GEOMORPHIC PROCESSES, LANDFORMS AND THEIR EVOLUTION

Concept of Landforms and Landscape

After weathering processes act on earth materials, various geomorphic agents such as running water, groundwater, wind, glaciers and waves perform erosion. Erosion leads to changes on the earth’s surface, and deposition follows erosion, further modifying landforms.A landform refers to small to medium tracts of the earth’s surface, whereas a landscape is a combination of several related landforms forming a large tract. Each landform has a specific shape, size, material composition and is the result of particular geomorphic processes.The action of geomorphic processes is slow and continuous, and every landform undergoes development and transformation over time. Due to climatic changes and tectonic movements (vertical or horizontal), the intensity and type of processes may change, leading to further modification. Landforms pass through stages comparable to life: youth, maturity and old age, indicating continuous evolution.

RUNNING WATER AS A GEOMORPHIC AGENT

In humid regions with heavy rainfall, running water is the most important agent of erosion.

Components of Running Water

• Overland flow (sheet flow over surface)
• Linear flow (streams and rivers in valleys)

Erosion is dominant in steep gradients (youthful rivers), while deposition increases as gradients become gentle. Over time, downward cutting reduces and lateral erosion increases, transforming hills and valleys into plains.

Stages of Landscape Evolution (Running Water)

Youth Stage

• Few streams with poor integration
• Shallow V-shaped valleys
• Narrow or absent floodplains
• Broad, flat interstream divides with marshes and lakes
• Presence of waterfalls and rapids

Mature Stage

• Well-developed stream network
• Deep V-shaped valleys
• Wider floodplains
• Sharp divides
• Waterfalls disappear

Old Stage

• Few tributaries with gentle gradients
• Extensive floodplains
• Features like:
  • Natural levees
  • Oxbow lakes
• Landscape becomes low relief near sea level

Erosional Processes of Running Water

Overland flow causes sheet erosion, which gradually develops into:

• Rills → Gullies → Valleys

Valleys deepen and widen, eventually forming a peneplain (almost flat surface) with resistant remnants called monadnocks.

EROSIONAL LANDFORMS (RUNNING WATER)

Valleys

Valleys evolve from rills and gullies. Types include:

• V-shaped valleys
• Gorges (deep with steep sides, equal width)
• Canyons (step-like sides, wider at top)

Potholes and Plunge Pools

• Circular depressions formed due to abrasion by pebbles and boulders
• At waterfalls, large depressions form called plunge pools

Incised or Entrenched Meanders

• Found in hard rocks
• Formed due to vertical erosion dominating over lateral erosion

River Terraces

• Represent old floodplain levels
• Formed by vertical erosion of rivers into their own deposits
• Can be:
  • Paired terraces (same level on both sides)

DEPOSITIONAL LANDFORMS (RUNNING WATER)

Alluvial Fans

• Formed where streams move from steep slopes to gentle plains
• Deposition of coarse materials in cone-shaped form
• Streams divide into distributaries

Deltas

• Formed at river mouths where sediment is deposited into the sea
• Well-sorted and stratified deposits
• Growth occurs through extension of distributaries

Floodplains, Natural Levees and Point Bars

• Floodplain: Major depositional landform
• Natural levees:
  • Raised ridges along river banks
  • Formed by coarse deposits
• Point bars (meander bars):
  • Formed on inner banks of meanders
  • Consist of mixed sediments

Meanders

• Loop-like river channels formed due to:
  • Gentle gradient
  • Lateral erosion
  • Coriolis force

Key features:

• Cut-off bank (concave, steep erosion)
• Convex bank (gentle deposition)
• Formation of oxbow lakes

GROUNDWATER AND KARST TOPOGRAPHY

Groundwater contributes mainly through chemical processes (solution and precipitation), especially in limestone and dolomite regions.

Karst Topography

• Developed in calcium carbonate-rich rocks
• Characterised by erosional and depositional landforms

Erosional Landforms (Karst)

Sinkholes and Dolines

• Funnel-shaped depressions formed by solution or collapse
• May connect to underground drainage systems

Lapies and Limestone Pavements

• Irregular surfaces formed due to differential solution

Caves

• Formed along bedding planes due to dissolution
• Can form:
  • Cave systems
  • Tunnels (open at both ends)

Depositional Landforms (Karst)

Stalactites

• Hang from cave roofs

Stalagmites

• Rise from cave floor

Pillars

• Formed when stalactites and stalagmites join together

GLACIERS

Glaciers are moving masses of ice:

• Continental glaciers (sheet form)
• Mountain glaciers (valley form)

Movement occurs due to gravity.

Glacial Erosion

• Caused by:
  • Abrasion
  • Plucking
• Leads to destruction of even hard rocks
• Reduces mountains into low hills and plains

Glacial Deposition

• As glaciers slow down:
  • Debris is deposited
  • Formation of:
    • Outwash plains
    • Other depositional features

Glaciers in India

• Found in:
  • Uttarakhand
  • Himachal Pradesh
  • Jammu & Kashmir

Important examples:

• Gangotri Glacier → Bhagirathi river
• Alkapuri Glacier → Alaknanda river
• Both join at Devprayag to form Ganga

OVERALL EVOLUTION OF LANDFORMS

Landforms evolve due to continuous interaction of:

• Erosion
• Deposition
• Climatic changes
• Tectonic movements

This leads to transformation through:

• Youth → Maturity → Old age

The earth’s surface is therefore dynamic, with every landform having a history of formation and continuous modification over time.

