Coasts Flashcards
(102 cards)
1
Q
What is the littoral zone?
A
The wider coastal zone including adjacent land areas and shallow parts of the sea.
Split into subzones:
- coast
- backshore
- foreshore
- nearshore
- offshore
2
Q
How can coasts be classified through formation processes
A
primary coasts - dominated by land-based processes such as deposition from rivers or new coastal land caused by lava flows.
secondary coasts - dominated by marine erosion or deposition processes
3
Q
How can coasts be classified through relative sea level change
A
Emergent coasts are rising relative to sea level, for example due to tectonic uplift.
Submergent coasts are being flooded by the sea, either due to rising sea levels and/or subsiding land
4
Q
How can coasts be classified through tidal range
A
Microtidal coasts (0-2m tidal range)
Mesotidal coasts (2-4m tidal range)
Macrotidal coasts (>4m tidal range)
5
Q
How can coasts be classified through wave energy
A
Low energy coastlines are sheltered with limited fetch and low wind speeds resulting in small waves. They are often sandy and the rate of deposition exceeds the amount of erosion
High energy coastlines are exposed, facing prevailing winds with long fetches resulting in powerful waves. They are often rocky and the rate of erosion exceeds the rate of deposition
6
Q
Cliff profile
A
The height and angle of a cliff face as well as its features such as wave-cut notches or changes in slope angle
7
Q
Coastal morphology
A
The shape and form of coastal landscapes and their features
8
Q
Lithology
A
The physical characteristics of particular rocks
9
Q
What are the 2 main types of coast
A
Rocky/cliffed coasts:
- have cliffs varying in height, angle and hardness of rock
-the transition from land to sea is abrupt
Coastal plains/alluvial coasts:
- the land gradually slopes towards the sea across an area of deposited sediment
- sand dunes and mud flats common
- if there are sand dunes, at high tide the beach is inundated, but the dunes are not
- Coast may be estuarine, with mudflats and salt marshes at the mouth of a river
10
Q
weathering
A
The chemical, biological and mechanical breakdown of rock into smaller fragments and new minerals in situ
11
Q
mass movement
A
The detachment and movement of weathered and eroded material downslope under the influence of gravity
12
Q
surface runoff
A
water that hasn’t permeated the rock flowing down a cliff face and causing erosion of it
13
Q
What is erosion resistance/ ‘hardness’ of the rock influenced by
A
- how reactive minerals in the rock are when exposed to chemical weathering
e.g. calcite in limestone can be weathered by solution, quartz in sandstone cannot - whether rocks are clastic (sedimentary, cemented particles) or crystalline.
Igneous and metamorphic rock are crystalline, as they are made out of interlocking particles, so more resistant - cracks, fissures and fractures. These are weaknesses exploited by weathering and erosion
14
Q
Coastal accretion
A
The deposition and buildup of sediment at the coast and the seaward growth of the coastline, creating new land. Often involved deposited sediment being stabilised by vegetation
15
Q
Dynamic equilibrium
A
The balanced state of a coastal system where inputs and outputs balance over times and positive and negative feedback loops maintain the internal equilibrium
16
Q
Fetch
A
The distance a wave travels. A long fetch creates a high energy wave
17
Q
swash
A
The flow of water up the beach
18
Q
backwash
A
The wave running back down the beach to meet the next incoming wave
19
Q
What creates a destructive wave
A
A weak swash and strong backwash creates high, plunging waves with a short wavelength. Increased erosion of the coast, with a steep beach profile.
20
Q
What creates a constructive wave
A
A strong swash and weak backwash creates low, surging waves with a long wavelength. Increased deposition on the coast, often creating a ridge of sediment.
21
Q
Strata
A
The different layers of rock within an area and how they relate to each other
22
Q
Bedding planes
A
horizontal cracks. Natural breaks in the strata caused by gaps in time during periods of rock formation
23
Q
Joints
A
Vertical cracks. Fractures caused by contraction as sediments dry out or by earth movements during uplift. Divides rock strata up into blocks with a regular shape
24
Q
Folds
A
Formed by pressure during tectonic activity which makes rocks buckle and crumple
25
Faults
formed by when stress or pressure to which a rock is subjected to (often by tectonic forces) exceeds its internal strength, causing it to fracture. Faults then slip or move along fault planes, moving rocks from their original positions on either sides of the fault line
26
Dip
The angle at which rock strata lie
27
What is a concordant coastline
When rock strata run parallel to the coastline. Bands of alternating resistant and non resistant rock leads to formations to bays and coves when marine erosion breaks through resistant rocks and then rapidly erode the soft rock behind.
e.g. the coast around Lulworth in Dorset
28
What is a discordant coastline
Formed when different rock strata intersect the coast at an angle, so geology varies across a coastline. Alternating bands of more and less resistant rock that run at right angles to the coast lead to alternating bays and headlands.
