How are Mountains, Plateaus and Plains created?
Mountains, plateaus and plains are created by the geomorphic processes which include, endogenic and exogenic forces. Endogenic forces are instrumental in creation of mountains plateaus and plains while exogenic forces are responsible for the destruction of them. Thus mountains, plateaus and plains are a nature’s creation in its own unique way.
Orders of Relief and Mountains, Plateaus and Plains
In order to make a systematic study of Earth’s Crustal features, all landscapes are divided into three orders of relief :
- First order of relief: This is the broadest category that includes huge continental landmasses which include all of the crust above the sea level (30 % of Earth’s surface) and ocean basins which includes the crustal areas below the sea level (70 % of Earth’s surface).
- Second order of relief: This order of relief includes regional scale continental features such as continental masses, mountains, plateaus, plains and low lands.
- Third order of relief: It includes individuals landform features that collectively make the second order relief features. They include mountain peaks, valleys, hills, beaches, lakes, volcanoes and other related land form features.
Among the three second order relief features namely mountain, plateaus and plains, mountains represent the most outstanding and intriguing features. This is a portion of land surface rising considerably above the surrounding country either as a single eminence range or chain. According to Oxford Dictionary “mountain is a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relatively to the adjacent elevation, is impressive or notable.” As such there is no universally accepted definition of a mountain. Criteria such as elevation, volume, relief, steepness, spacing and continuity have been used as for defining a mountain. The United Nation’s Environment Program has defined mountainous environment into 6 classes where Class 1 is above 4500 meters and Class 6 is above 300 meters.
Types of Mountains
Folded Mountains comprise the largest and most complex mountain system. Folding is the dominant process followed by faulting and igneous activity. Most of the fold mountains are the youngest mountains in the world. The Himalayas, the Alps, Rockies, Andes etc., are famous examples.
These fold mountains are formed by compression when horizontal forces act towards a common point that compresses the in between rock strata to produce fold mountains. The fold consists of two inclined parts called limbs, the upper portion is called anticlines, the lower portion is called syncline. It is agreed that folded mountains have been formed in long, harrow and shallow seas, termed as geosynclines. Thus geosynclines have been the cradles of mountains.
On the basis of the period of origin folded mountains are divided into:
- Old Folded Mountains: All the folded mountain originated before the tertiary period come under the category of old fold mountains. E.g., the old fold mountains of Caledonian and Hercynian period such as Aravalis, Appalachians. Many of them exist now as relict mountains due to long period of denudation.
2. New folded mountain : In this category comes the Alpine fold mountains of tertiary period, e.g. Alps, Himalayas, Rockies, Andes. These are gigantic mountains characterized by glacier-capped high peaks , intense erosion , complex folding and faulting , volcanism etc.
Volcanic mountains are formed by the extrusion of lavas and pyroclastic materials, which if continued long enough, produces gigantic volcanic piles. The Kilimanjaro (Africa), Cotapaxi (Andes) etc., are some of the examples. Mauna Kea volcanic mountain of Hawaii is 4200 mt. high but if its height is considered from the sea bottom it becomes 9140 mt. (higher than the mount Everest).
These are the result of faulting caused by tensional and compressive forces. They represent the upstanding parts of the ground between two faults or on either side of a rift valley. Noted examples are Vosges and Black forte mountains bordering the Rhine Rift Valley , Salt Range of Pakistan, Siera Nevada (USA) etc. Siera Nevada mountain of California is considered to be the most extensive block mountain of the world.
When mountains, plateaus or high plains take the form of mountains by continued erosion over a long period of time they are known as Relict mountains. Noted examples are Aravali, Satpura, Vindhyas in India and mountains of Scotland and Penine range of Europe.
Other Important Facts
- Nilgiri mountain of India is an example of block mountain.
- Ojas Del Saldo, situated in the Andes is the highest active volcanic mountain of the world.
- The Western Ghats of India is not a true mountain range. It is in fact a fault scrap whose western part has been displaced and subside to the west.
- Andes, the fold mountains of south America, is the longest one ( 7000 km) in the world.
- Fold mountains are made up chiefly of the sedimentary rocks but core is characterized by the massive granitic intrusion.
- Fold mountain are generally found in arc shape and they extend for greater lengths but their widths are far smaller.
- Marine fossils found in the rocks of fold mountains are of those marine organisms which can survive only in shallow water. All these things indicate that sedimentary rocks of fold mountains were deposited in long shallow seas called Geosyncline.
- Great Dividing Range of Australia is an old fold mountain.
- Fold mountains are generally found along the margins of the continents either in north-south direction (Rockies & Andes) or in East-West direction (Alps in Europe, Atlas in Africa, Himalayas etc.)
Plateaus is an elevated tract of relatively flat land, usually limited on at least one side by a steep slope falling abruptly to lower land. This second order relief feature covers about 33 % of the land surface of the globe. The essential criteria for plateaus are low relative relief and some altitude. Thus among mountains, plains and plateaus they are less conspicuous.
