Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 17 April
to 16:00 18 April 1996

The level of seismic activity at the Soufriere Hills volcano has increased again during the period under review. It is now at its highest level since the early morning of 16 April. The seismicity pattern is still dominated by the occurrence of small hybrid events. These are of a similar size to those of yesterday and occur at a rate of 1-2 per minute. Intermittent periods of low amplitude broadband tremor have also occurred, at times lasting upto one and a half hours. Large signals related to small explosions and/or rockfalls were recorded at 04:36, 12:37 and 14:13 on 18 April. The event at 12:37 was the largest signal for some time and was the result of a large piece of the northeastern dome breaking away. This fell down the Tar River valley and generated a significant ash cloud which drifted to the northwest over Farrell's Lookout.

Ground deformation measurements in the form of GPS and EDM surveys have been undertaken today. The GPS sites around the southern, western and northern sides of the volcano have been re-occupied. These data are still being processed. The eastern EDM triangle was re-occupied. The changes recorded are consistent with the slow trend of shortening seen on these lines over the last 4 months.

The EDM instrument was also used to take angular measurements of various parts of the dome in order to estimate volume and growth rate. The estimated volume of the dome is of the order of 14 million cubic metres. This corresponds to an increase of 8 million cubic metres since the last estimate. This change is equivalent to a growth rate of about 3 cubic metres per second. It should be noted that these are only estimates and are likely to be on the high side due to the technique of measurement.

Visual observations have been possible throughout the day. A large new spine has grown over the last 36 hours and has now reached a height of approximately 2990 feet above sea level.The new spine has a flat face and is very similar to the old Castle Peak spines. It is inclined towards the northeast, with a large amount of loose material at its base. Rockfalls have been seen in the northeastern and central areas of the dome. The new spine has also been the source of small ash clouds as parts of it periodically collapse. Steaming has also continued from several areas of the dome, in particular the area around the spine, producing a steam plume that has been continuous for most of the day. Variable amounts of pale blue sulphur dioxide have also been emitted from several parts of the dome.

The volcano remains extremely active, with continued dome growth at a high rate. The MVO scientists are highly concerned by the current activity, and urge that visits to the evacuated zone are 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