Montserrat Volcano Observatory

Activity Report, 1700H June 6, 1999

Activity at the volcano increased on the evening of 5 June. At 17:45, a large pyroclastic flow signal was recorded on all seismometers. The signal lasted for over 30 minutes at high amplitude on the Long Ground station and was followed by a further 20 minutes of low amplitude tremor.

Visual observations from Salem, and from the MVO remote camera, showed that pyroclastic flows were mainly down the Tar River, but that there were also flows down Tuitt^s Ghaut. A large dark ash cloud moved west and north-westwards from the volcano, travelling as far north as Salem. Thunder and lightning was associated with the cloud, and there was complete darkness in Salem for a short period as ash started to fall. Satellite imagery and estimates from the ground suggested that the ash cloud reached about 12,000 feet.

Observations from the helicopter on 6 June showed that there were new deposits in the Tar River as far as the sea, with new material covering about one half of the delta. There were also new deposits in Tuitt^s and White^s Ghaut, reaching to about 1.5 km down Tuitt^s Ghaut and about 2 km down White^s Ghaut. Fine grained surge material was also seen in the upper reaches of the White River. There was much fine ash in the Plymouth area, but no new pyroclastic flow material could be observed.

Clear views of the dome were obtained and a new scoop had been eroded into the dome above Tuitt^s Ghaut. A new ashy fumarole was visible in the base of this depression. There appeared to have been further erosion of the inside of the Tar River to Gages gully.

Measurements of ash fall in Salem, Old Towne and areas south of Belham showed that up to 1 cm of ash had been deposited in Salem and Old Towne. Less ash fall was recorded in the Cork Hill area. Correlation spectrometer measurements today indicated that gas production was still low at 230 tonnes per day of sulphur dioxide.

A smaller pyroclastic flow occurred at 10:30 pm, with an ash cloud probably reaching no more than 10,000 feet.

The events on 5 June occurred with no precursory activity, and so it is possible that similar events may occur in the future without any warning.

Residents of Montserrat are advised to keep listening to ZJB Radio Montserrat for information in case of any changes in the state of the volcano.

Montserrat Volcano Observatory