2.2. Coastal landforms of cliffed and constructive coasts Flashcards
Define cliff profiles
- the shape of a cliff cross-section is known as the profile
- they owe their form to geology, sub-aerial processes and wave energy along a given stretch of coastline
What do variations in cliff profiles reflect?
- Rock type and resistance to erosion
- Presence of lines of weakness
- Coastal structure
- Whether cliff is active/inactive (eroded/not)
Define composite/complex cliff
Cliffs composed of more than one rock type
Define geo
A widened crack or inlet
Factors influencing cliff form
- Sub-aerial processes of weathering and mass movement.
- Lithology and rock structure
- Isostatic (geology gravitational equilibrium between the earth’s lithosphere and asthenosphere) and eustatic (sea level changes due to an alteration in the volume of water or shape of ocean basin) changes
- Human activity
Define bay
An indented area of land normally found between two headlands. Bays are usually more sheltered so there is less erosive power, meaning you often find beaches in bays.
Define headland
A piece of land that sticks out into the sea
How do bay and headlands form?
They are formed when you get alternate layers of hard and soft rock. The sea is able to erode the soft rock a lot quicker than the hard rock making a bay. The harder rock forms a headland.
Process of coastal erosion
- Large crack opened up by hydraulic action
- The crack grows into a cave by hydraulic action and abrasion
- The cave becomes bigger and breaks through the headland forming a natural arch
- The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
- The stack will be attacked at the base. This weakens the structure and it will eventually collapseto form a stump.
Formation of wave cut platforms
- High steep wave breaks at the foot of a cliff. Hydraulic action and abrasion erodes a weakness in the rock at the base of the cliff to form a wave-cut notch
- The continual undercutting increases the size of the wave cut notch which increases the stress and tension in the cliff. The cliff eventually collapses leaving boulders at the base
- As these processes are repeated, the cliff eventually retreats leaving a wave cut platform
- Wavecut platform cannot exceed 0.5km in width as the waves break too far away from the cliff
Influence of dip of strataq
- Strata dipping inland -> relatively stable
- Strata dipping to sea -> relatively unstable
- Impermeable layers over permeable -> stable
- Permeable layers over impermeable -> unstable
Define shore platform
a rock shelf fringing the coastline between the low and high water marks
3 types of rocky shoreline
- Sloping shore platform
- Sub-horizontal shore platform
- Punging cliff
Bevelled cliff
- A form of composite cliff
- Vertical cliff was formed due to marine processes in the last interglacial period (warm) when sea levels were higher than they are today
- During the subsequent glacial phase (cold), sea levels dropped => freeze thaw affected the former sea cliff, forming a bevelled age
- When the sea level rose again during the following warm period, there was renewed wave erosion which removes the debris and steepens the base of the cliff leaving the upper part at a lower angle
2 types of coastline
- Swash aligned coasts:
- are orientated parallel to the crests of the prevailing waves.
- They are closed systems in terms of longshore drift transport and net littoral drift is 0
- Drift-aligned coasts:
- are orientated obliquely to the crest of the prevailing waves.
- The shoreline of a drift-aligned coast is primarily controlled by longshore sediment transport processes.
- Drift-aligned coasts are open systems in terms of longshore transport. Spits, bars, tombolos are features of this coast