Volcanology of the Mangaone Subgroup Tephras, Okataina Volcanic Center, New Zealand

Between 31 and ∼43 ka the rhyolitic Okataina Volcanic Centre in New Zealand's Taupo Volcanic Zone experienced more eruptions in less time than previously thought, producing 81 km3 of pyroclastic deposits known as the Mangaone Subgroup. New mapping indicates at least 12 plinian eruptions left deposits ranging from 0.41 to 19.9 km3. All vents lie within the Haroharo caldera, possibly migrating through time. There is no apparent correlation between eruption intensity (which ranged from 6.2 × 107 to 3.9 × 108 kg/s) and pyroclastic flow production. Deposit grain size variations indicate that plinian eruptions may pass through 7 states: inception, waxing, steady discharge, climax, waning, column collapse and shutdown. Copious amounts of water were involved in some of the eruptions but did not always produce efficient magma water-interactions. Evidence is presented for events occurring in part of the vent (or at a subsidiary vent) largely independent of the plinian discharge.