10.1 Erosional coastal landforms
4 min read•july 30, 2024
Coastal erosion shapes shorelines through wave action, tides, and environmental factors. , platforms, and form as waves batter coastlines, with rock type and structure influencing erosion rates and landform development.
distribution plays a crucial role in shaping coastal features. High-energy environments create steep cliffs and narrow platforms, while wave refraction concentrates erosion around headlands, forming and .
Coastal Erosion and Landform Development
Wave Action and Environmental Factors
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- Wave action drives coastal erosion with wave energy and frequency directly impacting erosion rates
- High-energy waves (storm waves) cause more rapid erosion than low-energy waves
- Wave frequency affects the continuity of erosional processes
- Tidal range influences the vertical extent of wave action and area susceptible to erosion
- Macrotidal coasts (tidal range >4m) experience erosion over a larger vertical area
- Microtidal coasts (tidal range <2m) concentrate erosion in a narrower zone
- Climate factors shape weathering rates and erosional event intensity
- Temperature fluctuations cause thermal expansion and contraction of rocks
- Precipitation increases chemical weathering and physical erosion
- Storms amplify wave energy and erosional potential
Geological and Anthropogenic Influences
- Coastal geology determines coastline susceptibility to erosion
- Rock type impacts resistance (granite more resistant than limestone)
- Structural features like joints and faults create erosional weak points
- Sea-level changes alter shoreline position and erosional patterns
- Eustatic changes result from global water volume variations
- Isostatic changes occur due to local crustal movements
- Human activities modify natural erosional processes
- Coastal development removes natural buffers (dunes, vegetation)
- Engineering structures (seawalls, groins) interrupt
Formation of Erosional Features
Cliff and Platform Development
- Coastal cliffs form through wave erosion undercutting slope bases
- Continuous undercutting leads to cliff instability and collapse
- Cliff retreat rates vary based on rock resistance and wave energy
- extend seaward from cliff bases
- Formed by continuous wave erosion and cliff retreat
- Platform width increases as cliffs recede landward
- Formation process progresses over time
- Cliffs retreat, platforms expand, and overall coastal profile evolves
- Rate of formation depends on rock resistance, wave energy, and tidal range
- Cliff profiles and platform widths vary with local conditions
- Steep cliffs often indicate resistant rock or high wave energy
- Wide platforms suggest prolonged erosion or less resistant rock
Sea Arch and Stack Formation
- Sea arches develop when waves erode through headlands or weak zones
- Initial formation begins with sea cave development on opposite sides
- Continued erosion eventually connects caves, forming an arch
- Arch collapse leads to stack or stump formation
- Isolated sea stacks remain as erosion-resistant rock pillars
- Further erosion reduces stacks to low-lying stumps
- Feature longevity depends on environmental factors
- Rock resistance influences the rate of arch and stack erosion
- Wave energy and storm frequency affect the speed of formation and destruction
Rock Type and Coastal Features
Lithological Influences on Erosion
- Rock type determines resistance to erosion
- Harder rocks (granite) form resistant headlands
- Softer rocks (shale) erode into bays
- Chemical composition affects weathering rates
- Carbonate rocks (limestone) susceptible to chemical dissolution
- Silicate rocks (quartz) more resistant to chemical weathering
- Differential erosion of varying rock types creates complex landscapes
- Alternating hard and soft rock layers form crenulated coastlines
- Resistant rock outcrops become isolated as sea stacks (Old Harry Rocks, UK)
Structural Controls on Coastal Morphology
- Joints, faults, and bedding planes create erosional weak zones
- Wave action exploits these weaknesses, forming sea caves and arches
- Orientation of structural features influences the alignment of coastal landforms
- Dip and strike of rock layers affect cliff stability and platform development
- Seaward-dipping beds often result in more stable cliffs
- Landward-dipping beds can lead to increased rockfall and cliff retreat
- Geological structure controls feature scale and distribution
- Fold axes may determine the location of headlands and bays
- Fault lines can create linear coastal features or influence cliff orientation
Wave Energy and Landform Morphology
Energy Distribution and Landform Shaping
- Higher wave energy environments produce steeper cliffs and narrower platforms
- Increased erosional force concentrates wave impact at cliff base
- Examples include exposed Atlantic coastlines (Cliffs of Moher, Ireland)
- Wave approach angle influences erosion direction and intensity
- Oblique wave approach can create asymmetrical headlands
- Longshore generated by angled waves transport eroded material
- Wave refraction concentrates energy around headlands
- Accelerated erosion in these areas forms sea caves and arches
- Examples include Durdle Door in Dorset, UK
Temporal and Spatial Variations in Wave Energy
- Seasonal wave energy variations create erosion and deposition cycles
- Winter storms often cause increased erosion
- Summer conditions may allow for temporary sediment accumulation
- Offshore bathymetry modifies wave energy distribution
- Submarine canyons can focus wave energy on specific coastal sections
- Offshore islands or reefs may provide protection, reducing erosion rates
- Long-term wave climate changes alter landform equilibrium
- Climate change-induced sea-level rise may accelerate
- Changes in storm frequency or intensity can modify existing features
- Example: Increased erosion rates along vulnerable coastlines (East Anglia, UK)
Key Terms to Review (17)
Arches: Arches are natural rock formations that are characterized by a curved structure with an opening beneath it, typically formed by erosion processes. These formations are created when softer rock erodes away faster than harder rock, leading to the development of an arch shape as the underlying material is gradually removed. The beauty and complexity of arches make them significant features along erosional coastal landscapes, where waves and weathering play key roles in their formation.
