Historic and prehistoric volcanic activity on St Kitts and Nevis, West Indies: Controls on future hazard

Abstract

Saint Kitts and Nevis lie in the northern part of the Lesser Antilles island arc, an archipelago formed by the subduction of the North American plate beneath the Caribbean plate. An integrated approach was undertaken to understand the most recent volcanic activity on the islands, and to assess likely future eruption styles and scenarios. A new analysis of archival records suggests that there may not have been activity at Mt Liamuiga in historic times. The 1690 activity may have been misattributed to St Kitts instead of Guadeloupe, whereas the 1843 activity remains unconfirmed. A field campaign characterised the nature of the pyroclastic density currents (PDCs) on St Kitts and Nevis. Pyroclastic density currents (PDCs) of pumice and ash flows, and surge deposits characterise the youngest products at both Mt Liamuiga and Nevis Peak, although subordinate lapilli fallout deposits also occur on St Kitts. The geochemistry of the youngest products at Mt Liamuiga, St Kitts and Nevis Peak have been analysed to characterise the nature of the magma storage conditions below both islands, and to understand the styles of the most recent eruptions. These geochemical analyses have shown that open-system processes dominated the magma storage conditions at both St Kitts and Nevis, and recharges of hot, primitive magma into the reservoirs led to mixing and magmatic differentiation. The geochemistry also showed that rapid crystallization, reheating and partial melting occurred in the shallow crust before eruption. Magma mingling occurred shortly before or syn-eruption. 9 Crystal Size Distribution (CSD) methods allowed decompression and ascent rates to be estimated, providing further evidence for the nature of the youngest eruptions at Mt Liamuiga and Nevis Peak. Ascent rate estimates suggest that the majority of the Mt Liamuiga deposits studied were the products of explosive eruptions, and the estimates calculated for the Nevis samples suggest a much slower decompression and ascent rate indicating a lava dome collapse origin, potentially associated with explosive activity. Future eruptive scenarios were modelled using VolcFlow based on parameters informed by fieldwork, geochemistry and CSD analysis. This modelling suggests that the main hazard from PDCs is in the northwest of the island, with multiple settlements lying directly in the path of the PDCs modelled, including Old Road Town, Newton Ground, Saddlers Village, and the southern portion of Sandy Point Town in larger volume scenarios.