the volcano. This makes it increasingly likely that any large flows will find their way into the Belham Valley and, if large enough, travel all the way to the sea.

The southern part of Montserrat remains extremely dangerous. Collapse of material from the dome may lead to further explosions and these may be more intense and longer lived than before. Explosions are possible without warning. If an explosion does occur, small rocks and ash can fall anywhere on the island. The central zone should be evacuated immediately, and people in the northern zone should seek shelter under a strong roof as soon as possible. Helmets or other head protection should be used and it should be remembered that ash and falling rocks make driving hazardous. After ash has fallen it will remain present in the atmosphere for some time and dust masks should be worn outdoors. People should remain vigilant and to listen to Radio Montserrat.

Montserrat Volcano Observatory