Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 11 May
to 16:00 12 May 1996

Activity at the Soufriere Hills Volcano during the period from 16:00 on 11 May 1996 to about 06:30 on 12 May 1996 was at a similar level to the immediate previous period. At about 06:30, a sequence of near-continuous rockfalls from the eastern flank of the dome started and lasted until about 07:20. This resulted in several ash clouds which were blown on the wind across Gages mountain and led to ash falls in the Gages, Lees, St. George's Hill, Weekes', Richmond Hill and Fox's Bay areas. From 07:20 to 09:45, the activity was characterised by intermittent, small-sized rockfalls which also resulted in ash clouds that affected the same areas as those mentioned above. At 09:45, the first significant pyroclastic flow in the Tar River Valley occurred. Three other significant pyroclastic flows were generated at around 09:52, 11:05 and 11:53. The 09:05 and 11:05 pyroclastic flows entered the sea and travelled on the water for more than 30 m while the event of 11:53 stopped just short of the sea. These events were all associated with large ash clouds which were blown by light and variable winds towards the northwest and north, resulting in the deposition of ash in several areas in southern and central Montserrat, including Farrell's, Rileys, Windy Hill, Gages, Lees, St. George's Hill, Weekes', Fox's Bay, Richmond Hill, Cork Hill, Garibaldi Hill, Isle Bay, Old Towne, Salem, etc. Small amounts of ash also fell in the Tar River, Long Ground and Whites areas. The maximum ash thickness was about 3 mm. No ash from today's events was deposited in Plymouth and areas to the south of Plymouth and areas north of Bazey's. Activity after about 12:20 has been dominated by intermittent small- to moderate-sized rockfalls. The pyroclastic flows during this morning did not result in the destruction of any manmade structures, including the Tar River estate house. However, as expected, trees were set ablaze in the Tar river Valley area.

Seismicity during the period has been dominated by signals associated with rockfalls and pyroclastic flows. A few small hybrid and long period earthquakes were recorded. One small volcano-tectonic earthquake was located at a depth of 1 km beneath the South Soufriere Hills . A regional earthquake of magnitude greater than 4 was also recorded by the seismic network at 00:51 this morning.

EDM and GPS surveys were not attempted today.

No COSPEC measurements were made today.

Visual observations of the crater area and dome were limited because of the low cloud cover but excellent views were obtained of the pyroclastic flows. The videos taken of these events will be shown on Local Access TV.

Residents of ash affected areas are strongly advised to wear dust masks when outside or when cleaning up ash inside. Drivers are warned of potentially hazardous driving conditions due to ash on the roads. The present level of activity at the Soufriere Hills Volcano continues to cause concern to the scientists. The MVO urges that visits to the evacuated zone are kept to a minimum. Given today's events in the east, it is important to again emphasize that the Tar River, Long Ground and Whites areas are extremely dangerous and should not be entered under any circumstances.

Montserrat Volcano Observatory