Coastal Landscapes Flashcards
1
Q
What is a system?
A
A system is a set of interrelated objects comprising of components (stores) and processes (links) that are connected together to form a working unit or unified whole
2
Q
What is an open system?
A
An open system had inputs and outputs of energy and matter across the system boundaries
3
Q
What is a closed system?
A
With inputs and outputs of energy across the system boundaries, but no input or output of matter
4
Q
What is an isolated system?
A
No inputs or outputs of energy and matter across the system boundaries
5
Q
What is dynamic equilibrium?
A
When inputs and outputs are balanced, the system is said to be in a state of dynamic equilibrium
6
Q
What is negative feedback?
A
When changes are met with responses that redress the imbalance and lead the system back to its original state. A kind of self regulation to lead to equilibrium
7
Q
What is positive feedback?
A
When changes occur that cause a system to travel further from its original state, this may cause the change to occur more intensely and so on. Disequilibrium (short term)
8
Q
What is the nearshore?
A
The zone extending seawards from the low waterline well beyond the surf zone; it defines the area influences by the nearshore or long shore currents
9
Q
What is a sediment cell?
A
A stretch of coastline and its associated nearshore area within which the movement of coarse sediment, sand and shingle is largely contained
10
Q
Are sediment cells open or closed systems?
A
Closed because generally no sediment is transferred from one cell to another
11
Q
How many sediment cells are around England and Wales?
A
11
12
Q
What are the boundaries of sediment cells?
Why not completely closed systems?
A
Are determined by the topography and shape of the coastline. Large physical features can act as huge natural barriers that prevent the transfer of sediment to nearby cells, unlikely to be completely closed systems due to variations in wind direction and presence of tidal currently, some sediment may be transferred. There are many sub-cells within major cells
13
Q
What is geomorphology?
A
The study of the physical features of the surface of the earth and their relation to its geological structures
14
Q
What are geomorphic processes?
A
Natural mechanisms of weathering, erosion and deposition that result in the modification of the surgical materials and landforms at the earth’s surface
15
Q
What factors influence coastal processes?
A
Waves Tides Currents Aeolian (wind) Geology Human activity
16
Q
What are waves?
A
Waves are the transfer of energy through the water by wind exerting a frictional drag on the ocean’s surface
17
Q
What is a current?
A
The transfer of water
18
Q
What do waves represent?
A
A major input of kinetic energy into the coastal system, also posses potential energy, by virtue of the waters height above the trough. This energy allows work to be done
19
Q
Crest of a wave? Trough? Wavelength? Wave height? Wave velocity? Wave steepness? Wave period? Wave frequency? Wave power?
A
The highest point of a wave
The lowest point of a wave
The average distance between successive wave crests
The vertical distance between a trough and crest
The speed at which the wave travels
The ratio of wave height to length
The average time between successive waves
The average number of waves per minute
The square of wave height x wave period, measure in kW of energy per metre of wave front
20
Q
Swell wave characteristics?
A
Long wavelength
Gentler gradient
Long wave period - up to 20s
Generated by distant winds blowing in the open ocean
21
Q
Characteristics of storm waves?
A
Short wavelength
Steeper gradient
Short wave period
Generated by local winds
22
Q
Why do waves break?
A
In deep water, the wave is not affected by friction with the seabed, it has a long wavelength and low wave height
As the wave enters shallower water near the coast it will be slowed by friction with the seabed
The front of the wave is slowed down earlier than the back, causing the back of the wave to ‘catch up’ with the front. This shortens wavelength and increases wave height
The base of the wave is slowed more than the top causing the top to ‘overshoot’ the base distorting the circular orbit of the water molecules to become more elliptical
Eventually when the water depth is less than 1.3x the wave height, the wave becomes too too heavy and unstable so it breaks
Water from the wave runs up the beach as swash and down as backwash under the influence of gravity
23
Q
What are spilling waves?
A
Steep waves breaking gently o to sloping beached, water spills gently forward as the wave breaks
24
Q
What are plunging waves?
A
Moderately steep waves breaking into steep beaches, water plunged down vertically as the crest curls over
25
What are surging waves?
Low angles waves breaking into steep beaches, the wave slides forward and may not actually break
26
What are constructive waves?
Waves that have a stronger swash than backwash, and so move material up the beach, building it up and increasing the gradient
27
What are destructive waves?
Stronger backwash than swash, comb material down the beach reducing the gradient of the lower beach, material may collect in a breakpoint or longshore bar
28
Characteristics and effect of constructive wave
```
Low height
Long length
Gentle steepness
Long period
Low frequency (6-8/min)
Long fetch (distant winds)
Broken wave spills up the beach
Swash stronger than backwash, long period means backwash has returned to sea before next wave, incoming swash not disrupted
Material is pushed up from lower to upper beach, creating steeper upper beach features such as berms
```
29
Characteristics and effects of destructive waves
High height
Short length
Steep steepness
Short period
High frequency (12-14/min)
Short fetch (local winds)
Water breaks vertically down in plunging motion
Backwash stronger than swash, plunging motion means little energy directed up the beach and a short period means the backwash of one wave affects the next
Material is combed from upper beach and deposited on lower beach creating features such as breakpoint bars
30
What shape coastline results in wave refraction?
Irregular shaped coastlines
31
Which two landforms particularly encourage refraction?
Headlands and bays
32
How does wave refraction occur?
When one side of a wave front enters shallower water it is therefore slowed by friction earlier than the other side, this means that the wave front is travelling at different speed and so the wave front bends (refracts)
33
Where is wave energy concentrated?
Headlands because the wave front ‘wraps around’ them whereas energy is dissipated in bays
34
What is wave energy dependent on?
Wind strength
Wind duration
Fetch
35
What is fetch?
The distance of open water over which the wind has blown to generate waves
36
Maximum wave height that is possible is a function of fetch and can be calculated using what?
H = 0.36 x square root of F
37
What are tides?
The periodic rise and fall in the level of the sea, caused by the gravitational pull of the moon and sun
38
What is a spring tide?
When the moon, earth and sun are aligned in a straight line, so the gravitational pulls of the sun and moon are working together and so are stronger. This leads to very high high tides and very low low tides, occurs twice a month during full and new moons
39
What is a neap tide?
When the earth, the moon and the sun are aligned at 90°, the gravitational pulls are acting in contrary directions, so the high tide isn’t too big/high and the low tide isn’t that low
40
What is tidal range?
