Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 15 June
to 4 pm 16 June 1997
The current alert level is ORANGE

Pyroclastic flows occurred in the Gages valley this afternoon, and reached almost to the Gages Lower Soufriere. The flows generated significant ash clouds which were blown over Plymouth. There were also smaller pyroclastic flows in Mosquito and Tuitt's Ghaut. The situation appears to have stabilised, but further pyroclastic flow activity is expected, and could occur in any of the ghauts or valleys to the east, north or west.

Observations were made of the Gages valley this morning from the helicopter. During the last few days, the main area of activity has been above Mosquito Ghaut, and a small amount of dome material had spilled further to the west from here and gone over the Gages wall. There was a sudden escalation in activity this afternoon just before 4 pm, with the generation of moderate pyroclastic flows lasting for about 30 minutes. The flows reached to about 50 metres above the lower Gages Soufriere, to just over 1 km from the dome. The flow deposits are quite blocky there, with several trees still standing within the deposit.

During the activity this afternoon pyroclastic flows also occurred in Mosquito Ghaut and to a lesser extent in Tuitt's Ghaut. The flows in Mosquito Ghaut were larger than yesterday's, and also moved faster. The flows reached to the first sharp bend in the ghaut, about 1.6 km from the crater rim. Several flows were also reported in the Tar River valley throughout the day.

The seismic activity today was about the same as yesterday, with rockfall signals dominating: there were 156 of those in the last 24 hours. The level of earthquakes remained low, with 5 hybrid, 6 volcano-tectonic and 4 long-period earthquakes recorded. Volcano-tectonic earthquakes have been rare recently, but small numbers occur occasionally. The largest VT was located at a depth of about 2.5 km beneath the dome.

A GPS survey was carried out on Chances Peak earlier today. The results will be processed shortly. The crack on Chances Peak was measured, and showed no changes from the last visit. The crack on Galway's Mountain was also measured, and had sheared by 25 cm since it was last measured on 3 May. This is an increased rate of deformation.

COSPEC runs were made along the road to the south this morning. The readings will be processed in due course.

The dome has been clear of cloud for most of the day, although visibility has been poor because of the haze. The top of the dome could be seen from Windy Hill and Harris, allowing photographs and measurements to be made that will be used to estimate the volume of the dome.

Further pyroclastic flows could occur in any direction, especially in Mosquito Ghaut, Tar River valley or Gages Valley. The authorities advise that the entire central corridor should be evacuated tonight. Plymouth was evacuated this afternoon, and access to this area will be reviewed overnight. Corkhill remains safe at this time. WH Bramble Airport should be open again in the morning unless there is further significant activity overnight.

Montserrat Volcano Observatory