Flash Card

LAKSHYA-75 [Day-15] Static Flash Cards for IAS Prelims 2020

Volcanoes; Evidence in Support of the Continental Drift; Plate Tectonics; Some Major Minerals and Their Characteristics; Igneous Rocks & Sedimentary Rocks; Weathering; Wind’s Erosional landforms; Inversion of Temperature; General circulation of the atmosphere; Koeppe N’s Scheme of Classification of Climate
By IASToppers
March 21, 2020



According to koeppe N’s Scheme of Classification of Climate, which type of climate is indicated by Group B?

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Dry Climate

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koeppe N’s Scheme of Classification of Climate

  • The most widely used classification of climate is the empirical climate classification scheme developed by V. Koeppen.
  • Koeppen identified a close relationship between the distribution of vegetation and climate. He selected certain values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.
  • It is an empirical classification based on mean annual and mean monthly temperature and precipitation data. The method introduced the use of capital and small letters to designate climatic groups and types.
  • Koeppen recognised five major climatic groups, four of them are based on temperature and one on precipitation.
  • Below table lists climatic groups and their characteristics according to Koeppen.
  • The capital letters: A, C, D and E delineate humid climates and B dry climates.
  • The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics.

The climatic types are listed in below table:



In the middle latitudes, the cold air coming from the poles sink and the warm air that blows from the subtropical high is rising. This circulation forms which cell?

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In the middle latitudes the circulation is that of sinking cold air that comes from the poles and the rising warm air that blows from the subtropical high. At the surface these winds are called westerlies and the cell is known as the Ferrel cell.

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General circulation of the atmosphere

  • The pattern of planetary winds largely depends on:
    • latitudinal variation of atmospheric heating
    • emergence of pressure belts
    • the migration of belts following apparent path of the sun
    • the distribution of continents and oceans
    • the rotation of earth
  • The pattern of the movement of the planetary winds is called the general circulation of the atmosphere.
  • The general circulation of the atmosphere also sets in motion the ocean water circulation which influences the earth’s climate.
  • The air at the Inter Tropical Convergence Zone (ITCZ) rises because of convection caused by high insolation and a low pressure is created.
  • The winds from the tropics converge at this low pressure zone. The converged air rises along with the convective cell. It reaches the top of the troposphere up to an altitude of 14 km. and moves towards the poles. This causes accumulation of air at about 30oN and S.
  • Part of the accumulated air sinks to the ground and forms a subtropical high. Another reason for sinking is the cooling of air when it reaches 30oN and S latitudes.
  • Down below near the land surface the air flows towards the equator as the easterlies. The easterlies from either side of the equator converge in the Inter Tropical Convergence Zone (ITCZ).
  • Such circulations from the surface upwards and vice-versa are called cells. A cell in the tropics is called Hadley Cell.
  • In the middle latitudes the circulation is that of sinking cold air that comes from the poles and the rising warm air that blows from the subtropical high. At the surface these winds are called westerlies and the cell is known as the Ferrel cell.
  • At polar latitudes the cold dense air subsides near the poles and blows towards middle latitudes as the polar easterlies. This cell is called the polar cell.
  • These three cells set the pattern for the general circulation of the atmosphere. The transfer of heat energy from lower latitudes to higher latitudes maintains the general circulation.
  • The general circulation of the atmosphere also affects the oceans.
  • The large-scale winds of the atmosphere initiate large and slow moving currents of the ocean. Oceans in turn provide input of energy and water vapour into the air.



What could be the ideal condition for inversion of temperature?

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A long winter night with clear skies and still air could be ideal situation for inversion of temperature.

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Inversion of Temperature

  • Normally, temperature decreases with increase in elevation. It is called normal lapse rate.
  • At times, the situation is reversed and the normal lapse rate is inverted. It is called Inversion of temperature. Inversion is usually of short duration but quite common nonetheless.
  • The heat of the day is radiated off during the night, and by early morning hours, the earth is cooler than the air above. Over polar areas, temperature inversion is normal throughout the year.
  • Surface inversion promotes stability in the lower layers of the atmosphere.
  • Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the atmosphere.
  • Dense fogs in mornings are common occurrences especially during winter season. This inversion commonly lasts for few hours until the sun comes up and beings to warm the earth.
  • The inversion takes place in hills and mountains due to air drainage. Cold air at the hills and mountains, produced during night, flows under the influence of gravity.
  • Heavy and dense cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottoms with warm air above. This is called air drainage. It protects plants from frost damages.



Name landforms created by erosional and depositional activities of wind.

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  • Pediments and Pediplains, Playas, Deflation Hollows and Caves and Mushroom, Table and Pedestal Rocks are wind’s erosional landforms.
  • Various types of sand dunes like Barchans, Parabolic dunes, Seif, Longitudinal and Transverse dunes are depositional landforms of wind.

