12.3 Coastal processes and landforms
3 min read•july 22, 2024
Coastal processes shape our shorelines through erosion, sediment movement, and landform creation. Waves, tides, and currents sculpt beaches, cliffs, and islands, while human activities like development and engineering alter these natural systems.
is influenced by wave energy, tides, and sediment supply. Managing coasts involves balancing human needs with environmental protection through strategies like integrated planning, , and marine protected areas.
Coastal Processes
Coastal erosion and sediment movement
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- Wave action erodes coastal rocks and structures
- Hydraulic action compresses air in cracks causing rock to break apart
- Abrasion occurs when sediment carried by waves erodes coastal features
- Attrition reduces sediment size through collisions between particles
- erode sediments during high tides and transport them during ebb tides
- Longshore currents generated by angled waves cause sediment transport parallel to the shoreline ()
- Rip currents carry sediment offshore as strong localized currents flowing seaward from the shore
- Sediment is deposited along the shoreline forming beaches due to wave action and longshore drift
- Elongated ridges of sand or gravel extending from the coast (spits) are formed by longshore drift
- Deltas form where rivers or streams deposit sediment as they enter a larger body of water
Formation of coastal landforms
- Beaches form by sediment accumulation along the shoreline influenced by wave energy, sediment supply, and coastal geology
- profile includes the flat, elevated berm and sloping foreshore towards the water
- Barrier islands are elongated, narrow islands parallel to the mainland coast
- Formed by sediment deposition through longshore drift and wave action
- Protect the mainland coast from wave energy and storm surges (Outer Banks, Padre Island)
- Sea cliffs are steep, vertical coastal faces formed by wave erosion
- Occur in areas with resistant rock and high wave energy
- Formed through undercutting, collapse, and retreat (White Cliffs of Dover, Cliffs of Moher)
Coastal Morphology and Management
Factors in coastal morphology
- Wave energy determines the erosive power and sediment transport capacity of waves
- Influenced by wind speed, duration, and fetch (distance wind blows over water)
- Higher wave energy leads to more erosion and sediment transport
- Tidal range is the difference between high and low tide water levels
- Macrotidal coasts (tidal range > 4 m) have extensive tidal flats and strong currents
- Microtidal coasts (tidal range < 2 m) have smaller tidal influence on morphology
- Sediment supply determines the availability of material for coastal landform development
- Sources include rivers, erosion, and offshore deposits
- Abundant supply promotes beach and formation
- Limited supply can lead to coastal erosion and retreat
Human impact on coastal systems
- disrupts natural processes and increases erosion
- Dredging and sand mining alter coastal morphology and sediment budgets
- Coastal engineering structures (seawalls, groins, breakwaters) interfere with longshore drift causing downdrift erosion
- Pollution and nutrient input degrade coastal water quality and harm marine ecosystems
- Coastal resource management strategies:
- Integrated Coastal Zone Management (ICZM) considers ecological, social, and economic factors in planning
- Setback lines and building restrictions regulate development in erosion-prone areas
- Beach nourishment artificially places sand to restore eroded beaches
- Marine Protected Areas (MPAs) restrict human activities to conserve coastal and marine ecosystems
- Coastal adaptation to climate change through managed retreat, nature-based solutions, and resilient infrastructure
Key Terms to Review (18)
Barrier Island: A barrier island is a long, narrow strip of land that runs parallel to the coastline, separated from the mainland by a body of water such as a lagoon or estuary. These islands serve as natural buffers against ocean waves and storms, protecting coastal regions from erosion and flooding while also providing unique ecosystems and habitats for various plant and animal species.
Beach: A beach is a landform along the shoreline of an ocean, sea, lake, or river that consists of loose particles such as sand, gravel, pebbles, or cobblestones. Beaches are dynamic environments shaped by the interplay of waves, tides, and currents, which continuously alter their shape and size. They often serve as important recreational areas and are critical to coastal ecosystems.
Beach nourishment: Beach nourishment is a coastal management technique that involves adding sand or sediment to a beach to counteract erosion and increase its width. This process helps protect coastal infrastructure, enhance recreational areas, and maintain natural habitats. Beach nourishment plays a crucial role in coastal processes and landforms by stabilizing shorelines and mitigating the impacts of storms and rising sea levels.
Cliff: A cliff is a steep face of rock and earth that often forms along coastlines or riverbanks, characterized by a vertical or nearly vertical drop. Cliffs are typically formed through processes such as erosion and weathering, and they are significant in shaping coastal landscapes and influencing the surrounding ecosystems. The interaction between water and land at these steep formations creates unique habitats and influences coastal dynamics.
