Chapter 6. Geomorphic Processes

Geomorphic Processes
• endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in configuration of surface of earth are called geomorphic processes.
• Diastrophism and volcanism are endogenic geomorphic processes.
• An agent is a mobile medium [like running water, moving ice masses, wind, waves & currents .] that removes, transports and deposits earth materials.

Endogenic Processes
• energy emanating from within earth is main force behind endogenic geomorphic processes.
• Due to variations in geothermal gradients and heat flow from within, crustal thickness and strength, action of endogenic forces is not uniform and hence tectonically controlled original crustal surface is uneven.

• All processes that move, elevate or build up portions of earth’s crust come under diastrophism.
• In process of orogeny, crust is severely deformed into folds.

• Volcanism includes movement of molten rock [magma] onto or toward earth’s surface and formation of many intrusive and extrusive volcanic forms.

Exogenic Processes
• exogenic processes derive their energy from atmosphere determined by ultimate energy from sun and gradients created by tectonic factors.
• Temperature and precipitation are two important climatic elements that control various processes.

• Weathering is action of elements of weather and climate over earth materials.
• Weathering is defined as mechanical disintegration and chemical decomposition of rocks through actions of various elements of weather and climate.

Chemical Weathering Processes
• A group of weathering processes viz; solution, carbonation, hydration, oxidation & reduction act on rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions by oxygen, surface and/or soil water and other acids.
• Water and air [oxygen and carbon dioxide] along with heat must be present to speed up all chemical reactions.

Physical Weathering Processes
• Physical or mechanical weathering processes depend on some applied forces.
• Many of these forces are applied both at surface and within different earth materials leading to rock fracture.

Special Effects of Weathering Exfoliation
• Exfoliation is a result but not a process. Flaking off of more or less curved sheets of shells from over rocks or bedrock results in smooth and rounded surfaces.
• Exfoliation can occur due to expansion and contraction induced by temperature changes.

Biological Activity and Weathering
• Biological weathering is contribution towards removal of minerals and ions from weathering environment and physical changes due to growth or movement of organisms.
• Decaying plant and animal matter help in production of humic, carbonic & other acids which enhance decay and solubility of some elements.

Significance of Weathering
• Weathering processes are responsible for breaking down rocks into smaller fragments and preparing way for formation of not only regolith and soils but effect erosion and mass movements.
• Weathering of rocks and deposits helps in enrichment and concentrations of certain valuable ores of iron, manganese, aluminium, copper ., which are of great importance to national economy.

Mass Movements
• These movements transfer mass of rock debris down slopes under direct influence of gravity.
• Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves & currents participate in process of mass movements.
• Heave [heaving up of soils due to frost growth and other causes], flow & slide are three forms of movements.

• These are relatively rapid and perceptible movements. materials involved are relatively dry.
• Slump is slipping of one or several units of rock debris with a backward rotation with respect to slope over which movement takes place.

Erosion and Deposition
• Erosion involves acquisition and transportation of rock debris.
• A deposition is a consequence of erosion. erosional agents lose their velocity and hence energy on gentler slopes and materials carried by them start to settle themselves.

Soil Formation
• Soil is a dynamic medium in which many chemical, physical & biological activities going on constantly.
• Organic matter increases when leaves falls or grasses die.

Process of Soil Formation
• Soil formation or pedogenesis depends first on weathering. This is this weathering mantle [depth of weathered material] which is basic input for soil to form.

Soil-forming Factors
• Five basic factors control formation of soils: [i] parent material; [ii] topography; [iii] climate; [iv] biological activity; [v] time. Soil forming factors act in union and affect action of one another.

Parent Material
• Parent material is a passive control factor in soil formation.
• Parent materials can be any in-situ or on-site weathered rock debris [residual soils] or transported deposits [transported soils].
• Nature and rate of weathering and depth of weathering mantle are important considerations under parent materials.

• Climate is an important active factor in soil formation.
• climatic elements involved in soil development are [i] moisture in terms of its intensity, frequency & duration of precipitation – evaporation and humidity; [ii] temperature in terms of seasonal and diurnal variations.

• Topography like parent materials is another passive control factor.
• influence of topography is felt through amount of exposure of a surface covered by parent materials to sunlight and amount of surface and sub-surface drainage over and through parent materials.

Biological Activity
• vegetative cover and organisms that occupy parent materials from beginning and at later stages help in adding organic matter, moisture retention, nitrogen.
• intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow.

• Time is third important controlling factor in soil formation.
• length of time of soil-forming processes operate determines maturation of soils and profile development.

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