Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 11 July
to 4 pm 12 July 1997

The alert level system has been revised by zones

There was a slight increase in the level of activity at the volcano since yesterday. The seismicity is still dominated by rockfall and small pyroclastic flow signals.

Although the volcano was overcast for most of the day, ash generation occurred throughout with ash drifting towards the western side of the volcano. Several small ash plumes were observed during the day and one at 9:16 am rose to 10,000 ft and produced ashfall at the MVO. A late morning observation flight indicated that there were no new material in Mosquito or Gages Ghaut which reached further than 0.5 km from the crater rim. Minor rockslides were noted at Galways. An ash eruption which emanated from the western side of the dome above Gages was observed at 11:20 am. A brief view of the dome obtained from high altitude indicated that it was conical in shape with thick steam emission from numerous points. The sound of rockfalls from the northern flanks of the dome was clearly audible to field teams working in the area of Waterworks.

The number of rockfall signals has increased since yesterday. 125 rockfall signals, 2 hybrid and 3 long period earthquakes were recorded by the seismic network today. There were no volcano-tectonic earthquakes recorded.

The EDM line between Waterworks and Lees Yard was surveyed again 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 safe 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 arrived in Montserrat today for a brief visit to the MVO.

Montserrat Volcano Observatory