29
Why do waves break?
As a wave nears the shore it rears up into a crest as the bottom moves slower than the top as there is friction with the sea bed. This means wave energy increases as it reaches the shore.
30
Why are waves more destructive at headlands?
Waves are more destructive at headlands as it is deeper, so the waves break closer to the headland. Waves are less destructive at beaches because it is shallower, so the waves lose energy before they reach the floor.
Wave refraction; in bays, wave crests curve to fill the bay and wave height decreases. The straight wave crests refract, becoming curved. This means the waves spread out in bays and concentrate on headlands
31
How does a horizontal dip influence the cliff profile
A near vertical profile with notches reflecting strata that are more easily eroded
32
Fissures
Small cracks in the rock, but represent weaknesses erosion can exploit
33
How does a seaward dip affect the cliff profile
Low angle - rocks gently dip towards the sea, vertical joints opened by weathering and pressure release. Overhanging rock, vulnerable to rock falls
High angle - Sloping profile with one rock layer facing the sea, vulnerable to rock slide along bedding planes.
34
How does a landward dip affect the cliff profile?
Stable, steep cliffs. reduced rock falls
35
Traction
sediment (pebbles, cobbles, boulders) rolls along sea floor, pushed by waves
36
Saltation
sediment (sand sized particles) bounce along because of the force of the water or wind
37
Solution
dissolved material (chemical compounds in solution) is carried in water
38
What conditions will produce the most erosion?
- when waves are at their largest (influenced by wind speed and fetch), waves have a lot of energy so can hurl sediment at a cliff face
- waves are 90 degrees to the cliff face
- tide is high
- heavy rainfall (surface runoff and percolation weakens the cliff)
- debris from previous erosion has been removed from the cliff foot
39
hydraulic action
air trapped in cracks and fissures is compressed by the force of waves crashing against the cliff face. The pressure forces cracks open. More air is trapped so greater force is experienced in the next cycle of compression. Blocks of rock are dislodged off the cliff face. Heavily jointed/fissured sedimentary rocks are vulnerable
40
Abrasion
sediment picked up by breaking waves is thrown against the cliff face. This gradually wears the cliff down by removing rock particles, chiseling away at the surface. Loose sediment needs to be available, softer sedimentary rocks are more vulnerable
41
Attrition
Acts on already eroded sediment. Collisions between sediment carried by waves slowly chips fragments off the sediment. Sediment gets more smaller and rounded over time
42
Corrosion/solution
Carbonate rocks (limestones) are vulnerable to solution by rainwater, spray from the sea and seawater.
43
Wave-cut notch
Hydraulic action and abrasion at the base of a cliff creates a notch. As the notch becomes deeper and the cliff becomes more overhanging, rockfall occurs
44
Blow hole
Forms when a coastal cave turns upwards and breaks through the flat cliff top. Usually because of erosion of weak strata or the presence of a fault line
45
Suspension
Sediment (silt and clay particles) is carried in the water column. On soft rock coasts, the sea is often muddy brown due to suspended sediment
46
Swash-aligned coasts
Wave crests approach parallel to the coast, so there is limited longshore movement of sediment
47
Drift-aligned coasts
wave crests break at an angle to the coast, so there is consistent longshore drift and the generation of elongated depositional features
48
Lateral shift
effect of net movement of sediment up and down the beach
49
Longshore drift
The prevailing wind is at an angle. The wind pushes waves up the beach at an angle, so the swash carries sediment up the beach. The backwash retreats down the beach at a different angle due to gravity. Sediment is pushed across the beach. Smaller sediment is carried further up the beach
50
Gravity settling
occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first followed by smaller sediment.
51
Flocculation
Clay particles suspended in water clump together as a result of electrical or chemical attraction and become large enough to sink
52
Spit
Sand or shingle beach ridge extending beyond a turn in the coastline. The end of the spit curves round as wave refraction carried material around into sheltered water behind the spit.
53
Tombolo
a beach/ridge of sand and shingle formed between an island and the mainland. Sometimes covered at high tide. Forms due to wave refraction and an area of calm water in between the mainland and the island.
