Montserrat Volcano Observatory

Daily Report
Report for the period 6 pm 9 December
to 6 pm 10 December 1997

Seismicity has changed slightly today, with rockfall and long period signals being present in equal numbers. 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 72 rockfall signals, 72 long period and 5 hybrid earthquakes. 18 of the long period events preceded rockfalls. This activity is still consistent with continued dome growth.

The active growth is still concentrated high up on the Galways sector of the dome, but a few rockfalls were also seen down Tuitts Ghaut this afternoon. Diffuse ash clouds have been produced throughout the day from the rockfalls. Measurements of the average dust levels over the last 24 hours in Woodlands and St. Johns were generally low.

The data from the recent GPS and EDM surveys on the north-west flank of the volcano show that there has been no significant movement of the points being measured.

Processing of the latest surveys of the deposits around the volcano have revealed that there is now 40 million cubic metres of material in the ghauts on the north and north-eastern flanks of the volcano. This is an increase of 24.7 million cubic metres since they were last measured in mid August. In total, the volcano has erupted at least 203 million cubic metres of material since November 1995.

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.

Godfrey Almorales (Seismic Research Unit) left Montserrat yesterday after a month long tour of duty.

Montserrat Volcano Observatory