GENERAL STUDIES

GEOGRAPHY MATERIAL for PRELIMS(General)

CONTINENTAL DRIFT

CONTINENTAL DRIFT THEORY (ALFRED WEGNER):

  • POSTULATION- Originally there existed ONE big Land mass which he called PANGAEA.
  • This PANGAEA was covered by one big ocean called PANTHALASSA.
  • Sea called TETHYS divided PANGAEA in to two huge Land Masses – LAURENTIA (North) Gondwanaland (South).
  • DRIFT: In two direction
    1. equator wards due to Interaction of Forces of gravity and Buoyancy.
    2. Westwards drift due to tidal current because of the earth motion.

 

EVIDENCE :

  1. Apparent affinity of physical features..
  2. Inter play of SIMA & SIAL.

 

CRITICISM:

  • Coast lines are temporary feature and are liable to change due to the erosion work of the Sea, rivers etc.

 

SEA FLOOR SPREADING (HESS, DIETZ, 1962):

  • AUTHORS of this theory recognized the existence of Pangaea, Tethys, Panthalassa.
  • Apparent movement of the Sea floor at specific locations.
  • Intense heat generated by radioactive substances in the mantle below the earth surface, Raising Limbs of these currents meet. Oceanic ridges are formed and falling limbs meet. Trenches are formed.
  • Rate of movement is Slow, Perhaps 2.5cm per year, but it is measurable.

 

PLATE TECTONICS:

  • LITHOSPHERE (Earth’s Crust) is broken in to Number of Plates/sections, each of which is capable of Independent Movement over ASTHENOSHERE (100-250 km below surface) (Partially Molten and capable of slow flow)
  • Movement of these CRUSTAL PLATES Causes the formation of various land forms and is the principal cause of all earth movements.

 

CRUSTAL PLATES

Six Major Plate

  • AMERICAN PLATE
  • EURASIAN PLATE
  • AFRICAN PLATE
  • INDO-AUSTRALIAN PLATE
  • PACIFIC PLATE
  • ANTARTIC PLATE

 

MINOR PLATES:

  • CARIBBEAN
  • PHILLIPINESS
  • NORTH AMERICAN
  • SOUTH AMERICAN

Average thickness of these Plates is around 100 kms and entire thickness is involved in CRUSTAL BENDIND AND DOWN BENDING.

 

INTERACTION OF PLATES AND THE RESULTS:

  1. DIVERGENT EDGE(CONSTRUCTIVE EDGE)

Basaltic Magma erups.

  1. CONVERGENT EDGE (DESTRUCTIVE EDGE)

Zone of collision

Orogenic Collision

  1. TRANSCURRENT EDGE (CONSERVATIVE)

Move past each other without directly interacting with each other.

 

CORAL REEFS & DELTAS

  • CORAL REEFS are significant SUB-Marine features.
  • It is formed due to accumulation and compaction of Skeletons of LIME-SECRETING ORGANISM known as CORAL POLYPS.
  • CORAL POLYPS thrive in the Tropical oceans confined between 250 N – 250 Latitudes and live on LIME.
  • Taking Coral animals as a whole (polyps) are the most abundant and also the most important.
  • Each POLYP resides in a tiny CUP of Coral and helps to form Coral Reefs. When they die, their lime-Skeletons are cemented in to coralline limestone.
  • There are also Non-reef Building species such as ‘Precious Corals’ (Pacific Ocean) and ‘Red Coral’ (Mediterranean), they survive in the colder and even the deeper waters.
  • Coral reefs exist in Numerous Species of many forms, Colours and Shapes.
  • Since Coral Polyps cannot survive above water level and hence coral reefs are always found either up to sea-level (or) below it.
  • Coral reefs are generally attached to submarine platforms (or) Island submerged under water.
  • Coral Reefs are more diverse than Tropical Rainforest because the coral reefs have above10,00,000 species of which only 10% have been studied. This is why coral reefs are called as “ Rainforests of the oceans”.

