Coasts - systems and processes

Systems

Groups of interrelated parts that work together by a driving process

Systems include

Inputs, outputs, flows and stores

What type of system is a coast

A natural, open system

Inputs

Material/energy moving into a system

Outputs

Material/energy moving out a system

Flows/transfers

Form in which material/energy moves between stores

Stores/components

Where material/energy is stored

Inputs of a coastal system

\-Energy from waves, wind, tides, sea currents

\-Sediment eroded from cliffs

\-Rivers carrying sediment

\-Geology of coastline

\-Sea level rise (can form estuaries)

Outputs of a coastal system

\-Sediment removed beyond local sediment cells

\-Accumulation of sediment above tidal limit

\-Dissipation of wave energy

Stores of a coastal system

\-Erosional landforms (cliffs, wave cut platforms, bays and headlands, caves, arches, stacks and stumps)

\-Depositional landforms (beaches, sand dunes, saltmarshes, mudflats, spits and bars)

Flows of a coastal system

\-Erosion

\-Weathering

\-Transportation

\-Deposition

Characteristics of a system

\-Structure that lies within a boundary

\-Function through inputs and outputs that can change size

\-Involves flow of material between stores

Properties within a boundary

\-Elements (things/substances)

\-Attributes (characteristics of elements)

\-Relationships (how elements and attributes work together)

Types of systems

\-Isolated

\-Closed

\-Open

Isolated system

\-No energy or matter can enter or leave

\-Eg. lab experiment

Closed system

\-Energy can enter and leave

\-Matter cannot enter or leave

\-Eg. Earth

Open system

\-Both energy and matter can enter and leave

\-Eg. coast

Dynamic equilibrium

\-When inputs and outputs are equal/balanced

\-No overall changes to the system

\-In reality, there are small variations in the inputs and outputs, but they are balanced on average

\-Large changes to the balance trigger feedbacks

Changes to dynamic equilibrium

Change in sea level, storm events, landslides etc can upset the balance

Positive feedback

\-Moves system further away from dynamic equilibrium (amplifies the change)

Negative feedback

\-Moves system back to dynamic equilibrium

Cascading systems

\-Systems interlinked by cycles and processes to keep the Earth system running

\-Includes hydrosphere, lithosphere, biosphere and atmosphere

What shapes coastlines

The processes operating in the system

High energy coastlines

\-High inputs of energy via large powerful waves

\-Have destructive waves

\-Strong prevailing winds and long fetch

\-Often have rocky landforms (caves, stacks, arches etc)

\-Rate of erosion higher than depostition

Low energy coastlines

\-Low inputs of energy through small gentle waves

\-Have constructive waves

\-Weak prevailing winds and short fetch

\-Often have saltmarshes, beaches and spits

\-Rate of deposition higher than erosion

Coast zones

\-Offshore

\-Inshore

\-Foreshore

\-Backshore

\-Nearshore

Offshore

\-Beyond the point where waves break

\-Deposition of sediments

\-Covered by low tide

Inshore

\-Where waves break and surge to land

\-Covered by low tide

Foreshore

\-Where many marine processes occur

\-Lies between low and high tide

Backshore

\-Limit of marine activity

\-Back of beach

\-Covered by high tide only

Nearshore

\-Cover inshore and foreshore area

Wind

\-Movement of air from higher to lower pressure

\-The greater the pressure gradient, the greater the wind speed

\-Wind speed determines wave types, which determines the amount of energy at a coast and the types of landforms made

\-Prevailing wind direction controls the direction that waves approach the coastline and therefore direction of longshore drift

Importance of wind as an energy input

\-Primary source of energy for other processes

\-Creates waves from frictional drag

\-Controls wave type

\-Controls direction of longshore drift

A primary source of energy for other processes

Wind

How does wind create waves

Wind transfers energy when blowing over the sea surface (frictional drag)

\-Energy of a wave is dependent on the strength of wind, duration and fetch

Fetch

\-Distance of water where wind blows over

\-Determines size and energy of waves

High wind speeds make what type of wave

Destructive (erosion)

Low wind speeds make what type of wave

Constructive (deposition)

What causes waves

Winds

Waves

Undulations on the surface of the sea, driven by wind

Factors affecting wave energy

\-Wind strength

\-Duration

\-Fetch

Large waves need what 3 factors

\-High wind strength

\-Long duration

\-Long fetch

Features of waves

\-Trough (bottom of wave)

\-Crest (top of wave)

