Sea caves A sea cave is a tunnel at the base of a cliff.
Formation: The hydraulic action of the waves erodes a weak spot on the cliff face. This creates an opening in the cliff. Compression and abrasion make this opening wider and deeper until a cave is formed.
Example of sea caves: The caves at Ballybunion in Co. Kerry.
Sea arches A sea arch is an arch-shaped tunnel that stretches through a headland.
Formation: A sea arch is formed through the processes of hydraulic action, compression and abrasion. It forms when two caves develop back to back and eventually meet, or when erosion causes one cave to reach the other side of the headland.
Examples of sea arches: The Bridges of Ross at Loop Head in Co. Clare and the Bull Rock at Dursey Island in Co. Cork.
Sea stacks and stumps A sea stack is a pillar of rock cut off from the cliff or headland and left standing on its own.
Formation:
A sea stack is formed when a sea arch collapses. Over time, the sea stack is eroded and it collapses. A sea stump is formed. These sea stumps can be seen at low tide.
Examples of sea stacks: Dún Briste off Downpatrick Head in Co. Mayo and Cnoc na Mara in Co. Donegal.
Blowholes
A blowhole is a passage that links the surface of the cliff top with the roof of a sea cave. They can be seen on OS maps as small blue circles near the coast. Formation:
When waves crash into a sea cave, air is trapped and compressed inside, causing the rock in the roof of the sea cave to shatter. The rock eventually collapses, forming a blowhole. During stormy weather conditions, sea spray can be seen coming out of the blowhole.
Examples of blowholes: The Two Pistols and McSwyne’s Gun on the Co. Donegal coast. Blowhole
Site of arch collapse
Original shape of headland
Stump
Lines of weakness
Sea cave Sea arch Sea stack : Figure 10.9 Landforms of erosion found at a headland 162
