Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 29 July
to 4 pm 30 July 1997

The alert level system has been revised by zones

Activity at the volcano have again been dominated by small to moderate sized rockfalls signals which increased in intensity at various periods during the day. Despite overcast conditions for the entire day, dilute ash plumes were visible from the MVO during periods of heightened rockfall activity.

A late evening observation flight indicated that fresh pyroclastic flow deposits had extended to just below the lower Soufriere in the Gages valley. This is most likely from the activity which occurred yesterday morning. Several small pyroclastic flow deposits from the activity earlier today were also noted at the top of Tuitts Ghaut and in the Tar River Valley. Three small new pyroclastic flows were also noted in the Galways area.

139 rockfalls, 10 long period events and one volcano-tectonic earthquake were recorded today. Most of the rockfall activity appear to have occurred towards the north-eastern end of the dome as well as over the Gages area. The volcano-tectonic earthquake was located at about 3 km beneath the volcano. Broadband tremor, mainly of low amplitude was recorded on the St George's Hill and St Patrick's seismographs for variable periods during the past 24 hours. A new short period seismic station was established at Lees Yard today. This replaces the Gages seismic station which was destroyed by pyroclastic flows last month and along with repairs undertaken yesterday of the seismic telemetry, brings the short period network close to its pre-June 25th operational level.

EDM measurements were conducted today on the north-western triangle between the MVO, Garibaldi Hill and Lees Yard and on the Waterworks to Lees Yard radial line. The results of measurements made on these lines yesterday continue to show no consistent trends.

The dome continues to grow and the potential for large pyroclastic flows onto the northern and western flanks of the volcano remains significant. The top of the Gages valley and Mosquito Ghaut have become substantially filled with debris from the growing dome. 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 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. 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