Activity at the Soufriere Hills volcano during the greater part of this reporting period was lower than that observed during the previous 24 hours. However, from 16:00 to around 18:00 on 11 August, near-continuous rockfall activity led to the largest pyroclastic flows during yesterday's sequence. These travelled into the sea and generated ash clouds at around 17:17 which reached heights greater than 30,000 ft.
Approximately 82 rockfalls, 7 volcano-tectonic (VT) and 56 hybrid earthquakes were recorded. Signals indicative of small pyroclastic flows in the Tar River Valley were recorded today at 01:30 and 07:32. From 13:00 to 14:00, a series of small rockfalls led to a few small pyroclastic flows which travelled as far as the Tar River Soufriere. Two periods of near-continuous low amplitude tremor embedded with rockfalls occurred around 06:16 to 07:10 and 09:00 to 10:50 today morning. The VTs were located at shallow depths beneath the crater.
Visibility was generally very poor throughout the day, with low clouds covering the dome.
EDM measurements were made on the western triangle and the results showed a 2.4 cm lengthening of the Amersham to Amersham slope distance line and a 2.8 cm shortening of the Amersham to Chances Peak steps line. These changes are compared to the results of the last measurements made on these lines on 15 July. COSPEC measurements of the amount of SO2 in the volcanic plume were also made today and these gave an average value of about 1195 tonnes per day.
Some ash thicknesses associated with yesterday's events include 20mm in Lovers Lane, 30mm at Plymouth Police Headquarters, 6mm in Trials, 2mm in Gingoes, 19mm on Fort Ghaut bridge, 3mm in Fox's Bay and 2mm in Weekes. Further rockfalls and pyroclastic flows will occur but all indications are that these will be confined to the Tar River Valley area. However, areas affected by associated ashfalls will obviously depend on the direction and strength of the wind at the time. There is no need at the moment for alarm. People in areas affected by ash falls should exercise great care when driving and should wear dust masks.
The Tar River Valley and surrounding areas are now extremely hazardous, and should not be entered under any circumstances. We urge individuals who continue to ignore this advice to think very seriously before making trips to these highly hazardous zones.