3.6 Coastal Processes and Landforms

Coastal processes shape our shorelines, creating diverse landforms through erosion and deposition. Waves, tides, and currents work tirelessly to sculpt cliffs, beaches, and barrier islands, while human activities and climate change add complexity to these dynamic systems.

Understanding coastal processes is crucial for managing our coastlines wisely. From protecting vulnerable communities to preserving vital ecosystems, knowledge of these forces helps us balance development with nature's power in these ever-changing environments.

Coastal environment formation

Processes shaping coastal environments

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• Waves are the primary process shaping coastal environments
  • Caused by wind blowing over the ocean surface
  • Wave energy erodes and transports sediment
• Tides influence coastal environments through the rise and fall of sea levels
  • Caused by the gravitational pull of the moon and sun
  • Tidal range determines the extent of the intertidal zone
• Longshore currents move sediment laterally along the coast
  • Generated by waves approaching the shore at an angle
  • Contribute to the formation of coastal features (spits, barrier islands)
• Rip currents transport sediment offshore
  • Strong, narrow channels of water flowing seaward near the shore
  • Occur at low spots or breaks in sandbars
• Weathering processes break down coastal rocks and cliffs, providing sediment
  • Chemical weathering (salt crystal growth, hydrolysis)
  • Physical weathering (abrasion, freeze-thaw cycles)
• Biological processes influence sediment deposition and stabilization
  • Growth of coral reefs and coastal vegetation (mangroves, seagrass beds)
  • Bioturbation by burrowing organisms

Factors influencing coastal environments

• Geology and lithology of the coastline
  • Rock type and structure affect erosion rates and landform development
  • Resistant rocks (granite) form cliffs, while softer rocks (shale) erode more easily
• Climate and weather patterns
  • Influence wave energy, storm frequency, and precipitation
  • Affect rates of weathering, erosion, and sediment transport
• Sea level changes
  • Rising sea levels can submerge coastal features and increase erosion
  • Falling sea levels expose more land and alter coastal processes
• Sediment supply and characteristics
  • Grain size, composition, and availability of sediment affect coastal landforms
  • Sources include rivers, cliff erosion, and offshore deposits (continental shelf)

Coastal landforms

Erosional landforms

• Cliffs are steep, vertical exposures of rock along the coast
  • Formed by wave erosion and mass wasting (rockfalls, slumps)
  • Sea stacks are isolated rock towers formed by differential erosion of cliffs
• Wave-cut platforms are flat, rocky surfaces extending from the base of a cliff
  • Created by wave abrasion during high tides
  • May be exposed during low tides, forming rocky intertidal zones
• Sea caves and arches are formed by wave erosion along weaknesses in cliffs
  • Caves are enlarged by hydraulic action and abrasion
  • Arches develop when caves on opposite sides of a headland connect
• Blowholes and geyser holes are vertical shafts in cliffs formed by wave erosion
  • Compressed air and water are forced upward through the shaft
  • Examples include Halona Blowhole (Hawaii) and Thor's Well (Oregon)

Depositional landforms

• Beaches are deposits of sand, gravel, or other sediment along the shoreline
  • Characterized by sediment composition and profile (backshore to offshore)
  • Examples include Copacabana Beach (Brazil) and Bondi Beach (Australia)
• Dunes are mounds or ridges of sand formed by wind deposition behind beaches
  • Provide a buffer against storm surge and support unique plant communities
  • Examples include the Dunes of Maspalomas (Gran Canaria) and the Namib Sand Sea (Namibia)
• Spits are elongated ridges of sand extending from the shore
  • Formed by longshore drift and often have a curved end due to wave refraction
  • Examples include Farewell Spit (New Zealand) and Arabat Spit (Crimea)
• Barrier islands are elongated, offshore deposits of sand parallel to the mainland coast
  • Separated from the mainland by a lagoon or bay
  • Examples include the Outer Banks (North Carolina) and the Frisian Islands (Netherlands/Germany)
• Tidal flats are broad, flat areas of sediment exposed during low tides
  • Formed by sediment deposition in sheltered areas (estuaries, bays)
  • Examples include the Wadden Sea (Netherlands/Germany) and the Bay of Fundy (Canada)
• Salt marshes are coastal wetlands vegetated by salt-tolerant plants
  • Develop in sheltered areas with fine-grained sediment deposition
  • Examples include the Camargue (France) and the Spartina marshes of the eastern United States

