Coasts Flashcards
What determines the waves energy?
The length of fetch, the strength of the wind, and the length of time over which the wind has blown.
What is a Coast line?
A coastline is where the sea and the land meet. They constantly change due to the action of the sea weather and humans.
Definition of ‘a constructive wave’
A wave that has a greater swash than backwash
Definition of ‘length of fetch’
The distance over which the wind has blown across the surface of the sea
Definition of ‘swash’
The transfer of a waves energy up the beach
Definition of ‘destructive wave’
A wave that has a greater backwash than swash.
Definition of ‘backwash’
Transfer of a waves energy down the beach
Definition of ‘wave’
The movement of the wind across the surface of the sea.
How are waves formed?
Waves are a result of the wind blowing over the sea. As they approach land the break. The bottom of the wave touches the sand and slows down due to increased friction. The top of the wave becomes higher and steeper until it topples over.
Name the two dominant processes of coastal erosion
Hydraulic action
Abrasion
Definition of ‘hydraulic action’
This process involves the force of water against the coast. The waves enter faults in the coastline and compress the air within the crack. When the wave retreats the air in the crack expands quickly causing a minor explosion. This process is repeated continuously.
Definition of ‘abrasion’
This is the process by which the coast is worn down by materials carried by the waves. Waves throw this sediment against the rock, sometimes at high velocity.
What are the 4 processes of transportation?
Traction - this is when large boulders are rolled along the sea bed.
Saltation - this is when smaller boulders are bounced along.
Suspension- this is when sand grains are carried along.
Solution - when a material dissolves into the sea to form a solution.
What are sub-aerial processes?
Weathering and mass movement.
Definition of ‘mass movement’
This is when rain water seeps through the land and saturates it. It can no longer hold its shape due to gravity and landslides occur. Holbeck hall in Scarborough is an example of this. This especially happens in areas of softer rock such as Boulder clay.
Definition of ‘ freeze thaw weathering’
Water finds its way into cracks in the rock. It then freezes and expands by 8-10% over night. This process is repeated over and over again putting pressure on the cracks in the rock. This is a slow process that can take many years.
Definition of ‘biological weathering’
Plant roots get into tiny cracks in rocks. As the roots push their way upwards to the surface of the rock, they force open the cracks further. This causes small pieces of the rock to break away. The roots can rot and leach out acids that can further weather the rock.
Definition of ‘chemical weathering’
Chemical weather is the dissolving of rocks caused by acid rain. Rainfall is slightly acidic due to the presence of carbon dioxide in our atmosphere. As it falls the the ground it reacts with the metal carbonates with rocks and slowly dissolves them. This causes a weak carbonic acid. Limestone is particularly prone to this type of weathering as it is an alkaline rock.
What coastal features are created by erosion?
Headlands and bays
Wave cut platforms
Caves, arches, stacks, and stumps
How are Headland and Bays created?
Waves erode the softer rock more quickly than the hard rock via abrasion. This is when the sea throws sediment against the coastline. A bay is formed in the softer rock such as clay. Beaches are formed in the bay’s due to constructive waves found there. An example is Selwick Bay at Flamborough Head in East Yorkshire.
How are wave cut platforms created?
Destructive waves hurl sediment at the base of the cliff undercutting it - this is abrasion. A wave cut notch is formed, making the cliff unstable. The wave cut notch grows and eventually the cliff collapses due to gravity. The backwash carries the rubble towards the sea forming a wave-cut platform. The process repeats and the cliff continues to retreat.
How is a stump formed?
Lines of weakness such as faults occur ing the headland.
Abrasion and hydraulic action erode the fault to from a cave.
The cave is widened an depend.
The sea cuts through the cave to form an arch.
The roof of the arch becomes too heavy and collapses.
Part of the former cliff is now isolated as a stack.
Over time the stack is undercut and collapses.
A stump is the remains of the eroded stack.
An example of this is in Selwick Bay at Flamborough in East Yorkshire.
Why is the Holderness coastline European fastest eroding coastline?
Because it is made out of Boulder clay which was deposited after the ice age.
Definition of ‘long shore drift (LSD)’
Longshore drift involves the zigzag movement of eroded material along a coastline. Waves approach a coast at a 45* angle and erode away part of the coastline. However the backwash transports material away from it at a 90* angle. The next waves then transports this material along the coast. Material is deposited when the seas energy is slowed down for example at a river entering the sea. It then deposited the material building a spit.
How are beaches formed?
The beach is the gently sloping area between the high and low tide. Beaches constantly change as sand, pebbles, and shingle keep being moved on and replaced by new material. Material forming a beach are carried by LSD. When the coastline becomes more sheltered, for example in a bay, constructive waves are more likely to occur. These waves have a greater swash which means that material accumulates over time and builds up a beach.
Give an example of a spit.
Spurn Head
How is a spit formed?
Spots are created by LSD. When the sea is slowed down, for example where it meets a river, deposition takes place. This extends out from the land. Fresh water and sea water are trapped behind the spit and marshes grow here. As the spit extends into deeper water, the end of the spit is affected by strong winds and it may curve.
What is a bar?
If a spit joins one part of the mainland to another it is called a bar.
What is a tombolo?
A spit connecting an island to the mainland e.g chesil beach, Dorset.
Definition of ‘hard engineering’
Man made
Definition of ‘soft engineering’
Natural
Name 6 hard engineering coastal defence methods
Sea wall Groynes Rock armour Offshore breakwater Revetments Gambions