Asia Essay Research Paper AsiaAsia is the — страница 4

  • Просмотров 558
  • Скачиваний 9
  • Размер файла 24

degrees F) and short, lasting for less than four months. Rainfall decreases from about 20 inches in coastal locations to less than 10 in in the interior. The extreme northern section of Asia is dominated by the polar tundra climate, where the low year-round temperatures (warmest month averages below 50 degrees F) create a permanently frozen subsoil known as permafrost. Drainage The major rivers of Asia, that is, those reaching the sea, include the Ob, Yenisei, and Lena, which flow northward to the Arctic Ocean; the Amur, Huang He, and Yangtze (the world’s third-longest river, after the Nile and the Amazon), which drain eastward to the Sea of Okhotsk, Yellow Sea, and East China Sea, respectively, all coastal seas of the Pacific Ocean; the Ganges, Indus, and Brahmaputra rivers,

which flow southward toward the Indian Ocean; the Mekong, Irrawaddy, and Salween, which rise in eastern Tibet and drain southward through the peninsulas of Southeast Asia; and the Tigris and Euphrates system, which flows into the Persian Gulf, an arm of the Indian Ocean. In addition, about 5,000,000 sq mi of land in Central Asia are drained by rivers that do not reach the sea. This is the internal, or inland, drainage area of Asia. The Ili flows into Lake Balkhash; the Syr Darya and the Amu Darya into the Aral Sea; and the Ural River into the Caspian Sea. Others are intermittent streams, which flow only after heavy rains; their waters evaporate in the deserts, and some end in salt lakes or playas, which may be dry part of the year. The Dead Sea, a saltwater lake whose shore is

the lowest point on Earth, is fed by the Jordan River. The Caspian Sea, also saline and the world’s largest inland body of water, loses more water by evaporation than it receives from streams and precipitation. The Aral Sea, about175 mi to the east, is also saline and once covered a much larger area. Lake Baikal in southern Siberia is the world’s deepest lake (5,712 ft) and has only one outlet, the Angara River. The waters of Lake Baikal are fresh. Soils Soil types correspond closely to their respective climatic and natural vegetation regions. In the permafrost region of northern Asia are tundra soils, unusable for agriculture because of the short growing season and impeded drainage but otherwise rich in organic matter. South of the tundra, in the vast coniferous forest

region of cold temperate Asia, are podzols with high acidity and low organic content. Farther south, in the zone of mixed coniferous and deciduous forests, the gray brown forest soils have higher humus content and are less acidic than the podzols. Between the temperate forests of northern Asia and the deserts of Central Asia a belt of chernozem and chestnut soils appears. These black to dark-brown soils are very rich in humus and mineral nutrients and are very productive when farmed. The desert and mountain soils of dry Asia have little to offer for agricultural production. Even where irrigation is possible, a danger of salt and alkali accumulation in the topsoil exists resulting from the evaporation of mineralized underground water through capillary action. Consequently,

cultivation in dry Asia is confined to well-drained alluvial soils along major river valleys. The soils of hot, humid monsoon Asia belong to the major soil category known as pedalfers. These soils are rich in iron and aluminum material. High temperatures promote rapid oxidation and contribute to their reddish or yellowish appearance. Heavy rainfall washes soluble mineral and organic matter from the topsoil to the subsoil, leaving insoluble minerals, such as aluminum, in the topsoil. These tropical red earths are generally infertile, and therefore agriculture in monsoon Asia is confined mostly to alluvial soils along river valleys. Some prominent exceptions exist: soils developed on basic volcanic ash in the northeastern Deccan Plateau (India) and in Java are among the richest

soils in monsoon Asia. Vegetation Much of the original green cover in monsoon Asia has been replaced by secondary growth or farmlands as a result of centuries of cultivation. Even in the equatorial region of Southeast Asia periodic burning by shifting cultivators has greatly reduced the extent of tropical rain forest, and tropical deciduous forests dominate what little forest area remains. These forests yield valuable tropical hardwoods, such as teak, sal, ironwood, and bamboo. In dry Asia limited vegetation, such as short grasses, will occur even on the edges of the most barren desert areas. Most of these desert plants are xerophytic (drought resistant) and halophytic (salt tolerant). More significant vegetation occurs where ground water is available near the surface. Separating