**GEOGRAPHY CLASS 11 – CHAPTER 6

1. INTRODUCTION

• Landforms on the Earth’s surface are not permanent; they continuously undergo changes.
• A combination of internal (endogenic) and external (exogenic) processes shapes the landscape.
• Running water, glaciers, winds, waves, and groundwater are the main external geomorphic agents.
• This chapter explains how different landforms are generated and modified by these geomorphic processes.
• Each geomorphic agent produces distinctive erosional and depositional features depending on climate, lithology, slope, and time.

2. RUNNING WATER (RIVERS)

Running water or fluvial action is one of the most dominant geomorphic agents on Earth.

2.1 Work of a River

The river performs three main functions:

1. Erosion – wearing away the land by hydraulic action, corrasion, corrosion and attrition.
2. Transportation – carrying loads such as silt, sand, clay, pebbles, gravel, and dissolved minerals.
3. Deposition – depositing materials when river velocity reduces.

2.2 Fluvial Cycle of Erosion / Stages of River Development

Rivers shape the landforms slowly over time. According to Davis, three stages exist:

2.3 YOUTH STAGE

Characteristics:

• Steep slopes
• High erosive power
• Vertical erosion dominates
• Waterfalls and rapids common
• Narrow, deep V-shaped valleys

Landforms in Youth Stage:

1. V-Shaped Valleys
   • Formed by rapid downcutting.
   • Have steep side slopes and a narrow floor.
2. Gorges and Canyons
   • Deep, narrow steep-sided valleys formed by intense vertical erosion.
   • A canyon is wider than a gorge.
3. Waterfalls and Rapids
   • Occur where resistant rocks lie over softer rocks.
   • Examples: Jog Falls, Niagara Falls.

2.4 MATURE STAGE

Characteristics:

• Reduced vertical erosion
• Increased lateral erosion
• Wider valleys with gentler slopes

Landforms in Mature Stage:

1. Wide Valleys
   • Valley floors broaden due to side cutting.
2. Meanders (Early Stage)
   • Curves or bends formed due to lateral erosion.
3. River terraces (Initial development)

2.5 OLD STAGE

Characteristics:

• Almost no erosion
• Deposition dominates
• Very gentle slopes
• Highly meandering river channel

Landforms in Old Stage:

1. Floodplains
2. Natural Levees
3. Oxbow Lakes
4. Delta (Near mouth of river)

3. DETAILED FLUVIAL LANDFORMS

3.1 VALLEYS

• Valleys are elongated depressions carved by rivers.
• Classified based on shape:
  • V-shaped valleys – youth stage
  • Wide valleys – mature stage
  • Broad floodplains – old stage

3.2 INCISED OR ENTRENCHED MEANDERS

• Deeply cut meanders formed when:
  1. The land uplifts rapidly, OR
  2. River rejuvenation occurs.
• Two types:
  • Entrenched meanders – symmetrical deep valleys
  • Incised meanders – asymmetrical, due to lateral erosion

Examples: Colorado River (USA), Narmada and Chambal river valleys.

3.3 RIVER TERRACES

• Step-like flat surfaces formed along valley sides.
• Created by the river when:
  • Downcutting increases due to rejuvenation
  • Change in sea level or climate occurs
• Types:
  1. Paired terraces
  2. Unpaired terraces
  3. Fill terraces

3.4 FLOODPLAINS

• Broad flat plains along river banks formed by repeated flooding.
• Made of layered alluvium.

Components:

• Backswamp
• Oxbow lakes
• Yazoo streams

3.5 NATURAL LEVEES

• Raised embankments formed naturally on both sides of river channels.
• Created when heavy sediments are deposited during floods.
• Protect the river from spilling over in small floods.

3.6 POINT BARS

• Also known as meander bars.
• Depositional features on the inner side of meander loops.
• Made of sand, silt, and gravel.

3.7 MEANDERS

• Large looping bends in rivers.
• Caused by:
  • Lateral erosion
  • Uneven resistance of rocks
  • Helical flow (corkscrew-like water motion)

Parts:

• Outer bank → cut bank
• Inner bank → slip-off slope

4. FEATURES OF KARST TOPOGRAPHY (GROUNDWATER ACTION)

Karst topography forms in limestone regions due to solution action of groundwater.

