Coastal Systems And Landscapes Flashcards
Define what a coast is
The part of the land adjoining or near the sea
Define:
Landform
A natural feature of the earth’s surface
Define:
Landscape
All the visible features of an area of land, often considered in terms of their aesthetic appeal
What are some landforms caused by deposition?
Give an example of a depositional landscape
Beach Spit Sand dunes River estuary Hooked end Marsh
Example: Blakeney Point- Norfolk
What are some landforms caused by erosion?
Give an example of an erosional landscape
Caves Arch Stack Stump Headland Cliffs
Example: Old Harry- Dorset
Why are coastal areas regarded as open systems?
Coastal areas are regarded as open because inputs of energy and sediment are often received e.g. sediment and wave energy, and outputs are transferred (flow) e.g. sediment transported by longshore drift, across the boundary of the system (section of coastline)
What does it mean by dynamic equilibrium in the coastal system
When the inputs and outputs within a coastal system are in balance, they remain in a relative state of equilibrium. If inputs change this leads to a change in processes, stores and outputs until a new equilibrium is reached. This is referred to as dynamic equilibrium.
Give an example of dynamic equilibrium
A higher rate of cliff erosion followed by deposition puts more material on the beach; this subsequently slows down the rate of cliff erosion as the extra material on the beach absorbs the wave energy and protects the cliff line. This is negative feedback. Eventually the sediment will be eroded and the coastline will become relatively stable
Examples of inputs to the coastal system
Human activities Changes in sea level Wind Waves Sediment Biogenic inputs Currents Tides
Examples of coastal processes
Erosion
Longshore drift
Deposition
Examples of coastal outputs
Arches Stacks Beaches Sand dunes Spits Cliffs Salt marshes Loss of wave energy Headlands
What factors affect the the coastal inputs, processes and outputs?
Sediments (shingle, sand and mud)
Relief (height and steepness of land)
Rocks (strength, jointing, bedding)
Describe and explain one factor that is likely to influence wave height
The fetch is the length of ocean the wind blows over. This is likely to influence wave height as a larger distance means more energy is transferred to the water so the larger the wave height will be. There is more time to transfer as much energy as possible to the wave which increases the wave height.
What is wave refraction?
Wave refraction occurs when waves approach an irregular coastline (curved or indented). As the waves approach the irregular coastline they curve and distort.
What would a diagram showing wave refraction look like?
It would show a headland separating two bays. As each wave nears the coast it drags in the shallow water. This causes the wave to become higher and steeper with a shorter wavelength. The part of the wave in deeper water moves forward faster, causing the wave to bend. The wave energy becomes concentrated on the headland, causing greater erosion.(cliffs, caves and arches). Where waves diverge they lose power and drop sediment (beaches)
What are tides?
The periodic rise and fall in the level of the sea. Caused by the gravitational attraction to the moon and the sun on oceans. This creates and outward bulge in the oceans closest to the moon and another on the other side of the Earth away from the moon.
What is a spring tide?
When the moon is between the earth and the sun the combined gravitational pull creates the biggest bulge of water and the highest tide. Height tides at highest and low tides at lowest. Tidal range is at its greatest
What is a neap tide?
When the Earth, moon and sun form a right angle, their gravitational pulls interfere with one another and this is when neap tides occur, giving the lowest high tides and the highest low tides (smallest tidal range)
What is the tidal range?
The vertical distance between low and high tides is called the tidal range. Spring tides have the highest tidal range whilst neap tides have the smallest tidal range
How does the tidal range influence coastal processes?
It controls the vertical distance over which erosion and deposition occur.
Affects the length of time that the littoral zone is exposed to sub aerial weathering.
Speed of incoming and outgoing tides effects coastline
How does the shape of the coast influence the tidal range?
Funnelled coast e.g Severn Estuary- as the tide advances it is concentrated in the narrowing space. This causes height to rise and produces a tidal bore.
Tidal ranges high in laces in British Isles giving a wide zone of wave attack resulting in wide wave cut platforms.
What is positive feedback?
A process in which an initial change will bring about an additional change in the same direction.
What are features of a constructive wave?
Low frequency (6-8 per minute) Stronger swash than backwash so material is deposited up the beach Sloping beach Long wavelength Low energy
What are features of a destructive wave?
Tall waves- steep gradient Short wavelength Steep beach Stringer backwash than swash Sediment taken away High frequency (10-14 per minute) High energy
Why are waves important?
Waves are the most dominant factor causing change in the coastal zone- they are responsible for erosion, transportation and deposition
What causes waves?
Created by wind blowing over the surface of water, this creates ‘drag’ which results in waves
Why do waves break?
