The characteristics of a multi-episode volcanic regime: the post-AD 960 Maero Eruptive Period of Mt. Taranaki (New Zealand)

Abstract

A volcanic regime classifies a specific volcanic hazard state during which eruption episodes and events share similar frequency, magnitude, composition, and style. The post-AD 960 Maero Eruptive Period (MEP) at Mt. Taranaki (New Zealand) exemplifies such a distinctive eruptive period of volcanism. The deposits from intermittent eruptive episodes during this period built a pyroclastic fan on the northwestern flanks of the volcano. These deposits correlate to fall and thin pyroclastic density current deposits on other flanks. We have defined a sequence of 11 events via stratigraphy, radiocarbon dating, and geochemical studies. Each MEP episode involved lava dome growth and destruction from the summit crater. The deposits of the first MEP eruption episode cover deep palaeosols formed during a ~ 7000-year gap in activity on the NW volcano flanks. The first lava domes breached the western crater rim, and a large portion of the rim collapsed during the Newall episode c. AD 1360. This gave rise to increasingly hot and widespread block-and-ash flows. During the MEP, changes in magma composition reflect magma injection and mixing processes in small reservoirs. The episodes are classified into four scenarios, from high to low hazard impact: (1) dome collapse leading to Subplinian eruption, (2) explosive dome destruction and directed blast, (3) repeated rapid dome growth and large-scale hot dome collapse, and (4) slow dome effusion and partial collapse. The MEP defines a distinct volcanic regime, with the interval between the most recent MEP eruption and present > 50 years longer than any previous gaps between MEP episodes. As such, volcanic mitigation and forecasting at Taranaki must consider changes in hazard type if the current regime comes to an end.