How a wave forms

\-Wave enters shallow water

\-Friction with seabed increases

\-Wave slows and

Swash

Water washing up the beach

Backwash

Water washing back towards the sea

Types of waves

Constructive and destructive

Constructive waves

\-Low frequency (6-8 per min)

\-Low height

\-Long length (100m)

\-Break as a gentle spill

\-Strong swash (deposition)

\-Weak backwash

\-Steepens beach

\-Deposition > erosion

Destructive waves

\-High frequency (10-14 per min)

\-Tall height

\-Short length

\-Break as an aggressive plunge

\-Weak swash

\-Strong backwash (erosion)

\-Flatterns beach

\-Erosion > deposition

Wave refraction

\-Waves breaking onto an irregularly shaped coastline (eg. headland and 2 bays)


1. Waves drag in shallow water approaching a headland
2. Wave becomes high and steep
3. Wave bends
4. Low energy wave spills into bays as much of wave energy is concentrated on the headland

Tides

\-Periodic rise and fall of sea level, caused by the gravitational pull of the moon and sun

\-The moon pulls water towards it, creating a high tide on opposite sides of the Earth (the areas between it have the lowest tides)

\-As the moon orbits Earth, the high tide follows it

Tidal range

\-Difference in water level of high and low tide

\-Affects position at which waves break on beach

\-Determines upper and lower limits of erosion and deposition

\-Determines amount of time cliffs are exposed to sub-ariel weathering

Spring tides

\-Large tidal range

\-High high and low low tides

\-Created when moon, Earth and sun are in a straight line

Neap tides

\-Small tidal range

\-Low high and high low tides

\-Created when moon, Earth and sun are at a 90 degree angle to eachother

Where are most landforms created and destroyed

Area of land between maximum high tide and minimum low tide

Storm surge

\-Abnormal rise in sea level during a storm

\-Measured how much taller above normal tide

\-Significant erosion occurs if a surge occurs with a spring tide

Causes of a storm surge

\-Storm winds pushing more water onshore with larger waves

\-Intense low pressure storm raises height of sea level

Currents

\-Permanent/seasonal movement of water in one direction

\-Includes upwelling, oceans, rip and longshore currents

Upwelling currents

\-Wind blows across the sea surface and pushes water away

\-Colder water rises up from beneath the surface to replace the water pushed away

\-Forms part of the global ocean circulation currents (key part of regulating climate and heat)

Ocean currents

\-Gyres formed by global wind patterns and forces from Earth’s rotation

\-Wind drags on the sea’s surface making the water move in the same direction

\-The Earth’s rotation provides the Coriolis effect and also changes the direction of the currents

\-Continents form boundaries, influencing the size of the gyres

Gyre

Large system of circular ocean currents

Rip currents

\-Strong movement of water moving away from the shore

\-Develop when sea water is piled up along the coast by incoming waves

Longshore currents

\-Waves approach the coastline at an angle, generating a flow of water running parallel to the shore

\-Moves water along the surf zone and transports sediment parallel to the shore

\-Determined by the prevailing winds direction

Sediment cells

\-Lengths of coastline bordered by 2 prominent headlands

\-Movement of sediment is mostly self-contained (sediment doesn’t move between cells)

\-Processes in one cell don’t affect another cell (closed system)

\-11 in England and Wales

What system is a sediment cell

Closed (however sediment can be lost as output during stormy weather)

Sediment budget

\-Balance between sediment entering and leaving the system

\-System is in dynamic equilibrium when the balance is equal

Positive sediment budget

\-More sediment enters the system

\-Coastline builds outwards

Negative sediment budget

\-More sediment leaves the system

\-Coastline retreats

Coastal processes

\-Weathering

\-Mass movement

\-Erosion

\-Transportation

\-Deposition

Weathering

\-The break down of material in situ

\-Makes cliffs more vulnerable to erosion as they are weakened

Freeze-thaw weathering

\-Type of mechanical weathering

\-Occurs in places where temperatures fluctuate above and below freezing

\-Water enters a crack

\-When temps go below freezing, the water freezes and expands

\-This puts pressure on the rock and this repeated, causes pieces to fall off

Salt weathering

\-Type of mechanical weathering

\-Salty sea water enters cracks in rocks

\-When the water evaporates, salt crystals are left behind

\-The crystals expand and put pressure on the rock, causing pieces to fall off

Chemical weathering

\-Breakdown of rock by changing its chemical composition

\-Includes oxidation, hydrolysis and carbonation

Oxidation

\-Type of chemical weathering

\-Oxygen reacts with rocks to form a powder

Hydrolysis

\-Type of chemical weathering

\-Acidic water reacts with rocks, creating weak clays

Carbonation

\-Type of chemical weathering

\-Carbon dioxide dissolved in rainwater makes a weak carbonic acid, which reacts with rocks containing calcium carbonate (limestone), dissolving it