 

CONDITIONS FOR THE OF CORAL POLYPS:

  1. WATER TEMPERATURE:
    • Corals are found mainly in the tropical oceans and Seas, because they required Mean Annual temperature between 200 – 210 C for their survival. Hence, it cannot survive in the waters having wither very low temperature (or) very high temperature.
    • Coral reefs are generally absent on the Western Coast of Continents where cold ocean currents flow.

 

   II ) DEPTH OF WATER:

  • It cannot live in deeper waters (Not more than 200-250 feet (66-77 mts) below sea level because they die in water deeper then 77meters due to lake of sufficient amount of sunlight and oxygen, which are very much required for the growth of Coral POLYPS.
  • There should be clean sediment–free water because muddy water (or) turbid water Close the mouth of Coral POLYPS resulting in to their death.
  1. Fresh water is Injurious for the growth of Corals. Thus, Corals avoid Coastal lands and live away from the areas of river mouths.
  2. Very high proportion of oceanic Salinity is injurious for the growtn of Coral polyps because such waters contain little amount of Calcium Carbonates where as lime is important food of Coral Polyps. Hence oceanic salinity ranging between 27% & 30% is most ideal for the Growth and development of Coral Polyps.
  3. Ocean currents and Waves are favorable for Corals because they bring through transportation Necessary food supply for the POLYPS. (Hence Corals grow in Ocean seas and Oceans but they die in Lagoons and Small enclosed seas because of lack of supply food).
  • There should be extensive Submarine Platforms for the formation of Colonics by Coral Polyps. Such Platforms should not be more than 300 feet or 91 meters below the Sea-level.

 

TYPES OF CORAL REEFS:

FRINGING REEFS:

  • Coral reefs developed along the continental margins (or) along the Islands are FRINGING REEFS.
  • Sea-ward slope is steep and vertical while Land-ward slope is gentle.
  • Usually, Fringing Reefs are attached to Coastal land but sometimes there is gap between them and land and thus Lagoon is formed between fringing reef and the land (Such Lagoon is called Boat Channel).
  • Fringing Reefs are generally long but narrow in width.
  • Continuity of the reefs are broken whenever river drains in to seas and oceans.
  • Outward edge grows rapidly because of the splashing waves that continuously renew the supplies of fresh food.

 

BARRIER REEF:

  • Barrier reef is separated from the coast by a much wider and deeper channel or lagoon.
  • The REEF is partially submerged, where it lies above the water level and where Sand can accumulate on it, where vegetation is possible.
  • Barrier Reefs have Narrow gaps at several places to allow the water from the enclosed lagoon to return to the open Ocean. Such gaps are useful for shipping.
  • Best known Barrier Reef is the GREAT BARRIER REEF off the Coast of QUEENS LAND, AUSTRALIA. It is 1,200 miles along, separates from the Coast by a channel 100 miles wide in places and over 200 feet deep.

 

ATOLLS:

  • ATOLLS are similar to Barrier reefs except that they are circular in shape enclosing a shallow lagoon without any Land in the center.
  • ENCIRCLING ring is usually broken in few places to allow the free flow of water.
  • Inside the reefs, Sand and Limestone debris collect and Palm trees like coconut may grow. Such vegetation thrive well in BRACKISH water of the LAGOON.
  • CALM waters of the Lagoon are useful for FISHING and CANOEING.
  • Examples of large ATOLLS are -Western part of SriLanka, Suva diva in the Maldives.

 

EARTH’S CRUST (LITHOSPHERE)

  1. Thickness – (Around 100 kms)
  2. It forms 0.5% of earth’s Volume.
  3. Outer Covering of Crust is Sedimentary material and below it lies crystalline, igneous and metamorphic rocks which are acidic in nature.
  4. Lower Layer of the Crust consists of basaltic rocks.
  5. Continents are composed of lighter silicates it is SIAL (Silica +Aluminum ) density (2.7)
  6. While Oceans have heavier Silicates it is SIMA (Silica + Magnesium) Density (3)

Earth Crust

  • Earth Crust is made up of various types of rocks differing from one another in texture, structure, colour, mode of occurrence etc.
  • Generally Speaking rocks are Classified as
  1. Igneous
  2. Sedimentary
  3. Metamorphic

(Based on their origin ad occurrence)

  • Rocks are made of aggregate of minerals often, these minerals are Specifically referred as rock forming minerals.

