Coastal Processes
Waves and wave types
Size and energy of waves depends on: the fetch (how far the wind has travelled), strength of the wind, how long the wind has been blowing for.
The water that rushes up the beach is known as the swash. The water that flows back towards the sea is known as the backwash.
Destructive waves
weak swash, strong backwash
strong backwash removes sediment from the beach
waves are steep and close together
tall waves with short wavelength
high frequency
Constructive waves
small waves, low wave height, long wavelength
occurs in calm conditions without much wind
strong swash, weak backwash
strong swash brings sediment and builds up the beach
backwash isn't strong enough to remove sediment
waves are low and further apart
Types of weathering
Exposed rocks along the coastline can be broken down by the processes of weathering
Freeze-thaw weathering
occurs when rocks are porous (contain holes) or permeable (allows water to pass through it)
- water enters cracks, 2. when temperature drops, the water freezes and expands causing the rock to widen, 3. ice melts and goes further in, 4. process repeats until the rock is fully split.
Biological weathering
- plant roots can get into small cracks in the rocks, 2. as the plants grow, the cracks become larger, 3. causes small pieces of rock to break away.
Chemical weathering
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
Types of mass movements
Mass movement is the downhill movement of sediment that moves because of gravity.
Rockfall
bits of rock fall off the cliff face, usually due to freeze-thaw weathering
Mudflow
saturated soil (soil filled with water) flows down a slope
Landslide
large blocks of rock slide downhill
Rotational slip
saturated soil slump down a curved surface
Erosion
It's the wearing away of rock along the coastline.
Hydraulic action
sheer power of the waves as they smash against the cliff
air gets trapped in the cracks in the rock and causes the rock to break apart
Abrasion
when pebbles grind along a rock platform, like sandpaper
over time the rock becomes smooth
Attrition
when rocks that the sea carries knock against each other
they break apart and become smaller and more rounded
Solution
when sea water dissolves certain types of rock
occurs in stormy conditions
Transportation
The movement of sediment carried along the coastline is longshore drift.
Longshore drift
waves approach the coastline at an angle because of the direction of the prevailing wind
the swash carries the material towards the beach at an angle
the backwash then flows back to the sea
the process repeats itself along the beach in a zigzag movement
Solution
when minerals in rocks are dissolved in sea water and then carried in solution
the load is not visible
Suspension
small particles are suspended in the flow of the water
Saltation
where small pieces of shingle bounce along the sea bed
Traction
where pebbles and larger material are rolled along the sea bed