Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 27 July
to 4 pm 28 July 1997

The alert level system has been revised by zones

Small to moderate sized rockfalls signals have again dominated activity at the Soufriere Hills Volcano. Overcast conditions persisted for most of the day and no views were obtained of the volcano.

102 rockfalls and 3 long period earthquakes were recorded today. 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. Two of these periods; one at 3:42 am and the other at 6:00 am today lasted for 20 and 30 minute duration respectively. They are believed to have been due to dilute mudflows in the Gages and Belham river valleys.

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 these measurements are not yet available.

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.

Professor Tim Druitt of the University of Clermont Ferrand arrived at the MVO today for a month long tour of duty.

Montserrat Volcano Observatory