The Probert Encyclopaedia of General Information

PLATEAU

A plateau or tableland generally denotes a large stretch of highland which is practically the same height above sea-level, and which descends on all sides to lower ground. Some plateaux, however, such as those of Tibet and Bolivia, that are fringed by high mountain ranges which tower above the plateau level, are known as intermont plateaux. Sometimes they are so completely enclosed as to have no outlet to the sea.

A plateau might be regarded as an elevated plain, but there is often a great difference between the surface of a plain and that of a plateau. As a plateau is high, rivers are swift and carve deep, narrow valleys instead of the broad, open valleys of the lower rivers of the plains. Such plateau areas as Wales and the Highlands of Scotland, are broken by deep, narrow valleys, and are termed dissected plateaux. On reaching the top of such an area one has a long view of a series of flat-topped mountain ridges. These ridges are all of approximately the same height, and if one imagines the clouds descending until they touched one ridge, then almost every other ridge would be similarly cloud-capped. Other good examples of plateaux are Tibet in Asia, the Ecuador and Bolivian plateaux in South America, and nearly the whole of the continent of Africa.

The Deccan of India is a plateau that has been tilted so that the western edge is much higher than the eastern edge, and all the main rivers drain eastwards. In many instances plateaux are formed by the denudation or wearing down of higher mountainous areas. Ultimately, such areas may become so low that they are nearly plains, i.e. peneplains, such as the land around Hudson Bay. Millions of years ago lava was forced up through cracks in the earth's crust, and spread out over the land in great sheets which have since hardened to form plateaux of basalt.

Two well-known examples of such plateaux are in Antrim (Ireland), and on the Deccan of India to the east of Bombay. Many of the most extensive areas of plateaux in the world are composed of very hard old rock. The Guiana Highlands, most of Africa, Arabia, the Deccan of India, and the West Australian plateaux are all composed of rocks of similar age. The ancient plateau lands are principally valuable for their minerals, such as the gold of Western Australia; the iron and manganese of the Brazilian Highlands; the gold, copper, and diamonds of the African plateau; and the gold of the Lena plateau in Siberia. Where plateaux are found in tropical areas they are important because, being cooler than the neighbouring lowlands, they offer greater possibilities for successful European settlement and development. The highlands of Brazil, Kenya, and Tanganyika are illustrations of this. Much of the tropical plateau area is covered by savannah grasslands. Most of these areas are not yet developed, but offer possibilities for the production of a large variety of both animal and vegetable products when communications have been developed and further settlement has taken place.
Research Plateau