Coastal landscapes

physical factors (landscapes)

hydraulic action

Hydraulic action is the sheer force of waves crashing against the shore and cliffs. The power of the waves forces air into cracks, compresses it and blows the rock apart as the pressure is released.

attrition

Attrition happens when rocks and pebbles carried by the waves smash into each other, wearing each other away and gradually becoming smaller, rounder and smoother.

abrasion

Abrasion (also called corrasion) is the process of rocks and pebbles carried by the waves wearing away rocks as they are thrown against cliffs.

solution

Solution (also called corrosion) is when chemicals in the seawater dissolve minerals in the rocks, causing them to break up.

cliffs

Cliffs usually form where there is harder more resistant rock such as limestone and chalk. This graphic shows the process of erosion that forms a cliff and wave-cut platform. Wave erosion is strongest where large waves break against the base of the cliff.

Cliff is undercut by wave erosion at its base.

A wave-cut notch forms and grows.

Eventually, the cliff becomes unsupported and collapses into the sea.

The cliff retreats and leaves behind a wave-cut platform, which is visible at low tide.

headlands and bays

Headlands and bays are created by differential erosion. Rocks along the coastline are formed in alternating bands of different rock types, e.g. sandstone and clay, which meet the coast at right angles.

caves, stacks and arches

All rocks have lines of weakness. The sea and its waves use hydraulic action, abrasion and solution to erode along any lines of weakness.

 These lines of weakness get enlarged and develop into small sea caves.

 The caves are deepened and widened on both sides of the headland until eventually the sea cuts through the headland, forming an arch.

 The rock at the top of the arch becomes unsupported as the arch is enlarged, eventually collapsing to form a stack.

 The stack gets eroded until only a stump remains.

 Over time the stump will disappear.

 As the headland retreats under this erosion, the gently sloping land at the foot of the retreating cliff is called a wave-cut platform.

longshore drift

A pebble or sand particle moves from point A to B, carried by the swash up the beach, the angle determined by the wave and wind direction.

It is then pulled down the beach from B to C, carried by gravity and the wave's backwash.

 This process is repeated over and over again and the particle moves along the shoreline. This process is called longshore drift.

spit

Spits form where the coastline changes direction and longshore drift continues to move material along the beach.

Longshore drift moves material along a beach in the direction of the prevailing wind.

When the coastline changes direction, longshore drift continues to deposit material in the sea, extending the line of the beach.

Over time the level of the sand deposited will build up until it is above sea level.

The beach appears to extend out into the sea and is known as a spit or sandspit.

Secondary wind and wave direction causes waves to strike the spit from a different direction.

This changes the line of the spit, giving it a curved or hooked end.

The spit creates an area of sheltered calmer water.

The flow of river water into the sea can prevent a spit developing right across an estuary.

The mixing of salt water fresh water and sediment carried into an estuary can form a salt marsh

.Sediment can build up to form dry land.

sandbar

A sandbar is formed when a spit extends across a bay from one headland to another.

Longshore drift moves sand out across the bay, forming a spit.

Where there is no river estuary or slow flow of water, the sand can be deposited faster than it is removed.

The deposited material eventually joins up with the other side of the bay and a strip of deposited sand blocks off the water in the bay from the sea.

This feature is called a sandbar and the area behind the newly formed bar is known as a lagoon.