Wave action leads to the formation of many features along the coast. Some of these coastal features are formed as a result of erosion by waves whereas others are formed by the deposition of material along the coast by waves. Let us examine these coastal features in turn.
Coastal Features formed by Wave Erosion
Cliffs and wave-cut platforms
A cliff is defined as a steep rock face. Where marine erosion is powerful, the coastline is eroded to form a cliff. Erosion is concentrated at sea level. A notch is cut in the rock at the level where wave attack is concentrated. When the notch is cut too far, the area above this notch collapses forming a cliff.
The process of erosion continues and the cliff retreats further and further back. As the cliff retreats, a flat area which is exposed at low tide is left at its base. This feature is known as a wave-cut platform. Watch the video below which explains how wave cut platforms are formed.
Click here for a diagram showing how a wave-cut platform is formed!
Headlands and bays
In some places, there are alternating bands softer and harder rock along the coastline. As waves attack and erode the coastline, areas with softer rock will be eroded faster than areas with more resistant rock. Over time, the bands of softer rock will be worn back forming bays. A bay is an inlet along the shoreline of a body of water. The bands of more resistant rock will be left jutting out into the sea as headlands. The video below shows how headlands and bays are formed.
Caves, arches and stacks
The rocks along the coast may contain joints, fissures or other weaknesses. These can be enlarged by wave action, eventually forming a cave.
If a cave is formed in an exposed headland, it may be enlarged until it runs right through this headland. The resulting feature is called an arch. Natural arches can be seen in the photos below.
This arch is found on the west coast of St. Lucia, near the city of Castries
Over time, erosion may act upon the arch, widening it until the roof collapses. The piece of rock which is left stranded away from the headland is called a stack. In the picture above, a stack can be seen next to the natural arch. The diagram below shows how caves, arches and stacks are formed.
Coastal Features formed by Wave Deposition
Constructive waves deposit material on the shore. Some features formed by wave deposition are:
Bayhead beach
Beaches are the most common features formed by wave deposition. One type of beach is the bayhead beach. This type of beach is formed when waves deposit material between two headlands. The picture below shows a bayhead beach in Brazil.
Bars
These are linear deposits of material which are approximately parallel to the coast. Some are submerged whereas others appear above the waves. They may be stabilized by vegetation and grow large enough to become barrier islands.
Some features are formed by a process known as longshore drift. Therefore it is important that this process is understood. Longshore drift is the process by which material is moved along the beach by wave action. This process is responsible for forming coastal features such as spits and tombolos. The video below explains the process of longshore drift.
Spits
These are formed when material is deposited along the coastline by longshore drift. They are usually linear. They are connected to the land at one end and free at the other. Spits usually form where there is a bend on the coastline.
Tombolo
This is a linear deposit of material formed by longshore drift which joins an island to the mainland. The diagram below shows how tombolos are formed.
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References
- http://julian-leha.blogspot.com/2012/07/mini-thailand-in-hongkong.html
- http://www.touropia.com/most-dramatic-sea-cliffs-in-the-world/
- http://www.panoramio.com/photo/26930851
- http://geobytesgcse.blogspot.com/2007/08/coastal-deposition-landforms-features.html
- http://pages.uoregon.edu/millerm/spits.html
- http://thebritishgeographer.weebly.com/coasts-of-erosion-and-coasts-of-deposition.html