Geography(physical)- Coasts

Mrs.Cross

Crest

Crest

Highest point of a wave

Trough

Bottom of a wave

Wavelength

Distance between two wave crests or troughs

Wave height

The vertical distance from the crest to the trough

Fetch

Maximum length of open water over which wind can blow unobstructed

Frictional drag

Work done by wind, transferring energy to water creating ripples

Dynamic Equilibrium

Balance in a system when inputs and outputs are equal

Positive feedback

Moving further away from dynamic equilibrium

Negative feedback

Getting closer to reaching equilibrium

Constructive waves

Build up the beach, swash stronger than backwash

Destructive waves

Erode the beach, backwash stronger than swash

Swash

Movement of water up the beach

Backwash

Return of water to the sea after swash

Constructive waves frequency

6-8 waves per minute

Destructive waves frequency

10-14 waves per minute

Positive feedback system

System moving further away from equilibrium

Negative feedback system

System getting closer to reaching equilibrium

Isolated system

Has no interactions beyond its bounds

Closed system

Transfers energy and matter across its boundary

Open system

Transfers both matter and energy across its boundary

Friction

Causes elliptical orbits in waves approaching shore

Formation of a wave

Waves are created by transfer of energy from wind over the sea surfaces (frictional drag). The energy acquired by waves depends on strength of wind, length of time it's blowing and fetch

Types of wave

Constructive and Destructive

Features of a constructive wave

Swash is stronger than backwash so more deposition

Steeper beach is created

Smaller wave frequency (6-8wpm)

Wave height is bigger

Features of destructive wave

Backwash is stronger than swash so material is eroded

Flatter beach created

Larger wave frequency (10-14 wpm)

Wave height smaller

Which type of wave creates a beach

Constructive

Which type of wave destroys a beach

Destructive

How do waves break

Friction at the top of wave which is prevailing wind. Waves at sea have circular orbits. As it approaches shore, base of wave slow down due to shore friction, Top of wave is still moving at same speed, therefore wave 'folds over' creating elleptical orbit. Wave tops over then breaks over

Negative Feedback System

Most beaches go through alternating cycle of constructive and destructive wave.

Constructive waves build up the beach resulting in steeper beach profile which encourages wave to become more destructive.

Destructive waves move material back towards the sea reducing the beach angle and encouraging more constructive waves

Cycle repeats

Spring tide

When the highest high tide and the lowest low tides occur when the sun and the moon are in alignment. Both of their gravitational forces combine to effectively pull the oceans towards them to cause the highest high tides. On the other side of the planet, this creates the lowest possible low tides.

Neap tide

The lowest high tide and the highest low tides occur when the sun and the moon are perpendicular to each other. Both of their gravitational forces act against each other , so the overall pull is minimised at high tide, but therefore creates a higher low tide.

What causes highest tidal range

Spring Tide

What causes lowest tidal range

Neap tide

What is wave refraction

process by which waves turn and lose energy around a headland on uneven coastlines.

Explain wave refraction

Waves drag in the shallow water approaching a headland so the wave becomes high, steep and short. The part of the wave in the deeper water moves forward faster causing the wave to bend. The low-energy wave spills into the bays as most of the wave energy is concentrated on the headland.

Discordant coastlines

Made up of alternating bands of hard and soft rock at perpendicular (right angles) to the coast

Concordant coastlines

Alternating bands of hard and soft rock parallel to the coast

Sediment cell

A length of the coastline that is relatively self contained as far as the movement of sediment is concerned

Marine input in sediment cells

Waves, Tides, Salt Spray

Atmospheric inputs in sediment cells

Sun, Air Pressure, Wind Speed and Direction

Human inputs in sediment cells

Pollution, Recreation, Settlement, Defences

Outputs in sediment cells

● Ocean currents

● Rip tides

● Sediment transfer

● Evaporation

Stores in sediment cells

● Beaches

● Sand Dunes

● Spits

● Headlands and Bays

● Nearshore Sediment

● Cliffs

Transfers in sediment cells

● Mass-movement processes

● Longshore drift

● Weathering

● Erosion

● Transportation

● Deposition

Explain positive sediment budget

More material added to cell than removed causing accretiom of material

Explain negative sediment budget

More material removed from cell than added

Weathering

The breaking down of rocks and other materials on the Earth's surface. This makes erosion take place easier and quickly

Mechanical weathering

the breakdown of rocks due to exertion of physical forces without any chemical changes taking place

Types of mechanical weathering

Freeze-thaw : Water enters cracks in rocks and then the water freezes overnight during the winter. As it freezes, water expands in volume which increases the pressure acting on a rock, causing cracks to develop. Over time these cracks grow, weakening the cliff making is more vulnerable to other processes of erosion

Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock, which forces the cracks to widen. Salt can also corrode ferrous rock due to chemical reactions

Wetting and Drying: Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up

Biological weathering

The breakdown of rocks by organic activity

Types of biological weathering

Plant Roots - Roots of plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rocks.

Birds - Some birds such as Puffins dig burrows into cliffs weakening them and making erosion more likely

Rock Boring - Many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face Seaweed Acids - Some seaweeds contain pockets of sulphuric acid, which if hit against a rock or cliff face, the acid will dissolve some of the rock's minerals.

