10.2 Depositional coastal landforms
4 min read•july 30, 2024
Coastal landforms are shaped by the constant interplay of water, wind, and sediment. Beaches, spits, and tombolos form as waves and currents deposit materials along shorelines. These features are dynamic, constantly evolving as environmental conditions change.
plays a crucial role in shaping coastal landscapes. This process moves sediment parallel to the shore, creating and maintaining features like barrier islands. Coastal dunes form above the high tide line, providing natural protection against storms and flooding.
Formation of Coastal Landforms
Beach Components and Formation
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components of a sandy marine beach – Physical Geology View original
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Coastal hydrodynamics and sediment transport – Homepage of David Gonzalez-Rodriguez View original
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components of a sandy marine beach – Physical Geology View original
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Top images from around the web for Beach Components and Formation
The formation of beach cusps and berms... © Eric Jones cc-by-sa/2.0 :: Geograph Britain and Ireland View original
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components of a sandy marine beach – Physical Geology View original
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Coastal hydrodynamics and sediment transport – Homepage of David Gonzalez-Rodriguez View original
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The formation of beach cusps and berms... © Eric Jones cc-by-sa/2.0 :: Geograph Britain and Ireland View original
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- Beaches accumulate sediment along the shoreline through and longshore currents
- Deposited materials include sand, gravel, and shells
- profiles consist of distinct components
- Foreshore extends from low tide line to high tide line
- Backshore lies above high tide line, only affected by waves during storms
- forms a raised platform above normal high tide level
- Beach cusps create crescentic patterns along the shoreline
- Form due to complex interactions between waves, currents, and
- Typically spaced at regular intervals (10-100 meters apart)
Spits and Tombolos
- Spits extend from the mainland into open water as elongated depositional features
- Often form where coastline direction changes
- Growth depends on consistent sediment supply and longshore drift
- Examples include Spurn Point (England) and Sandy Hook (New Jersey)
- Tombolos connect islands to the mainland or other islands with sand or gravel bars
- Form when waves refract around islands and deposit sediment in their lee
- Size and stability influenced by wave energy, sediment supply, and island-mainland distance
- Notable examples include Chesil Beach (England) and Monte Argentario (Italy)
Longshore Drift and Deposition
Mechanics of Longshore Drift
- Longshore drift moves sediment parallel to the shoreline
- Driven by waves approaching coast at oblique angles and longshore currents
- contributes to net sediment movement
- Waves push sediment up beach at an angle
- Gravity pulls sediment back perpendicular to shore
- Rate and direction influenced by various factors
- Wave energy
- Coastal orientation
- Sediment characteristics (size, shape, density)
Impact on Coastal Landforms
- Longshore drift shapes depositional landforms
- Crucial for formation and maintenance of spits, bars, and barrier islands
- Interruptions to drift patterns affect sediment distribution
- Groins or jetties cause on updrift side
- occurs on downdrift side of structures
- Contributes to zetaform beach development
- Curved planform shape results from gradual changes in sediment transport rates
- Essential for coastal management strategies
- Informs beach nourishment projects
- Guides design of coastal protection structures (seawalls, breakwaters)
Types of Coastal Dunes
Primary Dune Formation
- Coastal dunes accumulate wind-blown sand above high tide line
- Serve as natural barriers against storm surges and coastal flooding
- Embryo dunes initiate dune formation
- Develop when sand traps around pioneer vegetation or obstacles on upper beach
- Examples of pioneer plants include sea rocket (Cakile maritima) and sand couch grass (Elytrigia juncea)
- Foredunes form primary dune ridge parallel to shoreline
- Sand accumulates around vegetation like marram grass (Ammophila) or sea oats (Uniola paniculata)
- Provide first line of defense against coastal erosion and storm impacts
Advanced Dune Systems
- Parabolic dunes exhibit U-shaped formation
- Form when blowouts occur in established dunes
- Arms point upwind, often stabilized by vegetation
- Examples found in coastal regions of Australia and New Zealand
- Transgressive dune sheets create large, mobile sand masses
- Move inland over existing landscapes
- Form in areas with high wind energy and abundant sand supply
- Extensive examples in the Namib Desert coast and parts of coastal Brazil
- Backdunes represent older, more stabilized dunes
- Located further inland from foredunes
- Support diverse vegetation and ecosystems
- Often found in systems of the Netherlands and Denmark
Stability of Coastal Features
Natural Factors Affecting Stability
- Sediment supply balance critical for long-term maintenance
- Equilibrium between erosion and deposition required
