Montserrat Volcano Observatory

Daily Report
Report for the period 6 pm 17 November
to 6 pm 18 November 1997

Volcanic seismicity has again been dominated by rockfall signals today. Better visibility has enabled observations of part of the dome complex today. In addition, new volume measurements indicate continued fast growth of the dome.

Between 16:00 yesterday and 16:00 today there were 3 long-period earthquakes, 2 volcano-tectonic earthquakes, and 2 hybrid earthquakes. One of the long period earthquakes preceded a rockfall. There were 110 rockfall signals, some of which were of moderate amplitude. This is almost twice the number recorded yesterday. An observation flight early this afternoon showed that most of the current rockfall activity is in the southern part of the dome. Numerous rockfalls and small pyroclastic flows were seen down the White River as far as the area of Galways Soufriere. The main chutes for debris seem to have moved to the southern part of Galways Wall. An area of strong fumarolic activity is also present on the eastern flank of the dome.

The level of ash in the atmosphere in St Peter's and in St John's, as averaged over the last 24 hours, remained low.

Dome volumes have been calculated from surveys completed in early November. The volume of the dome after the explosions ended on October 21st was 68 million cubic metres. Measurements of the dome on November 3rd give a total volume of 73 million cubic metres, thus giving an average extrusion rate between October 22nd and November 3rd of 5 cubic metres per second. However, geometric calculations of the size of the new dome in late October gave an extrusion rate of 8 cubic metres per second, and so the dome was probably growing at a slower rate in early November.

It is estimated that the volume of the dome after the collapse on November 5th was 70 million cubic metres; nearly all this material was from the pre-explosion dome complex. The further collapse on November 6th shed an equivalent volume but was sourced from the October 22nd dome. A survey of the pyroclastic fan at the mouth of the White River was undertaken yesterday, and results from this exercise should help to better constrain the volume of the two collapses in early November.

The dome is still growing and the growth area may switch rapidly at any time. Although the main activity is currently in the south-west sector of the volcano, further pyroclastic flows are likely in any of the ghauts around the volcano.

Montserrat Volcano Observatory