The UK's evolving physical landscape - Coasts Topic 4, GCSE Geography
Factors affecting the landscape
Geology
Use carbon dating
As skeletons fall to the sea floor, they form horizontal lines (strata).
Two processes turn the skeletons into solid rock:
As skeletons fall, they crush those beneath, eventually squeezing out water and compacting them into rock
CaCO3 crystallises around the fragments; this cements them together and even preserves some fossils intact
Definitions Coasts
Carbon Dating
Uses radioactive testing to find the age of rocks which contained living material
Erosion
Wearing away the landscape
Tectonic Processes
Example of three processes in the Pennines:
Convection currents beneath the plate uplifted rocks from below the sea - becoming land
During uplift, some rocks snapped and moved along the faults in a series of earthquakes over thousands of years - each movement distributed the strata so they tilted
Sometimes the faults form a steep edge called a fault scarp where uplift has raised some parts more than others
The plate on which the UK sits shifted, away from the tropics!
Fault scarp
When a fault creates a steep edge
Glaciation
When the Pennines were uplifted , rivers like the Wharfe eroded into them causing V-shaped valleys
The most recent Ice Age (10 000 yrs ago) bought huge glaciers
Two effects:
Altering river valleys, making them deeper and widening them into U-shaped troughs
As they melted they left features like Malham Cove with a spectacular waterfall!
Rocks
Types of rocks
Sedimentary
Metamorphic
Igneous
Earth's oldest rocks
Formed from lavas and deep magmas
Once moten, then cooled and crystallised
Most are resistant to erosion
Formed when sediments eroded and deposited by rivers
Some are resistant yet some crumble easily
Sedimentary rocks that were heated and compressed during igneous activity
Heating and compression harden and make them resistant
Tees- Exe Line
To the N and W
To the S and E
Older rocks
More resistant igneous and metamorphic
More faults, where uplands were uplifted by tectonic activity
Younger rocks
Weaker sedimentary rocks - easily eroded
Examples:
Examples:
Examples:
Granite
Formed from magma cooling deep underground
Contains crystals of quartz, feldspar, mica; very resistant
Carboniferous limestone
Created in the Carboniferous period through compression in rock strata
Permeable, with underground rivers, passages and caves; generally resistant
Slate
Formed from heated muds or shale
Very resistant
Basalt
Formed from lavas rich in minerals
Almost black, and heavy; very resistant
Clay
Formed from muds deposited by rivers or at sea
Soft and crumbly; when compacted it becomes shale; generally weak
Sandstone
Formed from sand grains compacted together
Slightly porous; less than 100mya are weak; more than 300mya are resistant
Millstone grit
Sandstone which has been firmly cemented and compacted
Very resistant
Chalk
A purer, younger form of limestone
Very porous; medium resistance - stronger than most clays and younger sands
Schist
Formed by the further metamorphosis of slate, where it partially melted and solidified
Very resistant
Marble
Formed by heated limestone
Very resistant
Scree
Rock fragments which make the ground rough
Weathering
The physical, chemical or biological breakdown of solid rock by the action of weather or plants
Features
Wave-cut platform
Over time the base of the cliff will erode, leaving a wave cut notch
You are left with a wave cut platform
Destructive waves erode the cliff
Fetch
Size of open water the wave has come from
Waves
Factors affect the surf
Wind Speed
Wind Duration
The Fetch
Swash
When the water goes up the beach
Backwash
When the water goes back into the sea
2 types
Constructive
Destructive
Long wavelength - short height
Weak swash
Shallow gradient waves
Weak backwash
Strong swash
Strong backwash
Strong wavelength - tall height
Steep gradient waves
Beach built up by deposition of material bought up by swash
Beach erosion
Unfrequent
Frequent
Wide Gently sloping Beach
Steep Narrow Beach
Less violent
More violent
Coastlines
Concordant
Disconcordant
Rock strata are parallel to the sea
Rock strata are perpendicular to the sea
Formations: coves
Formations: headlands and bays
Processes
Erosion
Solution
Hydraulic Action
Attrition
The force of water forces the air into the cracks; air eventually causes the rock to expand and explode
Abrasion
Small particles dissolved in river due to chemical reactions between the salt water and rock
Material carried by river smashes into each other and break into smaller, smoother pieces
1⃣ Large crack opened by hydraulic action
2⃣ Crack grows into a cave by H.A. and abrasion
3⃣ Cave becomes larger
4⃣ Cave breaks through the headland forming a natural arch
5⃣ Arch is eroded and collapses
6⃣ Leaves a tall rock stack
7⃣ Stack erodes forming a stump
Sea's load (rocks and sand) is thrown against the base of the cliff eventually eroding it
Transportation
Saltation
Suspension
Traction
Solution
Heavy boulders get carried along the sea/river bed
Bounced along the river or sea bed
Materials carried in suspension along the sea bed
Chemical reaction between rocks and salt water; rocks are dissolved and are now carried in solution
Longshore Drift
Backwash carries sediment back down the beach under gravity
Another wave moves the material up the shore; cycle carries on
When the wave breaks, swash carries sediment up beach following angle of wave
Over time sediment will be carries parallel to the beach because of L.S.D
Waves approach beach at angle, depending on wind direction
By longshore drift
Bars
Tombolos
Spits
When the sediment is deposited by L.S.D
When it hooks around and joins to another place
When the spits connect to another island
Contrasting coasts
Geology/rock types
Hard Rock Coasts consist of resistant rocks ie. granite, limestone. E.g: Lulworth Cave (Devon) & Flamborough Head (East Yorkshire).
