Coastal Deposition

BEACHES Beaches are a buffer zone between the waves and the coast. They usually lie between high and low tide marks, but storms can throw material up beyond high tide marks.

The main activity of constructive waves is to deposit pebbles, sand and mud to form a beach. The sea sorts this material into different sizes according to its weight as it moves it about in the water.

LONGSHORE DRIFT Splash zone Backwash direction Swash direction High tide mark Intertidal zone Low tide mark On-shore winds make waves approach at an angle ( swash), but they go back down ( backwash) at right angles to the beach. What is the result of this process?

Features of coastal deposition Formation of a spit Clip

How do Sand Spits form? Longshore drift moves large amounts of material along the beach until there is a sudden change in the direction of the coastline. The sand keeps on moving in the original direction, even though there is not a coastline to follow. The sea has to be relatively shallow and sheltered allowing the accumulation of sand usually beyond a headland. Sometimes a curve develops if the on- shore wind changes direction. Spits can become permanent if the prevailing wind picks up sand and blows it inland forming sand dunes.

1. Longshore drift moves material along the coastline 1.Longshore drift moves material along the coastline.(in an exam you would need to describe this process) 2.A spit forms when the material continues to be deposited but the coastline changes direction. 3.Over time, the spit grows and develops a hook if wind direction changes further out. 4.Waves cannot get past a spit,this creates a sheltered area where silt is deposited and mud flats or salt marshes form. Change in wind direction Curves spit

Re-cap formation of depositional features

Bars, Lagoons and Tombolos Although you will not be asked to explain the formation of these features, it is worth knowing how they have been formed.

Bars and Lagoons

How Do Bars and Lagoons form? A bar is a barrier of sand stretching right across a sheltered bay. It usually stretches across the bay due to the absence of any large river that might wash it away. It can cut off a lagoon to the landward side. A lagoon is a body of brackish water- part salty, and part fresh. It often supports specialised plants and animals, and is protected as a nature reserve. .

Tombolo Tombolo Mainland Island

If a bar links up with an off-shore island, it creates a tombolo If a bar links up with an off-shore island, it creates a tombolo. Chesil Beach- one of the most famous bars in the UK has a tombolo called Portland Bill. tombolo Chesil beach from Portland Bill; the shingle is 29kms long.