Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 12 August
to 4 pm 13 August 1997

Activity at the Soufriere Hills Volcano has continued at an elevated level during the reporting period. The activity has been dominated by a single hybrid earthquake swarm which has continued for most of the day.

688 hybrid earthquakes, 11 rockfalls and 1 long period earthquake triggered the seismic network today. No volcano-tectonic earthquakes were recorded. All the hybrids occurred in a single swarm which began at 4:43 pm yesterday afternoon and is still continuing at the end of the reporting period. The actual number of hybrids can be assumed to be much higher than the number of triggered events as, at times, the swarm was very intense with earthquakes occurring very close together. When earthquakes get this close together many of them do not trigger the system. The swarm was most intense between 7 and 8 am and at about 3 pm.

Good views of the dome were obtained this morning. The very large spine seen yesterday is now in three parts. Theodolite measurements were taken on the top of the spine which was at a height of 950 m or 3117 feet. There also appeared to be considerable new growth infilling the crater formed by last weeks explosive events. A GPS survey of the new deposits on all flanks of the volcano is currently being undertaken and, together with static photographs of the dome taken this morning, a total figure for the current volume extruded from the volcano and rate of extrusion can be calculated.

Activity at the volcano is still dominated by hybrid earthquake swarms and dome growth. The small explosions which occurred yesterday and on Monday demonstrate the potential for explosions to occur with little or no warning during this period. Further explosions can occur in the future and these may be more intense and longer lived than those already experienced. If explosions do occur, the central zone should be evacuated immediately, and people in the northern zone should seek

Montserrat Volcano Observatory