Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 22 July
to 4 pm 23 July 1997

The alert level system has been revised by zones

The level of activity at the volcano has been slightly higher than yesterday. Seismicity consists mainly of rockfall signals with little visible signs of activity on the dome.

The summit was covered in low cloud today and no good views of the dome were obtained.

Seventy rockfalls signals were recorded by the broadband network today. In addition to these there were also 3 long period earthquakes, one volcano-tectonic and one regional event. The regional event was located approximately 100 km north-north-east of Montserrat in the region of Barbuda. There were several periods of low amplitude broadband tremor on the St George's Hill seismic station.

Measurements were made today on the EDM line between Waterworks and Lees Yard, but the lines do not yet show any long term trend.

Despite the apparent lull in seismic activity, the dome continues to grow and the potential for large pyroclastic flows onto the northern and western flanks of the volcano remains 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 flows 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