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Difficulty: MediumOceans, Coastal Processes, and Coastal Landforms

Arrange the following sequential stages in the progressive marine erosion of a rocky headland, from the initial concentration of wave energy to its final reduced landform.

  1. 1Hydraulic action and abrasion widen joints and bedding planes at the base of a cliff to form a sea cave.
  2. 2Continuous wave erosion cuts right through the headland or joins back-to-back caves to produce a sea arch.
  3. 3Subaerial weathering weakens the arch roof until gravity causes it to collapse, leaving an isolated sea stack.
  4. 4Persistent wave undercutting at the base of the rock pillar causes it to collapse into a low-lying sea stump.

Answer

The correct sequence of headland erosion begins with the formation of a sea cave, followed by its evolution into a sea arch, the collapse of the arch roof into a sea stack, and the final degradation of the stack into a sea stump.
Headland erosion follows a predictable geomorphic sequence: wave action exploits joints to form a sea cave, which enlarges into a sea arch. Subaerial weathering and gravity cause the arch roof to collapse into a detached sea stack, which is finally undercut by waves to leave a sea stump.

Step-by-Step Solution

1
Identify the initial erosional feature created where waves attack lines of weakness along a cliff base.
Marine forces excavate lines of structural weakness to produce a sea cave.
Hydraulic action and abrasion act first on weak joints at sea level.
2
Determine the landform created when wave erosion breaches completely through the headland.
The cave opens up through the headland, creating a sea arch.
Erosion from both sides of the headland meets or drives entirely through the wall.
3
Analyze the structural collapse of the unsupported arch roof due to subaerial processes and gravity.
The arch roof falls, leaving an isolated vertical column known as a sea stack.
Weathering destabilizes the roof, isolating the outer wall from the mainland.
4
Trace the final marine undercutting of the isolated pillar.
Wave action undercuts the base of the pillar, reducing it to a low sea stump.
Direct wave energy at the base destabilizes the stack until only a low remnant remains.

Key Concept

Sequential evolution of erosional coastal landforms on rocky headlands
Estimated Time:1m 0s
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Topics

Oceans, Coastal Processes, and Coastal Landforms

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