Coastal Environments (CE) Flashcards
(304 cards)
1
Q
What is a system?
A
A set of interrelated objects comprising components (stores) and processes (links) that are connected together to form a working unit or unified whole.
2
Q
What three types of energy may be available tot he coastal landscape system?
A
thermal, kinetic and potential
3
Q
What kind of systems are coastal landscapes mostly recognised as?
A
Open systems
4
Q
What is an open system?
A
One where energy AND matter can be transferred from neighbouring systems as an input and as an output.
5
Q
What is the coastal zone?
A
Interface zone between the land and see.
6
Q
What four factors do coastal systems witness the interaction of?
A
Marine processes, terrestrial, atmospheric and human.
7
Q
Input:
A
The transfer of matter and/or energy from a neighbouring system.
8
Q
Output:
A
The loss or matter and/or energy from a neighbouring system.
9
Q
Store:
A
Components within a system where energy and/ or matter is stored, which are connected by flows
10
Q
Flow/transfer:
A
processes that link stores within a system
11
Q
Throughputs:
A
the internal elements of a system
12
Q
Closed system:
A
Inputs and outputs of energy across system boundaries but no input/output of matter.
13
Q
Dynamic equilibrium:
A
When inputs and outputs in a system are balanced
14
Q
Negative feedback:
A
Where changes are met with responses that redress the imbalance and lead the system back towards its original state.
15
Q
Positive feedback:
A
Occurs when a change occurs that causes the system to travel further from its original state which in turn causes the change to occur more intensely.
16
Q
Example of a negative feedback loop:
A
- shingle encourages high rates of percolation of breaking waves
- swash is stronger than backwash
- material is deposited on upper beach steepening the beach gradient.
- steep shelving coastline promotes destructive waves
- material is combed from upper beach and deposited on lower beach, reducing beach gradient
- stable gradient on shingle beach
17
Q
Example of positive feedback loop:
A
- Vegetation colonises intertidal mudflat
- increased friction results in slower currents and less deposition.
- mudflat builds vertically upwards
- mudflat spends less of tidal cycle submerged so a greater number of plants are able to colonise mudflat
- more biomass…
18
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 self contained.
19
Q
What is a sediment cell regarded as?
A
A closed system.
20
Q
How many sediment cells does the uk have?
A
11
21
Q
How are sediment cells determined?
A
The boundaries are determined by the topography and shape of the coastline. Big physical features (i.e. Land’s End) act as natural barriers that prevent the transfer of sediment to adjacent cells, however it is unlikely that sediment cells will ever be completely closed.
22
Q
What are the four components of the sediment budget
A
terrestrial (rivers), terrestrial (cliff erosion), offshore and human
23
Q
What is the sediment budget?
A
the balance of the sediment volume entering and exiting a particular section of coast.
24
Q
What is the terrestrial (rivers) component of the sediment budget?
A
-major source of coastal sediment
-intermittent delivery
-in some locations 80% of sediment comes from rivers
-fluvial sediment is originally derived from erosion of land by rivers as well as weathering and mass movement.
25
What is the offshore component of the sediment budget?
-constructive waves move sediment onto beach from offshore locations, as do flood tides and offshore currents.
- rising sea level push a ridge of sediment up ahead that becomes beach sediment when sea level stabilises.
26
What is the terrestrial (cliff erosion) component of the sediment budget?
- cliff erosion increased by sea level rise and storm surges
- weak geology exposed to high wave energy can contribute to 70% of beach material.
-rock fall can comprise of large rocks and boulders.
27
What is the human component of the sediment budget?
- beach nourishment
28
What are the six factors affecting coastal processes?
waves, tides, current, geology, human activity, aeolian factors
29
What are waves?
The transfer of energy through the water, produced by wind exerting a frictional drag on the ocean's surface. They are not the transfer of water itself.
30
The higher the wind speed and longer the fetch...
The larger the waves and the more energy they possess.
31
Crest:
highest point of a wave
32
Trough:
Lowest point of a wave
33
Wavelength:
average distance between successive crests
34
wave height:
the vertical distance between the wave trough and crest
35
wave velocity:
the speed of a wave
36
wave steepness:
the ratio of wavelength to wave height
37
wave period:
the average time between successive waves
38
wave frequency:
average number of waves per minute
39
wave power:
the square of the wave height multiplied by the wave period
40
Four swell wave features:
long wavelength, gentler gradient, long wave period, formed by distant wind in open ocean
41
Four storm wave features:
steeper, short wavelength, short wave period, generated by local winds
42
Atlantic waves are .....
swell waves
43
Channel waves are....
storm waves
44
Why do waves break?
