Spits, Bars, Lagoons and Tombolos PDF

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Spits, Bars, Lagoons and Tombolos

Spurn Head, Holderness Coast, East Yorkshire

Slapton Ley, Slapton, Devon

The Angel Road, Japan

Spits

How are they formed?

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A spit is a stretch of sand or shingle extending from the mainland out to sea. Material is carried along the shore in a zigzag fashion by waves as they swash material up the beach at an angle and backwash material down the beach at a right angle. The angle of swash is determined by the prevailing wind. When the shape of the coastline changes substantially, longshore drift continues to transport material in the same direction rather than following the coastline. This transports the material out to sea. As the strength of the drift weakens away from the coastline, the sediment is deposited. The deposition of sediment forms a spit but its shape changes as a result of wave refraction. Refraction around the end of a spit curves it into a “hook” forming a recurved spit.

Bars/Lagoons  If a spit develops across a bay where there is no strong flow of water from the landward side, sediment may reach across the other side, joining two headlands forming a bar.  The body of water behind the bar is known as a lagoon.  A lagoon is a shallow body of water protected from a large body of water from sandbars, barrier islands or coral reefs  The size and depth of coastal lagoons often depend on sea level. When the sea level is low, coastal lagoons are swampy wetlands. When the sea level is high, they can look like coastal lakes or bays. Tombolos  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 then called a tombolo....