GLACIAL LANDFORMS

Erosional Landforms

Cirques

Cirques are the most common landforms in glaciated mountains, usually found at the heads of glacial valleys. They are formed by accumulated ice cutting into mountain tops, producing deep, long and wide basin-like depressions with steep concave or vertical walls. After glacier retreat, these basins often contain water bodies known as cirque or tarn lakes. Multiple cirques may occur in a stepped sequence.

Horns and Serrated Ridges (Arêtes)

Horns are formed due to headward erosion of cirques. When three or more cirques meet, they produce sharp, steep-sided peaks called horns. The ridges between cirques become narrow and jagged, forming serrated ridges or arêtes with a zig-zag outline.

Examples include Matterhorn (Alps) and Mount Everest (Himalayas).

Glacial Valleys / Troughs

Glacial valleys are U-shaped valleys with:

• Broad floors
• Steep and smooth sides

They may contain:

• Morainic debris
• Lakes formed by erosion or deposition

Additional features:

• Hanging valleys (tributary valleys at higher elevation)
• Truncated spurs (cut into triangular facets)
• Deep valleys filled with seawater form fjords

Depositional Landforms

Glacial Till and Outwash Deposits

• Glacial till: Unsorted mixture of coarse and fine debris, angular in shape
• Outwash deposits: Deposited by meltwater streams, sorted and stratified, with rounded particles

Moraines

Moraines are ridges of glacial till:

• Terminal moraine: Deposited at glacier end
• Lateral moraine: Along sides of glacier
• Medial moraine: In centre of valley (formed by joining lateral moraines)
• Ground moraine: Irregular sheet of deposits over valley floor

Eskers

Eskers are sinuous ridges formed by subglacial streams depositing coarse material in channels beneath ice. After melting, these deposits remain as winding ridges.

Outwash Plains

Formed by glacio-fluvial deposits beyond glacier limits. They consist of sand, gravel, silt and clay, forming broad flat plains.

Drumlins

Drumlins are oval-shaped ridges made of glacial till:

• Long axis parallel to ice movement
• Stoss end: blunt and steep
• Tail end: gentle slope

They indicate the direction of glacier movement.

COASTAL LANDFORMS (WAVES AND CURRENTS)

Coastal Processes

Coastal changes are driven mainly by waves, along with:

• Configuration of land and sea floor
• Nature of coast (emerging or submerging)

Two types of coasts:

• High rocky coasts (submerged)
• Low sedimentary coasts (emerged)

HIGH ROCKY COASTS

• Characterised by irregular coastline
• Presence of fjords (drowned valleys)
• Dominance of erosional features

Erosional Features

• Sea cliffs: formed by wave erosion
• Wave-cut platforms: flat surfaces in front of cliffs
• Wave-built terraces: formed by deposition offshore

Depositional Features

• Beaches and bars develop over time
• Barrier bars emerge above water
• Spits: bars attached to headlands
• Lagoons: formed when spits block bays

LOW SEDIMENTARY COASTS

• Smooth coastline
• Dominated by depositional features
• Presence of:
  • Deltas
  • Marshes
  • Swamps

Processes

• Sediment deposition forms:
  • Bars
  • Barrier bars
  • Spits
  • Lagoons

Indian Example

• West Coast → High rocky (erosional)
• East Coast → Low sedimentary (depositional)

COASTAL EROSIONAL LANDFORMS

Cliffs and Terraces

• Steep slopes formed by wave erosion
• Wave-cut terraces occur above wave action level

Sea Caves and Stacks

• Sea caves: formed by wave erosion at cliff base
• Sea stacks: isolated rock remnants after cliff retreat

COASTAL DEPOSITIONAL LANDFORMS

Beaches and Dunes

• Formed by sand and sediments
• May change seasonally
• Sand dunes form behind beaches due to wind

Bars, Barriers and Spits

• Offshore bars: submerged ridges
• Barrier bars: exposed ridges
• Spits: attached to coast or headlands
• Formation of lagoons behind barriers

AEOLIAN (WIND) LANDFORMS

Wind as a Geomorphic Agent

Wind is dominant in hot deserts. It causes:

• Deflation (removal of particles)
• Abrasion (wearing of surfaces)
• Impact (force of moving particles)

Desert erosion also involves:

• Sheet floods
• Mass wasting

Erosional Landforms

Pediments and Pediplains

• Pediments: gently sloping rocky surfaces at mountain base
• Formed by lateral erosion and sheet wash

Through parallel retreat, mountains reduce to:

• Inselbergs (residual hills)
• Pediplains (low featureless plains)

Playas

• Shallow basins where water accumulates temporarily
• Contain salt deposits (alkali flats)

Deflation Hollows and Caves

• Depressions formed by removal of loose particles
• Blowouts may develop into caves

Mushroom, Table and Pedestal Rocks

• Formed by abrasion and deflation
• Have:
  • Narrow base
  • Broad top

Depositional Landforms

Sand Dunes

Wind deposits well-sorted materials forming dunes:

• Barchans: crescent-shaped, horns pointing downwind
• Parabolic dunes: formed in vegetated areas
• Seif dunes: long ridges with one wing
• Longitudinal dunes: parallel ridges (low sand supply)
• Transverse dunes: perpendicular to wind direction

Dunes may:

• Shift with wind
• Stabilise near human settlements

OVERALL SIGNIFICANCE

Landforms in glacial, coastal and desert regions are shaped by:

• Erosion and deposition
• Climate conditions
• Nature of geomorphic agents

These processes create a variety of dynamic and evolving landscapes, each reflecting the interaction between natural forces and surface materials.