Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 25 September
to 4 pm 26 September 1997

There have been three more explosions in the last 24 hours. Pyroclastic flows following these explosions travelled down Tar River, Mosquito Ghaut, Tuitt's Ghaut, Tyer's Ghaut and Gages Valley.

The first explosion occurred at 8:05 pm. This event was preceded by a low intensity swarm of hybrid earthquakes between 5:11 pm and 9:37 pm yesterday evening. A loud, roaring noise was heard over a wide area of Montserrat during this event as far north as Cudjoe Head. This continued for some 20-30 minutes after the main pulse of activity. Wind carried the main part of the eruption column to the north where there was significant deposition of pumice clasts and sand-grade particles. Clasts up to 2cm (1 inch) in diameter fell at the Observatory on Mongo Hill. Fall-out from the eruption column is known to have fallen over a wide area of western and northern Montserrat. Pyroclastic flows from this event entered Gages Valley, Tuitt's Ghaut and Tyer's Ghaut (formerly unnamed). Tremor, associated with vigorous ash venting, went on for about two hours after the explosion. After this the volcano was quiet with only a few small rockfall signals being recorded on the seismic network.

The second explosion happened at 04:28 this morning with very little precursory seismic activity. A sluggish ash column developed from this event to heights above 10,000 feet (3000 metres). Ash and fine crystal fragments fell in the Old Towne-Woodlands area while further north at St. John's, there were reports of small pumice clasts. Pumice fragments from this event up to 1 cm (0.5 inches) in diameter were collected at the Observatory. Pyroclastic flows from this event definitely entered Gages Valley but it is not known currently if material entered any other valleys around the volcano. An episode of tremor lasted for approximately 1 hour after the main pulse of this event. The volcano was quiet following this activity with a few small hybrid earthquakes being detected by the seismic networks.

The third explosion occurred at 2:56 pm this afternoon and was heard at the Observatory on Mongo Hill. Hybrid earthquakes occurred prior to and after this event between 9:24 am this morning and 3:11 pm this afternoon. The ash column rose quickly and was confirmed above 25,000 feet (7600 metres or 7.6 kilometres) altitude by VC Bird control tower, Antigua. The upper part of column drifted toward the north-west. Pumice fragments fell over a wide area of northern and western Montserrat. These were up to 2cm in diameter at Little Bay. The duration and amount of fall-out at the MVO was less than for the previous two explosions, but fallout was more intense in the Salem and Woodlands area. Pyroclastic flows entered Tar River (reaching the sea), Tuitt's Ghaut, Tyer's Ghaut and Gages Valley. Tremor due to steam and ash venting lasted for approximately 1 hour after the explosion. Over the last 24 hours 50 hybrid earthquakes, 1 volcano-tectonic earthquake and 17 rockfalls triggered the seismic network.

Further explosions are very likely and these could be bigger than those experienced in the last few days. Pyroclastic flows are likely to reach the Belham valley and an event directed down the Belham valley of a similar size to the one on Sunday morning, which destroyed the airport, would reach the Belham bridge and impact upon Frith and Salem. All those remaining in the exclusion zone are urged to leave as soon as possible. If the sirens sound in this area, people should move north immediately.

When explosions happen fallout may occur anywhere on the island, so hard hats or other suitable protection should be worn. Preferably, people should seek shelter in a sturdy building and wait for the fallout to end rather than trying to move or drive anywhere during the fallout period. Falling ash and pumice reduces visibility and makes driving conditions extremely hazardous. The pumice and coarse ash deposited overnight has made many roads very treacherous. Plenty of time should be allowed for any journey and drivers should be very careful. The wearing of ash masks is recommended at all times. Everyone is advised to keep listening to Radio Montserrat for information on the activity.

Montserrat Volcano Observatory