THE NATURAL ENVIRONMENT
As the largest continent, Asia contains some of the world’s most spectacular natural features, including high mountain ranges, vast plateaus, majestic river basins, and lakes and inland seas. The centerpiece is the high mountains of the Himalayas and the associated Tibetan Plateau (Qing Zang Gaoyuan). To the far north are vast plateau regions of Siberia and open waterways such as Lake Baikal. Located in an arc around the eastern rim of the continent are the plateaus of China, dissected by great rivers, including the Yangtze River (Chang Jiang). In South Asia, the Deccan Plateau dominates India. Toward the west is the Arabian Peninsula, and in a northwesterly direction are the steppes of Central Asia.
A. Geological History
Highest and Lowest Elevations, by Continent According to the theory of plate tectonics, the crust of the Earth’s surface is made up of vast continental and oceanic plates. These are in constant motion, rubbing and pushing against one another, moving only small amounts each year. The Eurasian continental plate is the largest. It is composed of some of the most ancient rocks on Earth, originating in Precambrian time from 4.65 billion to 570 million years ago. These ancient materials can today be found in eastern Siberia, throughout the Arabian Peninsula, and in India south of the Indus and Ganges rivers.
A huge sea called Tethys covered most of the interior of Eurasia during the Paleozoic and Mesozoic eras, which lasted from 570 million to 65 million years ago. Thick deposits of sediment formed on the seafloor, eventually becoming the layers of rock that form the geological features of the present day.
The Indian subcontinent broke off from the southeastern corner of the African continental plate during the Cretaceous period. It drifted in a northeasterly direction and collided with the larger Eurasian plate, slipping partly underneath it. The impact created an enormous “deep” that eventually filled with sediments and became the Gangetic Plain. The collision also generated enormous pressure on the southern edge of the Eurasian plate, causing this region to crumple; this forced an uplift of rock that created the Himalayas, the world’s highest mountain system.
The Pacific Ocean plate drifted westward, scraping along the Eurasian plate and slipping under its coastal edge. This created the islands of Japan, Taiwan, the Kurils, the Ryukyus, and the Philippines. Southeast Asia lies at the intersection of the Eurasian, Pacific Ocean, and Indian Ocean plates. Over time the contact between these plates created the mountain ranges of mainland Southeast Asia. The continued slow movement of the plates causes friction and instability deep below the Earth’s surface, producing volcanoes and earthquakes.
B. Surrounding Waters and Islands
Asia is bounded on three sides by oceans: the Arctic to the north, the Pacific to the east, and the Indian to the south. Many seas, bays, and gulfs indent the continent’s coastline, which is 62,000 km (39,000 mi) long.
The most prominent seas along the northeastern rim of Asia are the Bering Sea in the far north between Asia and North America; the Sea of Okhotsk, located west of the Kamchatka Peninsula and north of the Kuril Islands; the Sea of Japan (East Sea), which fills the gap between Japan and the Asian mainland; and the Yellow Sea, situated between China and Korea. The Kuril Islands, Japan’s major islands of Hokkaido, Honshu, Shikoku, and Kyushu and Taiwan run along a thread from north to south.
The South China Sea lies adjacent to Southeast Asia, linking mainland countries to the Philippines and Indonesia. The Gulf of Tonkin sits between Vietnam and China’s Hainan Island, while the narrow Strait of Malacca separates the Indonesian island of Sumatra from the Malay Peninsula. Java Island lies across the Java Sea from Borneo, the world’s third largest island after Greenland and New Guinea. To the southeast is the Timor Sea separating the Asian island of Timor from the Australian continent.
The Indian subcontinent is flanked by the Bay of Bengal on the east and the Arabian Sea on the west. The island of Sri Lanka and the much smaller Maldives and Nicobar Islands trail away to the south.
The Arabian Sea’s Gulf of Aden, the Red Sea, the Mediterranean Sea, and the Black Sea form an arc along the western rim of Asia, providing natural boundaries with Africa and Europe. The Suez Canal, an artificial waterway excavated in the mid-19th century, provides a passage for ships between the Mediterranean and Red seas. The Persian Gulf provides Saudi Arabia, Iraq, and Kuwait access to the Arabian Sea.
