Activity at the Soufriere Hills volcano during this reporting period has been at a higher level than yesterday. Volcano-tectonic earthquakes and rockfalls continue to be the most dominant seismic signals and some areas have been affected by ashfalls associated with the larger rockfall events.
There were 195 volcano-tectonic earthquakes recorded during the 24-hour reporting period, an increase in numbers compared to yesterday. These occurred in three short swarms separated by periods of high rockfall activity. The first VT swarm occurred between 17:35 and 19:24 yesterday evening (15 September); the second between 02:10 and 04:20 this morning(16 September) and the third between 11:00 and 12:05 late this morning (16 September). These swarms are similar to those seen over the previous several weeks and were located beneath the crater at shallow depth (above 2 km). The number of rockfalls also increased today, with 104 rockfall events recorded today compared to 84 yesterday. The periods of most intense rockfalls activity occurred immediately following the volcano-tectonic swarms. A period of near-continuous rockfall and or pyroclastic flow activity occurred between 12:00 and 14:40 on 16 September. This was preceded by the shortest of the three volcano-tectonic swarm recorded during the reporting period. Ten small hybrid and twelve long period earthquakes were also recorded; both levels were similar to the last reporting period.
Visibility was generally poor for most of the day with low cloud cover obscuring the summit and flanks of the volcano. During the period of near-continuous rockfalls activity today an ash cloud was generated which drifted in a northwesterly direction depositing ash in Plymouth, Lovers Lane and surrounding areas.
EDM measurements were completed on the northern triangle between Windy Hill, St George's Hill and Farrells. The line lengths between Windy Hill and Farrells have not changed; the line between St Georges Hill and Farrells have shortened by 2.8cm since last occupation on 22 August. A GPS survey was undertaken today on the eastern triangle - 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.