Coastal Landscapes

OCR A Level Geography

Coast

Narrow zone of land where the sea influences geomorphology (shape) of the land

Systems

Set of interconnected components (stores) and processes (links/flows) which form a working unit.

Components of a System

Inputs, Processes (Stores & Flows), Outputs

Examples of a System

Digestive, Battery, Circulatory

Types of Systems

Open, Closed, Isolated

What is transferred in systems?

Energy and Matter

Inputs in Coastal Systems

Thermal Energy, Kinetic Energy, Potential Energy, Fluvial Sediment, Material from weathering, erosion and mass movement.

Stores in Coastal Systems

Beaches, Cliffs, Sand Dunes, Bars, Spits

Transfers/Flows in Coastal Systems

Long-shore Drift, Transportation Processes, Wind, Mass Movement

Outputs in Coastal Systems

Evaporation, Material blown/transported by sea

Open System

Matter and energy can freely enter/exit

Closed system

Only energy can enter/exit

Isolated system

No energy or matter can enter/exit

Equilibrium

The rate of input and output are the same.

Dynamic Equilibrium

When equilibrium is disturbed, the system will try to counteract the change.

Negative Feedback

Changes in a system causes processes that reduce the initial change to maintain stability.

Positive Feedback

Process where an initial change will be amplified and cause greater change.

Sediment Cell

11 self contained zones of coast around England and Wales where sand cannot enter or leave.

Sub-cell

A particular section of a sediment cell.

Littoral Zone

Area of the coast that can be affected by coastal action

4 Parts of Littoral Zone

Back shore, Foreshore, In shore, Offshore

Backshore

Area between the high water mark and the limit of marine activity. Limited activity.

Foreshore

Area between the high and low water mark. Most marine activity.

Inshore

Area below the low water mark and the point where the waves stop impacting the land around them. Limited activity

Offshore

Area beyond the point where waves cease to impact seabeds or land, and activity is limited to deposition of sediment. Almost no activity.

Nearshore

Foreshore and Inshore

Fetch

Distance the wind has blown for

Factors affecting wave size

Fetch, Time the wind has blown, Strength of wind

Direction of Travel

The direction the wave is moving

Wave Height

The distance between a wave peak and trough

Wave Length

Distance between two wave peaks

Wave Crest/Peak

The highest point of a wave

Wave Trough

The lowest point of a wave

Calm Water Mark

Water level when calm/at rest.

Constructive Wave

Low height, Long wavelength, Strong swash, Weak backwash, Gentle break

Destructive Wave

Tall, Short wavelength, Weak swash, Strong backwash, Violent break

Effect of constructive waves

Deposition of sediment. Gentle, sloped beach.

Effect of destructive waves

Erosion of sediment. Steep beach. Formation of off shore bars.

Ocean current

Continuous, predictable, directional movement of seawater

Causes of ocean currents

Sea temperature, Wind, Salinity

Driver of Near Surface Currents

Winds

Driver of Deep Water Currents

Difference in water’s density, controlled by temperature and salinity

Formation of Deep Water Currents (polar)

1. Very cold conditions means sea ice forms - Salt is left behind

2. Surrounding water gets saltier and so is more dense - It sinks.

3. The water sinks, and surrounding warmer water is pulled in to replace it - Experiences the same thing

4. Causes deep ocean currents driving the global conveyor belt.

Effect of ocean currents on geomorphological processes

Limited impact. Transfer of heat can be significant - Directly impacts sub aerial processes and air temperature

Wind

Source of energy for coastal erosion and sediment transport. 

Effect of wind

Significant. Impacts inputs and processes in coasts. E.g. erosion and transportation.

Energy of a wave equation

P=H² T

Factors influencing geomorphology

• Winds - Speed, height, fetch, frequency

• Wave type

• Tides - Cycles, range

• Geology - Lithology and strucutre

• Currents - Global patterns

Spacial variation

Factors impact different places on the coast differently.

Temporal variation

Factors change over time and impact the coast differently long/short term.

Tides

Alternating rising and falling of the sea - Usually twice a day at a particular place.

Tidal range

Vertical difference between high and low tide.

Impact of low tidal range

Wave action is restricted to a narrow area of land - Concentrated

Impact of high tidal range

Wave action impacts a wide area.

Temporal variation in tides

2 spring tides (weakest) and 2 neap tides (strongest) a month.

