Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 16 May
to 16:00 17 May 1997
The current alert level is AMBER

The last 24 hours has been characterised by frequent and regular rockfall flows from the north-eastern flank of the dome into the Tar River Valley. The most significant of these events occurred between 4:00 pm and 12:00 midnight and may have been responsible for light ashfall in the inhabited areas north-west of the volcano.

A total of 47 distinct rockfalls and 27 long period earthquakes were recorded by the seismic network. There were also 7 small hybrid earthquakes. Volcano-tectonic earthquakes were absent from the records during the period. Some of the long-period earthquakes occurred immediately before some of the rockfalls and pyroclastic flows. It is possible that LPs may have triggered the latter events. As observed during the past week it appeared that steam and gas emissions from the dome increased after some of the failure events.

Four small to moderate sized pyroclastic flows occurred in the Tar River valley last night. These events occurred at 4:44, 8:13, 10:39 and 11:51 pm. All four events lasted longer than six minutes and produced ash clouds. It seems that all of the flows originated from the north-east face of the dome. Another pyroclastic flow with similar characteristics occurred at 9:45 this morning, after which activity on the dome remained vigorous throughout the rest of the reporting period.

Due to low cloud cover no views of the dome were possible today. This rendered it impossible to carry out any EDM work, so the deformation team campaigned the northern and north-eastern GPS sub-networks. The environmental team visited several location in the evacuated zone to collect ash and water samples and change sulphur dioxide tubes. These locations included Upper and Lower Amersham, Brodericks, Gingoes, Governor's House and Police Headquarters in Plymouth. While at Amersham, the team reported hearing rockfalls at the summit of the volcano.

The recent style of activity shows that the volcano remains dangerous. The dome continues to get less stable and therefore further pyroclastic flows with attendant ash clouds will occur in the next few days. Only essential visits should be made to the evacuated zone, and ash masks should be worn when in the ashy areas. The Tar River and White River valleys are extremely dangerous, as pyroclastic flows can travel down these valleys with no warning. Zone A should not be entered under any circumstances.

Montserrat Volcano Observatory