Interactions Between Oceans and Coastal Places

Influence of Waves: Waves significantly affect coastal landforms through both erosional and depositional processes.
- Example: Wave refraction around rock platforms (e.g., Currumbin Beach, Australia).

The Coastal Zone: This area where land, sea, and air interact is crucial for landform development.
- Width varies: Rocky coasts may have narrow coastal areas (tens of meters) while estuaries and continental shelves can extend for kilometers.

Wave Base: The depth to which waves can transport sediments; can vary significantly.
- Example: 20 meters below sea level in high-energy coastlines like Australia.
- Low-energy coasts may have a wave base of only a few meters.
Wave Types:
- Wind waves are surface ripples caused by wind; stronger winds create larger waves.
- Swell: Larger waves traveling across the ocean, generally spaced with longer crests, which exert greater influence on coastal landforms.

Wave Measurements: Key parameters include:
- Wave Height (H): Distance from crest to trough.
- Wave Length (L): Distance between crests.
- Wave Period (T): Time between consecutive crests; can be related to wave length as $L = 1.56T^2$ .
- Wave Energy (E): Directly proportional to wave height's square; given by E = rac{1}{2}
  ho g H^2 , where $<br /> ho$ is water density, $g$ is gravity.

Erosional Processes: Dominated by hydraulic action, corrasion, and attrition.
- Hydraulic Action: Pressure exerted by waves, especially during storms, can exceed 7 kg/cm².
- Corrasion: Erosion caused by sediments being propelled against rock surfaces by waves.
- Attrition: Rounded and smoothed rocks from wave action.
Corrosion: Dissolution of minerals, more pronounced on limestone and coral reefs due to their soluble nature.

Two Main Sources:
1. Land: Sediments transported by rivers; includes gravel and sand.
2. Marine: Shells and skeletons from marine organisms add carbonate sediments.

Tides: Occur due to gravitational forces from the moon and sun, causing a rise/fall in water levels.
Tidal Range: Difference in water levels between high and low tides varies globally.
- Example: South Wales has a significant tidal range, impacting coastal morphology.

Marine Organisms:
- Coral and algae contribute substantially to coastal landforms, particularly in tropical and temperate zones.

High vs. Low Energy Coastlines:
- High-energy coastlines (e.g., Muriiwal, Australia) show significant erosion, while low-energy coastlines (e.g., Banjul, Gambia) promote deposition.

Longshore Drift: Movement of sediment along the coast influenced by wave approach.
Barriers: Natural structures that develop from sediment deposition, including beaches, barrier islands, and spit formation.
- Spits develop when sediment is deposited where ocean waves lose energy, extending out into the water.

Deltas: Form at river mouths where sediment deposition occurs, varying in shape:
- Arcuate Deltas: Smooth and protruding, like the Nile River.
- Birdfoot Deltas: Extended shapes with levees, characteristic of the Mississippi River.

Sand Dunes: Require moderate to strong onshore winds, fine sand supply, and vegetation for stabilization.
- Pioneer Species: Early colonizers like marram grass stabilize shifting sands and help in soil formation through humus accumulation.

Coastline Retreat/Advance: Movements based on sediment supply and geological changes.
- Eustatic Changes: Global sea level changes due to climatic variations; e.g., melting ice caps causing sea level rise.

Coastal landforms are a dynamic interplay of marine, atmospheric, geological, and biological factors that evolve continuously through processes of erosion and deposition.