Abstract
The c. 5600 cal. yrBP Whakatane eruption episode consisted of a sequence of intracaldera rhyolite eruptions from at least five vents spread over 11 km of the Haroharo linear vent zone within Okataina Volcanic Centre. Initial vent‐opening eruptions from the Haroharo vent produced coarse lithic clast “blast beds” and pyroclastic density currents (surges). These were immediately followed by eruption of very mobile pumiceous pyroclastic surges from the Makatiti vent 6 km to the southwest. Major plinian eruptions from the Makatiti vent then dispersed Whakatane Tephra pumice fall deposits (bulk volume c. 6 km3) across the northeastern North Island while smaller explosive eruptions produced pyroclastic flows and falls from the Haroharo‐Rotokohu vents and at the Pararoa vent on the caldera rim 11 km northeast from Makatiti. The pyroclastic eruptions at all vents were followed by the extrusion of lava flows and domes; extruded lava volumes ranged from 0.03 km3 for the Pararoa dome to 7.5 km3 for the Makatiti‐Tapahoro lava flows and domes. Minor variations in whole rock and glass chemistry show that the three main vent areas each tapped a slightly different high‐silica rhyolite magma. About 10 km3 of M‐type magma was erupted from the Makatiti‐Tapahoro vents; c. 1.3 km3of H‐type magma from the Haroharo‐Rotokohu vents, and 0.04 km3 of P‐type magma from the Pararoa vent. There are no significant weathering or erosional breaks within the Whakatane eruptive sequence, which suggests that all Whakatane eruptions occurred within a short time interval. However, extrusion of the Haroharo dome within the Makatiti pyroclastic eruption sequence suggests a duration of c. 2 yr for the main pyroclastic eruption phase. Emplacement of the following voluminous (7.5 km3) lavas from the Makatiti‐Tapahoro vents would have occurred over >10 yr at the c. 10–20 m3/s inferred extrusion rates.
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