Asian geography

Asia is the largest continent, occupying the northern portion of the eastern hemisphere, extending beyond the Arctic Circle, and nearly reaching the Equator. It contains about one-third of the whole of the dry land, and one-twelfth of the whole surface of the globe.

Geographically speaking, Europe is an appendix to Asia, and exact delimitation between the two is impossible. The Ural River and mountains are the common conventional boundaries with Europe north of the Caspian, while the Manych depression is used as the limit of Asia between the Black and the Caspian seas, and the Bering Strait, 60 km/37 mi wide, separates Asia from North America. Asia's northern boundary is the Arctic Ocean, the extreme north point being Cape Sievero-Vostochny. The southern boundary is impossible to fix exactly, but the volcanic chain of islands that can be traced through the Molucca and Sundra Islands may be taken as the limit. The southern coastline is much more irregular, and broken by the three great peninsulas of Arabia, India, and Indochina. The Mediterranean and Black seas form natural western limits to the continent, as does the Red Sea lying between Asia and Africa.

Relief Asia can be divided into five broad zones: northern, highland, arid, tropical, and insular. It is a continent of contrasts, containing both the highest point on the Earth's surface (Mount Everest) and the lowest (the Dead Sea).

The northern region This comprises the Arctic wastes of Siberia, a region of plains, plateaux, and folded mountain ranges, where the major influences on relief are frost weathering and permafrost. The far north has been subjected to several periods of glaciation and here erosive influences dominate, while in the south of the region, sedimentary features become more prevalent. South-north-flowing rivers such as the Ob, Lena, and Yenisey form the major transport arteries of the region, despite being frozen over for most of the year.

Highland Asia This region includes not only the Himalayas but also the great mountain ranges that radiate from the high Pamirs to the northwest of the Indian subcontinent: the Tian Shan to the northeast, the Kunlun Shan to the east, the Karakoram and Himalayas to the southeast, and the Hindu Kush to the southwest. Between these ranges are the high plateaux of Tibet (the most extensive in the world) and Mongolia. This central mass of mountains and plateaux forms an effective east-west and north-south barrier, enclosing regions of inland drainage such as the Tarim Basin, yet giving rise to many of the major rivers of Southeast Asia, namely the Indus, Ganges, Brahmaputra, Salween, Mekong, Chang Jiang, and Huang He. From this central mass, ridges like fingers point east and southeast into China and Southeast Asia, forming the mountainous backbone of Indochina and Peninsular Malaysia. The offshore islands are also very mountainous, forming a broken arc from the Kamchatka peninsula to Java and Sumatra, and are related formations.

The arid zone The isolating barrier effect of the mountain mass appears clearly in the area lying to the north: the Central Asian arid zone, comprising the Takla Makan, Gobi, and Ordos deserts. These are areas of inland drainage covered with wind-borne loess and silt deposited by rivers.

Tropical Asia This comprises South and Southeast Asia, the latter including the Indonesian and Philippine archipelagos. South Asia is usually limited to peninsular India, the island of Sri Lanka, and the Indo-Gangetic Plain. The peninsula is an uplifted and terraced plateau with lava intrusions (the Deccan. The Indo-Gangetic Plain is formed from the combined flood-plains of the Indus, Ganges, and Brahmaputra, and is a deep marginal depression running west-east parallel to the Himalayas. Mainland Southeast Asia is a complex region of folded mountain chains, decreasing in height southwards, interspersed with fertile river valleys.

The insular or island arc This consists of the archipelagos that border the southeast margin of Asia. These islands are a product of volcanism and coral reef building. They are bordered by deep ocean trenches and are characteristically unstable and mountainous.

Climate Differences between the climatic conditions of the various regions are determined to a considerable degree by topography. Extremes are again evident; Siberia is the world's coldest place, the wettest is Cherrapunji in Assam, and Asia also has the world's driest regions. The climates range from Arctic in the far north to equatorial in the south. To the south and east of the central mountain mass the dominant feature is the monsoon, where changes of pressure and temperature in the interior bring cool, dry, outward-blowing winds in winter and hot, moisture-laden, inward-blowing winds in summer. Vegetation and soil types correspond roughly to the climate regimes that prevail; a continental climate prevails over a large part of Asia. The Arctic air mass from the north and the tropical air mass from the south converge over the central mountain mass of the Himalayas, but it is the alternate heating and cooling of the land mass of Asia and the reversal of the trade winds causing the winter and summer monsoons that always dominate any discussion of Asia's climate.