Vertical distance between high and low tide
41
Macro-tidal
More than 4m range
42
Meso-tidal
2-4m range
43
Micro-tidal
Less than 2m
44
What two factors affect tidal range?
Coastal shape
| Position in lunar cycle (spring or neap)
45
What are currents?
A major input of kinetic energy into the coastal system, occur at local and global scales.
Currents represent the flow of ocean water
46
What do rip currents play an important role in?
The transport in the transport of coastal sediment
47
How are rip currents formed?
When water from broken waves moves up through the breaker zone and then parallel to the shoreline. this alongshore current causes water to pool up by the beach in particular locations, from where it will flow out to sea following the path of least resistance through a narrow (sometimes just 10m) neck
48
What happens when the cellular circulation of a rip current is formed?
erosion of beach material by the offshore rip current creates a beach cusp, this further channels water into the central location, intensifying the rip further
49
How fast and far do rip currents flow?
can flow at 8km/hr, but often do not travel far from the shore, once the current travels through the line of breaking waves, it can disperse sideways and quickly loses its power
50
picture of rip current
hello
51
Are ocean currents bigger or smaller than rip currents?
Much larger scale
52
How are ocean currents created?
By coriolis force (a function of the earth's rotation) and b convection
53
What are ocean currents particularly important in doing?
Distributing heat from the equatorial oceans to the high-latitude oceans, thereby helping maintain global atmospheric equilibrium
54
How are ocean currents set in motion?
By the movement of winds across the oceans surface
55
Where do warm water currents usually move from and to?
Usually from the western side of oceans to the eastern side, bringing warm onshore currents to western-facing coastlines (including Britain's)
56
Where do cold water currents usually move from and to?
From east to west and move more offshore
57
When looked at globally, what do ocean currents create?
Huge circulations of water, known are gyres
58
What is differential erosion?
The process of which adjacent rock types, of differing levels of resistance, are eroded at different rates
59
What three components determine the characteristics of rock?
Lithology, structure and dip
60
What is lithology?
The physical and chemical composition of the rocks
61
What is the lithology of clay?
Weak lithology with little resistance to erosion, weathering and mass movement, this is due to the unconsolidated nature of the rock - weak bonds that join the individual particles
62
What is the lithology of basalt?
Dense interlocking crystals lead to a highly resistant lithology
63
What is the lithology of limestone?
A strong physical lithology, with tightly bonded particles, creating a very resistant rock but a weaker chemical lithology which is vulnerable to solution in weak acid (corrosion, erosion and carbonation weathering)
64
What is structure?
Structure refers to the properties of individual rock types such as jointing (cracks), bedding (horizontal layers), and faulting. It also relates to the permeability of a rock
65
What is a concordant coastline?
The alternating bands of rock are parallel to the coastline
66
What is a discordant coastline? any known features?
The alternating bands of rock are perpendicular to the coastline this often creates bays and headlands
67
What is dip?
Dip is referring to how the strata in a cliff is bedded
68
How does a cliff line retreat when it has horizontally bedded strata?
Due to undercutting by wave action, it leads to rockfall, the cliffs retreat inland parallel to the coast
69
What happens to a cliff with seaward dipping strata?
Undercutting by wave action removes basal support, layers are loosened by weathering and slip into the sea along the bedding planes
70
What happens to a cliff with landward dipping strata?
Rocks are loosened by weathering and wave action, however they are difficult to dislodge and so the slope profile is gradually lowered by weathering and mass movement
71
Why is human activity becoming increasingly significant?
Coastlines are becoming managed more intensely for trade, tourism, fishing, oil and gas extraction, settlement and the protection of ecosystems
72
How can building groynes have a knock-on impact?
They trap sediment being transported by longshore drift, therefore causing a buildup of a store of sediment reducing erosion rates, adjacent locations may be starved of sediment and their stores depleted, increased levels of erosion downdrift
73
How can the extraction of sand have knock-on impact?
Depletes a store of sediment, often beaches and offshore bars are wave energy buffers, therefore increased rates of cliff erosion behind the beach may occur
74
What is wind an input of into the coastal system?
An input of kinetic energy, and has the capacity to erode finer materials, transport it and deposit it creating features such as sand dunes
75
What is marine erosion?
The wearing away and/or removal of material by the action of sea water. similar to fluvial erosion, although that is the product of a continuous flow, whereas marine erosion is more the result of regular high-energy impacts (waves)
76
What is abrasion (corrasion)?
When the sea's load is thrown against the rocks of the coast by breaking waves, wearing them away through a 'sandpapering' or 'scouring' action
77
What is attrition?
When particles of a load knock against against each other or against coastal rocks, causing them to become smaller and rounder
78
What is hydraulic action?
When a wave breaks against a cliff face, causing air and water in cracks in the cliff to be compressed, as the wave recedes. this pressure is released like a mini-explosion, and the rapidly expanding air can widen the crack, this pressure can be averaged at 11,000kg/m^3
79
What is pounding?
Simply the force of a wave on the rock, even without any load to wear the rock away, high-energy waves can exert a pressure of up to 30,000kg/m^2
80
What is solution (corrosion)?
When rocks containing soluble minerals such as calcium carbonate or magnesium carbonate are slowly dissolved by sea water. This process is generally insignificant because water has a pH of 7 or 8, unless the water is artificially acidic due to pollution
81
How can material be transported in a coastal system?
Waves, tides, currents, solution, suspension, saltation and traction
82
What is solution?
When materials that have been dissolved are transported in a mass of moving water. This type of load is invisible and the minerals will remain in solution until the water is evaporated and they precipitate out
83
What is suspension?
When small particles of sand, silt or clay are carried by currents, this accounts for the muddy brown colour of some sea water, especially near major river estuaries, or close to weak clay cliffs
84
What is saltation?
Describes a series of irregular 'leapfrogging' motions in which material that is too large to be carried continuously in suspension is bounced along the sea bed, having been entrained, the material will be deposited after a short distance and the impact of this may dislodge other sediment for further saltation
85
What is traction?
Sees the largest particles of load pushed along the sea bed by the force of waves or currents, often called rolling but movement is rarely continuous, with partial rotations of stones/boulders, followed by periods of rest
86
What happens in longshore drift?
Wind and waves approach the coastline at an angle, the waves break and the swash carries material up the beach face at the same angle as the waves approached, the backwash carries material straight back down the beach, perpendicular to the shore, due to gravity, the cycle repeats so material is transported down the beach in a zig-zag motion
87
How does the distribution of sediment along Chesil beach give evidence to longshore drift?
