Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 20 February
to 16:00 21 February 1997
The current alert level is AMBER

The level of activity at the volcano has remained the same, with a continuation of earthquake swarms. There were few visible changes to the dome.

Seismic activity has been dominated by two swarms of earthquakes, with a total of 261 hybrid and 100 volcano-tectonic earthquakes recorded. The first swarm was from 3:44 pm to 11:43 pm yesterday, and the second from 8:45 pm to 2:31 pm today. Both swarms were similar to the swarm earlier yesterday, with volcano-tectonic earthquakes followed by repetitive hybrid earthquakes. The established pattern continues, with about 14 hours between the swarms. The first swarm was slightly less intense than the second, with 121 hybrids and 137 hybrids, respectively. At it's maximum, the second swarm had hybrid earthquakes at a rate of one per minute, and afterwards developed into a short period of low-amplitude, continuous tremor. Otherwise, the level of seismic activity was low, with only 18 rockfalls recorded. As usual, the earthquakes were too small to be felt.

Visibility was mixed during the day. There were a few small pyroclastic flows around midday, coinciding with the hybrid earthquakes. A helicopter inspection of the dome revealed few changes in the last two days. Some deep gullies have developed at the top of the eastern face, and a small fan of fresh debris has developed on the north-east side of the dome. There continue to be gradual changes to the top of Galway's Wall, with fresh rockfall deposits almost reaching to the road at Galway's Soufriere.

The extensometer across the crack near the Galway's Wall, to the east of Chances Peak, has shown some changes in the last few days, coincident with swarms of volcano-tectonic earthquakes. The crack which is monitored continuously, has widened by between 3 and 10 mm at the same time as the last three earthquake swarms. This indicates that slow deformation of the wall continues, and is related to the earthquake swarms.

No EDM or GPS measurements were made today.

The dome is currently larger than ever before, and further dome collapses and pyroclastic flows are expected. These will probably follow the recent pattern, but a change in the activity could occur at any time. Visitors to zone C are reminded to remain alert at all times, and spend the minimum possible time in the evacuated zone. Ash levels in Plymouth are hazardous, especially during dry, windy weather, and so it is essential to wear masks in areas affected by ash. Flash floods could cut off access to areas south of Fort Ghaut; visitors should leave that area when it rains. The Tar River Valley and the upper Galway's area are very dangerous and should not be entered at any time.

Montserrat Volcano Observatory