World Physical Geography

Core concept

Continents and oceans

There are seven continents and five oceans. By area, largest to smallest, the continents are Asia, Africa, North America, South America, Antarctica, Europe and Australia. Asia is both the largest and the most populous, and it holds the highest point on land (Mount Everest) and one of the lowest (the Dead Sea shore). Africa is the only continent crossed by the equator, both tropics (Cancer and Capricorn) and the prime meridian, and it holds the longest river (the Nile) and the largest hot desert (the Sahara). South America has the longest mountain range above sea level (the Andes), the largest river by discharge (the Amazon), the largest rainforest, and the driest desert (the Atacama). North America has the Rocky Mountains, the Appalachians and the Great Lakes (the largest group of freshwater lakes). Antarctica is the highest, driest, coldest and windiest continent, a cold desert that holds most of the world's freshwater ice. Europe is the second smallest, deeply indented and the only continent with no hot desert. Australia is the smallest continent and the only one that is a single country, with the dry Outback interior.

The five oceans by size are the Pacific (largest and deepest), the Atlantic (the S-shaped second), the Indian (the only one named for a country), the Southern (Antarctic), and the Arctic (smallest and shallowest, largely ice-covered).

Mountains by origin

• Fold mountains: young, formed by crustal compression at convergent plate boundaries. The Himalaya (Asia), the Alps (Europe), the Andes (South America) and the Rockies (North America) are all young fold mountains. The Himalaya-Karakoram holds all fourteen peaks above 8,000 m.
• Block mountains (horsts): uplifted between faults, with rift valleys (grabens) between, such as the Vosges and Black Forest flanking the Rhine rift.
• Residual or relict mountains: old ranges worn down by erosion, such as the Aravallis (one of the world's oldest), the Appalachians, and the Urals (the conventional Europe-Asia divide).
• Volcanic mountains: built from erupted material, such as Kilimanjaro, Fujiyama and the Cascades.

Rivers and lakes

Rivers follow relief and rainfall. The Nile (Africa) is the longest river; the Amazon (South America) is the largest by discharge and drains the largest basin. The Yangtze is Asia's longest. Lakes occupy basins of varied origin: tectonic (Baikal, the Caspian, the East African Rift lakes Tanganyika and Victoria), glacial (the Great Lakes, the Finger Lakes), volcanic (crater lakes), and saline closed basins (the Dead Sea, the Aral Sea). The Caspian Sea is the largest lake by area; Baikal is the deepest and the largest by volume; Lake Superior is the largest freshwater lake by area; Lake Victoria is Africa's largest and the largest tropical lake.

Major rivers and what they drain

A divide (watershed) separates river basins; an interior or endorheic drainage system (the Volga to the Caspian, rivers vanishing in the Gobi) does not reach the sea.

Deserts

Hot deserts cluster under the subtropical high-pressure belts at about 30° N and S, where descending dry air suppresses rain (the Sahara, Arabian, Kalahari, Australian, Thar). They also form on cold-current western coasts where cool air gives little rain (the Atacama in Chile, the Namib in Namibia), and in continental interiors far from the sea or in rain shadows (the Gobi of Mongolia and China, the Patagonian). Cold deserts include the Gobi and the polar deserts of Antarctica and the Arctic. The Sahara is the largest hot desert; Antarctica is the largest desert overall.

Plateaus, highlands and the great plains

Plateaus are elevated, relatively flat uplands. The Tibetan Plateau ("the roof of the world") is the highest and largest, the source of Asia's great rivers; the Deccan Plateau covers peninsular India; other major ones are the Brazilian, the East African, the Iranian, the Anatolian and the Colorado plateaus. The world's largest lowland plains include the Indo-Gangetic plain, the North European plain, the West Siberian plain and the Amazon and Mississippi lowlands, the world's most fertile and densely settled regions.

Major lakes by type (high-yield)

World climatic zones

Climates grade from the equator to the poles, following the pressure belts and winds. The standard sequence (Koeppen-flavoured but in the descriptive form Leong uses):

• Equatorial (tropical rainforest): hot and wet all year, heavy convectional rain (the Amazon, Congo, Indonesia, Malaysia).
• Tropical wet and dry (savanna): a marked dry season; tall grass and scattered trees (the African Sudan belt, the Brazilian Campos, the Venezuelan Llanos, northern Australia).
• Hot desert: under the subtropical highs; extreme aridity and a large day-night temperature range (the Sahara, Arabian, Thar).
• Mediterranean: dry hot summer, wet mild winter, on the western margins of continents at about 30 to 40° (central Chile, California, the Mediterranean basin, the Cape region of South Africa, south-west Australia).
• Temperate grassland: continental interiors with hot summers, cold winters and moderate rain (the Prairies of North America, the Pampas of Argentina, the Steppes of Eurasia, the Veld of South Africa, the Downs and Canterbury of Australasia).
• Cool temperate: maritime west-coast (mild wet, north-west Europe, Pacific north-west USA) and continental interior types.
• Taiga (boreal): long cold winters with coniferous forest, across northern Canada and Siberia.
• Tundra: treeless, with permanently frozen subsoil (permafrost), on the Arctic fringe.
• Polar (ice cap): permanent ice, in Antarctica and Greenland.