20km long pebble beach in Dorset, material primarily comes from offshore from where it was pushed up to its current position by rising sea levels after the last glacial maximum. There is a long fetch and the prevailing wind is from the SW meaning that longshore drift is very effective from W to E transporting material of all sizes. However, there is a secondary prevailing wind from the SE with a shorter fetch means less effective longshore drift from E to W transporting smaller material, this means over a long period of time material will be sorted by size with the biggest material at the eastern end
88
What is marine deposition?
The laying down of material on the coast by the sea, when the sea no longer has the energy to carry its load
89
Where does marine deposition occur?
In sheltered environments (bays, behind spits)
When waves slow down due to friction immediately after breaking (breakpoint bar)
At the top of the swash, when the wave stops momentarily (berm)
During the backwash when some water percolates into the beach thus weakening it
Where the rate of sediment accumulation exceeds the rate of removal (delta)
Estuarine environments
90
What is settling velocity?
The water speed below which material of a certain size will be deposited, as the water lacks the energy to continue transportation.
Smaller material has a lower settling velocity, Larger material has a higher one
91
What determines net erosion or net deposition?
Often both erosion and deposition occur simultaneously, therefore whichever is dominant decides whether its net erosion or net deposition
92
What are sub-aerial processes?
Land based processes which shape the land
93
What three categories can Sub-aerial processes be split into?
Weathering, mass movement and fluvial (river/stream-based) processes. These typically act on cliff faces rather than cliff bases
94
What is weathering?
The breakdown of rocks by elements of the weather in situ, erosion is the breakdown an subsequent removal by moving agents (wind, waves, rivers, glaciers) whereas weathered material remains where it breaks up
95
What is physical (mechanical) weathering?
The breakdown of rocks into smaller fragments through physical stresses, with no change to the chemical composition of the minerals that make up the rock. As the rock breaks into smaller fragments the surface area increases allowing further weathering to take place, although around the UK the coast moderates temperatures so it rarely drops below freezing or rises above 30 degrees, this makes some processes less effective
96
What is chemical weathering?
The breakdown or decomposition of rocks through chemical reactions that alter the chemical composition of the minerals that make up the rock, this produces weak residues within the rock that may be easily removed by erosion to transportation processes. IN general chemical weathering is faster in the presence of water, and as temperature increases. Van't Hoff's law shows that a 10 degrees increase in temperature leads to a 2,5x increase in the rate of a chemical reaction - although this isn't always universally true, carbonation weathering works better in colder temperatures
97
What is biological weathering?
The breakdown of rocks through the action of flora and fauna, this could be through physical stresses (tree roots) or chemical reactions (chelation)
98
Examples of chemical weathering?
Oxidation, solution, carbonation, hydrolysis, hydration
99
Examples of physical weathering?
Thermal expansion, salt crystallisation, pressure release, freeze-thaw
100
Examples of biological weathering?
Tree roots, organic acids
101
What is mass movement?
Mass movement is the downslope movement of rock, soil and other material under the influence of gravity, whilst water is often a trigger for mass movement it is not a medium in which material is transported (river)
102
Where do the most significant mass movement events occur?
On cliffs, which lead to the addition of material to the sediment budget through the transfer of rocks and regolith (partially weathered rock) down onto the shore below
103
What happens during a rockfall?
Rockfalls often occur on steep cliff faces (40 degrees or more), involving resistant rocks, as high internal strength is need to support steep cliff faces. Rocks may become detached from the cliff due to weathering and then fall due to gravity. Falling material breaks up as it moves accumulating in a scree slope at the base of the cliff. Rockfall is promoted by basal undercutting of the cliff by wave action (wave cut notch), lines of weakness, weather conditions that promote weathering
104
What happens during a slide?
Material moves downslope due to gravity as a discrete block (doesn't break into smaller pieces), the slip plane is linear and can occur of softer materials such as clays (landslide) or resistant materials (rock slide)
105
What happens during a slump?
Material moves downslope due to gravity as a discrete block, the slip plane is curved, this means that the falling material rotates as it moves, common in weaker rocks and more likely after rainfall. A layer of permeable sandstone on top of the clay will further increase chances of slumping because water passes through the sandstone but not the clay and so the sandstone becomes saturated exerting a greater pressure on the clay below. Also promoted by slope loading (thick tree growth or building at cliff top), creates a characteristic back-tilted cliff profile
106
What happens in mudflows?
Saturated fine material flows downslope due to gravity, usually a slow process (a few cm/day). It is possible to identify a scar on the cliff, where material has come from, a flow track and a lobe or fan-shaped deposit of material where the flow moves onto the beach, this often occurs with slumping
107
What are fluvial processes?
Processes that work in rivers
108
What is fluvial erosion?
In the upper catchment during low-frequency, high-energy events, and using the same processes as waves is the river's main source of load, although mass movement of valley sides will also contribute. Attrition means that the material delivered to the coasts is smaller and smoother
109
What is fluvial transportation
Rivers transport material to the coast through traction, saltation, suspension and solution
110
What is fluvial deposition?
River velocity decreases at the mouth due to the effects of friction - a moving body of water entering a relatively static one (sea). Currents and tides may be moving in the opposite direction to river flow providing major resistance, energy reduction leads to deposition. Large particles are deposited first and finer sediment carried further out to sea, when fresh and salt water mixes, flocculation occurs. Particles grow in size and become heavier, forcing deposition, this is instrumental in delta formation
111
What is flocculation?
Fine clay particles clump together due to electrostatic attraction in saline conditions
112
Aeolian processes?
Due to their exposure to open sea surfaces, where there is little frictional drag, coastal locations often experience higher wind speeds than inland areas, and these winds - especially those blowing onshore, can influence coastal landscapes
113
What is aeolian erosion?
Wind picks up sand particles by deflation, at speeds of 40km/hr sand grains are moved by surface rolling (surface creep) and saltation, as grains of this size are relatively heavy they are rarely carried in suspension, this restricts erosion by abrasion to about 1m and so has limited effect of rocky coastlines are cliffs, erosive forces increase exponentially with wind velocity - a velocity increase from 2 to 4 m/s will see an 8 fold increase in erosive capacity
114
Why is dry sand easier for the wind to pick up rather than wet?
moisture increases cohesion between particles, attrition is particularly effective on land compared to the sea as particles carried in the wind lack the protective film of water when they bump into each other
115
What is aeolian transportation?
