Distribution, stratigraphy, and history of proximal deposits from the c. AD 1305 Kaharoa eruptive episode at Tarawera Volcano, New Zealand

Abstract

The c. AD 1305 Kaharoa eruptive episode consisted of a complex sequence of basalt‐triggered high‐silica rhyolite eruptions from at least seven vents along an 8 km linear zone across Tarawera Volcano. Initial plinian eruptions from a summit vent spread Kaharoa Tephra southeast across the North Island, accompanied by phreatomagmatic explosions and pyroclastic density currents from vents opened on the northern flanks of the volcano. The early plinian phase was ended by extrusion of Crater Dome in the summit vent, with explosive activity migrating to two adjacent vents (Tarawera and Ruawahia) to the southwest and northeast. Renewed plinian eruptions, apparently from the northern vents, produced tephra falls dispersed northeast‐northwest from the volcano. Extrusion of the three summit lava domes was accompanied by voluminous block‐and‐ash flows generated by collapse of the growing Ruawahia and Wahanga Domes, forming large fans to north, southeast, and northwest of the volcano. Calculation of Kaharoa lava volumes and comparisons with the extrusion rates of observed dome‐building eruptions suggest a duration of c. 4 yr for the c. 4 km³ Kaharoa eruptive episode. This estimate, of years rather than days or weeks, is significant for planning an effective response to a future similar rhyolite episode in New Zealand.