Decaying Vegetation - Water that flows through decaying vegetation and then over coastal areas, will be acidic, thus causing chemical weathering

Chemical weathering

The breakdown of rocks through chemical reactions

Types of chemical weathering

Carbonation: Rainwater absorbs CO 2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved. Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion

Oxidation: When minerals become exposed to the air through cracks and fissures , the mineral will become oxidised which will increase its volume causing the rock to crumble. The most common oxidation within rocks is iron minerals becoming iron oxide, turning the rock rusty orange after being exposed to the air

Solution: When rock minerals such as rock salt are dissolved

Erosion

Processes by which rock, sand, and soil are broken down and carried away (i.e. weathering, glaciation)

Hydraulic action

The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.

Wave quarrying

When waves break against sands and gravels and scoops out loose material

Corrosion

Material is thrown at base of a cliff, chipping away at the rock

Abrasion

A wearing away or rubbing away by friction. Sand paper effect

Solution

Acids in seawater can dissolve alkaline rocks

Types of Transportation

solution, suspension, saltation, traction

Traction

Large pebbles rolled along the seabed.

Saltation

Small pebbles and stones are bounced along the river bed

Suspension

Small particles are carried along by the water

Solution

Dissolved chemicals often derived from limestone or chalk

Longshore drift

The movement of water and sediment down a beach caused by waves coming in to shore at an angle

Beach

Accumulation of sand and shingles found along the shore of a lake or ocean

Pebble beach

Found where cliffs are being eroded by high energy waves

Formation of beaches

Waves refraction means that energy is concentrated on the headlands so not enough energy left to carry the material when in the bay so deposition by constructive waves to make a beach

Offshore zone

Beyond the influence of waves, Beyond breakpoint bar

Nearshore zone

Experiences breaking waves, between breakpoint and low water marks

Foreshore zone

Intertidal or surf zone, between low and high water marks

Back shore zone

Above influence of the waves. Beginning above high water mark

Characteristics of a sandy beach

More gentle. Flatter material has reduced pore space. More compact so backwash can drag the material back out towards sea. Flat gradient

Characteristics of pebble beach

Less gentle. Flat material has increased pore space. Less compact so swash can pull material away from the sea. Steep gradient

Sweep zone

Zone of change between the two profiles

Berms

Ridges of sand and pebbles found at high tide marks resulting from deposition at top of the swash

Why do constructive waves form steeper beaches

Strong swash moves material up the beach and the weak backwash can't flatten the profile. Overtime this will attract more destructive waves which will flatten the profile with strong backwash

Storm beach

At back of the beach, very strong swash during storm conditions may deposit larger material forming storm beach or ridge

Cave formation

Crack forms at side of headland by hydraulic action and abrasion. Crack widens forming a cave

Arch formation

Wave refraction causes cave on opposite sides of headlands to erode through to joint together forming arch

Stack formation

Arch is made wider and eventually collapses as it can't support its own roof, weathering on top of headland helps this. A stack is left

Stump formation

Erosion at base of stack causes it to collapse

Mass movement

The downhill movement of rock and soil because of gravity

Types of mass movement

Rockfalls, slides, slumps, flows, soil creep

Soil Creep

Slow movement of soil down a slope due to gravity.

Mudflows

A rapid downhill movement of a mixture of water, rock, and soil

Landslide

A slide of a large mass of dirt and rock down a mountain or cliff

Rockfall

A sudden collapse of individual rock fragments at a cliff face

Rotational slump

The term given to when saturated soil and weak rock slump along a curved slip plane.q

Swash aligned beach

A beach formed in a low energy environment by waves are parallel to the shore.

Drift aligned beach

A type of beach formed when waves approach at an angle and sediment is moved along the beach by longshore drift.

Formation of a simple spit

Longshore drift moves material along the coastline in a zigzag motions in direction of prevailing wind. When coat changes shapes or meets a river estuary, the LSD loses its energy and deposits material. Over time this build up to form a simple spit

Compound spit

When end of spit curves when wind direction changes

Salt marsh

Areas of flat, silty sediments temperate-zone estuary dominated by salt-tolerant grasses above the low-tide line but below high tide line

Formation of salt marsh

Pioneer plants colonise during high and low tide. Gradually mud levels rise ab0ve high tide and more plants can colonise as they no longer need to be able to cope with salty conditions. Soil conditions improve and vegetation succesion continues until shrubs can colonise to create climax community

Formation of tombolo

•A tombolo is formed when a spit connects the mainland to an island.

The process of longshore drift occurs and this moves material along the coastline.

When the coastline changes direction, the process of longshore drift continues and forms a sandspit.

If this feature moves in the direction of the island and connects it to the mainland, then it becomes a tombolo.

Formation of barrier beach

Continuation of a spit connecting it to another piece of land ususlaly a headland. Bar seperates the sea from the lagoon, making the lagoon a sheltered, low environment area

Offshore bar

submerged or partly exposed ridge of sand or coarse sediment that is built by waves offshore from a beach

Offshore bar formation

Sand is eroded from the beach with destructive waves and this material is deposited offshore. They act as a sediment store and potentially an input they also absorb the waves energy, reducing impacts of erosion

Sand dunes

Accumulations of sand shaped into mounds by the wind. They go through procces of succesion, where conditions change from sand to soil and forest.