Cave, arch and stack

• Here cliffs are of a resident rock where wave action attacks any line of weakness such as joins and faults. The waves widen the cracks by marine processes.
• Hydraulic action is when the power of the waves agains the coast, forces air into the cracks in the rock, compresses it and blows the rock apart when the preasure is released.
• Abrasion also takes place, this is where the waves pick up rocks and other material and throws it agains the coastline, causing further erosion.
• In time, the weak area will be eroded and enlarges to form a cave. The waves then attack the sides and back of the cabe until they cut through to the other side of the headland to form an arch.
• Continual marine and sub-aerial processes cause the arch to widen and the rock above the arch to become unstable. In time, the rock colapses to leave a piller of rock seperated from the headland, called a stack.
• An example is the Rock and spindle of fife