Class 11 Geography Notes Chapter 7 (Landforms and their evolution) – Fundamental of Physical Geography Book

Alright class, let's delve into Chapter 7: 'Landforms and their Evolution' from our Fundamentals of Physical Geography textbook. This is a crucial chapter, not just for understanding our planet, but also because concepts related to geomorphic processes and resulting landforms frequently appear in various government examinations. Pay close attention to the agents of change and the specific features they create.

Chapter 7: Landforms and their Evolution - Detailed Notes

1. Introduction: The Dynamic Earth Surface

• The Earth's surface is constantly changing. These changes are driven by geomorphic processes.
• Geomorphic Processes: Physical and chemical interactions between Earth materials and natural forces (energy) that shape the Earth's surface.
• Geomorphic Agents: The mobile mediums (like running water, wind, glaciers, waves, groundwater) that remove, transport, and deposit earth materials. Gravity is a directional force activating these agents and also causing mass movements directly.
• Landform: A natural feature of the Earth's solid surface (e.g., mountain, valley, plateau, plain, hill). Each landform has its own physical shape, size, materials and is a result of the action of certain geomorphic processes and agent(s).
• Evolution: Landforms are not static; they evolve over time under the continuous influence of geomorphic processes. Often conceptualized in stages (e.g., youth, maturity, old age), though this is a simplification.

2. Geomorphic Processes: Endogenic vs. Exogenic

• Endogenic Processes (Internal): Originate from within the Earth. Driven by Earth's internal heat.
  • Diastrophism: Slow processes that move, elevate, or build up portions of the Earth's crust (e.g., Orogenesis - mountain building; Epeirogenesis - continental uplift/subsidence). Creates large-scale relief features.
  • Volcanism: Movement of molten rock (magma) onto or toward the Earth's surface. Creates volcanic cones, lava plateaus, etc.
• Exogenic Processes (External): Originate from sources on or above the Earth's surface (atmosphere, solar energy). They primarily act to wear down the land surface (denudation).
  • Weathering: In-situ (on-site) breakdown and alteration of rocks at/near the Earth's surface. It prepares material for erosion.
    • Physical Weathering: Mechanical disintegration (e.g., frost wedging, thermal expansion, exfoliation, salt weathering).
    • Chemical Weathering: Decomposition via chemical reactions (e.g., solution, carbonation, hydration, oxidation-reduction). More effective in warm, humid climates.
    • Biological Weathering: Contribution by organisms (e.g., root penetration, burrowing animals, human activities).
  • Mass Wasting/Movement: Downslope movement of rock, regolith, and soil under the direct influence of gravity. Can be slow (creep, solifluction) or rapid (landslides, mudflows, debris avalanche). Water often acts as a lubricant.
  • Erosion: Acquisition and transportation of rock debris by geomorphic agents like running water, wind, glaciers, waves. Involves detachment and movement of material.
  • Deposition: Laying down of eroded material when the carrying capacity of the geomorphic agent decreases (due to loss of energy/velocity).

3. Geomorphic Agents and Associated Landforms

This is the core focus for exams – associating agents with their specific erosional and depositional features.

(A) Running Water (Fluvial Landforms)

• Most widespread geomorphic agent. Dominant in humid regions but also shapes arid landscapes during infrequent rain.
• Erosional Landforms:
  • Valleys: Start as shallow rills -> gullies -> mature valleys. Characteristic shape evolves.
  • V-Shaped Valleys: Formed by vertical downcutting (corrasion/abrasion, hydraulic action) by the river, accompanied by weathering and mass wasting of valley sides. Typical of youthful river stages in mountainous areas.
  • Gorges & Canyons: Deep, narrow valleys with steep sides. Gorges are typically steeper and narrower than canyons. Formed by active downcutting, often in resistant rock. (e.g., Grand Canyon - Colorado River).
  • Potholes: Circular depressions drilled into the rocky bed of a river by abrasion using swirling pebbles.
  • Plunge Pools: Deep depressions formed at the base of waterfalls due to the force of falling water and abrasion by churning debris.
  • Incised or Entrenched Meanders: Meanders (loops) that are cut deep into the bedrock, indicating rapid uplift of the land relative to the river's downcutting.
• Depositional Landforms:
  • Alluvial Fans: Fan-shaped deposits of sediments formed where a stream emerges from a confined valley onto a flatter plain, causing a sudden decrease in velocity. Common in arid/semi-arid regions at the foot of mountains.
  • Deltas: Fan-shaped (often triangular, like Greek letter Delta) deposits of alluvium at the mouth of a river where it enters a standing body of water (lake or sea), causing velocity to drop dramatically. (e.g., Nile Delta, Ganges-Brahmaputra Delta).
  • Floodplains: Flat area adjacent to a river channel, formed by deposition of fine sediment (alluvium) during floods. Very fertile.
  • Natural Levees: Ridges of coarser sediment deposited along the river banks during floods when water overtops the channel.
  • Point Bars (Meander Bars): Deposits of sediment (usually sand/gravel) accumulated on the inner (convex) side of a meander bend where velocity is lower.
  • Meanders: Sinuous bends or loops in a river channel, formed by erosion on the outer bank (cut bank) and deposition on the inner bank (point bar). Characteristic of mature river stages on gentle slopes.
  • Ox-bow Lakes: Crescent-shaped lakes formed when a meander loop is cut off from the main river channel.