 

MANTLE (MESOSPHERE)

  1. It lies between 100-2900 kms below the earth surface.
  2. It forms 16% of earth’s Volume
  3. Outer layer of Mantle is partly Simatic and behaves like a PLASTIC MASS, While Inner layer is composed of Wholly Simatic Ultra Basic rocks (Mainly of very dense Rocks Called “Olivine” )
  4. The boundary between crust and Mantle in a Surface of discontinuity which was discovered by “MOHOROVICIC” (Often referred as Simply “Moho” or “M” discontinuity)

 

CORE (Barysphere)

  1. It lies between 2900 kms to 6400 kms below the earth’s Surface.
  2. It accounts for 83% of earth’s Volume.
  3. Central Core has the Heaviest Mineral Material of highest density. It is composed of Nickel & iron (Ferrous) therefore called NIFE.
  4. Zone of mixed heavy metals and Silicates Separate the Core from outer layers.

 

LOCAL WINDS

Temporates                            : Central America, Monsoon winds.

Virazon                                  : Peru and Chile, Sea winds

Shamal                                   : Iran, Iraq, Arab: dry

Southern Burster                  : North South Wales-Australia: dry wind

Samoon                                  : Iran

Bise                                         : France: Cold

Purga                                      : Tundra region and Russia: cold

Ponente                                  : Mediterranean (France): cold

Papagayo                               : Mexico: hot

Baguis                                     : Philippines: Warm tropical

Berg                                        : South Africa

Gergale                                   : Southern Europe:Gold

Jorran                                                : Geneva Lake: cold dry

Leste                                       : hot

Levanter                                 : Southern Spain, strong easterly cold wind

Karaburan                             : Tarim Basin (Central Asia): hot

Maestro                                  : Mediterranean

Norte                                      : Central America: cold

North Western Wind            : New Zealand

Loo                                         : North India: dry

Haboob                                   : Sudan

Yamo                                      : A warm and dry wind in Japan

Zonda                                     : A Warm wind in Argentina

Tramontane                           : A warm wind in Central Europe

Bora                                        : Southern Europe: Cold

Mistral                                    : Southern Europe: Cold

Blizzard                                  : North America: cold

Buran                                     : Siberia (Russia): cold

Pampero                                 : Argentina

Norther                                  : Texas (USA)

 

DIFFERENT NAMES OF TROPICAL CYCLONES:

Hurricanes       :           North America& Caribbean

Typhoons        :           Western North Pacific

Willy-willy      :           Australia

Baguio             :           Philippines Island

Taifu                :           Japan

Cyclones         :           Indian Ocean

 

MAJOR GRASSLANDS

Grass lands                Continents/Countries

Prairies            :           North America

Pampas            :           South America

Pretoria            :           South Africa

Veld                :           South Africa

Steppes            :           Eurasia

Downs             :           Australia

Pustaz              :           Hungary

Cantanburry    :           New Zealand

Manchurian     :           China

 

 

MOUNTAIN, PLATEAU, PLAINS

Earth Movement (Diastrophic movement) (or) Mountain building):

  • Agents of denudation, Shape the land form systems.
  • Agents of denudation modify the pattern of mountains, plateau and plains which have been already modeled by slow movements of earth crust.
  • No less than nine orogenic (or) Mountain Building movement have taken place.
  • Three recent orogenics are Caledonian, Hercynian and Alpine.

 

Caledonian, (320 Million Years ago):

  • Mountains of Scandinavia and Scotland .
  • These have been worn down and no longer exhibit the striking forms that they had once.

 

Hercynian (240 Million Years Ago):

  • Ural Mountains, welsh High lands in Britain, Appalachians in U.S.A, High plateau of Siberia and China.

 

Alpine (30 million years ago):

  • Alps, Himalayas, Andes, Rockies are the loftiest and most imposing.

