Plateau

Basics

  • A relatively flat highland is called as plateau
  • Plateaus are also known as teblelands

Types

  1. Continental plateau
  • Also known as Tectonic or Intermonate plateau
  • Formed by the upliftment of earth due to plate tectonics
  • They are vast and have almost uniform altitude
  • g. Tibetan plateau is enclosed by Himalayas and Kunlun mountains
  1. Volcanic or lava plateau
  • lava flows in the form of successive layers of sheets and cools to form volcanic plateau
  • Important lava plateau
  • Deccan plateau
  • Columbian plateau
  1. Border plateau
  • Formed along the borders of Mountain ranges
  • g. Piedmont plateau, Colorado plateau
  1. Dissected or erosional plateau
  • Plateaus are worn down by the weathering processes to form the dissected plateau
  • g. Scottish Islands

Plains

Basics

  • Plains are extensive tracts of level or undulating open land
  • Plains are generally lower in altitude

Types

  • Structural plains
  • Structurally depressed lowlands are called structural plains
  • These plains are extensively flat
  • g. plains of Russia, USA, Argentina etc.
  • Depositional plains
  • Depositional plains are formed by the deposition of materials brought by various agents of transportation
  • These plains are highly fertile
  • Types
  • Alluvial plains
  • A flat resulting from repeated deposits of alluvial material by running water
  • Flood plains
  • A low plain adjacent to a river formed by river sediments
  • Deltanic plains
  • Nile delta
  • Ganges delta
  • Loses plain
  • A fine grained unstratified accumulation of clay and silt deposited by the wind over hills, plains and valleys
  • Outwash plain
  • formed by the deposition of sand gravel of glacial sediments
  • not fit for cultivation
  • Drift plain
  • formed by the deposition of boulders and clay of glacial sediments
  • Partly cultivable
  • Coastal plains
  • Marine swamps
  • tidal lowlands
  • Erosional plains
  • formed by the gradual erosion of landforms by the agents of erosion
  • Erosional agents include rain, wind, river, glarier, ice etc.
  • Types
  • Peneplains
  • a more or less level land surface representing an advanced stage of erosion
  • Pediplains
  • an extensive plain formed in desert by the coalescence of neighbouring pediments
  • Desert plains
  • Ice scored plains

Volcanism

Origin

  • Volcano erupts from the fissure in the earth’s crust through which molten lava and gases flows out
  • Volcanic Process
  1. The less dense crust floats above the denser mantle
  2. Mantle contains a weaker zone called Asthenosphere with molten rock materials
  • The molten rock material called magma moves towards the crust
  1. Magma opens the crust and henceforth flows as lava
  2. The continuous flow of lava results in larger volcanic mountains
  • Volcano exerts lava flows, pyroclastic debris, volcanic bombs, ash, dust and gases
  • Gases include CO2, nitrogen compounds, sulphur compounds and minor amounts of chlorine, hydrogen and argon

Types of lavas

  • Acidic lavas
  • are light coloured and rich in lighter elements such as silica
  • flow slowly with heavy explosions
  • form steep cone volcanoes
  • Basic lavas
  • are brightly coloured and rich in iron and magnesium
  • flow smoothly without explosions
  • form wider volcanoes with relatively flat dome or shield

Types of Volcanoes

  • Based on periodicity of eruption
  1. Active volcano
  • Volcanoes which erupt frequently or erupted in the recent past
  • g. Mt. Etna, Mt. Saint Helens
  1. Dormant volcano
  • Volcanoes which are known to erupt and has the signs of eruption in the future
  • g. Mt. Kilimanjaro
  1. Extinct volcano
  • Volcanoes without any active signs of eruption are called extinct
  • Based on form
  1. Shield Volcanoes
  • largest of all the volcanoes on the earth
  • mostly made up basaltic lava
  • these volcanoes are not steep
  • they are characterised by low explosions
  • lava moves in the form of a fountain and develops into cinder cone
  1. Composite Volcanoes
  • characterised by eruptions of cooler and more viscous lavas than basalt
  • also called as Strato-volcanoes
  • often result explosive eruptions
  1. Calderas
  • Most explosive type of volcanoes
  • during explosive eruption they collapse on themselves rather than building any tall structure
  • collapsed depressions are called calderas
  1. Flood Basalt Provinces
  • These volcanoes outpour highly fluid lava flows for long distances
  • Individual flows may extend for hundreds of km with thickness of around 50 meters
  • Deccan traps covering most of the Maharashtra plateau is a larger flood basalt province
  1. Mid-Ocean Ridge Volcanoes
  • Volcanoes in the oceanic areas

