Coastal Landscapes Flashcards
1
Q
What is a system?
A
A system is a set of interrelated objects comprising of stores and flows that are connected to form a working unit.
2
Q
What is an open system?
A
An open system has inputs and outputs of energy and matter accross the system boundaries.
3
Q
What is a closed system?
A
With inputs and outputs of energy accross the system boundaries, but no input or output of matter.
4
Q
What is an isolated system?
A
No inputs or outputs of energy or matter accross the system boundaries.
5
Q
What is equilibrium?
A
When inputs and outputs are balanced and the system is stable.
6
Q
What is dynamic equilibrium?
A
Wheh the inputs and outputs stay balanced through various negative feedback loops.
7
Q
What is negative feedback?
A
When changes are met with responces that restore the imbalance and lead to a state of equilibrium.
8
Q
What is positive feedback?
A
When changes occur that result in responces that move the system further away from equilibrium.
9
Q
What is a sediment cell?
A
A stretch of coastline and its associated nearshore area within which the movement of coarse sediment is mainly self contained.
10
Q
Is a sediment cell as closed or open system?
A
Sediment cells are regarded as closed systems in terms of coarse sediment. However they are most likely not completely closed as some sediment may transfer due to changing wind directions and currents.
11
Q
How many sediment cells are there?
A
In England and whales there are 11 sediment cells, the boundaries of there sare determined by large physical barriers such as headlands. There are also a large number of smaller sub-cells.
12
Q
What physical factors can affect coastal systems?
A
Wind, Waves, Tides, Geology and Currents
13
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 earths surface.
14
Q
What is geomorphology?
A
The study of the physical features of the surface of the earth and their relation to its geological structures.
15
Q
What are waves?
A
Waves are the transfer of energy through the water by wind exerting a frictional drag on the oceans surface.
16
Q
What is a current?
A
The transfer of water from one location to another. They are driven by wind, water density differences and tides.
17
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.
18
Q
What is the crest of a wave?
A
The highest point of a wave.
19
Q
What is the trough of a wave?
A
The lowest point of a wave.
20
Q
What is wavelength?
A
The average distance between successive wave crests.
21
Q
What is waveheight?
A
The vertical distance between a trough and the crest.
22
Q
What is wave velocity?
A
The speed at which the wave travels.
23
Q
What is wave steepness?
A
The ratio of wave height to wave length.
24
Q
What is wave period?
A
The average time between successive waves.
25
What is wave frequency?
The average number of waves per minute.
26
What is wave power?
The square of wave height times wave period, measured in kW of energy per meter of wave front.
27
Swell wave characteristics?
Long wavelength, gentle gradient, long wave period (up to 20s), generated by distant winds blowing in the open ocean.
28
Storm wave characteristics?
Short wavelength, steep gradient, short wave period, generated by local winds.
29
Why do waves break?
When waves enter shallow water, friction causes the front of the wave to slow. The rear of the waves catches up to the front, increasing wave height and decreasing wave length.
The base of the wave also slows more than the top causing it to break from the circular motion.
When the wave depth is less than 1.3 times the wave height, the wave becomes unstable and breaks.
30
What are spilling waves?
Steep waves breaking gently on to sloping beaches, water spills gently forward as the wave breaks.
31
What are plunging waves?
Moderately steep waves breaking into steep beaches, water plunged down vertically as the crest curls over.
32
What are surging waves?
Low angle waves breaking into steep beaches, the wave slides forward and may not actually break.
33
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.
34
What are destructive waves?
Stronger backwash than swash, comb material down the beach reducing the gradient. Material may collect in a breakpoint or offshore bar.
35
What are the characteristics of constructive waves?
low height, long wavelength, gentle steepness, long period, low frequency (6-8/min), long fetch, swash stronger than backwash, creates steeper beaches as material is moved up the beach.
36
What are the characteristics of destructive waves?
High height, short length, steep, short period, high frequency (12-14/min), short fetch, backwash stronger than swash, creates features such as bars and breakpoints.
