GEOMORPHOLOGICAL LANDFORMS, formation of mountain, type of mountain, formation of platue, formation of plain, formation of lakes, Geography notes UPSC, Geography optional Subject notes UPSC, Geography notes IAS, Geography optional Subject notes IAS
A mountain is defined as “a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relative to the adjacent elevation, is impressive or notable”. Mountains can be classified on the basis of their structure or their origin.
- Structural classification:
- Fold Mountains: These mountains have originated due to compressional tectonic forces and have been thrown up to form fold mountains e.g. Himalayas, Andes, Alps etc. The folds consist of two inclined parts called limbs, the upfold is called anticline and the downward portion is called syncline.
All young folded mountains have originated from geosynclines. Geosynclines are long narrow and shallow water depressions characterized by sedimentation and the subsequent subsidence. The conversion of geosynclines into folded mountains requires geologically long time with definite phases of mountain building process-
(b) Orogenesis: After horizontal compression has completed its task, vertical uplift starts. This is the real stage of mountain building.
(c) Glyptogenesis: In this phase the characteristic land forms are sculptured by erosion.
On the basis of age the Fold Mountains can be grouped into:
(i)New or Young fold Mountains: Example: The Alps, the Himalayas, the Circum-Pacific oceanic Mountains, etc. The main features of these mountains are the complex folding of the rocks, faulting, volcanic activities, and the erosion caused by running water, ice, winds, etc.
(ii) Old Fold Mountains: Example: The Caledonian and Hercynian mountains of central Europe, the Pennines, the Highland of Scotland, etc. These mountains were folded in very ancient times, and then subjected to denudation and uplift. Many faults were formed and the layers of the rock were wrapped. Many mountains exist as relicts due to erosion.
- Block Mountains: They are originated by tensile forces leading to formation of rift valleys. They are also called horst mountains e.g. black forest, Vosges, Vindhya, Satpura, Sierra Nevada etc. When the crust cracks due to tension or compression faulting takes place. A section of the landform may subside or rise above the surrounding level giving rise to Rift valley or Graben and Block Mountains or Horst. The Block Mountains have a steep slope towards the rift valley but the slope on the other side is long and gentle.
III. Dome Mountains: They are originated by magmatic intrusion and upwarping of crustal surface e.g. lava domes, Batholith domes etc.
IV Mountain of Accumulation: They are originated by accumulation of volcanic material e.g. cinder cones, composite cones etc. These are formed by the emission and deposition of lava and so they are also called volcanic mountains. The slope of the mountains becomes steep and the height increases due to the development of the cones of various types like Cinder cones, Composite Cones, Acid lava cones, Basic lava cones, etc. Some of the examples of this type are Popocatepetl of Mexico, Mount Rainier of Washington, Lessen Peak of California, the Vesuvius of Italy, the Fujiyama in Japan, the Aconcagua in Chile etc.
V Circum Erosional or Relict Mountain: e.g. Vindhyachal ranges, Aravallis, Satpura, Eastern and Western Ghats, Nilgiris, Parasnath, Girnar, Rajmahal. These mountains have been subjected to weathering and erosion for a long time and lowered down. They represent the old stage of mountain life cycle.
- Classification on the basis of Mountain Building periods
- Pre-Cambrian Mountains: Rocks of these mountains are older than the Cambrian era, and are found in older stable blocks or old shields which are now metamorphosed. Some of those old shields are Laurentia, Fennoscandinevia (Europe), Angaraland (Asia), Gondwanaland (Asia), etc.
- Caledonian Mountains: (320 m.yrs.): Mountains of Scandinavia, Scotland, N. America, Aravallis, Mahadeo, Satpura fall under this category. This mountain building process started at the end of the Silurian period or at the beginning of the Devonian period.
- Hercynian Mountains: (240m.yrs.): These Mountains were formed during Permian and Permo-Carboniferous period. They include Appalachian in N. America, Meseta in Spain, Vosges and Black Forest in Germany, Harz, Donetz area of Ural , Altai, Kinghan ,Tien Shan, Alai, Nan-Shan, etc. Meseta Mountains in Morocco; the High Atlas Mountains also represent this category.