1. waves enter shallow water, slowed by friction with seabed
2. front is slowed earlier than the back meaning the back of the wave catches, shortening the WL and increasing WH
3. Eventually when water depth is less than 1.3 times WH, wave becomes top heavy, unstable and collapses.
45
Spilling wave:
steep waves breaking onto gently sloping beaches, water spills gently forwards
46
Plunging wave:
moderately sweet waves breaking onto steep beaches, water plunges down vertically creating large arcs
47
Surging wave:
low angle waves breaking onto steep beaches, waves slide forwards but do not actually break
48
Constructive features:
low height, long length, gentle steepness, long period, low frequency of 6-8/minute and long fetch.
49
Destructive features:
high height, short length, steep, short period, high frequency of 12-14/minute, and short fetch
50
Constructive waves swash and backwash
swash > backwash
51
Destructive waves swash and backwash
swash < backwash
52
What results in wave refraction?
irregular shaped coastlines (particularly encouraged by headlands and bays)
53
When does wave refraction occur?
when waves move at different speeds causing the front of the wave to refract.
54
Explain wave refraction:
1. waves approach coastline at an angle
2. one side of wave reaches shallow water before the other
3. the side of wave front in deeper water travels faster, causing entire wave to bend
4. one side of wavefront is slowed by friction before the other side
5. overall effect is that wave fronts become increasingly parallel to coast
55
What happens when waves approach an irregularly shaped coastline?
wave refraction occurs around the headland and orthogonals converge. thus wave energy is focused on headland and erosion is concentrated here. In the bays, the orthogonals diverge causing energy to be dissipated, leading to deposition.
56
Tides:
the periodic rise and fall in the level of the sea
57
what are tides caused by?
the gravitational pull of moon and sun
58
why does the moon exert a stronger influence
it is much closer to the earth
59
how is high tide created?
a bulge of water is drawn towards the moon with a compensatory bulge developing on the opposite side of the earth. the areas of 'lost water' become areas of low tide
60
explain spring tide:
occurs when the moon, earth and sun are aligned in s straight line and so the pull fo the sun and moon are acting in the same plane and thus are stronger leading to very high and very low tides.
61
When does spring tide occur?
twice a month when there is a new and full moon
62
What happens during a neap tide?
when the su and moon are aligned at a 90 degree angle, so the gravitational pulls are acting in the opposite directions so the high tide bulge is not as big. so high tides are not as high and low tides are not as low.
63
What is tidal range?
the vertical distance between high and low tide
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macro tidal:
>4m
65
Meso tidal:
2-4m
66
Micro tidal:
<2m
67
What are currents:
the flow of ocean water
68
What are rip currents caused by?
tidal motion or by waves breaking at right angles to the shore
69
Explain rip currents:
A cellular circulation is generated by differing wave heights parallel to the shore. water from the top of breaking waves with large wave heights travels further up shore and returns through the adjacent area where the lower waves have broken
70
What are ocean currents created by?
the Coriolis force and by convection
71
Why are ocean currents important?
they distribute heat from the equatorial oceans to high latitude oceans, maintaining global atmospheric equilibrium
72
Warm water currents tend to move form...
west to east, bringing warm onshore currents to western facing coastlines
73
Cold water currents tend to move from...
east to west, and move more offshore
74
What are the huge circulations in ocean currents called?
gyres
75
what ocean does the Gulf Stream occur in?
atlantic
76
Gulf Stream heat and direction:
warm SW - NE (Caribbean to NW Europe)
77
Canaries current location?
atlantic
78
Canaries heat and direction:
cold NE-SW
79
Benguela current location, direction and temperature:
atlantic, cold, SW-NE (South Atlantic to west coast of Africa)
80
Agulhas current location direction and temperature:
Indian Ocean, warm, N to S
81
Differential erosion:
The process by which adjacent rock typed of differing levels of resistance are eroded at different rates.
82
Three components that determine the characteristics of rock:
lithology, dip and structure
83
Lithology:
the physical and chemical composition of rocks
84
Clay composition:
weak lithology, little resistance to erosion, weather and mass movement. unconsolidated nature, weak bonds join individual particles.
85
Basalt composition:
Dense, interlocking crystals lead to highly resistant lithology.