37
Where does wave refraction occur?
Around headlands and bays and irregular shaped coastlines.
38
How does wave refraction occur?
Whem one side of a wave front enters shallower water it is slowed by friction earlier than the other side. This means that the wave front is travelling at a different speed and so the wave bends (Refracts).
39
Where is wave energy concentrated?
Headlands becuase the wave front 'wraps around' them whereas energy is dissipated in bays.
40
What is wave energy dependent on?
Wind strength, wind duration and fetch.
41
What is the fetch?
The distance of open water over which the wind has blown to generate waves.
42
How is maximum wave height calculated?
H = 0.36 x square root of F
43
What are tides?
The periodic rise and fall in sea level, caused by the gravitational pull of the moon and sun.
44
What is a spring tide?
When the moon, earth and sun are aligned in a straight linse, so the gravitational pulls are strongest. This leads to very high tides and very low tides, occurs 2 times a month during full and new moons.
45
What is neap tide?
When the earth, moon and sun are aligned at 90 degrees and the gravitational pulls are acting in different directions. This results in less extreme tidal ranges.
46
What is tidal range?
Vertical distance between high and low tide.
47
What is macro-tidal?
More than 4m range
48
What is meso-tidal?
2-4m range
49
What is micro-tidal?
Less than 2m range.
50
What two factors affect tidal ranges?
Coastal shape and position in lunar cycle
51
What are currents?
A major input of kinetic energy into the coastal system, occur at local and global scales. Currents represent the flow of ovean water.
52
Why do rip currents play an important role?
They play an importnat role in the transport of coastal sediment. They aslo modify shore profile by creating cusps, which help to perpetuate the rip current, channeling flow through a narrow neck.
53
How are rip currents formed?
They are caused either by tidal motion or by waves breaking at right angles to the shore. A cellular motion is generated by differing wave heights parallel to the shore.
54
How fast and far do rip current slow?
They can flow at 8km/h, 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 lose its power.
55
Are ocean currents bigger or smaller than rip curents?
Ocean currents are on a much large scale.
56
How are ocean currents created?
By the coriolis effect and convection
57
How are ocean currents set in motion?
By movements of winds across the oceans surface.
58
Wha are ocean currents particularly important in doing?
Distributing heat from the equatorial oceans to the high lattitude oceans, therby helping to maintain global atmospheric equilibrium.
59
Where do warm water currents usually move from and to?
Usually from the western side os oceans to the eastern side, bringing warm onshore currents to western facing coastlines.
60
Where do cold water currents usually move from and to?
From east to west and move more offshore
61
When looked at globally, what do ocean currents create?
Huge circulations of water, known as gyres.
62
What is differential erosion?
The proces of which adjacent rock types, of differing levels of resistance are eroded at different rates.
63
What three components determine the characteristics of rock?
Lithology, structure and dip.
64
What is lithology?
The physical structure and chemical composition of the rocks.
65
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.
66
What is the lithology of basalt?
Dense interlocking crystals lead to a highly resistant lithology.
67
What is the lithology of limestone?
A strong physical lithology, with tightly bonded particles, creating a cery resistant rock but a weaker chemical lithology which is vulnerable to solution in weak acid (corrosion, erosion and carbonation weathering)
68
What is structure?
Structure refers to the properties of individual rock types such as jointing (cracks), bedding (horizontal layers), and faulting. It also realtes to the permiability of a rock.
69
What is a concordant coastline?
The alternate bands of rock are parallel to the coastline.
70
What is a discordant coastline?
The alternating bands of rock are perpendicular to the coastline this oftern creates headlands and bays.
71
What is dip?
Dip refers to how the strata of a cliff are bedded.
72
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.
73
What happens to a cliff with sesaward dipping strata?
Undercutting by wave action removes basal support, layers are loosened by weathering and slip into the sea along with bedding planes.
74
What happends to a cliff with landward dipping strata?
