OCR A Level Geography - Coastal Landscapes

System

System

set of interrelated objects comprising components and processes that are connected together to form a unified whole

Types of energy available to coastal landscape system

Kinetic

Potential

Thermal

Geomorphic Processes

Natural mechanisms of weathering, erosion and deposition that modify landforms

Open System

Energy and matter can be transferred from neighbouring systems as an input as well as to other neighbouring systems as an output.

Inputs to a coastal system

Kinetic energy from wind and waves

Thermal energy from heat of sun

Potential energy from position of material on slopes

Material from marine deposition, weathering and mass movement

Outputs from a coastal system

Marine and wind erosion from beaches and rock surfaces

Evaporation

Throughputs in a coastal landscape system

Stores e.g. beach and nearshore sediment accumulation

Flows e.g. longshore drift

Equilibrium

Rate of sediment accretion is equal to rate of sediment removal

When a systems inputs and outputs are equal

Dynamic equilibrium

when equilibrium is disturbed the system undergoes self-regulation changes in order to restore equilibrium.

Sediment Cell

Stretch of coastline and its associated nearshore area within the movement coarse sediment, shingle and sand is self-contained.

Example of sediment cell

River Thames

Why is it unlikely that sediment cells are completely closed?

Variations in wind direction and presence of tidal currents

Sub-cells within the major sediment cells

Milennia

Thousands of years

Aeolian

Wind

Wave height formula

0.36 square root of fetch

What three factors dictate the size and direction of a wave

Wind speed

Wind duration/fetch

Wind direction

Amount of energy in a wave in deep water.

P = H2T

Crest

Highest surface part of a wave.

Trough

Lowest part of a wave.

Wavelength

Horizontal distance between two adjacent crests or troughs.

Swell waves

waves generated in open oceans that can travel huge distances.

Storm waves

Locally generated waves with short wavelength, greater height and shorter wave period.

Spilling waves

Steep waves breaking onto gently sloping beaches

water spills gently forwards as the wave breaks

Plunging waves

Moderately steep waves breaking onto steep beaches

water plunges vertically downwards as crest curls over.

Surging waves

Low-angle waves breaking onto steep beaches

the wave slides forward and may not actually break.

How are waves created?

Frictional drag of winds over ocean surface

Wave frequency

Number of waves per minute

Process of wave break

Waves slow down as they encounter friction with sea floor

Wavelength decreases

Successive waves bunch up

Deepest part of wave slows down more than top

The wave begins to steepen as the crest advances ahead of the base

When water is less than 1.3x wave height, the wave breaks

Swash

Movement of a wave up the beach.

Backwash

Wave drawn back down the beach.

Constructive waves

Low in height

Low frequency 6-8 per minute

Spilling

Strong swash

Long wavelength means backwash returns to sea before next wave breaks so swash uninterrupted and retains energy

Swash energy > backwash

Destructive waves

Greater height

Shorter wavelength

Higher frequency 12-14 per minute

Plunging waves

Little forward transfer of energy

Swash energy < backwash

High energy waves (winter) impact on beach

Remove material from top of beach

Transport it to offshore zone

Reducing beach gradient

Low energy waves (summer) impact on beach profile

Build up beach face

Steepen profile

Tides

periodic rise and fall of the sea surface, produced by the gravitational pull of the moon and the sun.

Tidal range

Significant in development of coastal landscapes

In enclosed seas e.g. Mediterranean tidal ranges are low somwave action restricted to narrow area of land

Tidal range influences where wave action occurs

More spread out over bigger tidal range

Spring tides

When the moon and the sun align, creating the highest tides.

Neap tides

When the moon and the sun are at right angles to each other, so the gravitational pull is at its weakest so tidal range in low.

Lithology

Physical and chemical composition of rocks.

Clay lithology

Weak

Bonds between particles are weak

Basalt

Strong lithology

Dense interlocking crystals

Highly resistant

Chalk and Carboniferous limestone

Predominantly composed of calcium carbonate

Soluble in weak acids

Vulnerable to carbonation

Structure

Properties of individual rock types e.g. jointing bedding and faulting

Primary permeability

Pores that can absorb and store water.

Secondary permeability

Joints or faults in rocks.

Concordant Coastline

single geology that runs parallel to coast.

Discordant Coastline

Rocks lie at right angle to the coast.

Strata

Angle of dip of rocks.

Rip currents

Currents caused by tidal motion or waves breaking at right angles to the shore

Cellular circulation generated by differing wave heights parallel to the shore

Water from top of breaking waves with a large height travels further up shore and returns where lower wave heights have broken

Modify shore profile by creating cusps which help perpetuate rip currents - channeling flow through a narrow neck

Warm Ocean Currents

Currents that move from the equator to the poles and influence western-facing coastal areas

Driven by onshore winds , greater effect on coastal landscape systems

Ocean currents

Generated by earths rotation and convection

Set in motion by movement of winds

Severn eastuary tidal range

14m

Sub-aerial processes

weathering and mass movement

Why are currents significant?

Transfer of heat energy directly affects sub-aerial processes

Terrestrial Sources

Sediment derived from the erosion of inland areas by water, wind and as as well as sub-aerial processes of weathering and mass movement.