Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 3 September
to 4 pm 4 September 1997

Volcanic activity over the reporting period has remained relatively low, although the dome continues to grow and the cyclic behaviour of the volcano is becoming better developed again.

Over the reporting period 86 rockfalls, 6 hybrid earthquakes, 8 long-period earthquakes and one volcano-tectonic earthquake triggered the broadband seismic network. Cyclicity is defined by low amplitude tremor thought to be generated by semi-continuous rockfall activity, but larger rockfalls and small pyroclastic flows are occurring at any time. The period of the cycles is about 16 hours at present.

Visibility has remained poor today due to the low cloud, so no observations of the dome were possible. Several small pyroclastic flows were observed in the Gages valley around dawn, and a small explosion accompanying a strong long-period earthquake was heard just after 8 am. Vigorous ash venting was noted towards the end of the reporting period, associated with some build-up in rockfall activity.

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