Geography: Class 11 (Part 2) — Chapter 5: Geomorphic Processes

The earth's surface is continuously shaped by two opposing forces:

• Endogenic Forces: Internal forces originating from within the earth that continuously elevate or build up parts of the earth's surface (land-building forces).
• Exogenic Forces: External forces originating within the earth's atmosphere, driven basically by solar energy, that wear down relief variations (land-wearing forces).

The phenomenon of wearing down relief variations of the surface of the earth through erosion is known as gradation. It consists of degradation (wearing down of elevations) and aggradation (filling up of basins/depressions).

The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes.

A geomorphic agent is any mobile medium of nature (like running water, groundwater, glaciers, wind, waves, and currents) capable of acquiring and transporting earth materials.

Gravity is a directional force that activates all downslope movements of matter and causes stresses on earth materials, making it a fundamental force driving geomorphic processes.

All processes that move, elevate, or build up portions of the earth's crust come under diastrophism. They include:

1. Orogenic processes: Mountain building through severe folding, affecting long and narrow belts of the crust.
2. Epeirogenic processes: Continental building involving uplift or warping of large parts of the earth's crust.
3. Earthquakes: Local, relatively minor crustal movements.
4. Plate tectonics: Horizontal movements of crustal plates.

Volcanism includes the movement of molten rock (magma) onto or toward the earth's surface, forming intrusive and extrusive volcanic features.

Force applied per unit area is called stress. In solids, stress is produced by pushing or pulling, inducing deformation. Shear stresses are separating forces acting along the faces of earth materials that break rocks and cause slippage.

All exogenic geomorphic processes are covered under the general term denudation, which means to strip off or uncover. It includes:

• Weathering
• Mass wasting/movements
• Erosion
• Transportation

Exfoliation is a result of physical weathering (unloading and thermal expansion) where curved sheets of rock flake off, resulting in smooth, rounded surfaces like exfoliation domes.

Significance of Weathering:

• Breaks down rocks to form regolith and soils.
• Aids mass wasting, erosion, and reduction of relief.
• Leads to enrichment, where valuable minerals (iron, manganese, aluminium, copper) are concentrated through the leaching of soluble materials.

• Heave: Heaving up of soils due to frost growth or other causes.
• Flow: Rapid downslope movement of water-saturated clay or silt.
• Slide: Rapid sliding of dry, detached masses along a plane.

Landslides are rapid and perceptible movements of relatively dry materials. Types include:

• Slump: Slipping of rock debris with a backward rotation.
• Debris slide: Rapid rolling or sliding of earth debris without backward rotation.
• Debris fall: Free fall of earth debris from a vertical face.
• Rockslide: Sliding of individual rock masses down bedding, joint, or fault surfaces.

Erosion involves the acquisition and transportation of rock debris by geomorphic agents like running water, groundwater, glaciers, wind, and waves.

Deposition is a consequence of erosion. When erosional agents lose their velocity and energy on gentler slopes, materials settle, filling up depressions.

Soil is a dynamic medium in which chemical, physical, and biological activities go on constantly. Soil formation depends first on weathering, which provides the basic input (weathering mantle).