Landforms: Types of Mountains, Plateaus, and Plains

• Mountains, plateaus and plains are the three major relief features of the second order, standing between the continents and ocean basins (first order) and the small landforms carved on them (third order).
  • They are raised or lowered chiefly by endogenic forces (folding, faulting, warping, volcanism) and then shaped by exogenic processes (weathering, rivers, ice, wind, waves).
  • Plains formed wholly by erosion or deposition are, strictly, third-order features, but they are studied with the rest.
• The three differ in height above the surroundings, slope and extent of the summit surface, not in absolute altitude.
  • The Tibetan Plateau stands higher than most mountain ranges, and the western Great Plains of the USA, at over 1,500 m, lie higher than many plateaus.
• A classical estimate puts plains at about two-fifths, plateaus at about one-third, hills at about one-seventh and mountains at about one-eighth of the land surface.
  • Modern mapping that counts high plateaus and rugged uplands as mountain land puts mountains at roughly a quarter of the land surface, so the shares depend on the definition used.

Feature	Relief and slope	Summit	Chief origin	Indian example
Mountain	High local relief, steep slopes	Narrow peaks and ridges	Folding, faulting, volcanism	Himalaya, Aravalli
Plateau	Rises steeply on at least one side	Broad, nearly flat top	Uplift, lava flooding, warping	Deccan, Chota Nagpur
Plain	Low relief, gentle slopes	Flat to rolling	Deposition, erosion, emergence	Ganga plain, coastal plains

Mountains

Meaning of Mountain

• A mountain is a landmass that rises steeply and conspicuously above its surroundings, with high local relief, steep slopes and a small summit area.
  • A hill is lower and gentler; there is no universal dividing line, and many schemes treat local relief of about 600 m as the threshold.
  • The UN mapping of mountain land (UNEP-WCMC, 2000) combines elevation, slope and local relief rather than height alone.
• Mountains are built by tectonic forces or volcanism and worn down by rivers, glaciers and mass movement; most occur not as isolated summits but in long ranges and systems.
• Their human importance is out of proportion to their area:
  • They are home to about 1.1 billion people (15% of the world’s population).
  • They supply an estimated 60–80% of the world’s freshwater, through snow, glaciers and orographic rain.

Forms of Mountains

Form	Meaning	Example
Ridge	Long, narrow, high hill line; one slope often steeper	Siwalik ridges
Range	Linear belt of ridges, peaks and valleys of one age	Pir Panjal Range
Chain	Parallel ranges of different periods, at times separated by plateaus	Ranges of the Western Cordillera
System	Several ranges of the same period, separated by valleys	The Himalaya (Greater, Lesser, Siwalik)
Group	Irregular cluster of mountain systems	Pamir Knot and its offshoots
Cordillera	Community of ranges, chains and systems	Western North American Cordillera

Classification of Mountains

By Height

Class	Height
Low mountains	700–1,000 m
Rough mountains	1,000–1,500 m
Rugged mountains	1,500–2,000 m
High (lofty) mountains	Above 2,000 m

By Location

• Continental mountains stand on the land.
  • Coastal mountains run close to and parallel to a coast: the Rockies, Andes, Appalachians, and the Western and Eastern Ghats of India.
  • Inland mountains lie within the continent: the Urals, Vosges, Black Forest, Kunlun, Tien Shan, Altai, and in India the Himalaya, Aravalli, Satpura, Maikal and Kaimur.
• Oceanic mountains rise from the ocean floor and continental shelves; most are volcanic and many never reach the surface.
  • Measured from its base on the sea floor, Mauna Kea (Hawaii) is over 10,000 m tall, though its summit is only about 4,207 m above sea level.
  • The mid-ocean ridges form the longest mountain system on Earth, almost wholly submerged.

By Mode of Origin

• Tectonic (original) mountains are produced by forces from within the Earth:
  • Fold mountains, by compression.
  • Block mountains, by faulting under tension or compression.
  • Dome mountains, by magmatic intrusion or upwarping.
  • Volcanic mountains (mountains of accumulation), by piling up of erupted material.
• Residual (relict or circum-erosional) mountains are the worn-down remnants of older uplands.
• The contraction, drift and convection theories of mountain building differ on the driving force, but the resulting mountain types are the same.

