Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 20 July
to 4 pm 21 July 1997

The alert level system has been revised by zones

Activity at the volcano has been at a slightly higher level than yesterday with more rockfalls being recorded by the seismic network. Overcast conditions for most of the day prevented any clear views of the dome.

Seismicity was dominated by small to moderate sized rockfalls signals, none of which were of particularly long duration or high amplitude. The number of rockfall signals was higher than yesterday with 58 events being recorded. The only other seismic events recorded were 4 long period earthquakes and one volcano-tectonic event. One of the long period earthquakes triggered a rockfall. There were no hybrid earthquakes. Low amplitude tremor occurred on the St George's Hill seismometer throughout the day. The Chances Peak tiltmeter is not currently operational.

The volcano was covered in low cloud for most of the day, and no clear views of the dome were obtained. A field party visited the end of the June 25 flow in Trant's today and took temperature measurements in the deposits. It is now nearly a month since the pyroclastic flows occurred, but at 2 m depth the deposits were still 640 degrees centigrade. This emphasises that the ash and debris on the flanks of the volcano is extremely dangerous, and people should not attempt to go anywhere near the deposits.

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. 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. 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 still 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.

Montserrat Volcano Observatory