5.4 Erosion processes and landscape evolution
3 min read•july 22, 2024
Erosion shapes our planet's surface through water, wind, ice, and . These forces carve valleys, create , and sculpt coastlines. Understanding erosion helps us grasp how landscapes form and change over time.
and play key roles in shaping terrain. Rivers erode land through , rills, and gullies. and dramatically alter landscapes, moving soil and rock downslope under gravity's influence.
Agents of Erosion and Their Mechanisms
Agents of erosion
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- Water erodes through fluvial erosion (rivers and streams), coastal erosion (waves, tides, and currents), and (movement of glaciers and ice sheets)
- Wind erodes through aeolian erosion (particularly in arid and semi-arid regions), (wearing away of surfaces by windborne particles), and (removal of loose, fine-grained particles)
- Ice erodes through (glaciers removing large chunks of bedrock) and abrasion (grinding and scraping of bedrock by debris embedded in the base of a glacier)
- Gravity contributes to erosion and landscape modification through mass wasting (downslope movement of rock, soil, and other debris)
Fluvial Processes and Landscape Modification
Fluvial processes in landscapes
- Sheet wash (sheet erosion) uniformly removes soil and sediment from a surface by overland flow when rainfall intensity exceeds the soil's infiltration capacity
- forms small, shallow channels (rills) on hillslopes due to concentrated overland flow, typically a few centimeters deep and easily obliterated by tillage (plowing)
- forms deep, wide channels (gullies) due to prolonged, concentrated overland flow, larger than rills and not easily removed by tillage, significantly altering the landscape and contributing to sediment transport
Mass Wasting and Terrain Modification
Mass wasting and terrain modification
- Landslides involve the downslope movement of soil, rock, and debris under the influence of gravity, triggered by factors such as heavy rainfall, earthquakes, and human activities, significantly altering the landscape by creating scars, depositing debris, and damming rivers
- Rockfalls involve the detachment and rapid downslope movement of rock fragments from a cliff or steep slope, often caused by weathering, erosion, or seismic activity, modifying the terrain by accumulating debris at the base of slopes and creating talus cones (cone-shaped deposits of rock debris)
Erosion, Deposition, and Landform Development
Erosion vs deposition in landforms
- River valleys are formed by the erosive action of flowing water in rivers and streams, deepening and widening the valley over time, creating features like , (flat areas adjacent to the river), and terraces (step-like benches)
- Deltas are formed by the deposition of sediment at the mouth of a river where it enters a larger body of water (ocean or lake), creating a distinctive triangular or fan-shaped landform with various shapes depending on the balance between river discharge, wave action, and tidal currents
- Coastal features include:
- such as cliffs and wave-cut platforms (formed by the erosive action of waves and currents) and sea arches and sea stacks (formed by differential erosion of coastal rocks)
- such as beaches (formed by the deposition of sand and other sediments along the shoreline), and (elongated ridges of sand or gravel deposited by longshore currents), and (elongated, offshore islands formed by the deposition of sand parallel to the coastline)
Key Terms to Review (22)
Abrasion: Abrasion is the process of wearing down surfaces through friction and impact, often caused by the movement of particles in air, water, or ice. This mechanical weathering process plays a crucial role in shaping landscapes by breaking down rocks into smaller fragments and altering their surfaces. It also interacts with various natural processes such as erosion and sediment transport, highlighting its importance in the evolution of landforms over time.
Barrier islands: Barrier islands are elongated, narrow landforms situated parallel to the mainland coast, formed primarily by the accumulation of sand and sediments. They play a crucial role in coastal ecosystems by protecting the mainland from the direct impact of waves, storm surges, and erosion while providing habitats for various plant and animal species.
Bars: Bars are elongated landforms created by the accumulation of sediment, typically found in river channels, estuaries, and coastal environments. These structures can significantly affect water flow and sediment transport, influencing erosion processes and landscape evolution. By altering the dynamics of water movement, bars contribute to the shaping of landscapes over time through the deposition and erosion of materials.
Deflation: Deflation is the process by which loose, dry particles are removed from the surface of the ground by wind action, leading to the lowering of the land surface and changes in landscape features. This phenomenon contributes to erosion, shaping landforms and influencing sediment transport, particularly in arid and semi-arid regions where vegetation is sparse and soil is more vulnerable to wind forces.
Deltas: Deltas are landforms created at the mouth of a river where it meets a body of water, such as an ocean, sea, or lake. They form from the accumulation of sediment that is deposited as the river slows down and loses energy when it enters standing water. Deltas are dynamic environments that evolve over time due to processes of erosion and deposition, playing an important role in shaping landscapes, influencing sedimentary structures, and contributing to fluvial landforms.
Depositional features: Depositional features are landforms created by the accumulation of sediment that has been transported by natural processes such as water, wind, or ice. These features include structures like deltas, beaches, and moraines, which arise when the energy of transporting mediums decreases, causing materials to settle and accumulate in certain areas. Understanding these features is crucial for grasping how landscapes evolve over time due to erosion and sedimentation.
