Rangitoto

Te Rangi-i-totongia-a-Tama-te-kapua

Rangitoto is the largest, most recent and least modified volcano of the Auckland Volcanic Field. It forms a near symmetrical cone at the entrance to the Waitemata Harbour.

The Auckland Volcanic Field is comprised of monogenetic volcanoes which means it is unlikely that Rangitoto or any of the existing volcanoes will erupt again. The next eruption will probably occur in a new location.

Formation

With little warning, Rangitoto was formed through violent eruptions about 600 years ago. At the time Maori were living nearby on Motutapu Island. The early stages of the eruption would have been excessively violent, due to steam explosions where the molten rock came into contact with the shallow seawater. Large amounts of rock and ash soon smothered Motutapu. Rangitoto finally emerged from the sea as a broad eruption crater with liquid rock building up a number of cones.

Experts differ on the exact pattern of the Rangitoto eruption, some estimating it to have continued violently like this for a decade. Others believe it was built by a series of intermittent eruptions, starting 600 years ago and continuing for perhaps 200 years. Either way, Rangitoto produced a volume of lava equalling that of all the previous Auckland eruptions combined.

When the eruptions finally ceased, lava in the base of the cone cooled and shrank. As a result, the entire top of the mountain subsided by 10 to 20 metres leaving a moat-like ring around the summit. These are the small mounds either side of the central cone that gives Rangitoto its nearly symmetrical profile.

Most of the lava flows were of the rough textured a'a type, in which molten lava slowly moved along inside a thick tube. The outside of this tube is a crust of broken-up chilled lava. Sometimes lava caves form when hot lava drains out from inside the solidified outer crust of the flows leaving hollow tubes. There are about 7 known lava caves on Rangitoto, some of which are sign-posted and worth a visit.

Use and value

Rangitoto's name is derived from the phrase "Te Rangi i totongia a Tamatekapua - the day the blood of Tamatekapua was shed". Tamatekapua was chief of the Arawa canoe which arrived about 1350, and was engaged in (and lost) a major battle with the Tainui at Islington Bay.

There are several Maori myths associated with Rangitoto. One tells of the Tupua, children of the Fire Gods, who inhabited the Auckland area.

One night a husband and wife quarrelled and cursed the goddess of fire, Mahuika. Mahuika complained to Mataoho, the god of earthquakes and eruptions, who sent an eruption to destroy the Tupua's mountain home. It was swallowed by the earth and became Lake Pupuke on Auckland's North Shore, and Rangitoto rose out of the sea. When mist surrounds Rangitoto, it is the tears of the Tupua couple as they weep over their lost home.

Rangitoto is of international significance as a volcanic landform because each stage, from the initial colonisation of raw basalt and scoria to the formation of scrub to immature forest, can be seen. The lava field contains no soil in the usual sense of the word, although rich, fine, dark powder is accumulating in the fissures. Yet, more than 200 species of native trees and flowering plants, more than 40 kinds of fern, and several species of orchids grow on the island. Dominant among the trees is pohutukawa. Rangitoto has the largest remaining pohutukawa forest in New Zealand.

In general there are fewer bush birds than might be expected, probably because the newly-developed forests don't yet carry a lot of food and have a reduced diversity. In pre-European times, Rangitoto is said to have been a reserve for kaka, New Zealand's native parrot. Seabirds are common. Thousands of black-back gulls build their nests across the broken scoria fields, and have two major colonies on the island.

Rangitoto is part of the Hauraki Gulf Maritime Park and is administered by the Department of Conservation in conjunction with the Tangata Whenua Nga Tai and Ngati Paoa. It provides sheltered anchorage, swimming, fishing, walking, bird watching and opportunities for general nature study. Rangitoto Island is an Auckland icon, a conspicuous and important landmark that is visible from many parts of the region and contributes much to Auckland's natural setting.

Key facts

Maori name: Rangitoto, derived from the phrase 'Te Rangi i totongia a Tamatekapua - the day the blood of Tamatekapua was shed'.
Location: Auckland City, map reference NZMS 260: R11/762888
Height: 260 m
Age: Formed about 600 years ago (ca 1400 AD)
Volume lava: about 2,300 million cubic metres (equivalent to 468,000 Olympic sized swimming pools)
Volume tuff/ash/pyroclastics: about 19 million cubic metres (equivalent to 3,800 Olympic sized swimming pools)