Rangitoto (854 ft) is an island volcano of almost perfectly circular outline situated at the entrance to Waitemata Harbour. It serves as a beacon to all overseas ships and, together with nearby Motutapu Island and Waiheke Island, provides a natural barrier against north-easterly storms that would otherwise batter the marine suburbs of Auckland City and sweep into Waitemata Harbour.
Rangitoto means “bleeding sky” or, literally, “blood-red sky”, implying that volcanic activity with attendant outpourings of molten lava and fire fountains of ash and scoria was in progress during early Maori occupancy of New Zealand. This is further substantiated by modern geologic dating methods which indicate that the time of eruption was as recent as 750 years ago. The island is a lava cone spread symmetrically about a radius of 1 ½ miles and surmounted by a series of scoria cones, one within the other. The lava flows (slope 4°–5) are predominantly of the pahoehoe type (a Hawaiian term for basaltic lava flows typified by smooth, billowy, or ropy surfaces) and consists of dense to highly vesicular basalt with abundant green olivine crystals and rare inclusions of sugary white quartz. Although geologically very young, the basalt and scoria is sufficiently weathered and broken to permit the growth of a blanket cover of indigenous forest. This consists of some well-known trees and plants among the 200 and more species, and includes among the commoner flora manuka, pohutukawa, rewarewa, rata, akeake, tutu, and five-finger. The bush extends, with few interruptions, from the summit crater to the coast, where jagged rocks and reefs in the intertidal zone are packed with the succulent Auckland rock oyster (Saxostrea glomerata) or tio para of the Maori.
Rangitoto is a wild-life sanctuary.
by Barry Clayton Waterhouse, New Zealand Geological Survey, Department of Scientific and Industrial Research, Otahuhu, Auckland.