Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 on 5 Jan. 1996
to 16:00 on 6 Jan. 1996

This period was more active in terms of seismicity than any in the previous several weeks. Intermittent broadband tremor occurred between 16:00 and 18:00 on 5 January on the Gages seismometer and this was replaced between 18:00 and midnight by a succession of very low amplitude long-period events. Between midnight and 06:00 on 6 December, a return to broadband tremor with increased amplitude occurred on the Gages station, accompanied by small long-period events. After 06:00, a swarm of hybrid events occurred; hybrid events show characteristics of both volcano-tectonic and long-period earthquakes. A total of 302 hybrid earthquakes were recorded, located at depths of 0 to 3 km beneath the Soufriere Hills volcano. The events occurred at regular intervals of 2 to 3 minutes for most of the day, but this rate diminished after about 14:00. In addition to these hybrid events, 7 volcano-tectonic earthquakes were located at depths of 0 to 5 km beneath the St George's Hill and Harris areas.

The pattern of seismicity encountered during the day is similar to that seen during periods in late September and mid-November. On these occasions, several days of such activity was followed by onset of dome growth, and renewed dome growth may be anticipated over the next several days within English's Crater.

EDM measurements of the Windy Hill - St George's Hill - Farrell's triangle and the line between Castle Peak and White's Yard were made today. None of these lines showed any change from previous occupations above the error of the technique, although the Farrell's to St George's Hill line had not previously been measured.

Visual observations of the crater area were not made today due to the persistent low cloud cover over the volcano. Drs Hoblitt and Young visited the Tar River area to investigate deposits recently exposed by the heavy rains. Further work will be required before any firm conclusions on the deposits can be reached, but some of the deposits relate to the phase of lava dome growth in English's Crater which occurred 350 to 400 years ago.

Montserrat Volcano Observatory