GREAT BARRIER ISLAND
Great Barrier Island, known to the Maoris as Aotea — the land like a white cloud — is a detached piece of the Coromandel Peninsula; the subsidence that separated it from the mainland has given it an intricate rocky coastline with several offshore islets and pinnacles. Some 110 sq. miles in area, the island lies 55 miles north-east of Auckland. Discovered by Captain Cook in 1769, it has been exploited since for timber and minerals but its present permanent population is scarcely 300. Though its highest point (Mt. Hobson) is only 2,038 ft, its surface is extremely rugged with rocky bluffs rising steeply from the sea, especially along its western shore. Its few bay-head lowlands are scattered and small. The drowning of its margins has made some fine sheltered anchorages as at Whangaparapara, Port Fitzroy, and Port Abercrombie, but none of these has much easily accessible hinterland.
The structure of the island closely resembles that of the Coromandel Peninsula. The oldest rocks are sedimentary greywackes and argillites best displayed in the extreme north, while over these lie at least two series of volcanic rocks. The older and more widespread of these are andesites of various types, while acidic rocks, both rhyolites and rhyolitic tuffs and sinter, are found in the high interior around and south of Mt. Hobson. All these main rock systems are penetrated by a complex of dykes and sills. It is with these especially that ore bodies of gold, silver, and copper were found by the early prospectors and miners who worked over the island. In all this the Great Barrier Island closely resembles the Coromandel Peninsula, but the total mineral production of the island has been relatively small.
The island surface is very rugged, each rock type having its own characteristic surface forms. In the somewhat lower northern zone of greywackes and shales, surfaces are more subdued though the valleys are narrow, steep, and deep and the coastal cliffs precipitous. In the andesitic zone of most of the west and south, gentle hill slopes end abruptly in steep bluffs or are broken by turretlike pinnacles. It is about Mt. Hobson, however, that the more spectacular forms have developed from the weathering of the light-coloured (white and pink) acidic rocks. Here are deep ravines, steep cliffs, and jagged pinnacles making the centre of the island difficult to traverse. The east coast, exposed to the open ocean, is much simpler in outline than the west. Spurs have been trimmed back, bays are often closed by barrier beaches or spits, and bay-head beaches are common.
In pre-European time the whole island was clothed in the northern type of podocarp, mixed hardwood forest with magnificent stands of kauri. These latter have been completely cut out, but there is still a remnant of native forest covering most of the north, with some patches in the more rugged interior and south. Here, too, are areas of regenerating native forest, but over most of the rest of the interior is a secondary growth of manuka-kanuka scrub. It is this widespread cover of scrub that gives so much of the island an appearance of rather drab monotony.
Pasture grasses have been established in some extensive areas near the coasts, but most of these may be classed as “reverting deteriorated” or as danthonia. Patches of good-quality grassland are minute. Some undrained swamps (behind Kaitoki Bay and the Whangapoua estuary) account for 1,000 acres of the area. This is reflected in the limited amount of productive farmland. Sheep are grazed (for wool), and there are some dairy farms on the little flats around bays and river mouths. Settlement is restricted to scattered clusters on the margins of this rugged island, notably at Port Fitzroy and Okiwi in the north-west, and at Awana, Oruawharo, Okupu, and Tryphena in the east and south. Some 40 miles of metalled road provide the only communications between them apart from those by sea. Proximity to metropolitan Auckland makes the island attractive as a holiday resort.
by George Jobberns, C.B.E., M.A., D.SC., Emeritus Professor of Geography, University of Canterbury.
- Transactions and Proceedings of the New Zealand Institute, Vol. 53 (1921)
- “Notes on the Geology of Great Barrier Island”, Bartram, J. A.;New Zealand Geographer, Vol. 13 (1957), “Outlying Islands of Northland”, Cochrane, G. R.
- Descriptive Atlas of New Zealand, McLintock, A. H. (ed.), (1959).