How does the type of rock along a coast affect the rate of erosion?

The type and structure of rock are fundamental factors in determining the rate of coastal erosion. The resistance of bedrock to erosional forces—such as wave impact, hydraulic pressure, and abrasion—directly dictates how quickly a shoreline retreats.123

• Resistant Rock: Harder, more durable formations, such as igneous rocks (e.g., granite) or massive limestones, are highly resistant to erosion. These rocks often form prominent headlands or cliffs that project into the sea because they wear away much more slowly than surrounding materials.42
• Easily Eroded Rock: Softer materials, including clays, silts, and certain sandstones, are significantly more vulnerable to erosional processes. When these softer rocks are situated between harder formations, they erode more rapidly, often resulting in the formation of bays.4
• Structural Vulnerability: Beyond rock type, the physical structure of the rock plays a critical role. Shorelines composed of highly jointed or bedded rock are particularly susceptible to "quarrying," where wave action and hydraulic pressure pluck blocks of rock from the coast, accelerating the rate of retreat.3

Ultimately, the configuration of a coast is a result of these varying rates of erosion, where differential resistance leads to the development of diverse landforms like sea cliffs, arches, and bays.324