Theory question 203
Coastal LandformsWith the aid of diagrams, describe the formation and appearance of any two of the following features: (i) Stack (ii) Blow Hole (iii) Sand Bar
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(i) Stack: waves attack a headland and erode joints into caves (hydraulic action, abrasion); caves on both sides join to form an arch; the arch roof collapses, leaving an isolated pillar of rock standing in the sea; appears as a steep-sided column cut off from the cliff (e.g. Old Man of Hoy).
(ii) Blow hole: waves enlarge a sea cave along a joint; compressed air and water force their way up through a weakness in the cave roof to the cliff top; a vertical shaft forms through which spray is blown out at high tide.
(iii) Sand bar: longshore drift carries sand along the coast; where the coast changes direction or across a bay mouth the sand is deposited; it grows into a ridge of sand parallel to or across the coast, often enclosing a lagoon (e.g. Lagos lagoon bar); low, long and narrow.
Draw labelled diagrams showing the stages of formation.