86
Limestone composition:
strong physical lithology, tightly bonded particles creating very resistant rock but vulnerable to solution is weak acid.
87
Structure:
Properties of individual rock types such as jointing, bedding and faulting. also relates to permeability of rocks.
88
Primary permeability:
porous rock where water is transmitted through tiny air spaces between particles
89
Secondary permeability:
pervious rock where water is transmitted more rapidly along joints and bedding planes.
90
concordant:
bands run parallel to coastline
91
discordant:
bands run perpendicular to coastline
92
Horizontally bedded strata:
Undercutting wave action leads to rockfall. Cliff retreats inland, parallel to coast.
93
Seaward dipping strata:
Undercutting by wave action removes basal support. Rock layers loosened by weathering slide into sea along bedding planes
94
Landward dipping strata:
rocks loosened by weathering and wave action are difficult to dislodge, the slope profile is lowered by weathering and mass movement.
95
What are four main human activity interferences?
building groynes, planting marram grass, extracting sand from beach and offshore zone, beach nourishment
96
Explain the building of groynes:
traps sediment from longshore drift, creating larger store of material, reducing erosion rates. beach store of sediment may eventually be depleted.
97
Explain the effect of extracting sand from beach and offshore zone:
depletes store of sediments as beach material is a wave energy buffer. Increased erosion rates on cliffs behind beach.
98
Explain the effects of beach nourishment:
represents a new input and the larger the beach the less erosion on terrestrial area behind the beach.
99
Explain the effect of planting marram grass to stabilise sand dunes:
this facilitates deposition by disrupting the aeolian transport of sand and fine material.
100
abrasion/corrasion:
sea's load is thrown up against rocks by breaking waves, eroding cliff face away
101
Attrition:
particles of load knock into each other causing them to become smaller and smoother.
102
Hydraulic action:
wave breaks against surface of cliff face, causing air and water into cracks, which become pressurised and can release mini explosion when wave retreats, weakening the rock.
103
Pounding:
simply force of the wave on rock
104
Solution:
particular rocks containing soluble minerals are slowly dissolved by sea water
105
Coastal transportation - solution:
minerals that have been dissolved are transported in moving water. load is invisible
106
Suspension:
small particles are carried by currents
107
saltation:
irregular leapfrogging motions in which particle that is too large to be carried continuously is bounced along sea bed.
108
traction:
largest particles pushed along sea bed by force of waves
109
Marine deposition:
laying don of material on the coast by sea, occurs when sea no longer has energy to carry load
110
where can deposition occur?
sheltered areas, at top of swash, during backwash, when rate of sediment accumulation exceeds rate of removal
111
settling velocity:
water speed below which material of a particular size will be deposited
112
What has a lower settling velocity, large material or small?
small
113
Weathering:
Breakdown of rock by elements of the weather in situ.
114
Erosion:
the breakdown and sub sequential removal of rocks by moving agents
115
Physical weathering:
Breakdown of rocks into smaller fragments with stress, as rock breaks down SA increases furthering weathering.
116
Thermal weathering:
rock experiences large changes of temperature over a very short period of time causes layers of rock to break off
117
salt crystallisation:
sea water that evaporates off of rocks leave behind salt that can crystallise and weaken the rock
118
Freeze thaw weathering:
water in liquid form enters cracks in rock and freezes when temperature drops and expands as it does so weakening the rock
119
Oxidation:
some minerals in rocks react with oxygen in air or in water.
120
Chemical weathering:
breakdown of rocks due to change in chemical composition of minerals that make up rock. this occurs faster at higher temperatures. 10 degree increase leads to 2.5x faster rate
121
What are examples of inputs into the coastal landscape system?
kinetic energy from wind and waves, thermal energy form heat of the sun, potential energy from the position of material on the slopes, material from marine deposition, weathering and mass movement.
122
What are examples of outputs int he coastal landscape system?
marine and wind erosion from beaches and rock surfaces, evaporation
123
What are examples of throughputs in the coastal landscape system?
Stores such as beach and nearshore sediment accumulations and flows such as the movement of sediment along a beach by longshore drift
124
How do the developments of coastal landscapes and their operation as systems vary?
Temporally (over time) and spatially (from place to place).
125
Biological weathering:
breakdown of rocks through action of flora and fauna, can be physical or chemical.