Coastal erosion and deposition

Factors influencing coastal erosion

• Wave energy and storm intensity
  • High-energy waves during storms can erode beaches, dunes, and cliffs
  • Seasonal variations in wave conditions affect erosion rates
• Tidal range and currents
  • High tides allow waves to reach further inland, increasing erosion
  • Tidal currents can transport sediment and alter erosion patterns
• Coastal geology and lithology
  • Softer, less resistant rocks (shale, sandstone) erode more easily than harder rocks (granite, basalt)
  • Structural weaknesses (joints, faults) can enhance erosion
• Sea level rise
  • Increases the reach of waves and tides, leading to more erosion
  • Can cause coastal features to migrate inland or be submerged
• Human activities
  • Coastal development and hardening of the shoreline can disrupt natural processes
  • Dredging and damming of rivers can alter sediment supply and erosion patterns

Processes of coastal deposition

• Longshore drift and sediment transport
  • Waves and currents move sediment along the coast
  • Deposition occurs where longshore drift is interrupted (jetties, inlets)
• Beach and dune formation
  • Sediment is deposited onshore by waves and wind
  • Berms and beach ridges form during periods of accretion
• Tidal deposition
  • Sediment settles out of suspension in sheltered areas during high tides
  • Forms tidal flats, salt marshes, and mangrove swamps
• River and delta deposition
  • Rivers transport sediment to the coast, forming deltas and estuaries
  • Examples include the Mississippi River Delta (Louisiana) and the Nile River Delta (Egypt)
• Biological deposition
  • Coral reefs and shell deposits can contribute to sediment accumulation
  • Examples include the Great Barrier Reef (Australia) and the Bahamas Banks

Human impacts on coastlines

Coastal development and infrastructure

• Urbanization and population growth in coastal areas
  • Increases demand for housing, transportation, and recreational facilities
  • Can lead to the loss of natural habitats and disruption of coastal processes
• Construction of seawalls, groins, and breakwaters
  • Intended to protect property from erosion and storm damage
  • Can alter sediment transport and cause downdrift erosion
• Dredging of channels and harbors for navigation
  • Removes sediment from the coastal system and alters tidal flow patterns
  • Can lead to changes in coastal landforms and ecosystems
• Beach nourishment and sand replenishment
  • Adding sand to eroding beaches to maintain their width and protect infrastructure
  • May have unintended consequences on neighboring areas and marine habitats

Resource extraction and pollution

• Oil and gas exploration and production in coastal waters
  • Can lead to spills and leaks that damage coastal ecosystems
  • Examples include the Deepwater Horizon spill (Gulf of Mexico) and the Exxon Valdez spill (Alaska)
• Mining of coastal sand and gravel for construction materials
  • Removes sediment from the coastal system and can accelerate erosion
  • Examples include sand mining in Morocco and gravel extraction in the United Kingdom
• Agricultural and urban runoff
  • Carries nutrients, pesticides, and other pollutants into coastal waters
  • Can cause eutrophication, algal blooms, and degradation of marine habitats
• Marine debris and plastic pollution
  • Accumulates in coastal areas and harms wildlife through ingestion and entanglement
  • Examples include the Great Pacific Garbage Patch and microplastics in coastal sediments

Climate change and sea level rise

• Global warming and thermal expansion of the oceans
  • Causes sea levels to rise, increasing coastal flooding and erosion
  • Threatens low-lying islands and coastal communities
• Increased frequency and intensity of storms and hurricanes
  • Can cause severe damage to coastal infrastructure and ecosystems
  • Examples include Hurricane Katrina (New Orleans) and Typhoon Haiyan (Philippines)
• Ocean acidification and coral bleaching
  • Rising atmospheric CO2 levels lead to more acidic oceans, stressing coral reefs
  • Warmer water temperatures cause coral bleaching and mortality
• Coastal habitat loss and species migration
  • Rising sea levels and changing environmental conditions force species to adapt or relocate
  • Coastal wetlands and mangroves may be unable to migrate inland due to human development