Geomorphic Processes

Learning Outcomes:

1. Understand the interplay between exogenic and endogenic forces that shape the Earth’s surface.
2. Recognize the processes involved in weathering, mass wasting, and erosion.
3. Analyze how different forces affect the evolution of landforms over time.

Geomorphic Processes

The Earth’s surface is continuously reshaped by two opposing sets of forces: endogenic forces originating from within the Earth and exogenic forces driven by external factors like the sun. These forces are responsible for the unevenness of the Earth’s surface. Endogenic forces, such as diastrophism and volcanism, build up the crust, while exogenic processes like weathering, erosion, and deposition work to wear it down. The interaction between these forces explains why the Earth’s relief never achieves complete uniformity.

Important Note: Gradation is the process by which relief variations on the Earth’s surface are smoothed out, primarily through erosion and deposition.

1. Endogenic Processes: These include forces that act internally to build up or elevate parts of the Earth’s surface. The primary energy driving these processes comes from radioactivity, rotational friction, and the Earth’s primordial heat.
2. Exogenic Processes: These forces wear down elevated regions and fill depressions, making the Earth’s surface more level over time. They are powered by solar energy and act through geomorphic agents like water, ice, and wind. When these agents become mobile, they move materials across the Earth’s surface, altering its configuration.
3. Geomorphic Agents: Running water, glaciers, wind, waves, and currents all act as agents of geomorphic change. Each agent operates based on gradients created by tectonic movements or gravitational forces.

Diastrophism and Volcanism

Diastrophism involves movements and deformations of the Earth’s crust. It can be categorized into:

1. Orogenic processes: Mountain-building movements that create significant folding of the Earth’s crust, resulting in elongated belts of high relief.
2. Epeirogenic processes: Movements that affect large areas of the Earth’s crust by uplifting or warping them, creating broad structural deformations.
3. Earthquakes: Localized, minor movements caused by the sudden release of built-up energy.
4. Plate tectonics: Horizontal movements of large crustal plates, leading to continental drift and the creation of mountain ranges and ocean basins.

Volcanism refers to the movement of molten rock (magma) from the Earth’s interior to its surface. This can result in the formation of both intrusive and extrusive volcanic structures.

Weathering

Weathering is the breakdown of rocks through physical, chemical, and biological processes. It is primarily an in-situ process, meaning that it occurs where the rocks are located without significant transport of materials.

1. Chemical Weathering: Involves reactions between minerals in rocks and atmospheric agents like water, oxygen, and carbon dioxide. Processes include solution, carbonation, hydration, oxidation, and reduction, which break down rocks into finer particles.
2. Physical Weathering: Driven by forces such as temperature fluctuations, crystallization, and gravitational stress, which cause rocks to break apart without changing their chemical composition.
3. Biological Weathering: Organisms like plants, animals, and microorganisms contribute to the weathering process by physically breaking apart rocks or altering their chemical composition through biological activity.

Important Note: Weathering is essential for the formation of soils, which are crucial for sustaining ecosystems.

Mass Movements

Mass movements refer to the downslope movement of rock debris under the influence of gravity. Unlike erosion, mass movements do not involve transport by wind, water, or ice.

1. Creep: The slow, continuous movement of soil and rock down a slope.
2. Flow: More rapid movements that involve a mixture of water and debris, such as mudflows and debris avalanches.
3. Slide: A relatively fast movement where a mass of material moves along a well-defined surface.
4. Fall: The free fall of rock or debris from a steep slope or cliff.

Factors that influence mass movements include slope steepness, rock type, and climatic conditions. Human activities, such as deforestation and mining, can also trigger mass movements by destabilizing slopes.

Exogenic Processes and Erosion

Exogenic processes are the denudational processes that wear down the Earth’s surface. These include weathering, mass wasting, erosion, and transportation. The primary agents of erosion are running water, glaciers, wind, and waves.

Important Note: Erosion is the key process that wears down elevated landforms, transporting the debris to lower areas, where it is eventually deposited.

Erosion by Different Agents

1. Running Water: This is the most significant agent of erosion. Water flows over the Earth’s surface, dislodging and transporting soil and rock materials. The velocity of the water determines how much material it can carry.
2. Glaciers: Glaciers erode the land by plucking and abrasion, scraping away rocks and sediments as they move.
3. Wind: In arid regions, wind acts as a powerful erosional force, carrying fine particles like sand and silt, which erode rock surfaces through abrasion.
4. Waves: Coastal erosion occurs as waves crash against shorelines, slowly wearing them down and transporting sediments offshore.

Deposition

Deposition occurs when the energy of geomorphic agents decreases, causing them to drop the materials they have been carrying. Coarser materials are deposited first, followed by finer particles. This process fills depressions and builds new landforms like floodplains, deltas, and sand dunes.

Soil Formation

Soil is the result of weathering and the accumulation of organic matter. Soil formation depends on five factors:

1. Parent Material: The type of rock or sediment from which soil forms.
2. Topography: The shape of the land influences water drainage and the amount of sunlight, which affects soil development.
3. Climate: Precipitation and temperature control the rate of weathering and organic activity, which in turn influence soil characteristics.
4. Biological Activity: The presence of plants and organisms that break down organic matter and contribute to soil fertility.
5. Time: Soils develop and mature over long periods, often taking thousands of years to form distinct layers or horizons.

Special Effects of Weathering

Certain weathering processes produce unique landforms and features:

1. Exfoliation: Curved layers of rock peel away from the surface due to temperature changes, leading to the formation of exfoliation domes.
2. Granular Disintegration: Individual mineral grains break apart, leaving behind a rough, crumbly surface.

These processes are slow but, over long periods, can lead to significant changes in the Earth’s surface, contributing to the formation of soils and influencing ecosystem diversity.

Erosion, Mass Movements, and Deposition

Mass movements and erosion both involve the movement of materials, but they operate under different mechanisms. Mass movements are gravity-driven and occur without the aid of a geomorphic agent, whereas erosion involves the transport of materials by an agent like wind or water.

Deposition occurs when an erosional agent loses its energy, dropping the materials it has carried. Over time, these processes contribute to the constant reshaping of the Earth’s surface, forming new landforms and modifying existing ones.

Important Note: Erosion and deposition are aggradational processes, meaning they contribute to the building up of landforms over time.

Multi-Column Table of Erosional Agents and Their Effects

Pedology and Soil Factors

Soils are vital to agriculture, biodiversity, and the hydrological cycle. Understanding the factors that control soil formation can help in the conservation of ecosystems and the sustainable use of land resources.

MCQ

Which process is a gradational process?
(a) Deposition
Answer: (a) Deposition

This extensive coverage of geomorphic processes and their related factors provides a comprehensive view of how the Earth’s surface evolves and changes over time.