Coastal Landforms of Deposition Flashcards
Beaches
Beaches form when constructive waves deposit sediment on shore.
Shingle beaches are steep and narrow. They are made up of larger particles, which pile up at steep angles. Sizes of composition range from 2 to 200 millimetres. shingle beaches are typically steeper because waves can easily flow through the course, porous surface if the beach, decreasing the effect of backwash.
Sand Beaches form from smaller particles (less then 2mm in diameter). They are wide and flat.
Drift-Aligned Beaches - produced where waves break at an angle on the coast. The swash therefore occurs at an angle, but the backwash runs perpendicular to the beach. As a result, material is transported along the beach via longshore drift.
Swash-Aligned Beaches - Produced where waves break in line with the coast. Swash and backwash movements move material up and down the beach.
Spits
This is a long narrow strip of land which is formed when longshore drift causes the beach to extend out to sea. The length of the spit depends on any changing currents or rivers, which prevents sediment from being deposited.
A change in wind direction or wave direction can cause the end of the spit to curve (recurved end). Over time the spit may be left with multiple recurved ends, which is known as a compound spit.
In some areas a double spit may occur where the spits from opposite sides of the bay reach out towards each other, though unlikely to touch unless there are no changes to environmental conditions. This could lead to a barrier beach being formed.
Barrier Beach / Bars
A barrier beach occurs when a beach or spit extends across a bay to join two headlands. This traps water behind it leading to the formation of a brackish lagoon.
Some barrier beaches may have formed after the last ice age ended, when ice melt caused rapid sea level rise. The rising water flooded the land behind beaches and transported sand offshore, where it was deposited in shallow water.
If a barrier beach becomes separated from the mainland it becomes a barrier island.
They occur in areas with low tidal ranges and can be very large. Barrier beaches formed in the Netherlands.
Tombolo
A tombolo is a bar or beach that connects the mainland to an offshore island and is formed due to wave refraction off the coastal island reducing wave velocity, leading to deposition of sediments.
Offshore Bars
An offshore region where sand is deposited, as the waves don’t have enough energy to carry sediment to the shore. They can be formed when the waves break early, instantly depositing sediment as a offshore bar.
They may also be formed as a result of backwash from destructive waves removing sediment from a beach.
Offshore bars may absorb wave energy, reducing erosion in some areas.
Sand Dunes
Sand dunes occur when prevailing winds blow sediment up the beach. Onshore winds transport the sand up by saltation. The formation of dunes require large quantities of sand and a large tidal range. This allows and to dry, so it is light enough to be picked up and carried by the wind to the back of the beach.
Salt Marches
