Key Points at a Glance

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

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)

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)

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)

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

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)

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

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

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)

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

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

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