Week 4: Geomorphic Processes & Landforms

1. Introduction to Geomorphic Processes

The Earth's surface is constantly shaped by dynamic processes operating both internally and externally. These processes are categorized into:

• Endogenic Processes – Driven by internal heat and include tectonic movements, folding, faulting, volcanic activity, and earthquakes.
• Exogenic Processes – Powered by external forces such as solar energy, water, wind, and ice, leading to weathering, erosion, transportation, and deposition.

Significance of Geomorphic Processes

• Create diverse landscapes and ecosystems.
• Influence human settlements, agriculture, and infrastructure.
• Shape natural hazards like landslides, earthquakes, and tsunamis.

2. Weathering, Erosion, and Mass Movement

A. Weathering

Weathering is the in-situ breakdown of rocks due to physical, chemical, and biological processes.

1. Physical Weathering (Mechanical Breakdown)

• Exfoliation: Expansion and peeling of rock layers due to temperature changes.
• Frost Wedging: Water seeps into cracks, freezes, and expands, breaking the rock.
• Salt Weathering: Salt crystals grow in rock pores, leading to disintegration.

2. Chemical Weathering (Decomposition & Transformation)

• Dissolution: Soluble minerals (e.g., limestone) dissolve in water.
• Carbonation: CO₂ in rainwater forms carbonic acid, dissolving limestone (Karst topography).
• Oxidation: Reaction of minerals with oxygen (e.g., rusting of iron-rich rocks).
• Hydrolysis: Water reacts with minerals, forming new compounds.

3. Biological Weathering

• Plant roots widen cracks in rocks.
• Microorganisms produce acids that dissolve minerals.

Case Study: The Taj Mahal’s marble is undergoing deterioration due to acid rain (chemical weathering).

B. Erosion (Detachment & Transportation of Materials)

Erosion is the removal and transportation of surface material by water, wind, ice, or gravity.

• Fluvial Erosion: Carried out by rivers (hydraulic action, abrasion, attrition, solution).
• Aeolian Erosion: Wind-driven processes forming deserts and dunes.
• Glacial Erosion: Ice carves valleys, fjords, and cirques.
• Coastal Erosion: Wave action forms cliffs, sea arches, and stacks.

C. Mass Movement (Mass Wasting)

The downslope movement of rock and soil under gravity.

Types of Mass Movement:

• Slow Movement: Soil creep, solifluction (gradual).
• Rapid Movement: Landslides, rockfalls, debris flows (sudden).

Case Study: The 2013 Kedarnath Landslide in India due to intense rainfall and glacial lake outburst.

3. Landforms by Various Geomorphic Agents

A. Landforms Created by Rivers (Fluvial Landforms)

1. Erosional Landforms

• V-shaped Valleys & Gorges: Formed by river downcutting (e.g., Grand Canyon, USA).
• Waterfalls: Sudden vertical drop in river course (e.g., Niagara Falls).
• Meanders: S-shaped river curves due to lateral erosion.

2. Depositional Landforms

• Alluvial Fans & Cones: Cone-shaped deposits at foothills.
• Deltas: Sediment deposition at river mouths (e.g., Ganges-Brahmaputra Delta).

B. Landforms Created by Wind (Aeolian Landforms)

1. Erosional Landforms

• Mushroom Rocks: Wind abrasion sculpts rock into a mushroom shape.
• Inselbergs: Isolated rocky hills in deserts (e.g., Uluru, Australia).

2. Depositional Landforms

• Sand Dunes: Barchans (crescent-shaped), longitudinal dunes (parallel to wind).
• Loess Deposits: Wind-blown silt deposits (e.g., Loess Plateau, China).

C. Landforms Created by Glaciers (Glacial Landforms)

1. Erosional Landforms

• Cirques: Bowl-shaped depressions at mountain tops.
• U-shaped Valleys: Broad, deep valleys carved by glaciers (e.g., Yosemite Valley, USA).

2. Depositional Landforms

• Moraines: Accumulated glacial debris (terminal, lateral, medial).
• Drumlins: Oval-shaped hills formed by glacial deposition.

D. Landforms Created by Coastal Processes (Marine Landforms)

1. Erosional Landforms

• Sea Cliffs & Wave-cut Platforms: Formed by continuous wave erosion.
• Sea Arches & Stacks: Rock bridges and isolated pillars left after cliff erosion.

2. Depositional Landforms

• Beaches: Accumulation of sand along coasts.
• Spits & Tombolos: Narrow landforms formed by longshore drift.

Case Study: The White Cliffs of Dover (England) undergoing rapid erosion.

4. Karst Topography (Limestone Landscapes)

Karst landscapes result from the dissolution of soluble rocks like limestone.

Karst Features:

• Sinkholes: Depressions formed due to collapsed underground caves.
• Stalactites & Stalagmites: Mineral deposits in caves.
• Underground Rivers: Water channels beneath the surface.

Case Study: The Mammoth Cave System in the USA, the world’s longest cave network.

5. Desert Landforms

Arid regions shaped by wind and occasional water action.

Major Desert Features:

• Yardangs: Streamlined rock ridges sculpted by wind.
• Deflation Basins: Hollow depressions created by wind erosion.
• Ergs: Large areas covered by sand dunes (e.g., Sahara Desert).

6. Comparative Analysis of Geomorphic Processes

Factor	Fluvial (Rivers)	Aeolian (Wind)	Glacial (Ice)	Coastal (Waves)
Dominant Force	Water	Wind	Ice	Waves
Erosional Features	Valleys, Gorges	Mushroom Rocks	Cirques, U-valleys	Cliffs, Stacks
Depositional Features	Deltas, Floodplains	Sand Dunes, Loess	Moraines, Drumlins	Beaches, Spits
Typical Environment	Humid regions	Arid regions	Polar & High Altitudes	Coastal Areas