C. Plains and Deserts
Plains occupy more land area in Asia than any other type of physical feature. Most of the western and northeastern parts of Russian Asia consist of plains. Other large plains include those of the Tigris and Euphrates rivers in Southwest Asia, the Ganges River in northern India, the Mekong River in Southeast Asia, and the Yangtze River in China.
Deserts are a feature of the Asian interior north of the Himalayas and large parts of Southwest Asia, especially the Arabian Peninsula. There the Syrian Desert, a plateau strewn with rock and gravel, spreads through southern Syria, northeastern Jordan, and western Iraq. Farther to the south, in southern Saudi Arabia, lies the Rub‘ al Khali (Empty Quarter). It is the largest continuous body of sand in the world.
Large deserts are also spread throughout Central Asia. The Garagum (Turkic for “black sand”) occupies most of Turkmenistan. Southern Kazakhstan and northern Uzbekistan share the Qyzylkum (Turkic for “red sand”), which lies southeast of the Aral Sea.
Stretching east across Mongolia and into China’s Inner Mongolia Autonomous Region is the Gobi, a cold, high plateau with an average elevation of 900 m (3,000 ft). Southwest of the Gobi is the Takla Makan Desert in the Xinjiang Uygur Autonomous Region of China. Both deserts are in the rain shadow of the Himalayas, which blocks the movement of moist air from the Indian Ocean.
D. Mountain Ranges
International Climbing International Climbing Most of Kyrgyzstan lies in the lofty Tian Shan range amid many permanently snowcapped mountains. For their treks to the top, mountaineers from abroad prepare at international climbing camps such as this one. Encarta Encyclopedia Corbis
Asia’s mightiest mountain ranges radiate in great sweeping arcs from the Pamirs of Central Asia, a highland region where Tajikistan, Afghanistan, and China intersect. Southeast of the Pamirs are the Himalayas, spanning 2,400 km (1,500 mi) from the border between India and Pakistan in the west to the border between India and Myanmar in the east. The Karakorum Range lies just north of the western Himalayas. These two ranges contain all but two of the world’s highest peaks, including Mount Everest, which lies on the border between Tibet and Nepal. Smaller mountain ranges extend southward from the eastern Himalayas into the Indochinese Peninsula.
East and northeast of the Pamir knot, the Kunlun Mountains and the Tian Shan extend for more than 1,600 km (1,000 mi) into China. To the west, extending into central Afghanistan, is the Hindu Kush. Ranges connected to the Hindu Kush then extend into northern Iran, where they are known as the Elburz Mountains. A branch of the Elburz becomes the Caucasus Mountains between Europe and Asia.
A low range of mountains extends southwestward from the Pamir knot into western Pakistan, where they are known as the Sulaiman Range. These mountains then continue northwestward through Iran into southern Turkey, where they are known as the Taurus Mountains.
Other important mountain ranges of Asia, such as the low Nan Ling hills in central and southern China, are not directly connected to the high mountain chains that meet at the Pamirs.
E. Plateaus
Several plateaus lie between the mountain ranges of Central Asia. The highest is the Tibetan Plateau, often referred to as the Roof of the World, which is bounded by the Kunlun Mountains and the Himalayas. About 1,300,000 sq km (500,000 sq mi) of this plateau lies at an elevation above 4,300 m (14,000 ft). The principal plateaus of Southwest Asia are the Anatolian Plateau of central Turkey, the Arabian Plateau, and the Iranian Plateau. In South Asia, most of the peninsula of India consists of the great triangular Deccan Plateau. The Yunnan Plateau extends over much of the Indochinese Peninsula and the southwestern part of China. Much of the northern part of Russian Asia is occupied by the Central Siberian Plateau.
F. Rivers, Lakes, and Inland Seas
East Asia is the location of the continent’s longest river, the Yangtze, which flows 6,300 km (3,900 mi) eastward from Tibet to the East China Sea. The Huang He (Yellow River) also rises in the Tibetan highlands, flowing east across central China to its mouth at the Yellow Sea. The Zhu Jiang (Pearl River) rises in southwestern China and flows through the southern part of the country on its route to the South China Sea.
In Southeast Asia the major rivers flow southward between mountain ranges. The Mekong rises in eastern Tibet and flows southeast to the South China Sea. The Salween also originates in Tibet, where it is called the Nu Jiang, flowing south to the Andaman Sea. The Irrawaddy, which rises in the mountains of northern Myanmar, also empties into the Andaman Sea.
