Geography Paper 1 Coasts

coastal landscape systems

Open System

energy and matter can be transferred between neighbouring systems as inputs and outputs

Closed System

there are no inputs and outputs and matter and energy cant be transferred between systems

Inputs of coasts

Kinetic energy from wind/waves

Thermal energy from the sun

Potential energy from position of matter on slopes

Material from mass movement weathering and deposition

Outputs of coasts

marine/wind erosion from beaches/rock

evaporation

Throughputs of coasts

Stores like beaches and nearshore sediment

Flows such as longshore drift

Dynamic Equilibrium

When a system self regulates to restore equal inputs and outputs using negative feedback

Sediment cells

A stretch of coastline that has movement of sediment, sand and shingle within it

Features of sediment cells

• 11 large cells in England/Wales

• Boundaries are determined by topography and coastline shape

• Closed systems

• Wind and currents transfer materials between cells

Spatial Impacts

From place to place

Temporal Impacts

Over Time

Where does wave energy come from?

Generated by frictional drag of wind across ocean

What do high winds cause?

• Longer fetch

• Larger Waves

• More wave energy

What does win carry out?

• Aeolian processes

• erosion, transportation, deposition

What energy do waves have?

• potential energy due to position above the trough

• Kinetic energy due to motion of water within the wave

• Causes circular motion of water molecules

Wavelength

Distance between two troughs

Wave Height

Distance between trough and crest

Wave frequency

number of waves per minute

Wave period

Time between two consecutive crests

Swell waves

• Smooth ocean wave

• Long wavelength

Storm Waves

• Generated by high ocean winds

• Shorter Wavelength

3 types of breaking wave

• Spilling

• Plunging

• Surging

Spilling waves

• Steep waves

• Break on gentle sloping beaches

• Water spills gently forward

Plunging Waves

• Moderately steep waves

• Break onto steep beaches

• Water plunges down

Surging waves

• low angle waves

• Break on steep beaches

• Wave slides forward

How breaking waves form

• Water molecules come into contact with sea floor

• Friction slows and changes wave shape

• Wave bunches up and bottom of the wave slows more than the top

• Crest goes in front of trough and wave breaks

Swash

Water moves up the beach by energy from broken waves

Backwash

Water is pulled back down the beach by gravity

Constructive waves

• Low height

• Long wavelength

• Low frequency

• Spilling waves

• strong swash/weak backwash

• spilling waves

Destructive waves

• Greater wave height

• Shorter wavelength

• Higher frequency

• Weak swash/Strong backwash

• Plunging waves

What is a tide?

The periodic rise and fall of the sea surface

What produces tides?

• Gravitational pull of the moon and sun

• Moon has a gravitational pull towards water

• High tides follow moons orbit

Spring tides

• Happen twice a month

• When earth moon and sun are all in line

• Highest tides

Neap Tides

• Happens twice a month

• When moon and sun are at right angles to each other

• Lowest tides

What is lithology?

Physical and chemical composition of rocks

What rocks have strong/weak lithology?

• Clay has weak due to weak bonds between particles in rock

• Basalt has strong lithology due to dense interlocking crystals

Concordant coastline?

• Rows of rock parallel to the coastline

• Produces Straight coastlines

Discordant coastline

• Rows of rock perpendicular to the coastline

• Form headlands and bays due to different rates of erosion

Rip currents

• Transport sediment

• Caused by right angled waves breaking

• Creates cusps which cause the rip to have a narrow neck

Ocean currents

• Generated by convection and earths rotation

• Have motion due to movement of winds

Warm ocean currents

Transfer heat energy from low latitudes towards the poles

Cold ocean currents

Move cold water towards the equator

What are terrestrial sources of sediment?

• Rivers

• They directly deposit sediment at coasts with a steep gradient

• Mostly happens during floods

• Sediment comes from erosion, weathering and mass movement

What are offshore sources of sediment?

• Constructive waves bring sediment from offshore to shore by marine deposition

• Tides and currents also do this

• Wind also blows sediment from bars

• Generally in the form of sand as large particles are too heavy for wind

What are human sources of sediment?

• Beach nourishment when sediment budget is in deficit

• Sediment is brought by a lorry and dumped on the beach

• Or sand and water can be pumped by a pipeline

Weathering

• Uses energy to produce physical or chemically altered materials from rock

Physical weathering

• Breaks down rock and exposes surface area

• No chemical alterations

What is freeze thaw?

When water enters cracks in rock and expands by 10% when it freezes causing rock to break

What is thermal expansion?

When heated rock expand and contract when cooled and rock cracks and flakes off

Chemical weathering

• Decays rock by chemical reactions

• Increase in temp increases chemical reactions

• Sea water is neutral but becoming more acidic due to climate change

What is oxidation?

When rocks react with oxygen and become soluble in acidic conditions

What is carbonation?

• When CO2 combines with rainwater to produce carbonic acid

• Carbonic acid then reacts with calcium carbonate to become soluble

Biological weathering

• Biological plants and organisms affect the structure and stability of rock

What do plant roots do?

Grow into cracks and joints and exert pressure causing a release and rock breaks off

What do organic acids do?

Organic acids produced in decomposition of plants and animals break down sections of rocks and they become soluble

What is mass movement?

