Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 14 September
to 4 pm 15 September 1997

Volcanic activity has remained at a heightened level, similar to the last few days. Two high intensity periods of pyroclastic flow activity occurred last night and this morning. However, isolated events did occur outside these time windows demonstrating that high level activity, including pyroclastic flows can occur at anytime.

The first period of pyroclastic flow activity and dome collapse occurred between 2330 14/9/97 and 0200 15/9/97 and was preceded by a swarm of hybrid earthquakes. The second period began at 0724 this morning and ended at 1230. There was no precursory seismicity for the second period of activity. Flows were again restricted to the northern flanks of the volcano, with material being channelled down Mosquito ghaut and spreading across the Farrells plain. Material was also diverted into Tuitts ghaut to the east. The largest of the flows had a runout approximately 2km. There was no confirmation of flows entering the Belham river drainage system, although visual observations suggest that a surge component of the flows may have entered Tyers, previously unnamed, ghaut.

Seismicity during the dome collapse episodes was dominated by signals from the rockfall and pyroclastic flow activity; 95 rockfall signals were recorded on the short period network, with 31 hybrid events, 10 volcano-tectonic earthquakes and 12 long-period earthquakes. The swarm of hybrids started at 2051 last night and ended at 2323 and consisted of 25 discrete events. Some of the individual events displayed very high amplitudes and were as large as any seen in the eruption so far. The volcano-tectonic events were distributed throughout the reporting period. The largest of these events were located at depths of around 3km below the top of the dome. Again, many of the pyroclastic flows during the reporting period were preceded by long-period earthquakes which may be indicative of sub-explosive activity, triggering the pyroclastic flows.

Visibility, has been generally poor throughout the day, due to low cloud and ash so no clear observations of the dome were possible. However, a reconnaissance party has begun work establishing an observations post on the eastern ridge of the Centre Hills. This site will be used for a television camera whose pictures will be relayed back to the MVO, and also to relay signals from other monitoring equipment positioned around the volcano.

The large size of the dome, its rapid growth rate and the filling of ghauts on the northern flank of the volcano all suggest that there is still potential for large pyroclastic flows which could reach far down the Belham Valley. This makes areas south of the Nantes River very dangerous and anyone still living in this area is urged to move north as soon as possible.

In addition to generation of large pyroclastic flows, explosions could also occur. If an explosion occurs, 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.

Montserrat Volcano Observatory