126
Atlantic waves are ........ higher than English Channel waves but have ...... times more energy
eight times
70 times
127
In enclosed seas, such as the mediterranean, tidal ranges are...
low, and so wave action is restricted to a narrow area of land
128
In places where the coast is funnelled, such as the Severn Estuary, tidal ranges are...
high, up to 14m, therefore exposing more land to wave action
129
Draw a sediment budget:
see page 9 of textbook
130
Carbonation:
rainwater combines with dissolved CO2 from atmosphere to produce weak carbonic acid which reacts with calcium carbonate in rocks such as limestone to produce calcium carbonate, which is soluble.
131
Solution (weathering):
Some rock types are soluble in water. And some are soluble in very acidic water.
132
Hydrolysis:
chemical reaction between rock minerals and water. silicates combine with water, producing secondary minerals such as clays.
133
Tree roots:
tree roots grow into cracks in rocks and exert an outward pressure as they grow, weakening and breaking down the rock.
134
Organic acids:
Organic acids produced decomposition of plant and animal litter cause soil to become more acidic and react with some minerals in a. process called chelation. blue-green algae can have a weathering effect, producing a shiny film of iron and magnesium oxides on rocks. In addition molluscs secrete acids which produce small surface hollows in the rock
135
Mass movement:
occurs when forces acting on slope material, exceed the forces trying to keep the material on the slope.
136
Rock fall:
on cliffs 40 degrees or more, rocks may become detached from the slope by physical weathering processes. These then fall to the foot of the cliff under gravity. wave material may eventually remove this material.
137
Rotational slump:
slides often occur due to undercutting by wave erosion at the base of the cliff which reduces support for materials above. common in weak rocks such as clay which also becomes heavier when wet.
138
Longshore drift occurs when:
waves approach the coast at an angle due to the direction of the dominant wind. when the waves have broken, swash carries particles diagonally up the beach. under the influence of gravity the backwash the wave back down the beach. when this movement is repeated there is a net movement of material along the beach.
139
What do fluvial processes refer to?
river processes
140
What is the main source of river's sediment load?
Fluvial erosion
141
When does most channel erosion occur?
during high flow, high energy events
142
What four ways do rivers transport sediment?
traction, solution, saltation, suspension
143
When is there a noticeable reduction in a river's velocity?
As the flowing water enters the relatively static body of sea. as a result there is a major deposition event here
144
What is flocculation?
A process by which salt causes the aggregation of minute clay particles into larger masses that are too heavy to remain suspended in the water.
145
What do aeolian processes refer to?
Wind
146
What is deflation?
The wind's ability to pick up sand particles and move them
147
At speeds of 40km/h sand grains can be moved by...
surface creep and saltation.
148
Erosive forces increase exponentially with increases in....
wind velocity
149
In aeolian erosion, and increase in 2m/s in wind speed....
results in an eight fold increase in arose capacity
150
Is dry sand or wet sand easier for wind to pick up?
Dry sand and wet sand has moisture cohesion between the particles helping them stick together
151
Once particles have been entrained, they can be transported by velocities as low as...
20 km/h
152
Saltating grains are typically ..... in diameter
0.15-0.25 mm
153
Surface creep grains are typically .... in diameter
0.26-2 mm
154
Suspension grains are typically .... in diameter
0.05-0.14 mm
155
When will material carried by wind be deposited?
When the wind speed falls, usually as a result of surface friction.
156
What happens when destructive waves break repeatedly on relatively steep sloping coastlines....
undercutting can occur between the high and low tide levels where it forms a wave cut notch. continued undercutting weekends support for strata above causing it to eventually collapse producing a steep profile and a cliff. cliff debris is left at bottom but is removed by wave action
157
Bays and headlands typically form ...... to each other
adjacent
158
What is an example of a discordant coastline?
The Isle of Purbeck. The East facing coast is discordant, whilst the south facing is concordant.
159
What are geos?
narrow, steep sided inlets. even on coasts with resistant geology, there may be lines of weakness such as joints and faults which are eroded more rapidly by wave action.
160
What is an example of a geo?
Huntsman's Leap in Pembrokeshire which is 35 m deep and eroded along a large joint in carboniferous limestone.
161
Sometimes geos initially form as...
tunnel like caves, running at right angles to the cliff line which becomes enlarged with erosion, causing the roof to collapse and form a geo.
162
How are blowholes formed?
If a part of the roof of a tunnel like cave collapses along the master joint, it may form a vertical shaft that reaches the top.
163
What may occur with blowholes in storm conditions?
waves may force spray out of the blowholes as plumes of white aerated water.
