Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 17 July
to 4 pm 18 July 1997

Two year eruption anniverary

The alert level system has been revised by zones

Activity at the volcano has been at the same level as yesterday with rockfalls being the main type of seismic signals recorded. Clear conditions allowed some views to be obtained of the dome.

Good views were obtained of all but the summit of the dome for most of the morning. A late morning observation flight indicated that the new growth appear to have almost completely filled the scar produced by the 25th June activity. Spillage of material from the new dome is now occurring directly onto the north-eastern flank of the pre-June 25th dome. Talus has now built up to the rim of the crater in all areas above Whites Ghaut and further rockfalls in this area is likely to feed directly into the ghaut. Fresh pyroclastic deposits with very minimal runout distances were observed in Galways, Gages, Mosquito Ghaut and the eastern flanks of the dome. A few small rockfalls were observed down into the Gages valley during the flight.

The number of rockfall signals has increased slightly from yesterday with 29 events being recorded. Three long period earthquakes and two hybrid events were also recorded. There were several periods of low level tremor seen on St. Georges Hill seismometer throughout the day.

EDM Measurements of line lengths between Waterworks and Lees Yard with the Total Station was again made twice today. The data continues to show no change.

Although there appears to be very little seismic activity from the volcano, there have been periods in the past when the dome has continued to grow with few earthquakes apart from rockfalls. Thus material is currently building up above Gages wall and Mosquito Ghaut, and the potential for large pyroclastic flows onto the northern and western flanks into the Central corridor and Plymouth is significant.

Residents should note that pyroclastic flow and ash eruptions have occurred during the past week with no direct association with seismicity or tiltmeter readings. This means that people entering the designated exclusion zone put themselves at extreme risk. 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 is also an area for anxiety over safety. It may provide a pathway for further pyroclastic surges and there is also a risk of hot mudflows which may form rapidly if there is a period of heavy rain associated with the tropical depression heading towards Montserrat. Mudflows travel extremely fast and may be near boiling point, they may extend much further along the Belham River valley than the pyroclastic surges. The pyroclastic flow and surge deposits will remain extremely hot for several days. Residents must not approach, attempt to handle or walk on the deposits because of the risk of severe burning. Residents and workers are also reminded to wear a dust mask when there is ash in the air.

The Soufriere Hills Volcano has now been erupting for two years. During this time over 105 million cubic metres of fresh rock has been produced of which more than 60% has formed a viscous lava dome. The remainder has been deposited as pyroclastic rock fragments on the flanks of the volcano and in the sea. During the course of the eruption over 10,000 volcanic earthquakes have been recorded with very few of these being felt locally. In this the second year of its operation, the MVO would like to assure Montserratians that we would continue to do our best to provide adequate information and advise on the ongoing eruption.

Montserrat Volcano Observatory