MARINE DEPOSITION PROCESSES.

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?

Waves striking the coast at an oblique angle, causing longshore drift.

Make sure that you can explain how longshore drift works and draw a labelled diagram!

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.

Hurst Spit in Hampshire is an example that you can quote in the exam.

HURST SPIT, HAMPSHIRE

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.

This spit will become a bar if it reaches the other side of the estuary. Can you work out the direction of longshore drift?

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. bar tombolo Chesil beach from Portland Bill; the shingle is 29kms long.

Barrier beach and tombolo which retains The Fleet (lagoon) Chesil Beach

ORDNANCE SURVEY MAPWORK You need to be able to recognise coastal erosion landforms from a map. To practice this skill use the maps and landscapes book and work through a few of the exercises on coasts. THEY ARE NOT ALL NEEDED STICK TO THE MAPWORK!!

As you revise this topic, for each feature mentioned, look back through your textbooks and this presentation. You are looking for named examples of as many features as possible.

You have now completed the deposition section of this unit. You should be familiar with the following terms and be able to define and use them in your answers. Fort those not covered in the presentation you need to now research them yourself. BEACH BAY BAR SPIT TOMBOLO HEADLAND SORTING GROYNE LONGSHORE DRIFT LAGOON SALT MARSH SHINGLE SWASH BACKWASH ON-SHORE WIND