The major rivers of South Asia have their sources in the Himalayas. The Ganges rises in the western Himalayas and passes eastward through India. Just north of the Bay of Bengal it joins the Brahmaputra River, which rises beyond the Himalayas and then empties into the bay. The Indus River emerges from the western end of the Himalayas and flows through Jammu and Kashmir and western Pakistan into the Arabian Sea.
The only large rivers of Southwest Asia are the Tigris and the Euphrates. Both rivers rise in Turkey and flow southward through Syria into Iraq, where they join before emptying into the Persian Gulf.
The three longest rivers of Russian Asia are the Ob’, the Yenisey, and the Lena, all of which are more than 3,600 km (2,200 mi) long. These rivers rise in southern Siberia and flow northward into the Arctic Ocean.
River basins in tropical and temperate Asia support the highest population densities. The Gangetic Plain, which lies between the Himalayas and the Deccan Plateau; the basins of the Irrawaddy, Mekong, and Chao Phraya in Southeast Asia; and the basins of China’s great rivers, especially the Yangtze, Huang He, and Zhu Jiang rivers, are all densely settled. These valleys have fertile soils for agriculture and the rivers serve as a means of transportation.
Some of Asia’s important rivers flow into inland lakes. The Jordan River rises in the mountains of Lebanon and Syria and flows southward into the Dead Sea, a saltwater lake seven times more salty than the ocean. At 408 m (1,340 ft) below sea level, the surface of the Dead Sea is the lowest point on Earth. The Syr Darya and the Amu Darya of Central Asia both drain into the Aral Sea, also a saltwater lake. Since the 1960s the diversion of much water from the Syr Darya and Amu Darya for irrigation has caused the Aral Sea to shrink to less than half its former size. In 1988 the lake split in two, forming the Large Aral Sea, which receives water from the Amu Darya, and the Small Aral Sea, which receives water from the Syr Darya. The decreased water intake has also increased the salt content of the lake. The Caspian Sea is the largest saltwater lake in the world. Lake Balqash in Kazakhstan is another major saltwater lake.
Lake Baikal in southeastern Siberia is the deepest lake in the world and the largest freshwater lake in Asia. The Tônlé Sap, a shallow lake in western Cambodia, is the largest lake in Southeast Asia. It provides a lucrative source of fish for local residents. The Tônlé Sap becomes more than three times its normal size between June and October when floodwaters of the Mekong River empty into the lake.
G. Climates
Most of Asia’s climates are similar to the interior and eastern-coast climates of North America at similar latitudes. Like northern Canada, the northernmost areas of Asia have a subpolar climate with very long, cold winters and very short, cool summers.
A vast area with a subarctic climate lies farther inland and generally southward. It is isolated from the Arctic Ocean and is little influenced by the Pacific because the prevailing winds blow from the west. This area experiences great extremes of temperature. Summers are short, but temperatures can reach as high as 34°C (94°F), and winter temperatures are among the coldest in the world.
South of the subarctic regions is a broad stretch of land having a humid continental climate with short summers. Winters are severe, but summer days are warm or even hot. In Russia, the subarctic region extends from the border with Poland on the west to Siberia on the east, and includes much of the country’s best farmland. Northern China and central Japan also have a humid continental climate, but their summers are long. This is similar to the climate of the midwestern United States, although northern China generally has drier winters.
A humid subtropical climate, similar to that of the southeastern United States, occurs in southeastern China and southern Japan. Both areas receive precipitation throughout the year. Northern India south of the Himalayas also has a subtropical climate. Moisture-laden winds called monsoons carry heavy precipitation to the region in summer. The winters are dry. This rainy-and-dry, tropical climate, which is also characteristic of much of Indochina, is influenced by the seasonal movement of air masses. The summer monsoons usually occur between May and October in areas north of the equator. If the monsoons arrive late, the lack of rain may ruin crops or keep them from growing, causing food shortages for millions of people.
India’s southwestern coast and the coastal areas and islands of Southeast Asia experience heavy rain throughout the year. Near the equator, this rain results from hot humid air that rises and expands, then cools in the upper atmosphere and condenses into rain (see Rain: Process of Precipitation). In the coastal areas farther north of the equator, such as the southwestern coast of India, the rainy tropical climate is the result of constant moisture-laden winds coming largely from the sea.
Vast areas of Central and Southwest Asia are arid or semiarid. In Central Asia, mountains and highlands block moisture-bearing winds from the sea.