Distribution of volcanoes

  • Most volcanoes are found in three well defined belt
  1. Circum-Pacific belt
  • mountains of south America to Japan
  • Philippines
  • Indonesia
  • New Zealand
  1. Mid-World Mountain belt
  • Alps in Europe
  • Asia Minor
  • Himalayas region
  1. African Rift Valley belt
  • Volcanoes in India
  • There is only one dormant volcano in India located at Narcondam in Andaman and Nicobar Islands
  • Volcanoes occur along coastal mountain ranges, on islands and in the mid-oceans
  • Cameroon is the only active Volcano in Central West Africa

Seismic Waves

Basics

  • Waves generated by the earthquake are called seismic waves
  • Study of earthquake is called Seismology
  • Speed of seismic waves
  • in crust is around 2-8 km pr second
  • in mantle is around 8-13 km per second
  • Instruments used to measure seismic waves
  • Seismograph
  • Accelerometer
  • Geophone
  • Hydrophone

Earthquake Waves

  • Characteristics
  • The velocity of waves changes as they travel through materials with different densities
  • Waves travel with higher velocity in denser materials
  • Waves change their direction as they reflect or refract across materials with different densities
  1. Body Waves
  • generated due to the release of energy at the focus
  • Body waves travel through the body of earth in all directions
  • Two types

P- Waves

  • P-waves are faster and are the first to arrive at the surface
  • also called as primary waves
  • P-waves are similar to sound waves
  • they vibrate parallel to the direction of waves

S-Waves

  • S-waves arrive at the surface with some time lag
  • also called as secondary waves
  • they can travel only though solid materials
  • S-waves vibrates in the direction perpendicular to the wave direction
  • S-waves are more destructive than P-waves
  1. Surface waves
  • body waves interact with the surface rocks and generated new set of waves called surface waves
  • Surface waves travel along the surface

Shadow Zone

  • areas where the earthquake waves are not reported
  • for each earthquake, there exists an altogether different shadow zone
  • Observations
  • Seismographs located within 1050 from the epicentre, recorded the arrival of both P and S-waves
  • seismographs located beyond 1450 from epicentre, recorded P-waves, but not S-waves
  • entire zone beyond 1050 does not receive S-waves
  • The shadow zone of S-wave is much larger than that of the P-waves

Earthquake

Origin

  • Shaking and vibration at the surface of the earth is called earthquake
  • Earthquake releases energy, which generates waves that travel in all directions
  • Earthquake results from the underground movement along a fault plane or from volcanic activity
  • Process
  1. Rocks along a fault tend move in opposite directions
  2. But the overlying rock strata presses and locks them together
  • at some point they overcome the friction and the blocks get deformed and slide past one another abruptly
  1. this results in the release of energy, and the energy waves travel in all directions
  • Terms
  • Focus/Hypocentre
  • The point where the energy is released is called the focus of an earthquake or hypocentre
  • Epicentre
  • The point on the surface, nearest to the focus, is called epicentre
  • It points directly above the focus
  • It is the first point to experience the waves
  • Magnitude of earthquake
  • Quantitative measure of the size of the earthquake at is source
  • Intensity of earthquake
  • severity of earthquake shaking
  • intensity is variable over the area affected by the earthquake

Types of Earthquakes

  1. Tectonic earthquakes
  • due to sliding of rocks along a fault plane
  1. Volcanic earthquakes
  • confined to areas of active volcanoes
  1. Collapse earthquakes
  • due to intense mining activity
  1. Explosion earthquakes
  • due to the explosion of chemical or nuclear devices
  1. Reservoir induced earthquakes
  • earthquakes that occur in the areas of large reservoirs

