Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 28 July
to 16:00 29 July 1996

Activity at the Soufriere Hills volcano during this reporting period was significantly higher than that observed during the previous 24 hours. Many pyroclastic flows occurred in the Tar River Valley. These started at around 18:00 on 28 July and there were several discrete pulses of activity throughout the night and during the following day. The pyroclastic flows became progressively larger during the course of this activity and the last of them, at about 16:00, reached the sea. Large ash clouds were produced, reaching maximum altitude of 9,000 ft above sea level. There was significant ashfall downwind. Lightning discharges, and associated thunderclaps, were seen in the largest of these ash clouds. All the activity recorded today was caused by gravitational collapse of the growing lava dome.

Seismic activity was dominated by signals from the rockfalls and pyroclastic flows. The period of heightened activity started at about 18:00 on 28 July and lasted throughout the reporting period. There were four periods when continuous signal, saturated at most of the seismic stations, was recorded. These were from 18:05 to 19:19 on 28 July and from 11:46 to 12:06, 13:33 to 14:14 and from 15:18 to 16:00 on 29 July. The last of these was the largest in amplitude and was associated with the pyroclastic flow which reached the sea.

Other types of seismic events were difficult to detect due to the signals from the pyroclastic flows and rockfalls. However, 20 VTs, 1 LP and 20 hybrid earthquakes were detected. The LP and hybrid activity is similar to that recorded recently, but the VT seismicity is slightly higher.

Visibility was very poor late yesterday and for the early part of today. However, brief glimpses of the upper reaches of the Tar River Valley area revealed that the pyroclastic flows yesterday were from the eastern and northeastern parts of the lava dome and that green trees had been set alight. The largest flow yesterday seems to have travelled to within 300 ft of the sea. A pulsating glowing of the eastern flank of the lava dome was seen yesterday evening from Whites and Harris's during a period of intense activity. Observations from the ground and the helicopter on 29 July showed that the activity was in the same places. Most of the flows seemed to be channelled down the erosion channel just to the north of Castle Peak. Many of these then travelled into the southern part of the Tar River Valley, setting fire to trees. There were, however, at least two flows down the north flank of the dome into Farrell's Wall. None of the flows travelled out of the Tar River Valley.

Ash fall from the events in the evening of the 28th was slight, with 1 mm falling in the Lovers Lane area. Ashfall from the events on the 29th was greater. There was heavy ashfall in St Patricks at about 16:00, with about 2 mm falling.

Some GPS measurements were made today but the results are not yet available. EDM measurements were made for the eastern triangle involving Whites, Long Ground and Castle Peak, and also the Tar River Estate House to Castle Peak line These results are also still awaited.

COSPEC measurements were made offshore today from the Police launch. The COSPEC data from the last few days shows that the SO2 flux is still relatively low. The measured values are 335 tonnes per day for 26 July, 84 tonnes per day for 27 July and 213 tonnes per day for 28 July.

The Soufriere Hills Volcano is still considered to be highly dangerous to people and property on it's eastern and upper western flanks. Visits to the evacuated zone must be kept to a minimum. The Tar River and Long Ground areas to the east and upper Fort Ghaut, Gages Village and Upper Amersham areas to the west are all extremely dangerous. All access roads to these areas remain closed and people should not enter these areas under any circumstances. If they do, they put themselves and others at direct risk of serious injury or death.

Montserrat Volcano Observatory