New Volcanic Futures

Volcanic hazard scenarios for multiphase andesitic Plinian eruptions from lithostratigraphy: Insights into pyroclastic density current diversity at Mount Taranaki, New Zealand

Economic Impact & Health & Wellbeing | Mount Taranaki | 12.05.2023


Over the past 5000 yr at Mount Taranaki, a Plinian eruption has occurred at least every 300 yr, with the latest in A.D. 1655. Based on detailed lithofacies analysis, three Plinian eruption scenarios are possible during future magmatic unrest at this volcano’s andesitic summit crater (2500 m high), or at the basaltic Fanthams Peak satellite vent (1960 m). These scenarios involve comparable climactic phases of steady to oscillating eruption columns but contrasting pre- and postclimactic phases, represented by the deposits of diverse concentrated to dilute pyroclastic density currents. The most common scenario (I) encompasses sudden decompression of closed conduits via unroofing by dome collapse, generating block-and-ash flows and laterally directed blast-type pyroclastic density currents. Scenario II involves continuous shifting between transient open and clogged conduits by repeated plugging-and-release of chilled magma, producing a range of pyroclastic density current styles. Scenario III is mainly restricted to satellite vents, and it reflects a rapid progression into open conduits and quasi-steady Plinian phases. In the case of Mount Taranaki, in every case, pyroclastic falls would cover the most populated areas, at 20–30 km from the crater, with 10-cm-thick deposits, while pyroclastic density currents could threaten farmlands and urban locations at 15–18 km. These scenarios highlight the major role that pyroclastic density currents play in evaluations of volcanic hazards around Taranaki and other similar andesitic volcanoes. The scenarios can be tailored to different sites around the world by localized lithostratigraphic studies, and they can also be used to plan emergency management if specific magma compositions, eruption sites, or eruptive styles are confirmed at the outset of episodes.