Moving air is able to transport material using the same mechanisms as moving water, with the exception of solution, once particles have been entrained, they can be moved in winds moving at speeds as low as 20km/hr
116
The primary method of transportation of material is a function of particle size...
surface creep =
saltation =
suspension =
0,26-2.00mm
0. 15-0.25mm
0. 05-0.14mm
117
What is aeolian deposition?
Wind transported material will be deposited when wind speed, and therefore energy, falls usually as a result of friction, in coastal areas, this will occur inland where vegetation and uneven surfaces offer higher levels of friction than the open sea
118
What coastlines do headlands and bays form on?
Discordant coastlines
119
How does the focus of energy change once headlands and bays have formed?
Headlands become erosive environments because they are exposed, and wave refraction concentrates wave energy on them (orthogonals converge), this means that we see landforms such as caves, arches, stacks and stumps created as the headland slowly retreats. Wave energy dissipates in the sheltered bays (orthogonals diverge) therefore deposition occure in the low energy environment creating beaches
120
Why is Flamborough Head special?
In north Yorkshire and has 125m chalk cliffs with a wide shore platform
121
What happens to cliffs in exposed, high energy environments? when on headlands wave refraction will concentrate wave energy on them.
Flamborough Head:
Chalk cliffs, relatively resistant lithology although it has lines of weakness increasing vulnerability to erosion.
Marine erosion at the cliff base creates a wave cut notch between the high and low water marks, however chalk has a high shear strength so it can support an overhang to a point
Sub-aerial processes will weaken the cliff face further
Eventually the unstable overhand will collapse as a mass movement event, a rockfall
The cliff retreats inland, gaining height as it does
Rockfall debris builds up at the base which can be used for further abrasion of the shore platform and cliff
The base of the former cliff is left as a gently sloping rocky platform (less than 3 degrees) which is covered at high tide but exposed at low tide
122
What happens when the shore platform reaches a certain size (500m)?
The high tide loses its energy due to friction when crossing the platform and so will not have the energy to create a notch in the cliff, this means that the coast is at equilibrium at this point
123
What is the surface of a shore platform usually like?
Deeply dissected by abrasion due to the large amounts of rock debris that is dragged across its surface, making deep trenches
124
Why is there a 'cliff' at the seaward end and a 'ramp' at the cliff end of a shore platform?
Water levels are constant for longest at high and low tides, so more erosion takes place at these times, which helps form ramps and small cliffs. The cliff is steeper than the ramp because waves have more energy further from the cliffs, they both best develop when the tidal range is less than 4m, if higher then erosion would be spread over a wider area of the platform due to the water being at the high and low tide positions for a shorter amount of time
125
Where do caves, arches, stacks and stumps form?
On headlands, which are high energy environments because they protrude from the coastline and so are exposed an wave refraction concentrates wave energy on them. No matter the lithology of the headland rock, there is always likely to be cracks or lines of weakness which marine erosional processes will exploit
126
What causes a crack to become a cave? (and further)
Erosional processes cause the crack to be widened to form a cave at the base of the headland cliff.
Marine erosion will to continue to undermine the arch support, whilst subaerial processes will weaken the arch roof. The roof may collapse, leaving a stack of rock isolated from the rest of the headland, the roof collapse is a rockfall mass movement event, providing further material for abrasion
127
What will make a stack collapse into a stump?
Further basal undercutting and subaerial weathering weakening the base and top, it will collapse leaving a stump which will often be covered at high tide and exposed at low tide
128
What are geos?
Very narrow inlets incised into cliffs or rocky headlands, they form when a resistant rock mass contains a major line of weakness that is exploited by marine erosion. Erosion (particularly hydraulic action) cuts back along the line of weakness to create the geo, leaving the less jointed rock either side largely untouched.
In Cornwall, often they start as tunnel like caves running at right angles to the cliffs, as they become enlarged by erosion, the roof can be weakened by weathering and eventually the roof may collapse as a rockfall. They may also be associated with the collapse of old tin mining shafts, therefore human activity can help to enlarge and then collapse to become a geo in Cornwall
129
What are blowholes?
A hole in the top of a cliff or headland, connected to the sea via a vertical and horizontal shaft, through which sea spray may emerge in high energy conditions. It is formed when a resistant rock mass contains major lines of weakness, marine erosion at the cliff base can create a deep cave under the cliff and erosion by sea spray can then expand a vertical joint at the back of the cave to create a vertical shaft, occasionally roof of the blowhole can collapse and become a geo
130
What is a beach?
An accumulation of sediment at the coast, which is the most common landform
131
Name three sources of beach material?
```
Offshore zone (5%) typically during periods of marine transgression
Rivers (90%) enters rivers through fluvial erosion and weathering and mass movement of valley sides, and is transported to the coast
Cliff erosion (5%)
```
132
Why do sand beaches have gentler slopes?
Sand particles are very fine, they are compact when wet with very few air spaces between particles, there is little percolation of backwash into the sand, there is a strong backwash which carries material back down the beach reducing the gradient. Material accumulates in ridges separated by troughs which may be breached by channels draining water from the beach
133
Why do shingle beaches have steeper gradients?
Coarse particles have larger pores between particles therefore there are high rates of percolation on the beach, there is a weak backwash relative to swash, material can be transported up the beach but less transported down. Material accumulates on the upper beach increasing the beach gradient
134
why are beaches dynamic?
Their profiles evolve over time, from storm events to seasonal changes, beaches and their systems try to reach a stable equilibrium form
135
What is a swash aligned beach?
Are usually straight, waves approach perpendicular to the beach, so there is a little movement of material by longshore drift, they are usually closed systems no longshore drift means no movement of sediment to adjacent coastal areas
136
What is a drift aligned beach?
Occur when waves approach at an oblique angle, allowing movement of sediment along the coast by longshore drift in an open system
137
Why do drift aligned beaches often become swash aligned beaches?
The longshore drift causes the beach to become angled, one end is eroded and the other built up so the waves become head on waves to the beach
138
What are storm beaches?
Storm waves can hurl pebbles and cobbles to the back of the beach forming a storm beach/ridge
139
What are berms?
Smaller ridges that develop at the position of the mean high tide mark, resulting from deposition at the top of the swash.
Some beaches have several berms, each representing different high tide levels
140
What is a spit?