Coastal development: Coastal development refers to the process of altering coastal areas through construction, land use changes, and infrastructure improvements. This development can significantly impact coastal ecosystems, landforms, and processes, creating a complex relationship between human activities and natural environments.
Coastal morphology: Coastal morphology refers to the study and description of the shapes, features, and structures of coastlines and coastal landforms. It encompasses the processes that shape these features, such as erosion, sediment transport, and deposition, leading to the formation of various coastal landscapes like beaches, cliffs, and estuaries. Understanding coastal morphology is crucial for assessing coastal dynamics, managing resources, and predicting changes due to natural events or human activities.
Coral reef: A coral reef is a diverse underwater ecosystem formed by colonies of tiny coral polyps that secrete calcium carbonate to build protective structures. These reefs are found in shallow, tropical ocean waters and play a crucial role in supporting marine biodiversity, acting as habitats for countless species and providing important ecosystem services such as coastal protection and tourism opportunities.
Delta: A delta is a landform that forms at the mouth of a river, where it meets a body of water, such as an ocean, sea, or lake. It is characterized by the deposition of sediment carried by the river as it slows down and spreads out upon entering the standing water. This process creates a fan-shaped area of sediment that can support diverse ecosystems and affect both sedimentary rock formation and coastal landscapes.
Estuary: An estuary is a coastal area where freshwater from rivers and streams meets and mixes with saltwater from the ocean. This unique environment creates a highly productive ecosystem that supports diverse plant and animal life, making estuaries important for both ecological balance and human activities such as fishing and recreation.
Littoral Zone: The littoral zone is the coastal region of a body of water, where the land meets the water. This area is characterized by a dynamic environment influenced by tides, waves, and sediment transport, leading to unique ecosystems and landforms. It plays a crucial role in coastal processes, such as erosion and deposition, which shape the landscape and affect both terrestrial and aquatic life.
Longshore drift: Longshore drift is the process by which sediment is transported along a coastline by the action of waves and currents. This movement occurs due to the angle at which waves approach the shore, causing sand and pebbles to move in a zigzag pattern along the beach. Understanding longshore drift is essential as it influences coastal landforms and sediment distribution, impacting ecosystems and human activities along shorelines.
Mangrove swamp: A mangrove swamp is a coastal ecosystem characterized by the presence of salt-tolerant trees, known as mangroves, that thrive in intertidal zones where saltwater and freshwater mix. These ecosystems play a crucial role in coastal protection, biodiversity, and carbon sequestration, acting as a buffer against storm surges and erosion while providing habitat for various species.
Sea level rise: Sea level rise refers to the increase in the average level of the Earth's oceans and seas, primarily caused by two main factors: the melting of ice sheets and glaciers, and the thermal expansion of seawater as it warms. This phenomenon has significant implications for coastal processes and landforms, leading to increased flooding, erosion, and changes in coastal ecosystems.
Sedimentation: Sedimentation is the process by which particles settle out of a fluid, typically water or air, and accumulate as sediment. This process plays a crucial role in shaping the Earth’s landscape, influencing the formation of sedimentary rocks and the development of various geological features over time.
Shoreline management: Shoreline management refers to the planning and implementation of strategies to protect, preserve, and manage coastal areas against erosion, flooding, and other environmental impacts. It involves balancing human activities and natural processes, ensuring sustainable use of coastal resources while minimizing damage to habitats and communities. Effective shoreline management helps maintain the health of ecosystems and supports economic activities such as tourism and fishing.
Storm surge: Storm surge refers to the abnormal rise in seawater level during a storm, primarily caused by the strong winds and low atmospheric pressure associated with tropical cyclones or hurricanes. This phenomenon can lead to devastating flooding, particularly in coastal areas, and is a crucial factor in understanding coastal processes and the associated natural hazards.
Tidal Currents: Tidal currents are the horizontal movements of water that occur as a result of the rise and fall of sea levels due to tides. These currents are influenced by the gravitational pull of the moon and sun, creating a regular pattern of water movement that can significantly impact coastal environments. Tidal currents play a vital role in shaping coastal landforms, affecting sediment transport, erosion, and deposition along shorelines.
Wave-cut platform: A wave-cut platform is a flat, bench-like surface that forms at the base of a cliff due to the erosion caused by wave action. This geological feature is created as waves continually crash against the rock, gradually wearing it away, which can lead to the retreat of the cliff face. As the cliff erodes and retreats, it leaves behind a horizontal surface that may be exposed during low tide, demonstrating the dynamic processes at work along coastlines.