 

Types of Mountains

  1. Fold mountains
  2. Block mountains
  3. Volcanic mountains
  4. Residual Mountains

 

Fold Mountains:

  • Most widespread and most important.
  • Caused by large Scale earth movements when stresses are setup in the earth crust.
  • When Stresses are initiated rocks are subjected to compressive forces that produce wrinkling (or) Folding along the lines of weakness.
  • Upfold waves are called Anticlines and down fold waves are known as Synclines.
  • When Crest of the folds is pushed far, over fold is formed.
  • If it is pushed still further, it becomes recumbent fold.
  • In extreme cases fracture may occur in the crust, so that the upper part of the recumbent fold slides forward over the lower part along a thrust plane forming a over thrust fold. over riding portion of the thrust fold is termed as
  • Fold mountains may be elevated to great heights, Sometimes measurable in miles, which is also known as Mountains of elevation
  • Fold Mountains are Closely associated with volcanic activity. They contain many active volcanoes in the circum-pacific fold mountain system.
  • Fold Mountains contain rich mineral resources such as Tin, copper, gold and petroleum.

 

Block Mountains(Horst) :

  • Faulting maybe caused by tension (or) Compression forces which lengthen (or) Shorten the earth’s Crust, Causing a section of it to subside (or) rise above the Surrounding level.
  • Subsiding below the surrounding level causes Rift Valley (or) graben.
  • Rising above the Surrounding level causes the Black Mountain (or) Horst
  • Tensional Forces Create Block Mountains (or) Rift Valleys – Faulted edges are very steep with sharp slopes and the summit is almost level. Eg: Vosges and Black Forest of the Rhine land.
  • Tensional Forces also create central Portion to be let down between two adjacent fault blocks forming Rift Valleys.

Eg: African Rift Valley (3,000 miles long)

  • Compressional Forces Set up by earth movements may produce thrust (or) Reverse fault and Shorten the earth Crust.
  • In General, large Scale Block Mountains and Rift Valleys are due to tension rather than Compression.
  • FALUTS may occur in series and be further Complicated by Tilting and other irregularities.

 

Volcanic Mountains:

  • It is also known as Mountain of accumulation.
  • Mount Fujiyama (Japan), Mount Mayon (Philippines), Mount Merapi (Sumatra), Mount Cotopaxi (Ecuador)

 

Residual Mountains:

  • Known as Mountains of denudation.
  • General level of land is lowered by agents of denudation and some of the very resistant areas may remain and these forms Residual Mountains.
  • Residual Mountains may also be evolved from plateaus, which have been dissected by reverse fault into hills and Valleys.
    • Eg: Deccan Pleatean hi9ghlands of Scandinavia.

 

PLATEAUX:

  • Plateaus are Elevated Uplands with extensive level surface and usually descend steeply to the surrounding lowland.
  • They are sometime referred to as ‘Table–lands’

 

TYPES OF PLATEAUX (Based on their Made of formation and their Physical appearance)

 

Tectonic Pleateaux (By Earth Movements)

  • Formed due earth movements which cause Upliftment and are normally of a considerable size and fairly uniform altitude. They Include large continental blocks. Some of the tectonic Plateau may be tilted.

Eg: meseta of central Iberia

  • When Plateaus are enclosed by fold Mountains, they are known Inter-mount Plateau.

Eg: 1) Tibetan Plateau between Himalayas and KUNLAN.

  • Bolivian Plateau between two ranges of the ANDES.
  • INTER-MONT PLATEAU are some of the highest and the most extensive plateau in the world.

 

b)VOLCANIC PLATEAU:

  • Molten lava from the earth’s crust may spread over the surface to form successive sheets of basaltic lava . They solidify to form LAVA PLATEAU. Also referred as VOLCANIC PLEATEAU.
    • ANTRIM PLATEAU(North Iceland
    • North western of DECCAM plateau
    • COLUMBIA – SNAKE Plateau
  • Each layer of lava flow is over 100feet thick and entire depth of successive lava layers estimated to be almost a mile.

 

  1. c) DISSECTED PLATEAU:
  • Through continual process of Weathering and erosion.
    • Humid conditions – streams action (river)
    • Dry condition- Winds & Vertical corrosion by rivers .

