Geomorphic Processes and Landforms

The One Thing

Geomorphic processes continuously reshape the Earth through the interaction of internal forces that build or deform relief and surface processes that weather, erode, transport and deposit material. Landforms therefore reflect the combined effects of process, rock structure, climate, relief, tectonic activity, time and human activity.

Who and What

• Geomorphic process: A natural physical or chemical action that changes the shape and relief of the Earth’s surface.
• Geomorphic agent: A moving medium, such as running water, groundwater, glaciers, wind or sea waves, that causes erosion, transportation or deposition.
• Endogenic processes: Processes driven by the Earth’s internal heat and energy, including tectonic movements, folding, faulting, earthquakes and volcanism. They are mainly constructive or deformational.
• Exogenic processes: Processes operating mainly at or near the surface, powered largely by solar energy and gravity. They include weathering, erosion and mass movement and are mainly denudational and redistributive.
• Diastrophism: Large-scale deformation of the Earth’s crust caused by tectonic movements, including uplift, subsidence, folding and faulting.
• Volcanism: The movement and eruption of magma, gases and volcanic materials from the Earth’s interior onto or near the surface.
• Weathering: The breakdown or decomposition of rocks in their original place, without transportation.
• Mechanical weathering: The physical breakdown of rocks without chemical change, commonly caused by temperature changes, frost action, pressure release and salt growth. It is especially effective in deserts, high mountains and areas experiencing repeated freezing and thawing.
• Chemical weathering: The decomposition of minerals through reactions with water, oxygen, carbon dioxide or acids. It is generally most active in warm, humid climates.
• Biological weathering: Rock breakdown caused by plant roots, burrowing organisms, microorganisms and human activities.
• Mass movement: The downslope movement of weathered rock, soil or debris under gravity, without a principal transporting medium. Falls, slides, flows and creep are forms of mass movement; their speed depends on slope angle, water content, rock structure, vegetation and human disturbance.
• Erosion: The removal and wearing away of weathered material by running water, groundwater, glaciers, wind or waves. Unlike weathering, it includes removal from the original location.
• Transportation: The movement of eroded material from one place to another by a geomorphic agent.
• Deposition: The settling or accumulation of transported material when the transporting agent loses energy, velocity or carrying capacity.
• Denudation: The reduction of surface relief through weathering, mass wasting and erosion. Its basic relation is: Denudation = Weathering + Mass Wasting + Erosion.
• River or fluvial landforms: Landforms produced by running water, including V-shaped valleys, waterfalls, gorges, meanders, oxbow lakes, floodplains, levees, alluvial fans and deltas.
• V-shaped valley: A narrow valley formed mainly by vertical river erosion during the youthful stage of a river.
• Waterfall and gorge: A waterfall is a sudden vertical fall of river water. A gorge is a deep, narrow valley commonly formed by prolonged river erosion.
• Meander: A loop-like bend in a river channel formed by stronger erosion on the outer bank and deposition on the inner bank. Meanders commonly develop where lateral erosion and deposition dominate, especially on the middle and lower courses.
• Oxbow lake: A crescent-shaped lake formed when a meander loop is cut off from the main river channel.
• Floodplain: A level depositional surface beside a river, formed by repeated flooding and deposition of fine sediment.
• Delta: A depositional landform near a river mouth, formed when sediment is deposited faster than waves and currents can remove it. Deltas are favoured by high sediment supply and weak coastal waves, tides and currents.
• Groundwater landforms: Features formed by the solution and deposition of soluble rocks, especially limestone, including caves, caverns, sinkholes, stalactites and stalagmites.
• Karst topography: A landscape developed mainly in soluble limestone through groundwater solution.
• Carbonation: The formation of weak carbonic acid when carbon dioxide dissolves in water; the acid can dissolve limestone.
• Hydrolysis: A chemical reaction in which water reacts with minerals, especially silicates, producing new minerals and dissolved substances.
• Oxidation: A reaction commonly affecting iron-bearing minerals and producing iron oxides with reddish or yellowish colours.
• Glacial landforms: Features produced by moving ice, including cirques, arêtes, horns, U-shaped valleys, hanging valleys, moraines, drumlins and eskers.
• Moraine: A ridge or deposit of unsorted rock debris carried and deposited by a glacier.
• Glacial erosion: Glaciers erode through plucking and abrasion and transport material frozen within, beneath or on their surface. Glacial valleys are typically U-shaped, whereas river valleys are commonly V-shaped.
• Aeolian landforms: Landforms produced by wind action in dry, sparsely vegetated regions, including sand dunes, yardangs, deflation hollows and loess deposits.
• Sand dune: A mound or ridge of wind-deposited sand whose form depends on wind direction, sand supply and vegetation.
• Deflation: The removal of loose particles by wind.
• Abrasion: The wearing of surfaces by wind-driven sediment.
• Loess: A fine, wind-deposited sediment, commonly composed mainly of silt.
• Coastal landforms: Features shaped by waves, currents, tides and coastal deposition, including cliffs, wave-cut platforms, caves, arches, stacks, beaches, spits, bars and lagoons.
• Wave-cut platform: A gently sloping rocky surface formed at the base of a retreating sea cliff through wave erosion.
• Coastal erosion sequence: Where weaknesses in rock are enlarged by waves, coastal erosion may produce cliffs, caves, arches, stacks and wave-cut platforms.
• Isostasy: The approximate gravitational balance between the Earth’s crust and the denser material beneath it. Uplift or loading can disturb this balance.
• Base level: The lowest level to which a river can erode its channel; sea level is the ultimate base level.
• Geomorphic cycle: The sequence through which landscapes develop through uplift, erosion, transportation and deposition. Real landscapes may not follow a fixed or perfectly regular cycle.

