Diverse dynamics of Holocene mafic-intermediate Plinian eruptions at Mt. Taranaki (Egmont), New Zealand

Abstract

Over the last 5000 years, at least 53 eruptive episodes have occurred at Mt. Taranaki (western North Island, New Zealand), from either its summit crater (~ 2500 m) or a satellite vent on Fanthams Peak (~ 1900 m). The magmas erupted have a wide range of compositions from basaltic to trachy-andesitic (~ 48–60 wt% SiO2). Five large-magnitude episodes from this sequence were studied so as to characterize a typical range of explosive eruption styles at andesitic stratovolcanoes, including three eruptions from the summit crater and two from Fanthams Peak. Sustained eruption columns characterized the climactic phase of all five eruptions, but these were interspersed with pulsating, collapsing, or oscillating conditions. Eruption columns reached between 14 to 29 km in height and ejected minimum volumes of 0.1–1.1 km3 at mass discharge rates of 1 × 107–2 × 108 kg/s, indicating magnitudes of 4.1 to 5.1. The simplest eruptions occurred from Fanthams Peak with basaltic magmas producing high-climactic eruption columns rapidly after vent opening, followed by gentle waning phases or a passage into a lava-fountaining phase. Eruptions of higher-silica magmas at the summit vent, by contrast, showed longer pre-climactic eruptive phases with either dome growth or complex phases of vent clearance and blockage producing unsteady eruption columns. The latter eruption types produced block-and-ash flows, lateral-blast surges, and column-collapse pumice-and-ash flows, with run-out distances of 3–19 km, covering 5–70 km2 with volumes of up to 0.022 km3. Our results demonstrate that very different eruption scenarios may occur at different vent locations, or with subtly different compositions erupted, on the same stratovolcano so that emergency management planning must take such a range of possibilities into account.