Montserrat Volcano Observatory

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

Volcanic activity during the reporting period increased slightly with continued growth of the dome.

Over the reporting period 99 rockfalls, 3 hybrid earthquakes, 10 long-period earthquakes and 3 volcano-tectonic earthquake triggered the broadband seismic network. There is still some cyclicity in the seismic and rockfall activity, although the period between cycles has now lengthened to about 20 hours. The latest period of enhanced rockfall activity occurred from about 3 pm onwards today with many rockfalls from the dome and fairly vigorous ash production.

Excellent visibility late this morning enabled scientists to get a good view of the dome. Gas venting was vigorous from around several prominent spines and rockfall activity was seen to be common in Mosquito, Tuitts and Gages valleys. The dome is substantially larger than last time it was clear a week ago and this supports other information that dome growth is very rapid at the moment.

Throughout the day, rockfall activity and ash venting was vigorous, and a plume of ash could be seen many miles out to sea westwards from Montserrat.

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