A Level Geography - Coasts

What is wind?

What is wind?

The horizontal movement of air from an area of high pressure to an area of low pressure

What is fetch?

The distance the wind blows across the water without being interrupted by major land obstacles

How are waves formed?

Air moves over the surface creating frictional drag which disturbs the surface creating ripples. As the water becomes shallower the circular orbit of the water particles changes to an elliptical one. The wavelength and velocity decrease and the wave height increases causing the water to back up from behind and rise to a point where it topples over. The water rushes up the beach as swash and down as backwash.

What is the wave crest?

Highest point of a wave

What is the wave trough?

Lowest point of a wave

What is the wave height?

The distance between the highest and lowest part of the wave

What is wavelength?

The distance between corresponding points on successive waves

What is the wave period?

The time in seconds between two successive crests or troughs

What is wave frequency?

The number of waves per minute

What is swash?

Movement of water up the beach

What is backwash?

Movement of water down the beach

What are swell waves?

Waves in open water, characterised by long wavelengths and reduced height. They can reach up to 15m high and can travel huge distances

What are storm waves?

Waves generated by local winds which travel only short distances - seen near the coast

Formation of constructive waves

Distant weather systems generate these waves in the open ocean

Formation of destructive waves

Local storms generate these waves

Constructive vs Destructive waves - wave form/shape

Constructive - low, surging waves with a long wavelength

Destructive - high, plunging waves with a short wavelength

Constructive vs Destructive waves - breaking characteristics

Constructive - strong swash, weak backwash

Destructive - weak swash, strong backwash

Constructive vs Destructive waves - net effect on the beach

Constructive - beach gain

Destructive - beach loss

Constructive vs Destructive waves - beach profile

Constructive - gentle beach profile, overtime will get steeper due to sediment build up

Destructive - steeper beach profile, overtime will flatten

Constructive vs Destructive waves - wavelength

Constructive - long (up to 100m)

Destructive - short (less than 20m)

Constructive vs Destructive waves - wave frequency

Constructive - low (6-8wpm)

Destructive - high (13-15wpm)

Constructive vs Destructive waves - wave period

Constructive - 6-8 per minute

Destructive - 10-14 per minute

What is wave refraction?

The bending of waves as they approach an irregular shaped coastline

How does wave refraction at headlands affect deposition and erosion?

Deposition increases in bays due to a lack of energy. At the headland, wave energy is concentrated so there is lots of erosion. This eroded sediment is deposited in the bays

What are tides?

The periodic rise and fall of ocean water on the shoreline caused by the gravitational pull of the sun and the moon.

What is the tidal interval?

12hrs 25mins

What is the effect of the moon?

'Pulls the water towards it' or to create an outward bulge on oceans closest to the moon (also a compensatory bulge on the other side of the earth)

What is high tide?

Moon pulls water towards it creating a bulge of water creating a high water levels

What is low tide?

When the water reaches its lowest point

What is the tidal range?

The vertical difference between the high tide and the succeeding low tide

What is a spring tide?

Twice a lunar month, when the moon, sun and earth are in a straight line, the tide-raising force is the strongest. This produces the highest monthly tidal range.

What is a neap tide?

Twice a month, the moon and sun are positioned at 90 degrees (perpendicular) to each other in relation to the earth. This alignment gives the lowest monthly tidal range (usually 10-30% lower).

What is a macrotidal range?

More than 4m

What is a mesotidal range?

2-4m

What is a microtidal range?

Less than 2m

What is a storm surge?

An abnormal rise of water generated by a storm, over and above the predicted astronomical tide.

What is a storm tide?

Is the water level rise during a storm due to the combination of storm surge and the astronomical tide.

When do storm surges occur?

With low pressure weather systems - lower atmospheric pressure over the sea allows the water level to rise, whereas a higher pressure would cause it to fall.

What is the main cause of a storm surge?

High winds

What happens when a surge occurs at low tide?

The rise in water level may not be enough to cause damage, flooding or override defences.

What happens when a surge occurs at high tide?

Can be devastating to the local areas

What are currents?

A cohesive stream of seawater that circulates through the oceans

What are the two types of ocean currents?

Surface currents and Deep currents (300m)

What factors affect currents?

