Friday, June 1, 2012

Major Land Forms

  • Endogenetic forces are responsible for development of primary land form on 1st order and second order land form like Mountain, Continent, Plateaus etc.
  • Exogenetic forces are the destructive forces by the river, glacier, wind, wave etc. which transformed the first & second order land forms into 3rd order landform like plateau, plain etc.

Types of Mountains


Fold Mountains

  • They are caused by large scale earth movements, when stresses are set up in the earth's crust.
  • Such stresses may be due to the increased load of the overlying rocks, flow movements in the mantle, magnetic intrusions into the crust, or the expansion or contraction of some part of the earth. When such stresses are initiated, the rocks are subjected to compressive forces that produce wrinkling or folding along the lines of Weakness.
  • The up folded waves are called anticlines and the troughs or down folds are synclines. Ex - Himalaya, Rockies, Andes & Alps etc.
  • These are rich in mineral resources ex-tin, copper, gold, petroleum etc

Block Mountains

  • Tensional or compressional forces on the earth crust causes lengthen or shorten the earth crust lead to cracks or faulting in the crust.
  • This results one part subside or the other raised up and formed block mountains and rift valleys.
  • If the block enclosed by the faults remains as it is or rises, and the land on either side subsides, the up standing block becomes the Horst or Bloc Mountain.
  • The subsided crack or dip valley like structures are called Grabene or Rift Valley. Ex - Hunsrock Mountain, Vosges, Black forest of Rhine land and Great Rift Valley of Africa (IT is 3000 mile long stretching from East Africa through Red Sea to Syria).
  • Compressional forces set up by earth movements may produce a thrust or Reverse Fault and shorten the crust.

Volcanic Mountains

  • These are also called Mountains of accumulation.
  • These are accumulation of molten Lava, ash, dust, mud around the vent after eruption in a successive layers, building up a characteristic volcanic cone. Ex - Mt-Fuji-Japan, Mt Mayon - Phillippines, Mt. Merapi - Sumatra, Mt. Aguny - Bali and Mt. Cotopaxi - Ecuador etc

Residual Mountains

  • These are mountains evolved by denudation.
  • The general level of the land has been lowered by the agents of denudation, some very resistant areas may remain and these form residual mountains. Ex. : Mt. Mandnock - USA, Mt. Aravali, Mt. Vindhyan etc.
  • Sometimes plateaus are also dissected by rivers and formed up land-mountain. Ex: Deccan Plateau, Scandinavia High Land, Scotland and High Land etc.

Plateaus

Plateaus are elevated uplands with extensive level surfaces and usually descend steeply to the surrounding low land. They are also referred as table lands.

Tectonic Plateau

These are formed by earth movements which cause uplift, and are normally of a considerable size and fairly uniform attitude. Ex.: Deccan Plateau, Meseta - Central Iberia etc., Harz (Germany) faulted plateau

  • When plateau is enclosed by fold-mountains, is known as Intermont Plateau. Ex -Tibetan Pt. (between Himalaya & Kunlun).
  • Bolivian pt. (between Andes.)

Volcanic Plateaus

  • Moltenlava may issue from the earth's crust and spread over its surface to form successive sheets of basaltic lava.
  • These solidify to lava plateau or volcanic plateau. Ex. : Antrim Plateau - Northern Ireland, N.W. part of Deccan and Columbia - Snake pt.
  • Plains can be defined as flat areas with low heights generally below 500 ft.

Structural Plains

These are structurally depressed areas of the world. Ex.: Russia platform, Great Plains of USA and Central low lands of Australia.

Depositional Plain

These are plains formed by the deposition of materials brought by various agents of transportation.
Plains formed by Aeolian deposits as very fine particles are called Loess Plain. Ex - Potawar - Pakistan Pampas - Argentina N.W. China

Erosional Plains

  • These plains are carved by the agents of erosion, river, rain, ice, wind etc. help to smooth out the irregularities of the earth's surface and in terms of millions of years.
  • In arid of semiarid regions are called deflation hollow, reg, erg, pediments or pedi plains.

Karst Plain

  • Plains are formed due to weathering of Lime stone topography. Crate Lake when enlarged is called Caldera Lake. Ex: Lake Toba - Sumatra, Lake Avernus - near Naples (Italy).

Lake by Wind Action

Palaya Lake - Deflating action of wind formed palaya lake. These lakes are Characterized with inland drainage system. Ex: L.Eyre - Australia, Qattara Depression - Egypt, Great basin of Utah - USA

Lagoons

These are depositions in the coastal sea.
Merine deposits formed sand bars which enclosed the sea to form lagoons. Ex. :Chilika lake - Orissa and Vembanand lake - Kerala etc.


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