Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 12 January
to 16:00 13 January 1997
The current alert level is ORANGE

Rockfall and pyroclastic flow activity from the dome reached its highest level since September 1996 today. The activity occurred mostly between 11:30 am and 1 pm, although there were small pyroclastic flows throughout the afternoon. During the peak in activity around midday, pyroclastic flows reached the sea, and the ash clouds were estimated at 20,000 ft high. Heavy ash fall was experienced from Foxes Bay to the south. Further pyroclastic flows are likely in the next few days. A major collapse of the dome is possible, and could result in another explosion, similar to that of September 1996. It is expected that there would be several hours of a hig level of pyroclastic flow activity before any explosion. At the moment, the scientists are confident that zone E, which includes Cork Hill and the airport, remains safe. However, the situation could change rapidly, and residents of Montserrat should remain alert and listen to Radio Montserrat.

Visual observations of the pyroclastic flow activity were made from Whites and Harris. The largest flows originated from the south margin of the new lava dome and poured down to the south of Castle Peak and along the south gully of the Tar River valley. The largest flows were produced in a closely spaced series of pulses starting just before noon, which covered a large part of the delta at the mouth of the Tar River valley and just reached the sea at three points of the delta. The delta was extended at these points by about 10 metres. Boiling sea water produced abundant steam clouds over the Tar River valley for a few hours after the activity. Smaller flows occurred at intervals of about 15 minutes, the largest of which was at about 1 pm and got to within about 500 metres of the delta, but most of the flows got no further than the Tar River Soufriere. There were small rockfalls from other parts of the dome from time to time throughout the day. All of the activity was restricted to the Tar River valley and particularly the south part of the valley. Intermittent clearing of the clouds near the dome summit showed that there remain large overhanging slabs of lava close to the point of origin of the earlier pyroclastic flows. These are likely to continue to fall off and create significant pyroclastic flow activity and associated ash plumes.

The seismic activity was dominated by pyroclastic flow signals between 11:30 am and 1 pm. There was also a small swarm of 36 volcano-tectonic earthquakes between 08:47 am and 12:42 pm. Nineteen hybrid and two long-period earthquakes were also recorded.

The gravity survey of the volcano flanks was continued today, in the Farrells area. Samples of the new ash deposits from the west parts of the volcano were taken today for analysis.

Montserrat Volcano Observatory