Coasts

Question 1

What is a sediment cell? How many are there in the UK?

Answer 1

A stretch of coastline and its associated nearshore area, within which the movement of coarse sediment, sand and shingle is largely self contained
A closed system bounded by physical landforms such as headlands (sources) and bays (sinks) - where processes such as erosion, transportation and deposition occur
Little or no movement of sediment between cells
11 in the UK
There are sub-cells within cells

Question 2

What is a system?

Answer 2

A set of interrelated elements comprising stores and processes that are connected together to form a working unit - store and transfer energy and material

Question 3

Name some inputs, outputs and throughputs of energy in coastal systems

Answer 3

Inputs - thermal, kinetic, potential energy, material from marine deposition, weathering and mass movements
Outputs- Marine and wind erosion, evaporation
Throughputs - longshore drift (flows and transfers) or stores (e.g. sediment on a beach)

Question 4

What is mass movement?

Answer 4

Downslope movement of material under gravity, without the aid of a moving force

Question 5

What is equilibrium in coastal systems? What is dynamic equilibrium?

Answer 5

Inputs = outputs (rate at which sediment added to beach = rate at which it is removed)
System changes to restore equilibrium if it is disturbed - negative feedback

Question 6

How are waves formed and what affects their size and energy?

Answer 6

Frictional drag of wind across the ocean surface
Higher the windspeed and longer the fetch (distance of open sea over which wind blows), the larger the waves and the more energy they possess (more destructive)
Speed, direction and frequency of winds all influence wave formation and action processes

Question 7

What are swell waves? How do they differ from storm waves?

Answer 7

Swell waves are formed in open ocean and generally have long wavelengths and a wave period of up to 20 seconds
Storm waves are locally generated and typically have a shorter wavelength, greater height and a shorter wave period

Question 8

How do waves break?

Answer 8

As they move into shallow water, friction between sea floor and water causes them to slow down, their height to increase and wavelength to decrease - break when water depth is less than 1.3x wave height
Circular motion of waves becomes forwards motion when they break - transferring energy to the the coast

Question 9

What are the 3 types of breaking wave and briefly describe each?

Answer 9

Spilling - steep waves break on gently sloping beaches and spill gently forwards
Plunging - moderately steep waves break onto steep beaches - water plunges vertically downwards
Surging - low angle waves breaking onto steep beaches - wave slides forwards

Question 10

Describe and explain tides

How are they significant in coastal development?

Answer 10

Tides are the periodic rise and fall of the sea surface and are largely produced by the gravitational pull of the moon
Compensatory bulge on opposite side to moon (high tide) Between 2 bulges - low tide
Twice a month sun, earth and moon line up, creating strongest gravitational pull, leading to high tidal range (spring tides)
Twice a month sun and moon perpendicular - neap tides with low tidal range
Tidal range can be significant in development of coastlines (e.g. if low more concentrated wave action processes - more undercutting) - e.g. enclosed seas

Question 11

What are the 2 factors which make up geology?

Answer 11

Lithology - physical and chemical composition of rocks
Structure - properties of individual rock types such as jointing, bedding and faulting which affects the permeability of rocks

Question 12

How does lithology influence coastal landscape systems?

Answer 12

Some rock types have a weak lithology, with little resistance to erosion, weathering and mass movements
- because bonds between particles that make up rock are quite weak, as in clay
Other rock types (e.g. basalt) are made of dense interlocking crystals and are very resistant
Some (e.g. chalk) are largely composed of calcium carbonate and are soluble in weak acids - prone to weathering by carbonation

Question 13

How does rock structure influence coastal landscape systems?

Answer 13

Affects permeability of rocks
Cracks, joints, faults can be exploited by wave processes
Porous rocks (e.g. chalk) - small air spaces separate mineral particles - pores then absorb and store water (known as primary permeability)
Carboniferous limestone is permeable because of its many joints (secondary permeability)
Rocks with more cracks, faults etc. more susceptible to erosion and weathering processes

Question 14

What are currents and how do they influence coastal landscapes?