54
Barrier beach/bar
A spit that grows so long it extends across a bay to join two headlands. Can form a lagoon or a barrier island if separated from the mainland
55
Cuspate foreland
Triangular shaped headland that extends out from the main coastline. Longshore drift happen on both sides of the headland, so the sediment meets in the middle. What is wave refraction and the effect on bays and headlands. Vegetation stabilises it and new land is formed
56
Offshore sand bars
Created by destructive waves offshore from the coast. Eroded sand from the beach is deposited offshore in bars. Creates partially exposed ridges of sand or coarse sediment
57
Angle of repose
The steepest angle at which a sloping surface formed of weathered and eroded material is stable
58
Unconsolidated sediment
Sediment that is loosely arranged or unstratified (not in layers) e.g. boulder clay
59
Shear stress
The function of gravity pulling the object down. Shear stress increases from excessive rainfall (water weight on slope) and steeper slope angles
60
Shear strength
The resistance of an object to movement downhill. Higher when there is high friction and cohesiveness.
61
What are external factors relating to mass movement?
Climate:
- rainfall and temperature influences weathering rate
- weathered product makes the slope less stable
- saturated layers reduce friction
Vegetation and soil:
- finer materials have a lower angle of repose
- roots aid binding in soil
- decreases saturation
Anthropogenic:
- management strategies may result in slop no longer being at angle of repose
- building may result in higher shear stress
Geological structure:
-dip
- joints and fissures
62
Mass flows
Soil creep:
- individual particles of soil move downhill
- slow but continuous
Solifluction:
- occurs in areas of permafrost (Tundra)
- Top layer of soil thaws in summer but layer below remains frozen.
- top layer becomes saturated and flows over frozen subsoil below
Mud/earth flow:
- heavy rain reduces friction in soil
- earth turns into mud and slowly flows over bedrock
- material becomes jumbled up and flows down cliff
63
Mass slides
Rock fall:
- occurs when mechanical weathering breaks large chunks of cliffs away
- cliff has to be 40 degree angle or more
- material broken of is called scree and bounces down to the foot of the cliff
Rock/debris slide:
- Rocks that are jointed or have bedding planes parallel to the slope are susceptible to landslides
- slabs of rock slide over underlying rock, increase of water makes this easier
64
Slumps
- occur in saturated conditions
- has a rotational movement
- occur on moderate to steep slopes
- clays or sand overlying more resistant rock like limestone or granite
- causes rotational scars
- if repeated, creates a terraced cliff
65
Mechanical weathering
- freeze thaw
- salt crystallisation
66
Chemical weathering
- carbonation
- hydrolysis
- oxidation
67
Biological weathering
- plant roots
- rock boring (clams and molluscs)
68
Isostatic change
A local rise or fall in sea level
69
Eustatic change
A global rise or fall in sea level due to the volume of water
70
Eustatic fall in sea level
During glacial periods when ice sheets form on land. Water evaporated from the sea is locked up on land as ice, leading to a global fall in sea level
71
Eustatic rise in sea level
At the end of a glacial period when ice sheets melt and return water to the sea, and global temperature increase leads to thermal expansion of water, resulting in a rise in seal levels globally
72
Isostatic fall in sea level
The weight of ice sheets caused the Earth's crust to sag during the last glacial period. The land slowly rebounds upwards after the ice sheets melt over thousands of years. This post-glacial adjustment slowly lifts the land surface out of the sea
73
Isostatic rise in sea level
Land can sink at the coast due to accretion (a build up of deposited sediment)
74
Examples of concordant coastlines
Dalmatian coasts (e.g. Croatia):
- Coast has been folded by tectonic activity, creating valleys (synclines) and ridges (anticlines) running parallel to each other
- a rise in sea level in the Holocene era flooded the valleys, leaving the ridges as parallel offshore islands
Haff coasts:
- lagoons that are enclosed by long spits or dunes that run parallel to the coastline
75
Features of submergent (drowned) coastlines/ marine transgression
Rias:
- A drowned river valley in an unglaciated area caused by sea level rise flooding the river valley, making it much wider
- may still be slowly submerging
Fjords:
- drowned u-shaped glacially eroded valley
- very deep, often deeper that the adjacent sea
- submerged lip (moraine)
- possibly shallowing through glacial uplift
76
Features of emergent coastlines/ marine regression
- vegetated raised beaches and fossil cliffs with old sea caves and wave cut notches
- small cliff separating raised beach and present beach
77
Human causes of coastal retreat
Offshore dredging:
- scooping sediment up from the seabed usually for constructions or creating shipping channels
- decreases supply of sediment to beach so increases erosion
- deeper water may also allow waves to have more destructive energy closer inshore
Coastal defences:
- a defence in on area will limit sediment supply to somewhere else in the sediment cell. Less sediment to absorb wave energy
78
Storm surges
A short term rise in sea level caused by low air pressure from
- a depression
- a tropical cyclone
Made worse with strong wind pushing waves onshore or high spring tides coinciding
79
How do dams cause coastal erosion?
