Wave-cut notch: A part of the headland between high and low tide levels which has been undercut by destructive waves.
Sea stack/Stump Irish example: The Old Head of Kinsale, Co. Cork
Description: A sea stack is a pillar of rock jutting out of the sea near the coast (Fig. 9.10).
Formation: As the sea arch gradually gets bigger, it reaches a point where the weight at the top of the arch can no longer be supported, and it collapses due to the influence of gravity. When this happens, a headland is left on one side and a tall column of rock called a sea stack is left on the other. The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure which will eventually collapse to form a stump.
Fig. 9.10(a) Sea stack. Sea stack Sea stumps
Sea stack
Fig. 9.10(b) Sea stacks and stumps are found just off the coast on an OS map.
Blowhole Irish example: Hook Head, Co. Wexford
Description: A pipe-like opening that links the surface of a headland to the roof of a sea cave (Fig. 9.11).
Formation: Blowholes are formed close to the cliff face when a joint between a sea cave and the land surface above the cave becomes enlarged. As water flows into the cave, air and seawater is expelled through the pipe- like joint, producing an impressive blast of spray that seems to emerge from the ground.
Fig. 9.11(a) Blowhole.
Blowhole Fig 9.11(b) Blowholes can be labelled on an OS map using the word ‘Hole’ (or ‘Poll’ if the map is from a Gaeltacht area).