As the wave approaches shallow water, the base comes into contact with the ocean bed. The resulting friction causes the base to slow down and the wave starts to break (translators waves-energy moves in a forward motion).
What affects wave energy?
Fetch
Wind strength- weather conditions
Time- length of time the wind blows for
Features of a high energy coastline
Significant erosion Long fetch Destructive waves Strong tidal currents Frequent on-shore winds Substantial transportation of sediment
Features of a low energy coastline
Gentle tidal currents Constructive waves Deposition of sediment Less frequent storm events Short fetch
What are the sources of coastal sediment?
Rivers- fine grained silts, clays and sands bring sediment from the land to the coast. May form salt marshes and deltas
Biogenic inputs- the skeletons and shells of marine organisms
Cliffs- produces large amounts of material for beach building due to erosion by the sea
Sea- tides and waves bring sediment shore wards. May build offshore bars or build up the beach.
What is a sediment cell?
A length of coastline within which the movement of sediment is largely self contained
What processes operate in a sediment cell?
Erosion
Deposition
Transportation
How many sediment cells are there in the uk?
Eleven
Name a specific example of a sediment cell in the UK
Flamborough Head to The Wash
How are sediment cells separated from each other?
Well defined boundaries such as headlands and large stretches of deep water
What is meant by the term ‘sediment source’ in the context of a sediment cell?
Where sediment comes from
What does the term ‘sediment sink’ mean in the context of a sediment cell?
Where deposition occurs
Name some examples of sediment sources
Coastal cliff erosion
River erosion
Deposition at the mouths of rivers
Shoreward movement of offshore sediments by tides and waves
Give some examples of ‘sediment sinks’
Sand dunes - accumulation of material at the back of beaches
What is a sediment budget?
The amount of sediment gained from the sources and lost to the sinks is quantified to make a sediment budget
How are sediment budgets useful?
Highlight variations in the amount of source and sink sediments.
Assessing coastal change
Why are sediment cells not entirely closed systems?
It’s easy for fine sediments to find their way around headlands into neighbouring cells
What is weathering?
It is the breakdown of rocks in situ (in their original location without them being moved away). This produces finer particles that can then be moved away by agents of erosion such as wind and waves
What are the three types of mechanical weathering?
- Frost shattering- water freezes and expands by 10%. This exerts pressure on the rock which causes crack to widen
- Salt crystallisation- salt water evaporated to form salt crystals which grow and put stress on the rock causing it to break up
- Wetting and drying- rocks rich in clay expand when they get wet and contract as they dry. Causes them to break up
What are the four types of biological weathering?
- Thin plant roots grow into small cracks which widen as the roots grow
- Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
- Birds and animals dig burrows into cliffs
- Marine organisms are also capable of burrowing into rocks or of secreting acids
What are the three types of chemical weathering?
- Carbonation
air+water->carbonic acid
Limestone+carbonic acid->carbonic acid - Oxidation-reaction of rock minerals with oxygen leaves rocks more vulnerable to weathering
- Solution- the dissolving of rock minerals such as halite
What is mechanical weathering?
Break up of rocks without any chemical changes
What is biological weathering?
The breakdown of rocks by organic activity
What is chemical weathering?
A chemical reaction where salts may be dissolved or a clay (like deposit) may result which is then easily eroded
What is mass movement?
Movement of material, such as rock earth or debris, down the slope of a hill or cliff. They can happen suddenly or move slowly over long periods of time
What is erosion?
Erosion is the breakdown and subsequent removal and transportation of the land. It includes the wearing away of rock and it’s removal by wind, water or ice.
Hydraulic action
Air is trapped in cracks by waves
Wave quarrying
Waves take material away to sea
Abrasion
Rocks are thrown at cliffs by the waves
Solution
Rock worn away by solution in waves (chemical reaction)
Attrition
Rocks are hot against each other wearing away
What is transportation?
The movement of material from one part of the coast to another. Although dry sand can be moved by the wind the dominant transporter of material is the sea
What is soul creep?
Particles rise towards ground surface due to wetting or freezing then returning vertically due to gravity as soil dries out
What are mudflows?
Earth and mud flowing downhill usually over unconsolidated and weak bedrock like clay, usually after heavy rainfall. Water gets trapped increasing pore water pressure forcing rocks apart causing slope failure. Often sudden and fast flowing so can represent a significant hazard
What is a landslide?
A block of rock moves down the side plain. The rock remains fairly intact. Often triggered by earthquakes or heavy rainfall when the slip surface becomes lubricated and friction is reduced
What is a rockfall?
A sudden collapse of fragments of rock at a steep/ vertical cliff face caused by mechanical weathering or an earthquake.
