From Wikipedia, the free encyclopedia

For other uses of the term, see Spit.

Diagram showing a spit

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, headlands and 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 currents 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 when it is then called a tombolo or a bar.

Spits will occur when longshore drift reaches a section of headland where the turn is greater than 30 degrees. They will continue out into the sea until water pressure (such as from a river) becomes too much to allow the sand to deposit. The spit may then be grown upon and become stable and often fertile. A spit may be considered a specialized form of a Shoal.

Spits in the UK are caused by prevailing South-Westerly winds, these give the spits their direction. However, when the direction of the wind changes for a short while the spit may change in direction for a short while forming a hook. Many spits have hooked or curved ends.

A salt marsh is likely to develop in the sheltered water behind the spit.

• List of spits (landforms)
• Shoal