Theories of Geography Part 9 – Land Relief and Landforms

Relief Features of the Land and Landforms

Geological Provinces

The entire Earth has been divided into several Geological Provinces on the basis of their origin. A geologic or geomorphic province is an entity with common geologic or geomorphic attributes. The six Geological provinces include:

  • Continental Shield
  • Platform-which is a shield covered with sediment
  • Orogen-which leads to development of mountains
  • Structural Basins-which are geological depressions, and are the inverse of domes
  • Large igneous provinces-which are extremely large (More than 100,000 Km²) accumulation of igneous rocks—intrusive, extrusive, or both—in the earth’s crust. One example of large igneous province is India’s Deccan trap.
  • Extended Crust.

Continental Shields

The first order of relief contains Earth’s continents and ocean basin, which were created by the movements of plates on the surface of the Earth. The lithospheric shell of the Earth is divided into large pieces called lithospheric plates. A single plate can be as large as a continent and can move independently of the plates that surround it. This is very much similar to a great slab of ice floating on the polar sea.

The continents can be geologically derived into two types of regions viz.

  • Active mountain-making belts
  • Inactive regions of old, stable rock.

The mountain ranges in the active belts grow through two major complex geologic processes.

  • First of them is volcanism, in which massive accumulations of volcanic rock are formed by extrusion of magma.
  • Second process is the tectonic activity. The breaking and bending of the Earth’s crust under internal Earth forces. This tectonic activity usually occurs when great lithospheric plates come together in collision. Crustal masses that are raised by tectonic activity create mountains and plateaus. At some places, both volcanism and tectonic activity combine to produce a mountain range. Tectonic activity can not only form mountains but also lower crustal masses to form depressions.

Please note that the active mountain-making belts are narrow zones that are usually found along the margins of lithospheric plates. The rest of the Lithospheric plates are much older, comparatively inactive rocks. There are two types of stable structures— continental shields and mountain roots. The continental shields are regions of low-lying igneous and metamorphic rocks. The shields may be exposed or covered by layers of sedimentary rock. The core areas of some shields are made of rock dating back to the Archean eon, 2.5 to 3.5 billion years ago. Thus, continental shields are formed on ancient metamorphic rocks such as granitic, batholiths, and dikes. The oldest rocks on Earth are found in the shields.

Mountain roots are mostly formed of Paleozoic and early Mesozoic sedimentary rocks that have been intensely bent and folded, and in some locations changed into metamorphic rocks. Thousands of meters of overlying rocks have been removed from these old tectonic belts, so that only the lowermost structures remain. Roots appear as chains of long, narrow ridges, rarely rising over a thousand meters above sea level.



Mountain Formation: Orogeny

Orogeny is primarily the mechanism by which mountains are built on continents due to the large structural deformation of the Earth’s lithosphere caused by Plate Tectonics.  Orogenesis involves the following:

  • Structural deformation of the rocks
  • Faulting of rocks
  • Folding of rocks
  • Igneous Processes
  • Metamorphism
  • Glaciation
  • Erosion
  • Sedimentation

Mountains are born and have a finite life span. Young mountains are high, steep, and growing upward. Middle-aged mountains are cut by erosion. Old mountains are deeply eroded and often buried. We have to note here that the constructive processes, like deformation, folding, faulting, igneous processes and sedimentation build mountains up. On the contrary, the destructive processes like erosion and glaciation, tear them back down again.

Causes of Mountain Building

There are three primary causes of mountain building as follows, which have already studied:

  • Convergence at convergent plate boundaries.
  • Continental Collisions
  • Continent Rifting

Forms of Mountains

A mountain may have several forms. Important among them are:

  1. mountain ridge
  2. mountain range
  • mountain chain
  1. mountain system
  2. mountain group
  3. cordillera

Mountain Ridge

It is a linear, steep-sided high hill, or spur. The slope of one side of a ridge is steep, while the other side is of moderate slope. A ridge, however, may have symmetrical slopes on both sides. The Shimla Ridge is a good example of mountain ridge.

