Coasts Flashcards
High energy coastlines
-Face powerful waves for most of the year
-Erosion exceeds deposition and the landforms reflect this such as headlands with arches and caves eroded into them and wave-cut platforms.
Low energy coastlines
-The waves are less powerful and the coast is more sheltered.
-Deposition exceeds erosion at these coastlines creating beaches and spits.
Constructive waves
Waves with a low wave height, but a long wavelength and a low frequency of around 6-8/min. Swash is more powerful than backwash leading to buildup of beach material.
Destructive waves
-Waves with a high wave height with a steep form and high frequency (10-14/min). Backwash is stronger than swash, so more material is removed than added.
Backwash
The action of water receding back down the beach towards the sea (associated with removal/erosion of material)
Swash
The rush of water up a beach after a wave breaks (associated with deposition of material)
Erosion
The wearing away of the Earth’s surface by the mechanical action of the process of glaciers, wind, rivers, marine waves and wind.
Fetch
The distance of open water over which wind blows uninterrupted by major land obstacles. The length of fetch helps to determine the magnitude and energy of waves reaching the coast.
Mass movement
The movement of material downhill under the influence of gravity, but may also be assisted by rainfall.
Weathering
The breakdown and/or decay of rock at or near the earth’s surface by creating regolith that remains in situ until it is moved by later erosional processes. Weathering can be mechanical, biological or chemical.
Longshore/littoral drift
Where waves approach the shore at an angle and swash and backwash then transport material along the coast in the direction of the prevailing wind and waves.
Wave refraction
When waves approach a coastline that is not a regular shape, they are refracted and become increasingly parallel to the coastline. The overall effect is that the wave energy becomes concentrated on the headland, causing greater erosion. The low-energy waves spill into the bay, resulting in beach deposition.
Tides
The periodic rise and fall of the level of the sea in response to the gravitational pull of the sun and moon.
Outline factors leading to the formation of fjords (4 marks)
-Fjords are an example of coastal landforms of submergence.
-They are primarily a product of glacial erosion.
-As glaciers advanced towards coastal loactions in Norway for example, they carved out vast glacial troughs, through processes such as abrasion and plucking.
-A combination of localised isostatic re-adjustment and global eustatic sea level change has led to the flooding of these valleys.
-For example Sogne Fjord in Norway
-Interglacial period is also a factor leading to the formation of fjords.
Sources of energy in coastal environments
-waves
-wind
-tides
-sea currents
Outline the role of waves in the transportation of sediments at the coast (4 marks)
-Constructive waves tend to bring sediments on to the beach, due to their low energy nature. The swash is greater than the backwash and they have low frequency, height and limited backwash.
-Destructive waves tend to remove sediments from beaches and coastlines, they have powerful backwash and weak swash and high wave frequency and height and associated with high energy coastlines.
Outline littoral (longshore) drift
-Longshore drift is the gradual movement of sediments along a coastline
-Where waves strike the coast at an angle, sediments are moved up the beach at the same angle with the swash.
-The backwash returns sea water and sediments perpendicular to the coastline
-Repeated wave action in this way moves sediments along parallel to the coastline.
Eustatic sea level change vs isostatic sea level change
-Eustatic change is a global change in sea level resulting from an actual fall or rise in the level of the sea itself
-Isostatic change- local changes in sea level resulting from the land rising or falling relative to the sea
Fjord
Former glacial valley drowned by rising sea levels
Ria
Former river valley drowned by rising sea levels
Raised beaches
-Areas of former wave-cut platforms and their beaches which are at a level higher than the present sea level.
Explain the concept of the sediment cell
-A sediment cell is a closed system usually bounded by headlands or a change in longshore drift.
Concordant coast
A coastline where bands of alternate geology run parallel to the coast.
Dalmatian coast
A concordant coastline with several river valleys running perpendicular to the coast. They become flooded to produce parallel long islands and long inlets.
Discordant coast
A coastline where bands of alternate geology run perpendicular (or at right angles) to the shore.
Dynamic equilibrium
Where a natural system tries to achieve a balance by making constant changes in response to a constantly changing system.
Define a negative feedback loop
Changes are met with responses that restore the balance back to the orginal state
Define positive feedback loop
-One change from the original state that triggers continuous problems and cannot restore itself eg. cliff erosion.
What is a spring tide
-Gravitational pull of both sun and moon, when aligned gives a higher high tide and lower low tide, increasing the overall tide range.
-Occurs when the sun, earth and moon are in a straight line, twice a lunar month.
What is a neap tide
-Sun and moon are at right angles to the earth, gravitational pull is less effective in comparison to aligned in spring tide.
-High tide is less and low tide is higher, giving a smaller tidal range.
-Occurs on alternate week, twice a month.