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Wind’s Erosional landforms

Pediments and Pediplains

  • Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are called pediments.
  • Such rocky floors form through the erosion of mountain front through a combination of lateral erosion by streams and sheet flooding.
  • Once, pediments are formed, the steep wash slope and free face retreat backwards. This method of erosion is termed as parallel retreat of slopes through backwasting.
  • So, the pediments extend backwards and gradually, the mountain gets reduced leaving an inselberg which is a remnant of the mountain.
  • That’s how the high relief in desert areas is reduced to low featureless plains called pediplains.


  • In basins with mountains and hills around and along, the drainage is towards the center of the basin and due to gradual deposition of sediment from basin margins, a nearly level plain forms at the center of the basin.
  • In times of sufficient water, this plain is covered up by a shallow water body. Such types of shallow lakes are called as playas.
  • Water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts.
  • The playa plain covered up by salts is called alkali flats.

Deflation Hollows and Caves

  • Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows.
  • Deflation also creates numerous small pits or cavities over rock surfaces.
  • The rock faces suffer impact and abrasion of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs become deeper and wider fit to be called caves.

Mushroom, Table and Pedestal Rocks

  • Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear shaped cap above.
  • Sometimes, the top surface is broad like a table top and quite often, the remnants stand out like pedestals.

Wind’s Depositional Landforms

  • In depositional landforms made by wind, good sorting of grains can be found.

Sand Dunes

  • Dry hot deserts are good places for sand dune formation. Obstacles to initiate dune formation are equally important.
  • There can be a great variety of dune forms


  • Crescent shaped dunes called barchans with the points or wings directed away from wind direction i.e., downwind. It forms where the wind direction is constant and moderate and where the original surface over which sand is moving is almost uniform.
  • Parabolic dunes form when sandy surfaces are partially covered with vegetation.
  • That means parabolic dunes are reversed barchans with wind direction being the same.
  • Seif is similar to barchan with a small difference. Seif has only one wing or point. This happens when there is shift in wind conditions. The lone wings of seifs can grow very long and high.
  • Longitudinal dunes form when supply of sand is poor and wind direction is constant.
  • They appear as long ridges of considerable length but low in height.
  • Transverse dunes are aligned perpendicular to wind direction.
  • These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction. They may be very long and low in height.

When sand is plenty, quite often, the regular shaped dunes coalesce and lose their individual characteristics.



What happen to iron when it is exposed to chemical weathering processes especially oxidation and reduction?

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Red colour of iron upon oxidation turns to brown or yellow. Red colour of iron upon reduction turns to greenish or bluish grey.

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  • Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.
  • There are a number of processes within weathering which act either individually or together to affect the earth materials in order to reduce them to fragmental state.
  • As very little or no motion of materials takes place in weathering, it is an in-situ or on-site process.
  • Weathering processes are conditioned by many complex geological, climatic, topographic and vegetative factors.
  • Climate is of particular importance. Not only weathering processes differ from climate to climate, but also the depth of the weathering mantle.
  • Climatic regimes and depth of weathering mantles are shown in below figure.

There are three major groups of weathering processes: chemical; physical or mechanical; and biological weathering processes.

Chemical Weathering Processes

  • A group of weathering processes viz; solution, carbonation, hydration, oxidation and reduction act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids.
  • Water and air (oxygen and carbon dioxide) along with heat must be present to speed up all chemical reactions.
  • Decomposition of plants and animals increases the quantity of carbon dioxide underground.
  • These chemical reactions on various minerals are very much similar to the chemical reactions in a laboratory.


  • This process involves removal of solids in solution and depends upon solubility of a mineral in water or weak acids.
  • On coming in contact with water many solids disintegrate and mix up as suspension in water. Soluble rock forming minerals like nitrates, sulphates, and potassium are affected by this process.
  • So, these minerals are easily leached out without leaving any residue in rainy climates and accumulate in dry regions.
  • Common salt (sodium chloride) is also a rock forming mineral and is susceptible to this process of solution.


  • Carbonation is the reaction of carbonate and bicarbonate with minerals and is a common process helping the breaking down of feldspars and carbonate minerals.
  • Carbon dioxide from the atmosphere and soil air is absorbed by water, to form carbonic acid that acts as a weak acid.
  • Calcium carbonates and magnesium carbonates are dissolved in carbonic acid and are removed in a solution without leaving any residue resulting in cave formation.


  • Hydration is the chemical addition of water.
  • Minerals take up water and expand; this expansion causes an increase in the volume of the material itself or rock.
  • Calcium sulphate takes in water and turns to gypsum, which is more unstable than calcium sulphate.
  • This process is reversible and long, continued repetition of this process causes fatigue in the rocks and may lead to their disintegration.

