Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 11 September
to 16:00 12 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 continued dome growth and associated rockfalls.

The seismicity has once again been dominated by the occurrence of volcano-tectonic (VT) earthquakes. One hundred and ninety two (192) volcano-tectonic earthquakes were recorded during the 24-hour reporting period, which is somewhat higher than the total recorded yesterday. These occurred in two swarms, the first between 19:35 and 23:55 yesterday (11 September) and the other between 07:20 and 10:10 this morning. The VTs within these swarms were again located at shallow depths (less than 2 km) beneath the volcano. A total of 49 rockfall events were recorded today, the largest occurring at 01:34 and 11:50 this morning. Eighteen small hybrid and twelve long period earthquakes were also recorded, both levels very similar to the last reporting period. Broadband tremor at a very low amplitude was recorded on the Gages seismometer throughout the reporting period.

Visibility was poor again today, although the dome was glimpsed during brief clearances this afternoon. Little ashfall occurred today, with only small rockfalls occurring on the dome.

EDM measurements were not made today due to low cloud.

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