Chapter – 6

Landforms and their Evolution

In this post we have given the detailed notes of class 11 Geography Book 1 Chapter 6 (Landforms and their Evolution) in English. These notes are useful for the students who are going to appear in class 11 board exams.

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Chapter 6: Landforms and their Evolution

Introduction

• Landforms: Small to medium-sized parts of the Earth’s surface, each with its own physical shape, size, and materials.  
• Landscapes: Large areas of the Earth’s surface made up of several related landforms.  
• Geomorphic processes and agents: The forces and factors that shape landforms, including weathering, erosion, and deposition.  
• Weathering: The breakdown of rocks, soil, and minerals through contact with the Earth’s atmosphere, water, and biological organisms.  
• Erosion: The process of moving weathered material from one location to another by agents like wind, water, or ice.  
• Deposition: The laying down of sediment carried by wind, water, or ice.  
• Landform evolution: The process of change in landforms over time due to the continued action of geomorphic processes and agents.  

Running Water

• Running water: The most important geomorphic agent in humid regions, causing both erosion and deposition.  
• Overland flow: Water flowing over the land surface as a sheet.  
• Linear flow: Water flowing in channels as streams and rivers.  
• Youthful rivers: Rivers flowing over steep gradients, characterized by high energy and active erosion.  
• Mature rivers: Rivers flowing over gentler gradients, characterized by lower energy and more deposition.  
• Old rivers: Rivers flowing over very gentle gradients, characterized by meandering channels and extensive floodplains.  

Erosional Landforms

• Valleys: Formed by the downcutting and lateral erosion of streams and rivers.
  • V-shaped valley: A valley with a V-shaped cross-section, typical of youthful rivers.  
  • Gorge: A deep, narrow valley with steep sides, often formed in hard rock.  
  • Canyon: A deep valley with steep, step-like side slopes, often formed in horizontal bedded sedimentary rocks.  
• Potholes: Circular depressions in the rocky beds of hill-streams, formed by stream erosion and abrasion.  
• Plunge pools: Large, deep potholes at the base of waterfalls, formed by the force of falling water.  
• Incised meanders: Meanders that have been cut into hard rock, indicating a change in base level or uplift of the land.  
• River terraces: Surfaces marking old valley floor or floodplain levels, indicating changes in river activity or uplift of the land.  

Depositional Landforms

• Alluvial fans: Cone-shaped deposits of sediment formed where streams flow from higher levels onto lower plains, typically found in arid and semi-arid regions.  
• Deltas: Similar to alluvial fans, but formed where rivers flow into the sea, characterized by well-sorted and stratified deposits.  
• Floodplains: Flat areas of land adjacent to rivers, formed by the deposition of sediment during floods, comprising the active floodplain (river bed) and inactive floodplain (above the bank).  
• Natural levees: Low ridges of sediment along the banks of rivers, formed during floods when coarser materials are deposited closer to the channel.  
• Point bars: Sediment deposited on the inside of meander bends, formed by the slower flow of water on the inner curve.  
• Meanders: Loop-like channel patterns in rivers, formed by lateral erosion and deposition, typically found in mature and old rivers.  
• Oxbow lakes: Cutoff meanders that have been filled with water, formed as meanders become more sinuous and eventually cut through the narrow neck.  

Groundwater

• Groundwater: Water that exists below the Earth’s surface in underground streams and aquifers.  
• Karst topography: A landscape formed by the dissolution of soluble rocks, such as limestone, characterized by sinkholes, caves, and underground drainage.  
• Solution: The process of dissolving soluble rocks, such as limestone, by acidic water.  
• Precipitation: The process of dissolved minerals coming out of solution, forming depositional features like stalactites and stalagmites.  

