Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 19 March
to 16:00 20 March 1997
The current alert level is AMBER

The level of activity at the volcano has been slightly lower than yesterday. The earthquake swarm which began yesterday eventually died away at around midnight. The main activity since has been moderate sized rockfalls from the growing dome.

The earthquake swarm which began yesterday at 8:30 am ended at midnight. Since 4:00 pm yesterday, 49 hybrid earthquakes and 10 volcano-tectonic earthquakes have been recorded. The swarm was not as intense as other, most recent swarms. All of these earthquakes were located at shallow depths beneath the crater. Twenty-two (22) rockfall signals were recorded by the network today, which is an increase of 11 on the number recorded yesterday. Low amplitude tremor on the Gages station was present between 10:50 pm on Wednesday and 7:00 am this morning. Two (2) long period events have been recorded today.

Three large fractures were observed in the southern buttress of Galway's Wall during an observation flight late yesterday afternoon. This is the first time structures like this have been seen in this area. Incandescence was observed from the upper most part of the dome last night. The new spine was emitting a steady glow, enhanced by the occasional rockfall from this area. The areas of incandescence indicate that the January 20 dome has grown in the summit region and spread over the terrace formed by the October dome toward the north and north-west. An area of incandescence was also observed on the lower part of the dome, just to the north of the October dome. This suggests that there may be some deformation of the dome.

Static photographs of the dome taken yesterday from Whites and Harris Lookout were examined today in preparation for a dome volume calculation. The northern rim of the pre-September 17 dome has moved markedly toward the north to north-west. This is interpreted to be due to pushing by the growing January 20 dome.

The EDM line between Lower Amersham to Upper Amersham and Lower Amersham to Chances Steps were occupied today. Preliminary examination of the results indicates that there have been no major changes to these lines. The results of the recent long occupation of the Harris Lookout-Hermitage line by the GPS technique indicates that there is still slow movement of the Hermitage site. A further re-occupation will be carried out to cross-check these results.

During the last few days the eastern slope of the dome continues to be unstable. Given that the dome is now large and continuing to grow, albeit slowly at the moment, a large collapse and pyroclastic flows could happen with little warning. The increase in activity from the Galway's Wall makes this area particularly hazardous. It is dangerous to spend the night in evacuated areas, because the situation could worsen rapidly over a period of a few hours. The night-time visits by scientific teams into zones B and C are part of the routine monitoring and should not be taken as an indication that it is safe to spend the night in such areas. People entering Zone C are reminded to remain alert at all times, and spend the minimum possible time in the evacuated zone. The Tar River Valley and the upper Galway's area are very dangerous and should not be entered at any time.

Montserrat Volcano Observatory