Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 1 September
to 4 pm 2 September 1997

Activity during this reporting period has been relatively low. It increased slightly at about 3 pm today with a rise in rockfall activity and quite vigorous venting of ash-laden steam from the dome.

During this reporting period 14 hybrid earthquakes, 17 VT earthquakes, 18 long-period earthquakes and 73 rockfalls triggered the broadband seismic network. These counts are similar to counts over the last few days, except for the VT earthquakes. The VT earthquakes did not form a swarm, but were recorded throughout the day and were mainly too small to be located. Only one event was located, at a depth of about 1.8 km beneath the crater.

Visibility has been generally poor today, with cloud obscuring the dome. The only significant observed activity started at about 3 pm this afternoon, associated with an increase in rockfall signals recorded by the seismic network. Between then and the end of the reporting period, there were a few small pyroclastic flows into the area where Mosquito Ghaut used to be. From about 3:30 pm, there was continuous venting of ash-laden steam from the dome area. It was difficult to locate the source of this venting, although an inspection from the helicopter showed that it was not associated with any significant rockfall activity, and probably originated from a point source near the top of the dome.

Analysis of the recent survey of the dome and pyroclastic flow deposits is not yet complete. Preliminary results indicate that the current extrusion rate is about 6-7 cubic metres per second. This is the highest sustained extrusion rate since the eruption began.

The high extrusion rate and the now very large size of the dome make it more likely that a large collapse might occur in the near future, possibly without warning. The recent filling-up of Mosquito Ghaut and the Upper Gages Valley by pyroclastic flows means that any large flows will not be constrained by the ghauts. It is becoming 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.

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.

Jean-Pierre Viode from Martinique Volcano Observatory arrived on Montserrat today. He will be helping move the observatory to its new location over the next few days.

Montserrat Volcano Observatory