Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 26 September
to 4 pm 27 September 1997

The sequence of explosive eruptions has continued with two more explosive eruptions in the last 24 hours. Subsequent pyroclastic flows travelled down Tuitt's Ghaut, Tyer's Ghaut and Gages Valley. A further explosion occurred at 17:15 as this report was being written.

The first explosion occurred at 00:01 am. This event was preceded by three large hybrid earthquakes in the two hours leading up to the explosion. A sharp bang was heard, followed by roaring for several minutes, although not as long as previous eruptions. Light pumice fall was reported by MVO scientists stationed at the old observatory site in Old Towne. At 00:25 lapilli fell at the new MVO site on Mongo Hill. Hybrid earthquakes continued to occur after the eruption along with a tremor signal which continued for 30 minutes, but had a lower amplitude than previously observed after explosions.

The second explosion was at 09:46 this morning. Precursory activity was very similar to the previous eruption with only three hybrid earthquakes in the hour before the eruption. Again the explosion was followed by further earthquakes and volcanic tremor. Pyroclastic flows were observed from Old Towne to travel down Gages, Tuitts and Tyers ghauts. The ash cloud quickly rose to over 10,000 feet and drifted in a north-westerly direction. Later in the day an airplane pilot reported that the column eventually rose to a height of 50,000 feet. By 10:01 pumice was falling in Salem and Old Towne, with low level ash clouds gradually moving northwards. Vigorous steam and ash venting followed the explosion continuing for around 30 minutes. Again, this correlates well with the recorded volcanic tremor.

The morning observation flight confirmed that flows had travelled down Tuitts ghaut to 150m above the confluence with the Paradise river. New deposits were observed in Tyers ghaut to 100m above the road crossing at Dyers bridge. A very thin flow was also observed down the East side of the old Mosquito ghaut to the level of the Paradise estate. Over the last 24 hours 30 hybrid earthquakes, 3 long period earthquakes and 28 rockfalls triggered the seismic network. The periods between the explosions have been seismically very quiet, with only occasional small rockfalls. The tremor episodes following the last three explosions are thought to be lower amplitude and shorter duration than the previous days' explosions. Further explosions are very likely and these could be bigger than those experienced in the last few days. Pyroclastic flows could 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