Blowholes: Blowholes are natural openings found in coastal cliffs that allow seawater to be forced upward into the air, often creating a spectacular spray. These features typically form in volcanic or limestone rock along the coastline and are created by the erosive power of waves, which erode the rock and create cavities that channel water. When the waves crash into the shore, the pressure builds up in these cavities, and eventually, the water erupts through the blowhole, resembling a geyser.
Cliffs: Cliffs are steep, vertical, or near-vertical rock faces that form along coastlines due to the process of erosion. These impressive geological features are typically shaped by the action of waves, wind, and weathering, creating distinctive profiles along the shoreline. Cliffs can serve as dramatic backdrops to coastal landscapes and are often associated with various erosional coastal landforms like sea stacks and wave-cut platforms.
Coastal Retreat: Coastal retreat refers to the landward movement of coastlines due to natural processes such as erosion, rising sea levels, and human activities. This phenomenon can result in the loss of land, impacting ecosystems, infrastructure, and coastal communities. Coastal retreat is closely associated with erosional coastal landforms, which are shaped by the relentless action of waves and currents that erode the shoreline over time.
Coves: Coves are small, sheltered bays or coastal inlets typically characterized by a circular or oval shape, often formed through erosional processes. These landforms can provide calm waters and are frequently found along coastlines, playing a significant role in coastal ecosystems and human activities such as boating and fishing.
Currents: Currents are continuous, directed movements of seawater generated by various factors, including wind, temperature differences, and the Earth's rotation. They play a crucial role in shaping coastal environments by transporting sediments and influencing erosion, thereby contributing to the formation of erosional coastal landforms such as cliffs, sea stacks, and wave-cut platforms.
Dynamic Equilibrium: Dynamic equilibrium refers to a state of balance in which processes are constantly changing, but the overall system remains stable over time. In the context of Earth surface processes, this concept illustrates how landforms evolve due to various factors like erosion and deposition while still maintaining a certain degree of balance in their characteristics. Understanding this equilibrium helps in comprehending how landscapes respond to changes in environmental conditions, whether they be natural or anthropogenic.
Hard engineering: Hard engineering refers to the use of solid structures, such as seawalls, groynes, and breakwaters, to protect coastlines from erosion and flooding. This approach relies on physical barriers that are designed to withstand and mitigate natural processes like wave action and tidal forces, making it a common strategy in managing coastal environments and protecting valuable land and infrastructure.
Land loss: Land loss refers to the process where land, especially coastal land, is eroded or submerged due to natural forces like wave action, sea-level rise, and human activities. This phenomenon significantly alters landscapes, leading to the displacement of ecosystems and human communities while impacting the overall stability of coastal regions.
Longshore drift: Longshore drift is the process by which sediment is transported along the coastline, driven by the angle of wave approach and the resulting movement of water and sand. This natural phenomenon plays a crucial role in shaping coastal landforms, affecting both erosional and depositional features while influencing coastal management practices.
Sea caves: Sea caves are natural coastal formations created by the erosive power of waves against rock along shorelines. These unique geological structures often feature intricate shapes and can vary in size, providing insight into the processes of erosion and the dynamic nature of coastal environments. Sea caves are typically found in areas with strong wave action, where softer rock layers have been worn away more quickly than harder rock layers, resulting in hollowed-out spaces along the coast.
Sea stacks: Sea stacks are isolated columns of rock that are formed by the erosion of coastal cliffs, created through the relentless action of waves and weathering. These natural formations typically arise from the remnants of headlands or cliffs, where softer rock is eroded away faster than the harder rock, leaving behind tall, vertical structures standing in the ocean. Sea stacks serve as important indicators of coastal erosion processes and can also be habitats for various marine and bird species.
Sediment transport: Sediment transport refers to the movement of solid particles, typically resulting from processes such as erosion, weathering, and deposition, through various environmental mediums like water, wind, or ice. This process is crucial for shaping landscapes and influencing ecological systems, as it plays a key role in sediment delivery to river channels, coastal areas, and other depositional environments.
Soft engineering: Soft engineering refers to the use of natural processes and materials to manage and protect coastlines, often focusing on sustainability and minimizing environmental impact. This approach includes techniques such as beach nourishment, planting vegetation, and using wetlands to absorb wave energy. By working with nature rather than against it, soft engineering aims to create long-term solutions for coastal erosion and habitat preservation.
Tide: A tide is the regular rise and fall of sea levels caused by the gravitational forces exerted by the Moon and the Sun, along with the Earth's rotation. Tides create distinct patterns in coastal areas, influencing various erosional processes and landform development along shorelines. They play a crucial role in shaping coastal landscapes through sediment transport and erosion.
Wave energy: Wave energy refers to the energy generated from the movement of waves on the surface of oceans, seas, and other large bodies of water. This energy is a result of wind blowing across the water's surface and is harnessed through various technologies for practical use, such as electricity generation. Understanding wave energy is essential in examining how coastal processes shape erosional landforms along shorelines, where the intensity and frequency of waves can lead to significant geological changes.
Wave-cut platforms: Wave-cut platforms are flat, horizontal surfaces found at the base of coastal cliffs, formed by the erosional action of waves over time. They represent the remnants of a once higher cliff face that has been worn down by the relentless force of waves, leading to their retreat and the creation of this unique landform. Understanding wave-cut platforms involves looking at how waves generate energy, propagate towards the shore, and interact with coastal structures, leading to the gradual shaping of coastal landscapes.