• Tides - gravitational pull

• Imbalance in solar energy between the equator and poles

• Wind affects surface currents

• Ocean temperature creates density differences

• Salinity differences

What is a gyre?

A well-organised, roughly circular flow of surface water

What do ocean currents do?

Move water horizontally and vertically and occur at both local and global scales.

What do surface currents do?

Wind-driven so move water vertically and horizontally. Horizontal surface currents are local ad typically short term. They include rip currents, longshore currents and tidal currents. Upwelling currents is a vertical water movement and mixing bringing cold water towards the surface while pulling warmer, less dense water downwards where it condenses and sinks.

What are longshore currents?

Occurs as most waves do not hit the coastline 'head on' but approach at an angle to the shoreline. This generates a flow of water (current) running parallel to the shoreline. This not only moves water along the surface but also transports sediment parallel to the shoreline.

What are rip currents?

Strong currents moving away from the shoreline. Develop when seawater 'piles up' along coastline by incoming waves. Initially may run parallel to the coast before flowing out through the breaker zone, possibly at a headland or where the cost changes direction. Extremely hazardous to swimmers and small boats

Characteristics of low energy coasts

• Low wave energy

• Rate of deposition exceeds rate of erosion of sediment

• Often have: beaches, bays and spits

• Examples: estuaries, inlets and sheltered bays

Characteristics of high energy coasts

• Strong, steady prevailing winds create high energy waves

• Rate of erosion exceeds rate of deposition

• Often have: headlands, cliffs and wave-cut platforms

What is sediment?

Any naturally occurring material that has been broken down by the processes of erosion and weathering and has then been transported and subsequently deposited by the action of ice, wind and water

What are some sediment sources on the coast?

• Erosion on beaches, headlands, stacks, stumps, spits and sand dunes

• Cliff erosion

• Wind blown sources

• Rivers and estuaries

• Beach nourishment

• Glacier meltwater

• Offshore sources

What are sediment cells?

Areas along the coastline and in the nearshore area where the movement of material is largely self-contained. They are often determined by the topography and shape of the coastline which directs the movement of sediment within the cell. They are a closed system and sediment is largely recycled within them.

What are the boundaries of sediment cells?

Typically headlands and peninsulas which act as natural barriers.

What happens to sediment in sediment cells in high energy conditions?

Changes in wind direction and movements of ocean currents can remove sediment.

How many sediment cells are there in England and Wales?

11

What are sediment budgets?

The balance between charges in the volume of sediment held within the system and the volume of sediment entering or leaving the system.

What is a positive budget?

When there are more inputs than outputs to the system

What is a negative budget?

When the outputs are higher than the inputs to a system

What are geomorphological processes?

The study of landforms, their processes, formation ad sediments at the surface of the Earth and how they change overtime

Examples of geomorphological processes

Weathering, mass movement, erosion, transportation, deposition

At what rate do geomorphological processes operate at?

SLow rate

What are marine processes?

Processes that operate upon a coastline that are connected with the sea such as waves, tides and longshore drift (sea-based)

What are subaerial processes?

Includes processes that (usually) slowly break down the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily. Materials are broken down in-situ. These may affect the shape of the coastline, and include weathering , mass movement and run-off.

What is weathering?

The breakdown and/or decay of rock at or near the Earth's surface creating regolith that remains in-situ until it is moved by later erosional processes. It can be: mechanical, biological/organic or chemical.

What is mass movement?

The downhill movement of weathered material due to the force of gravity

What is run-off?

All the water that enters a river channel and eventually flows out of the drainage basin

What is marine erosion?

The wearing away of the Earth's surface by the mechanical action of processes of glaciers, wind, rivers, marine waves and wind

What is marine transportation?

The processes that move material from the site where erosion took place to the site of deposition

What is marine deposition?

Takes place where the waves are low energy or where rapid coastal erosion provides an abundant supply of material.

What is aeolian deposition?

Sediment transported and then deposited by wind.

What is mechanical weathering?

The breakdown of rock without changing its chemical composition

What is freeze-thaw weathering?

When water gets into cracks in the rock. The water freezes and expands, putting pressure on the rock. The ice then thaws releasing the pressure. If this is repeated, bits of the rock will fall off.