164
Crack ...
cave, arch, stack, stump
165
What are the six main landforms of deposition?
Spits, beaches, tombolos, deltas, onshore bars, salt marshes
166
What are the three main sources of beach sediment>
cliff erosion (5%), offshore (5%), rivers (90%)
167
Beaches:
Landform of deposition that represents an accumulation of material deposited between the lowest tides and highest storm waves.
168
Why does sand allow little percolation during backwash?
because its small particle size means that it becomes compact when wet, allowing little percolation during backwash.
169
How and why are runnels formed?
Little wave energy is lost by friction and little water volume is lost to percolation, material is carried back down the beach rather than left at the top, resulting in a gentle gradient and the development of ridges and runnels parallel to shore
170
How are storm beaches formed?
When storm waves hurl pebbles and cobbles to the back of the back forming a storm beach or storm ridge
171
How are berms formed?
Smaller ridges that develop at the position of the mean high tide mark, again resulting from deposition at the top of the swash
172
what are cusps?
small semi circular depressions formed by a collection of waves reaching the same point and when swash and backwash have a similar length.
173
Beaches are dynamic and......
their profiles change over time as wind strength and hence wave energy changes
174
High energy, destructive waves remove sediment....
offshore and create flatter beach profiles. this results in shallower water, more friction and a reduction in wave energy.
175
Low energy constructive waves transfer sediment.....
in the opposite direction to destructive, so onshore, producing a steeper profile. this process deeper water, less friction and an increase in wave energy.
176
What are spits?
long narrow beaches of sand or shingle that are attached to land at one end and extend across a bay, estuary or indentation in a coastline
177
how are spits formed?
by longshore drift occurring in one dominant direction which carries beach material to the end of the beach and then beyond into the open water.
178
what may make a spit more permanent and why?
storms as they build up more and larger material which make the feature more substantial
179
Why does the end of a spit become curved?
Because of wave refraction around the end of the spit and possible due to the presence of a secondary wind or wave direction
180
Where may spit length be limited and why?
Across and estuary due to river current
181
What is a good example of a spit?
Orford Ness in East Anglia. here the coastline is east facing so is largely unaffected by Britain's southwesterly prevailing winds. instead northeasterly winds winds and waves are locally dominant and has resulted in longshore drift from north to south.
182
Where has the spit at Orford Ness formed exactly?
across the River Ore estuary but the river current has prevented it reaching land on the other side so instead it has continued to grow parallel to the coastline, diverting the river some 12km south.
183
Where can onshore bars develop?
if a spit continues to grow across an indentation such as a cove or bay until it joins onto land again at the other side. this forms a lagoon of brackish water on the landward side.
184
Why is the onshore bar at Slapton Sands in Devon special?
Because there is not a significantly dominant direction of longshore drift there and there is no obvious pattern to the distribution of sediment sizes. so it is likely to be produced by onshore movement of sediment during the post glacial sea level rise.
185
What are tombolos?
Beaches that connect the mainland to an offshore island.
186
How are tombolos formed?
From spits that have continued to grow seawards until they reach and join onto an island
187
What is an example of a 30 km tombolo?
the shingle beach at Chesil near Weymouth, Dorset.
188
How is the tombolo at Chesil Beach Devon believed to be formed?
The onshore movement of sediments, as it reached its present position some 6000 years ago.
189
Name two features of the Chesil Beach tombolo:
At its Eastern end at Portland the ridge of shingle is 13m high composed of flinty pebbles. At the western end near Burton Bradstock the ridge is only 7m high and composed of smaller shingle.
190
Why is it not likely that the Chesil Beach tombolo was formed by longshore drift?
If longshore drift had been responsible it would be expected that the sediment further east would be smaller.
191
What are salt marshes?
features of a low energy environment such as estuaries and on the landward side of spits. they are vegetated areas of deposited silts and clays.
192
What are salt marsh adapted plants?
Eelgrass and spartina can handle salty water and submergence from high tides. they help trap sediment and therefore increase height of salt marsh
193
The higher the marsh becomes...
the shorter the period of submergence and the less saline the conditions
194
How is the low marsh characterised?
turbid water, salinity and long periods of submergence, low species diversity
195
Salt marshes have a .......... gradient that slopes........
shallow, seawards
196
Why are deposition rates still quite high at the top of salt marshes where there are lower rates of inundation?
As at the high water mark, low energy, slack water may be present for 2-3 hours. and the greater density of vegetation cover helps to stabilise sediment.