Explain the concept of a sediment cell (4 marks)
1) A sediment cell is a closed system usually bounded by headlands or a change in longshore drift
2) Within a sediment cell, there is erosion, transport and deposition of sediment
3)The only inputs come from erosion of seabed or headland
4)Little or no movement between cells
5) Human activity such as beach management can interrupt the natural system, creating imbalance within the cell, leaving some areas at risk of erosion
Describe the differences between constructive and destructive wave forms (4 marks)
-Both wave types depend on certain factors, such as fetch (how far the wave has travelled), strength and duration of the wind
-Constructive waves ‘build up’ a beach by depositing sediment, have a low wave height, stronger swash than backwash and longer wavelength
-Destructive waves erode and remove sediment from a beach and have a higher wave height, stronger backwash than swash and higher frequency (6-8/min constructive, (13-15/min)
Characteristics of destructive waves
-Erosional waves
-Short wavelength, high height
-High frequency (10-12/min)
-High energy
-Backwash greater than swash
Characteristics of constructive waves
-Depositional waves
-Long wavelength, low height
-Low frequency (6-8/min)
-Swash greater than backwash
-Low energy
What is ENSO- El Niño Southern Oscillation?
A reversal of the normal atmospheric circulation in the southern Pacific Ocean, bringing warm water and low pressure to the eastern Pacific and cool water and high pressure to the western pacific. It occurs once every 2-10 years.
What is La Niña?
An intensification of normal atmospheric processes, for example increased flooding in normally humid areas and increased drought in areas that are normally dry.
What is eustatic sea level change?
Worldwide changes in sea level caused by the growth and decay of icecaps, thereby releasing water from ice.
What is isostatic sea level change?
Localised change due to changes of the relative level of the land and the sea caused by depression of the earths crust such as due to an ice sheet. Following deglaciation, the crust beneath the weight begins to rise again and relative sea level therefore falls.
What is an advancing coastline?
Coastlines that are growing due to increasing deposition and falling sea levels
What is a retreating coastline?
Coastlines that are disappearing or getting smaller due to erosion or rising sea levels
What is a spit?
A spit is a beach of sand and shingle linked at one end to land, found on indented coastlines or at river mouths. For example along a coast where headlands and bays are common and near mouths (estuaries and rias) wave energy is reduced
Why do spits become curved?
As waves undergo refraction and cross currents or storm waves may assist, leading to smaller hooks or recurves.
Why do salt marshes form?
In shallow water, where there is an area of mudflats, salt marshes continue to grow as mud is being trapped by the marsh vegetation
What is managed retreat?
Protecting some areas, but allowing others to be eroded (cost-benefit analysis)
What are the future pressures on coastlines?
-Increasing population, greater number of people living in coastal areas
-Rising temperatures/sea levels
-growth of human activities such as industry and trade, energy developments, fishing, tourism and recreation
What are rias?
-Features of submerged coastlines or retreating coastlines where rates of erosion exceed deposition.
-Drowned river valleys caused by sinking land (isostatic) or sea level rise due to ice cap/glacier melt (eustatic)
What are fjords?
-Features of submerged or retreating coastlines where erosion exceeds deposition
-Caused by drowning U-shaped valleys
‘No amount of coastal intervention by people can halt the natural processes which continue to present potentially serious risks to coastal communities now and even more so in the future.’ 20 marks
-Physical processes affecting coastlines: waves, currents, tides, erosion and deposition
-High energy coastlines linked with erosion, destructive waves and increased flooding
-Eustatic and isostatic sea level change
-Coastal management
-Future increased storm events may exemplify effects on local area, low lying areas eg, Maldives only 8m above sea level at higher risk of sea level rise.
What is a shoreline management plan?
-The apparent negative impacts of many coastal management plans have created a need for a more sustainable and integrated approach
-This means different sections of the coastline are seen to function together rather than separated such as with more traditional methods like sea walls or groynes
-In the SMP, each of the 11 sediment cells in the UK have had a detailed document written to identify the natural processes, activities and risks in the area.
Who makes recommendations for all sections of the coastline in the UK?
DEFRA (the department for environment, food and rural affairs)
What are the 4 recommendations DEFRA make?
-Hold the line
-Advance the line
-Managed retreat
-Do nothing
What is hold the line?
-Maintaining the position of the coastline using mostly hard engineering methods
What is advance the line?
-Extending the coastline out to sea by building up the beach and land reclamation
What is managed retreat?
-Deliberate flooding of particular areas to manage the coastal retreat
What is do nothing?
-Letting nature take its course
What must DEFRA consider when making decisions?
-Must consider the value of the land and assets as well as the technical viability of management strategies
-This is a cost-benefit analysis
What is Integrated Coastal zone management?
-Large sections of the coastline are managed with one strategy- the 11 SMPs in the UK form a ICZM
-they recognise that the littoral (sediment) cells interact with eachother and that changes in one part of the coast impact other areas- such as the placement of groynes casing terminal groyne syndrome
-In the UK this can cross political and national boundaries meaning different councils have to work together.
