Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 21 April
to 16:00 22 April 1997
The current alert level is ORANGE

The alert level is Orange. Unless activity escalates overnight, the alert level will drop to Amber at 6 am tomorrow.

The level of rockfall activity has increased somewhat during the day. Events were generally of a small to moderate size and have been occurring from the active area of the dome above the Galway's Wall.

The broadband network has detected 4 volcano-tectonic earthquakes, 19 small long-period earthquakes and 2 hybrid earthquakes during the period under review. These figures are similar to those seen over the past few days. A total of 83 rockfall/small pyroclastic flow signals were recorded, a marked increase from the past few days. The largest event of the day was a pyroclastic flow in the White River at about 11:24 last night, and observers report seeing an ash cloud at this time.

Two regional earthquakes were recorded by the seismic network this morning, with the main event at 5:31 am being from a magnitude 5.9 earthquake located to the south of Tobago. An aftershock at 6:11 am had a magnitude of 4.1. These earthquakes follow a magnitude 5.7 event with a number of aftershocks in a similar area last month, and were felt over much of Trinidad and Tobago.

Visibility has been moderate today and ash clouds from the larger rockfalls and pyroclastic flows have been seen drifting westwards from the volcano. The increase in rockfall activity during the past 24 hours is a result of the piecemeal collapse of the active part of the dome above the Galway's Wall, which continues to grow at a similar rate to that seen over the past several weeks.

A combined GPS and total station survey of the northern triangle was undertaken today to try to further tie down any movements of the northern flank of the volcano. The results of this survey are currently being processed.

Further work has been undertaken by MVO over the past few days to assess the potential impact of mudflows within the ghauts draining the flanks of the volcano during the upcoming hurricane season. This work nears completion and the results will be passed to the relevant authorities.

The alert level remains at ORANGE, but will revert to Amber at 6 am tomorrow unless activity increases markedly overnight. However, pyroclastic flows could still occur without warning in both the Tar River and White River valleys, which makes these areas extremely dangerous. People are reminded to use ash masks when necessary and to listen to radio Montserrat for updates during periods of high activity.

Montserrat Volcano Observatory