197
What is the common rate of sediment accumulation in salt marshes?
10cm per year
198
What is a key factor required for formation of salt marshes?
flocculation. in salt water, clay particles attract each other forming flocs which are too heavy to be carried in river flow.
199
Deltas:
large areas of sediment found at the mouths of rivers. they form when river and tidal currents deposit sediments at a faster rate that waves and tides can remove it.
200
Deltas typically form where: (4)
- tidal ranges are low
- low energy energy environments
- rivers entering the sea are carrying large sediment loads
- a broad continental shelf margin exists at the river mouth to provide a platform for sediment accumulation
201
What are the three components of a delta?
The upper delta plain, the lower delta plain and the submerged delta plain
202
The upper delta plain:
Furthest inland, beyond the reach of tides and composed entirely of river deposits
203
The lower delta plain:
in the inter tidal zone regularly submerged and composed of both river and marine deposits
204
The submerged delta plain:
Lies below mean low water mark, is composed mainly of marine sediments and represents seaward growth of the delta
205
Deltas are criss crossed by a branching network of...
distributaries
206
Levées:
ridges of coarse deposits found alongside stream channels and elevated above the floodplain
207
What are the low lying areas between levées called?
crevasse splays
208
What are the three types of delta?
cuspate, bird's foot and arcuate
209
Overloaded with sediment, deposition in the channel forms...
bars which causes the channel to split into two producing two channels with reduced energy levels and so more deposition and dividing occurs
210
Cuspate delta:
a pointed extension to the coastline occurs when sediment accumulates but this is shaped by regular, gentle currents from opposite directions
211
Arcuate delta:
sufficient sediment supply is available for delta to grow seawards but wave action is strong enough to smooth and trim its leading edge
212
Bird's foot delta:
distributaries build out from the coast in a branching pattern with river sediment supply exceeding rates of removal by waves
213
What is the case study of a low energy coastal environment?
The Nile Delta, Egypt
214
Nile length:
6650 km
215
What is the catchment area of the Nile?
3 million km squared
216
Mean annual rainfall in river nile catchment?
600mm
217
A large proportion of the Nile flow originates in....
Ethiopia and its summer monsoon rains
218
The Nile has a relatively........ discharge of....
low, 3000m cubed/second
219
The river Nile carries a .......
huge sediment load
220
Suspended sediment load of the Nile:
30% clay, 40% silt and 30% fine sand
221
What are the three distinct subunits of the coastal plain in the Nile delta?
the sandy zone, frontal plane and foreshore plain
222
Nile: the foreshore plain is characterised by...
elongated ridges, salt marshes and lagoons
223
Nile: the sandy zone is characterised by...
variety of sand formations such as sheets, dunes and hummocks
224
Nile: the frontal plane is characterised by...
south of the foreshore plain, has scattered limestone outcrops and clay deposits
225
Prevailing wind direction in the Nile Delta:
for most of year: northwesterly, winds from here are most common in the summer, whilst gentle southwesterly winds are more common in spring and northerly are common in winter
226
What is the tidal range of the Nile delta?
Microtidal (just a few cm) due to enclosed nature of Mediterranean Sea
227
what is the geology of the Nile Delta?
The soft, unconsolidated sediments of the delta have very weak physical lithology and are therefore more vulnerable to marine erosion processes.
228
What two processes contribute to the sediment of the Nile?
Fluvial erosion, especially within wetter areas of the Nile catchment and Weathering processes in the arid regions of the Sahara, where there is no vegetation to anchor fine sediments
229
Where in the Nile are there nearshore underwater sand bars and why?
Off the Abu Quir headland and in-between Abu Qir and Port Said. They are typical of tideless seas. They run parallel to shore, reflecting dominant eastward longshore drift and currents
230
Why might the underwater sand bars by the Nile delta have a crescentic shape?
Due to rip currents
231
Net LSD in the Nile Delta?
Eastwards
232
Why is the Nile Delta a smooth concave Arcuate delta?
because the reshaping of deposited material by longshore currents creates a smooth concave arcuate delta, instead of a bird's foot delta. the reworked sediment forms a series of curved barriers closing off segments to form lagoons that soon fill with brackish water and fine sediment
233
Rapid population growth in Egypt...
of 2.5% per year leads to increased water abstraction decreasing sediment supply to delta
234
What is the purpose of the Aswan Dam?
