Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 12 September
to 4 pm 13 September 1997

Volcanic activity has been at an increased level today, with especially vigorous pyroclastic flow activity during this afternoon. There was also a hybrid earthquake swarm overnight, and every indication is that activity could pick up very quickly to a high level which might include pyroclastic flows in the Belham Valley and even explosive events.

The summit of the volcano was shrouded in cloud for much of the day. However, good visual observations were possible of ash plumes rising above the clouds and of pyroclastic flows down the northern flank of the volcano. The most vigorous activity in the middle of the afternoon produced pyroclastic flows into the uppermost part of the Belham valley in the Dyer's area and also at least one audible explosion from the dome. Ash clouds rose typically to 5,000 ft, being generated both from pyroclastic flows and from continuous venting from the summit. Helicopter observations during a GPS survey also revealed new flows in Tuitt's Ghaut and down the Tar River, and flows may also have got into the White River to the south-west of the volcano. However, the majority of activity is still concentrated on the northern flank of the volcano and it is thought that the northern parts of the dome are still the most active.

Seismic activity was dominated by signals from the rockfall and pyroclastic flow activity described above; 25 were recorded on the short period network, with 54 hybrid events in a swarm between 9 pm last night and 3 am this morning also recorded. Due to continued maintenance work connected with the move of MVO, these statistics are a minimum. The small explosion described above gave a very strong seismic signal of long-period character, and many of the pyroclastic flows during this afternoon were preceded by long-period earthquakes.

A GPS survey was carried out today involving measurement of stations at Harris, Windy Hill, Brodericks and O'Garra's. This survey was done with the aid of the helicopter, and the results are currently being processed. Unfortunately, ash prevented occupation of the Long Ground or White's stations.

Environmental monitoring by MVO continues, with regular measurement of ash levels and gas and water chemistry. Ash levels are currently high in areas to the west and east of the volcano, and anyone in areas where ash is being blown around is reminded that they should wear an ash mask. The large size of the dome, its rapid growth rate and the filling of ghauts on the northern flank of the volcano all make it more likely that large pyroclastic flows will 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