Lithology

Chemical and physcial composition, and strength

Structure

Arrangement of rocks on the coastline or a cliff profile

Rocks (ordered from most to least resistant)

Granite, Basalt, Limestone, Sandstone, Chalk, Shale, Clay

Weak lithology

Little resistance to erosion, weathering and mass movement.

Strong lithology

Highly resistant to erosion. Prominent features (Cliffs and headlands)

Concordant coastline

Layers or rock are parallel to the coastline, forming straighter coastline.

Disconcordant coastline

Layers of rock are perpendicular to the coastline.

Effects of disconcordant coastline

Differential rates of erosion between bands of rock, forming headlands and bays.

Seaward bedded strata

Strata dip towards the sea, so loose material slides down easily. Forms gentle cliff profiles.

Landward bedded strata

Strata dips towards the land, so it’s more resistant to erosion. Steep cliffs.

Horizontally bedded strata

Steep vertical cliffs. Erosion in the form of undercutting, leading to vertical rockfall.

Decay of rock

Chemical reactions between moisture and minerals in rocks, altering chemical or physical composition

Van’t Hoff’s Law

An increase by 10C leads to 2.5x the rate of chemical weathering (up to 600C)

Best conditions for chemical weathering

Warm, moist such as rainforests

Worst conditions for chemical weathering

Cold, polar climates

Oxidation

Reaction between oxygen in water/air. Iron becomes soluble and original rock structure collapses.

Carbonation

CO₂ + Rainwater forms weak carbonic acid, reacting with CaCO₃ in limestone to produce soluble substances.

Solution

Dissolving of some salts in water

Hydrolysis

Reaction between minerals and water. Felspar in granite reacts with hydrogen to form China clay.

Chelation

Effect of organic acids from humus or microorganism secretions on rocks. Increases rates of hydrolysis and carbonation.

Freeze thaw weathering

Stresses from repeated cycles of freezing water

Steps of freeze thaw weathering

1. Water collects into cracks, faults and joints

2. Temperatures reach sub zero, causing the water to freeze and expand by 9%.

3. The cracks expand slightly.

4. The ice melts, and even more water collects in the cracks.

Factors increasing freeze thaw weathering

• Porosity of rocks

• Rapid freezing (Temps <5C)

• Frequent freeze thaw cycles

Insolation weathering

Expansion and contraction due to extreme variations in temperature, like in deserts.

Steps of insolation weathering

• Rocks are poor conductors of heat, so only the top layers heat up and experience stress

• Exfoliation occurs - Top layers flake off.

• Rocks with different colours experience differential rates of heating, so granular disintegration.

Pressure release

• Rocks on top of others are eroded away by other processes, releasing pressure on them

• The rock expands, causing them to crack, making it vulnerable to weathering.

• Large sheets of rock can detach.

Salt weathering

High amounts of salt crystallises in hot, dry environments. Causes stresses on rocks (widening cracks) or man made objects like bridges.

Hydration

Expansion of minerals due to water absorption.

Example of hydration

Crystal clay structure, so water is easily absorbed. Constant wetting/drying causes stress, making it break and disintegrate so it can be eroded.

Rockfall

Fragments of rock breaking away from a cliff face

Mudflow

Saturated soil and weak rock flows down a slope

Landslide

Blocks of rock slide downhill

Rotational Slip

Slump of saturated soil or rock along a curved surface.

Rockfall angles

Steeper angle (80/90) - Harder drops, more scree and sediment.

Significance of rockfall angles on coastal land forms

Not too significant - Slight increase in action like pounding, or increased sediment

Pounding

Mass of the breaking waves exerts pressure on rocks, causing it to weaken

Factors affecting weathering

Climate, rock characteristics and vegetation

Clastic material

unconsolidated material formed in rocks.

Formation of wave cut platforms

1. Destructive waves break repeatedly at the foot of the cliff.

2. Undercutting occurs in the foreshore region, forming a wave cut notch.

3. The notch increases in size due to erosion, eventually causing collapse since the column above has no support.

4. Overtime, undercutting and wave action causes further retreat, making it steeper.

Wave refraction

Waves changing direction as they travel from deeper to shallower water.

Orthogonals 

Lines drawn on wave crests, showing direction of wave energy. 

Waves on headlands

Waves curve towards headlands due to shallower water. Energy focused on one spot.

Waves on bays

Waves diverge, energy dissipates and deposition occurs.