Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 8 September
to 4 pm 9 September 1997

Activity at the Soufriere Hills volcano has remained at a heightened level over the past 24 hours and indications are that activity may escalate further over the next few days. Escalations could be rapid and involve pyroclastic flows in the Belham Valley or even explosive activity. All people on Montserrat are thus asked to remain particularly vigilant at this time.

Two main episodes of pyroclastic flow activity due to collapse from the dome occurred during the reporting period. In both cases the flows were directed over the northern flanks of the volcano in the Mosquito ghaut and Farrells plain area. The first episode lasted between 0230 and 0430 and was preceded by a hybrid earthquake swarm. The second episode was more intense and lasted from 1005 until 1407 with several discrete pulses of activity. The peak of the episode occurred at 1300, when a series of vigorously convecting pyroclastic flows were observed from the observatory site in Old Towne. At least two of the flows deposited material in the unnamed ghaut.

A helicopter observation flight this afternoon revealed that a prominent scar has developed in the dome directly above Mosquito ghaut. All of today's activity originated from within this scar. Talus in the Mosquito ghaut has advanced so far that blocks have tumbled directly into the unnamed ghaut. This ghaut feeds directly into the Belham river drainage system, further increasing the possibility of flows in the Belham valley.

Seismic activity has been dominated by the signals from pyroclastic flows during the collapses described above. Many of the pyroclastic flow signal had long period precursors which in the past have been associated with gas venting and explosion. The earthquake count as measured on the broadband seismic network is as following: 56 hybrid earthquakes; 98 rockfalls and 29 long period earthquakes, 23 of which triggered, or preceded rockfall or pyroclastic flow signals.

Given the size of the dome further collapses are likely and these may take place with little or no warning. The collapses need not necessarily be preceded by hybrid swarms. Topography suggests that the Belham valley may be quickly filled with deposits allowing flows to impact upon Old Towne and Friths areas and associated surges could get to Salem. The southern part of Montserrat is thus extremely dangerous and all areas south of the Nantes River should be evacuated.

If an explosion does occur, small rocks and ash can fall anywhere on the island. People 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