Rocks are loosened by weathering and wave action, however they are difficult to dislodge and so the slop profile is gradually lowered by weathering and mass movement.
75
Why is human activity becoming more significant?
Coastlines are becoming managed more intensely for trade, tourism, fishing, oil and gas extraction, settlements and the protection of ecosystems.
76
How can building groynes have a knock on impact?
They trap sediment being transported by longshore drift, therefore casuing a buildup of a store of sediment reducing erosion rates, adjacent locations may be starved of sediment and their stores depleted, increasing levels of erosion downdrift.
77
How can the extraction of sand have a knock on impact?
Depletes a store of sediment, often beaches and offshore bars are wave energy buffers, therfore increased rates of cliff erosion behind the beach may occur.
78
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.
79
What is marine erosion?
The breakdown and removal of material by the action of sea water. Similar to fluvial erosion, although that is the product of continuous flow, whereas marine erosion is more the result of regular high energy impacts.
80
What is abrasion?
When the seas load is thrown against the rocks of the coast by breaking waves, wearing them away through a sandpapering or scouring action.
81
What is attrition?
When particles of a load knock against each other or against coastal rocks, casuing them to become smaller and rounder.
82
What is hydraulic action?
When a wave breaks against a cliff face, causing air and water in the cracks of the cliff to be compressed. As the wave receeds this pressure is released, and the rapidly expanding air can widen the crack. The amount of pressure can be averaged at 11,000kg/m^3
83
What is wave 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.
84
What is solution (erosion)?
When rocks containing soluble materials such as calcium carbonate or magnesium carbonate are slowly dissolved by sea water. This process is generally insignificant becuase water has a pH of 7 or 8, unless the water is artificially acidic due to pollution.
85
How can material be transported in a coastal system?
Waves, tides, current, solution, suspension, saltationa and traction.
86
What is solution (transport)?
When materials that have been disolved are transported in a mass of moving water. This type of load is invisible and the materials will remain in solution until the water is evapourated and they precipitate out.
87
What is suspension?
When small particles of sand, silt or clay are carried by currents, this allows for the muddy brown colour of some sea water, especially near major river estuaries or close to weak clay cliffs.
88
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.
89
What is traction?
When the largest pieces of material are pushed along the sea bed by the force of waves or currents, often called rolling but movement is rarely continuous, with partial rotations usually being followed by periods of rest.
90
What is LSD?
When 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 and material is transported down the beach in a zig-zag motion.
91
What is marine deposition?
The laying down of sediment on the coast by the sea, when the sea no longer has the energy to carry its load.
92
Where does marine deposition occur?
In sheltered environments. When waves slow down due to friction immediately after breaking. At the top of the swash, when the wave stops momentarily, creating a Berm. During the backwash when some water percolates into the beach thus weakening the wave. Where the rate of sediment accumulation exceeds the rate of removal, a Delta. Estuarine envirnments.
93
What is settling velocity?
The water speed bellow which meterial of a certain size will be deposited, asthe water lacks the energy to coontinue transportation. Smaller material has a lower settling velocity, larger meterial has a higher one.
94
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.
95
What are sub-aerial processes?
Land based processes which shape the land.
96
What three categories can sub-areial processes be split into?
Weathering, mass movement and fluvial processes. These typically act on cliff faces rather than cliff bases.
97
What is weathering and how is it different to erosion?
The breakdown and removal of rock in situ. Erosion is the breakdown and subsequent removal by moving agents whereas weathered material remains where it breaks up.
98
What is mechanical weathering?
The breakdown of rocks into smaller fragments through physicak stresses, with no change to the chemical compostion 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 bellow freezing or rises above 30 degrees, this makes some processes less effective.
99
What is chemical weathering?
Thre breakdown and decomposition of rocks through chmical 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 and transportation processes. In general chemical weathering is faster in the presence of water, as as temperature increases. Van't Hoff' law shows that a 10 degree increase in temperature leads to a 2.5x increase in the rate of chemical reaction, although this isnt always true as carbonation works best in colder temperatures.