Measurement of earthquakes

  • Earthquakes are measured using a device called seismograph
  • Earthquakes are scaled either according to the magnitude or intensity of the shock
  1. Magnitude scale
  • known as the Richter scale
  • Richter Magnitude scale measures the amount of seismic energy released by an earthquake
  • magnitude is expressed in absolute numbers, 0-10
  1. Intensity scale
  • Intensity is assessed using a descriptive scale called Modified Mercalli Intensity Scale
  • The intensity scale takes into account the visible damage caused by the event
  • the range of intensity scale is form 1-12

Earthquakes in India

  • Causes
  • Movement of Indian plate towards the Asian continental plate at the rate of 45 mm per year
  • Rotation of Indian plate in anticlockwise direction
  • Convergence of Indian plate with Tibetan plate
  • Seismic zones of India
  • Four zones

Zone – II- Low damage risk zone

Zone – III- Moderate damage risk zone

Zone-IV-High damage risk zone

  • Delhi
  • Bihar
  • Indo-Gangetic plain
  • Jammu

Zone-V-Highest risk zone

  • Kashmir
  • Punjab
  • Himalayas
  • North eastern states
  • Rann of Kutchch

Zone I has been removed

 

Volcanic Landforms

Intrusive

  • Sill
  • a flat mass of igneous rock between two layers of older sedimentary rock
  • Dyke
  • a vertical intrusion of igneous rock cutting across existing layers of rocks
  • Laccolith
  • a mass of igneous rock, typically lens-shaped, that has been intruded between rock strata causing uplift in the shape of a dome
  • Lopolith
  • a large saucer-shaped intrusion of igneous rock
  • Phacolith
  • A small lenticular igneous intrusion, shaped by folding in an anticline
  • Batholith
  • Large mass of intrusive igneous rock believed to have solidified deep within the earth

Extrusive forms

  • Crater
  • Cinder cones
  • Ash flows
  • Lava flows
  • Crater lakes
  • Calderas
  • Parasite cones

Weathering

Basics

  • Weathering is the gradual disintegration of rocks by the combined action of exogenic and endogenic forces of earth
  • Weathering elements include wind, temperature, rainfall, frost, fog, ice etc.
  • Various processes of weathering helps in producing different colours and properties of soil

Types

  1. Physical Weathering

Disintegration of rocks without any chemical change

  1. Block disintegration
  • disintegration of rocks by expansion and contraction of the rocks due to temperature variations
  • high diurnal range of temperature causes successive expansion and contraction of the rocks
  1. Exfoliation
  • peeling of rocks due to intense heating of outer layers of the rock
  • Frost Action
  • alternate freezing and melting of water inside the joints of the, splits them into fragments
  1. Chemical weathering
  • Change in the rocks through formation of new compounds
  • Chemical processes include oxidation, hydrolysis, and acid solution
  1. Oxidation
  • atmospheric oxygen reacts with the rock to produce oxides
  1. Carbonation
  • removal of rocks through carbonic acid
  1. Hydration
  • absorption of the rock increases and the grains lose their shape
  1. Solution
  • dissolution of minerals in water
  1. Biotic weathering
  2. Plants
  • Plants contribute to both mechanical and chemical weathering
  • growth of roots disintegrates the rocks
  1. Animals
  • Hooves of animals break the soil and thus assist soil erosion
  • Burrowing animals like earthworms, rats, rabbits, termites and ants breakdown the rocks
  1. Man breaks lot of rocks for construction, agriculture and mining activities

Soil Erosion

Definition

  • Removed of soil at a greater rate than its replacement by natural agencies is called soil erosion

Types

  1. Wind Erosion
  • Winds carry away vast quantity of fine soil particles and sand from deserts and spread it over adjoining cultivated land and thus destroy their fertility
  • Thar Desert is spreading wind erosion over parts of Gujarat, Haryana, Punjab and Rajasthan
  1. Sheet erosion
  • Water when moves as a sheet takes away thin layers of soil
  • common along the river beds and areas affected by floods
  1. Rill Erosion
  • Removal of surface soil by running water
  1. Gully Erosion
  • These lands are called bad lands or ravines
  • Ravines are common in Chambal and Yamuna river basins in U.P. and M.P.