Sediment is trapped by the reservoir and dam. The coast is starved of sediment, increasing erosion
80
Environmental refugees
Communities forced to abandon their homes due to natural processes including sudden ones such as landslides, or gradual ones such as erosion or rising sea levels
81
Hard engineering
Encasing the coastline in steel, concrete and stone. Aims to stop physical processes altogether or alter them to protect the coast
82
Advantages and disadvantages of hard engineering
+adv:
obvious to people something is being done to protect them
one-off solution that protects the coastline for decades
-disadv:
building and maintenance costs are high
prone to failure
visually unattractive or inaccessible to tourists
coastal ecosystems often overlooked
often affects processes further along the coast
83
Examples of hard engineering
- rip-rap/rock armour
- rock breakwater
- sea wall
- revetements
- groynes
84
Soft engineering
Attempts to work with natural processes to reduce coastal erosion and flood threats.
85
Advantages and disadvantages of soft engineering
+adv:
usually less obvious and intrusive
may be cheaper in the long term
works with ecosystems
-disadv:
ongoing costs such as sediment supply can be high, sustainable sediment source needs to be founds
86
Examples of soft engineering
- beach nourishment
- cliff stabilisation
- dune stabilisation
87
Sustainable coastal management
Managing the wider coastal zone in terms of people and their economic livelihoods, social and cultural wellbeing, and safety from coastal hazards as well as minimising environmental and ecological impacts
- adapting livelihoods and relocating buildings
- educating communities
88
Integrated coastal zone management (ICZM)
Requires different stakeholders to adopt a joined-up approach in order to harmonise policies and decision making.
-plan for the long term
-try to work with natural processes
- all stakeholders have a say in any policy decisions - 'participatory planning'
- the entire coastal zone is managed
- recognises the importance of the coastal zone to people's livelihoods
- recognises that management of the coast must be sustainable
89
Littoral cells/ The sediment cell model
The idea that all coastlines divide up into distinct cells containing sources, transport paths and sinks. Each littoral cell is isolated from adjacent cells, so mostly sediment is transported within cells. This means cells can be managed as a holistic unit
90
Examples of coastal management policy decisions
- No active intervention (no new investment in defences)
- Hold the line (build or maintain defences so shoreline position remains the same)
- Managed retreat/ strategic realignment (allows coastline to recede, protect certain areas)
- Advance the line (extending coastline out to sea using defences)
91
Cost benefit analysis (CBA)
A tool to help decide whether defending a coastline is 'worth it' economically
Value of property is dependent on how at risk it is. Some human costs are hard to quantify financially
92
Environmental impact assessment (EIA)
A process that aims to identify
- the short-term impacts of construction on the coastal environment
- the long-term impacts of building new sea defences or changing a policy from hold the line to no active intervention or managed realignment
May inform the final CBA.
May assess impacts on water movement and quality, possible changes to flora and fauna and wider impacts such as air quality and noise pollution during construction.
93
Conflict: winners and losers of coastal management policies
winners = people who have gained from the policy decision, either economically, environmentally or socially
losers = people who are likely to lose property, or see the policy as an environmental negative e.g. see the coast as 'concreted over'
94
psammosere
a sand dune ecosystem
95
halosere
a salt marsh ecosystem
96
Xerophytes
Coastal plants that can tolerate very dry conditions such as sand dunes
97
Halophytes
Coastal plants that can tolerate salty water
98
Mangrove swamps
A collection of trees suited to coastal environments found on tropical coastlines. A habitat for young fish and absorbs wave energy. Under threat from climate change (storms and rising sea levels)
99
Aeolian processes
processes due to wind activity
100
Salt marshes
Areas of flat, silty sediments that accumulate around estuaries or lagoons
They develop in sheltered areas where deposition occurs, where salt and freshwater meet, where there are no strong tides or currents to prevent sediment deposition/accumulation
Covered by high tide and exposed at low tide
101
Sand dunes`
Consist of sand that has been blown off the beach by onshore winds (saltation) and trapped by debris. Vegetation then helps to stabilise the dunes
102
Sand dune succession
Highly specialised pioneer plants colonise bare embryo dunes. Plants bind sand together. Plant succession occurs where other species invade and take over until a balance is reached. As the dune system moves inland/ over time:
- pH decreases
- humus % increases
- height increases
- diversity increases
Reaches climax community