WORLD’S PLATEAU HAVE RICH MINERALS

  • African Plateau – Gold, Diamond, Copper, Manganese and Chromium
  • Brazilian Plateau – Huge resources of Iron and Manganese particularly in the Minas Gerais
  • Deccan Plateau – Deposits of Coal, Manganese, Iron
  • Western Australian Plateau – Gold and Iron

PLAINS:

  • Plain is an area of Lowland either level or undulating.
  • It seldom (rarely) rises more than a few hundred feet above sea level.
  • If Low hills are present, it would give a typical Rolling topography.

 

TYPES OF PLAIN

  1. STRUCTURAL PLAINS:
    • STRUCTURALLY DEPRESSED areas of the world that make up some of the most extensive Natural Lowlands on the earth’s Surface.
    • They are formed by horizontally bedded rocks, relatively undisturbed by the Crustal Movements of the earth.

Eg: Great Plain as the Russian Platform.

Great Plains of USA.

Central Lowlands of Australia.

 

  1. DEPOSITIONAL PLAINS
  • Formed by deposition of materials brought by various agents of transportation
  • They are comparatively level lands, but rise gently towards adjacent highlands.
  • They are fertile and their economic developments depend greatly on the types of sediments that are laid down.

 

RIVER(Depositional):

  • Large depositional plains are due to deposition by large rivers. Active erosion in the Upper course results in large quantities of Alluvium being brought down to the lower course and deposited to form extensive- ALLUVIAL PLAIN, FLOOD PLAIN ,DELTAIC PLAIN.
  • These Plains form most productive agricultural area of the world, intensively tilled and densely populated.

Eg: Nile valley of Egypt (rice & Cotton)

Ganges delta (rice & Jute)

Plains of North China (Hwang Ho) (Spread out thick mantle of      alluvium).

 

GLACIER & ICE SHEETS (Depositional):

  • Deposits wide Spread Mantle of unsorted Fluvio-Glacial Sands and gravels in the outwash plain. They are usually barren lands.
  • Glacier may drop boulder clay (Mixture of boulders and Clay) to form a till Plain or drift Plain. They may be very valuable for farming.

eg: Mid West of USA, East Anglia in England.

 

COASTAL(Depositional):

  • Waves and Winds often drive beach Materials – Mud, Sand or Shingle towards land and deposit them on the Coastal Plain.

Eg: Gulf Coast of USA coastal Lowlands of Belgium.

  • Upliftment may raise the Coastal Low lands Slightly and they form an Emergent Coastal Plain. Eg: Coastal Margins from Florida to Texas.

 

WIND (Depositional):

  • Winds may blow Aeolian deposits, Very fine particles known as LOESS from Interior deserts (or) barren surface and deposit them upon hills, Valley (or) Plains to form LOESS PLAIN as in North-West China (or) Loess Plain. Similarly Pampas of Argentina.
  • It helps to level an undulating plain by filling up grooves and depressions.
  • They are agricultural regions.

 

EROSIONAL PLAIN:

  • Plains carved by agents of EROSION (river, Rain, Ice, Wind) to Smoothen out irregularities of the earth’s Surface and in terms of millions of years, even high mountain can be reduced to low undulating plains.Such Plains of denudation are described as peneplain (almost Plains)

 

 

RIVERS (EROSIONAL):

  • From source to Sea.
  • Higher land between the rivers is gradually lowered.

 

GLACIERS(EROSIONAL):

  • Glaciers and Ice-Sheets scoured and leveled forming ICE-SCOURED PLAINS
  • HOLLOWS SCOOPED out by Ice are now filled by lakes. Extensive Ice scoured Plains in Northern Europe and Northern Canada.

Eg: FINLAND estimated to have 35,000 lakes, occupying 10% of the total land Surface of the Country.

 

WIND (EROSIONAL):

  • Wind deflation sweeps away much of the eroded desert materials, lowering the level of the land and forming extensive Plains.

Eg:Gravelly Stony desert Plain called Reg in Africa.

  • Mechanical weathering in arid or Semi-arid regions wears back the mountain slopes to leave a gently sloping pediments or pedi-plains.

