NCERT Class 11 Geography Part 1 Chapter 7: Landforms and their Evolution YouTube Lecture Handouts

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Watch video lecture on YouTube: NCERT Class 11 Geography Part 1 Chapter 7: Landforms and their Evolution NCERT Class 11 Geography Part 1 Chapter 7: Landforms and Their Evolution
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  • Landforms: Small to Medium tract or parcel of earth surface

  • Each landform has its own shape, size & is result of geomorphic processes

  • Landforms change due to action of geomorphic agents

  • Landform has history of development and changes through time – passes stages of youth, mature and old age

  • Geomorphology: History of earth surface through study of its forms, material and process (erosion or destruction & deposition or construction)

  • Geomorphic agents depends on folds, faults, joints, fractures, hardness and softness, permeability and impermeability, etc.

  • Independent controls include stability of sea level, tectonic stability and climate

Running Water

  • In humid areas having heavy rainfall

  • Running water as overland flow on general land surface as sheet or as linear flow in streams – with time steep gradient turns gentler, lose velocity and facilitate active deposition. Gentler channels have higher deposition, lateral erosion of banks increases and hills turns to plains

  • Overland flow causes sheet erosion – because of friction of water column, material are removed in direction of flow and rills are formed.

Life Cycle of River:

Watch video lecture on YouTube: Life Cycle of a River - Stream Orders, Erosion, Transportation and Deposition Life Cycle of a River - Stream Orders, Erosion, Transportation and Deposition
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  • Youth: V-Shaped valley, stream divides are broad and flat, meanders, waterfalls and rapids

  • Mature: Deep valleys with wider flood plains – waterfall disappear

  • Old Age: Few tributaries with gentle gradient – oxbow lake, levees – landscape at or above sea level

Erosional Features

  • Valley: rills that deepen to form V-Shaped valley, gorge (top & bottom at equal width & form in hard rocks) or canyon (broad top and narrow bottom & form in horizontally bedded sedimentary rocks)

  • Pot Holes and Plunge Pools: Circular depression by stream erosion with abrasion of rock fragments – gets bigger with rotation of rock fragments – series join and get deepen to form plunge pools (deep hole at base of waterfall)

  • Incised or Entrenched Meanders: Deep and wide meanders found cut in hard rocks. Occur on steep gradient, erosion is mainly over bottom channel.

  • Paired & unpaired terraces: Vertical erosion. Unpaired terraces in case of slow land uplift due to receding water after a peak flow; change in hydrological regime due to climatic changes; tectonic uplift of land; sea level changes when rivers are closer to the sea

  • Erosional Landforms:

    Watch video lecture on YouTube: Tenacious Rivers - 5 Major Fluvial Erosional Landforms Tenacious Rivers - 5 Major Fluvial Erosional Landforms
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Depositional Features

  • Alluvial Fans & Cones: Streams from higher level break into lower level – load is carried over mountain slopes. In Humid areas show low cone with gentle slope while in arid areas show high cone with steep slope

  • Delta: Accumulates as low cone, coarsest settle first and finest carried closest to sea

  • Floodplains: fine grained material carried by slow moving water. Floodplain above the bank is inactive (flood deposit & channel deposit). In case of delta known as delta plains

  • Natural Levees: Found along river banks – low, linear parallel ridge of coarse deposit along river banks

  • Point Bars: Known as meander bars – found on convex side of large river

  • Meanders: Loop like channel because of propensity of water, unconsolidated nature of deposits and Coriolis force (deposition on convex or slip off bank & undercut on concave or cutoff bank) – cut at inflection points as ox-bow lakes

  • Braided channels: material deposited as islands and lateral bars, when discharge is less and load is more – channel bars develop on floor as multiple threads

  • Depositional Landforms:

    Watch video lecture on YouTube: 7 Major Fluvial Depositional Landforms - Carving the Face of The Earth 7 Major Fluvial Depositional Landforms - Carving the Face of the Earth
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Groundwater

  • Surface water percolates when rocks are permeable, thinly bedded and jointed – mechanical removal of material like limestone or dolomites rich in – Karst topography in Balkans (Adriatic Sea)

  • Details:

    Watch video lecture on YouTube: Karst Topography (By Underground Water) - Formation, 8 Erosional and 9 Depositional Landforms Karst Topography (By Underground Water) - Formation, 8 Erosional and 9 Depositional Landforms
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Erosional Features

  • Swallow holes Sink holes (circular at top with funnel shaped at bottom) – if formed by solution action it is known as solution sink & are more common, if by roof collapse it is called collapse sink (dolines)

