A sea stump is formed when a stack, an isolated column of rock in the sea, collapses due to continued erosion at its base.
Here's a breakdown of the formation process:
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Sea Arch Formation: Initially, wave action and erosion attack weaknesses in a headland (a piece of land projecting into the sea). This erosion widens existing cracks and forms caves. If two caves on opposite sides of the headland meet, a sea arch is created.
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Stack Formation: The base of the arch continues to erode, widening the arch. Eventually, the roof of the arch becomes too heavy and unstable and collapses into the sea. This leaves behind a stack, which is a tall, isolated pillar of rock standing in the water.
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Stump Formation: The stack is now vulnerable to further erosion, especially at its base. The relentless action of waves undercuts the base of the stack. This undercutting weakens the structure until it eventually collapses. The remaining base of the former stack, which is now a short, eroded platform usually only visible at low tide, is called a sea stump.
Therefore, a sea stump represents the final stage in the erosion process, following the formation and collapse of both a sea arch and a sea stack. It's essentially what remains after a stack has been eroded to its lowest point.
