Seismic activity as monitored by the MVO network continues to be dominated by rockfalls from the growing dome within English's Crater. More than 48 seismic signals interpreted as rockfall events were recorded by most stations of the seismic network. At about 20:43 on 31 March 1996, an extended seismic signal began on all seismic stations and lasted for nearly one hour. It comprised a series of pulses generated by a succession of moderate and large rock fall events from the eastern flank of the growing lava dome. The significant amounts of ash generated by these rock falls were blown on the wind towards the west and deposited on Plymouth and surrounding areas over an extended period. Another rock fall at 10:29 on 01 April 1996 generated an additional smaller quantity of ash which was deposited on Plymouth and environs.
Visual observations from the Helicopter this morning and from White's confirm that most of the rockfalls are occurring in the east and the west, thus indicating that these are the most active areas of dome growth. The block and ash flows generated by the rock falls last night are the largest observed so far. Although it is unclear how many individual block and ash flows travelled down the Hot River Ghaut, the longest one reached a distance of about 1 km from the base of Castle Peak dome and caused burning of trees and foliage over a considerable area around the Tar River Soufriere. This flow contained bigger blocks and had a wider dispersed hot ash cloud than the block and ash flow on Wednesday 27 March 1996.
One long-period and 2 hybrid earthquakes were also recorded but could not be located. Two small volcano-tectonic earthquakes were located: one off the southeast coast at a depth of 10 km and the second beneath the Heritage area at a depth of 2 km.
The Windy Hill - Farrells - St. George's Hill, Long Ground - Whites - Castle Peak and Galways - Ogarros - Chance's Peak EDM triangles were measured today. The results show only very small changes compared to those of the past several days.
Residents of Plymouth and surrounding areas are strongly advised to wear dust masks when outside or when cleaning up ash inside. Drivers are warned of potentially hazardous driving conditions due to ash on the roads. Members of the public are still strongly advised to keep out of the Tar River Valley area in the day and the Long ground area in the night.