An accumulation of sand and shingle found at a change in direction of the coastline, extending away from the coastline into the sea, with a characteristic hooked end and with a salt marsh behind it, they are attached to the land at one end and extend across a bay, estuary of indentation in the coastline.
Generally formed by longshore drift occurring in a dominant direction, which carries material to the end of the beach and then beyond into the open water
141
What are tombolos?
Beaches that connect the mainland to an offshore island, a bar of sediment that connects an island to the mainland. An example is Chesil beach and the Isle of Portland in Dorset.
142
Why was Chesil beach thought to be formed by longshore drift?
Due to the sorting of sediment size along the beach, (spit formation) however it was the 'bulldozing' up of offshore sediment during the Flandrian transgression (rising sea levels after the end of the Last Glacial Maximum). During the LGM the English Channel was a river valley covered in outwash sands and gravel, as sea levels rose, the material was pushed up in a ridge ending in its current position 6,000BP. This theory is now more accepted, if LSD had been responsible alone then material to become finer towards the East, due to prolonged effects of attrition, however in the west is the smallest sediment
143
What is Slapton sands?
A 5km long, 150m wide shingle bar in start bay, south devon, running from torcross in the south to strete gate in the north, enclosing slapton ley behind it. It was originally though that LSD extending the shingle at Torcross northwards across an indentation in the coastline. There were no strong currents in the bay, there was nothing to stop the beach being extended all the way to Strete gate. However, today it is thought that the bar is a ridge of sediment pushed up by the rising sea levels of the Flandrian transgression coming to rest in its present position 6,000BP
144
What is brackish water?
Small streams flow into the lagoon in Slapton Ley, salt water mixes with fresh water, they bring sediment which causes the Ley to slowly silt up (hydrosere succession)
145
What are salt marshes?
Tidal mudflats in a low energy environment, mud covered at high tide but exposed at low tide.
Colonised by pioneer community of plants, which trap sediment and therefore increase deposition which increases the height of the mudflat which decreases the length of time of submergence and decreasing salinity, increasing the number and height of plants, more sediment trapped and water is slowed down more
146
What is flocculation and how does it help salt marsh formation?
Due to electrostatic charges on their surface, clay particles aggregate together in salt water, in a manner that they don't in fresh water, this means that fine material that was transported in suspension in a fluvial environment becomes coarser and is deposited at the coast
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Why do most salt marshes have a dense network of drainage creeks?
Sinuous creeks help drain high tide water from the marsh as the tide ebbs.
45 hectares of salt marsh in the UK, mainly on the more sheltered eastern
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What are saltpans and how do they develop?
Spring high tide water inundates the upper marsh; some may get trapped in depressions when the tide ebbs, the water evaporates leaving behind a toxic saline crust on which no plant can grow
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What are deltas?
Deltas are large areas of sediment found at the mouth of many rivers, deltaic sediments are deposited by rivers or tidal currents, they form when rivers and tidal currents deposit sediment there at a faster rate than waves and tides can remove it
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Where/when do deltas form?
Rivers entering the sea have a large sediment load
There is a broad, shallow continental shelf to provide a platform for sediment accumulation
There is a low energy coastline, so deposited sediment is not removed by tides or currents
Tidal range is low
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Features of deltas?
Upper delta plain: furthest inland, beyond the reach of ride and composed entirely of river sediments
Lower delta plain: in the intertidal zone, regularly submerged and a mixture of river and marine sediments
Submerged delta plain: below mean low water mark, composed mainly of marine sediments and represents seaward delta growth
Distributaries: small channels formed when the main channel is forced to split as a deposition of fine material creates bars midstream
Levees: naturally raised banks of the distributaries
Crevasse splays: during times of flood, levees are breaches and sediment laden water spills between the distributaries, depositing lobes of sediment there
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What is a bird's foot delta?
Distributaries build out from the coast in a branching pattern; occur where rivers with a very large sediment supply enter very low energy coasts, with negligible tides, waves and currents to erode/reshape material
Mississippi delta, Gulf of Mexico, USA
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What is an arcuate (fan-shaped) delta?
There is sufficient fluvial sediment supplies for the delta to extend seawards, but wave action is strong enough to reshape 'claws' of sediment into smooth fan shapes.
Nile delta, Mediterranean sea, Egypt
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What is a cuspate (point or arrowhead) delta?
Fluvial sediments extend seawards, but are shaped into pointy triangles by longshore currents operating in opposite directions, and converging on the delta
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Flamborough Head background information
The coastal environment between Saltburn and Flamborough Head is a rocky, upland area. This 60km long coastal environment displays many coastal landforms and its characteristics reflect the high energy waves it receives. It is in Sediment Cell 1, Sub-Cell 1d. The northern boundary of Sediment Cell 1 starts at St Abb's Head in southern Scotland
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Flamborough Head energy
North-facing coasts (near Saltburn) are most exposed, so receive highest wave energy inputs. Floating buoys in Whitby Bay revealed that wave height often exceeds 4m, even in the summer months. Dominant waves from the north and northeast, with a fetch of over 1500km (from Norway or even Svalbard)
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Flamborough Head geology
Variations in geology account for differences in the coastal scenery, including cliff height and profile and the headland-bay sequence (discordant coastline). North York Moors rise up 400m above sea levels and comprise mainly Jurassic sandstones, shales and limestones (200-145MaBP). Flamborough Head is a chalk headland with rocks dating from the late Cretaceous (70-100MaBP), it is topped by till - a weak glacial deposit left behind by the glaciers of the Devensian glacial period (last 120,000 years)
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Flamborough Head processes
Weaker shales and clays experience erosion rates of 0.8m/year (average), whereas more resistant sandstones and limestones retreat at less than 0.1m/year. Net LSD from north-to-south; in places, this sediment movement is interrupted by headlands, allowing sand/shingle to accumulate in bays to form beaches (Filey Bay). Zones of erosion (back of the beach) and accretion observed in Filey Bay linked to winter storms in 2010/11
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Flamborough Head sediment
2008/11 net increase in beach sediment of 9245m^3 at Saltburn. Nearshore sediment source - seafloor sediments driven onshore by rising sea levels during the Flandrian Transgression (ending 6000BP). Sediment source - cliff erosion, sandstone and chalk from resistant chalk outcrops and weaker boulder clay deposits yield significant volumes of gravel. Only one large river (River Esk), which enters the North Sea at Whitby, it provides little sediment because of human management - reinforced banks trap sediment and weirs trap sediment in transportation. Despite active LSD there are few spits due to a high tidal range (increased energy input so less deposition) and there are few estuaries, which would naturally act as sediment sinks. Few well-developed beaches due to low sediment input there are few rivers, little erosion of resistant rocks, high wave energy and active LSD, where beaches are found (Scarborough, Filey Bay) it is because of local sheltered, low energy environments
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Flamborough Head erosional landforms
Between Robin Hood's Bay and Saltburn, cliffs are higher and have a stepped profile, reflecting varied geology; steeper segments are found on more resistant sandstone and limestone, gentler slopes on weaker clays and shales, which are more prone to mass movement. Discordant rock strata has led to the formation of a series of headlands and bays. Shore platforms are left behind by the retreating cliffs, likely to have been formed in the last 6000 years, although some believe they are relict features, formed during earlier interglacials, when sea levels were at a similar level to today. Flamborough Head is chalk - strong physical lithology which produced vertical cliffs 20-30m high with overlying stratum of glacial till lowered by mass movement to an angle of 45 degrees, joints, faults and other lines of weakness are exploited creating caves, arches stacks and stumps at Selwick's Bay, the headland has over 50 geo, aligned NE or NNE facing the dominant waves, with multiple blowholes forming and then causing the collapse of the overlaying chalk to create a funnel-shaped depression in the headland. Sedimentary rocks are horizontally bedded, so cliffs tend to have vertical profiles.
