Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 10 September
to 16:00 11 September 1996

Activity at the Soufriere Hills volcano during this reporting period has continued at about the same level as observed during the previous 24 hours, with better visibility enabling some views of the dome.

The seismicity has again been dominated by the occurrence of volcano-tectonic (VT) earthquakes. One hundred and fifty two (152) volcano-tectonic earthquakes were recorded during the 24-hour reporting period, which is almost identical to the total recorded yesterday. These occurred in two swarms, one between 17:15 and 20:00 yesterday evening (10 September) and the other between 04:58 and 09:45 this morning. The VTs within these swarms were again located at shallow depths (less than 2 km) beneath the volcano. A total of 86 rockfall events were recorded today, the largest occurring at 22:41 last night. Thirty two small hybrid and twelve long period earthquakes were also recorded, both levels slightly higher than the last reporting period. Broadband tremor at a very low amplitude was recorded on the Gages seismometer between 16:00 and 23:00 yesterday.

Visibility was good at times during today. Clearances were sufficient to see most of the dome during a helicopter flight around midday. Scientists noted the filling up of the scar left after the partial dome collapses of early last week. However, the growth rate of the dome was confirmed as being somewhat slower than in the recent past, and the eastern flank appeared to be the only active area at present. Some steep and thus unstable faces were seen on the active flank, and further pyroclastic flows are expected when these collapse. A number of today's rockfalls produced small ash clouds which drifted northwestwards from the volcano, but little ash actually fell to the ground. A dense plume of volcanic gases and steam was visible over the Upper Gages area during the day - the apparently thick nature of this plume today was probably due to wind conditions rather than any major change in the amount of gases being emitted by the volcano.

EDM measurements were made today on the White's Yard - Long Ground - Castle Peak triangle to the east of the volcano. The recent rain has washed ash off the reflector so that it is again visible to the measuring instrument. A shortening of 15 cm over the past 2 weeks or so was measured, indicating that some outward movement of Castle Peak is still occurring.

Further rockfalls and pyroclastic flows will occur as the lava dome continues to grow within English's Crater and its unstable flanks undergo partial collapses. Current indications are that the pyroclastic flows will be confined to the Tar River valley area. Areas affected by associated ashfalls will depend on the direction and strength of the wind at the time. Any rainfall will make ash-coated roads very slippery so extreme care should still be taken when driving in areas where there is still ash on the road. Dust masks should be worn at all times in ashy environments, and drivers should exercise caution and consideration for other road users.

The Tar River Valley and surrounding areas continue to be extremely hazardous, and should not be entered under any circumstances. We urge individuals who persist in ignoring this advice to think very seriously before making trips to these potentially deadly zones.

Montserrat Volcano Observatory