- Sea-level changes impact coastal landform stability
- Rising sea levels potentially increase erosion and landward migration
- Wave energy and storm frequency shape depositional landforms
- Extreme events (hurricanes, nor'easters) can cause significant changes
- Vegetation cover contributes to dune and feature stability
- Traps sand and reduces wind erosion
- Examples include beach grass (Ammophila breviligulata) and sea grape (Coccoloba uvifera)
Anthropogenic and Climate Influences
- Human activities disrupt natural sediment transport processes
- alters sediment pathways
- Sand mining reduces available sediment supply
- Feature orientation relative to prevailing winds and waves affects stability
- Alignment with dominant forces can enhance or reduce erosion potential
- Climate change impacts alter long-term stability of depositional systems
- Changes in storm patterns affect wave energy and frequency
- Altered precipitation regimes influence sediment supply from rivers
- Examples include increased erosion rates in Arctic coastal areas due to permafrost thaw
Key Terms to Review (25)
Accretion: Accretion is the process by which material is added to a landform or geological feature, often leading to the growth or expansion of that feature. In coastal environments, this typically occurs when sediments accumulate over time, influenced by waves, currents, and tidal actions, ultimately resulting in the formation of various depositional landforms such as beaches, spits, and barrier islands.
Backdune: A backdune is a type of sand dune that forms behind the primary dune line, typically located further inland from the beach. These structures develop as a result of wind patterns that carry sand away from the shore and deposit it in a higher, more sheltered area, allowing for the accumulation of sand over time. Backdunes often support unique vegetation and play a significant role in coastal ecosystems by providing habitat and protecting inland areas from storm surges.
Barrier island: A barrier island is a coastal landform that is a long, narrow strip of sand or sediment that runs parallel to the mainland, often separated by a lagoon or bay. These islands are formed by the accumulation of sediment through wave action and currents, serving as protective barriers against storms and high waves for the coastal areas they shield. Barrier islands play a crucial role in coastal ecosystems and provide habitat for diverse wildlife, as well as recreational areas for humans.
Beach: A beach is a dynamic landform located along the shoreline of an ocean, sea, lake, or river, composed primarily of loose sediment such as sand, gravel, or pebbles. Beaches are shaped by various processes including wave action, tides, and currents, making them key areas for understanding coastal environments and their changes over time.
Beach cusp: A beach cusp is a crescent-shaped formation that appears on sandy beaches, characterized by a series of small, alternating mounds and troughs. These features are formed by the interaction of wave action and sediment movement along the shore, leading to distinctive patterns that can vary in size and shape. Beach cusps are important indicators of coastal processes and can also affect beach morphology and sediment distribution.
Berm: A berm is a flat or gently sloping area of land that typically forms at the edge of a beach or a coastal feature. It often acts as a natural barrier against wave action and can play a significant role in the formation of various coastal landforms. The presence of a berm can indicate the level of sediment deposition in an area, showcasing how wave energy and tide cycles influence the shoreline.
Carl O. Sauer: Carl O. Sauer was an influential American geographer known for his work in cultural geography and the concept of landscape as a product of human activity and environmental interaction. His ideas shifted the focus of geography from physical features to the human imprint on landscapes, which is crucial for understanding how societies shape their environments. Sauer's emphasis on the cultural landscape also connects closely to techniques for analyzing landscapes and understanding various landforms shaped by deposition along coastlines.
Coastal development: Coastal development refers to the processes and activities that shape and modify coastal areas, often through human intervention, including construction, land use changes, and environmental management. This term encompasses various structures and features that arise from both natural processes and human actions, impacting ecosystems, sediment dynamics, and local communities. Understanding coastal development is crucial for managing resources and mitigating hazards in coastal zones.
Coastal dune: A coastal dune is a hill or ridge of sand formed by the wind, typically found along shorelines where sand is abundant. These dunes play a vital role in coastal ecosystems by providing habitat for various plants and animals, acting as a natural barrier against storm surges and erosion, and contributing to the dynamic landscape of depositional coastal landforms.
Dredging: Dredging is the process of removing sediment and debris from the bottom of water bodies, such as rivers, lakes, and coastal areas, often using specialized equipment. This activity is vital for maintaining navigable waterways, enhancing habitats, and managing sediment transport, while also having significant environmental impacts.
