Transport And Deposituon Flashcards
What is long shore drift (LSD) ?
It transports sediment along the beach and between sediment cells.
Waves hit the beach at an angle determined by the direction of the prevailing wind.
● The waves push sediment in this direction and up the beach in the swash.
● Due to gravity, the wave then carries sediment back down the beach in the backwash.
● This moves sediment along the beach over time.
● It is one of the reasons why when swimming in the sea, you often move along the coast in a particular direction.
What are the 4 other processes of transportation?
Other processes of transportation include:
● Traction – Large, heavy sediment rolls along the sea bed, being pushed by currents.
● Saltation – Smaller sediment bounces along the sea bed, being pushed by currents.
● Suspension – Small sediment is carried within the water column (a body of water)
● Solution – Dissolved material is carried within the water
Effectiveness of transportation
The impact of transportation depends on the severity of the angle that waves travel onto land.
▪ Swash-aligned – wave crests approach parallel to coast so there is limited longshore drift. Sediment doesn’t travel up the beach far.
▪ Drift-aligned – waves approach at a significant angle, so longshore drift causes the sediment to travel far up the beach.
When does deposition occur?
Deposition occurs when a wave loses energy meaning the sediment becomes too heavy to carry. Deposition tends to be a gradual and continuous process - a wave won’t drop all of its sediment all at once.
What are the types of depositional landforms?
Spits
Bars
Tombolos
Offshore bars
Sand dunes
What are spits?
A spit is a long narrow strip of land which is formed due to deposition. Longshore drift occurs along the coast line but as the waves lose energy (normally due to going into a sheltered area such as behind a headland) they deposit their sediment. Over time this creates a spit. Periodically, the prevailing wind will change direction causing a hook to appear. Over time, the sheltered area behind a spit can turn into a salt marsh. The length of a spit is influenced by surrounding currents or rivers.
What is a bar?
A spit which over time crosses a bay and links up two sections of coast (the water within the bay is called a lagoon)
Tombolo
A Tombolo is a bar or beach that connects the mainland to an offshore island and is formed due to refraction off the coastal island reducing wave velocity, leading to deposition of sediments. They may be covered at high tide if they are low lying
Offshore bars
A region where sand is deposited, as the waves don’t have enough energy to carry the sediment to shore. They can be formed as the wave breaks early.
Sand dunes
Sand dunes occur when prevailing winds blow sediment to the back if the beach and therefore the formation of dunes requires large quantities of sand and a large tidal range. This allows the sand to dry, so that it is light enough to be picked up and carried by the wind to the back if the beach. Frequent and strong onshore winds are necessary
What order are dunes developed by
Embryo dunes – Upper beach area where sand starts to accumulate around a small obstacle (driftwood, wooden peg, ridge of shingle)
○ Yellow dunes – As more sand accumulates and the dune growns, vegetation may develop on the upper and back dune surfaces, which stabilises the dune. The tallest of the dune succession.
○ Grey dunes – Sand develops into soil with lots of moisture and nutrients, as vegetation dies, enabling more varied plant growth.
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○ Dune slack – The water table rises closer to the surface, or water is trapped between hollows between dunes during storms, allowing the development of moisture-loving plants (e.g. willow grass) ○ Heath and woodland – Sandy soils develop as there is a greater nutrients content, allowing for less brackish plants to thrive. Trees will also grow (willow, birch, oak trees) with the coastal woodland becoming a natural windbreak to the mainland behind.
