Coastline Flashcards
What’s mechanical weathering?
The break up of rocks without any chemical changes occurring. Usually resulting in piles of rock fragments called scree found at foo of rocky outcrops
Define chemical weathering
When a chemical change takes place when weathering occurs. Acidic rainwater slowly dissolve soft rocks such as limestone/chalk. Minerals left behind form clay deposit
What’s biological weathering?
The actions of Flora and fauna. Eg: Plant roots grow and expand in rock cracks. Rabbits can burrow into weak rock (i.e: sand)
Freeze - Thaw
Water find it’s way into cracks when waves and rain water find their way into cracks. It freezes and thaws as temperatures fluctuate. This process repeats and gradually weakens the rock until sections break away from the cliff face
Mass movement
The downhill movement of material under the influence of gravity
Effects of mass movement
- people are evacuated
- houses/businesses destroyed
- roads/public services damaged
What is Rockfall?
fragments of rock break away from the cliff face (often due to freeze thaw)
What is a landslide?
Blocks of rock slide downhill
Mudflow
Saturated soil and weak rock flows down a slope
Rotational slip
Slump of saturated soil and weak rock along a curved surface
How are waves formed?
Waves are a result of wind blowing over the sea. Friction with the surfaces causes ripples to form and these turn into waves.
What does wave energy depend on?
It depends on the fetch (the distance which the wind has blown over) , the strength of the wind and the length of time over which the wind has blown
Compare the two types of waves
Constructive - low in proportion to height - shape is spilling - strong swash, weak backwash - build up beach - summer season -less than 11 per minute Destructive - high in proportion to length - shape is plunging - weak swash, strong backwash! - erode beach - winter season - 13+ per minute
What are the four types of erosion?
Hydraulic action
Corrosion
Attrition
Abrasion
Hydraulic action
The impact of a wave on a cliff face, air is forced into cracks under high pressure which widens them. Over long periods of time, the growing cracks break parts of the rock off
Corrosion
Carbon dioxide in the atmosphere is dissolved into water which causes a weak carbonic acid to form. When the water hits the rocks, this erodes the material. Acidic rain also plays a part in this.
Attrition
Beach material is knocked together in the water, which reduces their size and they become smoother and rounder
Abrasion
The repeated action of waves breaking on a cliff is enough to remove material from it over time. The sand and shingle in the water acts like sandpaper so erosion takes place faster
What four factors effect coastal erosion?
Rock type - some rocks easily erode
Fetch - the larger the fetch the more wave energy..so more erosion
Type of wave - destructive waves have a steep angle of break and have lots of energy
Shape of coastline - certain areas (eg: bays) are more sheltered by headlands so erosion is slower
What are the main coastal features caused by erosion?
1: headlands and bays
2: caves, arches and stacks
3: wave cut platforms
How are headlands and bays formed?
- alternating layers of (non)resistant rock at right angles to the coast
- less resistant rock erodes quicker which forms a dent in coastline (bay)
- more resistant rock to the north and South are eroded more slowly hence the coast at theses points protrudes into the sea (headlands)
Explain the process of caves, arches and stacks
1: the headland is made of resistant rock with natural cracks/ joints in it
2: the breaking waves exploit the cracks and erode them through hydraulic action & corrosion until small caves form
3: the sea continues to erode caves so they get larger. The caves on either side of the headland erode backwards until they meet in the middle to form an arch
4: the sea keeps eroding the arch which becomes larger until the roof collapses and forms a stack
5: the headland retreats and new caves are forming all the time
Definition of:
- cave
- arch
- stack
Cave - a hollowed out feature at the base of an eroding cliff
Arch - a headland that’s been partly broken through by the sea to form a thin roofed arch
Stack - an isolated pinnacle of rock sticking out of the sea at the end of a headland
Explain how a wave cut platform is formed
When waves break against the cliff face near the high tide line, the rock is attacked by the processes of erosion which form a wave-cut-notch. Over time and repetition the notch deepens and the overlying cliff collapses under the influence of gravity. Over time the cliff line retreats and extending seawards from the base of the cliff will be a rocky, gently sloping platform called a wave cut platform.
What is weathering?
