14.2 Coastal erosion and depositional features
3 min read•july 24, 2024
shapes shorelines, creating , platforms, arches, stacks, and caves. These features result from waves attacking rock faces, with varying resistance leading to unique formations. Understanding these processes helps explain the ever-changing coastal landscape.
builds , , , , and dunes. These landforms result from waves and currents moving and depositing sediments. Factors like , , and human activities influence erosion rates and sediment transport along coasts.
Coastal Erosional Features
Coastal erosional features
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- Cliffs form steep rock faces through wave erosion at base composed of resistant rock types retreat landward over time (Dover White Cliffs)
- create flat or gently sloping surfaces at cliff bases result from erosion and weathering of softer rock layers exposed during low tide (Giant's Causeway)
- develop natural rock openings in headlands or rocky outcrops through differential erosion of weaker rock layers (Durdle Door)
- stand as isolated rock columns in sea formed when sea arches collapse remnants of former headlands or cliffs (Old Harry Rocks)
- hollow out areas in cliff faces created by wave action exploiting weak points in rock may lead to sea arch formation (Fingal's Cave)
Coastal Depositional Features and Processes
Coastal depositional landforms
- Beaches accumulate sand, gravel, or pebbles along shoreline through wave action depositing sediments slope and composition vary with wave energy and sediment supply (Copacabana)
- Spits extend as elongated landforms from coast into open water formed by depositing sediments often curve at end due to wave refraction (Spurn Point)
- Barrier islands form long, narrow islands parallel to mainland coast from sand and sediments deposited by waves and currents protect mainland from storms create lagoons (Outer Banks)
- Tombolos connect islands to mainland or other islands with sand or gravel bars formed by wave refraction and sediment deposition (St Ninian's Isle)
- accumulate wind-blown sand behind beaches stabilized by vegetation over time provide natural storm surge protection (Indiana Dunes)
Factors in coastal erosion
- Rock type affects erosion rates resistant rocks (granite) erode slowly softer rocks (sandstone) erode quickly joints or fractures increase erosion
- Wave energy increases erosion with higher energy influenced by wind strength, fetch, and water depth storm waves cause rapid erosion
- Human activities alter natural sediment transport through coastal development seawalls may increase adjacent erosion sand mining depletes beach sediments
- Climate factors accelerate erosion through sea-level rise changes in storm patterns affect erosion
- Coastal geometry exposes headlands to more erosion than bays shoreline orientation to prevailing winds affects wave energy
- Tidal range exposes more area to wave action with larger ranges influences vertical erosion distribution
Sediment transport in coastal development
- Longshore drift moves sediments parallel to shoreline driven by oblique wave approach forms spits and barrier islands
- moves sediments perpendicular to shoreline influenced by wave energy and beach slope causes seasonal beach profile changes
- include rivers supplying coastal areas cliff erosion providing beach material offshore deposits transported onshore
- trap and remove coastal sediments in submarine canyons estuaries and lagoons act as sediment traps
- balances inputs and outputs in coastal system affects stability and evolution of landforms
- on transport include dams reducing river sediment supply groins and jetties interrupting longshore drift beach nourishment adding artificial sediment
Key Terms to Review (20)
Barrier islands: Barrier islands are long, narrow landforms that lie parallel to the coastline, serving as protective shields against ocean waves and storms. They are formed by the accumulation of sand and sediments deposited by wave action, currents, and tides. These islands play a crucial role in coastal ecosystems, providing habitats for wildlife and acting as natural buffers that protect inland areas from erosion and flooding.
Beaches: Beaches are dynamic landforms along coastlines where land meets water, typically consisting of loose particles such as sand, gravel, or cobblestones. These areas are formed by the accumulation of sediment deposited by waves and currents, and they serve as important recreational spaces, habitats, and buffers against coastal erosion.
Cliffs: Cliffs are steep, vertical, or near-vertical rock faces that are often found along coastlines and can result from processes of erosion and weathering. They are typically formed when waves continuously crash against rock formations, leading to their gradual wear and creating dramatic landscapes. Cliffs can serve as important indicators of geological history, revealing the layers of rock and sediment that have been deposited over time.
Coastal deposition: Coastal deposition is the process where sediments, such as sand and gravel, are accumulated along coastlines due to the action of waves, currents, and tides. This process can create various landforms, including beaches, sandbars, and deltas, as sediments settle in calmer waters or are deposited by longshore currents. The balance between deposition and erosion shapes the coastal landscape over time.
Coastal dunes: Coastal dunes are mounds or ridges of sand formed along shorelines, primarily through the processes of wind action and sediment deposition. These dynamic landforms play a vital role in coastal ecosystems, acting as natural barriers against storm surges and providing habitat for various plant and animal species.