Answer 14

Generated by the Earth’s rotation and convection - they are set in motion by movement of winds across the water surface.
Warm ocean currents transfer heat energy from low latitudes towards the poles. Cold ocean currents move water from polar regions towards the equator
Strength of current itself has limited impact but transfer of heat energy can be significant as directly affects air temperature and therefore subaerial processes of weathering and mass movement

Question 15

What is porosity?

Answer 15

How much of a rock is open space

Question 16

What are terrestrial sources of coastal sediment?

Answer 16

Fluvial deposition - origin of terrestrial sediment is erosion of inland areas by water, wind, ice, subaerial processes of weathering and mass movement - this sediment is transported to the coast by rivers, which deposit it at their mouths as they lose energy
Marine erosion - cliff erosion by waves - erosion of weak cliffs in high-energy wave environments can contribute to as much as 70% of overall material supplied to beaches - some may be large rocks and boulders often from mass movement on undercut cliffs
Aeolian deposition of very fine particles deposited as winds lose energy
Longshore drift - can sediment to one coastal area by moving along the coast from adjacent areas

Question 17

What are offshore sources of coastal sediment?

Answer 17

Waves deposit sediment onshore from offshore locations. Marine deposition occurs when waves lose energy, typically after breaking - same with tides and currents
Wind can also blow fine sediment from offshore locations, including exposed sand bars

Question 18

What are human sources of coastal sediment?

Answer 18

Beach nourishment - human management of beaches - sand or other sediment added as a feature of coastal management and protection against erosion - sand brought in from external sources and pumped onshore or brought by lorry

Question 19

Describe physical (mechanical) weathering and how it can develop coastal landforms

Answer 19

Freeze-thaw - water enters cracks/joints and expands by nearly 10% when it freezes - exerts pressure on rocks causing it to split or pieces to break off
Thermal expansion - rocks expend when heated and contract when cooled - frequent cycles of temperature change can cause outer layers to crack and flake off (onion-skin weathering)
Pressure release (exfoliation) - overlying rocks removed by weathering and erosion, underlying rock expands and fractures parallel to surface
Salt crystallisation - salt solutions enter rock (through pores and joints etc.) - salts precipitate and from crystals - the growth of these crystals creates stress in rock, causing it to disintegrate

Question 20

Describe chemical weathering and how it can develop coastal landforms

Answer 20

Oxidation - some minerals (especially iron) react with oxygen (in air or water) to form oxides, making them weaker and soluble under acidic conditions - original structure is destroyed
Carbonation - rocks containing carbonates react with weak carbonic acid rain or weakly acidic water to produce calcium bicarbonate, which is soluble in water
Solution - some minerals are soluble in water - as they dissolve they weaken the structure of a rock
Hydrolysis - chemical reaction between rock minerals and water - e.g. silicates combine with water producing secondary minerals, such as clays
Hydration - water molecules are added to rock minerals, creating new minerals of a larger volume, which can create stress. E.g. anhydrite forms gypsum

Question 21

Describe biological weathering and how it can develop coastal landforms

Answer 21

Tree roots grow into cracks or joints in rocks and exert outward pressure, causing rock to split
Burrowing animals may have a similar effect to the above
Organic acids may be secreted by certain organisms (e.g. molluscs) or released by algae, and these react with rock minerals, weakening them or making them more soluble

Question 22

What is weathering?

Answer 22

The in-situ breakdown and decay of rock through exposure to the Earth’s atmosphere, organisms and water

Question 23

What are the differences in the effects that physical and chemical weathering have?

Answer 23

Physical weathering breaks rocks into smaller fragments of the same rock. Chemical weathering alters the chemical makeup of substances in rocks, weakening them.

Question 24

What are the two main types of mass movements in coastal landscapes?

Answer 24

Rock fall - on cliffs of 40° or more rocks may become detached by physical weathering processes. These rocks then fall to the foot of the cliff under gravity. - can be cleared by wave processes or may accumulate and form a scree slope
Slides - May by linear, with movement along a straight line slip plane, such as a fault or a bedding plane between layers of rock, or rotational, with movement taking place along a curved slip plane (also known as slumps)

Question 25

What are the 5 main types of erosional wave (marine) processes?

