Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 18 December
to 16:00 19 December 1996
With Special 1800H Report
The current alert level is ORANGE

There was a moderate level of activity at the volcano during the last 24 hours. The December 11 dome continues to grow and generate rockfalls into the upper Tar River valley. There was one notable period of small pyroclastic flows at around 8 am this morning. The dome growth means that the Tar River and Long Ground areas are increasingly at risk from pyroclastic flows. Deformation of the Galway's Wall has slowed down but sudden failure of the wall could still occur and would have serious consequences for the rest of zone A/B. Nobody should be in this zone. Zone E remains safe at this time.

Visibility was excellent for most of the day. There was a helicopter inspection this morning of the new dome and Galway's Wall. The dome seems little changed from yesterday. The eastern face of the dome is near-vertical and appears very unstable. The dome was its most active since it appeared on December 11. Early this morning, there were discrete pulses of rockfalls and small pyroclastic flows a few minutes apart. The largest pyroclastic flows had a maximum runout of 1 km. There were two periods of near-continuous pyroclastic flow generation at about 8 am. All this activity was into a gully on the south side of Castle Peak. The activity created numerous small ash clouds which rose up to maximum of a thousand feet above the crater and drifted slowly westwards on the wind. Galway's Wall showed no signs of recent activity.

The level of seismicity was moderate during this period, and was dominated by rockfalls from the growing dome. There were 20 dome rockfalls, a slight increase on yesterday. Fifteen long-period earthquakes were recorded today, an increase from yesterday. No volcano-tectonic earthquakes were recorded. There was one period of continuous low-amplitude signal for 10 to 15 minutes around 8 am. This was due to the near-continuous pyroclastic flow activity at the time.

A dome survey was carried out this morning from the helicopter using laser-ranging binoculars. Preliminary analysis gives a volume of approximately 800,000 cubic metres for the 11 December dome. This gives an extrusion rate of just over half a cubic metre per second since the last survey on 13 December. This is a significant slowing of the extrusion rate.

Gravity measurements were made today on a line of stations on the western flank of the volcano. These are the first measurements since 17 July and will allow any density changes beneath the volcano to be detected.

Dr Simon Young returned to Montserrat this afternoon. He resumes duties as Head of MVO on Saturday. A video produced by MVO showing Galway's Wall and the new dome will be shown on Local Access Television, Channel 5, at 5 pm tomorrow.

18:00 Update

A series of pyroclastic flows into the Tar River Valley started at about 5 pm. These are coming from the new dome, and are flowing to the south of Castle Peak. The largest of these reached within 400 m of the sea. The scientists are monitoring the situation closely, and if there are further developments announcements will be made on Radio Montserrat.

16:00, 19 December 1996

Montserrat Volcano Observatory