weathering (the break down of rocks) and erosion can create caves, arches, stacks and stumps along a headland.
- Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
- If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
- The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
- The stack will be attacked at the base in the same way that a wave cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.
- One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.
Beaches are a common feature of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea.
Constructive waves help to build up beaches. The material found on a beach (ie sand or shingle) depends on the geology of the area and wave energy.
A cross-section of a beach is called a beach profile. The shingle ridges often found towards the back of a beach are called berms
The material found on a beach varies in size and type as you move further away from the shoreline. The smallest material is deposited near the water and larger material is found nearer to the cliffs at the back of the beach. Large material is deposited at the back of the beach in times of high energy, for example during a storm. Most waves break near the shoreline, so sediment near the water is more effectively broken down by attrition.
Sandy beaches have gently sloping profiles and shingle and pebble beaches are steeper.
Spits are also created by deposition. A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end.
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift. An example of a spit is Spurn Head, found along the Holderness Coast in Humberside.
- Longshore drift moves material along the coastline.
- A spit forms when the material is deposited.
- Over time, the spit grows and develops a hook if wind direction changes further out.
- Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.