Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 14 April
to 16:00 15 April 1997
The current alert level is ORANGE

The level of activity has been higher today, but without any large pyroclastic flows. There was an earthquake swarm overnight, and several episodes of pyroclastic flow activity which resulted in ash clouds. The dome continues to grow within the Easter scar, and has become more unstable.

The swarm of hybrid earthquakes lasted from 1:10 am to 10:19 am. Most of the earthquakes were small, with the largest two earthquakes being of similar size to the largest earthquakes in previous swarms. A total of 76 hybrid earthquakes were recorded by the broadband network, along with one volcano-tectonic and five long-period earthquakes. Four of the long-period earthquakes triggered rockfalls from the south side of the dome. There were a total of 28 rockfall signals, a slight increase since yesterday.

Good visual observations were made today in clear conditions. The pattern of recent dome growth continues, with the new extrusion almost filling the Easter scar. The extrusion appears to be slightly wider than the previous extrusion in this area, which collapsed last week. The new extrusion has a steep face on its southern side, which overlooks the Galway's Wall area. This steep face is unstable, and was the source of several moderate pyroclastic flows today. There was a period of enhanced rockfall and pyroclastic flow activity this afternoon, between 12:30 pm and 3 pm, which resulted in an ash cloud that rose to about 6,000 ft was carried to the north west, and resulted in light ash fall in the safe zone. Small pyroclastic flows were also observed from the north east side of the dome, but these did not travel beyond the base of the dome.

The amount of steaming from the dome has varied during the day. There was little steam this morning, and a helicopter survey of the new extrusion and the summit of the dome was undertaken. The steam production increased, and was quite vigorous at the time of increased activity this afternoon.

EDM measurements were made of the northern triangle. The results show shortening of the line between Windy Hill and Farrells. This result is preliminary, and will be checked by a subsequent measurement.

A brief trip was made in the helicopter to the lower part of the White River valley, to collect rock samples from the recent pyroclastic flows. These rocks will be sent away for analysis. Preliminary examination of the rocks has not revealed any significant differences from samples collected in the Tar River valley.

The alert level remains at ORANGE, because of the unstable dome above the Galway's Wall. Further collapses of the south side of the dome are expected. While these collapses will probably not be much larger than recent collapses, an escalation of the activity to more serious levels is always possible. Pyroclastic flows could occur without warning in both the Tar River and White River valleys, and surrounding areas remain extremely dangerous. Visits to zone C should be kept brief. Zone D should not be occupied again tonight.

Dr Paul Cole left Montserrat today after working at MVO for five weeks. Dr Willy Aspinall also left after a short visit.

Montserrat Volcano Observatory