Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 17 May
to 16:00 18 May 1997
The current alert level has been raised to ORANGE

Due to the increased level of activity over the last few days.

Volcanic activity was sustained at a high level until 18.30 last night and again between 8.00 and 9.00 am this morning. Despite persistent low cloud, observations today showed that most activity is occurring on the north eastern and eastern flanks of the dome. Several small rockfalls were also heard on the Galways side. There were three major rockfall chutes on the northeastern side of the dome, these have been particularly active today with numerous rockfalls and small pyroclastic flows. Rockfall material is building up against the Farrells wall at the base of one of these chutes. The largest pyroclastic flow today was initiated at 08.20am by a large LP earthquake, this flow passed down the northern side of the Tar River Valley and was within a few hundred metres of the delta. Ash from this event was deposited across Farrells and Hermitage. Most of the rockfalls and pyroclastic flows originated from the top of the dome, unfortunately this was obscured by cloud for most of the day.

Seismic activity was low around midnight last night but an intense swarm of mainly small hybrid earthquakes occurred between 2.18am and 7.25am this morning. At its peak there were up to 12 earthquakes per hour. Up to the reporting period there was a total of 55 hybrid earthquakes. A total of 53 distinct rockfalls and 25 long period earthquakes were also recorded by the seismic network. Volcano-tectonic earthquakes were absent from the records during the period. A total of 17 long-period earthquakes appeared to trigger rockfalls and pyroclastic flows. As observed during the past week it appeared that steam and gas emissions from the dome increased after some of the failure events.

A tiltmeter and 2 accelerometers were installed on Chances Peak today.

The recent style of activity shows that the volcano is very dangerous. The dome is very active and further pyroclastic flows with substantial ash clouds are likely. 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. Zones A and B should not be entered under any circumstances.

Montserrat Volcano Observatory