- Alpine Mountains (30m.yrs.): It started by the end of the Mesozoic era and continued upto the Tertiary period. These are the highest mountains of the world. Being newer, the erosional forces could not erode them into a Peneplain like the Himalayas, the Alps, the Rockies, the Andes, the Atlas, etc.
Stages of Mountains Building:
The life history of mountains can be divided into youth, maturity and old stage. Following are the characteristics of mountains in different stages:-
- The Youth Mountains:
- The rivers are youthful and the valleys are deep and their flow is fast.
- Landslide and volcanic activities are common.
- The mountains are high.
- The slopes are steep and the piedmont is bare.
- The sky line is irregular.
B. The Maturity of Mountains:
- The rivers are mature and many watergaps exist in the area.
- The height of the mountains is not much.
- The peaks are rounded, generally covered by thick vegetation.
- Landslides are uncommon and no earthquakes are experienced.
- Slopes are not steep. Pebbles and rock fragments are accumulated in the piedmont area.
The Old-Age of Mountains:
- The rivers have attained old age.
- Monadnocks are found denuded and are a common sight.
- The mountains are low. Peneplain condition seems imminent.
- The area is broad, low and leveled which has wavy hills at some places.
Plateaus are extensive upland areas characterized by flat and rough top surface and steep walls which rise above the neighbouring ground surface at least for 300 m.
On the basis of mode of formation the plateaus can be classified into:
- Plateaus Formed by Running Water: Many parts of the Deccan of India (Kaimur Plateau, Rewa Plateau, Rohtas Plateau, Bhander Plateau), Brazilian Plateau.
- Plateaus formed by Glacial Erosion: Plateau of Greenland and Antarctica, Garhwal Plateau.
- Plateaus formed by Glacial Deposition: Russian Plateau, Finland Plateau, Merg of Kashmir.
- Aeolian plateaus: Loess Plateau of China, Potwar Plateau of Rawalpindi in Pakistan.
- Plateaus formed by endogenic processes:
(a) Intermontane Plateaus: Tibetan Plateau, Bolivian Plateau, Peruvian Plateau, Columbian Plateau, Mexican Plateau.
(b) Piedmont Plateaus: Appalachian Plateau, Patagonian Plateau, Colorado Plateau.
(c) Dome Plateaus: Ozark Massif (USA), Chhotanagpur Plateau.
(d) Lava Plateaus: Columbian Plateau, Mahabaleshwar Plateau.
(e) Continental Plateau: Deccan plateau, Ranchi plateau, Shillong plateau, Columbia Plateau, Mexican Plateau etc. etc.
(f) Coastal Plateau: Coromandal coastal upland of India.
(g) Rejuvenated Plateau: Missouri Plateau (USA).
(h) Mature Plateau: Ranchi Plateau, Hazaribagh Plateau, Appalachian Plateau (USA).
(i)Young Plateau: Idaho Plateau (USA), Colorado Plateau (USA), Mahabaleshwar Plateau, Khandala upland (Maharashtra).
Plains can be defined as flat areas with low height. They may be above or below sea level e.g. coastal plains of Netherlands. The plains may be classified as under:
- Formation of plain due to deposition of sediments over submerged coastlands e.g. Coromandal coastal plains.
- River deposited plains e.g. north Indian plains
- Piedmont alluvial plain e.g. Bhabar plain
- Flood plains e.g. Khadar and Bhangar plains
- Lava plains e.g. plains of New Zealand, Iceland etc.
- Glaciated plains e.g. north west Eurasian plain.
- Erosional Plains
- Plains of Fluvial Erosion: The plains formed by river erosion have a lot of variation because of the stages of erosional development, the initial slope and the structure of basal rocks.
(a) The Dissected Plains of the Youth: The Colorado, Kansas, Nebraska, east of the Rockies belong to this category of plains. The broad water-divides, large valleys are the main characteristics of such plains. The drainage is dendritic in nature.
(b) The Dissected Plains of Maturity: Such plains are found in North Missouri, Southern Iowa and Eastern Nebraska of USA. Areas of gentle slope are very limited and plain areas are available more in the valleys and the water divides are reduced to small ridges.
(c) The Plains of Old Age: Peneplain and Panplains usually represent this stage of plains.
