African Continent

Africa is the second largest continent in terms of size, covering about one-fifth of the land area of the earth. Spread over 30,330,000 sq km, Africa is located between 35° 5 and 37° N latitudes and 50° E and 17° W longitudes. The African continent is separated from Europe by the Mediterranean Sea and from Asia by the Red Sea. The Strait of Gibralter in the north-west, the Suez Canal in the north east and the Strait of Bab-el Mandeb connect Africa to Eurasia.

Africa is an enormous plateau,. most of which is covered by deserts, forests and grasslands. The continent can be divided into two major land regions-Low Africa and High Africa. Low Africa, consisting of northern, west ern and central Africa, is further subdivided into the Coastal Lowlands, the Northern Highlands, the Saharan Plateau, the Western Plateau, the Nile Basin and the Congo (Zaire) Basin. High Africa covers eastern and southern Africa and may be further subdivided into the Rift System, the Eastern Highlands, the Southern Plateau, the Coastal Lowlands and Madagascar. The Rift System, a spetial physical feature of Africa, consists of the Great Rift Valley, which is a series of parallel cracks in the earth that form deep, steep-sided valleys. Many of these valleys house lakes. There are several large lakes in High Africa. Lake Victoria is the largest lake in Africa and is the source of River Nile, the longest river in the world. Other large rift lakes include the Tanganyika, Nyasa, Albert and Turkana. The Rift System extends from Ethiopia in the east to Mozambique in the south-east. It is rich in volcanic soil and has some of Africa’s best farmlands.

Deserts cover about two-fifths of Africa. The Sahara, the world’s largest desert, stretches across northern Africa from the Atlantic Sea to the Red Sea. Other deserts include the Namib desert and the Kalahari desert in southern Africa. Grasslands cover more than two-fifths of Africa. Forests cover less than a fifth of the continent.
Other major African rivers include the Congo (Zaire) which carries the greatest volume of water among all the rivers of Africa-and the Niger, which discharge into the Atlantic, and the Limpopo and the Zambezi which drain into the Indian Ocean. The Nile flows northward from east central Africa to the Mediterranean Sea.
Most of Africa’s highest mountains have been created by volcanic activity. Mt Kilimanjaro (5895 m) in Tanzania and Mt Kenye (5199) in Kenya are extinct volcanoes. The Atlas mountain range, extending from Morocco to Tunisia, forms Africa’s longest mountain chain and is of non volcanic nature.
About 90 per cent of the African continent lies within the tropics-Africa has the largest tropical area in the world.

Asian Continent

Asia is the largest contine] covering almost a third of the world’s land area. Asia, wi an area of 43,947,000 square kilometres, extends betwel 80° Nand 10° S latitudes, and 25°E and 170° W longitudE The entire Asian mainland lies north of the equator, b the islands associated with Asia extend into the southel
hemisphere. Most of Asia lies in the eastern hemispher and only a part of it extends to the western hemispher Asia extends from the Arabian peninsula, Turkey and Ur mountains eastward to the Pacific Ocean. From the Aret Ocean, it reaches south to the Indian Ocean.
Asia is home to a variety of natural features, rangin from the hot deserts of the south-west, the cold deser1 in the interior and the frozen north; and from barre un9ultivable regions to the fertile river valleys, coast” pl,ins and delta regions. The highest and lowest places OJ thr earth are in Asia. Mount Everest, the highest, rises 8,84: metres above sea level along the Nepal-Tibet border. Th,
Dead Sea shore, the world’s lowest land, lies about 39′ metres below sea level on the border between Jordan and Israel.

The five major physical divisions of Asia are the Northern Lowlands, the Central Mountains, the Southerr Plateaus, the Great River Valleys and the Island Groups The Northern Lowlands comprise the Siberian plain whid extends between the Ural mountains in the west and River Lena in the east.

Lake Baikal in Siberia is the deepest lakE in the world. The interior heartland of Asia is surrounded by mountains and deserts. The Central Mountains, com prising fold mountains and plateaus, lie south of the Northern Lowlands. Asia has more mountains than any other continent. The major Asian mountain systems meet to form a large group of rugged peaks and deep valleys, called the Pamir Knot. Sometimes referred to as the ‘roof of the world’, the Pamir Knot lies where Afghanistan, China, Pakistan and the Central Asian republics meet. From the Pamir Knot, the Hindukush range extends to the west, the Tian Shan to the north-east, the Kunlun to the east and the Karakoram and the Himalayas to the south-east. The Karakoram and the Himalayan ranges contain some of the highest peaks of the world. Some of the largest glaciers of the world are also found in the Karakoram range. Between the Karakoram and the Himalayas in the south and the Kunlun in the north lies the Tibetan plateau. Between the Kunlun and the Tien Shan in the further north lies the Tarim basin. In between the Tien Shan in the west and the mountain chains of north-east Siberia lie the ancient fold mountain ranges-the Altai, the Yablonoi and the Stanovoi-which house the Tarim basin and the vast cold desert of Gobi.

