Depositional Landforms - Beaches Rivers Offshore Cliff erosion Actual (%) My Guess (%) Source of beach material
Depositional Landforms - Beaches 95 Rivers 5 Offshore 5 Cliff erosion Actual (%) My Guess (%) Source of beach material
Beaches <ul><li>Depositional landforms are produced on coastlines where sand and shingle accumulate faster than they are removed. </li></ul><ul><li>This normally occurs in areas of coastline dominated by constructive waves of low energy. </li></ul><ul><li>Beaches are the most common landform of deposition and represent the accumulation of material deposited between the positions of the lowest tides and highest storm waves. </li></ul><ul><li>Beach material in the form of sand, shingle, pebbles and cobbles comes from three sources; cliff erosion, offshore and rivers. </li></ul>
Beaches <ul><li>Sand produces beaches with a gentle gradient; usually less than 5 º. </li></ul><ul><li>This is because its small particle size means that it becomes compact when wet, allowing little percolation during backwash. </li></ul><ul><li>Shingle produces steeper beaches; often 10-20º. </li></ul><ul><li>Shingle may make the upper part of the beach, where rapid percolation due to larger air spaces means that little backwash occurs and so material is left at the top. </li></ul>
Factors Affecting the Beach Profile <ul><li>Wave Energy. High energy waves tend to produce shingle beaches. Sandy beaches are found in low energy areas. </li></ul><ul><li>Wave Type. Destructive waves = stronger backwash = more material moving back down the beach = shallower profile. Constructive waves = strong swash = more material moved up the beach = steeper beach profile. </li></ul><ul><li>Longshore Drift. </li></ul><ul><li>Sediment Calibre. Shingle beaches are generally steeper as backwash percolates easily through the shingle reducing its energy and ability to comb material back down the beach. </li></ul>
Berms Smaller ridges that develop at the position of the mean high tide mark resulting from deposition at the top of the swash. Berms are generally created by smaller waves which have less energy so the material is smaller.
Storm Beach At the back of the beach, very strong swash during storm conditions may deposit larger material, forming a storm beach or ridge.
Ridges and Runnels The spreading out of the waves’ energy/work across a wide area of beach tends to produce ridges and intervening depressions called runnels. They are particularly common on shallow, sandy beaches.
Beach Cusps Cusps are semi-circular depressions; they are smaller and more temporary features formed by a collection of waves reaching the same point. The sides of the cusp channel the incoming swash into the centre of the depression and this produces a stronger backwash which drags material down the beach from the centre of the cusp.