Coasts key definitions Flashcards
high tidal range
- waves only reach part of cliff for small period of time
- less energy focused
- e.g. Bristol channel
low tidal range
- waves reach part of cliff for large period of time
- more energy focused (more erosion)
- e.g. Mediterranean
rip currents
- localised channels of fast-moving water
- localised high energy
high energy coastlines
- face powerful waves most of the year
- erosion exceeds deposition
- creates headlands and arches
low energy environments
- waves are less powerful and coast is more sheltered
- creates beaches and spits
constructive waves
- short fetch
- long wavelength
- low waves
- strong swash/weak backwash
- gentle beach profile
destructive
- long fetch
- high wavelength
- high waves
- weak swash/strong backwash
- steep beach profile
wave refraction
- changes amount of energy reaching shore
- wave energy concentrates on headland and increases rate of erosion
sources of sediments
- river
- cliff
- winds (can lead to sand dunes)
- glaciers break off into sea
sediment cells
- closed systems
- 11 in the UK
- can be divided into sub cells with inputs, sources, transfers and outputs can be identified
sediment budget
- balance between input and outputs of sediment in the system
- dynamic equilibrium
- however can be disturbed by human activity
coastal weathering
- breakdown of rocks
mechanical weathering
- when rocks break up with no chemical changes
- freeze thaw
- wetting and drying
- salt crystallisation
- exfoliation
freeze thaw (mechanical weathering)
- water forces into cracks
- water freezes and expands
- frozen water thaws
- repetitive and rocks break off
wetting and drying (mechanical weathering)
- same as freeze thaw but without ice
- occurs in inter-tidal zone (exposed at low/covered at high tide)
salt crystallisation
- water collects in cracks
- water evaporates in sun and salt forms
- creates stress over time and breaks rocks up
exfoliation
- occurs in hot climates
- rock expands when hot, contracts when cool
- over time, thin pieces of rock breaks off
biological weathering
- vegetation
- animals
- humans
- enter cracks and break rocks away
chemical weathering
- carbonation
- oxidation
- solution
carbonation (chemical weathering)
- rain is slightly acidic
- reacts with carbonate rocks (e.g. limestone)
- causes them to dissolve
oxidation (chemical weathering)
- iron minerals in rock react with oxygen in air
- causes rusting and rock breakdown
solution (chemical weathering)
- other salt minerals in the rock are dissolved
mass movement
- downhill movement of material under the influence of gravity
type of movement is determined by…
- angle of slope
- water
- type and structure of rock
- human activity
- climate
soil creep
- humid climates
- soil expands
- lifts at right angles to slope
- soil shrinks and falls straight down
- takes a long time
flow
- occurs on slopes between 5 and 15 degrees
- speeds of 1-15km per year
- happens after soil has become saturated
- vegetation is flattened and carried away with soil
slide
- movement of material
- ‘en masse’
- remains together until it hits the bottom of the slope
fall
- slopes are steep
- rapid
- extreme weathering
- rainfall
- earthquakes
- hot weather dries out soil
slump
- found on weaker rock types that become saturated and heavy
- rotational slip
- common at the coast
- large area of land moves down slope in one piece
- leaves curved, indented surface
hydraulic action
- water is forced into cracks and breaks it apart
abrasion
- breaking waves carrying sediment scrape against rock surface
attrition
- sediment particles in the water rub together
solution
- acid wears away rock
traction
- pebbles and larger material rolled along seabed
saltation
- small pieces of shingle are bounced along seabed
suspension
- small material such as clay and silt are held in the flow of seawater
longshore drift
- prevailing wind direction causes waves to approach beach at a similar angle
- swash and backwash takes place in a zigzag pattern
- material is carried along by longshore drift
how do waves lose energy
- wind slows or changes direction
- wave experiences friction as depth increases
- when coastline changes direction (estuary or headland)
high energy coastlines
- deposit large rocks and shingle but maintain enough to carry small sediment particles
- tend to have rocky beaches
low energy coastlines
- deposit smaller sediment due to low wave velocity
- creating sandy beaches
wave cut platforms
- hydraulic action and abrasion create a wave cut notch (undercutting)
- increases in size creating an overhang
- unsupported overhang collapses due to gravity and weathering at the top of the cliff
- backwash transports material from the cliffs base leaving a wave cut platform
cave, arch and stack formations
- large crack opened by hydraulic action
- crack grows into a cave via hydraulic action and abrasion
- cave becomes larger
- cave breaks through headland forming a natural arch
- arch is eroded and collapses
- leaves a tall rock stack
- stack is eroded forming a stump
beach formation
- build due to constructive waves
- drift aligned - LSD moves sediment along beach as waves approach at an oblique angle (usually turns into a spit during direction change)
- swash aligned - form when energy is low and waves are more parallel so there is little horizontal or lateral movement of sediment
spit formation
- LSD
- coastline changes direction
- waves no longer have energy to carry sediment so it is deposited
- sediment builds up out to sea (usually out to an estuary)
- curved end or hooks due to second prevailing wind
tombolo’s and bars
- sediment is deposited onshore or offshore
- where sediment level is high and sea is shallow
- bars extending from spits are known as barrier beaches
- water trapped behind is called a lagoon
salt marshes
- sheltered land behind spits leads to lots of deposition
- salt tolerant species colonise
- covered at high tide and exposed at low tide
sand dunes
- high deposition rates
- onshore prevailing winds
- sand is trapped towards the back of the beach due to obstacles
- pioneer plant species hold sand together and stabilise dune
- dune ecosystem forms
eustatic change
- change in water volume in ocean basins
- global
- changing ice levels
- thermal expansion
- tectonics (magma lifts crust)
isostatic change
- height of land changes relative to water level
- happens more slowly
- local
- post-glacial adjustment
- accretion (sediment cells deposition)
- subsidence (lowering of water table)
- tectonics
emergent landforms
- isostatic recovery
- recovery in sea level
- raised beaches
- fossil cliffs
groynes
- structures built perpendicular to the shore
- sediment is trapped
advantages
- not as expensive
- builds up beach
disadvantages
- unattractive
causes sediment starvation further up coast
- needs lots of maintenance
sea walls
- walls with curved surface that absorb and reflect wave energy
advantages
- highly effective
- can increase tourism as it can create walkways
disadvantages
- expensive
- ugly and intrusive
rock armour
- large boulders at the foot of the cliff
- reduces wave energy
advantages
- cheaper
- used for fishing
disadvantages
- dangerous when people are on them
- rocks from elsewhere and intrusive to local geology
revetments
- sloped or ramp-like structure that breaks up wave energy
advantages
- cost-effective
disadvantages
- needs lots of maintenance
- unnatural looking
- slopes are dangerous
offshore breakwater
- rock barrier a little out to sea
- breaks up wave energy
advantages
- effective
- away from beach so does not disrupt tourist potential
disadvantages
- can create navigation barrier in harbour areas
