Montserrat Volcano Observatory

Daily Report
Report for the period 6 pm 8 December
to 6 pm 9 December 1997

Seismicity has increased slightly today again over yesterday, with rockfall signals still predominant and an increase in the number of hybrid events. Visibility has been generally poor and no good views of the dome were obtained today.

Between 16:00 yesterday and 16:00 today, the broadband seismic network recorded 166 rockfall signals, 34 long period and 38 hybrid earthquakes. This activity is consistent with continued dome growth in line with recent days.

The active growth is still concentrated high up on the Galways sector of the dome, but continuing rockfalls from the western side of the talus slope are cutting into the side of Chances Peak from above as was seen yesterday. Small rockfalls over the shoulder of the old dome, into the southern side of Tar River valley also appear to be continuing. Diffused ash clouds have been produced throughout the day from these rockfalls. The wind direction today was in the more usual west-northwest quadrant, so onland ashfall remained minimal. Measurements of the average dust levels over the last 24 hours in Salem were generally the same as yesterday's, since the ash deposited recently remains very dry and mobile.

The data from the recent EDM, GPS and dome surveys are still being processed.

Although activity is still mainly focused on the southern side of the volcano, past experience as well as recent observations shows that the area of growth on the dome can change very quickly. Growth activity appears now to be backing up behind the major build-up of material in Galways, and rockfalls or pyroclastic flows starting to occur down Gages or Tar River in the near future would not be a surprise.

Montserrat Volcano Observatory