The Dynamic Coastline
Coastal processes are those that shape the coast, driven primarily by the action of waves and currents.
Wave Action
Wave Refraction: As waves approach an irregular coastline, they begin to 'feel' the bottom at different points. The parts of the wave in shallower water slow down, while the parts in deeper water continue at a faster speed. This causes the wave crests to bend and become more parallel to the shoreline.
Effect: Wave energy is concentrated on headlands (points of land that stick out), leading to erosion. Wave energy is dispersed in bays, leading to deposition.
Longshore Drift (or Longshore Transport): Waves often approach the beach at an angle. The incoming wave (swash) carries sand up the beach at an angle, but the outgoing wave (backwash) pulls the sand straight back down due to gravity. This zig-zag motion results in a net transport of sand along the coastline. This is the primary way sand is moved along a beach.
Coastal Landforms
Erosional Landforms: Typically found on high-energy, rocky coasts.
Sea Cliff: A steep coastal slope created by the erosive power of waves at its base.
Wave-Cut Platform: A flat, bench-like surface left behind as a sea cliff retreats.
Sea Arch and Sea Stack: A sea arch is formed when waves erode through a headland. When the arch collapses, it leaves behind a pillar of rock called a sea stack.
Depositional Landforms: Typically found on low-energy coasts where sediment is abundant.
Beach: An accumulation of sediment (sand, gravel) along the shore.
Spit: An elongated ridge of sand that projects from the land into the mouth of an adjacent bay. Formed by longshore drift.
Barrier Island: A long, narrow sandy island parallel to the mainland coast, separated from it by a lagoon. They are very dynamic and are constantly reshaped by waves and storms.