What causes tides
Gravitational pull between moon and earth
High tides are
12 hours apart
2 types of tides
Spring and neap
What’s a wave
Friction on water surface which agitates particles
Wave length
Distance between two successive troughs/peaks
Wave height
Distance between troughs and peaks
Fetch
Amount of open ocean wind has blown across
Waves break because
Particles become distorted and water is held back by friction on sea bed, surface of water carries on travelling and spills over the shoreline
Destructive waves
Longer, higher, more frequent, 14 pm, winter
Constructive waves
Lower, shorter, 10pm, summer
Weathering
The breakdown of rocks
4 type of weathering
Mechanical, physical, biological, chemical
Mechanical/physical weathering
Eg freeze thaw- water seeps into cracks, freezes, expands 9% causes rock to crack then melts and seeps further into rock
Chemical weathering
Eg limestone and rain- weak carbonic acid+CaCO2 causes corrosion
Biological weathering
Roots grow through rocks/animals burrow in cracks
Rockfalls
Fragments of rock break away from cliff face
Mudflow
Saturated soil and weak rock flows down slope
Landslide
Blocks of rock slide down hill
Rotational slip
Slump of saturated soil and weak rock along curved surface
General mass movement
Permeable/semi permeable rock collects on surface of impermeable rock- layer of water collect in between the two layers preventing them form join and so top layer eventually shifts
Hydraulic action
Water hits shore and enters cracks- air pushed back and when water seeps back out pressure built up with air being pulled forward again causes rock to crack
Wave pounding
Cliff worn away from force of waves hitting surface
Corrosion
Acid in sea water dissolves the rock
Attrition
Materials being carried by the water collide and become smoother and small particles
Formation of stump
- waves pick out weak spot in rock
- this becomes a notch and later a cave
- abrasion and solution persist so both side of headlands are wearing away
- 2 caves meet and become an arch
- sea rain and frost cause roof of arch to collapse creating a stack
- stack vulnerable to low tide and so becomes a stump
Examples of stacks/stumps
Old Harry’s Rocks’- Dorset
‘Needles’- Isle of Wight
‘Etratat’- Normandy
Features of deposition
Beaches, spits and tombolos
Where do beaches form?
Sheltered areas where swash is greater than backwash
Spits
Long narrow strips of land formed when coastline changes direction causing deposition
Examples of spits
Dawlish warren and slapton key
Cliff collapse
Permeable rock on top of impermeable rock- water pool created between layers saturating the permeable rock, causing it to slip off
Hold the line
Take action to preserve the coastline as it is
Advance the line
Improve coastal defence
Hard engineering
Artificial structures built to control nature- intrusive and expensive
Soft engineering
Working with nature to preserve coastline- low maintenance and inexpensive with low impact on landscape
Sea walls
Absorb wave energy/ send waves back to sea - sloped, recurved and stepped
Advantages of sea walls
Strong and effective
Disadvantages of sea walls
Expensive
High maintenance
Intrusive
Unattractive
Groynes
Right angle to shoreline to interrupt longshore drift
Advantages of grounds
Cheaper than sea wall
Sustainable
Low maintenance
Maintains beach tourism
Good for fishers
Disadvantages of groynes
Major construction
Interrupt coastline- destroy beaches along the coast
Must be frequently rebuilt
Rock amourment
Boulders at bottom of cliff to absorb wave energy
£1000-£5000 per metre
Could also be gabions (wire boxes full of rocks)
Advantages of rock amourment
Relatively cheap
Look more natural than others
Disadvantages of rock amourment
Difficult to get rocks
May be unattractive
Dangerous for animals/children
Tetrapods
Large concrete structures with 4-5 arms eg Scarborough
33 million to install
Advantages of tetrapods
Very effective
Protects coastline well
Disadvantages of tetrapods
Expensive
Ugly
Dangerous
Large construction
When they erode the metal structure is exposed
Beach nourishment
Extra sediment placed on beach to increase size
Advantages of beach nourishment
Relatively cheap
Looks natural
Remains attractive
Sustainable
Disadvantages of beach nourishment
Constant maintenance needed (twice a year) eg Seaford
Sand dunes/dune regeneration
Found on large beaches, occur when plants trap sediment being carried by wind and fences can be installed to encourage this
Advantages of sand dunes/dune regeneration
Natural looking
Maintains sand dune ecosystem
£2000 per 100m
Good for tourism
Brings plant diversity
Disadvantages of sand dunes/dune regeneration
Easily destroyed by people
Storms destroy them
Time consuming installation
Managed retreat
Allowing the sea to reclaim the land and flood it creating a salt marsh
Advantages of managed retreat
Cheap
Increased biodiversity
Natural
Disadvantages of managed retreat
Lost value of land
Farmers lose land
Tourism lost
Salt marshes
Causes mud accumulation in sheltered areas (spits or estuaries)as they provide habitats. Once it reaches water level it’s called a mud flat
Cord grass
Pioneer species- can grow in first stage of salt marsh as it tolerates being submerged in water. It traps sediment and holds land together with roots