Erosional Landforms

• Swallow holes: Small, round depressions in the surface of limestone, formed by solution.  
• Sinkholes: Larger depressions in limestone, often funnel-shaped, formed by solution or collapse.  
• Valley sinks (Uvalas): Long trenches formed by the joining of sinkholes, creating a complex underground drainage system.  
• Lapies: Irregular surfaces with sharp pinnacles, grooves, and ridges, formed by differential solution along joints and fractures.  
• Limestone pavements: Smooth surfaces formed by the solution of limestone, often found in areas with extensive karst development.  
• Caves: Underground cavities formed by the dissolution of limestone, often containing depositional features like stalactites and stalagmites.  

Depositional Landforms

• Stalactites: Icicle-like formations hanging from the ceilings of caves, formed by the precipitation of calcium carbonate from dripping water.  
• Stalagmites: Formations rising from the floors of caves, formed by the precipitation of calcium carbonate from dripping water that falls from stalactites.  
• Pillars: Formed by the fusion of stalactites and stalagmites, creating vertical columns within caves.  

Glaciers

• Glaciers: Masses of ice moving as sheets or linear flows, eroding and transporting vast amounts of rock and debris.  
• Continental glaciers: Vast sheets of ice covering large land areas.  
• Piedmont glaciers: Sheets of ice spread over the plains at the foot of mountains.  
• Mountain and valley glaciers: Linear flows of ice down mountain slopes and valleys.  

Erosional Landforms

• Cirques: Deep, bowl-shaped depressions at the heads of glacial valleys, formed by glacial erosion and plucking.  
• Horns: Sharp, pointed peaks formed by the headward erosion of cirques, where three or more cirques intersect.  
• Serrated ridges (Arêtes): Narrow, jagged ridges between cirques, formed by the erosion of the divides between glacial valleys.  
• Glacial valleys (Troughs): U-shaped valleys with broad floors and steep sides, formed by the scouring action of glaciers.  
• Hanging valleys: Tributary valleys that enter the main glacial valley at a higher elevation, often resulting in waterfalls.  
• Fjords: Deep glacial troughs filled with seawater, found in high-latitude regions where glaciers have carved valleys below sea level.  

Depositional Landforms

• Glacial till: Unsorted, angular rock debris deposited by glaciers, forming moraines and other landforms.  
• Outwash deposits: Glacio-fluvial deposits that are roughly stratified and sorted, formed by meltwater streams carrying sediment away from glaciers.  
• Moraines: Long ridges of glacial till, marking the former extent of glaciers.
  • Terminal moraines: Deposited at the end of glaciers, marking their furthest advance.  
  • Lateral moraines: Deposited along the sides of glaciers, parallel to the valley walls.  
  • Ground moraines: Irregular sheets of till deposited on the valley floor beneath the glacier.  
  • Medial moraines: Located in the center of glacial valleys, formed by the merging of lateral moraines from tributary glaciers.  
• Eskers: Sinuous ridges of sediment deposited by subglacial streams, formed as meltwater channels within or beneath the glacier.  
• Outwash plains: Broad, flat plains covered with glacio-fluvial deposits, formed by meltwater streams beyond the glacial terminus.  
• Drumlins: Smooth, oval-shaped ridges of glacial till, formed by the streamlined flow of ice over underlying sediment.  

Waves and Currents

• Waves: Generated by wind blowing over the water surface, causing the transfer of energy to the water and creating ripples that grow into waves.  
• Currents: Large-scale movements of water in the oceans, driven by wind, differences in water density, and the Earth’s rotation.  
• Coastal processes: The dynamic interplay of waves, currents, and tides, shaping the coastal landscape through erosion, transportation, and deposition.  

High Rocky Coasts

• High rocky coasts: Characterized by steep cliffs, irregular coastlines, and erosional features, formed by the submergence of land or uplift of the seafloor.  

