13.4.3 What is the role of deposition in coastal environments? Constructive waves lack the force of destructive waves, but still play a vital role in shaping and forming coastal landforms. They deposit materials like sand, shells, coral and pebbles on the shore. Over time, these materials form beaches, spits, dunes, lagoons and other features (see FIGURE5 ). Additionally, material from eroding cliffs and river silt might also be transported to the coast. Dried by the sun, sand is blown inland to create dunes.
FIGURE5 Depositional landforms: coastal landforms created by deposition
Longshore drift can build up sand to form a spit.
Prevailing winds
A spit can sometimes join two land areas. This is called a tombolo.
Inlet
Sea island
Bay mouth bar
Bay
Bay
A lagoon develops when a sandbar closes in an area.
A beach forms when material is brought to shore by waves. Sand dunes form when plenty of sand builds up on the land.
Beach
FIGURE6 The formation of sand dunes
Small plants and shrubs grow to form a backdune where there is more protection from wind and salt.
5
3
These grasses are adapted to cope with
2
The wind blows the sand from the beach to the foredune.
exposure to salt, sun and wind-blown sand.
Sand is moved to the beach in the swash.
1
Wind
Backdune
Foredune
The vegetation captures the sand helping to build the dune system.
4
The area between the dunes is known as the interdune corridor or swale.
Beach
6
Sea
Beach material is shifted by wind and waves. The wind influences the angle at which the waves move towards the coast. Waves come from the direction of the prevailing winds . Waves approach the shore at an angle and their swash pushes material onto the beach at an angle. The backwash returns to the sea in a straight line, creating a zigzag pattern of movement. This process of material moving along the beach is known as longshore drift , and it creates features such as spits and sandbars. If the prevailing wind changes direction, so does the direction of longshore drift.
296 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
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