1.2 Coastal landscapes and change Flashcards
Is the coast and open or closed system? Why?
- The coast can be considered as an open system as it receives inputs from outside the system and transfers outputs away from the coast and into other systems.
- These systems may be terrestrial, atmospheric or oceanic and can include the rock, water and carbon cycles.
Describe sediment cells (6)
- Coasts can be split into sections called sediment cells.
- a largely self-contained stretch of coastline
- typically considered a closed-system in terms of sediment.
- There are eleven sediment cells in England and Wales.
- Under normal conditions, the coastal system operates in a state of dynamic equilibrium.
- Sediment cells are not fully closed systems, so it is important to remember that actions within one cell may affect another.
Define dynamic equilibrium
- Dynamic equilibrium in a sediment cell is where input and outputs of sediment are in a constant state of change but remain in balance.
- Physical and human action can change this equilibrium.
Sources in sediment cells
– Where the sediment originates from (e.g. cliffs, offshore bars).
Through flows in sediment cells
The movement of sediment along the shore through longshore drift.
Sinks in sediment cells
Locations where deposition of sediment dominates (e.g. spits, beaches).
Define negative feedback
- mechanisms which balances changes, taking the system back towards equilibrium
- this lessens any change which has occurred within the system
Describe the negative feedback loop following a storm (5)
- a storm could erode a large amount of a beach, taking the beach out of dynamic equilibrium as there is a larger input of sediment than output
- When the destructive waves from the storm lose their energy excess sediment is deposited as an offshore bar.
- The bar dissipates the waves energy which protects the beach from further erosion.
- Over time the bar gets eroded instead of the beach.
- Once the bar has gone normal conditions ensue and the system goes back to dynamic equilibrium
Define positive feedback
- mechanisms which enhance changes within a system, taking it away from dynamic equilibrium
- this exaggerates the change making the system more unstable
Describe the positive feedback loop after sand dunes have been trampled (3)
- People walking over sand dunes destroys vegetation growing there and causes erosion.
- As the roots from the vegetation have been holding the sand dunes together, damaging the vegetation makes the sand dunes more susceptible to erosion. This increases the rate of erosion.
- Eventually the sand dunes will be completely eroded leaving more of the beach open to erosion taking the beach further away from dynamic equilibrium.
Define littoral zone
The littoral zone is the area of the coast where land is subject to wave action.
Factors affecting the littoral zone
- Short-term factors like tides and storm surges.
- Long-term factors like changes in sea level and climate change.
Subzones of the littoral zone (4)
- Offshore
- Nearshore
- Foreshore
- Backshore
Define offshore
- Where waves begin to break in the deeper water.
- Friction between the waves and the sea bed may cause some distortion of the wave shape.
Define nearshore
- Friction between the seabed and waves distorts the wave sufficiently to cause it to break.
- Possible breakpoint bar formation.
Define foreshore
- The area between the high tide and the low tide mark.
- this is land where most wave processes occur.
Define backshore
The area above the high tide mark, affected by wave action only during major storm events.
Describe valentine’s classification
- Valentine’s Classification describes the range of coastlines that can occur.
- An advancing coastline may be due to the land emerging or deposition being the prominent
process. - Alternatively, a coastline may be retreating due to the land submerging or erosion being the prominent process.
Define emergent coastline
As Sea Levels fall, coastline land is exposed which was previously covered by the sea
Describe a raised beach
- A raised beach is a former beach now above the high tideline.
- Some raised beaches may consist of several different levels, each indicating a different stage of uplift.
- Features such as rounded pebbles and boulders are likely to be present, but smaller particles have usually been removed.
Describe a fossil cliff
- A fossil cliff is a near-vertical slope initially formed by marine processes but now some distance inland.
- Other coastal erosional features, such as sea caves and a wave-cut platform, may still be visible.
Define submergent coastline
As Sea Levels rise, the land is covered
Define a ria
- A ria is a flooded river valley.
- During an ice age some land areas were not covered with ice but had frozen ground, so rivers carved valleys with steeper sides than normal.
- Then, after the ice melted, sea levels rose and drowned the mouths of these valleys.
- e.g. Sydney Harbour, Australia
Describe a fjord
- A fjord is a flooded glaciated valley.