Soft Rock Coasts consists of less resistant rocks i.e. clays,shales. E.g: Holderness Coast (East Yorkshire), Christchurch Bay (Dorset/Hampshire) and North Norfolk Coast.
Sand Dunes are formed when strong winds blow sand inland.
Human Activities
Effects of development
Office Devlopment
Housing
People working in London cannot afford housing there
Good place for retirement
Companies in London cannot afford rent cost
Popular with younger workers
Effects of agriculture
Price of farmland
Risen sharply
Climate change and rising sea levels
Effect of industry
Critical to UK Economy
Risks from costal flooding
World at risk
UK - London and Essex: Low lying, so at risk of flooding
Bangladesh: If water rises 1m, 15% of country will become flooded
Pacific/Indian Islands: Could disappear entirely
Flood Risks and Future
If air pressure falls to very low levels a storm surge occurs
Twice a month there are exceptionally high tides (spring tides)
Twice a day, due to moons gravity, high tides occur
Erosion
Cliff Processes
Waves
Geology
Depends on wave energy, in turn affected by fetch
Weak geology - suffer from cliff foot erosion, mass movement, sub-aerial proceses, cliff face erosion
Resistant or non resistant
Case Study: Christchurch Bay
Without management, cliff erodes 2m+ every year, threatening residential areas
Impacts
Rapid cliff collapses are dangerous for those on cliff and beach
Infrastructure gets destroyed
Erosion makes living here unattractive
Houseowners lose their homes to the sea; house values fall with insurance impossible to get
Managing the coast
Hard Engineering
Sea wall w/ steps and bullnose
Revetments
Sea Wall
Gabions
Rock armour (rip-rap)
Groynes
Reflects waves back into sea
Prevents easy access to beach
Suffers wave scour
£2000 per m
£5000 per m
Steps dissipates wave energy; bullnose throws waves back to sea
Breaks up incoming waves
Restricts beach access; looks ugly
£1000 per m
Can be distroyed by big storms
Absorbs wave energy as they are permeable
Cheap type of sea wall
Not very strong
£100 per m
Easy to build
Expensive if built in sea
£300 per m
Dissipates wave energy and looks 'natural'
£2000 per m
Prevents longshore drift, trapping sand/ shingle
Larger beach dissipates wave energy
May increase erosion downdirft
Dissipate
Reduce wave energy, which is absorbed as waves pass through/over sea defenses
Stakeholders
Local people living further inland - Unaffected, fear taxes will rise; want low cost options
Environementalists - Fear that coastal defences will affect environement
Local politicians & council - Want effective coastal protection but not at any cost
Residents/ Buisnesses downdrift - Want integrated approach to management
Coastal residents & buisness owners - Prefer to 'hold the line'
Fisherman/ Boat users - Priority is access to the sea
Holistic Management
Advance the Line
Strategic Realignment/Retreat
Hold the Line
Do nothing
Use sea defenses to stop erosion, so coast stays where it is; expensive
Use sea defenses to move coast further into sea; very expensive
Gradually let the coast erode and move people/buisnesses from risky areas; may include financial compensation when homes are lost
Take no action, let mother nature take her course
Soft Engineering
Beach nourishment
Planting vegetation
Offshore breakwaters
£20-50 per sq m; plants are used to make cliff more stable
£500-£1000 per sq m; sand is pumped onto beach to increase its size
£2000 per m; built using rip-rap, forcing waves to break before the beach
In cliff drainage
Variable; pipes reduce water pressure an prevent saturation