GCSE Geography | Landforms of Deposition: Beaches (Coastal Landscapes 7)

Deposition has led to the formation of distinctive coastal features - we call these depositional landforms.

Beaches are landforms that lie between the high and low tide levels - they are formed of sand, shingle or pebbles, or a combination, as well as some mud and silt. They are formed when the sea transports material that has been eroded elsewhere, to the shore.

There are two distinctive types of beach...

Sandy beaches

These tend to form in sheltered areas where the dominant waves are constructive and low-energy, so they transport material onto to the shore that has been eroded elsewhere. As the waves are constructive, the swash is stronger than the backwash, so material is pushed up the beach and not dragged back into the sea once the waves have broke.

What are they like?

• Shallow gradient, almost flat
• Constructive waves are dominant
• Long wide beach (stretches a long way back)
• Often have sand dunes at the back of the beach
• Sometimes pools of water form at low tides (called runnels)
• The wet sand often looks rippled

Pebble beaches

These tend to form along exposed stretched of coastline where the dominant waves are destructive and high energy. Because the waves are destructive, the backwash is stronger than the swash, so pebbles are not moved far up the beach, resulting in a steep beach profile, which is made worse when the destructive waves plunge down onto the beach. The beach profile can change significantly in storm conditions when the huge waves hurl boulders and large pebbles to the back of the beach.

What are they like?

• Quite a steep gradient - often has several ridges to the beach profile
• Destructive waves are dominant
• Narrow beach (doesn't stretch very far back)
• Often have storm beaches with large pebbles at the back of the beach
• As you move further inland from the sea the pebbles get larger

Why do beach profiles change?

Beach profiles show the gradient from the top of the beach (the bit closest to the land) to the sea. Sandy beaches usually have flat gentle profiles, whilst pebble beaches tend to have a much steeper profile, often with stepped ridges.

Beaches usually have berms along them - these are terraced steps that have formed at the back above the high tide level - there may be 2, 3 or even more berms on a wide beach, that all run parallel to each other and have formed under different wave conditions. Berms are formed by constructive waves during calm weather, where material is added to the beach. Storms and spring tides can move existing berms up the beach, meaning that a new berm can develop, which changes the beach profile.

How do beach profiles change throughout the year?

• Autumn and winter - destructive waves will erode the berms and sand dunes at the back of the beach - some of this material gets dragged out to see by the strong backwash, which lowers the beach height, and also leads to the creation of offshore bars. Damage caused by destructive waves results in a narrower and steeper beach

• Spring and summer - constructive waves will build up the beach, replacing some of the material that was removed over the winter (this is move effective if groynes are in place to trap sediment). Material is transported from the offshore bar to rebuild the berms, and the wind builds up the sand dunes, aided by saltation