Answer 25

Abrasion, pounding, attrition, hydraulic action, solution

Question 26

What is abrasion?

Answer 26

Material carried by waves is thrown at cliffs and coastline and rubs and hits against it, breaking it down an weakening it.

Question 27

What is hydraulic action?

Answer 27

Waves break against a cliff face and air and water trapped in cracks and crevices becomes compressed. As the wave recedes, pressure is released, the air and water suddenly expand and the crack is widened

Question 28

What is pounding?

Answer 28

The mass of a breaking wave exerts pressure on the rock, weakening it and breaking it down

Question 29

What is attrition?

Answer 29

Material carried by waves collide with each other and coastal rocks, becoming worn down and worn away into smaller particles

Question 30

What is solution?

Answer 30

Sea water dissolves certain materials and minerals in rocks, weakening the rock’s structure, leaving it more vulnerable to marine and subaerial processes

Question 31

How do wave processes lead to transportation of sediment?

Answer 31

Solution - dissolved minerals moved in water
Suspension - small particles are suspended and carried by water - salt, clay, sand carried by currents - accounts for brown/muddy appearance of some sea water
Saltation - series of irregular movements of material which is too heavy to be carried continuously in suspension - turbulent flow may pick up particles and carry them for a short distance, only to drop them again
Traction - largest particles may be pushed along the sea floor by the force of the flow - movement is seldom continuous

Question 32

How does longshore drift transport sediment in coastal landscapes?

Answer 32

Waves approach coast at an angle (due to direction of dominant wind) and after breaking the swash carries particles diagonally up the beach, then backwash drags them perpendicularly back down the beach (due to gravity) - this movement is repeated, causing a net movement of material along the beach

Question 33

How do wave processes lead to deposition of sediment in coastal environments?

Answer 33

Deposition occurs when the rate of sediment accumulation exceeds the rate of sediment removal
Material is deposited when there is a loss of energy caused by a decrease in velocity and/or volume of water
Deposition also occurs when:
- when waves slow down immediately after breaking
- At the top of the swash, where for a brief moment the water is no longer moving
- during the backwash, when water percolates into the beach material
- in low energy environments, those sheltered from winds and waves, such as estuaries

Question 34

Fluvial (river) processes are very similar to wave processes in terms of erosion and transportation (and mass movement processes on valley sides causes sediment to enter the channel). How does deposition occur from rivers?

Answer 34

Noticeable reduction in river velocity as they enter the sea, so energy is reduced. Some or all of river’s sediment load is deposited. Reduction in energy is progressive, so deposition is sequential (largest particles deposited first and smallest carried further out to sea)
Deposition also results from flocculation

Question 35

What is flocculation?

Answer 35

When salt causes the aggregation of minute clay particles into larger masses that are too heavy to remain suspended in water - these are deposited and can lead to the development of salt marshes and mudflats

Question 36

How do wind processes contribute to the development of coastal landscapes?

Answer 36

Wind is able to pick up sand particles and move them. This enables abrasion to occur, as it does in waves. Particles are also subjected to attrition. Transportation is the same as in rivers and waves (with the exception of in solution)
Material is deposited when wind speed falls (loss of energy so particles are deposited)

Question 37

How do bays and headlands form?

Answer 37

Bands of rock of different resistance to erosion (discordant coastline). Weaker rocks are eroded more rapidly to form bays, more resistant rocks remain between bays as headlands - can also lead to wave refraction, with converging orthogonals concentrating energy onto the sides of headlands
Rocks lying parallel to the coastline produce a concordant coastline - if resistant rock lies on seaward side it protects any weaker rocks inland from erosion - resultant coastline is quite straight and even - small bays or coves may occasionally be eroded at points of weakness, such as fault lines

Question 38

How do cliffs and shore platforms form?

