Coasts Flashcards
PROCESSES OF EROSION (DORSET COAST)
Hydraulic action - When the sheer power of the waves crashes into the cliffs, compressing the air and cracking the cliff. Cracks become wider until pieces fall off.
Corrasion - Sand, shingle and pebbles that waves carry hurls against the base of the cliff, causing pieces to fall off.
Solution - Salt and other chemicals in the sea dissolve minerals in the rocks such as limestone and chalk.
Attrition - Rocks which have already been broken away from the coast collide with one another and the rock face becomes smaller and rounded
FORMATION OF A CLIFF
Cliffs are formed when the sea meets high land. The land is eroded by the waves and the processes of hydraulic action, corrasion and solution.
Cliffs begin to form when waves attack the base of the rock where the sea meets the highland. Processes of hydraulic action, corrasion and solution undercut the base of the cliff to form a wave cut notch (explain processes).
As waves continue to hit, the wave cut notch becomes wider and deeper until the rock above begins to crack.
Pieces of the rock eventually breaks off and once the overhang is no longer supported, it collapses into the sea due to weight. Freeze thaw weathering also takes place and speeds up the process. (explain)
The waves gradually move the fallen rock and begin to attack the new cliff face.
Over time the cliff face retreats inland leaving a gently sloping rock surface at the foot off the cliff called the wave cut platform.
FORMATION OF HEADLANDS AND BAYS
- Waves erode soft rock faster than hard rock.
A headland is an area of hard rock which juts out into the sea.
A bay is a sheltered area between the headlands.
Headlands form along coastlines where bands of hard and soft rock meet the coast at right angles.
Differential erosion occurs as the soft , less resistant rock such as clay is eroded much faster than the hard rock.
The soft rock is eroded faster by the processes of corrasion, solution than the hard rock forming a bay. (explain)
The harder rock is eroded slower by the process of hydraulic action, leaving the hard rock sticking out into the sea as a headland. (explain)
The exposed headland then becomes vulnerable to the force of destructive waves but shelters the adjacent bays from further erosion.
Beaches can then build up in the bays.
FORMATION OF CAVES, ARCHES, STACKS AND STUMPS
Once headlands and bays form the headlands made of hard rock, the receive the full fire of waves on both sides.
The waves pound against the weakest parts and causes cracks due to the processes of hydraulic action and corrasion. (explain)
In this time, cracks will be eroded more until a cave is formed.
Sometimes a blow hole will form within the cave due to compressed air being pushed upwards by the waves and vertical erosion occurs.
Waves continue to erode the inside of the cave through corrasion (explain) until it breaks through the back wall to form an arch.
The rock around the bottom of the arch is attacked and becomes wider.
The top of the arch is weekend by freeze thaw weathering. (explain)
Overtime, cracks appear and the roof will collapse leaving a tall pillar of rock seperated from the headland called a stack.
The force of the waves attack the stack at the base, undercutting it and eventually it will collapse to form a stump.
This repeats through ver and over until the headland is completely worn back and the coastline is straight again.
FORMATION OF A SAND SPIT
A sand spit is a low tide of sand or shingle which slowly extends from the shore when the coastline changes direction and is caused by longshore drift.
When the coastline changes direction, swash will continue to pick up sand and the backwash will deposit it in the open water as it runs out of energy. In time it deposits enough material for it to build up in the water.
By this process, a long narrow stretch of sand extends out into the open water forming a sand spit and is relatively unstable as it has no coastline to protect it.
Sometimes a hooked end develops if the wind and currents change direction. As waves can’t go beyond the spit, the area behind it is sheltered and mud flats and salt marches can form here due to the deposition of material.
WHAT IS THE PROCESS OF LONGSHORE DRIFT
This means that material is moved from the south west up the beach at an angle due to the prevailing wind by the swash and is then carried back down the beach at a right angle by the back wash at a right angle due to gravity. This is how sand and shingle is transferred along the beach.
FORMATION OF A SAND BAR
A sand bar is a barrier of sand stretching across a sheltered bay and joining one headland to another. Material is moved south west due to long shore drift. (explain)
When the coastline changes direction swash will continue to pick up sand and the backwash will deposit it in the open water as it runs out of energy, and in time it deposits enough material for it to build up above sea level.
By this process, a long narrow stretch of sand extends out into the open water forming a sand spit.
If a sand spit builds out into the bay, in time it might extend beyond the bay and join up with the beach on the other side. This is a sand bar.
The shallow stangnent water trapped behind it is called a lagoon. In time this will be filled in with wind blown depositors, be colonised by vegetation and eventually become dry land.
