Coastal Landscapes

Landforms of Coastal Erosion

Introduction

Erosional processes shape the coastline, forming a variety of striking landforms. Each landform results from specific interactions between wave energy, rock type, and geological structure. This guide provides definitions and explanations of the formation of bays, headlands, cliffs, shore platforms, geos, blowholes, caves, arches, stacks, and stumps, combining the formation steps and processes involved.

1. Bays and Headlands

  • Description: Bays are curved, indented areas of coastline, often with sandy beaches, while headlands are protruding sections of harder rock that extend into the sea.
  • Formation: These features form along discordant coastlines, where alternating bands of hard and soft rock are exposed to wave action. Soft rock (e.g., clay) erodes quickly, creating bays, while hard rock (e.g., chalk or limestone) resists erosion, forming headlands. Hydraulic action and abrasion erode the soft rock, while wave refraction focuses energy on headlands, accelerating their erosion. Over time, bays widen, and headlands become more pronounced.

2. Cliffs

  • Description: Cliffs are steep rock faces along the coast, often forming as the coastline retreats.
  • Formation: Waves attack the base of the cliff through hydraulic action (compressing air in cracks) and abrasion (grinding rock against the base). This creates a wave-cut notch, which deepens over time, causing the overhanging cliff to collapse. The cliff face retreats inland, and the process repeats, maintaining a steep profile.

3. Shore Platforms

  • Description: Shore platforms are gently sloping, flat areas of rock found at the base of retreating cliffs, visible at low tide.
  • Formation: As cliffs erode and retreat, wave action smooths and flattens the base, leaving a wave-cut platform. Abrasion (grinding of sediment) and solution (chemical weathering of rock) wear down the surface, while biological weathering (from organisms like algae) further weakens the rock. Over time, the platform widens as the cliff continues to retreat.

4. Geos

  • Description: Geos are narrow, steep-sided inlets in the coastline, often extending inland from the sea.
  • Formation: Geos form where waves exploit weaknesses in the rock, such as faults or joints. Hydraulic action forces air and water into cracks, causing them to expand, while abrasion further widens the feature. Over time, the crack enlarges into a geo, which may extend deeper inland with continued erosion.

5. Blowholes

  • Description: Blowholes are vertical shafts that connect the surface to sea caves, often releasing water and air during high-energy waves.
  • Formation: A vertical shaft is created when erosion extends a geo or cave upwards. Hydraulic action and abrasion force water and air through the shaft during storms or high tides, eventually breaking through the surface. Blowholes often form in cliffs with vertical weaknesses or thin roofs.

6. Caves

  • Description: Caves are hollowed-out chambers at the base of cliffs, formed by wave action eroding weaknesses in the rock.
  • Formation: Waves attack faults, joints, or cracks through hydraulic action (forcing water into cracks) and abrasion (grinding sediment against the rock surface). Over time, the crack enlarges into a cave as erosion continues to hollow out the rock. Solution may also dissolve soluble rock like limestone, further enlarging the cave.

7. Arches

  • Description: Arches are natural openings in headlands, formed when caves erode through to the other side.
  • Formation: Waves erode caves on either side of a headland through hydraulic action and abrasion. As the cave enlarges, it eventually breaks through the headland to form an arch. Wave refraction concentrates energy on the headland, accelerating the process. Over time, arches become larger and more unstable.

8. Stacks

  • Description: Stacks are isolated, vertical columns of rock left standing in the sea after an arch collapses.
  • Formation: When an arch becomes unstable, sub-aerial weathering (e.g., freeze-thaw) weakens the roof, and wave erosion undermines its base. The roof eventually collapses, leaving a stack. Continued erosion at the base of the stack weakens it further.

9. Stumps

  • Description: Stumps are low, flat remnants of eroded stacks, often submerged at high tide.
  • Formation: A stack is eroded at its base by wave action, while weathering further weakens the structure. The stack eventually collapses, leaving a stump. Over time, stumps may become completely submerged due to continued erosion and rising sea levels.

Processes Involved in Erosion

  • Hydraulic Action: Waves force water and air into cracks, causing pressure that fractures the rock.
  • Abrasion: Sediment carried by waves grinds against the coastline, wearing it down.
  • Attrition: Rocks collide, breaking into smaller, smoother pieces.
  • Solution: Acids in seawater dissolve certain rock types (e.g., limestone).

Conclusion

Coastal landforms created by erosion result from the interaction of wave energy, rock type, and geological structure. By understanding the processes and steps involved, A-level Geography students can appreciate the dynamic and transformative nature of coastal environments.