Seismic activity at the Soufriere Hills volcano continues at a slightly lower level than yesterday, with a further earthquake swarm this morning, followed by an episode of volcanic tremor. At the peak of the tremor some pyroclastic flows were generated. Another pyroclastic flow also took place this afternoon. Both flows propagated to the delta at the base of Tar River and produced ash clouds that rose above 10,000 feet above sea level.
A total of 64 volcano tectonic and 59 hybrid earthquakes were recorded since 4:00 pm yesterday, Most of these were in a swarm from 3:59 am to 7:40 am. There were also 11 distinct rockfall signals. The earthquake swarm was followed by a period of high amplitude volcanic tremor from about 9:00 am to 10:30 am.
Visibility was generally not bad for observations today. The first ash column appeared within 20 minutes of the start of the volcanic tremor. This cloud rose to 11,000 feet and drifted to the west. Heavy ash precipitation was reported at the port in Plymouth. Several other small pyroclastic flows and near continuous rockfall activity were observed for the rest of the morning and well into the afternoon. The largest pyroclastic flow made it to half way across the delta. Some of the smaller pulses propagated down to the vicinity of the Tar River Estate house. The second pyroclastic flow occurred at 3:40 pm. This flow also made it to the delta and produced clouds that rose up to 10,000 ft and drifted south-west out to the sea. The some of the lower sections of the ash cloud also drifted northwards.
Further COSPEC measurements were taken throughout the day. The results of the partial dome volume survey that was conducted yesterday reveals that the extrusion rate in the localised area of recent activity has been about 2 cubic metres per second over the 10 day period following January 28. Due to poor weather only the area down-slope of this area on the south- eastern sector of the dome was surveyed.
The eastern face of the dome is steep, and likely to undergo further collapse soon. Any collapses are likely to be gradual, and follow the recent pattern. However, a larger collapse cannot be ruled out. An explosion similar to that of September 1996 could result in the event of a major collapse which lasted for several hours. Zone E, which includes Cork Hill and the airport, remains safe. The Tar River Valley and the upper Galway's area are very dangerous.