Causes and Consequences

• Endogenic processes build and deform relief. Tectonic movements produce uplift, subsidence, folding, faulting and earthquakes, while volcanism brings magma, gases and volcanic materials to or near the surface. These processes create or renew relief on which exogenic processes operate.

• Exogenic processes reduce and redistribute relief. Weathering breaks down rock in situ, mass movement shifts material downslope under gravity, and erosion removes material. Together, these processes constitute denudation and generally lower surface relief.

• Weathering supplies material for erosion. Mechanical weathering breaks rocks into smaller pieces, chemical weathering decomposes minerals, and biological weathering breaks rock through organisms and human activities. Erosion then removes the weathered material.

• Chemical weathering varies with climate. Warm, humid conditions favour chemical weathering because heat and moisture accelerate chemical reactions. Carbonation dissolves limestone, hydrolysis alters silicate minerals, and oxidation affects iron-bearing minerals. By contrast, physical weathering is particularly effective in deserts, high mountains and regions of repeated freezing and thawing.

• Mass movement is controlled by both physical and human conditions. Falls, slides, flows and creep are influenced by slope angle, water content, rock structure, vegetation and human disturbance. Increased water content or disturbance may reduce slope stability and accelerate downslope movement.

• River erosion and transportation depend on flow conditions. Hydraulic action, abrasion, attrition and solution erode river channels, while traction, saltation, suspension and solution transport sediment. A river’s ability to erode and transport generally increases with discharge, channel gradient and flow velocity. River discharge is expressed as: Discharge = Cross-sectional area of channel x Average flow velocity.

• River energy produces contrasting landforms. Vertical erosion in the youthful stage produces V-shaped valleys, waterfalls and gorges. Later, lateral erosion and deposition encourage meander development; continued erosion and deposition may produce oxbow lakes and floodplains. When a river loses energy near its mouth, it may form a delta.

• Tectonic uplift can rejuvenate rivers. Uplift increases channel gradient and encourages renewed vertical erosion, producing knick points, gorges and incised meanders. This shows that landform development is not necessarily a simple, uninterrupted progression.

• Groundwater produces karst landscapes. Groundwater movement depends on permeability, porosity, joints and the presence of soluble rocks. In limestone regions, groundwater solution forms caves, caverns and sinkholes, while deposition produces stalactites and stalagmites.

• Glaciers create distinctive erosional and depositional landscapes. Plucking and abrasion produce cirques, arêtes, horns, U-shaped valleys and hanging valleys. Glaciers transport and deposit debris, forming moraines, drumlins and eskers.

• Wind shapes dry, sparsely vegetated regions. Deflation removes loose particles and abrasion wears exposed surfaces with wind-driven sediment. These processes produce sand dunes, yardangs and deflation hollows, while deposition produces loess deposits. Sand-dune form depends on wind direction, sand supply and vegetation.

• Coastal processes alternate between erosion and deposition. Wave erosion enlarges weaknesses in rock, producing cliffs, caves, arches, stacks and wave-cut platforms. When wave energy decreases or longshore drift deposits sediment, beaches, spits, bars and lagoons may form.

• Deposition results from declining transport capacity. A geomorphic agent deposits material when its velocity, energy or carrying capacity decreases. The same agent can therefore erode in one location and deposit in another.

• Landforms reflect the interaction of process, structure and time. Rock type, resistance and geological arrangement influence landform shape, while climate controls the dominant processes: humid regions favour chemical weathering and river action, cold regions favour frost action and glaciers, and dry regions favour wind action and mechanical weathering.

• Landscape development is not always linear or uniform. Climate change, tectonic activity, sea-level change and human actions can interrupt or modify geomorphic cycles. Isostatic adjustment and changes in base level can also alter erosion and deposition.

• Geomorphic processes have practical significance. Understanding them helps explain landslides, floods, coastal erosion and glacial lake outburst floods, and supports soil conservation and land-use planning.

What Gets Asked

• Compare endogenic and exogenic processes in terms of their energy sources, mechanisms and effects on relief.
• Explain the distinction between weathering, mass movement, erosion, transportation and deposition, including the equation Denudation = Weathering + Mass Wasting + Erosion.
• Assess how climate, rock type, geological structure, relief, vegetation and human activity influence the strength and type of geomorphic process.
• Explain the formation and contrasts between V-shaped river valleys and U-shaped glacial valleys, and account for associated landforms such as waterfalls, gorges, moraines and hanging valleys.
• Describe how changes in river energy produce meanders, oxbow lakes, floodplains, levees, alluvial fans and deltas, including the conditions required for delta formation.
• Evaluate why landform development is not always a fixed or perfectly regular geomorphic cycle, with reference to tectonic uplift, sea-level change, climate change, isostasy, base level and human activity.