Explain the formation of a headland arch and its location above present day sea level.

Headland arches are formed when soft rock, for example sandstone occurs alternatively across a coastline, separated by bands of more resistant rock, such as gabbro. These different rock types experience differential rates of erosion, causing the formation of discordant coastlines, where prominent headlands are formed. Examples of such coastlines include those of South West Ireland, Western Scotland and Western Norway. Wave refraction is a process that affects the distribution of energy across a coastline and this influences the degree of erosion. As a wave approaches a coastline of an irregular shape, such as one with a prominent headland, they are refracted due to the seafloor gradient becoming shallower, influencing a change in wave propagation. As the refracted wave advances toward the headland, the shoaling effect exerted on it causes the wave to build in height and develop into a destructive wave, concentrating energy on the sides of the headland across the inter-tidal zone.As cracks emerge, they are exposed by hydraulic action pressurising air, forcing it to expand within the cracks, making them widen. At the same time sub-aerial processes such as water crystallisation is occurring as evaporated sea-salt water leaves behind salt crystals to grow and exert pressure on the rock, widening the crack until it becomes a wave-cut notch. Over time, abrasive tools and hydraulic forces catalyse the deepening of the notch, eventually forming a cave, eg. Merlin’s Cave in Cornall UK. Continual deepening of the cave due to waves at high-tide being able to flood the cave, swirling water around which erodes the spine leads to the formation of an arch. The developed arch is seen as a tall bridge-like landform, such as Green bridge of Wales, Pembrokeshire UK. This landform is typically found along emergent coastlines where the coast and its landforms are rising above sea level, such as those in the UK for example the North Antrim coast, due to the effect of isostatic rebound produced by post-glacial adjustment.