Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 25 November
to 16:00 26 November 1996
The current alert level is AMBER

The risk map was altered this afternoon. Observations of Galway's Wall indicate that failure is now a real possibility and that this could lead to a catastrophic event, potentially without warning. The area to the southwest of the volcano has been upgraded to zone A. This new zone extends from south of O'Garra's to Gingoes Ghaut. Zone B now includes the area between Gingoes Ghaut and Aymer's Ghaut. The volcano is in a dangerous state, and activity could escalate at any time. The St. Patrick's, Tar River and Long Ground areas are especially dangerous and anyone entering or remaining in these areas is risking death.

A close examination was made of the Galway's Wall this morning. Landslides on the outside of the wall have continued - several minor avalanches on the wall were seen during a two-hour observation period. The face shows several large fractures, more than one of which runs the full height of the wall. The top of the wall is also extensively fractured, although the dome does not press up against it. Steaming and gas production from the southern part of the lava dome indicate that there may be very hot material within the dome close to the Galway's Wall. The dangers from collapse of the Galway's Wall have increased dramatically over the past few days and continued and bigger rock avalanches will occur. There is also a small chance of a sudden, catastrophic failure of the wall which could produce a lateral blast of hot material over a wide sector of south-western Montserrat without warning.

Work will commence tomorrow to try and measure any deformation of the Galway's Wall, although the dangers in getting close to the wall may prevent good measurements from being taken. Visual observations will continue, and experts around the world are being asked for their input to the ongoing assessment of the situation by MVO.

Until these measurements are made and other opinions canvassed, Galway's Wall must be considered as likely to fail. In response to the potential hazards, the risk map has been rezoned and the residents of St. Patrick's and surrounding areas advised to leave at once.

A small swarm of VT earthquakes started at about 7 p.m. yesterday evening. A total of 43 events had been recorded by the end of the reporting period: the peak rate was five per hour between 1 and 3 p.m. today. These were all located at shallow depths beneath the crater. Only two small rockfall signals were recorded today. One regional earthquake has been recorded. Broadband tremor on the Gages seismometer has been recorded throughout the reporting period.

The short-period seismic network has been fully operational since yesterday evening.

An extensive helicopter survey of the dome was carried out in the early morning. This will enable estimates of the dome volume and growth rate to be made.

A GPS survey of the network on the eastern side of the volcano was undertaken today; the survey has only just been completed and the results have not yet been processed. EDM measurements were taken on the lines to Castle Peak. This data is also being processed.

Montserrat Volcano Observatory