Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 2 September
to 4 pm 3 September 1997

Volcanic activity over the reporting period has remained relatively low. The only noticeable change has been a swarm of VT earthquakes which occurred overnight.

Over the reporting period 63 rockfalls, 29 VT earthquakes, 1 hybrid earthquake, 8 long-period earthquakes, 3 of which caused rockfalls, triggered the broadband seismic network. A swarm of VT earthquakes started at 2229 2/9/97 and ended at 0124 3/9/97 and consisted of 24 events. These earthquakes were generally small although some larger events occurred. The larger events were located in the area of the crater at depths between 3.5-4.0 km below the top of the dome. Preliminary analysis of seismic amplitude data suggests that the rockfall activity has an approximate 16 hour period.

Visibility has remained poor today due to the low cloud, so no visual observations of the dome were possible.

The size of the dome coupled with the high extrusion rate suggests that a large collapse 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 not have the same constraint on subsequent flows. 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. In turn this will make it easier for other flows travel in this direction.

Pyroclastic flows may occur on any of the flanks of the volcano and 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 also possible without much 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.

Thomas Christopher left Montserrat today for the University of the West Indies in Jamaica, where he will be studying Geology.

Montserrat Volcano Observatory