4.1 POOLS (SOLUTION PITS)

• Depressions formed by chemical weathering of limestone.
• Vary in size from small pits to large basins.

4.2 SINKHOLES (DOLINES)

• Circular depressions formed due to:
  • Collapse of cave roofs
  • Solution of limestone
• Usually funnel-shaped.

4.3 LAPIES

• Grooved or ridged limestone surfaces formed by chemical corrosion.
• Sharp crests and deep hollows.

4.4 LIMESTONE PAVEMENTS

• Flat limestone surfaces with cracks, joints, and grooves.

4.5 CAVES

• Underground hollow spaces formed by long-term solution of limestone.
• Stream water enlarges joints and cracks to form chambers and tunnels.

Cave Features:

1. Stalactites – grow downward from the ceiling
2. Stalagmites – grow upward from the floor
3. Columns or pillars – when stalactite and stalagmite join

5. GLACIERS

Glaciers are masses of moving ice that shape the land by erosion, transportation, and deposition.

5.1 GLACIAL EROSIONAL FEATURES

(i) Cirques

• Amphitheatre-like hollows where glaciers originate.

(ii) U-Shaped Valleys

• Broad valleys with steep sides and flat floors.

(iii) Hanging Valleys

• Smaller valleys hanging above the main U-valley.

(iv) Horns

• Sharp pyramid-shaped peaks.
• Formed by erosion from three or more cirques.
• Example: Matterhorn (Alps).

(v) Serrated or Arête Ridges

• Knife-edged narrow ridges between two cirques.

5.2 GLACIAL DEPOSITIONAL FEATURES

(i) Moraines

• Accumulated glacial debris.
• Types: lateral, medial, terminal, ground moraines.

(ii) Drumlins

• Elongated hills formed by glacial deposition.

(iii) Outwash Plains

• Depositional plains formed in front of melting glaciers.

6. WAVES AND CURRENTS (MARINE PROCESSES)

Waves, tides, and currents reshape coastal landforms through erosion, transport, and deposition.

6.1 EROSIONAL FEATURES BY WAVES

(i) Cliffs

• Steep coastal slopes formed by wave cutting.

(ii) Sea Caves

• Hollow openings in coastal cliffs.

(iii) Sea Arches

• Formed when caves join through erosion.

(iv) Stacks or Chimneys

• Remnants of collapsed arches.

(v) Wave-cut Platforms

• Flat surfaces formed as cliffs retreat inland.

6.2 DEPOSITIONAL FEATURES BY WAVES

(i) Beaches

• Deposits of sand, gravel, pebbles along the coast.

(ii) Spits

• Narrow ridges of sand projecting into the sea.

(iii) Bars

• Ridge-like deposits parallel to coast.

(iv) Lagoons

• Shallow water bodies enclosed by bars/barriers.

(v) Tombolos

• Sandbars connecting an island with the mainland.

7. WIND-FORMED FEATURES (AEOLIAN PROCESSES)

Wind is the dominant agent in desert and semi-arid regions.

7.1 EROSIONAL FEATURES

(i) Deflation Hollows

• Depressions formed by wind removing loose particles.

(ii) Yardangs

• Ridge-and-groove structures carved by wind.

(iii) Mushroom Rocks

• Rocks shaped like mushrooms due to sand abrasion.

7.2 DEPOSITIONAL FEATURES

(i) Sand Dunes

• Hills of sand formed by wind deposition.

Types:

1. Barchans
2. Longitudinal dunes
3. Transverse dunes
4. Star dunes
5. Parabolic dunes

(ii) Loess

• Fine sand and silt carried by wind and deposited far away.

8. PLAYAS

• Dry, flat lake beds in deserts.
• Formed where water from intermittent streams evaporates leaving behind salts.
• Often associated with salt pans and mud flats.

9. SUMMARY OF AGENTS AND LANDFORMS

10. CONCLUSION

• Landforms are dynamic and continuously evolve under the influence of various geomorphic agents.
• Running water, glaciers, winds, waves, and groundwater contribute uniquely to shaping Earth’s surface.
• Erosion carves the landscape, while deposition builds new landforms.
• Understanding these processes helps in:
  • predicting natural hazards,
  • planning infrastructure,
  • managing soil and water resources,
  • designing land-use strategies.
• Landform evolution is gradual but powerful, shaping the Earth over millions of years.