Erosional features: Erosional features are landforms created by the removal and transportation of rock and soil by various erosion processes, such as water, wind, and ice. These features can dramatically shape the landscape over time, resulting in distinct formations like canyons, valleys, and cliffs. Understanding these landforms is crucial for studying how landscapes evolve and change in response to environmental forces.
Floodplains: Floodplains are flat or gently sloping areas adjacent to rivers and streams that are prone to flooding during periods of high discharge. These landforms are created by the accumulation of sediment from river overflow and play a crucial role in the surrounding ecosystem, providing fertile land for agriculture, habitat for wildlife, and natural filtration for water quality.
Fluvial Processes: Fluvial processes refer to the various actions and interactions of flowing water, primarily rivers and streams, that shape the landscape through erosion, transportation, and deposition of sediments. These processes play a vital role in the evolution of landforms, influencing river morphology, sediment transport dynamics, and landscape features such as valleys and floodplains.
Glacial erosion: Glacial erosion is the process by which glaciers wear away the landscape as they move, sculpting the land through the grinding action of ice and the transportation of debris. This process is a major factor in shaping valleys, mountains, and other landforms, revealing the powerful impact glaciers have had on Earth's surface throughout geological history. The interaction between glacial movement and geological features results in distinct landforms that illustrate the dynamic nature of Earth's landscape evolution.
Gravity: Gravity is the natural phenomenon by which all things with mass are attracted to one another, creating a force that pulls objects toward the center of larger masses, like planets and stars. This fundamental force is crucial in shaping landscapes and driving erosion processes, as it influences how water, soil, and rock materials move and interact with each other over time.
Gully erosion: Gully erosion is a form of soil erosion that occurs when water runs through small channels, creating larger and deeper ditches or gullies in the landscape. This process is driven by the flow of water during rainfall, which can remove soil and rock material, significantly altering the landscape over time. Gully erosion not only impacts agricultural land by reducing its fertility but also affects waterways and ecosystems as sediments are transported away.
Landslides: A landslide is the rapid movement of rock, soil, and debris down a slope due to gravity, often triggered by factors such as rainfall, earthquakes, volcanic activity, or human activities. These events are significant in understanding the stability of slopes and play a critical role in shaping landscapes, which is essential for studying geological processes, erosion, and natural hazards.
Mass wasting: Mass wasting refers to the downhill movement of rock and soil due to gravity. This process is crucial in shaping landscapes, as it contributes to erosion and influences the overall topography by transporting materials from higher elevations to lower ones. Understanding mass wasting helps us analyze its impact on landforms and the factors that trigger such movements, which can include weathering and environmental conditions.
Plucking: Plucking is a glacial erosion process where a glacier picks up and incorporates rock fragments from the bedrock beneath it. This action occurs as the glacier moves, effectively scraping the surface and causing erosion. Plucking plays a significant role in shaping landscapes, as it helps to create features like U-shaped valleys and fjords while also contributing to the overall material transport within glacial systems.
Rill erosion: Rill erosion is a type of soil erosion that occurs when small channels, or rills, form on the surface of the soil due to the concentrated flow of water. This process typically happens during heavy rainfall or rapid snowmelt when water accumulates and begins to flow over the land, cutting into the soil and creating these small, narrow grooves. Rill erosion plays a significant role in the overall erosion processes and landscape evolution by altering the topography and contributing to sediment transport.
Rockfalls: Rockfalls are rapid downward movements of rock fragments or boulders that occur when they detach from a cliff or steep slope. These events can happen due to various factors, including weathering processes, geological instability, or human activities that compromise the slope's integrity. Rockfalls contribute significantly to landscape evolution by reshaping terrains and creating features such as talus slopes and debris cones.
Sheet wash: Sheet wash is a process of surface runoff where a thin layer of water flows over the ground, transporting soil and other materials as it moves. This type of erosion is significant because it occurs uniformly across a landscape, leading to widespread soil loss and altering landforms over time.
Spits: Spits are narrow landforms that extend from the shoreline into a body of water, formed by the accumulation of sediment deposited by longshore drift. They are typically characterized by their elongated shape and can serve as natural barriers, protecting coastal areas from wave action and erosion. The formation and evolution of spits are closely linked to processes of erosion, sediment transport, and deposition, playing a significant role in landscape evolution.
V-shaped valleys: V-shaped valleys are narrow, steep-sided valleys formed primarily by the process of river erosion. As a river flows through an area, it cuts downwards into the landscape, creating a characteristic 'V' shape in cross-section. This formation results from the combination of vertical erosion by the river and lateral erosion of the valley sides, reflecting the dynamic interplay between water flow and geological materials.
Water erosion: Water erosion is the process where soil and rock are removed from the Earth's surface by water flow and transported to other locations. This process can significantly alter landscapes over time, shaping valleys, riverbanks, and coastlines as water moves sediments and sculpts terrain through mechanisms like rainfall, runoff, and river flow.
Wind erosion: Wind erosion is the process by which soil, sediment, and rock particles are removed from one location and transported to another by the force of wind. This natural phenomenon significantly influences landscape evolution by shaping landforms, redistributing materials, and altering ecosystems, especially in arid and semi-arid environments where vegetation cover is sparse.