Fold Mountains

• Fold mountains are formed when thick piles of sedimentary rock are crumpled into anticlines and synclines by lateral compression.
  • In plate terms they rise at convergent boundaries, by ocean–continent subduction (Andes) or continent–continent collision (Himalaya, Alps).
  • They are the highest and most extensive mountains, found on every continent.

Formation

• The sediments accumulate for long periods in elongated, subsiding marine troughs, the geosynclines of the classical account.
  • Shallow-water marine fossils in rock sequences more than 12 km thick show that the trough floor sank as it filled.
• As the bordering plates converge, the fill is squeezed into folds, reverse faults and thrust sheets, thickened and lifted.
  • Weak layers such as salt or shale let the cover slide and fold more intensely.
• Compression rising in intensity turns open anticlines, synclines and recumbent folds into overthrust sheets and nappes carried tens of kilometres.

Types of Fold Mountains

Basis	Type	Features	Example
Nature of folds	Simple	Open, wave-like anticlines and synclines	Jura (Switzerland–France)
Nature of folds	Complex	Tight recumbent folds and nappes	Alps, Himalaya
Stage of denudation	Young	Little worn, sharp crests, high relief	Himalaya, Andes
Stage of denudation	Mature	Worn into monoclinal ridges and valleys	Appalachians
Period of origin	New (Alpine)	Formed in the last ~66 million years	Rockies, Alps, Himalaya
Period of origin	Old (pre-Alpine)	Formed over 250 million years ago, now relict	Aravalli, Urals

• A truly “young” fold mountain hardly exists in the strict sense, because denudation begins while uplift is still going on.

Characteristics

• Sedimentary and marine: built mainly of folded sedimentary rocks bearing marine fossils, often partly metamorphosed.
• Great thickness of sediments, pointing to prolonged subsidence of a shallow sea floor.
• Length far exceeds width:
  • The Himalaya run about 2,400 km west to east but are only 150–400 km wide.
  • The Andes stretch about 7,000 km, the longest continental range.
• Arcuate plan, with one slope convex (outer) and the other concave (inner): the Himalayan arc is convex to the south.
• Location along continental margins, trending either north–south (Rockies, Andes, facing the Pacific) or east–west (Alps, Himalaya, along the site of the former Tethys Sea).
• Active tectonics: young fold belts are seismically active and still rising, and carry the world’s highest peaks.

World and Indian Examples

• Himalaya: formed by the collision of the Indian and Eurasian plates, which began about 50 million years ago; convergence continues at a few centimetres a year.
  • Indian fold ranges also include the Purvanchal hills (Patkai, Naga, Mizo) and the partly submerged Andaman–Nicobar arc.
• Andes: raised by subduction of the Nazca Plate beneath the South American Plate.
• Alps, Atlas, Zagros, Rockies: other members of the young fold belts, the first three formed as Africa and Arabia closed against Eurasia.

Block Mountains

• Block (fault-block) mountains are upstanding blocks of crust bounded by faults, left high when neighbouring blocks sink or raised as a unit.
  • They often flank a rift valley or graben; the upstanding block is a horst.
  • Flat or gently sloping tops and steep, straight fault-scarp sides are their hallmark.

Modes of Formation

1. Middle block rises between two normal faults: a true horst with a flat summit and steep sides.
2. Side blocks sink while the middle block stays in place; common on high plateaus and broad domes.
3. Middle block sinks between two faults, forming a rift valley, and the side blocks stand up as block mountains, as with the Vosges and Black Forest on either side of the Rhine rift.

Types

• Tilted block mountains: one side a steep fault scarp, the other a gentle back slope; the Sierra Nevada of California (about 640 km long) is the classic case.
• Lifted block mountains (horsts): tabular summits with fault scarps on both sides.

Fault Theory and Erosion Theory

• Fault theory: Grove Karl Gilbert (1875), working in the Basin and Range province of the western USA, explained the ranges as faulted and tilted blocks; William Morris Davis and George Davis Louderback supported this view.
• Erosion theory: Josiah Edward Spurr (1901) argued that the same ranges were shaped by differential erosion of older Mesozoic mountains.
  • It found little support, because denudation can modify relief but cannot create a mountain.
• Current view: the Basin and Range is a province of crustal extension, where the stretched and thinned crust breaks along normal faults into alternating horsts and grabens.

