Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 5 January
to 16:00 6 January 1997
The current alert level is ORANGE

Growth of the October 1 dome continues at a rapid rate, with abundant rockfall and pyroclastic flow activity resulting. Ash is being produced almost continuously from the dome and is being blown westwards over Plymouth. As growth of the dome continues, its flanks become more unstable and a large collapse becomes more likely. Such a collapse could start at any time over the next few days and could develop into an explosive eruption such as occurred on 17/18 September 1996. MVO will continue to keep the administrators and public aware of the developing situation through the morning and evening reports, and any rapid changes in activity will be reported immediately.

Visibility has been moderate for most of the day. During a helicopter flight this afternoon, there was continuous rockfall activity and ash production. The dome in the area above Castle Peak appeared extremely steep and is currently the hottest and most active area. However, the entire northeastern flank of the dome is active and material is shedding into many parts of the upper Tar River valley and against Farrell's Wall. Observations from the ground in the late morning revealed generation of moderate-sized pyroclastic flows at irregular intervals down the main Castle Peak chute - the longest flow at about 11:00 am reached to the break in slope in the central part of the Tar River valley, over a kilometre from the dome.

Seismic activity was again dominated by rockfalls during this reporting period. 95 rockfall signals were recorded today, more than double the number seen yesterday. The peak in rockfall activity occurred during the late morning, synchronous with the longest pyroclastic flows. Only 4 hybrid events and no other types of seismic activity were seen today. Rapid dome growth with little seismic activity apart from rockfalls has been seen before at the Soufriere Hills volcano and a further increase in seismic activity should not necessarily be expected prior to a major dome collapse.

EDM measurements were made on stations in the Northern triangle. These measurements showed no change in line lengths above the error of the technique. Attempts to measure from White's to Castle Peak late yesterday afternoon failed due to ash on the reflector. No measurements have been made today.

The photographs taken yesterday are being used to calculate the current volume of the dome, in combination with theodolite measurements. The top of the dome has remained constant at about 2900 ft over the past few days, but it is spreading out towards the northeast. Once the volume of the dome is known, its rate of growth can be calculated. The last growth rate of the dome around Christmas time was the highest yet calculated for any dome during the current eruption.

Water, ash and gas samples were collected today as part of the routine environmental monitoring undertaken by MVO. These samples are currently being analysed in the MVO laboratory.

Montserrat Volcano Observatory