Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 19 April
to 16:00 20 April 1996

Seismic activity at the Soufriere Hills Volcano during this period has remained at about the same slightly reduced level seen during the previous 24 hours. It is still dominated by the occurrence of small , repetitive hybrid earthquakes at a rate of about one per two minutes. The size of these hybrid earthquakes has remained almost constant.

The number of seismic signals interpreted as representing rockfalls from the growing dome has increased. Some of these generated small ash clouds. A moderate sized explosion at 08:05 on 20 April was probably the largest since the events of Monday 08 April 1996. It generated an ash column which rose to a maximum height of about 6,000 ft above sea level and a very small pyroclastic flow down the Tar River valley area. The ash drifted towards the northwest and very small amounts fell on the St. George's Hill, Cork Hill and Old Towne areas. Several periods of low amplitude broadband tremor, the longest of which lasted for about 90 minutes, were recorded on the Gages seismic station.

EDM measurements were made of the eastern and northern triangles. The results for the eastern triangle confirm the slow shortening of about 1 mm per day for the slant distances to Castle Peak seen since early December 1995.

Excellent viewing conditions today permitted visual observations of the crater area from various ground points around the volcano and from the helicopter. The top part of the inclined spine has broken off, with some of the debris falling to the base of the northeastern part of the old dome. A near-continuous emission of small amounts of ash was observed from the top of the eroded gully in the northeastern dome and from around the base of the inclined spine. Vigorous steam emission from the area around the spine and from several areas of the dome continues, generating a plume which drifted towards the northwest and a pale blue haze in the Upper Gages area. Persistent rockfalls were observed from the southwestern, southern and northern parts of the dome during the day.

The estimates of the volume of the new lava dome and the current rate of extrusion given in the report of 16:00 on 18 April 1996 are incorrect. The revised values will be given in tomorrow's report.

In spite of the slightly reduced level of activity at the volcano during the past two days, scientists at the MVO still view the situation with grave concern. The MVO continues to urge that visits to the evacuated zone be kept to a minimum. The Tar River, Long Ground and Whites areas are extremely dangerous and should not be entered under any circumstances.

Montserrat Volcano Observatory