Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 24 July
to 4 pm 25 July 1997

The alert level system has been revised by zones

Activity at the volcano continues to be dominated by rockfalls and small pyroclastic flow signals. A very brief view of the dome was possible at lunch-time, but there was insufficient time to make any measurements or assess the location of the latest growth.

115 rockfalls, one long-period event and one volcano-tectonic earthquake were recorded by the seismic network today. This is a significantly higher count than yesterday. Broadband tremor, which was generally of a low amplitude, was recorded for variable periods on the St George's Hill station throughout most of the period.

EDM measurements were conducted today between MVO, Garibaldi Hill and Lees Yard. This is another new triangle to be established on the western flanks of the volcano, and will be measured routinely to assess the deformation.

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 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.

Today, Dr. Maggie Mangan (US Geological Survey, Hawaii Volcano Observatory) and Mr Rob Watts (Independent) left Montserrat after one month and 10 week long tours of duty respectively.

Montserrat Volcano Observatory