Answer 38

Undercutting can occur between high and low tide levels (due to constant breaking of waves between these levels and not as much above it) can form a wave-cut notch. Continued undercutting weakening support for the rock above, which eventually collapses producing a steep profile and a cliff - regular removal of debris at foot of cliff ensures cliff profile remains relatively steep and cliffs retreat inland parallel to the coast.
As the process continues and is repeated cliff retreat continues (and cliff becomes higher). At its base a gently sloping platform, called a wave-cut platform is cut into the solid rock - also deeply dissected by abrasion due to the large amount of rock debris dragged across the surface by wave action and weathering processes such as salt crystallisation at low tide. Mass movement from the cliff may leave large rocks and boulders on the platform

Question 39

How are geos and blowholes formed?

Answer 39

Geos are narrow steep sided inlets - weak points eroded more rapidly by wave action than the more resistant rock around them - hydraulic action particularly important
If part of the roof of a cave collapses it may form a vertical shaft that reaches the cliff top, known as a blow hole. In storm conditions large waves may force spray out of blow holes as plumes of white, aerated water

Question 40

How do caves, arches, stacks and stumps form?

Answer 40

Wave refraction concentrates wave energy towards sides of headlands (orthogonals converge). Points of weakness, such as faults or joints, are exploited by erosional processes and a small cave may develop on one or even both sides of a headland. Wave erosion is concentrated between high and low tide - it is here that caves form. Caves may be exploited further and enlarged to a point where they extend through to the other side of the headland, forming an arch (or could be 2 caves on opposite sides meeting). Sub-aerial processes may lead to the collapse of the arch - an isolated stack may remain, separated from the rest of the headland (e.g. Old Harry). Further erosion and weathering may lead to its collapse and the formation of a stump (a small, flat portion of the original stack - may only be visible at low tide)

Question 41

What is the most common depositional landform?

Answer 41

Beaches

Question 42

How do beaches form?

Answer 42

Beaches result from the accumulation of material deposited between the lowest tides and the highest storm waves
Sand produces beaches with a gentle gradient due to its small particle size - it becomes compact when wet, allowing little percolation during backwash - little energy lost to friction and little volume lost to percolation, so material is carried back down the beach rather than left at the top, resulting in a gentle gradient.
Shingle produces steeper beaches (pebbles, small to medium size cobbles) a swash is stronger than backwash so there is net movement of shingle onshore. May make up the upper part of a beach where rapid percolation (due to larger air spaces) means little backwash occurs and material is left at the top of the beach
Storm waves hurl pebbles and cobbles to the back of the beach, forming a storm beach or storm ridge.

Question 43

What are some features found on beaches?

Answer 43

Berms - small ridges that develop at the position of the high tide mark, resulting from deposition at the top of the swash
Cusps - small semicircular depressions - temporary features formed by a collection of waves reaching the same point and when swash and backwash have similar strength and direction - rip currents
Ripples may develop in sand due to orbital movement of water in waves

Question 44

How do spits form?

Answer 44

Spits are long, narrow beaches of sand and shingle attached to land at one end and extended across a bay, estuary or indentation in a coastline
Generally formed by longshore drift occurring in one dominant direction - carrying beach material to one end of the beach and then beyond into open water
End often becomes recurved as a result of wave refraction and/or a secondary wave/wind direction
May continue to grow and a number of recurves may develop
In the sheltered area behind a spit energy is reduced, which may lead to more deposition as wave energy is reduced. Silt and mud deposited build up and eventually salt tolerant vegetation may colonise, leading to the formation of a salt marsh

Question 45

How do onshore bars form?

Answer 45

If a spit continues to grow across an indentation (e.g. a cove or bay) in the coastline until it joins onto land on the other side - lagoon of brackish (salt and fresh mixed) water on landward side.
May also have been formed by onshore movement of sediment during the post-glacial sea-level rise that ended around 6000 years ago

Question 46

How do tombolos form?

Answer 46

Tombolos are beaches that connect the mainland to an offshore island - they are often formed from spits that have continued to grow seawards until they reach and join an island.
Like onshore bars may have been formed by onshore movement of sediment due to post glacial sea-level rise

Question 47

How do salt marshes form?

