Report for the period 4 pm 23 June
to 4 pm 24 June 1997
The activity over the last 24 hours has been dominated by swarms of hybrid earthquakes. The first swarm began last night at 8:51pm and ended at 10:07pm, it involved 30 hybrid earthquakes. The second swarm which began at 3:56am and ended at 8:26 am this morning, consisted of 202 stronger hybrid earthquakes. Seismic activity was then low today until about 3:15 this afternoon when another hybrid earthquake swarm began. There have been a total of 248 hybrid earthquakes during the reporting period. There were also 3 volcano-tectonic earthquakes, 8 long-period events and 119 rockfall signals.
Observations of the dome last night showed that most activity was concentrated on the eastern to northeastern flanks of the dome. Observations today also showed that most rockfall activity has occurred on the east side of the dome with one or two small pyroclastic flows travelling into the Tar River valley. The dome was clear at 6:00am this morning and a blocky summit was visible with three stubby spines. By 10:45am the appearance of the summit had changed and two new steep-sided spines had grown. This clearly shows that the dome is still growing in the summit area.
The amount of sulphur dioxide emitted from the volcano is measured daily using the COSPEC machine. Values for the last four days vary between 438 and 1170 tonnes per day, these values are well above the usual background flux of 2-300 tonnes per day reflecting the elevated level of activity.
An EDM survey has been completed today and results will be processed soon.
Further pyroclastic flows 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. Bramble Airport is operational, but the public are reminded that it is open only for essential travel purposes.