Types of Polynesian Islands

The islands of Polynesia vary in type and size, and both these factors influenced the culture which developed upon them. They may be thought of as forming three main classes: volcanic, or high islands; coral, or low islands; and raised coral islands.

The volcanic islands, as the name implies, were formed by volcanic agency, which pushed basaltic masses high above the surface of the sea. Time and wear have produced high hills or mountains and intervening valleys with rivers, streams, and fertile, alluvial land. The natural assets, however, vary from the abundant rainfall and rich soil of the Society Islands to the meager water supply and poor soil of Easter Island. The coast line is fringed with a coral reef, in places close to the shore and in others running out some distance to enclose an page 6outer lagoon, in which fish abound. Some lagoons have deep water with good passages through the outer reef, as do those of Tahiti, and others have but small, shallow passages such as those in the Cook Islands. At the outer side of the reef edge, the sea falls suddenly to such depth that ships cannot obtain anchorage. Hence, the character of the reef and the lagoon have exercised an important influence on the visits of foreign ships. Some volcanic islands have an outer fringing reef which surrounds the group of individual islands with their own fringing reefs, the Mangarevan Islands, for instance. Volcanic islands have many advantages, apart from their size. They provide a variety of raw material in the form of plants, timber, and stone, and the alluvial soil is suitable for the growth of cultivated plants. At the time of Polynesian discovery, however, the native flora provided little food beyond a few berries and roots and the pith of tree ferns. However, fish, crustaceans, and shellfish were abundant in the surrounding waters.

The coral islands were built by coral animals on a submerged reef which formed a large ring enclosing a central lagoon, sometimes several miles in extent. The islands, irregularly spaced on the reef, range in size from those of several acres in extent to mere rocky protuberances bare of vegetation. This combination of reef, islands, and central lagoon is termed an atoll. The individual islands are narrow, because they are limited by the width of the reef; and their length is determined by the breaks in the supporting reef. They are low and rarely rise more than 10 to 20 feet above sea level. The surface is flat and without streams. Water, which is brackish though potable, can be obtained by sinking wells. Some atolls, termed wet atolls, have sufficient rainfall to produce fairly abundant vegetation though limited as regards the variety of plants. Other, dry, atolls have poor, stunted, and sparse vegetation because of meager rainfall. The soil, formed of broken down coral, is capable of growing the coconut and pandanus in profusion, but the food plants such as the breadfruit, banana, taro (Colocasia esculenta), yam, and sweet potato, did not grow on Polynesian atolls. When the Polynesians settled on them, the only native plants that could be used for food were pigweed (Portulaca) and the fruit of the Morinda citrifolia. A large-leaved coarse taro, termed puraka (Cyrtosperma chamissonis), was cultivated in trenches dug down to subsoil water, but this plant was introduced. The paper mulberry, which provided the material for tapa cloth, and the Hibiscus tiliaceus, which provided a suitable fiber for lines and nets, did not grow. The lagoons, however, were rich in fish, crustaceans, and shellfish, and the shell of the Tridacna was a poor but useful substitute for basalt in the manufacture of tools.

Some atolls have deep passages through the reef capable of admitting schooners into the shelter of the central lagoon, but in most, the passages are so narrow and shallow that only canoes can be piloted through them. Immediately outside the reef, the sea sinks to unanchorable depths.

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The raised coral island, as illustrated by Niue, was originally a small atoll which was raised by volcanic forces. After a fringing reef was formed, another volcanic elevation took place which formed an island with a central, high plateau, depressed in the middle, and an encircling lower plateau with cliff-girt shores 80 to 90 feet high in places. The formation is entirely coral with large blocks and broken down soil, somewhat reddish in color. The soil is evidently much more fertile than that of atolls, for the native vegetation includes some fairly large trees and the Hibiscus tiliaceus, the bark of which provides fiber for cordage and skirts. The taro, giant taro, yam, sweet potato, arrowroot, coconut, banana, and paper mulberry all grow there, as does the breadfruit, which is a late introduction. The rain does not supply streams but flows into underground reservoirs which provide the water supply of the people. Thus, conditions on a raised coral island enabled a richer native culture to be developed than was possible on atolls.