Fig. 7 Residual Mountains

An island is a piece of land surrounded on all sides by water. It may occur individually or in a group, in open oceans or seas. Smaller ones of only local significance are found even in lakes and rivers. Generally speaking all islands may be grouped, based on their mode of formation, under the following two broad types.

2.1. Continental Islands

These islands were formerly part of the mainland and are now detached from the continent. They may be separated by a shallow lagoon or a deep channel. Their separation could be due to subsidence of some part of the land or to arise in sea level, so that the lowland links are submerged by the sea.

Their former connection with the neighbouring mainland can be traced from the similar physical structure, flora and fauna that exist on both sides of the channel. In the course of time, modification by men and other natural forces may give rise to different surface features. Continental islands can be further classified as under:

1. Individual Islands: These lie just outside the continent, very much associated with the characteristic features of the mainland of which they were once part. Some of the outstanding examples are New foundland, separated from the mainland by the Strait of Belle Isle; Madagascar, by the Mozambique Channel.

2. Archipelagoes or island groups: These comprise groups of islands of varying sizes and shapes, e.g. the British Isles, the Balearic Islands of the Mediterranean and also those of the Aegean Sea.

3. Festoons or island arcs: The islands form an archipelago in the shape of a loop around the edge or the mainland, marking the continuation of mountain ranges which can be traced on the continent. Most of these island arcs are formed as one oceanic tectonic plate subducts another one and, in most cases, produces magma at a depth below the overriding plate, e.g. Andaman and Nicobar Islands, the East Indies, the Aleutian Islands, RyukyuIs lands, Kurile Islands and other island arcs of the Pacific coasts.