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Nile Delta background information
One of the largest delta's in the world - 160km from north to south, 240km from west to east and covering approx. 20,000km^2 of land. The River Nile is the longest river in the world (6650km) with a catchment area of more than 3 million km^2, the mean annual rainfall of the catchment is 600mm, but the average discharge is less than 3000 cumecs (compared to over 200,000 cumecs for the Amazon), much of the Nile runs through arid and semi-arid regions of the Sahara Desert, with high evaporation rates, the area within the catchment with the highest rainfall is the Ethiopian highlands (2000mm+ of monsoon rain), which feeds the Blue Nile tributary, whilst the White Nile tributary flows from Lake Victoria in central East Africa
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Nile Delta energy
For most of the year, the prevailing wind direction on the Nile Delta is northwesterly; winds from the northwest are more common in summer in particular, whilst gentle southwesterly winds are more common in spring, northerly winds are more common in winter. Micro-tidal range (a few cm) due to the enclosed nature of the Mediterranean Sea therefore there is a low tidal energy input. 55-60% of the waves come from the west, northwest and north with only 8% coming from the east.
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Nile Delta sediment
Rapid population growth in Egypt (98 million and an annual growth rate of 2.5% (2017)) leads to increased water abstraction from the Nile and its distributaries, decreasing sediment supply to the delta. Despite low discharge, teh River Nile carries a huge sediment load, suspended sediment load is 30% clay (<0.002mm diameter), 40% silt (0.002-0.02mm) and 30% fine sand (0.02-0.2mm), the average annual sediment yield is 4.2 tonnes/hectare/year and the total is 91.3 million for the Blue Nile basin in Ethiopia. In 1964 Aswan High Dam in southern Egypt was constructed, regulating discharge downstream and trapping sediment behind it, before construction the whole delta was briefly submerged during the Nile's annual flood, with alluvial deposits reaching depths of 4m at Aswan, 9.6m at Cairo and even deeper on the delta itself, since construction, sediment accretion on the delta has dropped from 120 million tones/year to negligible amounts today. The annual flood of the delta no longer occurs
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Nile Delta geology
The soft, unconsolidated sediments of the delta have a very weak physical lithology and are therefore vulnerable to marine erosion processes
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Nile Delta processes
Deposition of alluvial material has occurred at a faster rate than erosion by marine processes for over 3000 years, building the Nile Delta, deposition is aided by flocculation, plant colonisation and a reduction in fluvial energy as the Nile enters the sea. Prevalent northwesterly winds enhances constant eastern movement of water and sediment in the eastern Mediterranean, surface currents velocities vary seasonally, spring (8.4cm/s), summer (9.26cm/s), autumn (4.46cm/s) and winter (23.4cm/s - strong winds). Since the building of the Aswan dam, there is an imbalance between sediment accretion and erosion, the shoreline of the northwest Nile Delta has seen accelerated erosion and rates of retreat as high as 148m/year. Rising sea levels in the Mediterranean of 1.2mm/year also have contributed to higher erosion rates, deeper water produces larger waves with higher energy levels and the potential to reach further inland, a 1m rise in sea level would result in 20% of the delta being submerged. Northern parts of the delta are experiencing isostatic sea level rise of 9mm/year sur to compaction of unconsolidated sediments. Aeolian erosion and transportation is also a significant process in the arid Sahara, where there is little vegetation to anchor fine sediments. Weathering processes in the arid/semi-arid regions of the Sahara (thermal expansion) also contribute sediment. Fluvial erosion, especially within the wetter areas of the Nile catchment contribute sediment to the Nile
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Nile Delta landforms
Nearshore underwater sandbars off Abu Qir headland, typical of tideless seas, rip currents create a crescentic bar shape. Higher sediment yields in the two main distributaries create two lobes that extend beyond the rest of the delta. Reshaping of the deposited material by longshore currents creates a smooth concave arcuate delta shape instead of a bird's foot delta, the reworked sediment forms a series of curved barrier bars, closing off segments of the Mediterranean to form lagoons that quickly become brackish water and fill with fine sediment. Nearshore underwater sandbars off between Abu Qir and Port Said, typical of tideless seas, run parallel to shore, reflecting dominant eastward longshore currents and drift. The Nile splits into two major distributaries - Rosetta and Damietta - at Cairo, 160km away from the coast, with multiple smaller distributaries spreading throughout the delta, each contained within levees and separated by crevasse splays of land. Frontal plain: south of the foreshore plain, scattered eroded limestone outcrops and clay deposits. Sandy formations - sheets, dunes and hummock. The coastal plain occupies the northern part of the Nile Delta, running parallel to the Mediterranean coastline and close to or below sea level, it consists of the foreshore plain, the frontal plain and the sandy zone. Foreshore plain: elongated ridges running parallel to the present shoreline, with brackish lagoons, salt marshes and alluvial deposits occupying the troughs between them.
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What is Eustatic sea level change?