Only a few areas of Asia have climates that are typical of the west coasts of continents. A portion of Asia bordering on the Mediterranean Sea in Lebanon and Egypt has a subtropical climate with dry summers. This is similar to the climate of southern California.
H. Vegetation
Asia incorporates many different biomes, which are landscapes having similar combinations of climate, vegetation, and animal life.
The northernmost areas of Asia, which experience a subpolar climate, have tundra vegetation consisting of grasses, mosses, and other small plants. Farther inland from the Arctic coast, the tundra gives way to the taiga, a region of vast coniferous forests composed of trees such as spruce, larch, and fir. Farther south, the taiga merges with forests of broadleaf trees, or mixed forests of broadleaf and needleleaf trees.
In Asia’s north central interior the forests merge into vast grasslands, much of which is short, steppe grasses. Large portions of Southwest Asia and the continent’s interior have semiarid or desert vegetation. Short grasses and other vegetation that require minimal precipitation surround many of the most barren areas in the deserts.
Although tropical rain forest predominates along the southern coastal strip and on the island of Sri Lanka, the eastern side of South Asia is characterized by semiarid tropical vegetation. The Deccan Plateau has mainly tropical dry forest vegetation.
Mainland and island Southeast Asia once supported extensive areas of tropical rain forest, which thrived in the warm, moist climate. Significant tracts of forest remain in most countries, but legal and illegal harvesting are too rapid to support sustainable regrowth.
Inland from the coastal strips of mainland Southeast Asia and stretching into southern China, tropical seasonal forests predominate. These merge into temperate forests farther north. Around the rim of the Bo Hai gulf the vegetation is chaparral, woody shrubs that grow to 4 m (13 ft) in height.
Asia has three main crop production systems. Across a broad band encompassing the Middle East, Central Asia, much of Russian Asia, and the inner regions of China, subsistence livestock production is the mainstay. Around coastal China, and most of South and Southeast Asia, the major form of agricultural activity is subsistence crop production. Scattered throughout the region—especially in Japan, Southeast Asia, the western parts of Russia, and some fertile patches of the Middle East—are pockets of commercial crop production.
Economically important activities throughout Central Asia and Russia include the production of wheat and other grains, cotton, and vegetables. Southeast Asia and the southern parts of China and India are major rice-growing areas, although grain production and consumption is more common in the northern regions of China and India. Rubber trees and oil palm plantations are significant in Malaysia and Indonesia. Tea plantations are significant in India, Sri Lanka, and Indonesia.
I. Soils
Asia’s soils are related mainly to climate and vegetation. In some areas the origins of soils, perhaps from volcanic action or from materials carried by streams, may be more important. Such volcanic or alluvial soils are especially fertile.
The tundra soils of the northernmost part of the continent are acidic and infertile. Many of these areas are underlain by permanently frozen subsoils that never thaw during the brief summers. Subsoils of this type, known as permafrost, cover a very large area in the northern part of Siberia.
South of the tundra, the soils of the taiga are also acidic and relatively infertile. Somewhat less acidic and more fertile soils are found in the mixed forests and the broadleaf forests farther south.
Prairie and black chernozem soils are south of the forests. Because these soils developed where there is limited precipitation, their desirable minerals have not been absorbed or washed away, a process known as leaching. These soils are among the most fertile in the world. The best farmland of Russian Asia occurs largely on black soils and on the more inferior soils of the mixed and broadleaf forests.
The unleached soils of the semiarid and arid areas of the continent are often fertile, except where they are too saturated with salts or alkaline minerals. The availability of water for irrigation largely determines their use. Continued irrigation, however, may increase the concentration of salts or alkaline minerals and make the growing of crops impossible.
The soils of the rainy tropics are generally infertile. High precipitation and high temperatures cause most of the valuable minerals to be leached from the soil. Less leaching occurs in the rainy-and-dry tropics and the humid subtropics.
Many of the red and yellow soils of the humid subtropical area of China have been improved by thousands of years of care, which has included the use of compost, or rotted plant refuse. In some semiarid regions of China, however, natural vegetation with deep roots—which kept the soils in place—was cleared for food crops that lacked sufficient root systems and caused the topsoil to become terribly eroded.
8:25 PM
Categories:
Author: shankar
MY ASIA MY PRIDE
