In-Depth Notes on Marine Processes and Coastal Features

Topographic Features of Marine Erosion

  • Marine erosion results in various topographic features classified into two groups:
    • Features connected with the configuration of the coast
    • Features developed as a result of coastal recession

Coastal Configuration

  • Dependent on geological structure, characterized by:
    • Nature of Rock (Lithology): Composition influences erosion patterns.
    • Hardness: Harder rocks resist erosion, shaping the coastline.
    • Toughness: Determines how rocks withstand erosive forces.
    • Resistance: Affects the rate at which coastal features evolve.
Structural Characteristics
  • Rocks can be massive or bedded, affecting erosion:
    • Importance of bed orientation
    • Presence of cracks, joints, and fissures leads to differential erosion.
Coastline Features
  • Alternating headlands and bays form in areas with varying rock hardness:
    • Examples:
    • S.E coast of Barbados
    • Tor Bay (hard limestone vs soft New Bed Sandstone)
  • Major features resulting from these processes include:
    • Caves
    • Arches
    • Sea stacks

Evolution of Coastal Features

  1. Initial Stage:
    • Smooth, gently sloping area below sea level under wave attack.
  2. Notch Formation:
    • A small notch forms due to:
      • Battering by waves
      • Solvent action of seawater
      • Swirling shore material's horizontal growth.
  3. Cliff Development:
    • Notch enlargement leads to cliff face formation.
    • Erosion deposits material offshore.
  4. Cliff Retreat:
    • Cliff faces increase in height, forming a rock platform at the base.
  5. Ongoing Erosion and Deposition:
    • Development of:
      • Broad wave-cut platforms
      • Lowering of cliffs
      • Decreased steepness due to weathering.

Shore Profile of Equilibrium

  • Describes balance between erosion and deposition along coastlines:
    • Characterized by a slope (AB) undergoing erosion while the lower part (CD) experiences deposition.
  • Achieves a gentle profile of equilibrium (compare with river graded profiles).
  • Examples of disruptions to this equilibrium include:
    • Storms
    • Slow earth movements
    • Fluctuating tides

Major Coastal Features Developed

  1. Cliffs:
    • Height influenced by geological structure and erosion rate.
    • Harder rocks lead to steeper, more resistant cliffs.
  2. Caves:
    • Formed at weak points in cliff faces via hydraulic action.
    • Sometimes lead to blowholes.
  3. Wave-Cut Platforms:
    • Formed by undercutting of the cliff face; rocky benches emerge.
    • Gentle slope extending seawards from the cliffs.
    • Example: STRANDFLAT of N.W. Norway
Formation Process of Wave-Cut Platforms
  • Waves attack cliffs, forming wave-cut notches and platforms:
    • Wave action causes erosion through hydraulic action and abrasion.
    • Platform formation is a slow process, especially in resistant rocks.

Coastal Transportation and Deposition

  • Majority of coastal material comes from riverine processes, not coastal erosion.
  • Modes of Material Movement:
    1. Suspension
    2. Saltation
    3. Rolling (similar to river transport)
Transportation Agents
  • Waves:
    • Movement via swash and backwash.
  • Currents:
    • Undertows transport shingle, sand, and mud.
  • Wind:
    • Transports loose materials inland.
Longshore Drift
  • Occurs when waves break obliquely to the shore, creating a zigzag pattern of material movement along the beach.

Marine Deposition Processes

  • Occurs when transporting power of waves or currents is obstructed by factors like:
    • Headwinds
    • Rivers
    • Conflicting currents
    • Coastal projections
  • Formation of features includes:
    • Beaches
    • Bars
    • Spits
Beach Characteristics
  • Defined as the area between low water mark and highest storm wave line.
  • Influenced by factors like:
    • Slope
    • Material quality
    • Storm events
  • Dynamic features subject to seasonal and daily changes.

Depositional Forms

  1. Offshore Bars:
    • Ridges of sand/shingles parallel to shores or across inlets.
  2. Spits:
    • Attached to the coast, built by longshore drift.
  3. Tombolo:
    • Bar connecting a former island to the mainland.
  4. Marshes:
    • Form on inner sides of spits and bars through sediment accumulation.
Conclusion on Sand Dunes
  • Formed from accumulated sediments, require:
    • Sufficient elevation
    • Abundant sand
    • Vegetative growth for stabilization.
  • Dunes are essential for coastal protection and habitat.

Summary

  • Understanding coastal processes is vital for managing erosion, deposition, and the ecological impact on coastal environments. The interaction between geological structures, biological factors, and human activity shapes the coastal landscape.