- During an ice age, glaciers eroded U-shaped valleys down to the coast of the time and then, after the ice melted, the sea level rose again and flooded into the valley over a shallow threshold, creating a very deep water inlet with steep sides,
- All the features of a normal U-shaped valley are present, such as hanging valleys and truncated spurs.
Types of erosional processes (6)
- corrasion
- abrasion
- attrition
- hydraulic action
- corrosion (solution)
- wave quarrying
Describe corrasion
- Sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled against the cliffs at high tide, causing the cliffs to be eroded.
- The shape, size, weight and quantity of sediment picked up, as well as the wave speed, affects the erosive power of this process.
Describe abrasion
This is the process where sediment is moved along the shoreline , causing it to be worn down over time .
Describe attrition
- Wave action cause rocks and pebbles to hit against each other , wearing each other down and so becoming round and eventually smaller.
- Attrition is an erosive process within the coastal environment, but has little to no effect on erosion of the coastline itself.
Describe hydraulic action
- As a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock.
- The high pressure causes the cracks to force apart and widen when the wave retreats and the air expands.
- Over time this causes the rock to fracture.
- Bubbles found within the water may implode under the high pressure creating tiny jets of water that over time erode the rock. This erosive process is cavitation
Describe corrosion (solution)
- The mildly acidic seawater can cause alkaline rock such as limestone to be eroded and is very similar to the process of carbonation weathering.
- This is a potential link between the carbon cycle, global warming and coasts.
Describe wave quarrying
- This is when breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m ².
- It is very similar to hydraulic action but acts with significantly more pressure to directly pull away rocks from a cliff face or remove smaller weathered fragments.
- The force of the breaking wave hammers the rocks surface , shaking and weakening it and leaving it open to attack from hydraulic action and abrasion.
Erosion rates are highest when… (5)
- waves are high and have a long fetch (the distance the wind has travelled over the wave)
- waves approach the coast perpendicular to the cliff.
- at high tide - waves travel higher up the cliff so a bigger area of cliff face is able to be eroded.
- heavy rainfall occurs - water percolates through permeable rock, weakening cliff.
- in winter - destructive waves are the largest and most destructive during winter
Factors affecting the resistance of a rock (3)
- whether rocks are clastic or crystalline - crystalline rocks are more resistant to erosion
- The amount of cracks, fractures and fissures – the more weaknesses there are in the rock the more open it is to erosional processes, especially Hydraulic Action.
- The lithology of the rock (rock type)
Define clastic
rocks composed of broken pieces of older rocks.
Define crystalline
any rock composed entirely of crystallized minerals
Describe igneous rocks (3)
- e.g. Granite, Basalt
- Very slow erosion rate (<0.1cm/year)
- Interlocking crystals which allow for high resistance
Describe metamorphic rocks (3)
- e.g. Slate, Schist, Marble
- Slow erosion rate (0.1-0.3cm/year)
- Crystal all orientated in the same direction
Describe sedimentary rocks (3)
- e.g. Limestone
- Very fast erosion rate (0.5-10cm/year)
- Lots of fractures & bedding planes making them weak
Describe how caves, arches, stacks, & stumps are formed (4)
- Marine erosion widens faults in the base of the headland, widening over time to create a cave.
- The cave will widen due to both marine erosion and sub-aerial processes, eroding through to the other side of the headland, creating an arch.
- The arch continues to widen until it is unable to support itself, falling under its own weight through mass movement, leaving a stack as one side of the arch becomes detached from the mainland.
- With marine erosion attacking the base of the stack, eventually the stack will collapse into a stump.
Describe how a wave-cut notch and platform is formed (3)
- Marine erosion attacks the base of a cliff, creating a notch of eroded material between high tide height and low tide height.
- As the notch becomes deeper (and sub-aerial weathering weakens the cliff from the top) the cliff face becomes unstable and falls under its own weight through mass movement.
- This leaves behind a platform of the unaffected cliff base beneath the wave-cut notch.
Describe retreating cliffs
Through the process of repeat wave-cut notches and platforms, new cliff faces are created, whilst the land retreats
Describe a blowhole (4)
- A Blowhole is a combination of two features: a pot hole on top of a cliff, created by chemical weathering, and a cave, formed by marine erosion.
- As the cave erodes deeper into the cliff face and the pothole deepens, they may meet.
