Coastal Deposition
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Coastal Deposition

Deposition occurs where the inputs exceed the outputs.

Spits

• A long narrow accumulation of sand with one end jointed to mainland and the other projecting out to sea or across an estuary. E.g. Spurn Head / Hirst Castle (South Coast) Blakeney Point.

Different Types of Spits

• Sandy Spits - formed by constructive waves.

• Shingle Spits - formed by destructive waves.

• Composite Spits - shingle deposited before the finer sand (made of both).

• Spits are formed by longshore drift, which carries material along the coast and continues in the same direction when the coastline retreats E.g. Estuary.

Spurn Head, Holderness Coast

• A drift lined spit formed when longshore drift occurred to the south. The spit receives sediment drifting south as far north as Flambrough Head. It receives glacial deposits that are as easily eroded and a abundant sediment supply. The wind is from the north and northeast and that is why the drift is to the south. It is projecting into a Humber Estuary. In the slack water the finer sediment is stored. Due to the projection into the estuary the Humber is diverted south. The spit has moved west due to the eroding coastline.

Hooked or Re-curved Spits

• As spits build out into deep water they require increasing volumes of sediment to build above the high mark. The tip or distal turns towards the land where it's shallower. If it built out in deep water it would be eroded. Once formed hooks are sheltered from the dominant waves by the spit and become permanent curves also formed by the second dominant wind.

Double Spits

• Are spits, which extend from an embayment this may be due to two dominant winds. Due to a spit extending across a bay (bar) and it gets breached E.g. Christ Church Harbour in Bournemouth Bay at one point the southern spit spreached right across the harbour.

Forelands

• A cuspate foreland is a complex depositional feature formed when longshore drift is from two directions, which meet to produce a series of ridges at right angles to each other. This forms a low-lying triangle area E.g. Dungeness.

2000 years ago when the sea level in southeast England was 2m lower than it is today, the coastline at Dungeness was 15km inland. The wind and the fetch were both over 500km from the southwest. Beach material is carried by Longshore drift from west to east along the channel coast. Some fiercest storms are when the wind blows from the northeast the second greatest fetch is 600km in storms shingle is carried east to west. Storm waves have built up shingle ridges each ridge protects the one behind it. The triangle feature is a site for Lydd Airport and power stations.

Bars

• If a spit extends across a bay it links two headlands and straightens the coastline. E.g. Chesil Breach off the Dorset Coast smoothes 30km of coastline.

Tombolo

• This is when a spit joins an island to the mainland E.g. Chesil Links, The Isle of Portland and Llanddwyn Island.

Barrier Beaches and Islands

• The most extensive extends from New Jersey down the east coast of the USA to include Cape Hatteras and Florida Miami beach is easily identified. The beaches form as offshore bars of sand, which accumulate below the low tide mark and move inland. The shallow water generates constructive waves, which transport material landwards creating a long smooth coastal feature topped by sand dunes and separated by a lagoon.

Sand Dunes

• Longshore drift may deposit sand in inter tidal zones. As the tide ebbs the sand dries out when the wind blows from the sea the sand will move up the beach by saltation. This occurs when the prevailing winds come from the sea and large tidal range, which exposes more sand at low tides. Sand can become trapped by seaweed and driftwood on berms and high spring tides. Plants colonise the area stabilising the sand and encouraging accumulation. The regolith has a high PH due to the calcium from the seashells.

Embryo Dunes

• Likely to develop and the surface becomes arid due to percolation in the sand. Marram grass is featured it has long roots to tap underground water supplies. Spinifex has long growth which reduces transpiration in strong winds these are the first plants to colonise the sand dunes. As more sand accumulates, embryo dunes join up to form Foredunes, which can reach a height of 5m due to the lack of humus colour = yellow dunes. These are grey as humus and bacteria from plants and animals are added and become acidic and vegetation covered. They reach 10-30m before their increasing distance from the beach cuts off the supply of sand. There maybe several parallel ridges of old dunes separated by low-lying damp slacks. Health plants dominate the area as acidity humus and moisture contents increase. Paths expose areas of sand the wind funnels along these paths and blowouts may form.

Salt marches

• Where there is shelter in river estuaries or behind spits, silt and mud are deposited by the rising and falling tide or the river. Plants like algae and salicornia can tolerate the submergence and the high levels of salinity. They trap more mud around them allowing the slope zone to remain exposed for longer periods between tides. Spartina grows all year round and has colonised most estuaries. The land at the side is marked by a cliff above it is the sword zone which maybe covered by sea for less than one hour. Seawater collects in hollows, which increases following evaporation and enlarging into saltpans. As the tide retreats water drains into creeks.

Other Notes in this Category

1. Beach Materials
2. Changes in Sea Level
3. Coastal Deposition
4. Coastal Erosion
5. Coastal Erosion Landforms
6. Coastal Transportation
7. Erosion Landforms

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