 

ROCKS

Igneous Rock (IGNIS – Meaning “Fire”)

  1. Rocks formed through Solidification of molten material (magma) originally within the earth crust.
  2. When molten material either Cools down on reaching the earth’s Surface or within the Fissures and Cavities of earth.
  3. On the Basis of place and time take for the molten material to cool down is divided in to following types.

 

  1. Plutonic Rocks (Instructive Rocks)
  • When molten material is not able to reach the earth’s Surface and instead Cools down very slowly at great depths. This slow cooling allows Big Sized crystals to be formed. Granite is a typical example. It appears on the Surface only after being uplifted or denuded (eg. Granite, dibrite, gabbro)

 

  1. Lava or Volcanic Rocks (extrusive Rocks)
  • It is formed by Rapid Cooling of lava movements by volcanic eruptions. This rapid Cooling prevents Crystallization as a result of this rocks are fine-grained Basalt is a typical example.
  • Deccan Plateau in Indian peninsular is of Basaltic Origin.
  • Basaltic is a common volcanic or extrusive rock
  • Antrim in northern island, Colombia Snake plateau in U.S.A.
  • Molten Lava pushes its way to the upper surface of the earth through “Clefts and passages” and Solidify as (Vertical Dykes) or (Horizontal Sills).

 

  1. Hypabyssal (or) Dyke rocks :
  • These rocks occupy an intermediate position between deep-Seated plutonic rocks and the surface volcanic lava flows.
  • Hence Dyke rocks are Semi Crystalline in nature.

 

Based on the form of the Molten Magma acquires after Cooling, Igneous Rock could be divided in to several types.

  1. Batholith
  • When molten magma spreads across a wide area cutting through various layers it is known as (Huge mass of IGNEOUS Rocks). At Times it may be exposed above the Surface.

 

  1. Lacolith
  • When acetic Magma Cools down fast it gets hardened at ordinary temperature. Further push from below gives its doom like appearance. These are Laccoliths. Large igneous mound with a doom-shaped upper surface and a level-base fed by a PIPE –LIKE conduit from below.

 

  1. Lapolith
  • Another Variety of Igneous Intrusion with a SAUCER Shape. A Concave variant of the Batholiths

 

  1. Phacolith
  • When Solidified magma acquired a wave like form it is phacolith. Lens-shaped mass of igneous rocks occupying the crest of an anticline or the bottom of a syncline and being fed by a conduit from beneath.

 

  1. Sheet
  • When molten magma cools down in thin horizontal layers parallel to surface of the earth it is called sheet.

 

  1. Sill
  • If the Sheet is thick it is called Sill.
  1. Boss
  • When Magma after cooling is not parallel to the layers around it and makes a angle with them it is called Boss.

 

  1. Dyke
  • If the above mentioned angle is 900 it is called Dyke.

 

  1. Volcanic Neck
  • Solidified lava in the form of a cylinder is found as plugs in the vent of the volcano .It is known as Volcanic Neck.

 

Sedimentory Rocks:

  • Sedimentary Rock covers 75% of earth surface. But volumetrically occupy only 5% of the earth crust.
  • Sedimentary Rocks are those formed by the deposition of the solid materials carried in suspension by transporting agents.
  • The deposited material under the pressure of overlaying layer is transformed into Sedimentary rocks with passage of time.
  • As Sedimentation is favoured by water, most of the sedimentary rocks have been formed under water.
  • These are characterized by layer formation and are termed as stratified rocks.
  • These are non-crystalline and often contain fossils of animals, plants and other micro organisms.
  • They are classified according to age and different kinds of rocks formed during the same period are grouped together.

 

Classification:

  • Most Common form of classification in based on the mode of their formation. It is through mechanical, Chemical and organically formed Sedimentary rocks.

 

  1. Mechanically formed:
  • These are formed by mechanical agents like running water, wind, Ocean currents, ice etc.
  • Some of these rocks have more sand, big size particles and are very hard. These are called “arenaceous” e.g. Sand store.
  • While some are mechanically formed rocks have more clay, fine grained, Softer impermeable and porous. These are called “argillaceous” rocks . These are easily weathered and eroded. e.g.

