Coasts - Systems & Processes Flashcards
What is the backshore?
Backshore is the area between the high water mark and tha landward limit of marine activity. Changes noramlly take place here only during storm activity.
What is the foreshore?
Foreshore is the area lying between the high water mark. It is the most important zone for marine processes in times that are not influenced by storm activity.
What is the inshore?
The area between the low water mark and the point where waves cease to have any influence on the land beneath them.
What is the offshore?
The area beyond the point where waves to cease to impact upon the seabed and in which acitivity is limited to deposition of sediment.
What is the nearshore?
Nearshore is the area extending seaward from the high water mark to the area where waves begin to break. It includes: the swash zone, surf zone and breaker zone.
What is the swash zone?
The area where a turbulent layer of water washes up the beach following the breaking of a wave.
What is the surf zone?
The area between the point where waves break, forming a foamy, bubbly surface and where the waves then move up the beach as swash in the swash zone.
What is the breaker zone?
The area where waves approaching the coastliune begin to break, usually where the water depth is 5 to 10m.
What are some examples of inputs in a coastal system?
1) Energy from waves, wind, tides and sea currents.
2) Sediment
3) Geology
4) Sea level change
What are the components in a coastal system?
Characteristic erosional and depositional coastal landforms
What are some example of outputs in a coastal system?
1) Dissipation of wave energy.
2) Accumulation of sediment above the tidal limit.
3) Sediment removed beyond local sediment cells.
Define erosion
The wearing away of the Earth’s surface by the mechanical action of processes of glaciers, wind, rivers, marine waves and wind.
Define fetch
Refers to the distance of open water over which a wind blows uninterrupted by major land obstacles. The length of fetch helps to determine the magnitude and energy of waves reaching the coast.
Define mass movement
The movement of material downhill under the influence of gravity, but may also be assisted by rainfall.
Define weathering
The breakdown and/or decay of rock at or near the Earth’s surface creating free sodil material that remains in situ intil it is moved by later erosional processes. Weathering can be mechanical, biological/organic or chemical.
What are the features of wind as an input into a coastal system?
1) Spatial variations in energy result from variations in the strength and duration of the wind.
2) The length of fetch helps to determine the magnitude and energy of waves reaching the coast.
3) The energy acquired by waves depends upon the strength of the wind, the length of time it is blowing and the fetch.
4) Wind acts as an agent of erosion as it can firstly pick up and remove sediment from the coastline and use it to then erode other features.
Define waveheight/amplitude
This is the height difference between a wave creast and the neighbouring trough.
Define wavelength
This is the distance between successive crests.
Define wave period
This is the time for one wave to travel the distance of one wavelength, or the time between one crest and the following creast passing a fixed point.
Define backwash
The action of water receding back down the beach towards the sea.
What are constructive waves?
Waves with a low wave height, but with a long wavelength and low frequency of around 6-8/min. Their swash tends to be more powerful than their backwash and as a consequence beach material is built up.
What are destrcutive waves?
Waves with a heigh wave height with a steep form and high frequency of 10-14/min. Their backwash is genrally stronger than their swash, so more sediemnt is removed than is added.
Define swash
The rush of water up the beach after a wave breaks
What are longshore currents?
Longshore currents occur as most waves do not hit the coastline ‘head on’ but approach at an angle to the shoreline. This generates a flow of water running parallel to the shoreline. This not only moves water along the surf zone but also transports sediment parallel to the shoreline.
What are rip currents?
Rip currents are strong currents moving away from the shoreline. They develop when seawater is ‘piled up’ along the coastline by incoming waves. Initially the current may run parallel to the coast before flowing out through the breaker zone, possibly at a headland or where the coast changes direction.
What is upwelling?
Upwelling is the movement of cold water from deep in the ocean rowards the surface. The more dense cold water replaces the warmer surface water and craetes nutrient-rich cold ocean currents.
Define longshore 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.
Define wave refraction
When waves approach a coastline that it 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.
What are tides?
The periodic rise and fall of the level of the sea in response to the gravitational pull of the sun and the moon.
How does the moon affect tides?
The moon pulls water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the earth.
What is a spring tide?
Twice in a lunar month, when the moon, sun and earth are in a straight line, the tide-raising force is strongest. This produces the highest monthly tidal rnage known as a spring tide.
What is a neap tide?
Twice in a lunar month, the moon and sun are positioned at 90 degrees to each other in relation to the earth. This alignment gives the lowest monthly tidal range, known as a neap tide.
What are the three classifications of tidal range?
1) Macrotidal: more than 4m.
2) Mesotidal: 2 to 4m.
3) Microtidal: less than 2m.
What is a tidal/storm surge?
Tidal or storm surges are occasions when meteorological conditions give rise to strong winds which can produce much higher water levels than those at hight ide.
What is a coastal sediment budget?
The balance between sediment being added to and removed from the coastal system, that system being defined within each individual sediment cell.
What is a high energy coast?
A coastline where strong, steady prevailing winds create high energy waves and the rate of erosion is greater than the rate of deposition.
What is a low energy coast?
A coastline where wave energy is low and the rate of deposition often exceeds the rate of erosion of sediment.