Examples

• World: Vosges and Black Forest (Europe), Sierra Nevada, Wasatch Range and the Basin and Range ranges (USA), the Salt Range (Pakistan), and the shoulders of the East African Rift.
• India: the Satpura range stands as a horst between the Narmada and Tapi rift valleys; the Vindhyan scarp along the Narmada is also fault-controlled.

Volcanic Mountains

• Volcanic mountains (mountains of accumulation) are built where lava, ash and cinders pile up around a vent, layer upon layer.
  • Magma reaches the surface through cracks linked to plate boundaries (subduction zones, rifts) or hotspots.
  • Build-up takes thousands of years; on the ocean floor it can raise volcanic islands.
• Main forms of these volcanic cones:
  • Cinder cones: small, steep heaps of ejected fragments.
  • Shield volcanoes: broad, gentle domes built by fluid basaltic lava, such as Mauna Loa (Hawaii), which last erupted in 2022.
  • Composite cones (stratovolcanoes): steep cones of alternating lava and ash, such as Fuji, Vesuvius, Kilimanjaro.
• India: Barren Island (Andaman Sea) is India’s only active volcano; Narcondam is dormant.

Dome Mountains

• Dome mountains form where the crust is arched upwards by rising magma or by upward flexure, without much folding or faulting.
  • Varieties include laccolithic domes (Henry Mountains, Utah), batholithic domes, lava domes and salt domes.
  • Erosion strips the arched cover to expose a resistant core ringed by outward-dipping ridges, as in the Black Hills of South Dakota.
• India: the granite-gneiss batholithic domes that stud the Ranchi plateau are exhumed domes of this kind.

Residual Mountains

• Residual (relict) mountains are the resistant remnants of once-higher uplands, lowered by long denudation by running water, ice, wind and weathering.
  • They are mountains of denudation: their form now reflects erosion more than the force that first raised them.
  • Isolated survivors on a lowered surface are monadnocks or inselbergs.
• India has classic examples on the ancient Peninsula:
  • The Aravalli, a Precambrian fold belt reduced to low ridges, with Guru Shikhar (1,722 m) in Mount Abu as its highest point.
  • Parasnath (1,365 m) in Jharkhand, the Rajmahal hills, the Eastern Ghats and the Vindhyan ranges.
• How far a residual range extends is itself contested: the Supreme Court’s acceptance in November 2025 of a 100 m local-relief definition of the Aravalli hills was put on hold in December 2025 pending fresh expert review.

Classification by Period of Origin

Orogeny	Age	World examples	Indian examples
Precambrian	Before ~540 million years	Laurentian and Algoman (Canada), Fennoscandia, NW Highlands of Scotland	Aravalli, Eastern Ghats belt, Satpura belt, Dharwar ranges
Caledonian	Ordovician to Devonian (~490–390 million years)	Scotland, Ireland, Scandinavia, Taconic belt of the Appalachians, Brazilides	Absent as a distinct orogeny
Hercynian (Variscan)	Late Devonian to Permian (~380–280 million years)	Urals, Appalachians (final phase), Vosges, Black Forest, Harz, Brittany, Meseta, Tien Shan, Altai	Absent as a distinct orogeny
Alpine	Late Cretaceous to present (last ~66 million years)	Alps, Pyrenees, Carpathians, Atlas, Caucasus, Zagros, Taurus, Rockies, Andes	Himalaya, Purvanchal, Andaman–Nicobar arc

• The pre-Alpine belts are now old, deeply denuded and mostly relict, while the Alpine belts are young, high and seismically active.
• The Rockies were raised mainly in the Laramide phase (roughly 80–55 million years ago) at the Alpine end of this scale.
• Each orogeny records the closing of an ocean: the Caledonian closed the Iapetus, the Hercynian assembled Pangaea, and the Alpine is closing the Tethys, as plate tectonics explains.

Major Mountain Ranges and Peaks

Range	Continent	Length	Highest peak	Height
Himalaya	Asia	~2,400 km	Everest (Nepal–China)	8,848.86 m
Andes	South America	~7,000 km	Aconcagua (Argentina)	6,961 m
Alaska Range	North America	~650 km	Denali (USA)	6,190 m
Kilimanjaro massif	Africa	Isolated volcano	Uhuru Peak, Kibo (Tanzania)	5,895 m
Caucasus	Europe–Asia	~1,200 km	Elbrus (Russia)	5,642 m
Ellsworth Mountains	Antarctica	~350 km	Vinson Massif	4,892 m
Sudirman Range	Oceania	–	Puncak Jaya (Indonesia)	4,884 m
Alps	Europe	~1,200 km	Mont Blanc (France–Italy)	~4,806 m
Rockies	North America	~4,800 km	Mount Elbert (USA)	4,401 m

• The height of Everest (8,848.86 m) is the figure announced jointly by Nepal and China in December 2020.