Continental Drift

Facts

  • The gradual movement and formation of continents is called continental drift
  • Conceived by the German scientist Alfred Wegener
  • Indian sub-continent has broke away from Gondwanaland during cretaceous period

Continental Drift Theory

  • About 280 million years ago, there was a super continent called Pangea
  • The huge water body surrounding the Pangea was known as Panthalasa
  • Both of them drifted away and in between a shallow sea emerged known as Tethys sea

Evidences for Continental Drift

  1. Jig-saw-fit of continents
  • coasts of continents could be fit like jigsaw puzzle
  1. Geological similarities
  2. Coal and Vegetation evidences
  • south America, Africa, India and Australia were together in geological past
  1. Evidences from paleomagnetism
  2. Sea floor spreading
  3. Glacial deposits

 

Plate Tectonics

Process

  1. Solid mantle and upper crust together forms the lithosphere
  2. The lithosphere is broken into several known as plates, which moves over the Asthenopshere
  • Plates move due to Convectional current initiated by radio-active minerals, 100 to 250 km below the surface
  1. Plates move continuously with relative direction of movement called as plate tectonics

Plates

  1. 7 Major plates
  2. Eurasia and the adjacent oceanic plate
  3. Africa with eastern Atlantic floor plate
  4. India-Australia-New Zealand plate
  5. Pacific plate
  6. North American plate
  • with western Atlantic floor separated from the South American plate along the Caribbean islands
  1. South American plate and
  • with western Atlantic floor separated from the North American plate along the Caribbean islands
  1. Antarctica and the surrounding oceanic plate
  2. 20 Minor plates
  • Important minor plates
  1. cocos plate : Between Central American and Pacific plate
  2. Nazca plate : Between South American and Pacific plate
  • Arabian plate : Mostly the Saudi Arabian landmass
  1. Philippine plate : Between the Asiatic and Pacific plate
  2. Caroline plate : Between the Philippine and Indian plate
  3. Fuji Plate : North-east of Australia
  • The Major and minor plates together constitute the whole surface of the earth

Plate boundaries

  1. Divergent boundary
  • Diverging currents produce tension at the contact-zone of crust leading to fracture
  • This process pushes the plates in opposite direction and creates a zone called “zone of construction”
  1. Convergent boundary
  • Converging currents produce compression at the contact-zone of crust leading to collision
  1. When both are continental plates, then the collision leads to mountain formation
  2. When both are maritime plates, then the collision leads to formation of trenches and Island volcanic arcs (Japan, Indonesia etc)
  • When continental and maritime plates collide, continental plate subdues the maritime plate forming volcanic landforms

In all three situations, surface area is reduced, therefore, this is also known as “zone of destruction”

III. Fracture or transform boundary fault

  • Transform fault is the one when two adjacent plates slide past each other
  • Direction of movement may be along or against but they move parallel to each other
  • There is no construction or destruction of areas and hence, it is known as “zone of preservation”

Earthquakes and Volcanoes are widely distributed and concentrated along the plate boundaries

 

River

Definition

  • Path followed by a river is called its course or its valley
  • The course of a river is divided into three sections

River course

  1. The upper course or the stage of youth
  • Begins from the source of the river in hills or mountains
  • Weathering leads to formation of ‘V’ shaped valleys
  • Brahmaputra and Indus forms deep gorges in India
  1. The middle course or the stage of maturity
  • Lateral corrosion widens the ‘V’ shaped valley
  • Alluvial fans and Meanders are formed along the course
  1. The lower course or the stage of old age
  • Heavy deposition of sediments in lower plains
  • Flood plains, Ox-bow lakes, deltas, levees and estuaries are formed

Facts

  • Favourable conditions for Delta formation
  1. large amount of sediments
  2. coast with less tidal activity
  3. shallow sea, adjoining the delta
  4. no strong current at the river mouth
  • Ganga-Brahmputra Delta is the largest delta in the world
  • River discharge its water through several channels called distributaries
  • Rivers emptying into sea with the shape of a gradually widening mouth cutting deep inland are called estuaries
  • Narmada and Tapi form estuaries when they join the Arabian Sea