The break up and decay of exposed rock at the Earths surface
What is longshore drift?
The transport of sediment along a stretch of coastline caused by waves approaching the beach at an angle
Which direction does backwash flow during longshore drift
At right angles to the cliff due to the force of gravity
Main landforms of costal deposition
1- Beaches
2- Spits
3- Tombolos and Bars
What is coastal deposition?
When the sea loses energy and deposits sand, rock particles and pebbles that it’s been carrying.
When is coastal deposition likely to occur?
It’s often associated with constructive waves and is likely to occur when waves enter shallow water or an area of shelter and no wind. This is because it’s the times when waves lose energy
What are beaches and what are the main sources of material?
Beaches are made up of material lying between the high & low tide mark. Sources: - cliff erosion - constructive waves - longshore drift
What is it called when waves enter a bay and mirror the shape of the coastline?
Wave refraction
What does wave refraction result to?
Wave refraction spreads out and reduces wave energy so deposition occurs.
What is a tombolo?
It’s a spit connecting an island to the mainland. It’s an accumulation of sand and shingle.
What is a bar? What feature will it create?
And accumulation of sand and shingle (also known as spit) that blocks off a bay or river mouth.
It will create a lagoon around it.
Why is the sea level rising and at what rate?
- Global warming!
- 2mm per year
- 20 in past century
Name some effects of Coastal flooding
Economic: - loss of tourism - damage repair - loss of agricultural land Social: - deaths - water supplies affected - loss of housing/businesses (jobs) Environmental: - ecosystems affected - vegetation killed - increased erosion
What’s the cause of cliff collapse?
The rocks that make up the cliff are weak and easily eroded by the sea. Also permeable sands sit on impermeable clay which means when water infiltrates into the cliff, it will ‘pond up’ when it reaches the layers of clay. Over time the weight of the cliff increases and so it will collapse.
What is
- hard engineering
- soft engineering
Hard engineering - building artificial structures such as sea walls aimed at controlling natural processes
Soft engineering - a sustainable approach to managing the coast without using artificial structures
Examples of hard engineering. What are they
Sea wall - curved concrete/rock barrier placed at base of cliffs or top of a beach which reflects the waves back into the sea
Groynes - Timber/rock structures built out to sea from the coast at 90degrees. They trap sediment being moved by LSD. So the beach area is increased
Rock armour - pile of large boulders dumped at foot of cliff. They absorb the waves energy, protecting cliffs
Examples of soft engineering. What are they?
Beach nourishment - addition of sand to existing beach to make it higher or broader.
Dune regeneration - sand dunes act as buffers to the sea. Marram grass is planted to stabilise them
Marsh creation - Allowing low lying coastal areas to be flooded by the sea to become salt marshes that act as barriers to the sea.
Advantages & disadvantages of hard engineering process.
- sea wall
- groynes
- rock armour
Sea wall - expensive! (6m per km), looks unnatural but very effective
Groynes - not too expensive (£10,000 each at 200m intervals). Forms bigger beach for tourism:) starve beaches downdrift causing erosion in other places
Rock armour - £1000/4000 per metre. (Quite cheap) easy to maintain. Expensive to transport. Obtrusive
Benefits and drawbacks of soft engineering processes
- beach nourishment
- dune regeneration
- marsh creation
Beach nourishment - quite cheap (3000 per m), blends in, bigger beach so tourism increase. Needs constant maintenance
Dunes - cheap (2000 per m), natural! Time consuming, damaged by storms
Marsh creation - cheap option, crates habitat for wildlife, farming land is lost
Cost of schemes per 1km
Sea wall - 6 million
Groynes - 50,000
Rock armour - 1-4 million
Beach nourishment - 3 million
How is a salt marsh formed?
- start as accumulation of mud in a sheltered coastal area (eg: behind spit)
- as more sediment builds up, mud level rises so becomes less covered in water
- improves fertility of soil
- plant species colonise (vegetation succession)
Describe impacts of sea level rising in maldives
- 350,000 people would evacuate
- wildlife (180 bird species, 18 dolphin species, 1000 fish species)
- TOURISM LOSS
- job losses (fishing community)