Economic Significance of Mountains

• Storehouse of resources: metallic minerals, building stone, timber, medicinal herbs, lac and pasture.
• Water towers: snow- and rain-fed perennial rivers (Indus, Ganga, Brahmaputra) sustain irrigation and cities far downstream.
• Hydroelectricity: steep gradients and assured flow make mountain rivers ideal for hydel power.
• Fertile plains below: rivers carry silt from the ranges to build the alluvial plains at their feet.
• Climatic divides: the Himalaya block cold Central Asian winds and force orographic rain from the monsoon.
• Frontiers and defence: ranges act as natural political boundaries.
• Tourism, pilgrimage and biodiversity: hill stations, shrines and endemic species.
• Hazards: young ranges are prone to earthquakes, landslides and glacial lake outburst floods, as the Joshimath subsidence (2023) and the South Lhonak GLOF in Sikkim (October 2023) showed.

Plateaus

Meaning of Plateau

• A plateau is an extensive upland with a broad, nearly flat top, standing well above the neighbouring land and bounded on at least one side by a steep slope or escarpment.
  • Vernor C. Finch and Glenn T. Trewartha defined plateaus as tabular uplands with relief of more than about 500 feet (150 m).
  • Side walls commonly rise 300 m or more above the ground below.
• Plateaus cover about one-third of the land surface and occur on every continent.
• Heights vary widely: the Appalachian Plateau rises to about 1,000 m, the Colorado Plateau stands mostly above 1,500 m, and the Tibetan Plateau, averaging over 4,500 m across about 2.5 million km², is the highest and largest in the world.

Characteristics

• Flat to rolling summit surface with minor relief: scattered hills, domes and shallow valleys.
  • The Ranchi plateau rises abruptly about 300 m above the Damodar valley, and its top carries granite domes 50–100 m high.
• Steep margins and deep valleys: rivers leaving a plateau cut gorges and canyons and plunge over waterfalls.
  • Rivers draining north off the Rewa plateau to the Yamuna and Ganga have cut the Chachai, Keoti and Odda gorges, roughly 100–145 m deep.
  • The Grand Canyon of the Colorado River is about 446 km long and up to about 1.8 km deep.
• Varied surface materials:
  • Basalt-capped, as on the Mahabaleshwar and Panchgani tablelands, where thick laterite crowns the lava.
  • Sedimentary, as on the Rewa, Bhander and Rohtas plateaus of Vindhyan sandstone, shale and limestone.
• Dissection into flat-topped remnants: the North Koel and its tributaries have cut the Ranchi–Palamau uplands into mesas and buttes, locally called pats (Netarhat, Jamira, Khamar and Bagru pats, several bauxite-capped).
• Setting: some plateaus are enclosed by mountains (Tibet), some lie between mountains and a plain or sea (Appalachian Piedmont), and some are vast continental tablelands (Deccan, Siberian, Arabian).

Origin of Plateaus

• Downwarping of the surroundings, leaving a block standing high.
• Upwarping of part of a landmass by a few hundred metres, as in the western patlands of Ranchi and Palamau.
• Flooding by basaltic lava from fissures, as in the Deccan and Columbia plateaus.
• Uplift of unfolded forelands during mountain building, keeping the strata horizontal: the Cumberland Plateau west of the Appalachians preserves nearly flat coal beds.
• Uplift of a median mass: the unfolded core of a geosyncline, ringed by fold ranges, rises as a plateau (Tibet, Iran, Anatolia).
• Prolonged denudation of mountains into rugged uplands, as in parts of the Appalachians.
• Thick wind-borne deposits, as in the Loess Plateau of China (about 640,000 km²).