What is salt crystallisation weathering?

When salt water evaporates it leaves salt crystals behind. They grow overtime and exert stress on the rock (like ice) causing it to break up. Salt can also corrode rock, especially if it has traces on iron in it.

What is wetting and drying weathering?

Frequent cycles of wetting and drying are common on the coast. Rocks rich in clay (e.g shale) expand when they get wet and contract as they dry. This can cause them to crack and break up.

What is biological weathering?

The breakdown of rocks by organic activity

What do plants have to do with biological weathering?

Their roots grow into small cracks in a cliff face. These cracks widen as the rocks grow, which breaks up the rock.

What does water have to do with biological weathering?

Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering.

What do animals have to do with biological weathering?

Birds - e.g puffins and sand martins Animals - e.g rabbits dig burrows into the cliff, weakening it

What do marine organisms have to do with biological weathering?

Piddocks - burrow into the rocks Limpets - secrete acids

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 carbonation weathering?

Rainwater combines with dissolved carbon dioxide in the atmosphere to produce a weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone and chalk to produce calcium bicarbonate, which is soluble.

How does temperature affect carbonation rates?

When the rainwater is cooler more carbon dioxide is absorbed - this means that carbonation is more effective in winter.

What is oxidation weathering?

Causes rocks to disintegrate when the oxygen dissolved in water reacts with some minerals, forming oxides and hydroxides. It especially affects ferrous, iron-rich rocks, and is evident by a brownish or yellowish staining of the rock surface.

What is solution weathering?

Any processes by which a mineral dissolves in water is known as solution.

What is hydrolysis weathering?

Where mildly acidic water reacts or combines with minerals in the rock to create clays and dissolvable salts; this itself degrades the rock , but both are likely to be weaker than the parent rock, thus making it more susceptible to degradation.

What is acid rain weathering?

Formed by the presence of sulphur dioxide and nitric oxides creating rainwater with weak sulphur acid and nitric acids. The acid rain then reacts with various minerals in different rocks, weakening or even dissolving them.

What is mass movement?

The downhill movement of weathered material due to the force of gravity

What is soil creep?

• Very slow movement of individual particles downhill - few mm per year

• Soil build up behind walls/fences

• Bases of trees turned downslope

• Evidence = terraces

• Zig-zag movement of particles

What is a mudflow?

• Earth and mud flowing downhill suddenly in a fast rate

• Often happens after rainfall

• Usually over unconsolidated or weak rock e.g clay

Why does a mudflow happen?

Water gets trapped within the rock which increases the pore water pressure. This forces rock particles apart and leads to the slope failure.

What is a slump?

• A sharp break of slope and the formation of a scar

• Can create a terraced appearance if multiple happen

• Often occur in weak and unconsolidated clays and sands and when permeable rock overlies impermeable rock which causes a build-up of porewater pressure

What is a landslide?

• Blocks of rock moving very rapidly downhill along a plane

• Often a bedding plane that is roughly parallel to the ground

• Frequently triggered by earthquakes or very heavy rainfall - slip surface becomes lubricated and friction is reduced

• Tend to be very rapid and pose a significant threat to people and property.

• Block of rock stays largely intact

What is a rockfall?

• Fragments of rock break away from the cliff face, often due to freeze-thaw weathering.

• Once broken away they fall or bounce down the slope to form scree

• Commonly associated with heavily jointed, steep resistant rock cliffs

• Sudden

What is scree?

Temporary store within the coastal system with material gradually being removed and transported. (Sediment cell INPUT)

What is erosion?

The breakdown of sediment in-situ e.g headlands or cliffs - marine processes

What is hydraulic action?

When a wave attacks on a cliff or platform edge exerts tremendous hydraulic pressure and erosive force along lines of weakness. The water trapped in cracks become compressed by the incoming waves, followed by expansion and eventual cracking of rocks

What is wave quarrying?

The removal of rocks and other debris on cliffs or wave-cut platforms from their original position by wave actions

What is cavitation?

Occurs when there is intense erosion due to the surface collapse of air bubbles found in rapid flows of water. The tiny micro-ket puts great pressure and extreme stress on a very small area of a surface.