When forces acting on slope material(gravity) exceed the forces keeping the material of the slope(friction)

Rock Fall

• On cliffs more than 40 degree angle

• Rocks become detached by physical weathering

Slides

• May be linear

• A fault or bedding plane between layers of rock causes it to slide

• Rotational slides are slumps

• Happen because of undercutting and erosion

• Common in weak rock

5 kinds of erosion

• Abrasion

• Attrition

• Hydraulic action

• Pounding

• Solution

Abrasion

Waves with rocks in them scour the coastline and rub against other rock

Attrition

Rocks collide and wear away to become smoother and more well rounded and eventually become sand

Hydraulic action

Waves break against cliffs and air/water trapped in cracks becomes compressed and releases pressure

Pounding

Mass of a breaking wave exerts pressure on rocks causing them to weaken

Solution

• Dissolving materials in rock

• Has a small impact as water pH is 7/8

5 types of transportation

• Solution

• Suspension

• Saltation

• Traction

• Longshore Drift

Solution

Minerals dissolve in water until they evaporate

Suspension

Small particles of sand and silt are carried by currents

Saltation

Material moves irregularly and bounces along the surface

Traction

Largest particles are pushed along the sea floor by water flow

Longshore drift

• Waves approach the coastline at an angle due to wind and move up the beach with swash

• Move with backwash perpendicular to the beach and carry sediment within the wave

Deposition

When there is a loss of energy caused by a decrease in velocity or volume of water

When does deposition occur?

• Rate of sediment accumulation exceeds removal rate

• Waves slow immediately after breaking

• Low energy environments

• During backwash when water percolates into the beach

• During swash when water is not moving

What are fluvial processes?

• River mouths and river processes

• Erosion is the main source of rivers load

• Transportation

• Deposition when rivers enter the sea due to reduced velocity

• Tides/currents move in opposite directions to river flow so energy reduced

What are aeolian processes?

• Processes carried out by wind

• Erosion when wind picks up sand and moves it by deflation and surface creep

• Transportation by wind instead of water apart from solution

• Deposition when wind speed falls and material is deposited

How do cliffs form?

• Destructive waves break repeatedly on steep slopes

• Undercutting causes a wave cut notch

• Continued undercutting weakens above rock and breaks off causing a cliff

Horizontally bedded strata

• Undercutting leads to rockfall

• Cliffs retreat parallel to coast

Seaward dipping strata

• Undercutting removes basal support

• Rock layers loosened by weathering and they slide into the sea

Landward dipping strata

• Rocks loosened by weathering and wave action

• Strong rock is hard to dislodge

• Gradually lowered slope profile due to weathering and mass movement

Why do headlands and bays form?

• When a discordant coastline has bands of rock perpendicular to coastline

• Stronger rock less easily eroded so form headlands

• Weaker rock is easily eroded so forms bays

Wave refraction

• Waves approach an irregularly shaped coastline often a bay/headland

• Slowed by friction in shallower water of the headland

• Refract around the headland

• Energy dissipates in the bays and this leads to deposition

Geos

• Narrow steep sided inlets

• Weak points are eroded by wave action

• Initially form as tunnels/caves

• When the roof collapses this is a geo

Blowholes

• If part of the roof of a tunnel or cave collapses along a major joint a vertical shaft is formed

• This reaches the cliff top

• Large waves force water to spray out

Formation of a stump

1. Wave refraction focuses energy on the sides of headlands

2. Faults and joints are exploited by erosion and a small cave can form

3. Cave extends to the other side of the headland causing an arch

4. Erosion widens arch and weakens supports by weathering and arch collapses

5. This leaves a stack

6. Further erosion causes the formation of a small stump

Beaches

• Accumulation of material deposited between low tides and highest storm

• Material comes from cliff erosion, offshore and rivers

Sand beaches

• Produce a 5 degree beach angle

• compact particles when wet and little friction so material can be carried back down the beach

Shingle beaches

• Produces steeper beaches

• This is because swash is stronger than backwash

Strom Beaches

• Formed by pebbles being hurled by storm waves

What are cusps?

• Small semi circular depressions that form by collection of waves reaching the same point

What do destructive waves create?

• Flatter beaches

• Shallower water

• More friction

• Less wave energy

What do constructive waves create?

• Steeper beaches

• Deeper water

• Less friction

• More wave energy

Spits

• Long narrow beaches of sand/shingle attached to land at one end

• Extend across bays and estuary’s

• Formed by longshore drift carrying sediment to the end of the beach and into open water

Onshore bars

• When a spit continues to grow across until it joins the other side

• Form lagoons of brackish water

Tombolos

• Beaches that connect the mainland to an offshore island

• Formed from spits that grow seaward until they join an island

Salt Marshes

• Low energy environments

• Vegetated areas of deposited silt and clay

• Salt tolerant plants e.g. eel grass trap sediment and increase height

• Roots stabilise sediment

What do low marshes have?

• High salinity

• Turbid water

• Long periods submerged

• Poor species diversity

What do high marshes have?

• Lower salinity

• Lower turbidity

• Shorter period of submergence

• Higher species diversity

What are saltpans?

Small depressions that trap water

Deltas

• Large areas of sediment formed at the river mouth due to deposition and tidal currents

Where do deltas form?

• Rivers entering the sea carrying large sediment

• Low energy environments

• Low tidal ranges

What’s the structure of a delta?

• Upper delta plain is the furthest inland and composed of river deposits

• Lower delta plain is in the inter tidal zone and regularly submerged and has both marine and river sediment

• Submerged delta plain is below mean water level and has marine sediments

3 types of delta

• Cuspate shaped by gentle currents

• Arcuate which has a lot of sediment but not enough wave energy to smooth the edge

• Birds foot which has branching patterns when river sediment exceeds wave removal