Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 10 September
to 4 pm 11 September 1997

There have been two hybrid earthquake swarms during the reporting period. The first swarm began last night at about 1.00am and lasted for two hours. It was followed by a period of increased rockfall and pyroclastic flow activity probably dominantly on the northern flanks of the volcano. Ash from this activity was blown westwards over the Plymouth area. The second swarm began at roughly 1.00pm this afternoon and also lasted for about two hours. but the level of rockfall activity this afternoon has remained relatively low.

Due to the moving of the MVO yesterday, the number of seismic events recorded have been counted since 6.30pm last night rather than 4.00pm. There have been 43 hybrid earthquakes and no long period or volcano-tectonic earthquakes. There were 51 rockfall and pyroclastic flow signals.

Visual observations confirmed that the level of activity was relatively low this afternoon with only ash and steam venting on the northern and eastern flanks of the dome. No pyroclastic flows or substantial rockfalls were observed on the northern flanks.

The dome is very large and unstable so further collapses are likely and these may take place with little or no warning. The collapses need not necessarily be preceded by hybrid swarms. The Belham Valley may be quickly filled with deposits allowing flows to impact upon Old Towne and Friths areas and associated surges could get to Salem. The southern part of Montserrat is thus extremely dangerous and all areas south of the Nantes River should be evacuated.

If an explosion does occur, 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.

Measurements of dust levels today show that there is still a considerable amount of fine ash in the air after yesterday's ashfall. People are urged to wear their dust masks particularly near roads or if walking through vegetation where ash can be remobilised.

Montserrat Volcano Observatory