Oxidation and Reduction

  • In weathering, oxidation means a combination of a mineral with oxygen to form oxides or hydroxides.
  • Oxidation occurs where there is ready access to the atmosphere and oxygenated waters.
  • The minerals most commonly involved in this process are iron, manganese, sulphur In the process of oxidation rock breakdown occurs.
  • When oxidised minerals are placed in an environment where oxygen is absent, reduction takes place.
  • Such conditions exist usually below the water table, in areas of stagnant water and waterlogged ground.



Based upon the mode of formation, classify the sedimentary rocks.

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Depending upon the mode of formation, sedimentary rocks are classified into three major groups:

  • mechanically formed — sandstone, conglomerate, limestone, shale, loess etc.
  • organically formed — geyserite, chalk, limestone, coal etc.
  • chemically formed — chert, limestone, halite, potash etc.

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There are many different kinds of rocks which are grouped under three families on the basis of their mode of formation. They are:

(i) Igneous Rocks– solidified from magma and lava

(ii) Sedimentary Rocks– the result of deposition of fragments of rocks by exogenous processes

(iii) Metamorphic Rocks– formed out of existing rocks undergoing recrystallization

Igneous Rocks

  • As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks.
  • The igneous rocks (Ignis – in Latin means ‘Fire’) are formed when magma in its upward movement cools and turns into solid form it is called igneous rock.
  • The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth.
  • Igneous rocks are classified based on texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials.
  • If molten material is cooled slowly at great depths, mineral grains may be very large.
  • Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks.
  • Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.

Sedimentary Rocks

  • The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling.
  • Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited.
  • These deposits through compaction turn into rocks. This process is called lithification.
  • In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification.
  • Hence, a number of layers of varying thickness can be seen in sedimentary rocks like sandstone, shale



It is a hard mineral virtually insoluble in water. It is white or colorless and used in radio and radar. It consists of silica. Which Mineral is this?

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Some Major Minerals and Their Characteristics


  • Silicon and oxygen are common elements in all types of feldspar and sodium, potassium, calcium, aluminium etc. are found in specific feldspar variety.
  • Half of the earth’s crust is composed of feldspar. It has light cream to salmon pink colour. It is used in ceramics and glass making.


  • It is one of the most important components of sand and granite.
  • It consists of silica. It is a hard mineral virtually insoluble in water. It is white or colorless and used in radio and radar.
  • It is one of the most important components of granite.


  • Pyroxene consists of calcium, aluminum, magnesium, iron and silica.
  • Pyroxene forms 10 per cent of the earth’s crust. It is commonly found in meteorites. It is in green or black


  • Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles.
  • They form 7 per cent of the earth’s crust. It is in green or black colour and is used in asbestos industry.
  • Hornblende is another form of amphiboles.


  • It comprises of potassium, aluminium, magnesium, iron, silica etc.
  • It forms 4 per cent of the earth’s crust.
  • It is commonly found in igneous and metamorphic rocks. It is used in electrical instruments.


  • Magnesium, iron and silica are major elements of olivine.
  • It is used in jewellery. It is usually a greenish crystal, often found in basaltic rocks.
  • Besides these main minerals, other minerals like chlorite, calcite, magnetite, hematite, bauxite and barite are also present in some quantities in the rocks.



Pacific plate and Eurasian plate can be referred to as the continental plate or oceanic plate?

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Pacific plate is largely an oceanic plate whereas the Eurasian plate may be called a continental plate.

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Plate Tectonics

  • Since the advent of the concept of sea floor spreading, the interest in the problem of distribution of oceans and continents was revived.
  • McKenzie, Parker and Morgan, independently collected the available ideas in 1967, and came out with another concept termed Plate Tectonics.
  • A tectonic plate (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
  • Plates move horizontally over the asthenosphere as rigid units.
  • The lithosphere includes the crust and top mantle with its thickness range varying between 5 and100 km in oceanic parts and about 200 km in the continental areas.
  • A plate may be referred to as the continental plate or oceanic plate depending on which of the two occupy a larger portion of the plate.
  • The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates.
  • Young Fold Mountain ridges, trenches, and/or faults surround these major plates.