 

  1. Chemically Formed:
  • After coming in contact with running water, (It is both surface and sub Surface) many minerals get dissolved in it. This Chemically charged water often leaves layers of these chemicals after the water has been evaporated. Such deposits occur at the mouth of the spring salt lakes and deposits of lime etc.
  • Rocks Salts are desired from strata, which once formed the beds of seas or lakes.
  • Gypsum or calcium sulphate is obtained from the evaporating of salt lakes. Such as Dead Sea which have a very high Salinity.

 

  1. Organically formed:
  • Formed from the remains of plants and animals.
  • These plants and animals are buried under sediments and due to heat and pressure from overlaying layers, their composition undergoes a change. E.g. Coal and lime Stone.
  • Plant remaining in the coal gives different grades depending upon the proposition of Carbon and the degrees of over lying pressure.

 

 

Coal Formation:

  • First Stage: Peat and lignite having 45% Carbon.
  • Second Stage: Bituminous Variety having 60 – 70% Carbon.
  • Third Stage: Anthracite – 90% Carbon.
  • Most of the rocks formed from the remains of living organisms are classified into calcareous and carbonaceous.

 

Economic Significance:

  • Not rich in minerals and have economic value as igneous rocks. Important Minerals such as Hematite, Iron ore, Phosphates, Coals, Petroleum and Materials used in cement industry are found in sedimentary rocks.

 

Metamorphic:

  • All rocks whether igneous or sedimentary may become metamorphic or changed rocks.
  • Original Character and appearance may be greatly altered by such forces particularly during intense earth movements.

 

  • Original State –          Metamorphic State
  1. a) Lime stone    heat              Marble
  2. b) Coal heat              anthracite, graphite
  3. c) Sand Stone heat Quartzite
  4. d) Granite Pressure Gneiss
  5. e) Clay, Shale heat Slate
  6. f) Clay, Shale Pressure Schist

 

SOILS

Alluvial Soil: (Rich in potash, poor in nitrogen & Organic matter)

  • Derived from debris brought by rivers and the silt left behind by old Sea.
  • Coastal alluvium is of tidal Origin.
  • Desert alluvium or “Loess” is brought by wind erosion.
  • These are best agricultural soils because they contain.
  • Variety of salts derived from rocks.
  • They are light and porous, therefore easily tillable.
  • These Soils are not good for crops requiring water retention around the roots, because these Soils are porous and allow water to go deep.

 

Black or Regur Soil (Poor in nitrogen, Phosphorous, Potassium, Organic matter , Rich in iron, Carbonates of magnesium, Calcium and Alumina)

  • Very Clayey up to 50% clay content and therefore highly retentive of water. This makes them suitable for dry land farming.
  • Because of high Clay content these soils expand when wet and shrink while dry. Thus, it becomes difficult to till when wet and during dry season black soil shrinks and develop big cracks up to one meter wide.

 

Red Soils :

  • These are red due to presence of iron oxides. Poor in nitrogen, Phosphorous, Potassium and organic matter.
  • Red Soils are derived from weathering of old crystalline and metamorphic Rocks.
  • These soils are loamy or Sandy and have Low water retention capacity.

 

Laterite Soils: ( Poor in – N2 ,K,P and Organic Malter)

  • These Soils are typical of tropical areas and are the end product of decomposition when high rainfall leaches away Calcium and Silica. Leaving behind iron and Silica. Iron content gives these soils a red colour.
  • These Soils are agriculturally unimportant because of their intensive leaching and their acidic in nature.

 

Forest Soils:

  • Forest Soil Rich in decomposed Organic matter. (Sometimes referred to as mountain soils or hill soils)
  • These are dark soils confined in the altitude 3000 meters height in coniferous region.

 

Mountain Soils ( Altitude : 2000 – 3000 m)

  • These Soils or Subject to dislodgement due to land Slides and snowfall.
  • These are Shallow, Silty loam, Well drained, Stony and poorly endowed with organic water.
  • Used in growing potatoes and Sub tropical fruits.

 

Desert Soils (or) Arid Soils:

(Rich in soluble salts of phosphates and nitride, and low nitrate content)

  • These Soils are covered with thick brown mantle which inhibits Soil growth
  • These are derived from adjoining rocks and from the nearby Coastal region.
  • These are actually fertile Soils, water being the only limiting factor for agricultural purpose.

