The Chatham group of islands lies some 500 miles east of Lyttelton, about latitude 44°s and longitude 176w. In the group are 10 islands but only three are of considerable size – Chatham Island (formerly alternatively known as Rekohu or Wharekauri) of 224,000 acres; Pitt Island (Rangiauria) of 15,000 acres; and South-east Island (Rangatira) of 640 acres. Some of the others are little more than rock pinnacles.
The islands are named after the naval ship Chatham, commanded by William R. Broughton, who sighted the group on 29 November 1791 as he sailed to his Tahiti rendezvous with Captain George Vancouver who himself landed on the main island in 1798. At the time of Broughton's discovery there was a Moriori population estimated to be over 1,000, and sealers and whalers had bases there before the Maori invasion from the New Zealand mainland in 1832. German missionaries arrived in 1842 as the first of the few early European settlers who supplied potatoes, pork and the like to visiting sealers and whalers. Sealing and whaling stations had almost disappeared by 1861 when the total population was estimated at 413 Maoris, 160 Morioris, 17 half-castes, and 46 Europeans. A new era of sheep farming was opened by Chudleigh and the Ritchies in 1865, but farming has always been handicapped by isolation from the mainland. The present population is only some 500, the Europeans voting in the Lyttelton parliamentary electorate and the Maoris in the Western Maori electorate. The Morioris have disappeared. The chief revenue of the group today is from sheep and wool. For local administration a Chatham Islands County was established in 1901, but the first council was not elected until 1925.
The Chatham Islands lie far out on the edge of the submarine shelf above which all the New Zealand islands rise. The oldest rocks are schists similar to those of Central Otago. Elsewhere are basic volcanics, tuffs, and some Tertiary limestones. All these are displayed in the main Chatham Island, much the largest of the group. Here the basic volcanics form the higher country in the south bounded by a line of steep cliffs and rising to heights of over 900 ft. In the north the land is much lower and flatter, its surface broken by some scattered mounds of volcanic rock that may rise as high as 300–500 ft.
Nearly 22 per cent of the island area is covered by shallow lakes and lagoons, the Te Whanga Lagoon alone occupying 40,000 acres. It is mainly along the western margin of this big lagoon that the limestone beds are found, while older sandy beds and banks and dunes of younger unstable beach sands enclose it in the east and north. Over most of the land area, too, are beds of peat that may be as much as 30 ft thick. This widespread blanket of peat is the most remarkable feature of the island surface.