Regulates discharge downstream, trapping sediments behind it. Before construction the whole delta was briefly submerged during its annual flood with alluvial deposits reaching depths of 4m
235
Since construction of the Aswan Dam (POS):
sediment accretion on the delta has dropped from 120 million tonnes a year to negligible amounts today so there is no longer the annual flooding of the delta.
236
Since the construction of the Aswan Dam (NEG):
There has been an imbalance between sediment accretion and erosion rates. So now there are rates of retreat of 148m/year.
237
Nile: Rising Sea Levels in mediterranean...
Have contributed to higher erosion rates as deeper water produces larger waves with higher energy levels and the potential to reach further in land.
238
Nile: A 1m rise in sea level would ...
result in 20% of the delta being submerged
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Temporal changes in the nile delta:
- marine processes showed seasonal patterns (longshore currents strongest in winter)
- with no seasonal flood and reduced sediment input we are seeing year on year net erosion
-sea level change
- single local events such as a storm
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What is an example of a high energy coastline?
Saltburn to Flanborough Head, Yorkshire
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How long is the SbFb coastline?
60km
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What sediment cell is the SbFh coastline in?
Sediment cell 1, sub cell 1d
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How are the rocks bedded on the SBFH coastline?
horizontally, so cliffs tend to have a vertical profile
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SBFH net lsd?
From North to South. In places it is interrupted by headlands, allowing sand and shingle to accumulate in bays to form beaches such as Filey Bay
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Describe the Geology of Flamborough Head:
-chalk
-strong physical lithology with tightly bonded minerals
-produces vertical cliffs 20-30m high
-overlying stratum of glacial till lowered by mass movement to an angle of 40 degrees
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How many geos does Flamborough head have?
over 50 geos aligned NE with multiple blowholes
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What has happened to joints and faults on Flamborough Head?
They have been exploited by waves, creating caves, arches, stacks and stumps
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Where is the dominant wave action on the SBFH coastline coming from?
From North and North East with a fetch of over 1500km
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What is the effect of SBFH being a discordant coastline?
it has led to the formation of headlands and bays such as Robin Hood's Bay (relatively weak shales) and Ness Point (resistive sandstone).
250
Why are there few well developed beaches on SBFH?
Due to low sediment input (few rivers, little erosion, high wave energy and active LSD). Beaches are only found in sheltered locations such as Filey Bay.
251
SBFH: what do variations in geology account for?
differences in coastal scenery including cliff height and profile and the headland bay sequence
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SBFH: why are there few spits?
despite active LSD there are few spits due to high tidal range which reduces deposition and there are few estuaries.
253
What is the only large river at SBFH?
River Esk
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Why does the river Esk provide little sediment?
Human management - reinforced banks trap sediment
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What are the two main sediment sources at SBFH?
Cliff erosion and nearshore sediment source created by the rising of sea level
256
Why is SBFH so high energy?
As it is relatively north facing so is very exposed and receives highest wave energy.
257
SBFH: clay erosion rate versus sandstone erosion rate:
0.8m/year versus 0.1m/year
258
SBFH: What is a feature left behind by retreating cliffs?
Shore platforms.
259
Eustatic change:
Changes in the volume of water in the global ocean store.
260
How does Eustatic change come about?
Changes in the mean global temperature.
261
Isostatic:
Change in the level of land relative to the sea
262
What are four factors that can change the earth's global temperature?
-variations in the Earth's orbit around the sun
-variations in the amount of energy produced by the sun
-changes to composition of atmosphere (e.g. volcanic eruption)
-variations in tilt of Earth's axis
263
What does a decrease in global temperature do to sea level?
-more precipitation falls as snow
-snow turns to ice and so water is stored on land rather than in sea in liquid form
-results in a reduction in the volume of water in the ocean
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On a molecular level what can a decrease in global temperature do to sea level?
As temp falls, water molecules contact leading to an increased density and reduced volume. estimated that a one degree fall in temp leads to 2m sea level drop
265
What are emergent landforms?
Landforms shaped by processes during times of high sea level and are left exposed once the sea level drops.
266
Raised beaches:
areas of former shore platforms that are left at a higher level than the present sea level. often found a distance inland form present costline
267
Behind the beach along emergent coastlines it is not uncommon to find...
abandoned cliffs with wave cut notches and even caves, arches, stacks and stumps
268
What is an example of a raised beach?
On the southern tip of the Isle of Portland there is a raised beach at about 15m above present ay sea level. Thought to be formed 125,000 years ago during Tyrrhenian inter glacial period.
