COASTS

Read more information on this site; 

https://www.geoforcxc.com/water/coastal-features/

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.

These cliffs are found on the coast of Peru

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!

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.

This cave is found on the coast of California, USA

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

This arch is found near the village of Etretat, France

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.

This diagram shows how a cave can develop into an arch and eventually a stack

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.

This bayhead beach is found in Buzio, 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.

A sand bar off the coast of Barton in the Philippines

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.

Dungeness Spit, Washington

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.

This tombolo is found near Hong Kong, China. Notice how the small island is joined to the mainland by the deposition of sand.

Take the Coastal Features quiz!

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