Source, age, and eruptive mechanisms of Rotorua Ash

Abstract

Rotorua Ash is a widespread (>10 000km²) pyroclastic fall deposit erupted during extrusion of a rhyolite lava complex sited adjacent to the Lake Tikitapu basin, 10 km south-east of Rotorua City, North Island, New Zealand. The eruption was plinian in character, with maximum rate of emission occurring early in the eruption sequence to produce a high (c. 20 km) eruption column. Later explosions accompanied extrusion of lavas. Local, near-vent, pyroclastic flow and surge deposits may have resulted from periods of column collapse. Extrusion of a lava flow from the main pyroclastic vent appears to have terminated the eruption. A ¹⁴C age of 13 800 ± 250 years B.P. (new T 1/2) has been obtained for Rotorua Ash close to the source.