100
What is biological weathering?
The breakdown of rocks through the action of flora and fauna, this could be through physical stresses or chemical reactions.
101
Examples of chemical weathering?
Oxidation, solution, carbonation, hydrolysis, hydration.
102
Examples of mechanical weathering?
Thermal expansion, salt crystallisation, pressure release, freeze thaw.
103
Examples of biological weathering?
Burrowing, tree roots, chelation.
104
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.
105
Where do the most significant mass movement event occur?
On cliffs, which lead to the addition of material to the sediment budget through the transfer of rocks and regolith down onto the shore bellow.
106
What is regolith?
Partially weathered rock.
107
What happens during rockfall?
Rockfalls occur on steep cliff faces, involving resistant rocks , as high internal strength is needed 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 undercuttin of the cliff by wave action, lines of weakness and weather conditions that promote weathering.
108
What happens during a slide?
Material moves downslope due to gravity as a discrete block, the slip place is linear and can occur of softer materials such as clays or resistant materials.
109
What happens during a slump?
Material moves downslope due to gravity as as discrete block, the slip plae is curved, this means that the falling material rotates as it moves, common in weaker rocks and more likely after rainfall. A layer of permiable 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 bellow. Also promoted by slope loading, creates a characteristic back-tilted cliff profile.
110
What happens in mudflows?
Saturated fin material flows downslope due to gravity, usually a slow process. It is possible to identify scar on the cliff, where material has come from, a slow track and a lobe or fan shaped deposit of material where the flow moves onto the beach, this often occurs with slumping.
111
Whata re fluvial processes?
Processes that work in rivers.
112
What is fluvial erosion?
In the upper catchment during low-frequency, high energy events and using the same processes as waves is the rivers main source of load, althouh mass movement of valley sides will aslo contribute. Attrition means that the material delivered to the coasts is smaller and smoother.
113
What is fluvial transportation?
Rivers transport material to the coast through traction, saltation, suspension and solution.
114
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. Current and tides may be moving in the opposite diection to river flow providing a 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 become heavier, forcing deposition, this is instrumental in delta formation.
115
What is flocculation?
Fine clay particles clump together due to electrostatic attraction in saline conditions.
116
What are aeolian processes?
Due to their exposure to open sea surface, where there is little frictional drag, coastal location often experience higher wind speeds than inland areas, and these winde, especially those blowing onshore can influence coastal landscapes.
117
What is aeolian erosion?
Wind pick up sand particles by deflation, at speeds of 40km/hr sand grains are moved by surface rolling or 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 on rocky coastlines. Erosive forces increase exponentially with wind velovity, a velocity increase from 2 to 4m/s will see an 8 fold increase in erosive capacity.
118
Whis is dry sane easier to pick up rather than wet?
Moisture increases cohesion between particles, attriction is particularly effective on land compared to the sea as particles carried in the wind lack the protective film of water when hey bump into each other.
119
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.
120
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.
121
What coastlines do headlands and bays form on?
Discordant coastlines
122
How does the focus of energy change once headlands and bays have formed?
Headlands become erosive environments ebcause they are exposed, and wave refraction concentrates energy on them, 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 therefore deopsition occurs in low energy environments, creating beaches.
123
What happens to cliffs in exposed, high energy environments?
Marine erosion at the base creates a wave cut notch between the high and low tide arks, however challk has a high shear length so it can support an overhang to a point.
Sub aerial processes will weaken the cliff face further eventually the unstable overhang will collapse as mass movement (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 which is covered at high tide but exposed at low tide.
124
What happens when the shore paltform reaches a certiain size (500m)?
The high tide loses its energy due to friction when crossing the platformand so will not have the nergy to create a notch in the cliff, this means that the coast is at equilibtium at this point.
125
What is the surface of a shore platform usually like?
Deeply dissected by abrasion due to large amounts of rock debris that is dragged accross its surface, making deep trenches.
126
Why is there a cliff at the seward end and a ramp at the cliff end of a shore platform?
