Volcanic hazards on St Kitts and Montserrat, West Indies

Abstract

Pyroclast flows constitute the main potential hazard on both St Kitts and Montserrat. Radiocarbon dating indicates that the last major series of eruptions on St Kitts occurred about 2000 years ago, although a more recent phase of activity (1620 ± 50 years B.P.) produced the pyroclast surge and blast deposits of the Steel Dust ‘Series’. On Montserrat the last major eruptive episode occurred about 19000 years ago and there is rather uncertain evidence for a small near-historic eruption. Pyroclast flow material tends to have a basaltic andesite composition on St Kitts and that of a more siliceous andesite on Montserrat. At Mt Misery, St Kitts, the present configuration of the summit region has exercised considerable control over the distribution of pyroclast flows and the western side of the volcano remains the most vulnerable to future activity of this kind. The summit morphology of the Soufriere Hills, Montserrat is more complex and appears to have changed during relatively recent times, making the preferred pathway down the eastern slopes over the less populated side of the island. Pyroclast falls, regarded as a negligible hazard on Montserrat, may attain a critical destructive thickness of c . 50 cm once every few thousand years on St Kitts. Lava flows, which may be considered unimportant on Montserrat, are also likely to be a minor and very infrequent hazard on St Kitts.