Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 16 March
to 16:00 17 March 1997
The current alert level is AMBER

Activity at the volcano has been at a higher level today. Another earthquake swarm started early this morning and is still continuing. Several small rockfalls and pyroclastic flows were seen from both the eastern face of the dome and also over Galway's Wall. Small ash clouds from the rockfalls have been intermittently observed as they were carried westward by the prevailing winds. In general it appears that the dome is continuing to grow at a low rate.

Seismic activity at the volcano has been dominated by the start of another hybrid and volcano-tectonic earthquake swarm. 82 hybrid earthquakes and 3 volcano-tectonic earthquakes have occurred during this swarm which started at 6.44 am and is still continuing. All of these earthquakes were located at shallow depths beneath the crater. Seven rockfalls were recorded by the network today, which is about the same number as yesterday. Three long period events were also recorded by the network together with low amplitude tremor on the Gages station.

Good views were obtained of Galway's Wall and the eastern side of the dome. Several small pyroclastic flows were seen to originate from high up on Galway's Wall and travelled to slightly more than 1 km away from the wall. These flows almost always occurred directly after strong hybrid earthquake signals. A few small pyroclastic flows were also observed from the eastern and south-eastern side of the dome. The helicopter is now back in action and closer views of the volcano will now be possible.

A volume calculation from photographs taken on the 14th March showed that the dome had increased in volume by about 1 million cubic metres since 1st March. This suggests a decrease in eruption rate over this period.

A long occupation GPS survey was started today between Hermitage and Harris. The occupation will finish tomorrow and the results will be released in a future report.

COSPEC measurements were carried out today along the coastal road between O'Garro's and north of Plymouth. 14 traverses were completed and results will be processed shortly.

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. 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