Depositional landforms Flashcards
What is a key source of sediment for depositional landforms on coasts?
Longshore drift
In what two main ways can deposition occur?
Gravity settling occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first followed by smaller sediment.
Flocculation is a depositional process that is important for very small particles, such as clay, which are so small they will remain suspended in water. Clay particles clump together through electrical or chemical attraction and become large enough to sink.
List of depositional landforms
Spit Bayhead beach Tombolo Barrier beach/ bar Hooked/recurved spit Cuspate foreland
How is a spit formed?
Sand or shingle beach ridge extending beyond a turn in the coastline, usually greater than 30 degrees.
At the turn, the longshore drift current spreads out and loses energy, leading to deposition.
The length of a spit is determined by the existence of secondary currents causing erosion, either the flow of a river or wave action which limits its length.
How is a bayhead beach formed?
Waves break at 90 degrees to the shoreline and move sediment into a bay, where a beach forms.
Through wave refraction, erosion is concentrated at headlands and the bay is an area of deposition.
How is a tombolo formed?
A sand or shingle bar this links the coastline to an offshore island.
Tombolos form as a result of wave refraction around an offshore island which creates an area of calm water and deposition between the island and the coast.
Opposing longshore currents may play a role, in which case the depositional feature is similar to a spit
How is a barrier beach/bar formed?
A sand or shingle beach connecting two areas of land, with a shallow-water lagoon behind.
These features form when a spit grows so long that it extends across a bay, closing it off.
How is a hooked/recurved spit formed?
A spit whose end is curved inward, into a bay or inlet. The seaward (distal) end of the spit naturally curves landward into shallower water and the 'hook' may be made more pronounced by waves from a secondary direction to the prevailing wind.
How is a cuspate foreland formed?
Roughly triangular-shaped features extending out from a shoreline.
There is some debate about their formation, but one hypothesis suggests that they result from the growth of two spits from opposing longshore drift directions.
