Physical Geography: Understanding Continental Landforms
Continental landforms result from billions of years of geological processes. The theory of plate tectonics, confirmed in the 1960s, explains how continents drift across Earth's surface, colliding to form mountains, splitting to create oceans, and constantly reshaping the planet's surface. Understanding these processes helps explain why continents look and function as they do today.
The supercontinent Pangaea, existing 335-175 million years ago, contained all current continents fused together. Its breakup created the Atlantic Ocean and separated the Americas from Africa and Europe. Evidence for Pangaea includes matching fossils and rock formations across now-separated continents, similar glacial deposits in tropical regions, and the jigsaw-puzzle fit of continental margins. This continental drift continues today - Africa and South America separate by 2.5 centimeters annually, while India pushes into Asia at 5 centimeters per year, raising the Himalayas.
Mountain ranges define continental geography and influence everything from weather to human settlement. Asia's Himalayas, formed by India's collision with Asia, include all 14 peaks above 8,000 meters. The Americas' cordillera system runs from Alaska to Tierra del Fuego, including the Rockies and Andes. Africa's Great Rift Valley, stretching 6,000 kilometers from Lebanon to Mozambique, marks where the continent is slowly splitting apart. Europe's Alps, Pyrenees, and Carpathians create natural boundaries between nations. Australia's Great Dividing Range, though modest in height, influences the continent's entire climate pattern by blocking moisture from reaching the interior.
River systems shape continental interiors and support huge populations. Asia's Yangtze, Yellow, Ganges, and Mekong rivers sustain billions of people. Africa's Nile, the world's longest river at 6,650 kilometers, enabled ancient Egyptian civilization. South America's Amazon carries more water than the next ten largest rivers combined, draining 40% of the continent. North America's Mississippi-Missouri system drains 41% of the continental United States. Europe's Rhine, Danube, and Volga have served as trade routes for millennia. Australia's Murray-Darling system, though often dry, supports most of the continent's agriculture.
Deserts occupy significant portions of most continents, created by global atmospheric circulation patterns, mountain rain shadows, or distance from moisture sources. Africa's Sahara, Earth's largest hot desert at 9 million square kilometers, equals the United States in size. Asia contains the Gobi, Arabian, and Thar deserts. North America's Mojave, Sonoran, and Chihuahuan deserts result from mountain rain shadows. South America's Atacama Desert, Earth's driest place, receives less than 1 millimeter of rain annually in some areas. Australia's interior deserts cover 70% of the continent. Only Europe lacks major deserts, though Spain contains semi-arid regions. Antarctica, technically Earth's largest desert, receives less precipitation than the Sahara but in the form of snow.
Continental shelves, the submerged edges of continents, extend far beyond visible coastlines and contain vital resources. These shallow seas, typically less than 200 meters deep, support most ocean life and contain oil, gas, and mineral deposits. The Siberian Shelf extends 1,500 kilometers into the Arctic Ocean. The Patagonian Shelf supports one of the world's richest fisheries. Northwest Europe's continental shelf once connected Britain to mainland Europe during ice ages when sea levels were lower. Understanding continental shelves is crucial for maritime boundaries, resource exploitation, and climate change impacts as rising seas flood these areas.