In physical geography, a spit is a deposition landform found off coasts. A spit is a type of bar or beach that develops where a re-entrant occurs, such as at a cove, bay, ria, or river mouth. Spits are formed by the movement of sediment (typically sand) along a shore by a process known as longshore drift. Where the direction of the shore turns inland (reenters) the longshore current spreads out or dissipates. No longer able to carry the full load, much of the sediment is dropped. This causes a bar to build out from the shore, eventually becoming a spit.
Water currentss and waves moving from the sea, at 90° to the direction of sediment flow move the sediments towards the land creating a recurve.
If the supply of sediment is interrupted the sand at the neck (landward side) of the spit may be moved towards the head, eventually creating an island. If the supply isn't interrupted, and the spit isn't breached by the sea (or, if across an estuary, the river) the spit may become a bar, with both ends joined to land, and a lagoon behind the bar. If an island lies offshore near where the coast changes direction, and the spit continues to grow until it connects the island to the mainland it is called a tombolo.
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