Section C- Physical landscapes in the UK -- Coasts (coastal processes)…
Section C- Physical landscapes in the UK -- Coasts (coastal processes)
Wave types and characteristics
strong swash and weak backwash
the strong swash brings sediments to build up the beach
the backwash is not strong enough to remove the sediment
the waves are low and further apart
weak swash (the water flowing towards the beach when a wave breaks) and strong backwash (the movement of water down the beach)
the strong backwash removes sediment (small fragments of rock and soil which form layers) from the beach
the waves are steep and close together
Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through)
Water enters cracks in the rock.
When temperatures drop, the water freezes and expands causing the crack to widen.
The ice melts and water makes its way deeper into the cracks.
The process repeats itself until the rock splits entirely.
Plants and animals can also have an effect on rocks. Roots burrow down, weakening the structure of the rock until it breaks away.
Plant roots can get into small cracks in the rock.
As the roots grow, the cracks become larger.
This causes small pieces of rock to break away.
Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.
Mass movement is the downhill movement of sediment that moves because of gravity. There are four different types of mass movement:
- Bits of rock fall off the cliff face, usually due to freeze-thaw weathering.
- Saturated soil (soil filled with water) flows down a slope.
- Large blocks of rock slide downhill.
Rotational slip -
Saturated soil slumps down a curved surface.
Erosion is the wearing away of rock along the coastline. Destructive waves are responsible for erosion on the coastline. There are four types of erosion:
Hydraulic action - this is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart.
Abrasion - this is when pebbles grind along a rock platform, much like sandpaper. Over time the rock becomes smooth.
Attrition - this is when rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded.
Solution - this is when sea water dissolves certain types of rocks. In the UK, chalk and limestone cliffs are prone to this type of erosion.
Beach material can be moved in four different ways. These are:
Solution - when minerals in rocks like chalk and limestone are dissolved in sea water and then carried in solution. The load is not visible.
Suspension - small particles such as silts and clays are suspended in the flow of the water.
Saltation – where small pieces of shingle or large sand grains are bounced along the sea bed.
Traction – where pebbles and larger material are rolled along the sea bed.
Sediment is carried by the waves along the coastline. The movement of the material is known as long shore drift. (movement of a material along a coast line due to the angled approach of waves)
Waves approach the coast at an angle because of the direction of prevailing wind. The swash will carry the material towards the beach at an angle. The backwash then flows back to the sea, down the slope of the beach. The process repeats itself along the coast in the zigzag movement.
When the sea loses energy, it drops the material it has been carrying. This is known as deposition. Deposition can occur on coastlines that have constructive waves.
Factors leading to deposition include:
waves starting to slow down and lose energy
sheltered areas, eg bays
little or no wind