14.2 Coastal erosion and depositional features

Coastal erosion shapes shorelines, creating cliffs, platforms, arches, stacks, and caves. These features result from waves attacking rock faces, with varying resistance leading to unique formations. Understanding these processes helps explain the ever-changing coastal landscape.

Coastal deposition builds beaches, spits, barrier islands, tombolos, and dunes. These landforms result from waves and currents moving and depositing sediments. Factors like rock type, wave energy, and human activities influence erosion rates and sediment transport along coasts.

Coastal Erosional Features

Coastal erosional features

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• Cliffs form steep rock faces through wave erosion at base composed of resistant rock types retreat landward over time (Dover White Cliffs)
• Wave-cut platforms create flat or gently sloping surfaces at cliff bases result from erosion and weathering of softer rock layers exposed during low tide (Giant's Causeway)
• Sea arches develop natural rock openings in headlands or rocky outcrops through differential erosion of weaker rock layers (Durdle Door)
• Sea stacks stand as isolated rock columns in sea formed when sea arches collapse remnants of former headlands or cliffs (Old Harry Rocks)
• Sea caves hollow out areas in cliff faces created by wave action exploiting weak points in rock may lead to sea arch formation (Fingal's Cave)

Coastal Depositional Features and Processes

Coastal depositional landforms

• Beaches accumulate sand, gravel, or pebbles along shoreline through wave action depositing sediments slope and composition vary with wave energy and sediment supply (Copacabana)
• Spits extend as elongated landforms from coast into open water formed by longshore drift depositing sediments often curve at end due to wave refraction (Spurn Point)
• Barrier islands form long, narrow islands parallel to mainland coast from sand and sediments deposited by waves and currents protect mainland from storms create lagoons (Outer Banks)
• Tombolos connect islands to mainland or other islands with sand or gravel bars formed by wave refraction and sediment deposition (St Ninian's Isle)
• Coastal dunes accumulate wind-blown sand behind beaches stabilized by vegetation over time provide natural storm surge protection (Indiana Dunes)

Factors in coastal erosion

• Rock type affects erosion rates resistant rocks (granite) erode slowly softer rocks (sandstone) erode quickly joints or fractures increase erosion
• Wave energy increases erosion with higher energy influenced by wind strength, fetch, and water depth storm waves cause rapid erosion
• Human activities alter natural sediment transport through coastal development seawalls may increase adjacent erosion sand mining depletes beach sediments
• Climate factors accelerate erosion through sea-level rise changes in storm patterns affect erosion
• Coastal geometry exposes headlands to more erosion than bays shoreline orientation to prevailing winds affects wave energy
• Tidal range exposes more area to wave action with larger ranges influences vertical erosion distribution

Sediment transport in coastal development

• Longshore drift moves sediments parallel to shoreline driven by oblique wave approach forms spits and barrier islands
• Cross-shore transport moves sediments perpendicular to shoreline influenced by wave energy and beach slope causes seasonal beach profile changes
• Sediment sources include rivers supplying coastal areas cliff erosion providing beach material offshore deposits transported onshore
• Sediment sinks trap and remove coastal sediments in submarine canyons estuaries and lagoons act as sediment traps
• Sediment budget balances inputs and outputs in coastal system affects stability and evolution of landforms
• Human impacts on transport include dams reducing river sediment supply groins and jetties interrupting longshore drift beach nourishment adding artificial sediment