Plateaus Based On mode Of Origin
- Plateaus formed by Exogenetic Processes
- Glacial Plateaus: Garhwal plateau, plateau of Greenland (by erosion) by deposition-Russian plateau, Marg of Kashmir.
- Fluvial Plateau: Bhander plateau of central India, Brazilian plateau.
- Aeolian plateau: Loess plateau of China, Potwar plateau of Pakistan.
- Tectonic plateaus
- Intermontane Plateaus : Tibetan plateau (the largest and highest plateau situated between Kunlun Mt. in the north and Himalayas in the south, Bolivian plateau between the Andes mountain, Mexican plateau between the eastern and western Sierra Madre mountains etc.
- Piedmont plateaus: Plateaus formed at the foothill zone of extensive mountains, e.g. Piedmont Plateau at the eastern margin of Appalachian mountains and Patagonian Plateau in the east of Andes.
- Dome Plateaus : Ozark plateau of USA , Chhota-Nagpur plateau of Jharkhand.
- Lava Plateaus : Deccan plateau, Columbia plateau ( USA )
Geographical Location Based Plateaus
- Intermontane Plateaus : Tibetan plateau Mexican plateau, Iranian plateau (between Zagros and Elburz), Anatolian plateau (between pontic and Taurus).
- Border plateau : Piedmont plateau ( USA ), Patagonian plateaus ( Argentina).
- Continental Plateaus: Arabian plateau , peninsular Indian plateau, Australian plateau, South African plateau, Mexican plateau etc.
- Coastal plateaus: Coromandal coastal upland of India.
Plateaus Based On Stages Of Erosion
- Young plateau: Colorado plateaus (USA), Idho plateaus (USA), Khandala upland, etc. In these plateaus rivers from deep & narrow valleys through vertical erosion.
- Mature Plateaus: Ranchi plateaus, Appalachian plateau.
- Old Plateaus: Agents of denudation erdode it to their base level and the plateau appears as a featureless plain except some Monadnocks are steep-sided resistant rocks surviving the onslaught of erosion. Exact examples are difficult to find.
- Rejuvenated plateaus: These are formed due to upliftment of old plateau , e.g. Missouri plateau (USA).
Classification on the basis of climate
- Desert or Arid plateau: Arabian plateau, Patagonian plateau.
- Humid plateau: Shillong plateau, Mahabaleshwar plateau.
- Ice-capped plateau: Greenland plateau.
Plain is an extensive tract of flat land or a gently undulating terrain without prominent hills or depressions. Plains are major centers of population concentrations in the world. They generally do not change much in elevation, and are primarily treeless. They may exhibit gentle slopes and small local relief. Among mountains, plateaus and plains, they hold a second position as 30 % of the continental surface is covered by plains.
Their categories are :
It must be born in mind that plains are seldom formed by a single process. Hence categorisation of plains is done on the basis of dominant role in the evolution of great plains of USA , hence they are called diastrophic plains i.e. formed by gradual and slow action. These plains are formed on regions that were once submerged under ocean or sea e.g. Great plains of U.S.A which extend till Canada.
River eroded plains : Peneplains are regarded the end-product of normal cycle of erosion ( fluvial cycle of erosion ). A peneplain is an undulting surface of low relief, interspersed with occasional redisual hills, known as monadnocks.
Glaciated plains : plains of northern part of north America and western Europe are dominated the imprints of glacial features. Laddakh plain of India in the east of shyok river is also a glacial eroded plain.
Wind-Eroded plain : Wind-eroded plains of shyok ( Africa)
Karst Plains : Plains of former Yugoslavia ( karst region), Chitrakoot ( India ).
River-deposited plains: These include plains formed in the foot hill zones (e.g. Bhabar& Tarai of Ganga-Yamuna plain), flood plains are formed due to deposition of fine sediments in the flood affected areas. Delta plains are formed at the end of the river course ( e.g. Ganga-Brahmaputra delta).
Lacustrine plains: Formed by the filling up of lakes with sediments. Kashmir valley and Imphal Basin are regarded as a lacustrine plain.
Lava plains: Formed of thin sheets of lava coming through fissure eruption , e.g. lava plains of Iceland, Argentina, New Zeeland , etc.
Wind-Deposited plains: They include sandy dessert plains and Loess plains, e.g. Thar desert plain, Sahara desert, loess plain of China.
Glacially-Deposited plains: Plains of north Germany, N.W. Russia ,etc.
Uplifted Peneplains are found in the Appalachian region ( USA )and Chhota-Nagpur region Jharkhand ( India). A Peneplain is a gently undulating plain with no features formed by protracted erosion by rivers and rain e.g. plains of East Central Africa. It is often interspersed with occasional residual hills.
Diastrophic Plains, Erosional Plains, Depositional plains, Peneplains
The Qinghai-Tibetan plateau, southwestern China.
Volcanic, fold, plateau, fault-block and dome.
fold mountains, fault-block mountains, and volcanic mountains
Endogenic Forces – Folding, Faulting, Earthquakes And Volcanism
Interior Structure Of The Earth