Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 28 September
to 16:00 29 September 1996

Activity at the Soufriere Hills volcano during this reporting period has continued at a relatively elevated level compared with early in the week. Seismicity is dominated by volcano-tectonic and hybrid earthquakes, with rockfall activity still very low. Despite cloudy conditions for most of the day some clear observations were possible of the interior of the scar. Field investigation of the deposits of last Tuesday's eruption has continued, along with processing of data already collected.

There have been 54 volcano-tectonic earthquakes during the day, and 63 smaller hybrid events. The VT events have reduced in size and number compared with yesterday but continue to have similar characteristics to the hybrid events. A review of the seismic records indicate that VT earthquakes with similar characteristics were recorded during August 1995. The events then were more widely scattered around the volcano and were sometimes large enough to be felt. The VT events on this occasion are most likely related to rock fracture caused by magma movement within the volcano. Only three rockfall signals were recorded by seismic stations today. Two small long period earthquakes were also recorded. The levels of broadband tremor on the Gages seismic station was higher than yesterday.

Visibility was generally poor for most of the day, but some good views were obtained of the interior of the scar. Vigorous steaming was evident from several areas along the base of the scar and fresh sulphur deposits has formed at most of the small steam vents. Areas to the south west and along the base of the scar appear to be undergoing some slight swelling. This may be due to new dome growth beneath the blocky deposits which line the base of the scar. The northern part of the scar was visible and appear to have a vertical cliff face with a nearly horizontal, bowl shaped base which grades down and outward to the Tar River valley. Several unstable blocks were observed on the top, inner parts of the north eastern sides of the scar. These are expected to produce further rockfalls as the dome stabilises.

Further investigation of ballistic clasts produced by the 17-18 September explosion, was undertaken on the eastern side of the island today. These would be used to help scientists determine the maximum extent of projectiles from last Tuesday's activity. This will the MVO to better understand the volcano and would assist in microzonation of the hazard zones around the volcano.

No EDM measurements were taken. Measurement of new deposits from the 17-18 September eruption located in the Tar River valley was undertaken using the GPS equipment today. The data collected today would be compared to similar measurement conducted previously so as to obtain volume estimates for the new deposits.

MVO scientists expect that rockfalls and possibly pyroclastic flows will occur during the next few days as the unstable sides of the new scar feature at English's Crater stabilise. All indications are that the rockfalls and pyroclastic flows will be confined to the Tar River valley area. Dust masks should be worn at all times in ashy environments, which may persist for some time as ash dries out and blows around. Drivers should exercise caution and consideration for other road users, especially when driving through areas still affected by ash or gravel.

Individuals put themselves in extreme danger if they venture beyond the Long Ground area into the Tar River valley. All individuals passing checkpoints in whatever part of the island are reminded that they are entering areas which may become unsafe very quickly, and everyone should be on maximum alert in all of these areas. All residents of southern Montserrat are asked to once again ensure that they are familiar with evacuation procedures.

Montserrat Volcano Observatory