At around 5:30 am today, a large pyroclastic flow swept down the Tar River valley and a large amount of material reached the sea. The activity was short-lived, and resulted in an ash cloud to over 20,000 ft which was blown to the southwest and east. Since then, the volcanic activity has returned to a low level, with only a few small pyroclastic flows occurring. The entire south-eastern part of the dome however remains in an unstable state, and further pyroclastic flows are likely in the next few days. The brief but intense nature of this morning's flows indicate that the Tar River valley is extremely hazardous, as the activity can escalate rapidly. Yesterday a visit to the Tar River area confirmed that during the previous pyroclastic flow activity, temperatures of over 200 degrees centigrade occurred close to the edge of the valley, near the estate house. Anyone entering this area risks death, and the scientists will not make any further visits to this area until the situation stabilises. A major collapse of the dome is possible, and could result in another violent explosion, similar to that of September 1996. However, it is expected that there would be several hours of high level pyroclastic flow activity before any explosion since deep parts of the dome would need to be excavated. Zone E, which includes Cork Hill and the airport, remains safe.
This morning's pyroclastic flows occurred between 5:30 am and 6:30 am, and came from the chute to the south of Castle Peak. The activity picked up very rapidly. Pyroclastic flows went down the south of the valley and entered the sea and deposited fresh material over most of the surface of the fan. Boulders 6 feet across were carried to the sea. A lot of material was lost from the area at the top of the chute, resulting in a large scallop-shaped scar in the dome, directly behind Castle Peak.
The ash cloud from this event reached to over 20,000 ft and was blown to the south-east and east at high levels. An American Eagle pilot reported ash to 30,000 ft. Ash fall to the south of Montserrat was reported by a cruise ship sailing to Antigua. At lower levels, most of the ash went to the south-west, over Plymouth, and there was light ash fall up to Salem. No ash fell at the airport or other areas in the east of the island.
Before and after the pyroclastic flows, the level of seismic activity was low. A swarm of 25 volcano-tectonic earthquakes occurred before the pyroclastic flow activity, similar to the last two dome collapses. Also today there were 9 hybrid and 3 long period events recorded. There were 22 significant rock falls recorded although visual observations from Whites and Harris showed that small rock falls were nearly continuous from the north, northeast, east and south margins of the dome, all falling into the Tar River Valley. There was a single period from approximately 3:50 to 4:00 when a series of small pyroclastic flows fell from the scoop-shaped scar on the south margin of the dome, and travelled south of Castle Peak and reached no more than a few hundred metres from the base of Castle Peak. There is a small hump on the top eastern part of the dome which appears to be the focus of active growth. This feature is directly above both Castle Peak and the areas of pyroclastic flow generation, and is likely to continue to shed pyroclastic flows and rock falls in the next few days.
COSPEC measurements were made today to determine the gas production rate of the volcano. The results are being processed and will be ready by tomorrow. An experiment was also done with the GPS to see if the precision of the method can be improved.