Answer 47

Salt marshes are features of low-energy environments such as estuaries and landward sides of spits.
They are vegetated areas of deposited silts and clays (in low-energy coastal environments)
Deposition of fine sediment occurs as rivers lose energy when the slow upon entering the sea, and also due to flocculation.
They are subjected to twice-daily inundation and exposure as tides rise and fall.
Salt-tolerant plant species such as spartina and eel grass help trap sediment, gradually helping to increase the height of the marsh.
Extensive networks of small, steep-sided channels, or creeks, drain the marsh at low tide and provide routes for water to enter the salt marsh as the tide rises.
Between the creeks, shallow depressions are often found. These trap water when the tide falls, and these areas of saltwater, called saltpans, are often devoid of any vegetation.

Question 48

How do deltas form?

Answer 48

Deltas are large areas of sediment found at the mouths of rivers
They form when rivers and tidal currents deposit sediment at a faster rate than the waves and tides can remove it
Criss-crossed by a branching network of distributaries
Levées (raised embankments formed by deposition during flooding) form on the banks

Question 49

What are the 3 distinctive components of deltas?

Answer 49

The upper delta plain - furthest inland - beyond reach of tides and composed entirely of river deposits
Lower delta plain - intertidal zone - regularly submerged and composed of both marine and river deposits
Submerged delta plain - below mean low tide mark - composed mainly of marine sediments and represent the seaward growth of the delta

Question 50

What are 3 types of delta

Answer 50

Cuspate, bird’s foot, arcuate (fan-shaped)

Question 51

Describe climate change and resultant sea level fall, and the types of landforms that it creates

Answer 51

130,000 years ago - Tyrrhenian inter-glacial period - global mean annual temperatures almost 3°C higher than today and sea level about 20m higher
Riss glacial period - dropped to minimum of 7°C lower than today (about 108,000 years ago) - less water returned to ocean store - sea levels dropped over 100m (83m below present day)
Decrease in global temperature leads to more precipitation in the form of snow - turns to ice and water is stored on land in solid form rather than being returned to the ocean store as liquid - decrease in volume of water in oceans and fall in sea level (+water molecules contract when cooled)
Sea level fall results in emergent landforms such as raised beaches, abandoned cliffs and marine terraces

Question 52

What are emergent landforms?

Answer 52

Landforms shaped by wave processes during times of high sea level are left exposed when sea level falls - may be found well inland, some distance from the modern coastline

Question 53

How are raised beaches and abandoned cliffs formed?

Answer 53

Raised beaches are areas of former shore platforms that are found at a higher level than present sea level - often found a distance from present coastline. Behind the beach, along emergent coastlines, it is not uncommon to find abandoned cliffs with wave cut notches, caves and even arches and stacks.
During inter-glacial periods when sea levels were much higher, erosion rates were higher due to deeper water allowing wave energy to be greater, with less being lost to sea-floor friction.

Question 54

How are marine terraces formed?

Answer 54

Sometimes sea level falls in a series of stages - marine erosion is able to develop a number of marine terraces, appearing as steps in the landscape - each one represents a period of stable temperatures and sea level during which wave action had a sufficient time to act significantly on the landscape to produce a flat, eroded terrace. Usually associated with falling sea levels due to cooling climate (eustatic changes), but can also be related to rising land levels (isostatic changes)

Question 55

How are emergent landforms modified?

Answer 55

After emergence, landforms no longer affected by wave processes, but continue to be affected by weathering and mass movement.
In post-glacial period, warmer and wetter conditions have led to development of vegetation cover on many such landforms, often making them more difficult to recognise (+biological weathering). With further warming of the climate predicted for the future, continued degradation is likely to occur with higher rates of chemical weathering and mass movement. Chemical weathering on the raised beach may also become more significant in warmer, wetter climatic conditions (and more carbonation in acid rain)
If temperatures increase sufficiently, associated sea-level rise could lead to these emergent landforms again being found much closer to, or even at, the coastline - would then be subjected to wave processes once more.
e.g. 1.5m layer of frost-shattered limestone debris on top of abandoned cliff on isle of Portland, deposited when the area experienced periglacial conditions during the last glacial period - evidence of frost weathering processes and cryoturbation in cliffs