Landforms

• Cliffs: Steep rock faces formed by wave erosion, where waves undercut the base of the slope, causing collapses and retreat of the cliff face.  
• Wave-cut platforms: Flat or gently sloping platforms at the base of cliffs, formed by the continuous erosion of the cliff face by waves.  
• Wave-built terraces: Formed by the deposition of sediment in the offshore zone, creating a submerged platform that can become exposed over time.  
• Beaches: Deposits of sand and gravel along the shoreline, formed by the accumulation of wave-deposited sediment.  
• Bars: Long ridges of sand or shingle parallel to the coast, formed by the deposition of sediment by waves and currents.  
• Barrier bars: Exposed bars, forming a barrier between the sea and the lagoon behind.  
• Spits: Barrier bars that are attached to headlands, extending outward into the sea.  
• Lagoons: Bodies of water separated from the sea by barrier bars or spits, often forming sheltered environments for marine life.  

Low Sedimentary Coasts

• Low sedimentary coasts: Characterized by gentle slopes, sandy beaches, and depositional features, formed by the emergence of land or deposition of sediment.  

Landforms

• Beaches: Areas of sand or pebbles along the coast, formed by the accumulation of wave-deposited sediment.  
• Bars: Long ridges of sand or shingle formed in the offshore zone, parallel to the coast.  
• Barrier bars: Exposed bars, forming a barrier between the sea and the lagoon behind.  
• Spits: Barrier bars that are attached to headlands, extending outward into the sea.  
• Lagoons: Bodies of water separated from the sea by barrier bars or spits, often forming sheltered environments for marine life.  
• Deltas: Formed by the deposition of sediment at the mouth of a river, where it enters the sea.  

Erosional Landforms

• Cliffs: High, steep rock faces formed by wave erosion, where waves undercut the base of the slope, causing collapses and retreat of the cliff face.  
• Wave-cut terraces: Flat or gently sloping platforms at the base of cliffs, formed by the continuous erosion of the cliff face by waves.  
• Sea caves: Formed by wave erosion at the base of cliffs, where weaker zones in the rock are eroded.  
• Sea stacks: Isolated remnants of rock left behind as cliffs recede, formed by the differential erosion of headlands.

Depositional Landforms

• Beaches: Areas of sand or pebbles along the coast, formed by the accumulation of wave-deposited sediment.  
• Sand dunes: Formed by wind-blown sand behind beaches, where sand is transported and deposited by the wind.  
• Off-shore bars: Ridges of sand and shingle formed in the offshore zone, parallel to the coast.  
• Barrier bars: Exposed off-shore bars.  
• Spits: Barrier bars that are attached to headlands, extending outward into the sea.  
• Lagoons: Bodies of water separated from the sea by barrier bars or spits, often forming sheltered environments for marine life.

Winds

• Wind: A significant agent of erosion and deposition in arid and semi-arid regions, where vegetation is sparse and wind speeds are high.  
• Deflation: The process of wind lifting and removing loose particles from the ground.  
• Abrasion: The process of wind-blown sand and dust eroding rock surfaces.  
• Impact: The force of wind-blown sand impacting rock surfaces.  

Erosional Landforms

• Pediments: Gently inclined rocky floors at the foot of mountains, formed by lateral erosion and sheet flooding.  
• Pediplains: Low, featureless plains formed by the extension of pediments, as mountains are eroded and reduced.  
• Playas: Shallow lakes that form in desert basins, often drying up to leave salt deposits.  
• Deflation hollows: Shallow depressions formed by wind erosion, where loose material is removed by the wind.  
• Blowouts: Deeper depressions that can form into caves, created by more intense wind erosion.  
• Mushroom rocks, Table rocks, and Pedestal rocks: Remnants of resistant rock shaped by wind erosion, where the base of the rock is eroded more quickly than the top.  

Depositional Landforms

• Sand dunes: Formed by the deposition of sand by wind, where the wind speed decreases or encounters an obstacle.
  • Barchans: Crescent-shaped dunes, with the points or wings directed downwind.  
  • Parabolic dunes: Reversed barchans, with the points directed upwind, often formed in areas with partial vegetation cover.  
  • Seifs: Dunes with a single wing, formed by shifting wind directions.  
  • Longitudinal dunes: Long, low ridges of sand, parallel to the prevailing wind direction.  
  • Transverse dunes: Aligned perpendicular to the wind direction, formed when the sand source is elongated and perpendicular to the wind.

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