The 4-km-wide Tuhua/Mayor Island, offshore of North Island in the Bay of Plenty, is the emergent portion of a 15-km-wide peralkaline shield volcano constructed between about 120,000 and 35,000 years ago. A 3-km-wide composite caldera was formed in two or three collapse events, the last of which took place about 6,300 years ago, and was accompanied by a Plinian eruption that produced tephra deposits up to 70 cm thick on the mainland. Post-caldera eruptions generated a series of lava domes and flows emplaced from NNE-trending vents within the caldera that have filled it to depths of at least 180 m. The latest eruption has not been dated, but was considered by Houghton et al. (1992) to have occurred perhaps only 500-1,000 years ago.