Classification of Plateaus

By Geographical Situation

• Intermontane plateaus are enclosed wholly or partly by fold mountains and rise with them; they are the highest and most extensive plateaus.
  • They are commonly the uplifted median mass between two marginal ranges.
  • Tibet (between the Kunlun and the Himalaya), the Bolivian–Peruvian Altiplano (averaging about 3,750 m, holding Lake Titicaca), the Mexican plateau (between the Sierra Madre Occidental and Oriental), Iran (between the Zagros and Elburz) and Anatolia (between the Pontic and Taurus ranges).
  • The Mexican plateau is tectonically unstable, as the Mexico City earthquakes of 1985 and 2017 showed.
• Piedmont plateaus lie at the foot of a mountain range, bordered by a plain or the sea on the other side.
  • Their plain-facing edge is an escarpment, so rivers crossing it form waterfalls.
  • The Appalachian Piedmont meets the Atlantic coastal plain along the Fall Line, whose falls powered early mills and cities; the Patagonian plateau is another example.
• Continental plateaus are vast uplands away from mountains, bordered by coastal plains or the sea.
  • They rise by broad continental uplift or by extensive lava flooding.
  • The Deccan, Arabian, Western Australian and South African plateaus; the ice-covered tablelands of Greenland and Antarctica are sometimes added.
• Coastal plateaus are low uplands next to the coast, such as the Coromandel coastal upland.

By Mode of Origin

Type	Formed by	World example	Indian example
Diastrophic (tectonic)	Uplift, warping and faulting of the crust	Colorado Plateau	Meghalaya (Shillong) Plateau
Dome plateau	Upwarping over intrusions	Ozark Plateau (USA)	Chota Nagpur Plateau
Volcanic (lava)	Stacking of fissure basalts	Columbia Plateau	Deccan Traps, Malwa Plateau
Sedimentary (fluvial–marine)	Uplift of thick horizontal strata	Cumberland Plateau	Kaimur (Panna, Bhander, Rewa, Rohtas)
Aeolian	Thick loess accumulation	Loess Plateau (China)	–
Glacial	Pre-existing uplands scoured or mantled by ice	Laurentian Shield, Greenland	Glacial margs of Kashmir

• Diastrophic plateaus are the true plateaus, and include the intermontane, piedmont, continental and dome types.
  • The Meghalaya Plateau, a detached block of the Peninsula, is now read as a “pop-up” block raised between bounding reverse faults (the Dauki fault on the south), an interpretation advanced by Roger Bilham and Philip England (2001) from the great 1897 Assam earthquake.
• Dome plateaus rise where intrusions arch the surface.
  • Chota Nagpur is studded with Archaean batholithic domes, exposed after the overlying Dharwar rocks were stripped away.
  • The Ozark Plateau was uplifted, peneplaned twice and uplifted again; it now comprises the Salem and Springfield plateaus and the Boston Mountains, drained by a radial pattern.
• Lava plateaus are built by fluid basalt erupted quietly from fissures, flow upon flow.
  • The Deccan Traps were erupted about 66 million years ago, close to the Cretaceous–Palaeogene boundary, over the Réunion hotspot; they now cover about 500,000 km² (perhaps 1.5 million km² originally) and exceed 2 km in thickness in the west.
  • The Columbia Plateau (USA) holds more than 300 basalt flows over about 210,000 km², most of them erupted 17–14 million years ago; ringed by ranges on three sides, it is also partly intermontane.
  • Pyroclastic plateaus are built instead by thick ash-flow (ignimbrite) sheets, as on the Volcanic Plateau of New Zealand’s North Island.
• Sedimentary plateaus: the Kaimur series descends eastward from Panna through Bhander and Rewa to Rohtas, built of Vindhyan sandstones, shales and limestones laid down in a Proterozoic sea and later uplifted.
• Glacial plateaus are modified, not created, by ice: glaciers round and lower uplands, and moraines can build low plateaus, as in north Germany.

By Shape and Surface

• Dome-shaped: Chota Nagpur.
• Dissected: the Deccan, broken by rivers into many smaller plateaus separated by elongated hill ranges.
  • The Catskill Mountains of New York are a dissected plateau that looks mountainous but lacks folding, metamorphism or major faulting.
• Step-like: the Kaimur series from Panna to Rohtas.
• Flat-topped (tableland): Tibet, Bhander, Rewa, and the Mahabaleshwar and Panchgani tablelands.
• Uneven: the Appalachian Plateau.
• Rejuvenated peneplain: the Missouri Plateau (USA) and the patlands of Ranchi and Palamau.

