Coastal Deposition Key idea: Distinctive landforms result from different processes. NT page 154 – 155 CGP pg 67
Landforms resulting from deposition –
To describe and explain the characteristics and formation of:-
Beaches are usually found in sheltered bays between two headlands. The headlands protect the area from erosion.
Low constructive waves deposit material on the shore and gradually a beach builds up.
Beaches may be of sand or shingle
Beach material is usually well sorted – most is of a similar size.
The larger the material is, the steeper the beach. Shingle and pebble beaches area steeper than sand beaches
At the top of the beach there may be a steep ridge where larger material has been thrown during storms .
Beach : a zone of deposited sand and shingle above the low water mark Processes : Constructive waves Destructive waves Deposition Transportation Longshore drift Sediment grading Words to use: storm beach gradient sand shingle swash backwash
A spit is a long, narrow accumulation of sand or shingle, with one end attached to the land and the other sticking out at a narrow angle either into the sea or across a river estuary.
Conditions that favour the formation of spits:
The sea must be relatively shallow
There must be a good supply of sand
Waves must approach the beach at an angle
The sea must be fairly calm with constructive waves
Many spits have a hooked or curved end
They form where longshore drift moves large amounts of sand and shingle along the coast and where the coastline suddenly changes direction to leave a shallow, sheltered area of water
Spits become permanent when sand is blown up the beach to form sand dunes
Salt marsh is likely to develop in the sheltered water behind the spit
The spit is unable to grow across the estuary as the river current carries material out to sea
If there is no river the spit may grow across the bay to form a bar.
The Formation of a Spit The processes of long shore drift and deposition combine to form coastal spits.
Spurn Head Spurn Head Spit is a example of a spit on the east coast near Hull.
Spit : a long, narrow accumulation of sand or shingle formed by longshore drift with one end attached to the land Examples: Dawlish Warren (below),Spurn Head, Orford Ness, Blakeney Point Processes: Longshore drift Transportation Deposition Words to use: Hooked end Direction of longshore drift Prevailing winds Change in coastline direction/estuary Second dominant wind direction beach Stabilised shingle and sand saltmarsh dunes Zig zag movement Silt and mud accumulates
Bars are ridges of sand and other material that run roughly parallel to the coast.
They block off river mouths and bays
Water dammed up behind a bar is a lagoon
Lagoons may become filled in by sediment from waves breaking over the bar or from stream flowing into the lagoon
Bar and lagoon: a spit linking two headlands and trapping water on the landward side such as at Slapton Ley in Devon (below) Processes: Longshore drift Transportation Deposition Words to use: bay headland bar lagoon brackish silting and infilling beach Direction of longshore drift
Your turn …
Explain how a beach forms and mention why the formation of a beach depend upon constructive waves
Why does the material on a beach affect its gradient?
Explain how longshore drift may lead to the formation of a spit
Locate three spits on the shoreline of Britain. Produce a well anotated photograph for each one, describing the location of the spit, the direction of longshore drift and note any other characteristic features. (Spurn Head, Dawlish Warren, Blakeney Point, Hengistbury Head)
Explain why bars may be temporary coastal features.