Coastal Deposition

This occurs in areas where the amount of deposited material exceeds that of the depleted material.

Spits: These are long, narrow accumulations of sand and/or shingle, with one end attached to the mainland and the other extends into the ocean. The diagram below

illustrates a typical spit.

Dunes (G): These occur when winds blow dry sand from the beach, inland and then deposits them, to form dunes.

Saltmarsh (H): When quantities of marram grass anchors in the sheltered area where silt collects.

Tombolo: These occur when a beach grows out to join up with an offshore island, forming a small peninsular.

Bar: These develop when a spit extends across a bay with no major river, and thus extends the whole way across, linking two headlands.

Barrier Islands: Sandy islands that run parallel to the coastline forming a tidal lagoon between them and the shoreline. These can extend in for several hundred kilometres and form 13% of the world’s coastlines.

Sand Dunes: There are four types of sand dunes. Embryo dunes are the first to develop, and are stabilised by the growth of lyme and marram grass. As these dunes join up they form fore dunes which can attain a height of 5m, their lack of humus gives them the name yellow dunes. As humus, bacteria and other matter infiltrate their way into the dune, it becomes more covered with vegetation and thus are given the name grey (mature) dunes, reaching up to 10-30m, before growth is limited by the low supply of new sand due to their length from the coast. As the wind funnels through paths cut by animals and humans, they create blowouts, which may form on the wasting dunes.

Saltmarshes: These occur in river estuaries or behind spits, where silt and mud will be deposited either by the gently rising and falling tide or by the river, thus forming a zone of inter-tidal mud flats. These may only be uncovered by sea water for 1 hour every 12-tide cycle, however these areas are colonised by plants such as algae Salicornia, which can tolerate these harsh conditions, these trap more mud so that the area is exposed for longer and longer durations of time. On the land side of the mud flats there is a small cliff and beyond is the sward zone where the seawater covers for less than 1hr per 12hr cycle, here creeks form to drain the sea water. However some seawater evaporates and leaves salt behind, creating a saltpan, which are only habituated by algae and the odd halophyte.

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