By Climate

• Arid plateaus: Arabian, Iranian.
• Humid plateaus: Meghalaya (Cherrapunji and Mawsynram), Mahabaleshwar.
• Ice-capped plateaus: Greenland, Antarctica.

By Stage of Erosion

• Armin K. Lobeck (1939) grouped plateaus by their stage in the cycle of erosion, following the Davisian cycle of erosion.

Stage	Surface	Valleys	Example
Young	Nearly horizontal beds, broad flat interfluves, escarpment margins	Few, deep and narrow (gorges, canyons)	Colorado, Idaho; Mahabaleshwar, Khandala
Mature	Thoroughly dissected, uneven, crowded with peaks (sharp in dry, rounded in humid climates)	Many, wide	Ranchi, Hazaribagh; Appalachian Plateau
Old	Worn to a peneplain	Broad, shallow	Mesas and buttes on low surfaces
Rejuvenated	Uplifted old surface, rivers re-incising	New gorges and falls	Missouri Plateau; Ranchi patlands

• As a plateau is dissected, the table-top shrinks from a mesa (broad, flat-topped, cliff-bounded) to a butte (small and tower-like) and finally disappears.
• On the Ranchi plateau, rejuvenation shows in knickpoint falls such as Hundru (on the Subarnarekha) and Dassam (on the Kanchi).

Major Plateaus of the World and India

Plateau	Location	Type	Notable feature
Tibet	Asia	Intermontane	Highest and largest; source of the Indus, Brahmaputra, Yangtze and Mekong
Altiplano	Bolivia–Peru	Intermontane	Lake Titicaca, about 3,810 m
Colorado	USA	Diastrophic, young	Grand Canyon
Columbia	USA	Lava	Over 300 basalt flows
Mongolian	Asia	Continental, arid	Gobi Desert
Brazilian	South America	Continental	Iron ore, coffee
African (South African)	Africa	Continental	Gold, diamonds
Western Australian	Australia	Continental shield	Gold, iron ore
Arabian	Asia	Continental, arid	Tilted block, oil-bearing margins
Iranian, Anatolian	Asia	Intermontane	Median masses
Deccan	India	Continental, lava-capped	Black cotton soil
Chota Nagpur	India	Dome, mature	Coal, iron, mica
Malwa	India	Lava	Northern Deccan basalt tableland
Meghalaya	India	Tectonic block	Among the world’s wettest places
Ladakh	India	High cold desert plateau	Part of the Tibetan high plateau

• Apart from the young intermontane uplands, most major plateaus of the world are old shields or lava tablelands, and the Indian Peninsular plateau, among the oldest landmasses on Earth, combines both.

Economic Significance of Plateaus

• Storehouses of minerals: much of the world’s metallic wealth comes from old plateau shields.
  • Gold from Western Australia and South Africa, copper and diamonds from Africa, and coal, iron ore, manganese, mica and bauxite from Chota Nagpur, which makes Jharkhand and Odisha India’s mineral heartland.
• Hydroelectric power: waterfalls at plateau edges give ideal hydel sites.
• Cooler climate: high plateaus in the tropics are pleasant, as in the East African highlands and the Deccan hill towns.
• Pastoralism and agriculture: grassy plateaus support sheep, goats and cattle; lava plateaus weather into fertile black soils (regur) suited to cotton.
• Limits: rugged terrain, thin soils on old surfaces and mining-driven deforestation and displacement constrain their use.

Plains

Meaning of Plain

• A plain is a relatively level area of low relief and gentle slope, lower than the land around it.
  • Plains may lie below sea level (the polders of the Netherlands), a few metres above it (the Ganga–Brahmaputra delta of Bangladesh) or well over 1,000 m up (the western Great Plains of the USA), but never above their surroundings.
• They are the simplest and most extensive second-order relief, covering roughly two-fifths of the land and found on every continent except Antarctica.
  • The largest, such as the Great Plains of North America and the North European Plain running into Siberia, extend for thousands of kilometres.
• Surfaces are usually covered by young sediments over older rock, and become undulating as erosion proceeds.