Water levels are constant for the 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 becuase waves have more energy further from the cliffs, they both best develop when the tidal range is less than 4m, if higher than erosion it 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.
127
Where do caves, arches, stacks and stumps form?
On headlands, which are high energy environments becuase they protrude from the coastline and so are exposed and 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.
128
What causes a crack to become a cave, arch, stack then stump.
Erosional processes cause the crack to be widened to form a cave at the base of the headland cliff. Marine erosion will continue to undermine the arch support, whilst subaerial processes will weaken the arch roof. The roof may collapse in a rockfall mass movement event, providing further material for abrasion.
129
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 wil often be covered at high tide and exposed at low tide.
130
What are geos?
Very narrow inlets in cliffs or rocky headlands, they form when a resistant rock mass cotains a major line of weakness that is exploited by marine processes. Erosion cuts back along the line of weakness to create the geo, leaving the less jointed rock either side largely untouched.
131
What are blowholes?
A hole in the top if 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 base of the cliff can create a deep cave under the cliff and erosion by sea spray can then expland the vertical joint at the back of the cave to create a vertical shaft, occasionally the roof of the blowhole can collapse and become a geo.
132
What is a beach?
An accumulation of sediment at the coast, which is the most common landform.
133
Name 3 sources of beach material?
Offshore zone 5% typically during periods of marine transgression. Rivers 90% enters rivers through fluvial erosion, weathering and mass movement of valley sides, and is transported to the coast. Cliff erosion 5%.
134
Why do sand beaches have gentler slopes?
Sand particles are very fine, they are compact when wet with very few 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.
135
Why do shingle beaches have steeper slopes?
Coarse particles have larger pores between particles therefore there are high rates of percolation on the beach, there is 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.
136
Why are beaches dynamic?
Their profiles eveolve over time, from storm events to seasonal changes, beaches and their systems try to reach a stable equilibrium form.
137
What is a swash aligned beach?
Are usually straight, waves approach perpendicular to the beach, so there is little movement of material by longshore drift. They are usually closed systems, no longshore drift means no movement of sediment to adjacent areas.
138
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.
139
Why do drift aligned beaches often become swash aligned beaches?
The longshore drift causes the beach to become angled, one end is erosded and the other is built up so the waves become head on waves to the beach.
140
What are storm beaches?
Storm waves can hurl pebbles and cobbles to the back of the beach forming a storm beach/ridge.
141
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.
142
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. They have a characteristic hooked end with a salt marsh behind it. They are attached to the land at one end and extend accross a bay, estuary or indentation in the coastline. Generally formed by longshore drift occuring in the dominant direction, which carries material to the end of the beach and then beyond into the open water.
143
What are tombolos?
Beaches that connect the mainland to an offshore island with a bar of sediment.
144
What are salt marshes?
Tidal mudflats in a low energy environment, mud covered at high tie 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, decreasing the length of time of submergence and decreasing salinity, increasing number and height of plants. So more sediment is trapped and water is slowed down more.
145
What is flocculation and how does it help salt marsh formation?
Due to electrostatic charges on their surface, clat particles aggregate together in salt water, in a manner that they dont in fresh water. This means that the fine material that was transported in suspension in a fluvial environment becomes coarser and is deposited at the coast.
146
What 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.
147
Where are salt marshes in the uk?
45 hectares of salt marsh in the uk, maily on the most sheltered eastern side.
148
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 plants can grow.
149
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.
150
Where and when do deltas form?
Where 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 ranges are low.
151
What are the features of deltas?
Upper delta plain: furthest inland, beyond the reach of the tides 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 distributaries.
Crevasse Splays: during times of flooding, levees are breached and sediment laden water spills between distributaries , depositing lobes of sediment.
152
What is a birds 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 currets to erode/reshape material. Mississippi delta and gulf of mexico
153
What is an arcuate delta?
There is sufficient 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
154
What is a cuspate delta?
fluvial sediments extend seawards, but are shaped into pointy triangles by longshore currents operating in opposite directions, and converging on the delta.