Question 56

Describe climate change and resultant sea-level rise and the types of landforms it creates

Answer 56

End of Würm glacial period (25,000) temperatures about 9°C lower than today and sea level about 90m lower. Since then temperatures and sea-level rise is known as the Flandrian Transgression
Increase in global temperature leads to higher rates of melting of the ice stored on the land in glaciers - as a consequence there is an increase in the volume of water in the ocean store and a consequent rise in sea level. (+ water molecules expand as temperatures rise, leading to increased volume)
Sea level rise leads to submergent landforms such as rias, fjords and shingle beaches

Question 57

What are submergent coastal landforms?

Answer 57

Landforms shaped by wave processes during times of lower sea level are left submerge, or drowned when sea level rises

Question 58

How are rias formed?

Answer 58

Rias are submerged river valleys, formed as sea level rises - lowest part of river’s course and floodplains alongside the river may be completely drowned - higher land forming tops of valley sides and upper and middle part of the river’s course remain exposed. In cross section have relatively shallow water, becoming deeper in the middle (a v-shaped profile). Exposed valley sides are quite gently sloping. In long-section exhibit smooth profile and water of uniform depth. In plan view they tend to be winding, reflecting the original route of the river and its valley, formed by fluvial erosion within the channel and subaerial processes on the valley sides
e.g. poole harbour

Question 59

How are fjords formed?

Answer 59

Fjords are submerged glacial valleys - steep, cliff-like valley sides - water uniformly deep (often reaching over 1,000m). U-shaped cross section reflects original shape of the glacial valley itself, carved out by glaciers during glacial periods. Consist of a glacial rock basin with a shallower section at the end, known as the threshold - results from lower rates of erosion at the seaward end of the valley where the ice thinned in warmer conditions. Tend to have much straighter planforms than rias as the glacier would have truncated any interlocking spurs present
Due to depth of water what occupied fjords during the Flandrian Transgression, marine erosion rates remained high and in some cases the fjords were further deepened
e.g. Milford Sound, New Zealand

Question 60

How do shingle beaches form?

Answer 60

When sea level falls, large areas of ‘new’ land emerges from the sea. Sediment accumulates on this surface, deposited by rivers and low-energy waves. As sea level rose at the end of the glacial period, wave action pushed these sediments onshore. In some places they were deposited at the base of former cliff lines. Elsewehere they form tombolos and bars
e.g. Chesil Beach (not formed by LSD)

Question 61

How are submergent landforms modified?

Answer 61

Rias and fjords modified by wave processes acting on their sides at the present-day sea levels. Valley sides also may be affected by operation of subaerial processes in today’s climatic conditions or in any different climatic conditions of the future - may eventually lead to a reduction in the steepness of the valley sides of fjords
Sea levels predicted to rise by a further 0.6m in next 100 years, water depth in rias and fjords will increase. Marine erosion also likely to increase due to stormier conditions and larger waves
Shingle beaches (composed of unconsolidated material rather than solid rock) are especially vulnerable to modification.

Question 62

What is eustatic sea level change?

Answer 62

Eustatic change is when the sea level changes due to an alteration in the volume of water in the oceans or a change in the shape of an ocean basin and hence a change in the amount of water the sea can hold. Eustatic change is always a global effect.

Question 63

What is isostatic sea level change?

Answer 63

Isostatic sea level change is the result of an increase or decrease in the height of the land. When the height of the land increases, the sea level falls and when the height of the land decreases the sea level rises. Isostatic change is a local sea level change whereas eustatic change is a global sea level change.
During a glacial period, isostatic change is caused by the build up of ice on the land. As water is stored on the land in glaciers, the weight of the land increases and the land sinks slightly, causing the sea level to rise slightly. This is referred to as compression. When the ice melts at the end of an ice age, the land begins to rise up again and the sea level falls. This is referred to decompression or isostatic rebound. Isostatic rebound takes place incredibly slowly and to this day, isostatic rebounding is still taking place from the last ice age.