5.3 Coastal and Marine Landforms

Coastal and marine landforms shape our shorelines through erosion and deposition. Waves, tides, and currents sculpt beaches, cliffs, and barrier islands. These processes are influenced by factors like geology, climate, and human activities.

Human impact on coastlines is significant. Development alters natural processes, while climate change brings sea-level rise and stronger storms. Coastal management strategies aim to balance human needs with ecosystem preservation, adapting to these ongoing challenges.

Coastal Erosion and Deposition

Processes of Coastal Erosion and Deposition

• Coastal erosion involves the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, drainage or high winds
• Coastal deposition is the process of sediment being added to a coastal landform through the action of waves, currents, and wind

Factors Influencing Coastal Erosion and Deposition

• Factors influencing coastal erosion include wave action, tidal range, coastal geology, climate, and human activities such as coastal development and land use changes
  • The rate of erosion is influenced by the frequency and intensity of storms, sea-level rise, and the hardness and structure of the coastal rocks
• Factors influencing coastal deposition include the availability of sediment, wave and current characteristics, and the shape and orientation of the coastline
  • Sediment can be transported from inland sources by rivers and streams or from offshore sources by longshore currents
• Longshore drift transports sediments along a coast parallel to the shoreline, which is dependent on the prevailing wind direction, wave energy, and the angle of wave approach
  • This process can lead to the formation of depositional features like spits and barrier islands
• Beach nourishment is a coastal management practice that involves the addition of sand or sediment to a beach area to combat erosion and maintain a wide beach
  • This process can be influenced by factors such as the grain size and composition of the added sediment, as well as the placement location and timing of the nourishment project

Coastal Landform Formation

Beaches

• Beaches are accumulations of sediment along the shoreline that are shaped by waves, tides, and currents
  • They can be composed of various materials, including sand, gravel, and shells
  • The profile of a beach can vary depending on factors such as wave energy, sediment size, and tidal range
• The formation of a beach depends on the balance between sediment supply and removal
  • When the rate of sediment deposition exceeds the rate of erosion, beaches will grow and prograde
  • Conversely, when erosion rates are higher, beaches will retreat and erode

Cliffs and Barrier Islands

• Cliffs are steep, vertical faces of rock along the coastline that are formed by the erosive action of waves and weathering processes
  • The formation of cliffs is influenced by factors such as rock type, structure, and wave energy
  • Wave action at the base of a cliff can lead to undercutting, which destabilizes the cliff face and leads to mass wasting events like rockfalls and slumps
  • The rate of cliff retreat is influenced by the resistance of the rock to erosion and the frequency and intensity of wave attack
• Barrier islands are elongated, offshore deposits of sand or sediment that are parallel to the coastline and separated from the mainland by a lagoon or bay
  • They are formed by the combined action of waves, tides, and currents, and can migrate over time in response to changes in sea level and sediment supply
  • The formation of barrier islands begins with the accumulation of sediment offshore, which is then shaped by longshore currents and wave action
  • As the island grows and becomes more stable, vegetation can colonize the surface, helping to anchor the sediments and promote further growth

Other Coastal Landforms

• Spits are elongated deposits of sediment that extend from the shore into a body of water (Dungeness Spit in Washington)
• Tombolos are sand or gravel bars that connect an island to the mainland or another island (Mont Saint-Michel in France)
• These features are formed by the complex interaction of waves, currents, and sediment transport processes

Coastal Environments: Shaping Forces

Waves

• Waves are the primary agent of erosion and sediment transport in coastal environments
  • The energy and direction of waves can influence the shape and morphology of coastlines, as well as the distribution of sediments along the shore
  • Wave energy is determined by factors such as wind speed, duration, and fetch (the distance over which the wind blows)
  • Higher energy waves have greater erosive power and can transport larger sediments, while lower energy waves are more likely to deposit sediment
• The angle at which waves approach the shore can influence the direction and magnitude of longshore currents, which are responsible for the transport of sediments along the coast

Tides and Currents

• Tides are the rise and fall of sea levels caused by the gravitational pull of the moon and sun
  • Tidal range, which is the difference between high and low tide, can vary depending on the location and shape of the coastline
  • Tidal currents are the horizontal movements of water associated with the rise and fall of tides
  • These currents can transport sediments and shape coastal landforms, particularly in areas with high tidal ranges
• The effects of tides on coastal environments can include the exposure and flooding of intertidal zones, the formation of tidal flats and salt marshes, and the influence on the distribution and behavior of coastal organisms
• Ocean currents are large-scale movements of water that are driven by wind patterns, temperature and salinity gradients, and the rotation of the Earth
  • These currents can transport sediments and nutrients over long distances, influencing the distribution of marine organisms and the formation of coastal landforms
  • Longshore currents are generated by waves approaching the shore at an angle, and are responsible for the transport of sediments along the coast
  • Rip currents are strong, narrow channels of water that flow seaward from the shore, and are often associated with breaks in sandbars or other underwater features

Human Impact on Coastlines

Coastal Development and Land Use Changes

• Coastal development, such as the construction of buildings, roads, and seawalls, can disrupt natural sediment transport processes and alter the shape and stability of coastlines
  • The removal of coastal vegetation, such as dunes and mangroves, can also increase the vulnerability of coasts to erosion and flooding
  • The use of hard stabilization structures, such as seawalls and groins, can provide short-term protection against erosion, but can also lead to the loss of beaches and the disruption of longshore sediment transport
  • Soft stabilization approaches, such as beach nourishment and dune restoration, aim to work with natural processes to maintain coastal stability
• Land use changes in coastal watersheds, such as deforestation, agriculture, and urbanization, can alter the flow and quality of freshwater and sediments delivered to the coast
  • These changes can impact the health and productivity of coastal ecosystems, such as estuaries and coral reefs
  • Increased nutrient and pollutant loads from human activities can lead to problems such as eutrophication, harmful algal blooms, and the degradation of water quality in coastal environments
  • The loss of natural filtration systems, such as wetlands and oyster reefs, can exacerbate these impacts

Climate Change Impacts

• Climate change is expected to have significant impacts on coastal regions, through the effects of sea-level rise, changes in storm intensity and frequency, and alterations to ocean temperature and chemistry
  • Sea-level rise can lead to increased coastal flooding, erosion, and saltwater intrusion into freshwater aquifers and wetlands
  • The loss of coastal habitats, such as tidal marshes and mangroves, can reduce the natural buffering capacity of coastlines against storms and flooding
• Changes in storm patterns, such as the increased intensity of hurricanes and typhoons, can lead to more severe coastal damage and loss of life
  • The warming of ocean waters can also alter the distribution and behavior of marine organisms, with potential impacts on coastal fisheries and ecosystems

Coastal Resilience and Management

• Coastal communities and ecosystems are facing increasing pressures from the combined impacts of human activities and climate change
  • Adapting to these challenges will require a combination of strategic planning, nature-based solutions, and the reduction of greenhouse gas emissions to mitigate the long-term effects of climate change
  • Coastal resilience strategies, such as the use of living shorelines, the restoration of coastal habitats, and the incorporation of green infrastructure, can help to reduce the vulnerability of coastal communities to erosion, flooding, and sea-level rise
• Collaborative efforts among scientists, policymakers, and stakeholders will be essential for developing and implementing effective coastal management plans that balance the needs of human communities with the conservation of coastal ecosystems in the face of a changing climate