Plateaus and Plains

Plateaus and Plains

Introduction & Conceptual Foundation

• Plateau: An elevated flat landmass that rises abruptly above the surrounding area on at least one side. They are often referred to as "tablelands." Plateaus cover about 45% of the Earth's land surface and are characterized by a flat or gently undulating summit and steep side slopes.
• Plain: A broad, relatively flat or gently rolling area of land with low relief and low elevation. Plains are generally located below 200 meters above sea level, although some high-altitude structural plains exist. They represent the most stable and agriculturally productive zones of the continental crust.

UPSC Prelims Perspective

1. Classification of Plateaus

• Intermontane Plateaus: These are the highest, largest, and most complex plateaus on Earth. They are partially or completely surrounded by fold mountain ranges.
  • Examples: Tibetan Plateau (enclosed by the Himalayas and Kunlun Mountains), Bolivian Altiplano (Andes), and the Anatolian Plateau (Turkey, flanked by Pontic and Taurus ranges).
• Piedmont Plateaus: These plateaus are flanked by mountains on one side and by a plain or an ocean on the opposite side.
  • Examples: Patagonian Plateau in South America (east of the Andes) and the Piedmont Plateau in the eastern United States (east of the Appalachians).
• Continental Plateaus: Large-scale plateaus that rise abruptly from the surrounding lowlands or seas. They are associated with tectonic uplift of stable continental blocks (shields).
  • Examples: Deccan Plateau of India, Laurentian Shield of Canada, and the Brazilian Highlands.
• Volcanic (Lava) Plateaus: Formed by the accumulation of successive sheets of basaltic lava erupted through fissures (non-explosive eruptions).
  • Examples: Columbia-Snake Plateau (USA) and the Deccan Traps (India).
• Dissected Plateaus: Plateaus that have been deeply eroded by rivers and wind, leaving behind rugged, hill-like features separated by deep canyons.
  • Example: Colorado Plateau (USA).

Global Distribution & Resources of Major Plateaus

Plains Classification

1. Erosional Plains

• Peneplains (Rivers): Developed during the final stage of the fluvial cycle of erosion (concept popularized by W.M. Davis). Rivers erode the highlands down to base level, leaving a gently undulating plain. Residual, resistant rock outcrops that escape erosion are called Monadnocks (or residual hills).
• Pediplains (Winds): Formed in arid and semi-arid regions through the retreat of mountain slopes (pediment coalescence) due to wind action and sheetwash (concept by L.C. King). The residual hills in pediplains are known as Inselbergs.
• Glacial Plains: Created by ice-sheets stripping away topsoil and leaving flat, scoured rocky surfaces (e.g., plains of Finland).

2. Depositional Plains

• Alluvial Plains: Formed by river deposition. When a river loses velocity, it deposits silt, clay, and sand. Key sub-types include floodplains, alluvial fans, and deltaic plains (e.g., Indo-Gangetic Plains, Mississippi Plain).
• Coastal Plains: Formed by the deposition of marine sediments by waves and currents, or due to the tectonic emergence of a shallow continental shelf (e.g., East Coastal Plain of India).
• Loess Plains: Formed by wind-blown deposits of fine, non-stratified, yellowish silt and clay transported over long distances (e.g., Loess Plains of Northern China).
• Lacustrine Plains: Formed when a lake basin is filled with silt and sediment over time, and the lake eventually drains (e.g., Valley of Kashmir, Manipur Basin).

3. Structural Plains

UPSC Mains Perspective

Economic and Ecological Significance of Plains and Plateaus

1. Economic Geography of Plateaus

• Mineral Wealth: Plateaus are the geological repositories of the Earth's ancient mineral wealth. The Precambrian shields (e.g., Chhota Nagpur Plateau in India, Canadian Shield) contain the largest deposits of metallic ores.
• Hydroelectric Power: The steep margins of plateaus where rivers plunge down (forming waterfalls) provide ideal sites for generating hydroelectric power (e.g., waterfalls of the Western Ghats and Chhota Nagpur).
• Agriculture limitations: Agricultural activities are generally restricted to volcanic plateaus with fertile soils (like the Deccan lava plateau) or river valleys, as the rocky terrain and semi-arid climates of many plateaus limit extensive farming.

2. Socio-Economic Geography of Plains

• Cradles of Civilization: Plains support over 80% of the global population. The availability of flat land, fertile alluvial soils, and perennial water supply makes them ideal for intensive agriculture (e.g., the Indo-Gangetic Plains support one of the highest population densities in the world).
• Industrialization and Infrastructure: Flat terrain minimizes the cost of constructing railways, roads, canals, and urban settlements, transforming plains into major industrial and transport corridors.
• Vulnerability to Natural Disasters: Being low-lying, depositional plains are highly susceptible to river floods (e.g., Koshi in Bihar, Yangtze in China) and coastal storm surges, which are increasingly aggravated by climate change.

Practice Questions

Prelims Practice Question

• Peneplains are formed by river (fluvial) erosion at the end stage of the geomorphic cycle, and their characteristic residual resistant hills are called Monadnocks (hence, A matches with 2 and X).
• Pediplains are formed by wind and sheetwash erosion in arid/semi-arid regions, and their characteristic residual steep-sided hills are called Inselbergs (hence, B matches with 1 and Y).

Mains Practice Question

Answer Framework / Approach:

• Introduction (30-40 words): Define plateaus and plains. Briefly state how their geological origins (endogenetic upliftment vs. exogenetic deposition) govern their resource profiles.
• Body Section 1: Plateaus as Mineral Storehouses (90-100 words):
  • Explain that ancient continental plateaus (shields) consist of igneous and metamorphic rocks rich in minerals.
  • Provide examples: Chhota Nagpur Plateau (India's mineral heartland - coal, iron, mica), Katanga Plateau (copper belt), Laurentian Shield (iron, nickel), and Western Australian Plateau (iron ore, gold).
  • Mention volcanic plateaus forming fertile black soils suitable for cash crops (e.g., cotton in the Deccan Traps).
• Body Section 2: Plains as Agricultural Breadbaskets (90-100 words):
  • Detail how depositional plains (alluvial, loess) are formed by constant river siltation, creating deep, fertile, moisture-retentive soils.
  • Provide examples: Indo-Gangetic Plains (paddy and wheat cultivation), Great Plains of USA (wheat belt), Loess Plains of China (agriculture along the Yellow River).
  • Discuss the ease of irrigation, mechanization, and transport infrastructure in plains.
• Conclusion (30-40 words): Emphasize that a balanced regional development strategy must integrate the mineral-rich extraction industries of plateaus with the agricultural output and food security provided by plains, while addressing ecological challenges like mining-induced degradation and agricultural runoff.

Recommended Articles for Deeper Study

• Previous Topic: Classification and Orogenesis of Mountains
• Next Topic: Igneous Rocks Classification
• Related Topic: Sedimentary Rocks
• Related Topic: Metamorphic Rocks
• Related Topic: Rock Cycle