Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 25 August
to 4 pm 26 August 1997

Activity at the volcano continued at a similar level to the previous 24 hours. Seismicity was again dominated by rockfall and pyroclastic flow signals. Over the last 24 hours 4 hybrid earthquakes, 14 long period earthquakes and 104 rockfalls triggered the broadband seismic network. The underlying pattern is still cyclic activity, although the period between cycles has lengthened to about 15 hours.

There were two periods of high rockfall activity during this reporting period. The first started at about 7:30 pm last night and continued until about 11 pm. Some glow was seen from the dome during this period, although it was not possible to determine the exact area of the dome from which it was coming. There was at least one small pyroclastic flow into the Gages Valley, at around 9:30 pm. There was a moderate-sized isolated pyroclastic flow into Gages at about 2:30 am this morning, which probably travelled as far as the Lower Gages Soufriere. The second period of enhanced rockfall activity was around noon today. This was smaller than the first one and involved no pyroclastic flows.

Visibility has been quite good today, particularly at midday and during the afternoon. The dome was generating a lot of steam and some ash and it was only possible to see the northern and western flanks of the dome clearly. There were no obvious changes to these since they were last seen about ten days ago. The pyroclastic flows into Gages suggest that dome growth is currently focused on the western part of the dome.

Collapse of material from the dome may lead to further explosions and these may be more intense and longer lived than those already experienced. Explosions are also possible without much precursory activity - as in early August. If explosions do occur, the central zone should be evacuated immediately, and people in the northern zone should seek shelter under a strong roof as soon as possible. After an explosive event, small rocks and ash can fall anywhere on the island. Ash and falling rocks can make driving hazardous. Ash is present in the atmosphere and dust masks should be worn outdoors.

All ghauts on the volcano are now filled with hot pyroclastic flow deposits. The enhanced pyroclastic flow activity indicates increasingly instability of the dome and further pyroclastic flow activity is anticipated. This makes all of the exclusion zone extremely dangerous. Material accumulating against St. George's Hill may now make it possible for pyroclastic flows to reach into the Belham river valley from the Gages Valley as well as from the upper part of Mosquito Ghaut. Access to the exclusion zone is completely restricted, and people should stay away from the flanks of the volcano. People should remain vigilant and continue to listen to Radio Montserrat for any announcements.

Montserrat Volcano Observatory