Corrasion: This is caused by the waves picking up stones as they reach the shore and hurling them at the cliffs, causing a gradual breakdown of the cliff face.
Attrition: Material carried by the waves will become rounder and smaller over time.
Salt weathering: When the salt water of a wave hits a rock or cliff, the area is covered in salt water. In dry, warm areas, the water is evaporated quickly leaving behind the salt which over time chemical breaks down the surface of a rock, a form of weathering associated with salt weathering is Honeycomb weathering: Honeycomb weathering is when sea spray is soaked into rocks and the spray dries causing salt crystals to form, this then breaks of sand grains one by one forming a honeycomb effect.
Biotic weathering: weathering caused by living organisms.
The fetch influences how destructive a wave becomes. The longer the fetch the more destructive the wave, this means it is more likely to erode the coastline, especially where rock is less resistant. Erosion creates an array of features none more prominent than bays and headlands. Bays are made of less resistant rock e.g. clay and are more easily eroded. These results in this section of the coastline being eroded more rapidly and a bay forming. The area that is eroded less quickly, juts out into the sea and is called a headland. The process of longshore drift then transports the eroded material to form the beach in the bay (see diagram below)
Erosion also creates the features found in a headland. The sheer force of the waves, traps air in the weaknesses in cliffs. This will eventually weaken the rock and form cracks to develop in the headland. Further erosion creates caves. The caves then erode through the cliff to form arches. The processes of weathering and erosion cause the roof of the arch to collapse and a stack is formed.
Erosion also forms wave cut notches and platforms. Broulee is a good example of a rock platform. The diagram below demonstrates how waves cut notches and platforms are formed.
The diagram to the left is an example of a wave cut notch Waves erode the base of cliffs by hydraulic action, abrasion and solution. This results in a wave cut notch at the high tide line.
Beaches are one of the most common features of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited here by the sea. Constructive waves help to build up beaches. The type of material found on a beach (i.e. sand or shingle) is influenced by the geology of the area and wave energy.
Spits are also created through the process of 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 commonly formed where there is a prevailing wind and where there is a longshore drift. The development of a spit is shown below:
When a sand spit has formed with an island a tombolo is formed. A perfect example of a tombolo is Broulee island. The tombolo was formed because the island caused wave refraction, depositing sand and shingle behind the island. Over time more depositionion through lolng shore drift and the colonisation of plants has resulted in the tombolo being formed.
Along Emily miller beach it is evident that destructive waves are a prominent feature along this section of the coastline, hence the landforms of erosion.
Sand Dunes
On sandy shorelines, coastal dunes represent the last line of defence against erosion by providing a reservoir of sand for waves to utilise during storms. As well as limiting the landward intrusion of waves, wind and salt spray, dunes act as a barrier to oceanic inundation and they provide for an important morphological and ecological transition from marine to terrestrial environments.
Three things are required for dune formation to occur: a large supply of sand, wind speeds capable of moving it, and an ideal location for its accumulation.
Factors needed for sand dune formation:
- Source of abundant sand
- Consistent wind
- Water level (dune growth accelerated by higher water levels)
- Vegetation (traps and stabilises sand)
In Figure 18 (below) we can see how open beaches(withput headlands for protections) like caseys beach are more subject to erosion of the foredunes during king tides and storm events. Beaches are dynamic entities, whose shape and locations naturally vary over time. In most cases when left undisturbed by human activities, these beaches are 'self-protecting' and establish a dynamic equilibrium over time. In this case, the sand eroded from the foredune is carried a short way out to sea during the erosional events, there forming an offshore bar, which absorbs wave energy there and helps protect the beach from further erosion.Then in the weeks-to-months that follow, during low tide the sand will be blown back against the duneface, restoring the foredune to its former condition.
Figure 18: Eroded Foredune (Sandy Point)
