Caves, arches, stacks and stumps

Where do these landforms form

On discordant coastline usually along headlands

How does a cave form

• When a crack forms at base of cliff due to hydraulic action, and are widened due to weathering

• Over time crack develops as a wave-cut notch due to abrasion and hydraulic action

• Then wave refraction causes destructive waves to concentrate energy on sides deepening cave

How does the arch form

• Wave refraction means all three sides of headlands targeted

• Two caves align as waves cut through forming the arch

How does a stack form

• When wave-cut notches form at base of arch due to hydraulic action

• Arch becomes unstable and collapses under its own weight to form stack

How does a stump form

• Stack eroded at is base creating wave-cut notches and sub-aerial processes weaken stack from above

• Stack eventually collapses forming stump which can be further eroded and sediment be transported

What is a blowhole and how does it form

A blowhole forms when a cave in a headland is eroded upwards until it breaks through to the surface, allowing water and air to be forced out under wave pressure