Mountains, Plateaus and Plains
Master the geomorphology of the Earth's primary landforms. Understand the classification of fold, block, and volcanic mountains, the economic significance of mineral-rich plateaus, and depositional plain formations.
1. Mountains: Classification & Major Ranges
Mountains are elevated landforms rising abruptly above the surrounding terrain. Based on origin, they are classified into four main types:
A. Fold Mountains
Formed by compressional forces at convergent plate boundaries. Earth's crust folds into synclines (troughs) and anticlines (crests).
- Young Fold Mountains: Characterized by high, rugged peaks and deep valleys. Examples: Himalayas (Asia), Alps (Europe), Rockies (North America), Andes (South America), Atlas (Africa).
- Old Fold Mountains: Geologically older, low height, rounded peaks due to millions of years of erosion. Examples: Urals (Russia), Appalachians (USA), Aravallis (India). *The Aravallis are the oldest fold mountains in the world.*
B. Block Mountains (Horst & Graben)
Formed when the Earth's crust fractures due to tensional or compressional forces, causing blocks to move vertically.
- The uplifted blocks are called Horsts (Block Mountains), and the subsided blocks are called Grabens (Rift Valleys).
- Examples: Black Forest (Germany) and Vosges (France) separated by the Rhine Rift Valley; Salt Range (Pakistan); Satpura and Vindhya ranges in India separated by the Narmada Rift Valley; Sierra Nevada (USA - largest block mountain in the world).
C. Volcanic Mountains
Formed by the accumulation of lava and pyroclastic materials around a volcanic vent.
- Examples: Mount Fuji (Japan), Mount Kilimanjaro (Tanzania), Mount Cotopaxi (Ecuador), Mount Vesuvius (Italy), Mount Popa (Myanmar), Krakatoa (Indonesia).
D. Residual / Relict Mountains
Formed by the denudation of existing mountains or plateaus by erosional agents (water, wind) leaving resistant rocks standing.
- Examples: Aravallis, Nilgiris, Parasnath, Rajmahal, and Western/Eastern Ghats in India; Catskill Mountains in the USA.
2. Plateaus: Types & Economic Significance
Plateaus are elevated, flat-topped tablelands rising steeply from surrounding areas. They cover about 33% of the land surface. Based on geographical location, they are classified as:
A. Classification of Plateaus
- Intermontane Plateaus: Highest and most extensive, surrounded by fold mountains on all sides. Examples: Tibetan Plateau (highest on Earth, ~4500m, bounded by Himalayas and Kunlun), Anatolia Plateau (Turkey, Pontic and Taurus ranges), Bolivian Plateau (Andes), Colorado Plateau (Rockies).
- Piedmont Plateaus: Bordered by mountains on one side and plains or oceans on the other. Example: Patagonian Plateau (Argentina), Piedmont Plateau (USA).
- Continental Plateaus: Rise abruptly from plains or oceans, far from mountain belts. Examples: Deccan Plateau (India), Canadian Shield, Katanga Plateau (Central Africa).
- Volcanic / Lava Plateaus: Formed by quiet fissure eruptions of highly fluid basaltic lava. Examples: Deccan Traps (India), Columbia-Snake Plateau (USA).
B. Major Global Plateaus & Mineral Wealth
Plateaus are geological storehouses of minerals, making them highly significant economically:
| Plateau Name |
Location |
Major Mineral Resources |
RO/ARO Key Fact |
| Chhota Nagpur Plateau |
Eastern India (Jharkhand/West Bengal) |
Coal, Iron Ore, Mica, Bauxite |
Known as the 'Ruhr of India' due to massive industrial concentration. |
| Katanga Plateau |
Democratic Republic of Congo |
Copper, Cobalt, Uranium |
Crucial source of global cobalt for rechargeable batteries. |
| Kimberley Plateau |
Western Australia |
Diamonds, Gold, Iron Ore |
Hosts the Argyle diamond mine, famous for pink diamonds. |
| Laurentian Plateau (Canadian Shield) |
Canada |
Nickel, Copper, Iron, Gold |
One of the oldest geological shields on Earth. |
| Potwar Plateau |
Pakistan |
Rock salt, Petroleum, Limestone |
Bounded by the Salt Range block mountains. |
| Loess Plateau |
Northern China |
Highly fertile windblown soil |
Formed by deposition of yellow dust from the Gobi desert. |
3. Plains: Structural, Erosional & Depositional Forms
Plains are relatively low-lying, flat or gently undulating land surfaces. They are divided into three categories based on origin:
A. Structural Plains
Formed by the upliftment of a portion of the seafloor or continental shelf, or by horizontal bedding of rocks.
