Platform, arch, cave and stack
Platform, arch, cave and stack

Sea Caves
Caves are formed when there is softer rock between layers or cracks of harder rock on cliff faces due to the force of the ocean waves. These weak zones are normally zones where waves can go through the rock or where the sediment is really soft. Caves start as very small cracks and eventually become
external image T12865728607896c5aaeb1326c92a0a9d2fef474cd95e.jpg external image sea-caves-from-the-boat.jpg

If a cave is formed on a headland, it might eventually break through the other side and form an arch.

external image holei-sea-arch.jpg Holei Sea Arch, Hawaii!
external image f-p-vta3.jpgPort Campbell Coast, Australia
As the arch becomes bigger, it will eventually not be able to support the top of the cave or arch. The top of the arch collapses and leaves the headland, and a bit further away something what is called a stack (column of rock).
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external image ruby%20beach%20sea%20stacks%20(low).jpg
The stack will be attacked by the waves at its base. This eventually weakens the stack and it collapses forming a stump.

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Formation Of Stacks...

So that is how
Caves, arches, stacks and stumps are formed.