Mountain Range

A mountain range is a linear system of mountains and hills having several ridges, peaks, summits and valleys.

Mountain Chain

A mountain chain consists of several parallel long and narrow mountains of different periods.

Mountain System

A mountain system consists of different mountain ranges of the same period. In a mountain system, different mountain ranges are separated by valleys.

Mountain Group

A mountain group consists of several unsystematic patterns of different mountain systems


It is a Spanish term referring to a system or major group of mountains. A cordillera consists of several mountain groups and systems. In other words, cordillera is a community of mountains having different ridges, ranges, mountain chains and mountain systems. It usually refers to an orogenic belt at a continental scale, e.g., the Western Cordillera of the U.S.A., which includes all the ranges between the Pacific and the Great Plains.

Types of the Mountains

No two mountains are the same. They, however, can be classified on the basis of their most dominant characteristics into:

  1. folded mountains
  2. volcanic mountains
  • fault-block mountains
  1. upwarped (dome) mountains

Folded Mountains

Folded mountains comprise the largest and most complex mountain systems. Although folding is the dominant characteristic, faulting and igneous activity are always present in varying degrees in folded mountains. The Alps, Himalayas, Rockies, Andes, Appalachians, Tien Shan, Caucasus, Elburz, Hindu Kush, etc., are all of this type. The folded mountains present the world’s major mountain systems. They are the youngest mountains in the world.

Volcanic Mountains

Volcanic mountains are formed from the extrusion of Java and pyroclastic materials, which if continued long enough, produces gigantic volcanic piles. The Kilimanjaro (Africa), Cotopaxi (Andes), Mt. Rainier, Hood and Shasta (U.S.A.), are some of the examples of volcanic mountains.

Fault Block Mountains

Fault-block Mountains are bounded by high angle normal faults. Some of them are associated with rift valleys such as those in East Africa, while others appear to be formed by vertical uplifting. A notable example of fault-block Mountain is found in the Basin and Range Province of the southwestern USA. The Salt Range of Pakistan, and Siena-Nevada of California (U.S.A.) are also the typical examples of fault-block Mountains.

Upwarped (Domed) Mountains

Upwarped or domed mountains are formed by magmatic intrusions and upwarping of the crystal surface. The lava domes, batholithic domes, laccolithic domes, salt domes, etc., are the examples of Dome Mountains. The Black Hills of South Dakota, and the Adirondack mountains of New York may be cited as the examples of upwarped (domes) mountains.

Different Stages of Orogeny

Mountains can also be divided on the basis of their making i.e. Orogeny during different geological periods.

Pre-Cambrian Orogeny

This was the first ever Orogeny on earth and represents the oldest mountains of the earth. The examples are Laurasian of North America, Elogoman etc.

Caledonian or Mid Paleozoic Orogeny

It occurred during Silurian and Devonian periods. The example are Aravallis of India, Brazilian Highlands in America, Scotland of Europe etc.

Harcynian or Late Paleozoic Orogeny

This occurred in the Permian period. Example are Appalachian of North America, Black Forest of Europe etc.

Alpine Orogeny

This took place in Tertiary period and represents the youngest and newest mountain ranges of Earth. The examples are Himalaya, Rocky, Andes, Apennines, Alps etc.


Plateau is an elevated tract of relatively flat land, usually limited on at least one side by a steep slope falling abruptly to lower land. It may also be delimited in places by abrupt slopes rising to residual mountains or mountain ranges, as in the Tibetan plateau, where it occurs as an intermontane plateau. The term is also used to refer to a structural surface such as Meseta of Spain, in which case it is a tectonic plateau. It is also used to describe extensive lava flows (lava plateau). The surfaces of plateaus may be plain-like in quality, very flat, rolling or hilly, or they may be so dissected by streams and glaciers that it is difficult to recognize their original plateau characteristics.