Peneplain: Very few areas like Guinea plain in the north-east S. America are fully developed peneplains. The Appalachian had developed into peneplains in the ancient times but was later uplifted again. Here the high summits are of equal heights.
Panplains: A plain formed of flood plains joined by their own strength. It is a product of lateral erosion by streams.
- Glaciated Plains : When the ice sheet melted specially in N. America and W. Eurasia , the area eroded by ice was exposed . Here the rivers have adjusted themselves before the extension of ice sheet. Lakes, swamps, waterfalls and rapids are common.
- Aeolian Plains: Winds blow the sand and starts the activities of deflection, abrasion, etc. The plains produced by the wind actions are Reg, Serir and Hamada.
- Plains of Semi-arid Denudation : This type of plain includes the peneplains of USA and the pediplains of south-west of Africa.
- Plains at Continental Edges: Theses have evolved at the sea coast by the action of waves and later uplifted. The flat plains situated at the coast of Norway fall into this category.
- Karst Plains: They are found in limestone areas. The underground water removed the limestone layer by the process of solution. A large number of depressions are produced in these plains e.g. the coastal plain of Adriatic Sea and the Karst plain of Florida (USA).
- Depositional Plains
- Plains of Alluvial Deposition : The deposition of the sediments takes place in three areas – the floor , the mouth and the valley of the river where the slope suddenly decreases. The shape of such depositional plain changes according to the method and place of deposition and forms three types of plains.
- Flood Plains: Here the river deposits its sediments by meandering through its course. The flood plains of Mississippi, Ganga, Indus and Nile are good examples.
- Deltaic Plains: When the river terminates in the sea or lake, the deltas are formed due to deposition. The deltaic plains resemble flood plains but the existence of large number of distributaries provides them with a distinction. Marshes and natural levees are common here. The Deltaic plains of the Ganga, the Indus, the Nile and the Mississippi are famous.
- Piedmont Alluvial Plains: The piedmont alluvial fans combine together and form a plain. Rough particles are found at the apex but the particles of debris get finer as we move towards the periphery.
- Plains of Glacial Deposition: These are found in N. America and Europe, in areas which were affected by glacial action. The surface is slightly undulating and has low and broad ridges and depressions.
- Desert Plains of Wind Erosion: The Loess Plain of China was formed by the windblown deposition of Gobi desert, situated west of it. Some other examples of such plains are the Sahara of Africa, the Koum of Russian Turkistan, the northcentral Nebraska, etc.
- Plains of Marine Deposition: They develop near the coast of shallow sea. Sand, alluvium, vegetation, etc. are deposited at the coastal areas of Netherlands, Germany, Denmark, The Gulf of Mexico in U.S.A., etc.
Lakes may be defined as non-permanent features of static water on the land surface. The lakes can be classified as under:
- Fresh water lakes e.g. the great lakes of U.S.A.
- Saline lakes e.g. great salt lake of Utah, Caspian sea, dead sea, lake van etc.
- Fluvial lakes e.g. Wular lake, Marigot lake, Mayeh lake
- Lakes formed by volcanic Activity: Crater and Caldera Lakes- Lake Oregon (USA), Lakes Toba (Sumatra)
Lakes formed by earth movements:
- Tectonic Lakes: – Lake Titicaca (Andes), (highest Lake of world), Caspian Sea (Largest Lake of the world).
- Rift valley Lakes:- Tanganyika, Malawi, Rudolf, Edward, Albert, Dead Sea (1256 ft below mean sea level the world’s Lowest Lakes)
Lakes formed by deposition:
- Due to river deposits – Ox-bow Lakes
- Due to marine deposits – Lagoons, Delta
Lakes formed by Erosion:
- Karst Lakes – Lake Scutari (Yugoslavia)
- Wind – deflated Lakes (Salt Lakes & Playas)
Lakes formed by Glaciations:
- Cirque Lakes of Tarns – Lake Red Tarn (U.K.)
- Kettle Lakes – Orkney (Scotland)
III. Rock-hollow Lakes – Lakes of Finland (the land of lakes)
- Lake due to Moraines – Lake Windermere (U.K.)
V. Lakes due to deposition of glacial driftsNorth Ireland.