The period under review began with the continuation of the low seismic episode that commenced on 6 February. This pattern was abruptly interrupted at 04:30 today with a swarm of volcano-tectonic earthquakes beneath the Windy Hill area at depths between 2.0 and 4.5 km. In a three hour period, 40 earthquakes with magnitude greater than 1.3 occurred, with the largest a magnitude 3.2 at 05:13. This earthquake and five others (magnitude range 2.5 to 3.0) were reportedly felt across the central parts of the island. An interesting feature of this swarm was that most of the larger earthquakes preceded the mainshock. Many smaller v-t earthquakes occurred at a rate of 2 to 3 per minute but were too small to locate. The activity subsided as quickly as it began at about 07:30. There were very occasional v-t earthquakes from the main series, all with magnitudes less than 1.0, but even these ceased at 14:30 today. Other activity consisted of very occasional small hybrid events (dominant frequencies 3-5 Hz) that were only observed on the seismic stations closest to the volcano . Other seismic signals associated with small rockfalls were also only observed on the closest stations.
EDM measurements were made on the eastern triangle to Castle Peak today. The changes recorded on these lines since their last occupation(9 February), were all less than 1cm. The general long trend of shortening on these lines continues but the daily changes are usually within the error of the instrument.
Visual observation of the volcano was made from the helicopter twice today and from Long Ground and Whites Yard during the morning. The central spine which was first observed two days ago from Chances Peak is now equal in height to the northern part of the dome. This new spine is located in the western parts of the dome just west of the observation point at Chances Peak. During the late afternoon helicopter flight a large vertical crack was observed along the top of the southern part of the dome. Talus deposits from numerous rockfalls in English's Crater are now in contact with all parts of the crater wall. Emission of magmatic gases (mainly steam), was quite vigorous from the top central part of the dome for most of the day. Strong local winds continue to channel most of these gases through Gages gap.