Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 25 January
to 16:00 26 January 1997
The current alert level is ORANGE

The level of volcanic activity has remained quite low during the last 24 hours. There have been two volcano-tectonic earthquake swarms, and very little other seismic activity. Good views of the new dome growth were possible from the helicopter this morning. The rate of growth appears to have slowed somewhat, and the new extrusion seems to be quite stable at the moment.

Good views of the dome were possible today. Further dome growth has occurred in the last few days, continuing to in-fill the scar left by the 20 January collapse. The new extrusion has reached the height of the scar rim, and it is composed of large blocks. The chute below the scar does not have new material in it, indicating that there have been few rockfalls. The new extrusion seems to fit snugly into the scar, and at the moment there are no over-steep slopes.

A total of 58 volcano-tectonic earthquakes were recorded, in two swarms between 12:30 am and 4:00 am, and 1:10 pm and 15:20 pm. All of the earthquakes that could be located were in the same place as previous swarms- that is, at shallow depths beneath the volcano. There were only 9 rockfall signals during the last 24 hours; this is the lowest amount of rockfall activity since 24 December. No long-period earthquakes were recorded.

There have been further landslides from the upper part of the outside of Galway's Wall, and new cracks have appeared in it. A trip was made by helicopter to Chances Peak this afternoon, to measure the width of the two large cracks across the crater rim between Chances Peak and Galway's Wall. One of these cracks has opened by 7 cm during the last few days, which is a significant increase on the pervious rate of deformation. The scientific team will monitor the area around the Galway's Wall closely in the next few days, to check for signs of further deformation.

EDM measurements were made from O'Garros to the reflector on Chances Peak. Only a small change of 4 mm shortening was detected in the line length since it was last measured in December. This change is within the error of the EDM measuring technique.

A detailed survey of the dome was completed this morning using laser-ranging binoculars from the helicopter. The results of this survey will help to determine the rate of recent dome growth.

As the new extrusion in the south-east of the crater continues to grow, it is likely that it will collapse and cause further pyroclastic flows in the next few days. Although the dome is likely to collapse gradually, a larger collapse cannot be ruled out. An explosion similar to that of September 1996 could result in the event of a major collapse. It is however expected that there would be several hours of high level pyroclastic flow activity before any explosion. Zone E, which includes Cork Hill and the airport, remains safe.

Montserrat Volcano Observatory