Depositional Landforms Flashcards
What are some depositional landforms?
-beaches
-tombolos
-barrier/island beaches
-sand dunes
-bars
-spits
Describe the basic formation of a beach?
Beaches occur in the littoral zone between high and low tide. Constructive waves with their strong swash and weak backwash allow increase of material. These ways are flatter and smaller than destructive waves, and material ‘spits’ forward building up the beach. In addition to these swash processes, beach drift caused by long shore currents
Describe the different gradients in the formation of beaches?
Many beaches form in bays, where ther are more sheltered conditions and shallower water. Others are found in a range of situations, where their shape and gradient vary considerably, as does the calibre of material in them. Despite variations of energy, waves, currents and sizes of material, many beaches do seem to have similar features
Describe ridges and runnels at the beach:
At the lower edges of beaches, sand accumulates to form long shore bars, parallel to the waves. This material has been pulmed from the destructive waves. Breaks in these ridges result from rip currents which form in the strong backwash. In land of these, runnels form, separating pools of running water at low tide. As the slope of the beach increases, small ripple marks appear, made as the tie moves over the beach.
Describe the seasonal changes at the beach:
Beach profiles show marked short term and seasonal changes. The sweep zone variation is often related to the type of waves involved.
In summer = profile steepens in calm swell conditions and pushes material up the beach
In winter = profile flattens in storm contains and material is ‘combed’ seaward
Describe the pebbles at the beach:
Material at the top of the beach is larger and this supports steeper, concave slopes. Beach cusps occur when this coarser material is absorbing wave swash. Beyond the foreshore, the most landward feature is the storm beach which will consist of larger pebbles. This forms only in the high energy conditions of a surge or a spring tide
What is a swash aligned coast?
Wave crests approach perpendicular to the coast, so there is limited LSD. Sediment doesn’t travel far along the beach. Wave refraction may reduce the speed of high energy waves, leading to the formation of a shingle beach = larger sediment
What is a drift aligned coast?
Waves approach at a significant angle, so LSD causes the sediment to travel far along the beach, which may lead to the formation of a spit. Generally, larger sediment is found at the start of the beach and weathered sediment moves further down through LSD, becoming smaller as it does = smaller sediment
What is a spit?
A long, narrow feature that extends from the mainland at the end of a drift aligned beach
How is a spit formed?
Process of LSD will move material along the coastline by prevailing wind. As the coastline change as direction, the finer material will continued to be transported out to sea. This will build up to develop a permanent feature. The material will not be able to extend across to meet the mainland due to the presence of river currents in the estuary. Wave refraction and a second dominant wind direction will force the material to move in a different direction resulting in a curved end.
How is a salt marsh formed?
As low energy waves enter the area behind the spit, finer silt and mud is deposited. This is then colonised by vegetation, becoming a salt marsh
What is a tombola?
Form in very similar ways to spits, but are unique in that they join the mainland to an offshore island via deposition
What is a famous example of a tombolo?
Angle road of Shordo Island, japan.
How do tombolos form?
They are formed when spits extend from the coast to an island. Alternatively, they may form in the ‘shadow’ of wave refraction caused by an offshore island
Why are tombolos connected to an island?
As they form as an accumulation that connects the mainland to an offshore island. Overtime, as sediment builds up, it creates land bridge that connects the island to the mainland, especially during low tide. The presence of calm water, and the right conditions for sediment deposition contribute
How do bars form?
When the waves approach a gently sloping coast, friction between the waves and the sea bed causes the waves to break at some distance from the coast. Over time, more materials are built up parallel to the coast to form ridges of sand which causes offshore bars.
A body of coastal water may be particularly or completely cut off from the open sea by a bar. The body of water is called a lagoon, these only form when the bar connects to headland on either side of a bay and is larger enough to be above the levels of the sea water
What is a barrier island?
A long, narrow island that runs parallel to the mainland and is separated from it by a shallow body of water, such as a lagoon
What is a barrier beach?
A barrier beach is a narrow strip of sand that runs parallel to the mainland and is separated from it by a beach berm
What are some examples of spits?
Hurst castle spit, Hampshire, UK
Minnesota Point, Duluth, USA
What are some examples of tombolos?
Lindisfarne, Northumberland, UK
Apostle Islands, Wisconsin, USA
What are some examples of barrier islands?
Scolt head island, Norfolk, UK
Padre Island, Eastern Texas
Examples of Barrier beaches?
Eastern Seaboard, USA
Cape Cod, Atlantic Coast
