Plains — Types and Distribution

4.1 Types of Plains

1. Structural Plains

Formed from flat-lying sedimentary rocks where erosion has not significantly altered the horizontal structure.

• Great Plains (Prairies) — USA and Canada: 1.3 million km² of flat to gently rolling grassland between Rocky Mountains and Mississippi River. Underlain by horizontal Cretaceous-Eocene sedimentary rocks. Breadbasket of North America (wheat, maize, sorghum) — also known as Tornado Alley (Oklahoma, Kansas, Texas).
• Russian Plain / East European Plain: The vast flat terrain of European Russia — one of the world's largest structural plains.

2. Depositional / Alluvial Plains

Formed by deposition of river sediments. Most fertile and densely populated lands on Earth.

Plain	Rivers	Length	Key Fact
Indo-Gangetic Plain	Indus, Ganga, Brahmaputra	~3,200 km	World's largest alluvial plain; 700 million people; 25–300 m thick alluvium
Mississippi Delta Plain	Mississippi-Missouri	—	Vast river delta and coastal plain; New Orleans below sea level
Amazon Basin	Amazon + 1,100 tributaries	~6,000 km	Tropical rainforest on alluvial plain; largest river basin by discharge
Nile Delta	Nile River	—	Historically most productive farmland; ancient Egyptian civilisation
Mekong Delta	Mekong River	—	Vietnam's rice bowl; 18 million people; sinking due to groundwater extraction

3. Erosional Plains

Formed by wearing down of elevated terrain over long periods.

• Peneplain: "Almost a plain" — ancient mountains reduced to gently rolling near-flat surface (e.g., Canadian Shield, Saharan Shield)
• Pediplain: Desert erosion creates flat surfaces around residual hills (inselbergs) — found in arid Africa and Australia
• Karst Plain: Dissolution of limestone creates sinkholes, caves, and flat ground (Florida, Yucatán, Guizhou China)

4. Coastal Plains

Formed by marine deposition (beaches, tidal flats) or by uplift of former sea floor.

• Atlantic Coastal Plain (USA): Extends from Long Island to Florida; width 50–300 km; gently slopes seaward
• Gulf Coastal Plain (USA): Mississippi Delta; extensive petroleum-bearing sediments
• Eastern and Western Coastal Plains of India: Coromandel Coast (SE) and Malabar Coast (SW); major rice-growing areas

---