Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 18 September
to 4 pm 19 September 1997

The level of volcanic activity over the last 24 hours has been significantly lower than the previous few days. Activity overnight was dominated by small and medium sized rockfalls. Scattered rockfall activity continued throughout the day. The well-developed 12 hour periodicity in the activity has now broken down and any periods of higher activity were poorly defined.

The principle change in the seismicity has been a significant increase in the number of long period events. Over the reporting period, 36 long period events triggered on the broad band network. Six of these were precursors to rockfalls. These events have occurred throughout the day at irregular intervals rather than in swarms. There have also been 32 triggered rockfalls, much fewer than the previous days.

The area above Tuitt's ghaut is the main active area on the dome at the moment and rockfalls have been confined to this region. However, visual observations confirm that there is a large overhanging mass above the Gages valley which appears highly unstable. The instability and volume of dome material mean that the probability of further larger collapse episodes remains relatively high. Large pyroclastic flows generated on either the northern and western sides of the dome are likely to reach the Belham valley. The surge component of these flows could reach areas such as Friths, Old Towne, Salem and Olveston. Such flows and surges could occur with no warning and so people still living in these areas are urged to move north as soon as possible.

In addition to generation of large pyroclastic flows, explosions could also occur. If an explosion occurs, small rocks and ash can fall anywhere on the island. People should seek shelter under a strong roof as soon as possible. Helmets or other head protection should be used and it should be remembered that ash and falling rocks make driving hazardous.

Montserrat Volcano Observatory