Biological weathering

\-Burrowing animals can weaken cliffs (eg. rabbits and birds)

\-Plant roots can grow into rock cracks and expand them

Mass movement

\-The downhill movement of material under the influence of gravity

\-More likely to occur when cliffs are undercut by wave action (causes an unsupported overhang

\-Includes soil creep, slumping, mudflows, rockfalls and landslides

Soil creep/solifluction

\-Type of mass movement

\-Very slow, continuous movements of soil particles downslope

Slumping/rotational slip

\-Type of mass movement

\-Soft, permeable material overlies hard, impermeable rock

\-Rain saturates the slip plane, causing a rotation of a concave soft rock

Mudflow

\-Type of mass movement

\-Heavy rain causes fine material to flow downhill

\-Soil becomes saturated and excess water cannot percolate, so the surface becomes fluid and flows

Rockfall

\-Type of mass movement

\-Rocks break away from the cliff face and fall since they are weakened through mechanical weathering

Landslides

\-Type of mass movement

\-Straight cliff of softer rocks slips due to heavy rainfall saturating and reducing friction between planes

Factors affecting nature of mass movement

\-Geology (permeable rock overlying impermeable rock means water can only infiltrate into the first layer, making it heavier)

\-Slope angle (a steeper slope puts more stress on the rocks)

\-Rainfall (more saturated ground makes heavier planes and reduces friction, making them more likely to slip)

\-Temperature (prior freeze-thaw makes rocks weak)

\-Type of material (unconsolidated rock has little friction between particles and so have lower levels of cohesion, making them more prone to collapse)

Erosion

The wearing away of land surfaces and removal by water

Types of erosion

\-Hydraulic action

\-Wave quarrying

\-Cavitation

\-Abrasion/corrasion

\-Attrition

\-Solution/corrosion

Hydraulic action

\-Type of erosion

\-Waves that break at the foot of a cliff compress air in the cracks

\-The pressure builds up and breaks pieces off

Wave quarrying

\-Type of erosion

\-The intense energy and force of a wave is large enough to remove chunks of rock through vibrations

Cavitation

\-Type of erosion

\-As waves retreat, the compressed air violently expands, putting pressure onto rock and making pieces fall off

Abrasion/corrasion

\-Type of erosion

\-Small rocks transported by waves, smash and grind against cliffs, breaking bits off and smoothing the surfaces

Attrition

\-Type of erosion

\-Rocks smash against each other in the sea and break into smaller, rounder pieces

Solution/corrosion

\-Type of erosion

\-Weak acids in the seawater gradually dissolve and erode soluble rocks

Factors affecting rate of erosion

\-Geology (quicker with soft rocks)

\-Rock structure (concordant coastlines have same rate, discordant is different)

\-Sea depth (bigger waves at smaller depths)

\-Size of fetch (bigger fetch = bigger waves)

\-Beach presence (friction slows waves down)

\-Wave height (taller waves = more area of cliff face eroded)

Transportation

\-Movement of eroded material

\-Includes traction, saltation, suspension, solution and longshore drift

Traction

\-Type of transportation

\-Large boulders are pushed along the sea bed by the force of the water (they are too heavy to be picked up)

\-In high energy environments

Saltation

\-Type of transportation

\-Large particles/small stones bounce along the sea bed (they are too heavy to flow in the water)

Suspension

\-Type of transportation

\-Fine material (eg. sand and clay) is whipped up by turbulence and carried along in the water

\-Can cause a murky sea appearance

\-Most eroded material is transported this way

Solution

\-Type of transportation

\-Dissolved materials are carried within the moving water

Longshore drift/littoral drift

\-Type of transportation

\-Occurs when waves approach the shore at a 90 degree angle

\-The swash carries sediment up the beach in the same direction of the prevailing wind

\-The backwash carries the sediment back down at the steepest gradient (perpendicular to the shore, a right angle)

\-This zigzag pattern moves sediment along the shoreline

\-Material thats carried further is smaller and rounder (more attrition and abrasion)

\-Groynes interfere with the drift and sediments accumulates on one side

Deposition

\-Material being transported is dropped on the coast

\-Marine is deposition by seawater

\-Aeolian is deposition by wind

\-Occurs when sediment load exceeds carrying ability of wind or water