Seismic activity at the Soufriere Hills volcano continues at a high level, with two further earthquake swarms followed by episodes of high-amplitude volcanic tremor. The intensity and duration of tremor were at the highest level experienced since volcanic tremor reappeared.
The highlight of today's activity were two episodes of volcano-tectonic earthquakes followed by volcanic tremor. Both earthquake swarms and tremor episode were more intense than previous events to date. The first earthquake swarm started at around 3:10 pm yesterday, and lasted until the tremor started at 7:10 pm. The tremor episode ended at about 9:00 pm. No ashfall was reported during or after this episode. A small pyroclastic flow was recorded at 11:27 pm last night. Between mid-night to 4:00 am a few flood signals were registered on most seismic stations. The second earthquake swarm started at 10:10 am and lasted until the tremor started at 3:30 pm. This tremor episode ended at about 4:30pm. A few small pyroclastic flows were generated.. Except during the periods of tremor, rockfall activity remained at a moderate level throughout.
There was a backlog of seismic data to be processed at the end of the day. However, more than 103 volcano tectonic and 18 hybrid earthquakes were recorded between 4:00 pm yesterday and 2:00 pm today This was significantly more than yesterday and some of the events were slightly larger than recent ones.
In variable cloud cover conditions, the lower slopes of the dome were inspected during a late afternoon flight yesterday. Very little changes were noticed at the surface of the dome and also along the Galways side of the crater. Conditions were better for visual observations today. A dome volume survey was done this morning. Observations were also made from Whites from midday until late afternoon. During the early stages of the high level tremor that occurred this evening, near continuous small rockfall activity occurred at the south-eastern section of the dome. These then developed into a series of small pyroclastic flows. The largest flow took place at 3:51 and propagated as far as the Tar River Estate house. Estimated height of the associated ash clouds was 5000 ft above sea level.
Cospec measurements were taken today. The results are still being processed.
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.