Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 25 June
to 4 pm 26 June 1997
The current alert level is ORANGE

The level of seismic activity remained low last night until about 4am this morning when another hybrid earthquake swarm began. Although this swarm was less intense than previous swarms, several earthquakes in the swarm were particularly large events. This swarm ended at about 7am and was followed by a lull in the seismic activity until about 11am when another hybrid earthquake swarm began. This swarm lasted for just over two hours and was again of low intensity. There have been a total of 64 hybrid events in the last 24 hours and there were also 3 long period events. From 1pm until the end of the reporting period there have been regular rockfall events with a total of 34 recorded over the last 24 hours.

The tiltmeters on Chances Peak have shown two full cycles of rapid inflation and deflation today implying that more magma is being fed into the dome.

The pyroclastic flows yesterday were the most voluminous flows experienced so far during this eruption. A minimum estimate is that the deposits have a volume of 4-5 million cubic metres. The period of collapse lasted for only 20 minutes and generated the largest seismic signal seen yet during this eruption. The seismic signal was larger than that recorded during the explosive eruption of September 17th 1996.

The scar left by yesterdays collapse was seen today from the helicopter and is a spoon-shaped hollow with a steep back wall situated on the lower flanks of the dome above Mosquito Ghaut. The area of land covered by pyroclastic flow and surge deposits has been revised to at least 4 square kilometres. Deposits have covered a fan-shaped area across Farrells, extending west to Dyers and north to the lower slopes of Windy Hill, seriously affecting the village of Streatham. Beyond Dyers the deposits are confined to the Belham River valley but material extends to within 1.5km of the Belham bridge. East of Mosquito Ghaut the deposits extend from Farms and Trants in the north to Bethel and Spanish Point in the south.

The pyroclastic flow deposits will remain hot for several days. Residents must not approach, handle or attempt to walk on the deposits because of the risk of severe burning.

As a result of the moderate ashfall there is likely to be heavy resuspension of ash in the air, especially if it does not rain. Residents are urged to wear a dust mask.

The entire central corridor and the eastern side of the volcano are very dangerous, and people should not enter this area at all. The Belham River valley is also potentially dangerous and people should not enter the ghaut. The MVO advise that people living on low ground or on the lower slopes of the Belham River valley in the Corkhill area do not sleep there tonight. Further pyroclastic flows are likely and could happen at any time. Mosquito Ghaut is still the most likely pathway for pyroclastic flows, but activity in Gages, Tuitt's and the Tar River valley is also probable. Access to Plymouth has been completely restricted.

The airport is closed and will remain closed until further notice.

Montserrat Volcano Observatory