- Examples: Great Plains of the USA, Russian Platform, Central Lowlands of Australia.
B. Erosional Plains (Peneplains & Pediplains)
Formed when agents of erosion wear down elevated landforms over long periods.
- Peneplain: A nearly flat featureless plain formed in humid regions by river erosion (W.M. Davis model). Residual hills left behind are called Monadnocks.
- Pediplain: Formed in arid or semi-arid regions by wind action and scarp retreat (L.C. King model). Residual hills are called Inselbergs.
- Karst Plain: Formed by limestone dissolution.
C. Depositional Plains
Formed by the deposition of sediments transported by wind, water, glaciers, or lakes.
- Alluvial / Flood Plains: Deposited by rivers. Example: Indo-Gangetic Plains.
- *Bhabar:* Porous gravelly belt at foothills where streams disappear.
- *Terai:* Marshy, damp belt next to Bhabar with dense forest.
- *Bhangar:* Older alluvial soil, dry, less fertile, containing calcareous nodules (Kankar).
- *Kadar (Khadar):* Newer, highly fertile alluvial soil replenished annually by floods.
- Loess Plains: Deposited by wind-borne fine silt. Highly fertile. Example: Loess Plain of North China.
- Lacustrine Plains: Formed when lakes are filled with sediments and dry up. Example: Kashmir Valley, Manipur Basin.
- Glacial Plains: Formed by outwash deposits of melting glaciers.
Geological Orogenies (Mountain Building)
- > 570 Mya — Pre-Cambrian Orogeny: Oldest mountain building phase. Formed residual ranges like the Aravallis in India and Laurentian shields.
- 400 Mya — Caledonian Orogeny: Silurian-Devonian periods. Formed the Appalachian Mountains of North America and Scottish Highlands.
- 300 Mya — Hercynian Orogeny: Permocarboniferous period. Formed the Ural Mountains, Pennines (UK), and Tien Shan range in Central Asia.
- 60 Mya to Present — Alpine Orogeny: Tertiary period. Formed the highest young fold mountains: Himalayas, Andes, Rockies, Alps, and Caucasus.
Key Questions & Answers
- What is the difference between a Horst and a Graben?
- A Horst is an uplifted block of crust between two faults (Block Mountain), while a Graben is a subsided block between two faults (Rift Valley).
- Which plateau is known as the 'Ruhr of India' and why?
- The Chhota Nagpur Plateau . It is extremely rich in mineral resources like coal, iron ore, and mica, resembling the Ruhr industrial region of Germany.
- What are Loess plains and how are they formed?
- They are depositional plains formed by the accumulation of windblown silt/dust (usually yellow in color, highly fertile, prominent in Northern China).
- What is the difference between Peneplains and Pediplains?
- Peneplains are formed by water erosion (fluvial cycle of Davis) in humid areas, whereas Pediplains are formed by wind erosion and scarp retreat (King's cycle) in arid/semi-arid regions.
Memory Aids
- Mnemonic 1: Major Young Fold Mountains: Recalls the young fold mountains formed during the Alpine phase: • U — Urals (often grouped with Hercynian but has Alpine roots) • R — Rockies (North America) • A — Andes (South America) • A — Alps (Europe) • H — Himalayas (Asia) • M — Atlas (Africa)
- Mnemonic 2: Block Mountains vs Rift Valleys: Recalls tectonic block terms: • Horst is the Upthrown block (forming Block Mountains). • Graben is the Downthrown block (forming Rift Valleys).
- Mnemonic 3: Intermontane Plateaus: Recalls plateaus surrounded by mountain ranges on all sides: • T — Tibet (surrounded by Himalayas & Kunlun) • A — Anatolia (Turkey; surrounded by Pontic & Taurus) • C — Colorado (USA; surrounded by Rockies) • B — Bolivian Plateau (surrounded by Andes)
Common Exam Traps
- Trap 1: Classifying the Ural Mountains as young fold mountains. While they are fold mountains, they are old fold mountains formed during the Hercynian orogeny (300 Mya), similar to the Appalachians, and are highly denuded.
- Trap 2: Believing the Deccan Plateau is an intermontane plateau. The Deccan Plateau is a volcanic/lava plateau (Deccan Traps) and a continental plateau, not bounded by fold ranges like Tibet.
- Trap 3: Confusing Vosges and Black Forest block mountains. The Black Forest (Germany) and Vosges (France) are horsts separated by the Rhine Rift Valley (graben). Don't mix their locations.
- Trap 4: Assuming all plains are formed by rivers. Plains can also be structural (crustal uplift), erosional (glaciated/karst peneplains), or wind-deposited (loess plains).