What is a sediment cell?
A distinct area of coastline seperated from other areas by well-defined boundaries, such as headlands and stretches of deep water.
What are some sources of coastal sediment?
Stream or rivers flowing into the sea, estuaries, cliff erosion and offshore sand banks.
Define hydraulic action
Hydraulic action refers to the impact on rocks of the sheer force of the water itself. This can exert enormous pressure upon a rock surface, thus weakening it.
Define wave quarrying
A breaking wave traps air as it hits a cliff face. The force of water compresses this air into any gap in the rock surface, creating enormous pressure within the fissure or joint. As the water pulls back, there is an explosive effect of the air under pressure being released. The overall effect of this over time is to weaken the cliff face.
Define abrasion/corrasion
Where material carried by moving water or wind hits exposed rock surface, thus wearing them away. Often referred to as sandblasting or sandpapering effect.
Define attrition
The rocks in the sea which carry out abrasion are slowly worn down into smaller and more rounded pieces.
Define solution (corrosion)
The process of solution includes the dissolving of calcium-based rocks.
What are some factors that affect coastal erosion?
1) Wave steepness and breaking point. 2) Fetch. 3) Sea depth. 4) Coastal configuration. 5) Beach presence. 6) Human activity.
Define lithology
Lithology refers to the characteristics of rocks, especially resistance to erosion and permeability.
Define differential erosion
Variation in the rates at which rocks wear away
What is a concordant coastline?
Has the same type of rock along its length, resulting in fewer headlands and bays.
What is a discordant coastline?
Has alternating bands of more and less resistant rock that run perpendicular to the coastline, resulting in the formation of headlands and bays.
Define traction
Large stones and boulders are rolled and slid along the seabed and beach by moving seawtaer. This happens in high energy environments.
Define saltation
Small stones bounce or leapfrog along the seabed and beach. This process is associated with relatively high energy conditions.
Define suspension
Very small particles of sand and silt are carried along by moving water.
Define solution
Dissolved materials are transported within the mass of moving water.
What are four situations where deposition occurs?
1) When sand and shingle accumulate faster than they are removed. 2) As waves slow following breaking.
3) As water pauses at the top of the swash before backwash begins. 4) When water percolates into the beach material as backwash takes it back down the beach.
What are aeolian processes?
Refer to the entrainment, transport and deposition of sediment by wind.
Define surface creep
A process similar to traction, where wind rolls or slides sand grains along the surface.
Define saltation (aeolian process)
Where the wind is strong enough to temporarily lift the grains of sand into the airflow to heights of up to one metre for distances up to 20 to 30m.
What is sub-aerial weathering?
Sub-aerial weathering includes processes that slowly break down the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily.
What are the three categories of weathering?
1) Mechanical/physical weathering.
2) Biological weathering.
3) Chemical weathering
Describe the process of mechanical/physical weathering
These processes depend on the nature of the climate and can be freeze-thaw weathering or pressure release.
Describe the process of freeze-thaw weathering
In latitudes where temperatueres fluctuate above and below freezing, free-thaw action is common, especially as there is a ready supply of water. Water that enters cracks in the rocks freezes as temperatures remain below zero. As it freezes, the water expands by almost 10%, meaning the ice occupies more space and so exerts pressure on the surrounding rock. As the process repeats and continues, the crack widens, and eventually pieces of rock break off.
Describe the process of pressure release
Pressure release is where processes of erosion, weathering, and mass movement remove overlying material, the rock beneath is said to experience pressure release. As the overlying mass is unloaded, mechanisms within the rock cause it to develop weaknesses, or cracks and joints, as it is allowed to expand. This makes the rock susceptible to other processes of erosion and weathering.
Describe the process of biological weathering
These are the processes that lead to the breakdown of rocks by the action of vegetation and coastal organisms.
Describe the process of chemical weathering
This occurs where rocks are exposed to air and moisture so chemical processes can break down the rocks. There are 6 processes of chemical weathering: Solution, Oxidation, Hydration, Hydrolysis, Carbonation and Acid Rain.
What does the nature of the mass movement experienced depend upon?
1) The level of cohesion within the sediment.
2) The height of the slop and slope angle.
3) Grain size within the sediment.
4) Temperature and level of saturation.
What are landslides?
Occur on cliffs made from softer rocks or deposited material, which slip as a result of failure within it when lubricated, usually following heavy rainfall.
What are rockfalls?
These occur from cliffs undercut by the sea, or on sloped affected by mechanical weathering like frost action.
What are mudflows?
Heavy rain can cause large quantities of fine material to flow downhill. Here it become saturated and if excess water cannot percolate deeper into the ground, surface layers become very fluid and flow downhill. The nature of the flow is dependent on the level of saturation, type of sediment and slope angle.
What is rotational slumping?
Where softer material overlies much more resistant materials, cliffs are subject to slumping. With excessive lubrication, whole sections of the cliff face may move downwards with a slide plane that is concave, producing a rotation movement.
What is soil creep?
This occurs where there is a very slow, almost imperceptible, but continuous movement of individual soil particles downslope.