Origin of Plains

• Emergence of land that lay beneath shallow epicontinental seas: the Great Plains of the USA.
• Filling of a foredeep that forms in front of a rising mountain range: the Ganga–Yamuna plain.
• Unfolded median mass of low height between ranges: the Hungarian plain between the Carpathians and the Dinaric Alps.
• Sedimentation on submerged coasts, then emergence: the Northern Circars.
• Retreat of the sea exposing marine flats: the Rann of Kutch, still advancing seaward.
• Long denudation of plateaus to low surfaces.
• Outpouring of fluid lava over wide areas.

Classification of Plains

• A plain is seldom made by one process; it is named after the dominant process in its origin.

Class	Sub-types	World example	Indian example
Diastrophic	Uplifted, subsided, lava plains	Great Plains, Atlantic Coastal Plain	Kutch, Eastern coastal plain
Erosional	Peneplain, pediplain, karst plain, glaciated plain, etchplain, desert plain	Canadian Shield, Yucatán	Ranchi surface, Marwar plain
Depositional	Alluvial, lacustrine, glacial, aeolian, marine	Mississippi, Yangtze, Po	Ganga plain, Kashmir Valley

By Relief

Type	Local relief
Flat plain	Below 15 m
Undulating plain	15–50 m
Rolling plain	50–75 m
Dissected plain	75–100 m

• This relief grouping follows Finch and Trewartha; by location, plains are also grouped as inland or coastal.

Diastrophic Plains

• Uplifted or emerged plains form when marine floors rise by epeirogenic movement.
  • The Great Plains (USA), between the Rockies and the Central Lowland, lay under a Cretaceous sea, emerged at its close, were lifted again with the Rockies, and were later reshaped by rivers and Pleistocene ice sheets.
  • The Atlantic Coastal Plain was submerged until the Miocene and emerged by the Pliocene; its marine terraces mark stages of uplift.
  • A wide coastal plain usually pairs with a narrow continental shelf, and a narrow plain with a wide shelf.
• Subsided and built-up plains form where a coast sinks gently and is then filled.
  • India’s Coromandel and Northern Circar coasts were formed by mild subsidence, sedimentation and later uplift, as the Peninsula tilted eastward.
• Lava plains form from thin, widespread fissure flows, as on the Snake River Plain (USA) and in Iceland, France and Argentina.

Erosional Plains

• Peneplain: the low, featureless end-surface of the normal (fluvial) cycle, dotted with monadnocks; low surfaces of the Peninsula such as the Ranchi surface are read as uplifted peneplains.
• Pediplain: the coalesced pediments of arid and semi-arid lands, formed by scarp retreat and pedimentation, as at the foot of the Aravalli in Marwar.
• Two other erosional surfaces complete the set: the panplain of coalesced floodplains and the etchplain, formed by deep chemical weathering and stripping in the humid tropics.
• Karst plain: the subdued, pitted end-surface of solution in massive limestone, such as the Yucatán Peninsula, formed at the close of the karst cycle.
• Glaciated (ice-scoured) plain: ice sheets grind uplands into rounded knobs, broad valleys and lake-filled hollows, as over the Canadian and Fennoscandian shields.
• Wind-eroded desert plains: the hamada (bare rock), reg and serir (gravel) of the Sahara.
• Cryoplain: flattened by frost action in periglacial regions.

Depositional Plains

Alluvial Plains

• Alluvial plains are the most extensive depositional plains, built as rivers fill wide depressions with sediment: the Ganga, Mississippi, Yangtze, Huang He and Po plains.
• Piedmont alluvial plain: where rivers leave the mountains, the fall in gradient drops boulders, cobbles and gravel as alluvial fans, which coalesce into a continuous apron.
  • In India the coarse, porous upper belt is the Bhabar, about 8–16 km wide, where streams sink underground.
  • They re-emerge in the marshy, forested Terai belt to the south.
• Floodplain: fine sand, silt and clay laid down across the valley floor during floods, renewed almost every year, and marked by meanders, natural levees and oxbow lakes.
  • In India the Khadar is the newer alluvium of the active floodplain, flooded nearly every year.
  • The Bhangar is the older alluvium of the higher terraces, beyond flood reach and marked by kankar nodules.
  • Floodplains are the granaries of the world, but also its most flood-exposed land, as the Kosi embankment breach at Kusaha (2008) showed, flooding much of north Bihar.
• Delta plain: built where rivers meet the sea and split into distributaries.
  • The Ganga–Brahmaputra delta, covering over 105,000 km² (about two-thirds in Bangladesh), is the largest in the world; its higher tracts are chars and its low marshy hollows beels.
• Scroll plains of meander scars and oxbows are local variants, as along the Taieri River of New Zealand.