A global rise or fall in sea level associated with climate change
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What happens if there is a global decrease in temperatures?
There will be more precipitation falling in the form of snow, if the snow doesn't melt in the summer, it will accumulate in annual layers until it becomes compressed into ice. This means water is stored on the land as glaciers and ice sheets, rather than being returned to the oceans as river runoff. This will reduce the volume of water stored in the oceans, and therefore a global decrease in sea level will occur. This will also lead to thermal contraction of water, the water will have less energy and stay closer together (denser) and occupies less volume
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What happens if there is an increase in global temperatures?
Ice sheets will melt causing more water to enter the Earth's oceans, and thermal expansion will produce a sea level rise
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What is natural climate variability?
Part of the Earth's climatic system, even without human carbon emissions, since the Pleistocene Epoch, 2.4 million annum BP, the Earth has been in an iceage (permanent ice on surface) with long, cold glacial periods interspersed by shorter, warmer interglacial periods (such as out current Holocene interglacial)
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What is a Milankovitch cycle?
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These describe cyclical and predictable variations in the shape of Earth's orbit and the nature of the Earth's axial tilt:
The eccentricity of the Earth's orbit describes a predictable progression from a more circular to a more elliptical orbit over a time period of 100,000 years
The degree of tilt of the Earth's axis, which varies from 22.5-24.5 degrees over a 41,000 year cycle
The precession (wobble) of the Earth on its axis, which varies on a 23,000 year cycle
These effect the amount of insolation (solar radiation) the earth receives, and therefore global temperatures
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What do volcanic eruptions do?
Aerosols (dust and sulphur dioxide) from major volcanic eruptions can reflect incoming solar radiation, reducing global temperature. Following the 1815 eruption of Tambora in Indonesia, global climatic deterioration saw 1816 called 'the year without summer' There is no regularity or cycle to volcanic activity
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What do sunspots do?
There is an 11 year cycle in sunspots, which are areas of intense solar radiation on the sun's surface, a peak in sunspot activity sees the Earth receive more solar radiation
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What is Isostatic sea level change?
Local relative rise or fall in sea level associated with an actual rise or fall in the level of the land. Rising land = isostatic sea level fall, falling land = isostatic sea level rise. Tectonic uplift can lead to rapid rise of land. Post-Glacial isostatic rebound is a more gradual process - 18,000 BP NW Scotland was underneath an icesheet a mile thick, this compressed the land beneath it, when the ice age ended and the icesheet melted, the weight was lifted and the land slowly rebounded upwards, as this happens Britain acts like a see-saw pivoting around Yorkshire, and southeast England dips into the sea.
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Name two landforms of submergence?
Fjords and rias
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What are fjords?
Submerged glacial valleys, the water comes from rising sea levels, not from meltwater. They have steep cliff-like valley sides, with uniformly deep water (can be 1000m+). They have a U shaped cross-section reflecting the original shape of the glacial valley and the immense power of the glacier that carved it. Shallower section at the mouth because the glacier was thinner and less erosive and because deposition of glacial debris may have raised land level. Fjord are usually straight because glaciers are erosive enough not to zig-zag around landscape features but bulldoze straight through them. As fjords are so deep, they can support high energy waves and therefore marine erosion may deepen them further.
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What are rias?
Submerged river valleys, the lower part of a river's course and floodplains are drowned whereas the higher land is left unsubmerged. They are relatively shallow in cross-section but get increasingly deep towards the centre. They have gently sloping valley sides formed by fluvial erosion by the river and subaerial weathering and mass movement of the valley sides. The valley sides may be asymmetrical, which is common of meandering rivers. They have a winding plan view reflecting the original river course, as well as a long profile with uniform depth, smooth and concave.
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What is buried beneath present day rias?
Often there are the buried channels of much older rivers, which flowed at slower levels, when sea levels were lower than today.
As sea levels rose during the Flandrian transgression, the rivers lost the extra gravitational potential energy that the lower sea levels gave them, an so the lower energy meant it had to deposit material filling in the deep channels
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How are barrier beaches formed?
During the Wurm Glacial Maximum, 25-18,000BP, sea level was 110-120m lower than today, large areas of what is now shallow sea, was low-lying land. An example of this is the English Channel, which was a large river valley of which the Rhine and Thames were just tributaries
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What modifies landforms of submergence?
They are modified by present day wave processes acting at present day sea levels, also subaerial weathering and mass movement processes that reflect present climatic conditions and can reduce steepness of valley sides. Sea levels are predicted to rise by 0.6m by 2100
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Landforms of emergence are?
Landforms shaped by wave processes during times of high sea levels are left exposed when sea levels fall; as a result, they may well be found inland, some distance from the modern coastline due to a relative fall in sea levels
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What are raised beaches and abandoned cliffs?
Former shore platforms left 'high and dry' by falling sea levels are called raised beaches, they are often found a distance inland from the present coastline, behind raised beaches it is common to find abandoned cliffs with relics cave, wave cut notches and even arches and stacks
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Raised beach at the southern tip of the Isle of Portland, Dorset
Raised beach at a height of 15m above present sea level.
Thought to have been formed 125,000BP during the Tyrrhenian Interglacial period, when sea levels were much higher than today.
When this was an active shore platform, the Portland Limestone is thought to have been eroded by hydraulic eave action, exploiting bedding plane weaknesses, at rates of up to 1m/year.
In other part of the Isle of Portland, raised beaches are thought to date to an even older interglacial 210,000BP
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What modifies landforms of emergence?
They are no longer affected by marine processes but can still be shaped by weathering and mass movement.
On top of the abandoned cliff on the Isle of Portland, a 1-1.5m layer of frost-shattered limestone debris was deposited when the area experienced periglacial conditions during the Wurm glacial, whilst the cliff face was degraded by freeze-thaw weathering leading to rockfall.
Other periglacial processes, such as cryoturbation (upheaval of sediments associated with repeated freezing and thawing) have contorted the fragmented limestone.
During the current Holocene interglacial, warmer and wetter conditions have lead to the growth of vegetation on exposed rock, which obscures features such as raised beaches.
Weathering and mass movement has seen the degradation of the features, they become 'softer' and more blended into the landscape.