Diastrophic Plateaus

Diastrophism is the large-scale deformation of the earth’s crust which produces continents, ocean basins and mountain ranges, etc. All the highest plateaus of the earth are the direct products of diastrophism. Since their uplifts they have been modified by various agents of erosion and in many cases by volcanism and minor earth movements. For convenience they may be classified as:

  • Intermontane plateaus
  • Mountain border plateaus
  • Domed plateaus
  • Volcanic plateaus
  • Erosional plateaus

Intermontane Plateau

Intermontane Plateaus include the highest, largest and in many respects most complex plateaus of the world. Their surfaces show an extraordinary variety of topographic features. The best example is the

  • Tibetan Plateau. It stretches approximately 1,000 kilometers north to south and 2,500 kilometers east to west. The average elevation is over 4,500 meters (14,800 ft), and all 14 of the world’s 8,000 metres (26,000 ft) and higher peaks are found in the region. Sometimes called “the roof of the world,” it is the highest and biggest plateau, with an area of 2.5 million sq. km or about four times the size of France. The Tibetan Plateau is bounded on the north by the Kunlun mountains, and in the south by the mighty Himalayas. These two systems meet to make the western boundary of the plateau, while on the east is the less sharp demarcation between the plateau proper and the lower mountains of western China.
  • The Qinghai-Tibet Plateau not only gives rise to most of Asia’s major rivers, it also holds a constellation of salt- and freshwater lakes.
  • Another example of Intermontane Plateau is Plateau of Bolivia and Peru. It lies largely in Bolivia at an average elevation of more than 3,692 metres (12,000 ft) above the sea level.
  • One more example is Mexican Plateau which extends from the United States border in the north to the Cordillera Neovolcánica in the south, and is bounded by the Sierra Madre Occidental and Sierra Madre Oriental to the west and east, respectively.

Border Plateaus

Many plateaus border mountain ranges and owe their present position to the same uplifts that raised the mountains.

  • Piedmont plateau is an excellent example of border plateaus. This plateau is a strip of land that stands between tile Atlantic coastal plains and the Appalachian Mountains. Its eastern side is marked by a more or less definite fall-line where the gradient of the rivers is steepest. On the west it terminates against the mountains of the Blue Ridge.
  • Plateau of Colorado is also an example of the border plateau. It is bounded on the northeast by the Rocky Mountains and on the southwest by the Basin and Range Province.

Domed Plateaus

The plateau of Ozark (U.S.A.) is a good example of domed plateau. Ozark plateau was uplifted by folding and faulting into a broad dome some 65,000 sq km (40,000 square miles) in area during the Appalachian Revolution which occurred at the close of the Paleozoic Era.

Volcanic Plateaus

Volcanoes also form several varieties of plateaus. The largest are built by the lava flow. Smaller, degraded plateaus are formed by the resistant lava caps that protect the land from erosion and maintain its high elevation after the surrounding land has been worn away.

Erosional Plateaus

Such plateaus are formed particularly in semiarid regions where streams have cut away portions of high lands.

Land Forms

Landforms are defined as the geomorphologic units defined by its surface form and location in the landscape. Landforms are typical elements of the topography. The water body interfaces also called landforms. They are categorized on the basis of elevation, slope, orientation, stratification, rock exposure, and soil types as follows:

  • Aeolian landforms
  • Coastal and oceanic landforms
  • Erosion landforms
  • Fluvial landforms
  • Mountain and glacial landforms
  • Slope landforms
  • Volcanic landforms

Aeolian landforms

Aeolian landforms refer to the Landforms that are formed by the winds. There are two types of the Aeolian Landforms viz. Erosional and Depositional.