Embryo dune: An embryo dune is a small, newly formed sand dune that occurs in coastal environments, typically at the initial stage of dune development. These dunes form when sand accumulates around obstacles such as vegetation or debris, which slows down wind and allows sand particles to settle. Over time, embryo dunes can grow into larger, more complex dune systems that play an essential role in coastal protection and ecosystem stability.
Erosion: Erosion is the process by which soil, rock, and other surface materials are worn away and removed from their original location by natural forces such as water, wind, ice, or gravity. This process is essential in shaping landscapes and influencing sediment transport, which connects various components of the Earth's surface system.
Fores dune: A fores dune is a type of coastal sand dune that forms just inland from the beach and is typically the first line of dunes encountered as one moves away from the shore. These dunes are shaped by wind and wave action, playing a crucial role in coastal ecology and protection against erosion. Fores dunes are important for stabilizing the shoreline, providing habitat for various plant and animal species, and acting as a natural barrier against storms and high tides.
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.
Mangrove: Mangroves are coastal ecosystems characterized by salt-tolerant trees and shrubs that thrive in intertidal zones where saltwater and freshwater mix. These unique habitats are crucial for stabilizing shorelines, reducing erosion, and providing a rich environment for diverse wildlife, making them important for both ecological balance and human communities.
Parabolic dune: A parabolic dune is a type of sand dune characterized by its crescent shape with the tips pointing upwind. Unlike other dune types, parabolic dunes are formed primarily in areas with abundant vegetation that stabilizes the sand and allows for a unique shape as wind scours the center, creating a depression. These dunes often form in coastal and desert regions where the interaction of wind and sand creates distinct landforms.
Robert G. Dean: Robert G. Dean is a prominent coastal engineer known for his significant contributions to understanding coastal processes and the development of methodologies for managing coastal erosion and sediment transport. His work has been instrumental in the design of coastal structures and understanding the dynamics of beach systems, which directly connects to the formation of depositional coastal landforms.
Salt marsh: A salt marsh is a coastal ecosystem characterized by salt-tolerant plants, found in the intertidal zones between land and salty or brackish waters. These ecosystems play a crucial role in coastal protection, nutrient cycling, and providing habitats for a variety of wildlife, including birds and fish. Salt marshes are typically located in sheltered areas such as behind barrier islands or along the edges of estuaries, making them an essential feature in the context of coastal landforms.
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.
Sedimentation: Sedimentation is the process through which solid particles settle out of a fluid, typically water, and accumulate over time to form sediment layers. This process plays a crucial role in shaping landscapes, influencing river channel patterns, and impacting drainage basin morphology and evolution.
Spit: A spit is a narrow landform that extends from the mainland into a body of water, typically formed by the accumulation of sand and sediment deposited by longshore drift. Spits often create sheltered areas behind them, leading to the formation of lagoons or estuaries, and serve as important coastal features that influence local ecosystems and human activities.
Swash-backwash process: The swash-backwash process refers to the movement of water up and down a beach due to wave action, which plays a crucial role in shaping coastal landforms. When a wave breaks on the shore, the water rushes up the beach as swash, and then it flows back down as backwash. This constant cycle of swash and backwash transports sediment and alters the beach's profile, contributing to the formation of various depositional coastal landforms.
Tombolo: A tombolo is a depositional landform that connects an island to the mainland or to another island through a narrow strip of land, typically formed by the accumulation of sediment. This feature often results from the interaction of waves and currents, which deposit sand and gravel in a manner that gradually builds up the landform. Tombolos are significant in coastal geomorphology as they illustrate the dynamic processes of sediment transport and deposition along shorelines.
Transgressive Dune Sheet: A transgressive dune sheet is a coastal landform characterized by extensive, low-lying dunes formed by the movement of sand across a landscape, often as a result of rising sea levels and prevailing winds. These dune sheets are typically found in areas where sediment supply is abundant, and they can migrate landward as coastal environments change. Their formation is closely linked to coastal dynamics and processes like erosion and sediment deposition.
Wave action: Wave action refers to the energy and movement generated by waves as they break upon the shoreline, influencing coastal processes such as erosion, sediment transport, and the formation of landforms. This dynamic interaction between waves and the coastal environment plays a crucial role in shaping coastlines, redistributing sediments, and contributing to the development of various coastal features.