74. Mountains, Plateaus, Plains, Deserts: Types and Distribution — Full Notes

CORE Key Points at a Glance

1. 1

   Fold Mountains

   • Most common and highest mountain type
   • Formed when tectonic plates collide, compressing sedimentary strata into folds
   • Himalayas — India-Eurasia collision, ~50 Ma
   • Andes — Nazca-South American plates, ~25 Ma
   • Alps — Africa-Eurasia, ~35 Ma; Rockies — Farallon-North American, ~85–55 Ma
2. 2

   Block Mountains / Horsts

   • Form when land between parallel faults is uplifted
   • Raised block = Horst; sunken block = Graben
   • Vosges and Black Forest flank Rhine Graben, Germany
   • Vindhyas and Satpura (India); Sierra Nevada (USA)
3. 3

   Volcanic Mountains

   • Form by accumulation of lava, ash, and volcanic material
   • Shield volcanoes — broad, gentle slopes, basaltic lava: Mauna Loa (Hawaii, 10,210 m from ocean floor — Earth's largest by volume)
   • Composite/Strato volcanoes — steep-sided, explosive, andesitic: Mt. Fuji (Japan, 3,776 m), Mt. St. Helens (USA)
4. 4

   Plateaus

   • Elevated flatlands with steep sides — often called "tablelands"
   • Intermontane — surrounded by mountains: Tibetan Plateau avg 4,500 m (world's highest)
   • Continental/Lava — basaltic flows: Deccan Plateau (600 m avg), Columbia Plateau (USA)
   • Piedmont — at mountain foothills: Appalachian Plateau, Malwa Plateau (India)
5. 5

   Plains

   • Low-lying, flat or gently undulating land
   • Structural — flat rock beds: Great Plains (USA, Canada)
   • Depositional/Alluvial — river sediments: Indo-Gangetic Plain, Mississippi Delta
   • Erosional — peneplains, pediplains (worn-down landscapes)
   • Coastal — Atlantic Coastal Plain, USA
6. 6

   Deserts

   • Cover ~33% of Earth's land surface
   • Hot deserts (subtropical, 20°–30° lat.): Sahara (9.2 million km², world's largest hot desert), Arabian Desert (2.3 million km²), Thar (Rajasthan, 0.2 million km²)
   • Cold deserts: Gobi (Mongolia-China, 1.3 million km²), Patagonia (South America), Ladakh (India, rain shadow)
7. 7

   Australian Deserts — 2023 PYQ (2 marks)

   • Australia has six major deserts covering ~44% of its land
   • Great Victoria Desert — largest, 424,400 km²
   • Great Sandy (267,250 km²), Tanami (184,500 km²), Simpson (176,500 km²)
   • Gibson Desert (156,000 km²), Little Sandy Desert (111,500 km²)
   • All located in the interior and western regions
8. 8

   Rocky Mountains — PYQ 2021 (5 marks)

   • Extend 4,800 km from northern British Columbia (Canada) to New Mexico (USA)
   • Fold and thrust mountain system — formed during Laramide Orogeny (85–55 Ma)
   • Highest peak: Mount Elbert (4,399 m)
   • Form the Continental Divide — separates Pacific drainage from Atlantic/Gulf of Mexico drainage
9. 9

   Himalayan Mountain System

   • Spans ~2,400 km; contains 10 of the world's 14 peaks above 8,000 m
   • Himadri (Greater Himalayas, avg 6,000 m+; Mt. Everest 8,848.86 m at Nepal-China border)
   • Himachal (Lesser Himalayas, 3,700–4,500 m)
   • Shiwaliks (Outer Himalayas, 900–1,200 m)
10. 10

    Andes Mountains

    • World's longest continental mountain range — approximately 7,000 km along South America's western coast
    • Highest peak: Aconcagua (6,961 m) in Argentina — highest point in Western and Southern Hemispheres
    • Formed by subduction of the Nazca Plate under the South American Plate
11. 11

    Tibetan Plateau

    • World's highest and largest plateau — elevation averaging 4,500 m, area ~2.5 million km²
    • Called the "Roof of the World" and "Third Pole" — stores 37% of world's freshwater in glaciers
    • Source of major Asian rivers: Yangtze, Yellow River, Brahmaputra, Mekong, Indus, Salween
12. 12

    Desert Formation Mechanisms

    • Subtropical high pressure (Hadley Cell subsidence) — Sahara, Arabian Desert
    • Rain shadow effect — Gobi (blocked by Himalayas/Tibetan Plateau), Patagonia (Andes), Thar (Aravalli partially)
    • Cold ocean currents (coastal deserts) — Namib (Benguela Current, Africa), Atacama (Humboldt Current, Chile — world's driest; some areas no rainfall in 400 years)
    • Continental interiors (distance from oceanic moisture) — Central Asian steppes