The Islands of Polynesia
The Islands of Polynesia
(A) There are three main types of island in the Polynesian triangle, each different in terms of geology, and characterised by a different environment in terms of flora and fauna.
(B) The high island is composed mainly of basalt. Islands of this type are elevated to impressive heights above sea level, although rarely above 2 000 metres. An extreme example is Mauna Loa on Hawaii which towers 4 000 metres into the clouds and can be seen 160 kilometres away at sea.
(C) Soil on the high islands is usually thick and rich, and water is abundant. Consequently the flora is varied and plentiful and usually divided into zones according to the altitude. Grass, vines, and palms are found near the beach, while further up the valleys these give way to hardwood trees such as the casaurina. The high plateaus, forming the island roof, are clad in tree ferns, low ground ferns, and wind-gnarled shrubs of various kinds. Insect life is also abundant.
(D) Most high islands are protected by reefs, which support numerous varieties of edible fish. A few, such as Easter Island and some of the Marquesan group, do not have reefs due to unfavourable water temperatures and bottom conditions.
(E) Coral atolls form the low island group and are the type portrayed by Hollywood as idyllic paradises. Although some may be as large in area as the high islands, they are no more than 4 metres above sea level. Darwin, the great naturalist, considered that such atolls were formed by the upward growth of a coral reef around a slowly sinking volcano. Eventually the coral reef enclosed a lagoon where the volcano's crater was. Scientific investigations have shown that Darwin was basically correct.
(F) Although the reef teams with life, the flora and fauna are impoverished due to the lack of fresh water and the poor soil. And while some plants, such as coconut palms and pandanus, can be cultivated, people living on coral atolls are constantly threatened with famine. Add to this the menace of tidal waves and fierce ocean storms and the island 'paradise' loses some of its appeal.
(G) Within the Polynesian triangle, the islands of the Tuamotu group, such as Motutunga and Takaroa, provide the best examples of the low island type. Better known examples of atolls, such as Bikini, Eniwetok, and Tarawa, are found in Micronesia.
(H) The third common type is known as Makatea, a name that has also been given to an island on the northern fringe of the Tuamotu group. These are coral atolls, which have been uplifted and have steep undercut shores. The land surface is rugged and pitted due to the differing rates of erosion of the coral. In time these 'pits' fill with soil and leaf mould, which support lush vegetation.