Montserrat Volcano Observatory

Daily Report
Report for the period 16.00 19 May
to 16:00 20 May 1997
The current alert level is ORANGE

Volcanic activity has remained at a fairly elevated level during the last 24 hours, with two swarms of hybrid earthquakes and further small pyroclastic flows from the north to north-east sector of the dome. The northern side of the crater continues to be filled up, threatening to spill over in the Tuitt's and White's Ghauts.

Views of the upper flanks of the volcano have been restricted for most of the day, but evidence from the seismic records, and numerous ash plumes that travelled through the cloud cover suggests that activity is still focused in the same area of recent growth and that small pyroclastic flows are still being produced. The most dominant feature of the activity over the last day has been hybrid earthquake swarms. Two swarms have occurred, with the first starting at around 5:00 pm yesterday and lasted five and a half hours. It was followed by a period of pyroclastic flows activity. The second swarm started at 9:22 this morning and was still in progress at the end of the reporting period. A total of 247 hybrid earthquakes were recorded, a large increase since yesterday. There were also 1 volcano tectonic earthquake, 8 long-period earthquakes and 38 rockfalls.

Preliminary results of the partial survey of the dome that was done from the helicopter yesterday were completed today. The volume is now estimated at 63 million cubic meters - almost twice the volume before the September explosion. The average rate of extrusion since the last survey on April 15 is estimated to be 3.7 cubic meters per second - slightly higher than the long term average. The survey also revealed and confirmed some other developments on the dome These are summarised as follows:

The recent shift in the focus of activity, producing rockfalls and pyroclastic flows on the north and north-east faces of the dome has accelerated the build up of debris behind the Farrells crater rim in the last six days. The deposits in this area are now around 20 to 40 meters thick.

Comparison of photographs that were taken one month apart suggests that the north-east face bulged, probably due to internal growth, before the recent collapse. The rate and extent are not yet determined

The thickest part of the dome relative to the original crater floor is located about 200 meters behind Galways wall. This part of the dome is around 265 meters thick.

There is no evidence to suggest that the eruption is slowing down. The dome continues to grow and with it so does its danger potential, should there be a major collapse. As it outgrows the crater walls, there is less protection against the possible hazardous by-products of a sector collapse.

With these considerations , the recent switch in volcanic activity and signs that the gas pressure within the dome is high, the volcano is now thought to be in a dangerous phase. The Tar River valley, Long Ground, White's and Tuitt's areas are very dangerous, and should not be entered, as pyroclastic flows in all these areas are now possible. Nobody should enter zones A and B, and only essential visits should be made to the evacuated zone. Ash masks should be worn when in the ashy areas.

Montserrat Volcano Observatory