(B) Groundwater (Karst Landforms)

• Effective primarily in regions with soluble rocks like limestone or dolomite. Chemical weathering (solution, carbonation) is dominant.
• Erosional Landforms:
  • Sinkholes (Dolines): Funnel-shaped or cylindrical depressions formed by dissolution of surface limestone or collapse of cave roofs. The most common karst feature.
  • Lapies (Karren): Highly irregular and jagged rock surface with small ridges and grooves, formed by differential solution on exposed limestone.
  • Caves/Caverns: Underground voids formed by dissolution along joints and bedding planes in limestone.
  • Uvalas: Large depressions formed by the coalescence (merging) of several sinkholes.
  • Poljes: Very large, flat-floored depressions with steep sides, often covering many square kilometers. May have disappearing streams (swallow holes).
• Depositional Landforms (Speleothems - formed in caves):
  • Stalactites: Icicle-like formations hanging from the ceiling of caves, formed by dripping water depositing calcium carbonate (calcite). (TIGHT to the ceiling).
  • Stalagmites: Upward-growing mounds of calcium carbonate deposited on the cave floor by dripping water. (MIGHT reach the ceiling).
  • Pillars/Columns: Formed when a stalactite and a stalagmite meet.

(C) Glaciers (Glacial Landforms)

• Large masses of moving ice. Found in high latitudes and high altitudes. Powerful agents of erosion (plucking and abrasion) and deposition.
• Erosional Landforms:
  • Cirque (Corrie): Armchair-shaped, steep-walled depression formed at the head of a glacial valley by ice plucking and abrasion. Often contains a small lake (tarn) after the ice melts.
  • Horns: Sharp-pointed, pyramidal peaks formed where several cirques erode back-to-back. (e.g., Matterhorn).
  • Arêtes: Sharp, knife-edged ridges formed between two adjacent glacial valleys or cirques.
  • U-Shaped Valleys (Glacial Troughs): Valleys modified by glaciers, having a characteristic parabolic U-shape with steep sides and a flat floor. Glaciers straighten, deepen, and widen pre-existing river valleys.
  • Hanging Valleys: Tributary glacial valleys whose floors are at a higher level than the main glacial valley floor. Often marked by waterfalls after ice melts.
  • Fjords: Deep, steep-sided inlets of the sea, formed when U-shaped glacial valleys are drowned by rising sea levels.
• Depositional Landforms: Glacial deposits are typically unsorted and angular (called Till).
  • Moraines: Ridges or mounds of till deposited by a glacier.
    • Lateral Moraines: Along the sides of the glacier.
    • Medial Moraines: Formed where two glaciers merge, combining their lateral moraines. Found in the middle of the combined glacier.
    • Terminal Moraines: Ridge deposited at the furthest extent (terminus) of the glacier.
    • Ground Moraines: Thin layer of till deposited beneath the melting glacier.
  • Drumlins: Elongated, streamlined hills made of till. The steeper, blunter end faces up-ice (direction from which ice came). Often occur in groups (drumlin fields). "Basket of eggs" topography.
  • Eskers: Long, winding ridges of sand and gravel, deposited by meltwater streams flowing within, under, or upon a glacier.
  • Outwash Plains: Flat plains formed by deposition of sand and gravel (stratified drift) carried by meltwater streams flowing away from the glacier terminus.

(D) Wind (Aeolian Landforms)

• Dominant agent in arid and semi-arid regions with sparse vegetation and abundant loose sediment. Erosion occurs via deflation (lifting and removal of loose particles) and abrasion (sandblasting).
• Erosional Landforms:
  • Pediments: Gently sloping, rock-floored surfaces found at the base of mountains in arid regions. Formed by erosion and weathering, often covered by a thin veneer of debris.
  • Deflation Hollows (Blowouts): Depressions created by wind removing fine particles. Can range from small dimples to vast basins.
  • Mushroom Rocks (Gour): Isolated rock outcrops eroded more at the base (where abrasion is concentrated) than at the top, resembling a mushroom.
  • Yardangs: Streamlined, elongated ridges of rock aligned parallel to the prevailing wind, separated by troughs. Formed by wind abrasion and deflation in areas with alternating hard and soft rock layers.
  • Ventifacts: Rocks faceted, grooved, or polished by wind-driven sand.
• Depositional Landforms:
  • Sand Dunes: Hills or ridges of sand deposited and shaped by wind. Classified by shape:
    • Barchans: Crescent-shaped dunes with horns pointing downwind. Form in areas with limited sand supply and unidirectional wind. Migrate.
    • Parabolic Dunes: U-shaped or V-shaped dunes with arms pointing upwind. Often form where vegetation anchors the arms. Common in coastal areas or partially stabilized sand regions.
    • Transverse Dunes: Long ridges oriented perpendicular (transverse) to the prevailing wind direction. Form in areas with abundant sand and consistent wind.
    • Longitudinal Dunes (Seifs): Long, narrow ridges oriented parallel to the prevailing wind direction. May extend for many kilometers. Form with strong, bi-directional, or variable winds.
  • Loess: Extensive deposits of fine-grained, wind-blown silt. Highly fertile but easily eroded. Covers large areas in China, USA, Argentina etc. Source often glacial outwash plains or deserts.

