Module 46. Physical Geography – Landforms and Processes

Physical geography focuses on the study of the Earth’s natural features, processes, and phenomena that shape the landscape. Central to this discipline are landforms, the natural physical features of the Earth’s surface, and the geomorphic processes responsible for their creation and transformation. The interaction between the Earth’s internal and external forces continually remodels the planet’s surface, giving rise to a vast variety of terrains and landforms.

Internal and External Geomorphic Processes

Geomorphic processes can broadly be divided into endogenic (internal) and exogenic (external) forces.

1. Endogenic Processes: These are caused by forces originating within the Earth, driven by its internal heat and tectonic activity. They are primarily responsible for mountain building, volcanic activity, and earthquakes.
   • Tectonic Movements: The movement of lithospheric plates creates fold mountains (e.g., Himalayas, Alps) and rift valleys (e.g., East African Rift Valley).
   • Volcanism: The eruption of magma leads to the formation of volcanic cones, lava plateaus, and calderas.
   • Earthquakes: Sudden release of energy along fault lines modifies landscapes, sometimes forming features like fault scarps.
2. Exogenic Processes: These processes occur at or near the Earth’s surface and are driven by solar energy and gravity. They include weathering, mass wasting, erosion, and deposition.
   • Weathering: The disintegration and decomposition of rocks in situ through physical (mechanical), chemical, and biological means.
   • Mass Wasting: Downhill movement of weathered material under gravity, such as landslides and soil creep.
   • Erosion and Deposition: Agents like rivers, glaciers, wind, and sea waves erode existing landforms and deposit sediments, constantly reshaping the surface.

Major Landforms of the Earth

Landforms are broadly classified based on the processes that create them and their stage of development.

1. Mountains: Elevated portions of the Earth’s surface, mountains may be formed by tectonic forces or volcanic activity.
   • Fold Mountains: Formed by the compression of crustal plates (e.g., Andes, Rockies).
   • Block Mountains: Created by faulting, leading to uplifted blocks (horsts) and downthrown areas (grabens), such as the Vindhyas and Satpuras in India.
   • Volcanic Mountains: Built by successive lava eruptions, such as Mount Fuji in Japan.
2. Plateaus: Uplifted flat-topped areas resulting from either tectonic uplift or lava flow. Examples include the Deccan Plateau in India and the Colorado Plateau in the USA. Plateaus often contain rich mineral deposits and form important watersheds.
3. Plains: Extensive flat or gently undulating areas formed mainly by deposition. Alluvial plains (e.g., Indo-Gangetic Plain) result from river action, while coastal plains develop due to marine sedimentation or subsidence.
4. Hills and Valleys: Hills are lower elevated areas than mountains, while valleys are elongated depressions often carved by river or glacial erosion, such as the Kashmir Valley.

Fluvial Processes and Landforms

Rivers are among the most powerful agents of erosion, transportation, and deposition. Their action produces distinct landforms during their course — youthful, mature, and old stages.

• Erosional Landforms:
  • V-shaped valleys (e.g., upper Ganga valley) formed by vertical erosion.
  • Waterfalls and rapids where hard rock layers resist erosion.
  • Gorges and canyons, such as the Grand Canyon, formed by prolonged downcutting.
• Depositional Landforms:
  • Alluvial fans and cones at foothills where rivers lose velocity.
  • Floodplains, created by repeated deposition during floods.
  • Deltas, formed where rivers deposit sediments at their mouths (e.g., Ganga-Brahmaputra Delta).

Aeolian (Wind) Processes and Landforms

In arid and semi-arid regions, wind acts as a major geomorphic agent, shaping the landscape through erosion, transportation, and deposition.

• Erosional Landforms:
  • Deflation hollows formed by the removal of loose material.
  • Mushroom rocks and yardangs, sculpted by wind abrasion.
• Depositional Landforms:
  • Sand dunes, varying in form from crescent-shaped barchans to long seif dunes.
  • Loess deposits, formed when fine dust is carried over long distances and settles in thick layers, as seen in northern China.

Glacial Processes and Landforms

In polar and high mountain regions, glaciers shape the land through plucking, abrasion, and deposition.

• Erosional Landforms:
  • Cirques (Corries): Bowl-shaped depressions formed at glacier heads.
  • U-shaped valleys and hanging valleys created by glacial erosion.
  • Arêtes and horns, sharp ridges and peaks formed between adjacent glaciers (e.g., Matterhorn).
• Depositional Landforms:
  • Moraines, consisting of rock debris deposited by glaciers.
  • Eskers and drumlins, formed from subglacial meltwater and deposition.

Coastal Processes and Landforms

The sea continuously acts upon the land through erosion, transportation, and deposition, shaping diverse coastal features depending on wave energy, tidal range, and rock type.

• Erosional Landforms:
  • Sea cliffs, caves, arches, and stacks formed by wave action on headlands.
  • Wave-cut platforms, resulting from cliff retreat.
• Depositional Landforms:
  • Beaches, spits, bars, and lagoons formed by sediment accumulation.
  • Deltas and estuaries representing fluvial-marine interaction zones.

Karst and Solutional Landforms

In regions of limestone and dolomite, chemical weathering through carbonation creates karst topography.

• Erosional features: Sinkholes (dolines), caves, and underground streams.
• Depositional features: Stalactites and stalagmites formed by calcium carbonate deposition inside caves.

Volcanic Landforms

Volcanic activity creates a wide range of surface and subsurface landforms depending on the type of eruption and lava composition.

• Extrusive features: Shield volcanoes, composite cones, lava plateaus, and craters.
• Intrusive features: Batholiths, sills, dykes, and laccoliths, formed when magma solidifies within the crust.

Interrelationship of Processes and Human Impact

The Earth’s surface is a dynamic system where endogenic and exogenic forces act simultaneously. For instance, while tectonic uplift creates mountains, erosion gradually wears them down. Human activities—such as mining, deforestation, urbanisation, and dam construction—have increasingly altered geomorphic processes, accelerating erosion and land degradation.