Lacustrine Plains

• Formed where lakes are filled with sediment or their beds are uplifted.
• The floor of the Kashmir Valley is an old lake basin, and its Karewa terraces are lake deposits; the Imphal valley around Loktak lake is another Indian example.

Glacial and Glacio-fluvial Plains

• Till plain: undulating spreads of unsorted till dropped by melting ice sheets, with drumlins and eskers, as in northern Ohio and the Midwest.
• Outwash plain (sandur): sorted sand and gravel spread by meltwater beyond the ice front; Skeiðarársandur in Iceland (about 1,300 km²) is the largest.
• Both spread widely under the Pleistocene ice sheets of North America and north-west Europe, together with moraines and other glacial landforms.

Aeolian Plains

• Sandy desert plains, uneven with dunes and ripples: the Sahara and the Thar.
• Loess plains of fine wind-blown silt, laid down beyond desert or ice margins.
  • Desert loess: north China, around the Huang He.
  • Glacial loess: the US Midwest and central Europe.

Marine and Coastal Plains

• Built by waves, currents and emergence along coasts: beach ridges, lagoons, tidal flats and wave-built platforms.
• India: the eastern coastal plain is broad, deltaic and emergent, while the western coastal plain (Konkan, Kanara, Malabar) is narrow and largely submergent.

Abyssal Plains

• Abyssal plains are the flat floors of the deep ocean, about 3,000–6,000 m down, where land-derived sediment buries the rough volcanic crust; they are part of ocean-floor relief rather than land relief.

Great Plains of Northern India

• The Great Plains, the northern plains of India, are a transitional belt between the Himalaya and the Peninsula, formed by the Indus, Ganga and Brahmaputra systems.
  • They cover about 7 lakh km², run about 2,400 km west to east and are 240–320 km wide.
  • They are almost level, mostly below 150 m above sea level, and built of Quaternary alluvium whose base boreholes have not reached.

Origin

• Eduard Suess: the plains fill a foredeep formed in front of the rising Himalaya, with an irregular floor; rivers from the Himalaya filled it with sediment.
• Sidney Burrard: the plains fill a rift valley bounded by two normal faults.
  • The rift view is rejected, since no bounding faults of that kind have been found along the Peninsular edge.
• Composite view: the plains grew by repeated sedimentation and subsidence in the trough, together with withdrawal of the sea.
  • Marine limestones in Garhwal–Kumaon and the Eastern Gulf reaching the Shillong area point to former sea arms.
  • The saline Sambhar and Pachpadra lakes of Rajasthan are also cited as relics of a former sea.
• Current view: the plains occupy a foreland basin, formed as the Indian lithosphere flexes down under the weight of the Himalaya.
  • The alluvium thickens northwards towards the mountain front, and the basin keeps subsiding as the thrust belt advances.

Regional Divisions

• Ram Lochan Singh (1971) divided the Great Plains into six meso-level regions: the Rajasthan plain, Punjab plain, Upper, Middle and Lower Ganga plains, and the Assam (Brahmaputra) valley.
  • The Upper Ganga plain shows the Ganga–Yamuna doab, bhur sand ridges and ravines along the Yamuna and Chambal.
  • The Middle Ganga plain has shifting, flood-prone rivers such as the Kosi, and many tals and palaeochannels.
  • The Lower Ganga plain is largely the delta: moribund in the north, mature in the middle and active in the Sundarbans, with the Rarh lateritic plain on its western edge.
• Relief within the belt is tiny, yet the Indo-Gangetic plains carry one of the densest rural populations on Earth.

Economic Significance of Plains

• Fertile soils and easy irrigation: deep alluvium and level land make plains the food baskets of the world, from the Ganga plain to the Mississippi and Yangtze.
• Agro-based and other industries thrive on raw materials, labour and markets.
• Transport: flat land eases the building of roads, railways, canals and airports.
• Cradles of civilisation: the Nile, Mesopotamian, Indus and Huang He plains.
• Cities and trade: most large cities, ports and trade centres, and a large share of humanity, stand on plains.
• Constraints: floods, waterlogging and salinity, and falling groundwater in the intensively farmed north-western plains.