Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 15 September
to 4 pm 16 September 1997

Volcanic activity has been at a moderate level during today, with two periods of enhanced rockfall and pyroclastic flow generation. The largest flows moved most of the way down the Farrell's plain and some were also seen in Tuitt's Ghaut.

The first period of enhanced pyroclastic flow activity occurred between midnight last night and about 2:30 this morning and the second between about 11:00 am and 1:00 pm today. Both of these periods of enhanced flow generation were preceded by a build up in background tremor accompanied by ash and steam venting. Flows were again mainly on the northern flanks of the volcano, with most material being channelled into Tuitt's Ghaut or onto the Farrell's plain. The main areas of growth on the dome appear still to be on the northern side, and there is no indication of any slow-down in growth rate.

General seismicity was at a moderate level, with no particular swarms of events occurring. A total of 47 rockfalls signals were logged, with 20 long-period events, 3 hybrid and 13 volcano-tectonic earthquakes. Long-period events have preceded many of the pyroclastic flows, and a small explosion was audible from the dome synchronous with a long-period event.

Visibility has been poor all day and the dome has not been seen. Some accuracy tests were undertaken this morning with the laser range-finding binoculars used to assist in mapping of the size of the dome. The results from these tests will help MVO further assess the accuracy of dome volume calculations and to refine techniques.

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. Surges of hot ash from such flows could wash high up the sides of the 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