🌋Physical Geology Unit 14 – Coastal Processes and Landforms

Coastal Zone Basics

• Coastal zones are dynamic areas where land meets the ocean and are shaped by various processes such as waves, tides, and currents
• Coastal zones can be divided into different regions based on their physical characteristics (nearshore, foreshore, backshore)
• The intertidal zone is the area between high and low tide marks and experiences regular exposure and submersion
• Coastal zones are influenced by factors such as wind, waves, tides, and sediment supply which contribute to their constant evolution
• The shape and composition of the coastline depends on the type of rock or sediment present (cliffs, beaches, estuaries)
• Coastal zones provide important habitats for a wide range of plant and animal species adapted to the unique conditions
• Human activities such as development, recreation, and resource extraction can have significant impacts on coastal zones and their ecosystems

Wave Dynamics and Energy

• Waves are generated by wind blowing over the surface of the ocean and transfer energy from the wind to the water
• Wave height and period are determined by wind speed, duration, and fetch (distance over which the wind blows)
• As waves approach the shore, they undergo transformations such as shoaling, refraction, and breaking
  • Shoaling occurs when waves enter shallower water and their height increases while their wavelength decreases
  • Refraction is the bending of waves as they approach the shore at an angle, causing them to align more parallel to the shoreline
• Wave energy is proportional to the square of the wave height and is a major factor in coastal erosion and sediment transport
• Constructive waves have a longer period and lower height, depositing sediment on the beach and building it up
• Destructive waves have a shorter period and higher height, eroding sediment from the beach and causing it to retreat
• Rip currents are strong, narrow currents that flow seaward from the shore and can pose a hazard to swimmers

Erosional Processes

• Coastal erosion is the removal and transport of rock and sediment from the shoreline by waves, currents, and tides
• Hydraulic action is the force of water striking the coast, causing loose material to be dislodged and carried away
• Abrasion occurs when sediment particles carried by waves and currents grind against the coastline, wearing it down over time
• Attrition is the gradual reduction in size of sediment particles as they collide with each other during transport
• Solution is the chemical weathering of rocks by seawater, particularly in areas with limestone or other soluble rocks
• Wave-cut notches form at the base of cliffs due to concentrated erosion by waves, eventually leading to cliff collapse
• Coastal erosion rates vary depending on factors such as rock type, wave energy, and sea level change
  • Soft rocks (clay, sand) erode more quickly than hard rocks (granite, basalt)
  • Areas with high wave energy experience faster erosion rates

Sediment Transport and Deposition

• Sediment transport refers to the movement of sand, gravel, and other particles along the coast by waves, currents, and wind
• Longshore drift is the zigzag movement of sediment parallel to the shore, driven by waves approaching at an angle
  • Sediment is moved up the beach at an angle by the swash (incoming wave) and returns directly downslope by the backwash (outgoing water)
• Tides and tidal currents also play a role in sediment transport, particularly in estuaries and tidal flats
• Deposition occurs when the energy of waves and currents is insufficient to keep sediment in suspension, causing it to settle
• Beaches are formed by the accumulation of sediment deposited by waves and currents
  • The size and composition of beach sediment depends on the source material and the wave energy
• Spits are elongated ridges of sand or gravel that extend from the shore into the mouth of an estuary or bay, formed by longshore drift
• Tombolos are sand or gravel bars that connect an island to the mainland or another island, formed by wave refraction and deposition

Coastal Landforms

• Cliffs are steep, vertical faces of rock formed by erosion and often found in areas with resistant rock and high wave energy
• Wave-cut platforms are flat or gently sloping surfaces at the base of cliffs, formed by wave erosion during high tides
• Sea arches are natural openings in cliffs or headlands, formed by differential erosion of weaker rock layers
• Sea stacks are isolated pillars of rock standing offshore, formed by the collapse of sea arches or the erosion of headlands
• Beaches are accumulations of sand, gravel, or other sediment along the shore, shaped by waves and currents
  • The profile of a beach changes seasonally, with wider, flatter beaches in summer and narrower, steeper beaches in winter
• Barrier islands are long, narrow islands parallel to the mainland coast, formed by the deposition of sediment by waves and currents
• Estuaries are partially enclosed coastal bodies of water where freshwater from rivers mixes with saltwater from the ocean
  • Estuaries are important nursery areas for many marine species and are often highly productive ecosystems

Coastal Protection Strategies

• Coastal protection strategies aim to reduce the impacts of erosion, flooding, and storm damage on coastal communities and infrastructure
• Hard engineering structures such as seawalls, groins, and breakwaters are designed to absorb or reflect wave energy and prevent erosion
  • Seawalls are vertical or sloping structures built parallel to the shore to protect against wave action and erosion
  • Groins are perpendicular to the shore and trap sediment moving alongshore, building up beaches on the updrift side
• Soft engineering approaches work with natural processes and include beach nourishment, dune stabilization, and managed retreat
  • Beach nourishment involves adding sand to a beach to replace eroded material and maintain its width
  • Dune stabilization uses vegetation (grasses) or fencing to trap sand and build up dunes as a natural buffer against waves and flooding
• Managed retreat involves relocating or abandoning coastal development in areas at high risk of erosion or flooding
• Integrated coastal zone management (ICZM) is a holistic approach that considers the interactions between different coastal processes and stakeholders
• Nature-based solutions such as living shorelines and oyster reefs can provide coastal protection while also enhancing biodiversity and ecosystem services

Human Impact on Coasts

• Coastal development such as urbanization, tourism, and industrial activities can alter natural coastal processes and ecosystems
• Construction of ports, marinas, and coastal infrastructure can disrupt sediment transport patterns and cause erosion or accretion
• Dredging of navigation channels and beach nourishment projects can affect the balance of sediment supply and distribution
• Pollution from land-based sources (runoff, wastewater) and marine activities (oil spills, marine debris) can degrade coastal water quality and habitats
• Overfishing and destructive fishing practices can disrupt marine food webs and damage sensitive habitats (coral reefs)
• Coastal aquaculture, such as shrimp farming, can lead to the loss of mangrove forests and other important coastal ecosystems
• Extraction of resources such as sand, gravel, and oil can alter coastal geomorphology and contribute to erosion and subsidence
• Human activities can also introduce invasive species to coastal ecosystems, which can outcompete native species and alter community structure

Climate Change and Coastal Systems

• Climate change is expected to have significant impacts on coastal systems through sea level rise, changes in storm intensity and frequency, and ocean acidification
• Sea level rise is caused by thermal expansion of the oceans and melting of land-based ice (glaciers, ice sheets) due to increasing global temperatures
  • Higher sea levels can lead to increased coastal flooding, erosion, and saltwater intrusion into groundwater and estuaries
  • Low-lying coastal areas and small island nations are particularly vulnerable to the effects of sea level rise
• Changes in storm patterns, such as more frequent and intense hurricanes, can cause severe damage to coastal communities and infrastructure
• Ocean acidification, caused by the absorption of excess atmospheric carbon dioxide, can impair the growth and survival of marine organisms with calcium carbonate shells or skeletons (corals, mollusks)
• Warming ocean temperatures can lead to coral bleaching events and the loss of critical habitats for marine biodiversity
• Climate change can also alter the distribution and abundance of coastal species, with implications for fisheries and ecosystem functioning
• Coastal adaptation strategies, such as nature-based solutions and resilient infrastructure, can help mitigate the impacts of climate change on coastal systems
• Reducing greenhouse gas emissions is crucial for limiting the long-term effects of climate change on coastal zones and the communities that depend on them