The major plates are as follows:

  1. Antarctica and the surrounding oceanic plate
  2. North American (with western Atlantic floor separated from the South American plate along the Caribbean islands) plate
  3. South American (with western Atlantic floor separated from the North American plate along the Caribbean islands) plate
  4. Pacific plate
  5. India-Australia-New Zealand plate
  6. Africa with the eastern Atlantic floor plate
  7. Eurasia and the adjacent oceanic plate

Some important minor plates are listed below:

  • Cocos plate: Between Central America and Pacific plate
  • Nazca plate: Between South America and Pacific plate
  • Arabian plate: Mostly the Saudi Arabian landmass
  • Philippine plate: Between the Asiatic and Pacific plate



A contiguous landmass ‘Lemuria’, which supports the Continental Drift, links which three landmasses?

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The observations in support of the Continental Drift considers a contiguous landmass ‘Lemuria’ linking India, Madagascar and Africa.

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Evidence in Support of the Continental Drift

The Matching of Continents (Jig-Saw-Fit)

  • The shorelines of Africa and South America facing each other have a remarkable and unmistakable match.
  • A map produced using a computer programme to find the best fit of the Atlantic margin was presented by Bullard in 1964. It proved to be quite perfect.
  • The match was tried at 1000- fathom line instead of the present shoreline.

Rocks of Same Age Across the Oceans

  • The radiometric dating methods have facilitated correlating the rock formation from different continents across the vast ocean.
  • The belt of ancient rocks of 2000 million years from Brazil coast matches with those from western Africa.
  • The earliest marine deposits along the coastline of South America and Africa are of the Jurassic age. This suggests that the ocean did not exist prior to that time.


  • It is the sedimentary rock formed out of deposits of glaciers.
  • The Gondawana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere. Counterparts of this succession are found in Africa, Falkland Island, Madagascar, Antarctica and Australia.
  • Overall resemblance of the Gondawana-type sediments clearly demonstrates that these landmasses had remarkably similar histories.
  • The glacial tillite provides unambiguous evidence of palaeoclimates and also of drifting of continents.

Placer Deposits

  • The occurrence of rich placer deposits of gold in the Ghana coast and the absolute absence of source rock in the region is an amazing fact.
  • The gold bearing veins are in Brazil and it is obvious that the gold deposits of the Ghana are derived from the Brazil plateau when the two continents lay side by side.

Distribution of Fossils

  • When identical species of plants and animals adapted to living on land or in fresh water are found on either side of the marine barriers, a problem arises regarding accounting for such distribution.
  • The observations that Lemurs occur in India, Madagascar and Africa led some to consider a contiguous landmass ‘Lemuria’ linking these three landmasses.
  • Mesosaurus was a small reptile adapted to shallow brackish water. The skeletons of these are found only in two localities: The Southern Cape province of South Africa and Iraver formations of Brazil. The two localities are presently 4,800 km apart with an ocean in between them.



A wall-like structure of lava that solidifies in the cracks and the fissures of the land is known as?

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A wall-like structure of lava that solidifies in the cracks and the fissures of the land is known as Dykes.

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  • A volcano is a place where gases, ashes and/or molten rock material– lava escape to the ground. A volcano is called an active volcano if the materials mentioned are being released or have been released out in the recent past.
  • It is from volcano that the molten rock materials find their way to the surface.
  • The material in the upper mantle portion is called magma. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.
  • The material that reaches the ground includes lava flows, pyroclastic debris, volcanic bombs, ash and dust and gases such as nitrogen compounds, Sulphur compounds and minor amounts of chlorine, hydrogen and argon.
  • Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.
  • Volcanoes are classified on the basis of nature of eruption and the form developed at the surface. Major types of volcanoes are:
    • Shield Volcanoes
    • Composite Volcanoes
    • Caldera
    • Flood Basalt Provinces
    • Mid-Ocean Ridge Volcanoes

Volcanic Landforms

  • The lava that is released during volcanic eruptions on cooling develops into igneous rocks.
  • The cooling may take place either on reaching the surface or also while the lava is still in the crustal portion.
  • Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust).
  • The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.


  • Batholiths are the cooled portion of magma chambers.
  • A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
  • They appear on the surface only after the denudational processes remove the overlying materials.
  • They cover large areas, and at times, assume depth of several km. These are granitic bodies.


  • These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below.
  • It resembles the surface volcanic domes of composite volcano, located at deeper depths.
  • It can be regarded as the localized source of lava that finds its way to the surface.
  • The Karnataka plateau is spotted with domal hills of granite rocks are examples of lacoliths or batholiths.

Lapolith, Phacolith and Sills

  • As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.
  • It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called lapolith.
  • A wavy mass of intrusive rocks is found at the base of synclines or at the top of anticline in folded igneous country. Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.
  • The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material.
  • The thinner ones are called sheets while the thick horizontal deposits are called sills.


  • When the lava makes its way through cracks and the fissures developed in the land, it solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes.
  • These are the most commonly found intrusive forms in the western Maharashtra area. These are considered the feeders for the eruptions that led to the development of the Deccan traps.

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