Coastal erosion: Coastal erosion refers to the process by which coastlines are gradually worn away by the action of waves, currents, tides, and human activities. This natural phenomenon can lead to significant changes in coastal landscapes, affecting habitats, human structures, and sediment distribution. Understanding coastal erosion is essential for managing shoreline stability and addressing the impacts of sea-level rise and climate change.
Cross-shore transport: Cross-shore transport refers to the movement of sediment and materials between the shoreline and the offshore zone, primarily driven by wave action and currents. This process plays a crucial role in shaping coastal landforms, affecting both erosion and deposition along beaches, and contributing to the dynamic nature of coastal environments.
Human impacts: Human impacts refer to the various ways in which human activities affect the natural environment, particularly in coastal areas. These impacts can significantly alter coastal erosion and depositional features through processes such as urbanization, pollution, and resource extraction. Understanding human impacts is crucial for assessing changes in coastlines, sediment transport, and ecosystem health.
Longshore drift: Longshore drift is the process by which sediment is transported along a coastline parallel to the shore, primarily driven by the action of waves and currents. This movement plays a crucial role in shaping coastal landscapes, affecting beach formation, erosion, and the creation of various depositional features such as spits and bars.
Rock type: Rock type refers to the classification of rocks based on their origin, mineral composition, and texture. These classifications include igneous, sedimentary, and metamorphic rocks, each formed through different geological processes. Understanding rock types is crucial in studying coastal erosion and depositional features because they influence the stability of coastlines and the types of sediment available for deposition.
Sea arches: Sea arches are natural rock formations that occur when waves erode a section of rock along a coastline, creating an arch-shaped opening through the rock. These formations often develop from sea caves, which form as the waves wear away softer rock, while the harder rock remains, resulting in a stunning coastal feature that highlights the power of erosion and the dynamics of coastal environments.
Sea caves: Sea caves are natural rock formations created by the erosion of coastal cliffs due to wave action. They typically form along rugged shorelines where powerful ocean waves continuously strike the rock, carving out hollow spaces and tunnels over time. These caves can provide unique habitats for marine life and are often seen as picturesque features of coastal landscapes.
Sea stacks: Sea stacks are tall, often isolated columns of rock that rise from the ocean due to erosion processes acting on coastal cliffs. These natural formations are remnants of headlands or coastal cliffs that have been worn down over time by wave action, weathering, and erosion, leaving behind these unique structures. They serve as significant indicators of coastal erosion and contribute to the diversity of coastal landscapes.
Sediment budget: A sediment budget refers to the balance of sediment input, output, and storage within a specific area, typically along coastlines. This concept helps to understand how coastal features evolve over time by accounting for the processes of erosion, transportation, and deposition. By analyzing a sediment budget, it's possible to assess the dynamics of sediment movement and predict changes in coastal landforms due to natural forces and human activities.
Sediment sinks: Sediment sinks refer to areas where sediment is deposited and accumulates, typically found in coastal environments where erosion and deposition interact. These sinks play a vital role in shaping coastal landscapes, as they can form features like deltas, beaches, and tidal flats that are essential for both ecological balance and human activity. Understanding sediment sinks is crucial for comprehending the processes of coastal erosion and deposition that influence landforms along shorelines.
Sediment sources: Sediment sources refer to the locations or processes that supply sediments to a particular environment, particularly in coastal areas. These sources can include rivers, eroding cliffs, beach sand, and human activities like construction or mining. Understanding sediment sources is crucial for assessing coastal erosion and the formation of various depositional features along shorelines.
Spits: Spits are narrow landforms of sand or gravel that extend from the mainland into a body of water, often forming at coastal locations where sediment is deposited by longshore currents. These features act as natural barriers, influencing local ecosystems and altering the flow of water and sediment along coastlines. Spits can lead to the formation of lagoons on one side and are indicative of ongoing coastal processes.
Tombolos: Tombolos are narrow landforms that connect an island to the mainland or another island, formed by the accumulation of sand and sediment. These features arise due to the interaction of waves, currents, and sediment transport processes, leading to the deposition of materials in a way that creates a bridge-like structure. They serve as important indicators of coastal dynamics and can influence local ecosystems.
Wave energy: Wave energy is the energy generated by the movement of waves on the surface of the ocean, caused primarily by wind. This energy can be harnessed to produce electricity and is a significant factor in coastal processes, influencing erosion and sediment deposition along shorelines. Understanding wave energy is essential to grasp how waves shape coastal landforms and affect marine ecosystems.
Wave-cut platforms: Wave-cut platforms are flat, bench-like surfaces found along the shoreline that are created by the erosive action of waves against coastal cliffs or rock formations. As waves continuously crash against these cliffs, they erode the rock and sediment, leading to the formation of a relatively smooth and level surface at the base of the cliff. This geological feature is a clear indicator of coastal erosion processes and helps illustrate the dynamic interactions between land and sea.