(E) Waves and Currents (Coastal Landforms)

• Shaped by the action of sea waves, currents, and tides. Erosion is prominent on exposed coasts, deposition in sheltered areas.
• Erosional Landforms:
  • Sea Cliffs: Steep rock faces formed by wave erosion (hydraulic action, abrasion, corrosion) undercutting the land at the coast. Retreat landward.
  • Wave-Cut Platforms (Shore Platforms): Gently sloping, relatively flat surfaces formed at the base of retreating sea cliffs by wave erosion. Often exposed at low tide.
  • Sea Caves: Caves formed along lines of weakness (joints, faults) in headlands by wave action.
  • Sea Arches: Formed when wave erosion cuts through a headland, often starting from caves on opposite sides.
  • Sea Stacks: Isolated pillars of rock standing offshore, formed when a sea arch collapses or a resistant portion of a headland is isolated by erosion.
• Depositional Landforms:
  • Beaches: Accumulations of sand, pebbles, or shells along the shoreline, deposited by waves.
  • Bars: Elongated ridges of sand or shingle deposited offshore or across bay mouths by waves and longshore drift. (e.g., Offshore bars, Bay bars).
  • Spits: Elongated ridges of sand or shingle projecting from the land out into the sea or across a bay, formed by longshore drift. Often curved at the end (hooked spit).
  • Tombolos: Sand or shingle ridges connecting an island to the mainland or another island.
  • Lagoons: Shallow bodies of water separated from the open sea by barriers like bars or reefs.

4. Landform Evolution

• The concept suggests landforms undergo changes through time, influenced by the interplay of Structure (rock type, geological structure), Process (geomorphic agents and their actions), and Stage (time, duration of processes).
• While cyclical models (like Davis's cycle of erosion: youth, maturity, old age) provide a framework, reality is complex due to factors like climate change, tectonic activity, and variations in rock resistance, which can interrupt or modify the 'stages'.
• The key takeaway is that the landscape we see today is a snapshot in a long, continuous process of change.

Multiple Choice Questions (MCQs)

1. Which of the following landforms is primarily created by the depositional action of running water at the foot of mountains in arid/semi-arid regions?
   (a) Delta
   (b) Alluvial Fan
   (c) Floodplain
   (d) Pothole

2. Stalactites and stalagmites are characteristic features found in which type of topography?
   (a) Glacial
   (b) Aeolian
   (c) Fluvial
   (d) Karst

3. A U-shaped valley is a distinctive erosional feature formed by:
   (a) River action in its upper course
   (b) Wind abrasion in deserts
   (c) Glacial erosion
   (d) Wave action on coastlines

4. Barchans are a specific type of:
   (a) Glacial moraine
   (b) River meander
   (c) Sand dune
   (d) Coastal spit

5. Which of the following is an example of an erosional landform created by coastal processes?
   (a) Beach
   (b) Spit
   (c) Sea Stack
   (d) Lagoon

6. Lapies, characterized by highly irregular and jagged rock surfaces, are formed by the action of:
   (a) Wind deflation
   (b) Glacial plucking
   (c) Groundwater solution on limestone
   (d) River abrasion

7. Drumlins, often described as having a "basket of eggs" topography, are depositional features associated with:
   (a) Rivers
   (b) Winds
   (c) Glaciers
   (d) Waves

8. Which geomorphic process involves the in-situ breakdown of rocks without significant movement of the resulting material?
   (a) Erosion
   (b) Mass Wasting
   (c) Deposition
   (d) Weathering

9. Mushroom rocks (Gour) are typically formed by the erosional action of:
   (a) Glaciers
   (b) Running water
   (c) Wind
   (d) Groundwater

10. An ox-bow lake is formed as a result of:
    (a) Glacial meltwater deposition
    (b) A river cutting off a meander loop
    (c) Coastal processes isolating a body of water
    (d) Volcanic activity creating a crater lake

Answer Key:

1. (b) Alluvial Fan
2. (d) Karst
3. (c) Glacial erosion
4. (c) Sand dune
5. (c) Sea Stack
6. (c) Groundwater solution on limestone
7. (c) Glaciers
8. (d) Weathering
9. (c) Wind
10. (b) A river cutting off a meander loop

Study these notes thoroughly. Focus on understanding the process behind the formation of each landform and be able to differentiate between features created by different agents, as well as distinguishing between erosional and depositional features. Good luck with your preparation!