Activity at the Soufriere Hills volcano during this reporting period was at about the same level as yesterday. Dome growth continues, with associated rockfalls and a period of vigorous steam and ash venting was also noted today.
The seismicity today has again been dominated by rockfall events and volcano-tectonic (VT) earthquakes. Seventy two (72) VTs were recorded during the 24-hour reporting period, which is slightly lower than the total recorded yesterday. These occurred in two swarms, between 23:39 last night (14 September) and 01:30 this morning and between 08:51 and 10:38 this morning (15 September). These earthquakes were again located at shallow depths (less than 2 km or 1.3 miles) beneath the crater. A total of 84 rockfall events were recorded today, the largest signals occurring at 17:24 yesterday afternoon and at 12:33 today. Fifteen small hybrid and fourteen long period earthquakes were also recorded, both levels similar to the last reporting period. Broadband tremor at a low amplitude was recorded on the Gages seismometer between 16:10 and 19:35 yesterday and between 11:08 and 14:00 today.
Visibility was good for periods during today, with observations possible from the helicopter and from White's Yard. Rockfalls are still concentrated on the eastern flank of the dome and were especially frequent around lunchtime today. Several small pyroclastic flows were noted, one late yesterday afternoon and one at around 13:10 today which reached beyond the Tar River Soufriere. Ash clouds from rockfalls and flows were generally blown northwestwards over Garibaldi Hill, although a change in the wind direction at lunchtime today meant that some ash was blown northwards from the volcano. A period of intense ash and steam venting occurred between 12:50 and 13:20 today, sourcing from the highest part of the dome to the west of the active face, which is still very steep and looks liable to collapse over the next few days.
EDM measurements were attempted on the lines to Castle Peak today but no reflection was obtained probably due to ashing of the reflector from rockfalls which are now occurring between the reflector site and Castle Peak itself. A new reflector may have to be installed to replace the existing one as rockfalls may soon remove it. A GPS survey was undertaken today on the lower flanks of the volcano - the results are still being processed.
MVO scientists are expecting significant rockfall and possible pyroclastic flow activity over the next few days as the eastern flank of the dome undergoes partial collapse due to its unstable state. All indications are that the pyroclastic flows will be confined to the Tar River valley area. Areas affected by associated ashfalls will depend on the direction and strength of the wind at the time. Dust masks should be worn at all times in ashy environments, and drivers should exercise caution and consideration for other road users.
The Tar River Valley and surrounding areas continue to be extremely hazardous, and should not be entered under any circumstances. We urge individuals who persist in ignoring this advice to think very seriously before making trips to these potentially deadly zones.