Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 21 July
to 4 pm 22 July 1997

The alert level system has been revised by zones

The level of activity at the volcano has been about the same as yesterday. Seismicity consists mainly of rockfall signals with little visible signs of activity on the dome.

The flanks of the volcano was clear for most of the day, although the summit was always covered in low cloud. A clear view of three incandescent chutes of hot rock was obtained from the MVO at about 5:00 am this morning. The chutes were observed above Gages and Mosquito Ghaut and on the flank of the dome further east. This suggests that dome growth continues to be focused above Mosquito and Gages Ghaut as has been evident during the past week. An observation helicopter flight at 9:30 am today indicated that there were no new deposits in Gages, Galways or Tuitts Ghaut as well as in the Tar River valley. A small rockfall into Mosquito Ghaut was observed during the flight; this travelled to about 500 m from the dome.

Twenty-five rockfalls signals were recorded by the broadband network today. In addition to these there were also five long period earthquakes, one volcano-tectonic and two regional events. There were several periods of low amplitude broadband tremor on the St George's Hill seismic station.

Despite the apparent lull in seismic activity, the dome continues to grow and the potential for large pyroclastic flows into the northern and western flanks of the volcano remain significant. There have been periods in the past when the dome has continued to grow with few earthquakes apart from rockfalls. Residents should note that pyroclastic flow and ash eruptions have occurred during the past few weeks with no direct association with seismicity. This means that people entering the designated exclusion zone put themselves at extreme risk. In addition, people in the northern and central zones should stay alert and listen to Radio Montserrat. The current area of activity in the crater makes Mosquito Ghaut and Gages valley the most likely pathways for pyroclastic flows, but further flows in Tuitt's, Tar River or White River are possible as well.

The Belham River valley provides a pathway for mudflows which may develop rapidly following a period of prolonged rainfall. It therefore remains an area for anxiety over safety since it is also a potential pathway for pyroclastic surges. Mudflows can travel very fast and may be quite close to boiling point. In addition, they may extend much further along the river valley than the pyroclastic surges. As our recent temperature measurements in the area just north of Farm's River indicate, pyroclastic flows and surges retain their high temperatures for several weeks after they were deposited. Residents are therefore urged not to approach, attempt to handle or walk on these deposits since they could sink in, due to the uncompacted nature of the deposit, and become severely burnt. Dust masks should always be worn when there is ash in the air.

Montserrat Volcano Observatory