Stratigraphy and lithosedimentological properties of subplinian eruptions from Mt. Taranaki, New Zealand, encompassed by the Ngaere and Pungarehu edifice collapses

Abstract

The sudden removal of large portions of a volcanic edifice through collapse can cause depressurisation in the subvolcanic magmatic system, influencing the nature of subsequent eruptions. At Mt. Taranaki, edifice failure has occurred frequently and at different timescales throughout the volcanic history, forming a broad pattern of cyclic collapse and regrowth. About 20–30,000 years ago, Mt. Taranaki experienced two such cycles in short succession, emplacing the 27.3 ka Ngaere and the 24.8 ka Pungarehu debris-avalanche deposits, which were preceded and followed by a sequence of twenty-eight closely spaced tephra deposits known as the Poto and Paetahi Formations. Here, we reconstruct the tephrastratigraphic framework of the Poto and Paetahi Formations, revealing a minimum total eruptive volume of 3 km3. While eruptions directly following edifice failure were larger compared to those prior to collapse, this 4,000-year long eruptive period was characterised by consistently large subplinian eruptions. In contrast, large explosive events within the Holocene sequence are less frequent, with more multi-phase periods of effusive and explosive activity recorded. Our new data highlights the need to include longer-term eruptive records in volcanic hazard modelling since the most recent volcanic history might not cover the full nature of volcanic processes occurring at long-lived stratovolcanoes.