  • Sinkholes or dolines join together due to roof collapse: uvalas

  • Irregular ridges or grooves are formed – due to differential solution along parallel to sub-parallel joints – lapies form limestone pavements

  • Caves: When limestone is dense and massive with thick beds – cave formation is prominent – have opening on both ends and is called tunnels

Depositional Landforms

is soluble in carbonated water ( absorbed rainwater) Stalactites, Stalagmites, Pillars or Columns

Glaciers

  • Mass of ice moving as sheets over land (continental glacier or piedmont glacier) or as linear down the slope

  • Movement is due to force of gravity

  • Alkapuri glacier: Feeds Alakananda River

  • Gangotri Glacier: Feeds Ganga River

Details:

Watch video lecture on YouTube: Glacial Landforms: 25 Erosional & 3 Depositional Features Glacial Landforms: 25 Erosional & 3 Depositional Features
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Erosional Features

  • Cirque: At head of glacial valley, ice cuts it while moving down – lake could be seen as cirque or Tarn Lake – can be stepped

  • Horns: headward erosion of cirque walls – 3 or more glaciers cut headward and meet

  • Arete – sharp crest with zig zag outline – saw toothed ridge

  • Glacial valley – U-Shaped valley

  • Fjords: deep glacial trough filled with sea water and makes up shoreline

Depositional Landforms

  • Glacial till: unassorted coarse and fine debris – angular and subangular

  • Outwash deposits: glacio-fluvial deposits which are stratified and assorted

  • Moraines: Terminal, Lateral and Medial

  • Eskers: in summer when glacier melts it runs as streams below glacier – rock debris is carried and has sinuous ridge

  • Outwash Plains: Lies at foot of glacial mountains or beyond limits of continental ice sheets

  • Drumlins: Oval ridge like deposits – stoss (blunted due to pushing of ice and gives indication of glacier movement direction) and tail (steeper)

Waves and Currents

  • When waves break on shore – lot of force – churning of sea sediments

  • It depends on configuration of land and sea floor, advancing or retreating coastline

  • High, rocky coasts (submerged coasts) – river disappears to have been drowned with irregular coastline – erosion feature dominates – waves break with force to form wave-cut platform. Bars are submerged, bars above water are barrier bars, gets keyed to form spits and further to form lagoons

  • Low, smooth and gently sloping sedimentary coasts (emerged coasts) – forms lagoons and tidal creeks, marshes and swamps abound and depositional features dominate, lagoons turn into swamps and finally to coastal plains

Details:

Watch video lecture on YouTube: Coastal Landforms (By Waves & Currents): 18 Erosional & 18 Depositional Features Coastal Landforms (By Waves & Currents): 18 Erosional & 18 Depositional Features
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Erosional Features

  • Cliffs: Steep sides

  • Wave-cut terrace: Platform occurring at elevation above average height of waves

  • Sea caves: waves creates hollows

  • Sea Stack: resistant mass of rock that remains – temporary and disappear

Depositional Features

  • Beaches: Shoreline dominated by deposition, temporary features, made of sand-sized material

  • Sand dunes forming long ridges parallel to the coastline are common

  • Off-shore bar – ridge formed parallel to coast - offer 1st buffer or defense against storm or tsunami by absorbing most of their destructive force, so if sediment budget is disturbed or mangroves removed – coast will be eroded

  • Formation of Spits & later lagoons

Winds

  • Desert floor gets heated up leading to upward movement in hot air with turbulence

  • Deflation: Lifting and removal of dust and smaller particles from the surface of rocks

  • Wind moves fine materials and general mass erosion is accomplished by sheet floods or sheet wash

  • Erosional Features

  • Pediments: Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris

  • Pediplains: Low featureless plains

  • Playas: shallow lakes – with salt deposits these are called alkali flats

  • Deflation hollows: shallow depressions with small pits – blowouts are created which gets deeper to form caves

  • Mushroom rocks: Rock outcrops with resistant rocks that remains as pedestal rock

Depositional Features

  • Sand Dunes: Dry hot desert with obstacle to initiate dune formation

  • Barchans: crescent shaped dunes with wings away from wind, sand is uniformly moving

  • Parabolic Dunes: Sandy surface covered with vegetation – are reversed barchans with wind direction being same

  • Seif: Longitudinal dunes when supply of sand is poor and wind direction is constant – long ridge of low height

  • Transverse dunes: aligned perpendicular to wind direction, wind direction is constant and sand is elongated at right angles

Details:

Watch video lecture on YouTube: Aeolian Landforms (By Wind) - 13 Erosional & 3 Depositional Landforms Aeolian Landforms (By Wind) - 13 Erosional & 3 Depositional Landforms
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