155
What is eustatic sea level change?
A global rise or fall in sea level associated with climate change.
156
What happens if there is a global decrease in temperatures?
There will be more precipitation falling in the form of snow, if the snow doesnt melt in summer, it will accumulate in annual layers until it becomes compressed into ice. This means that water is stored in the land as glaciers and ice sheets, rather than being returned to oceans as river runoff. this will reduce the volume of water stored in oceans and therfore decrease sea level. This will also lead to thermal contraction of water, the water will have less energy and be denser, therfore having a reduced volume.
157
What happens if there is a global increase in temperature?
Ice sheets willmelt causing more water to enter the earths oceans and thermal expansion will produce a sea level rise.
158
What is natural climate variability?
Part of the earths climatic system, even without human interaction since the pleistocene epoch, the earth has been in an iceage with long, cold glacial periods interspersed by shorter, warmer interglacial periods, such as our current holocene period.
159
What are the Milankovitch cycles?
These decribe cyclical and predictable variations in the shape of earths orbit and the nature of the earths axial tilt.
The eccentricity of the eath orbit describes a predictable progression from a more cicular to a more eliptical orbit over a time period of 100,000 years.
The degree of tilt of the earth axis which varies from 22.5-24.5 degrees over a 41,000 year cycle.
The procession or wobble of the earth on its axis, which varies on a 23,000 year cycle.
These all effect the amount of insolation the earth recieves and therefore have an effect on global temperatures.
160
What do volcanic eruptions do?
Aerosols sucha s dust and sulphur dioxide from major eruptions can reflect incoming solar radiation, reducing global temperatures. Following 1815 eruption of tambora in indonesia, global cimatic deteriation saw a 1816 called the year without summer. There is no regularity or cycle to volcanic activity.
161
What do sunspots do?
There is an 11 year cycle in sunspots, whicha re areas of intense solar radiation on the suns 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. Tectonic uplift can lead to rapid rise of land. post glacial isostatic rebound is a more gradual proces, 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 the southeast of england dips into the sea.
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Name 2 landforms of sumbmergence?
Fjords and rias
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What are fjords?
Submerged glacial valleys where the water comes from rising sea levels, not from meltwater. they have steep cliff like valley sides with uniformly deepwater, can be 1000m+. They have U shaped cross sections reflecting the original shape of the glacial valley and the immense power of the glacier that carved it. Shallower sections at the mouth because the glacier was thinner and elss erosive and because deposition of glacial debris amy have raised land level. Fjords are usually stright because glaciers are erosive enough to not zig zag around landscape features but bulldose straight through them. As fjords are so deep, they can support high energy waves and therfore marine erosion may deepen them further.
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What are rias?
Submerged river valleys. the lower part of a rivers course and flooplains are drowned whereas the higher land is left unsubmerged. Theya re 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 widening plan view reflecting the original river course,a s well as a long profile with uniform depth, smooth and concave.
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What is burried beneath present day rais?
Often there are buried channels of much older rivers, which flowed at lower 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, and so the leower energy meant it had to deposit material filling up the deep channels.
167
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 submergent landforms?
Theya re modified by presen day wave proceses acting at present day sea levels, also subaerial weathering and mass movement processes that reflect present day climatic conditions and can reduce steepness of valley sides.
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What are emergent landforms?
Landforms shaped by wave processes during times of high sea level are left exposed when sea levels falls; 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 cliff with relic caves, wave cut notches and even arches and stacks.
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What modifies landforms of emergence?
There are no longer affected by marine processes but can still be shaped by weathering and amss 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 have contorted and 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 have seen the degradation of the features, they become softer and more blended into the landscape. Present and furture sea level rise could see these emergent landforms at sea level once more, where they would experience wave action and become active beaches, shore platforms and cliffs.
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What is a process that causes unwanted change to coastlines?
Sand mining which affects the sediment budgets, starving beaches of sediment.