 

Saline and alkaline Soils( Salts of Calcium magnesium and Sodium)

  • These Soils cover arid and Semi-arid regions
  • These Soils are associated with sub-Soil impervious layer, high water table, Channel irrigation (helping the Salts to come up to the Surface) and an inadequate surface drainage.
  • Local names of Saline and alkaline Soils include Reh, Usar, Kallar, rakar, Chopan.
  • Presence of Salt, Cemented layer and bad water retention makes these Soil unsuitable for agriculture.

 

Peaty Soil and Marshy Soils (deficiency of nitrogen & Organic Malter) :

  • These Soils cover high rainfall areas. These are heavy, dark and acidic and are formed under condition of submergence.
  • Remains submerged during monsoon and experience accumulation of organic matter with large quantities of soluble salts. Such as Ferrous & aluminum

 

Soil Erosion: Types.

  • Wind erosion Inter-rill erosion
  • Sheet erosion Inter-gully erosion
  • Rill erosion
  • Gully erosion
  • Splash erosion

 

Wind Erosion:

  • It involves actual removal of dry and unconsolidated material by transportation of Wind.
  • It is mostly felt in desert region of the world.
  • Wind deflation in desert areas leads to excavation of wide shallow basins known as deflation hallows (or) blow outs.
  • Sometimes desert floor is lower to the level of ground water, hence water-table is found to be lower than the Sea level , such depressions is called ‘Oasis’ (or) ‘Oasas’. Eg:Pans in South Africa and Kalahari desert, Tsaidam sarang in Mongolian desert.
  • Desert pavements form when fine particles flown away by wind, Pebbles and boulders are left behind as lag deposits.

 

Splash Erosion:

  • Soil breaks down in to fine particles, when Raindrops Strike against the bare ground Surface, erosion is accelerated in the absence of vegetative cover hence kinetic energy of this type of erosion is great. This process is known as Splash erosion.
  • It causes resettling of up thrown Soil particles in the upper most horizons of the Soil profile which causes plugging and sealing of large pore spaces. It forms impervious thin layer that prevents water infiltration. During heavy rain, surface runoff carries away Soil particles. This is known as ‘Entrainment’.

 

Sheet Erosion (Rain Wash):

  • It occurs as the Soil is eroded in thin layers.

 

Rill erosion:

  • Heavy precipitation along with Rain Storms transforms Sheet flow in to linear flow called ‘Rills’. This resultant erosion produced by Rills known as Rill erosion.
  • During Rill erosion several inter connected Rills merge to form Shoes-string rills.

 

Gully erosion:

  • If Rills are not destroyed, they enlarge and deepen to form Gullies.
  • Erosion caused by both Rills and Gullies is known as Rill and Ravine erosion. This is the most destructive form of Soil erosion. It often leads to formation of bad land Topography.

Inter- Rill erosion:

  • Soil Erosion caused by Splash erosion and Sheet erosion in areas located between two Rills is known as ‘Inter-Rill erosion’.

 

Inter – Gully Erosion:

  • Soil erosion between two gullies is known as Inter-Gully erosion.

 

Causes of Soil erosion:

  • Deforestation
  • Over grazing of pastures
  • Shifting Cultivation
  • Faulty methods of Cultivation
  • Diversion of natural drainage course by Road (or)
  • Rail– embankment.

 

Effects of Soil erosion:

  • Reduction of Soil fertility and in turn
  • Heavy floods in Rivers.
  • Lowering down of Sub Soil Water level.
  • Accelerates aridity.
  • Lowers water tables.
  • Silting of Streams and Water Courses.
  • Diminishes Rainfall.

 

Soil Conservation Measures:

  • Afforestation
  • Controlled grazing
  • Appropriate agricultural practices
  • Crop rotation
  • Strip cropping
  • Seasonal Cover Cropping and Green Manure

 

Mechanical Methods of Soil Conservation

  • Terrace Cultivation and contour farming
  • Rill and Gully plugging

 

 

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