269
After emergence, landforms are not affected by wave action but they do remain affected by...
weathering and mass movement
270
What happens on a molecular level to the sea level when the global temperature increases?
Water molecules expand and this also leads to increased water volume.
271
Rias:
submerged river valleys formed as sea level rises
272
Three features of a ria
- gently sloping exposed valley sides
- winding plan view
-relatively shallow water becoming increasingly deep towards the centre
273
When were the majority of rias on the south coasts of Devon and Cornwall formed:
during the post glacial sea level rise of the Flandrain Transgression
274
Fjords:
submerged glacial valleys that have steep almost cliff like valley sides where the water is uniformly deep
275
How long is the Sogne Fjord in Norway?
200km
276
What shape is the cross section of a Fjord?
U
277
What is the plan view of a fjord like?
A lot straighter than rias
278
What are shingle beaches and how do they form?
When sea levels fall as the volume of land based ice grows, large areas of 'new' land emerge from the sea. Sediment accumulates on this surface, deposited by rivers, meltwater streams and low energy waves. As sea level rose at the end of the last glacial period, wave action pushed these sediments onshore.
279
Both rias and fjords may be modified by the...
wave processes acting on their sides at the present day sea level
280
How much are sea levels predicted to rise in the next 100 years?
0.6 m
281
Human activity will cause change, either ...... or .....
intentionally or unintentionally
282
What are physical barriers to wave processes referred to as?
Hard engineering
283
What are non-physical more environmentally friendly methods to counteracting wave processes called?
Soft engineering
284
What are two examples of hard engineering?
groynes and rip rap
285
What are two examples of soft engineering?
beach recharge and vegetation planting
286
What is a case study of intentional change?
Sanbanks Peninsula, Dorset
287
What Sediment cell is the sandbanks peninsula located?
Sediment cell 5
288
What is the direction of LSD at the Sandbanks peninsula?
east to west (due to wave refraction)
289
What direction is LSD at Hengistbury Head by the sandbanks peninsula in Dorset?
west to east
290
How does Hengistbury head provide sediment?
It is undefended from wave action by a beach
291
What are the four main reasons/needs for management at Sandbanks?
- beach is a major tourist attraction due to its gently sloping profile and blue waters
- climate change means 0.6m of sea level is predicted in next 100years which would cause flooding of many properties and could flood roads and cute peninsula off from mainland
-large number of high value commercial properties including hotels and VERY high value residential buildings which provide significant employment and boost local economy are at risk
- the peninsula shelters lots of salt marshes and wetlands
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What is the purpose of rock groynes at sandbanks?
to maintain a deep and wide beach by minimising movement of sediment by LSD. this also restricts sediment from entering harbour protecting shipping lanes.
293
What is the purpose of beach recharge
Sand is dredged from offshore and sprayed onto beach at the cost of £20 per cube metre in order to conserve the beaches
294
What is a case study for unintentional change?
Mangawhai and Pakiri beaches located on New Zealand's north island
295
What is special about the sand at Manawhai Pakiri?
It is of very high value suitable for the building industry
296
The Hauraki Gulf is currently...
The site of the biggest sea bed mining operations
297
NZ legislation on seabed mining is ....
less restrictive than in many other countries
298
MP: Sand is an essential mineral resource for:
construction, concrete, glass manufacturing and beach replenishment
299
How long has sand dredging occured on the 20km long stretch of Mangawhai Pakiri coastline?
70 years (although it ended in 2005 at Mangawhai, it continued at Pakiri)
300
What are the current rates of extraction at Pakiri?
75000 cubic metres per year
301
What are the impacts of the Mangawhai Pakiri coastline essentially being a closed system?
The sand is a non renewable source and so the outputs of sand are not replaced by inputs from rivers
302
What city is the sand extraction at Mangawhai Pakiri convenient for and why?
-Aukland is located 50km south (it is NZs most economically dynamic city)
-population of over 1.5 million
-accounts for 35% of country's gap
-rapidly growing region with over 2.3 foreign visitors in 2015
-much of the sand extracted has been used to replenish tourist beaches in Aukland
303
Why is there little fluvial sediment input at Mangawhai Pakiri?
Because there are few sizeable rivers
304
What is the issue with deeper water being created offshore at Mangawhai Pakiri due to the dredging?
Allows for higher energy waves to approach shoreline increasing rates of erosion along beaches and dunes.
