Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 6 September
to 4 pm 7 September 1997

Rockfall and small pyroclastic flow signals have again dominated the seismicity today. The level of activity has remained at a similar level to that observed yesterday. During the reporting period 78 rockfalls, 18 hybrid earthquakes, 12 long-period earthquakes and 3 volcano-tectonic earthquake triggered the broadband seismic network. Peaks in activity are still occurring with a spacing of approximately 10-12 hours. However the peaks in activity are not so well defined at present. The monitoring indicates that the dome is continuing to grow.

Visibility has been hindered today due to persistent low cloud on the volcano. A number of ash clouds have been observed being carried to the north-east by the unusual winds being experienced on Montserrat. Pyroclastic flows have occurred in Mosquito Ghaut, Tuitt's Ghaut and possibly the Tar River Valley, although the latter needs to be confirmed.

A broad area of activity was apparent during night-time observations last night, extending over the western and northern flanks of the dome. Small pyroclastic flows were seen in Mosquito Ghaut and Gages Valley during the early part of yesterday evening and in the late afternoon today.

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