"Coastlines constantly change due to the processes of erosion and deposition".
Australia's coastline measures over 36000 kilometres. About 85 per cent of the population live in coastal towns or cities. More than 25 per cent live within 3 kilometres of the coast. The coast is important as a natural and human resource. Many people use coasts for recreation as well as industries, fishing locations and ports, but not many people realise that coasts are constantly changing. These changes are due to the processes of erosion and depositon.
Erosion is the wearing away of the earths surface by agents such as wind and water. Waves are constantly striking against a coastline and when the weather is windy, the waves are larger and more powerful. As the wave hits the coastline, the energy in them is used to erode rocks and move sand, pebbles and other material. Bays and headlands are formed by erosion; they result from rocks eroding in different ways. Soft rocks are worn away more readily and form bays. The harder rocks take longer to erode and form headlands. An example of a coastal feature caused by erosion is a cave. A cave will be formed where weak rocks are eroded on each side of a headland. Over time the caves will erode enough to join, forming an arch. Further erosion of the rock supporting the arch will cause it to collapse, leaving a stack. Sometimes where we have only one cave, forming in the face of a cliff. The water can sometimes find a weakness in the cliff face and find a way to the surface, forming a blowhole.
Deposition also plays a major part in the constant change of our coastlines. Waves carry sand and other material on and off the shore. When a wave breaks, the water from it runs up the beach. This is called swash. The movement of water back down the beach to the sea is called the backwash. When storms occur and waves are large, more material is carried in the backwash to deep water. These are called destructive waves.