Aeolian Landforms: Erosional

  • Zeugen or Rock Mushrooms: They are also known as rock pedestal or a pedestal rock or Zeugen. Usually Found in Desert Areas.
  • Yardangs: Yardangs form in environments where water is scarce and the prevailing winds are strong, unidirectional and carry an abrasive sediment load. They consist of an elongated ridge carved by the unidirections erosion.
  • Dreikanter: Dreikanter exhibits a 3 faced Pyramidal Shape. They typically form in Deserts due to wind erosion.
  • Blow Outs: Blowouts refer to sandy depressions in a sand dune ecosystem, which are caused by the removal of sediments by wind.
  • Inselbergs: Inselbergs refer to the prominent steep sided hill of solid rock rising abruptly from a plain of low relief. Inselbergs are generally composed of resistant rocks such as Granites.
  • Desert pavement: Desert pavement refers to mountain wash containing pebbles, gravels and sand particles exposed to wind and surface appears as a pavement with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size

Aeolian Landforms: Depositional


  • Erg or Sand Sea: Erg is a sand sea or a dune sea. They are flat area of desert covered with wind-swept sand with little or no vegetative cover. The area is generally more than 100 square miles and is deposited by windblown sand. Largest Hot Desert in the World viz. Sahara has several sand Seas. The Ergs have 85% of Earth’s mobile sand.
  • Ripples: Ripples are well marked small waves produced on the surface of sand, mud and even rock by the drag of the wind / water moving over it. They are most common in deserts.
  • Barchan: Barchan refers to crescent shaped dunes, which have tips or horns pointing downwards. Barchans are found in desert areas which have low sand quantity.
  • Longitudinal dunes: Longitudinal dunes are also known as Seif dunes. Seif is a arabic word for Sword. These are long, slightly sinuous, ridge shapped dunes which are parellel to the wind direction, elongate parallel to the prevailing wind, possibly caused by a larger dune having its smaller sides blown away. Seif dunes are sharp-crested and are common in the Sahara.
  • Transverse Dunes: Transverse Dunes are asymmatrical sands in deserts which are at right angle to the wind direction. They are most probably caused by a steady build-up of sand on an already existing minuscule mound.
  • Star Dunes: Star Dunes are giant star shapped dunes with 3 or more sinuous arms extending outwards from the center. These shapes can alter due to windspeeds.

Fluvial Landscapes

The landforms which develop as a result of the water action are known as Fluvial Landforms. Running water such as rivers are the most important agent of erosion. Other agents such as Glaciers, Groundwater, wind and sea water are locally dominant agents of erosion.  The Fluvial processes are most important of all the exogeneric processes as landforms associated with them have overall dominance in the environment of terrestrial life. These fluvial processes can be divided into three phases viz. erosion, transportation and deposition.

Erosional Landforms

The Erosion can be normal erosion which takes place by the natural physical processes or the Accelerated Erosion, which is produced by human interference. The Sheet Erosion refers to the surface flow removing soil in thin layers. It can be accelerated in the Steep slopes, where innumerable closely spaced channels are formed, which grows larger form in gullies (steep-walled canyon like trench). The Erosion can be of following types:

  • Chemical erosion: Corrosion (Or solution) and carbonation.
  • Mechanical erosion.
  • Impaction (effect of blow upon the river bed or banks by large boulders).
  • Cavitation (shattering and breaking up of the stream load through collisions and mutual abrasion).
  • Hydraulic action (lifting and quarrying effect of rushing water).
  • Corrosion or abrasion (stream uses its load to scrape away its bed, particularly in steep confined sections of stream channels).

Landforms made by River Erosion

  • V-shaped Valley
    • Valley starts as small and narrow rills which gradually develop into long and wide gullies. The gullies will further deeper widen and lengthen to give rise to valleys which is V-shaped. The River valley is an important erosional landform. They are formed in the youthful stage of fluvial cycle of erosion. The vertical erosion or valley deepening causes the V-shaped valleys.
  • Gorge & Canyons
    • The V-shaped valley can be a Gorge, where steep precipitous wall within which a narrow river is confined (e.g. – Indus, Sutlej, Brahmaputra, Rhine, Zambezi). Thus, we can say that Gorge is a V- shaped valley but its sides becomes so steep that they look almost vertical. Or it can be a Canyon, which is basically a very deep and extended gorge. The Grand Canyon in Arizona, United States of America is the largest Canyon in the world.
  • Meander
    • The meanders or meandering rivers are the low slope rivers which are not choked with the sediment and move back and forth in a zig-zag order of loops. The meander has thus a serpentine path and it helps in accommodating in extra volume of water.
  • River Terraces
    • River terraces are abandoned floodplains that formed when a river flowed at a higher level than it does today. Thus, these are the surfaces that mark an old valley floor or floodplain levels.
  • Peneplain
    • When an extensive area has been eroded sufficiently to give the look of almost a plain, it is called a Peneplain.