What is a land slip or slump?
Slide surface is curved rather than flat. Often occurs in weak, unconsolidated clays or sand. Permeable over impermeable. Build up of pore water pressure.
What is runoff?
The link between the coastal system and the water cycle. Pieces of small sediment carried along to littoral zone and then to sediment cell.
What is solifluction?
Like soil creep but specific to periglacial environments. In summer, active layer thaws as rock beneath is frozen therefore permafrost slides down due to heave and flow.
What are the factors that affect mass movement?
Plate tectonics Geology Gradient- steeper slope mass movement more likely Water Vegetation and buildings
How would geology affect the rate of erosion on a coastline?
If the rock at a coastline is more resistant (e.g granite) ten the rate of erosion will not be high. Weaker rock (e.g glacial till) will mean erosion will be high. If rock has lines of weakness and faults then erosion will be higher the same rock that has no faults.
How does refraction affect the rate of erosion on a coastline?
Wave energy is concentrated on the headland (especially sides). Low wave energy in the bays which decreases the rate of erosion.
How does the width of beach affect the rate of erosion?
A large width means the waves will lose more energy as they have to travel further than if the beach had a smaller width. So rate of erosion decreases the larger the width of the beach is.
How does coastal management affect the rate of erosion on a coast line?
If coastal management is in place the rate of erosion decreases. However this may mean that another area within the sediment cell had a higher rate of erosion
How do wave steepness and breaking point affect the rate of erosion on a coastline?
If the waves break close to the beach then sediment is more likely to be taken away. Steeper waves have more energy so erode the coast at a higher rate
Why does deposition take place?
Deposition takes place when the velocity of the water falls below a critical value for a particular size of particle and can no longer be transported
What are the four forms of transportation?
- Traction- large particles like boulders are pushed along the sea bed by the force of the water
- Suspension- small particles like silt and clay are carried along in the water
- Saltation- pebble sized particles are bounced along the sea bed but he force of the water
- Solution- soluble materials dissolve in the water and are carried along
What are sediment sinks?
A point or area at which beach material is irretrievably lost from a coastal cell, such as an estuary or a deep channel in the seabed. Areas of deposition are all sediment sinks or sediment stores.
How does particle size effect deposition?
Small particles settle more slowly than than the larger particles due to the pull of gravity. The smaller particles tend to stay in suspension for longer periods of time
What is differential erosion?
Erosion that occurs at irregular or varying rates caused but he resistance and hardness of surface materials
How was Lulworth Cove formed?
In Purbeck the rocks run parallel with the coast. Continued erosion can breach the more resistant rocks on the coast and begin to attack the weaker strata left behind. A cove forms which can be enlarged into a bay by erosion. In Purbeck the sea has breached the more resistant Portland stone to form Lulworth Cove in the clay behind.
How is a blowhole formed?
If erosion continues upwards after the cliff is undercut to form a cave then it is possible for the cave to be extended to the top of the cliff
How is a geo formed?
Sea attacks the weaker parts of the cliff such as cracks, joint or along bedding planes. The sea will cut inland, widening crack to form a narrow, steep inlet
What is accretion?
The process of the growth of landforms by deposition
What is a beach?
Stores of sand, shingle or a mixture of both depending on the available sediment
How is a swash aligned beach formed?
Movement of sediment straight up and down the beach. No sediment is moved along the beach
How is a drift aligned beach formed?
Movement transferred by longshore drift. Waves come at the beach at a 40-50 degree angle. And, due to gravity, go straight down moving sediment.
What are ridges and runnels?
They run parallel to the shoreline and are broken by channels that drain the water off the beach. Developed at the low water mark
Why does a shingle beach create a 10-20 degree angle?
Water rapidly percolates through shingle, so the backwash is somewhat limited. This means little material is moved down the beach.
What is a storm beach?
A ridge composed of the biggest boulders thrown by the largest waves. Created by strong swash at spring tide.
What are berms?
Berms are a series of ridges marking successively lower high tides as the cycle goes from spring to neap. Found below the storm beach
What are cusps?
Semicircular-shaped depressions which form when waves break directly onto the beach and swash and backwash are formed. Junction of the shingle and sand beaches
What are ripples?
Developed on the sand by wave action or tidal currents. Found below beach cusps
How and why does the profile of beaches change between summer and winter?
Beach profiles are steeper in summer as, generally, constructive waves occur more than destructive. Constructive waves have a larger swash than backwash. They deposit sediment onto the beach making it steeper.
In winter destructive waves occur more often. They have a strong backwash so they transport sediment offshore which means the beach becomes less steep as berms erode