Present and future sea level rise could see these emergent features once more at sea level, when they would be subject to wave action once more and would become active beaches, shore platforms and cliffs
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Mangawhai-Pakiri - human activity, unintentional change - background information
The beaches are located on New Zealand's North Island. they are on the Pacific (east) coast of the Northlands Peninsula, about 50km north of Auckland. The sand is high quality and suitable for the construction industry. Hauraki gulf is currently the biggest seabed mining operations in NW waters. NZ legislation on seabed mining is less restrictive than in many countries
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Mangawhai-Pakiri need for sand
Much of the sand mined has been used to replenish Auckland's tourist beaches. Auckland is NZ's largest urban area (pop 1.5 million (1/3 of NZ population)) and accounts for 37% of GDP and 35% of its workforce. Auckland is home to thriving financial and high tech industry as well as tourism, centred around the outstanding coastal amenities. Auckland is 235% larger than the next largest urban area (Wellington). In the 2016 Unitary Plan, Auckland City Council announced plans to build 422,000 extra houses over the next 25 years - that's the same number of houses that were built in the previous 160 years, and will require a construction rate 2.5x than that achieved in the pervious 25 years. Between 1995 and 2016, Auckland's population increased by 20,000 per year, its fastest ever period of growth. Sand is an essential mineral resource for construction, concrete, glass manufacture, beach replenishment. Sand is sold for approx. NZ$50/m^3 of which the NZ government takes NZ$1.70 in royalties
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Mangawhai-Pakiri offshore mining/sediment budget
The sediment budget is essentially a closed system - the outputs from sand mining exceed the inputs from rivers and offshore factors by a factor of 5. Nearshore sand dredging on the 20km coastline has been taking place for 70 years. Between 1994-2004, 165,000m^3/year was extracted using suction dredging from water 5-20m deep. Extraction at Mangawhai ended in 2005 but continues at Pakiri at rates of 76,000m^3/year. There are few sizeable rivers on this stretch of coastline, so little fluvial sediment input. In 2006, NZ's Environment Court granted two extraction permits for Pakiri, lasting until 2020 despite strong opposition on environmental grounds. The beach and nearshore sediment at Mangawhai-Pakiri dates from the last 9000 years (the Holocene) which was pushed up from offshore by rising sea levels (Flandrian Transgression) was Earth's climate warmed in the late Pleistocene/early Holocene, this process ended c.6000BP when sea levels stabilised. Holocene sand lies 6-10m deep in the dunes at the back of the beaches, 2-6m deep on the beach and only 0.3m deep in the offshore zone, it is underlain by older Pleistocene sand, but this is of less value due to iron impurities. With inputs
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Mangawhai-Pakiri impact on coastal landforms
Beaches starved of sediment become wider and flatter, and are less effective at absorbing wave energy. Higher energy waves can erode landforms such as dunes and spits. In 1978, storms caused at 28m breach at the base of the Mangawhai spit, altering tidal currents and causing increased sedimentation in the Harbour, shallower water in the harbour was a threat to boat navigation and threatened seafront properties with flooding, dredging and groyne construction has been used to restore some equilibrium. Foredune ridges are undercut by wave action, creating steep seaward-facing scarps and loss of vegetation cover makes them vulnerable to wind erosion. By 2100, 35m retreat along the Mangawhai-Pakiri coastline is expected, with the width of coastal zone vulnerable to erosion between 48-111m, both these figures are higher than for any of the Auckland region's other 123 beaches
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Mangawhai-Pakiri other impacts
In 2005, the ARC paid NZ$20million to purchase 50 hectares of land to create Pakiri regional Park, the sand dunes are home to two endangered birds - the NZ fairy tern and the NZ dotterel. Reduction in quality of local surf and adverse impact on fisheries
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Sandbanks - human activity, intentional change - background information
Sandbanks peninsula is situated in Dorset, on England's south coast. Sandbanks peninsula in located in Sediment Cell 5. Sandbanks peninsula is a spit that separates Poole Harbour (an estuary) from Poole Bay, Management of the Sandbanks peninsula is the joint responsibility of Pool Borough Council, Pool Harbour Commission and the Environment Agency, management strategies are defined in the Two Bays Shoreline Management Plant, which covers the Poole Bay and Christchurch Bay sediment sub-cell
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Sandbanks processes
LSD from west to east (towards Christchurch Bay). Undefended cliffs at Hengistbury Head provides sediment input. Onshore and offshore transport of sediment by constructive and destructive waves. LSD from east to west due to refraction. Refraction of prevailing SW waves around Isle of Purbeck. Tidal currents flowing into and out of Poole Harbour, transporting fine sediments
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Sandbanks need for management
The sheltered waters of Poole Harbour make it a suitable port for cross channel ferries and cargo ships, without Sandbanks, LSD would transport sediment into the Harbour, resulting in deposition within the navigation channels. A large number of high value commercial properties, including Sandbanks Hotel and the Haven Hotel, both of which provide significant employment opportunities and generate spending in the local economy. Residential properties in high demand and command premium prices, large, detached houses cost >£10 million, luxury flats >£2million, with no active intervention, there will be £18million damage to residential properties over the next 20 years. Sandbanks shelters Poole Harbour from high energy waves, making it popular and safe for windsurfing, sailing, kayaking and other water sports, the harbour is home to numerous yacht clubs are marinas, it is also the location of internationally important wetlands and salt marshes. Climate change means 0.6m of sea level rise is predicted here by 2100, this would cause flooding of many properties and could breach the peninsula at its lowest (2m asl) and narrowest (50m) point at the junction of Shore Road and Banks Road, this would cut the peninsula off from the mainland. The beach is a major tourist attraction, with a Blue Flag for water quality and a gently shelving profile that makes it safe for swimming.
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Sandbanks management techniques
Rock groynes have been constructed to maintain a deep, wide beach by minimising the movement of sediment from NE to SW by LSD, this restricts sediment from entering the Harbour, protecting shipping lanes, but also absorbs wave energy and reduces erosion - without groynes, retreat rates estimated to be 1.6m/year. Beach recharge is used to conserve beaches; sand is dredged from offshore and sprayed onto the beach ('rainbowing') at a cost of £20/m^3, a recent trial of dumping sediment offshore, and using natural currents to transport it onto the spit, costs just £3/m^3, in total, over 3.5million m^3 of sediment has been added to Poole Bay beaches. If all of the sediment recharge in Poole Bay had been conducted using natural currents rather than rainbowing, approx. £60million would have been saved. The aim of the SMP for Sandbanks is 'Hold the Line', the combined rock groyne/beach recharge strategy is so effective that the width of the beach at Sandbanks is increasing slightly - the line is actually advancing.