Landforms made by River Deposition

  • Alluvial Fans
    • When the velocity of the running water, as it comes out of hills and meets the plain, decreases, it dumps the transported material at the foothills. The structure made are called alluvial fans. The alluvial fans are formed due to  accumulation  of materials  in the form of fan  and cones  respectively at the base of foot hills Alluvial  cones are made of coarse materials than the alluvial
  • Natural leaves
    • Narrow belt of ridges of low height built by the deposition of sediments by the spill water of the stream on its either bank.
  • Food plain
    • Surfaces on either side of a stream that is frequently inundated.
  • Crevasse splays
    • Formed by breaching of leaves when water escapes through a series of distributaries channels.
  • Back swamps
    • Plain area adjoining a levee may contain marshes called back swamps.
  • Yazoo streams
    • Distributions of rivers occupying lateral positions.
  • Delta
    • Delta is the triangular deposition at the mouth of a river debouching in a lake or a sea. The Factors that help in delta formation are as follows:
      • Long courses of rivers
      • Medium size sediments
      • Calm or sheltered sea
      • Suitable place (shallow sea and lake shores)
      • Large amount of sediments
      • Accelerated Stable condition of sea coast
    • On the basis of shape delta can be divided into following categories such as arcuate, bird-foot, Estuarine, Cuspate, Truncated etc.
  • Arcuate (lobate form) Delta
    • The Arcuate delta resembles the fan and is convex towards the Sea. It is semicircular in shape and is commonly found in semi-arid region; growing delta such as Nile, Niger, Ganga, Indus, Mekong, Irrawaddy, Rhine, Volga, Danube, Rhone, Lena rivers.
  • Bird-foot Delta
    • Birdfoot Delta is also known as a finger delta. In these deltas, the sediments deposited are composed of those fine particles which are received from the limestone rocks. The rivers with high velocity carry suspended finer load to greater distance inside the oceanic water (such as Mississippi).
  • Estuarine delta
    • When a river enters the sea through the single mouth or estuary, then the Estuarine Delta is formed which is submerged under marine water. Examples are Narmada River, Congo River, Amazon River and Hudson River.
  • Cuspate Delta
    • Cuspate delta are pointed. They are shaped by regular, opposing, gentle water movement as seen at the Tiber river.
  • Oxbow lakes
    • The Oxbow lakes are formed by the depositional and erosional actions taking place simultaneously. Please note that excessive meandering would result in Oxbow lakes.
    • How Oxbow lakes are formed?
      • On the inside of the loop, the river travels more slowly leading to deposition of silt. Meanwhile water on the outside edges tends to flow faster, which erodes the banks making the meander even wider. Over time the loop of the meander widens until the neck vanishes altogether. Then the meander is removed from the river’s current and the horseshoe shaped oxbow lake is formed.
        • Black Swamps
          • When the water spills out onto the flood plains, the heaviest material drops out first and finest material is carried over a greater distance. This fine grained alluvium would hold much water and would give rise to a wetland which is called Black swamps or simply swamps.

Landforms made by River Transportations

The dissolved solids in the rivers travel downstream and become a part of Ocean. The particles of clay, silt and fine grains are carried in suspension. Whenever a soft rock obstructs the course of stream and is eroded and sediments are scattered all around, it would be called Eddies. These Eddies sometimes look like discs and so are called potholes. The large potholes are called Plungepools.

January 13, 2018

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