How do geological structure and rock type influence coastal landforms?
What is a landform?
You will always come across the term ‘landform’ in physical geography. A landform is a feature of the landscape that has been formed or sculpted by processes of:
Both rock type and structure can have a significant impact on coastal landforms.
As more resistant rocks (e.g. chalk, limestone) erode more slowly than less resistant rocks, they project into the sea as headlands.
Less resistant rocks (e.g. clays and sands) have less structural strength and are eroded easily. Less resistant rocks typically produce lower cliff profiles that experience mass movement, such as mudslides and slumping. Bays are also often found in areas of less resistant rocks.
The coast is called concordant if the rock beds run parallel to the edge of the sea. High cliffs and coves can identify concordant coasts. If the rock beds run perpendicular (at a right angle) to the sea’s edge, the coast is called discordant. Headlands and bays can identify discordant coasts.
Geological structure includes the way that layers of rocks are folded or tilted. This can be an important factor in the shape of cliffs. Faults are cracks in rocks. Enormous tectonic pressures can cause rocks to ‘snap’ rather than fold (bend), and movement (or displacement) happens on either side of the fault. Faults form lines of weakness in rocks and are easily carved out by the sea forming landforms such as caves and arches.
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