The Southern Plateaus lie to the south of the Central Mountains. Formed of very old rocks, the Southern Pla teaus (comprising the plateau of Arabia, the Deccan plateau and the plateau of Yunnan) constitute the major part of the peninsulas projecting southward from mainland Asia. The Great River Valleys lie in-between the mountains and plateaus. Some of these river systems-the Tigris-Euphrates, the Indus, the Ganga-Brahmaputra, the Ayeyarwaddy, the Mekong, the Sikiang, the Chang Jiang (Yangtze-Kiang) and the Huang He-are very old. The Yangtze is Asia’s longest river.
Three major island groups are located to the south east and east of Asia-Indonesia, the Philippines and Japan. Most of these islands have a mountainous core surrounded by narrow coastal plains. Some islands still have active volcanoes.
Asia’s coastline measures about 129,077 km.

Because of its tremendous size and varied physical
features, Asia experiences a variety of climates-the bitter cold of the polar north; the hot, dry desert environment of the centre and the southwest; and the hot, humid conditions of the tropical south.

Distribution of Continents and Oceans

About 71 per cent of the globe is water and about 29 per cent is land surface. The continents into which the land surface is broadly divided are: Asia, Africa, North America, South America, Europe, Australia, and Antarctica. If the seas were to drain away, it appears that broad areas lying close to continental shores are actually covered by shallow water less than 180 m deep. Disregarding the earth’s curvature, the continents can be visualised as platform-like masses; the oceans as broad, flat-floored basins. Most of the land surface of the continents is less than 1 km above sea-level, while a predominant part of the ocean floor lies between 3 and 6 km below sea level.
Relief features of continents are being discussed here, while those of oceans will be dealt with in a separate chapter Ocean and Oceanography.
RELIEF FEATURES OF CONTINENTS
The continents consist of two fundamental kinds of geological units: (i) the shields, and (ii) the mountain belts or orogenic belts.
The shields are extensive, rigid and permanent part of the earth’s crust, composed of Precambrian rocks (more than 590 million years old). These are the oldest rocks on the earth’s surface. The mountains of earlier periods were eroded to their roots. The shields today are, therefore, largely plains and low plateaus and are highly stable parts of the earth’s continental crust. Crustal movement of
1. Laurentian Shield 2. Brazilian Shield 3. Baltic Shield
4. African Shield
5. Arabian Shield
6. Siberian Shield 7. Deccan Shield
8. China Shield
9. Austra.lian Shield

shields in the later geologic time have been epeirogenic movements, i.e., rise and fall of the crust over broad areas without breaking or bending the rocks. Negative epeirogenic movement resulted in submerging of shields, shallow seas and continental shelves. Later, positive epeirogenic move ment brought the sedimentary cover that had gathered over time above sea level where it has been carved up by streams into hills and plateaus. The Canadian Shield in North America and the Russian-Baltic Shield of Europe are well-known shields of the northern hemisphere. Similar shield areas occupy parts of Australia, Africa, South America, India and Antarctica. Rocks in these areas date back to the oldest geological time from one to three billion years ago.

Mountain belts of continents are along narrow a genic zones in which crust has been compressed and fon to buckle into tight folds and at the same time to
strongly elevated. The older, inactive mountain ranges he usually been reduced to hill belts. In some places, they i still moderately elevated possessing a rugged relief. 1 young ranges are still active zones of crustal deformati and volcanic activity in some areas. They rise as speetacu alpine mountains.

Distribution of Continents and Oceans

About 71 per cent of the globe is water and about 29 per cent is land surface. The continents into which the land surface is broadly divided are: Asia, Africa, North America, South America, Europe, Australia, and Antarctica. If the seas were to drain away, it appears that broad areas lying close to continental shores are actually covered by shallow water less than 180 m deep. Disregarding the earth’s curvature, the continents can be visualised as platform-like masses; the oceans as broad, flat-floored basins. Most of the land surface of the continents is less than 1 km above sea-level, while a predominant part of the ocean floor lies between 3 and 6 km below sea level.
Relief features of continents are being discussed here, while those of oceans will be dealt with in a separate chapter Ocean and Oceanography.
RELIEF FEATURES OF CONTINENTS
The continents consist of two fundamental kinds of geological units: (i) the shields, and (ii) the mountain belts or orogenic belts.
The shields are extensive, rigid and permanent part of the earth’s crust, composed of Precambrian rocks (more than 590 million years old). These are the oldest rocks on the earth’s surface. The mountains of earlier periods were eroded to their roots. The shields today are, therefore, largely plains and low plateaus and are highly stable parts of the earth’s continental crust. Crustal movement of
1. Laurentian Shield 2. Brazilian Shield 3. Baltic Shield
4. African Shield
5. Arabian Shield
6. Siberian Shield 7. Deccan Shield
8. China Shield
9. Austra.lian Shield

shields in the later geologic time have been epeirogenic movements, i.e., rise and fall of the crust over broad areas without breaking or bending the rocks. Negative epeirogenic movement resulted in submerging of shields, shallow seas and continental shelves. Later, positive epeirogenic move ment brought the sedimentary cover that had gathered over time above sea level where it has been carved up by streams into hills and plateaus. The Canadian Shield in North America and the Russian-Baltic Shield of Europe are well-known shields of the northern hemisphere. Similar shield areas occupy parts of Australia, Africa, South America, India and Antarctica. Rocks in these areas date back to the oldest geological time from one to three billion years ago.

Mountain belts of continents are along narrow a genic zones in which crust has been compressed and fon to buckle into tight folds and at the same time to
strongly elevated. The older, inactive mountain ranges he usually been reduced to hill belts. In some places, they i still moderately elevated possessing a rugged relief. 1 young ranges are still active zones of crustal deformati and volcanic activity in some areas. They rise as speetacu alpine mountains.