Montserrat Volcano Observatory

Morning Report
Report for the period 16:00 27 December
to 07:00 28 December 1996
The current alert level is ORANGE

The bands of high hybrid and tremor activity which have dominated the seismicity over the past few days have broken down, and the records now show a mixed bag of seismic signals without any obvious pattern. Seismic signals continue to include tremor and hybrid activity as well as abundant rockfalls from the rapidly growing October 1 dome.

Cloud is low on the volcano this morning so no visual observations of the dome have been possible yet.

Analysis of the EDM measurements made late on Thursday afternoon (26 December) show a small amount of shortening, much less than the 3 cm per day recorded immediately before that. This change in deformation rate coincides approximately with appearance of new material at the surface on the October 1 dome.

COSPEC runs were undertaken yesterday to measure the amount of sulphur dioxide coming from the volcano. Overnight processing reveals amounts of around 300 tonnes per day, which is a similar amount to that seen during October and November.

The rapidly changing seismicity and changes in deformation rate and growth style all indicate that the volcano is in a state of constant adjustment and must thus continue to be regarded as dangerous. A collapse from the eastern flank of the October 1 dome is possible with the addition of new material at a high rate, and this would generate pyroclastic flows in the Tar River area which could also affect areas outside of the valley itself. Such a collapse could lead to lateral or vertical explosions. The Galway's Wall continues to be unstable and a sudden collapse of part or all of the wall is still possible, despite the reduction in pressure on the wall.

Montserrat Volcano Observatory