- a channel is created for incoming waves to travel into and up the cliff face
- occasionally water splashes out of the top of the blowhole when energetic waves hit the cliff face
Describe long shore drift (LSD) (4)
● Waves hit the beach at an angle determined by the direction of the prevailing wind.
● The waves push sediment in this direction and up the beach in the swash.
● Due to gravity, the wave then carries sediment back down the beach in the backwash.
● This moves sediment along the beach over time.
Processes of transportation (4)
- traction
- saltation
- suspension
- solution
Define traction
Large, heavy sediment rolls along the sea bed, being pushed by currents.
Define saltation
Smaller sediment bounces along the sea bed, being pushed by currents.
Define suspension
Small sediment is carried within the water column (a body of water)
Define solution
Dissolved material is carried within the water
Factors affecting the effectiveness of transportation
The impact of transportation depends on the severity of the angle that waves travel onto land.
Define drift-aligned
waves approach at a significant angle, so longshore drift causes the sediment to travel far up the beach.
Define swash-aligned
wave crests approach parallel to coast so there is limited longshore drift. Sediment doesn’t travel up the beach far.
When does deposition occur?
- Deposition occurs when a wave loses energy meaning the sediment becomes too heavy to carry.
- Deposition tends to be a gradual and continuous process - a wave won’t drop all of its sediment all at once.
Define gravity settling
the wave’s energy becomes very low and so heavy rocks and boulders are deposited followed by the next heaviest sediment.
Define flocculation
clay particles clump together due to chemical attraction and then sink due to their high density
Describe the formation of a spit (5)
- A spit is a long narrow strip of land which is formed due to deposition.
- Longshore drift occurs along the coast line but as the waves lose energy (normally due to going into a sheltered area such as behind a headland) they deposit their sediment. Over time this creates a spit.
- Periodically, the prevailing wind will change direction causing a hook to appear.
- the sheltered area behind a spit can turn into a salt marsh.
- The length of a spit is influenced by surrounding currents or rivers.
Describe a bar
A spit which, over time, crosses a bay and links up two sections of coast (the water within the bay is called a lagoon).
Describe the formation of a tombolo
- A tombolo is a bar or beach that connects the mainland to an offshore island and is formed due to wave refraction off the coastal island reducing wave velocity, leading to deposition of sediments.
- They may be covered at high tide if they are low lying.
Describe the formation of cuspate forelands
- Only occurs with triangular shaped headlands.
- Longshore drift along each side of the headland will create beaches, which where they meet, will form a cuspate foreland.
Describe the formation of offshore bars
- A region offshore where sand is deposited, as the waves don’t have enough energy to carry the sediment to shore.
- They can be formed as the wave breaks early, scouring the seabed and instantly depositing its sediment as a loose-sediment offshore bar.
Conditions required for sand dunes to form
- Sand dunes occur when prevailing winds blow sediment to the back of the beach and therefore the formation of dunes requires large quantities of sand and a large tidal range.
- This allows the sand to dry, so that it is light enough to be picked up and carried by the wind to the back of the beach.
- Frequent and strong onshore winds are also necessary
Embryo dune
Upper beach area where sand starts to accumulate around a small obstacle (driftwood, wooden peg, ridge of shingle)
Yellow dune
- As more sand accumulates and the dune grows, vegetation (marram grass) may develop on the upper and back dune surfaces, which stabilises the dune
- The tallest of the dune succession
Grey dune
Sand develops into soil with lots of moisture and nutrients, as vegetation dies, enabling more varied plant growth.
Describe a dune slack
The water table rises closer to the surface, or water is trapped between hollows between dunes during storms, allowing the development of moisture-loving plants (e.g. willow grass)
Climax community
Sandy soils develop as there is a greater nutrients content, allowing for less brackish plants to thrive. Trees will also grow (willow, birch, oak trees) with the coastal woodland becoming a natural windbreak to the mainland behind.
Describe the stability of depositional landforms (3)
- Depositional landforms consist of unconsolidated sediment and are therefore vulnerable to change.
- During major storms, large amounts of sediment can be eroded or transported elsewhere removing a landform from one region of the sediment cell.
- Depositional landforms depend on a continuous supply of sediment to balance erosion, which may see some landforms changed as their dynamic equilibrium shifts.