Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 12 July
to 4 pm 13 July 1997

The alert level system has been revised by zones

The level of activity at the volcano has been about the same as yesterday. The seismicity is still dominated by rockfall and small pyroclastic flow signals.

The volcano has been clear for short periods today and some good views of the dome were obtained from the MVO, Garibaldi Hill and above the airport on the east. Photographs and video footage were taken, and theodolite measurements were made in order to get an estimate of the current volume of the dome. These data are currently being processed. The visual observations suggest that there is a steep area of new growth in the centre of the dome, and this appears to be its new high point. From a brief observation flight in the early afternoon the top of Gages gap could be seen. A notch has been cut in the top of the wall by rockfalls and pyroclastic flows.

Several small ash plumes were observed during the day and one at 2.36 pm, which rose to over 10,000 ft, originated from a moderate pyroclastic flow in the Gages Valley.

The number of rockfall signals has decreased since yesterday. 71 rockfall signals and only 1 long period earthquake were recorded by the seismic network today. There were no volcano-tectonic or hybrid earthquakes recorded.

The EDM line between Waterworks and Lees Yard was surveyed twice today. The data collected from these stations are still insufficient for any clear trends to be defined.

The cyclic pattern which had been defined by the Chances Peak tiltmeter has now ended. There is still an overall deflationary trend on the data but there are no peaks or troughs in the trend as existed previously.

Residents should note that pyroclastic flow and ash eruptions have occurred during the past week with no preceding increase in seismicity or direct association with the tilt cycle. 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.

Plymouth is particularly vulnerable since pyroclastic flows have begun to enter the Gages valley without warning and have the potential to reach the coast. Persons entering these areas place themselves in extreme danger.

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 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.

Dr John Bennett of the British Geological Survey left Montserrat today after a brief visit to the MVO.

Montserrat Volcano Observatory