Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 21 June
to 4 pm 22 June 1997
The current alert level is ORANGE

There was moderate pyroclastic flow activity in the Tar River valley early this morning, and a subsequent change in the pattern of seismic activity.

After a quiet night, the level of activity started to increase at about 5:10 am this morning, and by 6 am there were continuous moderate pyroclastic flows down Tar River. The main flows travelled down the south side of the valley and reached to within 1 km of the delta, as observed from the airport. The flows generated a moderate ash cloud that was blown to the west. One small rockfall was seen at the top of Tuitt's Ghaut during this episode, but no other activity has occurred in Mosquito and Tuitt's Ghauts or in the Gages valley. The level of activity dropped rapidly after the pyroclastic flow and remained low until about 2pm this afternoon, when a moderate increase in rockfall activity, ash cloud generation and seismicity developed. By 4pm, this activity seemed to be in decline again.

The MVO airport observers reported low cloud on the mountain throughout the day. Most of the activity occurred as rockfalls on the eastern face of the dome, with runouts into the Tar River valley.

The nature of the seismic activity changed today at, or shortly after, the pyroclastic flow episode at 6am this morning. While rockfall signals remained the most common type of signal on the records, with 149 counted in the 24 hours, there was a short burst of about six volcanic tectonic earthquakes following the pyroclastic flows, and these were then followed by a swarm of hybrid events which led into the increase in activity this afternoon. Today's totals were 64 hybrid earthquakes, 18 long period earthquakes, and 9 volcano-tectonic earthquakes.

The two tiltmeters on Chance's Peak indicated a change in the short-term pattern of deformation of the volcano from the recent regular cycles of the last several days. There was a small short inflationary surge before the pyroclastic flows this morning, followed by a marked and quite rapid deflation. This levelled out by mid-morning and then went into a slower but sustained inflation which peaked in mid-afternoon, accompanied by the increase in rockfall and seismic activity, noted above.

GPS measurements were being conducted over the network of stations which surround the volcano this afternoon.

The level of activity has increased today and the seismicity has changed character. This may indicate some change in dome growth in the crater but, until this is confirmed by visual sightings, it must be assumed that further pyroclastic flows and surges could travel into Gages valley, Mosquito Ghaut, Tuitt's Ghaut or the Tar River valley at any time. Access to Plymouth remains restricted. Zones A and B, which include Tuitt's, Bramble, Bethel, Spanish Point, Farms, Harris and Trants, are extremely dangerous and nobody should go into this area at all.

Bramble Airport is operational, but the public are reminded that it is open only for essential travel purposes.

Dr Keith Rowley joined the MVO team today.

Montserrat Volcano Observatory