Coasts

Question 1

Explain hydraulic action, abrasion, attrition and solution

Answer 1

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.

Question 2

describe what long shore drift is

Answer 2

Transportation of particles along a coastline is influenced by the strength of waves and the angle at which the waves strike the shoreline. This is determined by the direction from which the prevailing wind blows:

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.

Question 3

explain the formation of caves, arches, stacks and stumps

Answer 3

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.

Question 4

explain the formation of headlands, bays, sand bars and spits

Answer 4

Headlands and bays are created by differential erosion, where rocks along the coastline are formed in alternating bands of different rock types, eg sandstone and clay, which meet the coast at right angles.
Clay is a softer rock than the sandstone so is eroded more quickly - the softer rocks erode backwards faster, to form sheltered bays (which may have beaches).
The harder sandstone areas are more resistant to erosion and jut out into the sea to form exposed headlands.

Spits form where the coastline changes direction and longshore drift continues to move material along the beach.
Longshore drift will deposit material in the sea after the coastline has changed direction.
Over time the level of the sand deposited will build-up until it is above sea level.
The spit cannot develop right across the bay as a river’s estuary prevents the build-up of sand.
Sand spits often have a curved or hooked end. This is created when secondary wind and wave direction causes waves to strike from a different direction.
The beach therefore appears to extend out into the sea and is known as a spit or sandspit.
The spit creates an area of calmer water, sheltered by the spit. A lagoon, salt marsh and finally dry land can develop in this sheltered area.