Guiana Highlands(redirected from Guiana Shield)
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Guiana Highlands,mountainous tableland, c.1,200 mi (1,930 km) long and from 200 to 600 mi (322–966 km) wide, N South America, bounded by the Orinoco and Amazon river basins, and by the coastal lowlands of the Guianas. It is located in SE Venezuela, Guyana, Suriname, French Guiana, and N Brazil, with an outlying section. The Pacaraima Mts., which culminate in Mt. Roraima (9,219 ft/2,810 m high) on the Venezuela–Guyana–Brazil border, form the highest section of the highlands. Geologically, the Guiana Highlands is a shield—a stable mass of Precambrian rock—and is related to the Brazilian Highlands; an outlying section of the shield extends into SE Colombia. It consists of vast plateaus of ancient crystalline rocks overlaid by geologically recent sandstone and lava caps. The tablelands rise one after another, like gargantuan steps, in sheer escarpments hundreds to thousands of feet high. Numerous rivers, fed by heavy rainfall, rise in the highlands and pour over the edges to create deep gorges and magnificent waterfalls. Angel Fall (3,212 ft/979 m high) in Venezuela is the world's highest waterfall. The sparsely populated region, romantically depicted in W. H. Hudson's Green Mansions, is famous for the exuberance of its semideciduous tropical rain forests and for its rich fauna, including many varieties of brilliantly colored tropical birds. Its inaccessibility is attested by the discovery in the mid-1900s of the headwaters of the Orinoco River in the southwestern section and of a hitherto unknown indigenous tribe of tall people, the Panares. The crystalline rocks of the Guiana Highlands yield gold and diamonds. Large deposits of iron ore, manganese, and bauxite have been made accessible by new roads and railroads, but the enormous potential wealth of the highlands is still largely untapped because of the dense cover of vegetation. The region has great hydroelectric-power potential that could form the base for industrial development. The highlands remains one of the world's few frontiers although it is yielding to the development process that has transformed Santo Tomé de Guayana, Venezuela, into the region's chief industrial center and the gateway to the interior.
a plateau in northeastern South America, surrounded by the Orinoco and Amazon lowlands on the north and south and by the Andes and the Atlantic Ocean on the west and east. The Guiana Highlands is part of the territories of Colombia, Venezuela, Brazil, Guyana, Surinam, and French Guiana. The highest elevation is Mount Neblina (3,014 m). The plateau is the projection of the ancient foundation of the South American platform.
The Guiana Highlands are composed primarily of Archeozoic metamorphic rocks, covered in places by Proterozoic quartzite sands and conglomerates of sedimentary mantle-rock. The Upper Archeozoic rocks contain major deposits of iron ore (primarily in the north) as well as gold and diamonds, while the thick weathered crust contains bauxite and manganese ores (primarily in the east). The relief is dominated by denuded socle plains (elevation, 150-400 m), with separate insular heights that become lower toward the periphery and in the upper reaches of the Orinoco-Rio Negro basin. The most mountainous relief is in the central region along the border between Brazil and Venezuela, and north of it there are sandstone table plateaus with steep slopes (the Serra-Imery, Sierra Parima, Pakaraima, and the Auyán-Tepuí and La-Gran-Sabana massifs). Sandstone mantles are also found in the western areas of the highlands (maximum elevation, 910 m). Crystalline block massifs and ridges are typical in the west central area (maximum elevation, 2,400 m), along the border of Guiana and Brazil (maximum elevation, 1,000 m), and in central Surinam (maximum elevation, 1,280 m). Along the shores of the Atlantic Ocean, the Guiana Highlands are bordered by the Guiana Lowlands. A hot subequatorial climate prevails, with average monthly temperatures ranging from 22° to 28° C. In the east there is a short dry season in the autumn, where precipitation is up to 3,500 mm annually. In the central regions there is a longer winter dry season, with 1,200-1,700 mm of precipitation per year. Western areas of the Guiana Highlands have a constant wet equatorial climate. The extremely dense network of rivers includes the Orinoco basin (including the Inirida, Ven-tuari, Caura, and Caroni rivers), the Amazon Basin with its sources and tributaries (the Rio Negro, Trombetas, and Paru rivers), and rivers flowing directly into the Atlantic Ocean, such as the Essequibo, Courantyne, Maroni and Oyapock. All these rivers have many rapids and an abundance of waterfalls, including the highest one on earth—Angel Fall in the Caroni basin, which is 1,054 m high. Enormous hydroelectric resources are available. The water flow in winter decreases two to five times, primarily in the rivers of the central region.
The western and eastern regions of the Guiana Highlands are covered by humid evergreen forests (with valuable types of timber) on reddish yellow lateritic soils. The central regions contain mainly deciduous and evergreen forests on red soils. Windward regions (relative to the northeast trade winds) have areas of savannas. The animal world belongs to the Brazilian subregion of the Neotropical region. There are platyrhine monkeys, sloths, anteaters, armadillos, tapirs, peccaries, opossums, and jaguars, as well as many types of birds, reptiles, fish, and insects. The sparse Indian population engages in hunting, fishing, and primitive agriculture. In the northern and eastern regions mining is carried on, and some lumbering is done, primarily in the eastern areas of the highlands.
REFERENCELukashova, E. N. Iuzhnaia Amerika. Moscow, 1958.
E. N. LUKASHOVA