Coasts - Key Terms

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Backshore
The area between the high water mark to dunes/extreme inland limit of the beach. It is only affected by waves during exceptional high tides.
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Foreshore
This is the area lying between the high and low water marks, often submerged during high tides and exposed to lots of wave action.
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Offshore
The area of deep waters where waves cease to impact the seabed and in which activity is largely limited to the deposition of sediments.
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Inshore
Area comprising only shallow waters close to shore. Waves have considerable impact upon the land at this point.
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Wave period
The time interval between wave crests in seconds.
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Swell wave
A relatively smooth ocean wave that travels some distance from the area of its generation.
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Storm wave
A wave generated locally by high wind energy.
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Wave refraction
The reorientation of wave fronts as they enter shallow water so that they approach parallel (or roughly parallel) to the shoreline.
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Swash
The movement of water up a beach after a wave has broken.
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Storm surge
Elevated sea surface near the coast most often caused by extreme storms.
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Backwash
Flow of water down a beach perpendicular to the beach after a wave has broken.
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Fetch
The distance of open water in one direction from a coastline, over which the wind can blow.
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Coastal system
A system is a set of interrelated objects comprising components and processes that are linked together to form a working unit. Coastal systems include the store and transfer of both energy and material.
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Geomorphic processes
Processes to do with movement on the land.
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Equilibrium (of a coastal system)
When all of a coastal landscape's inputs and outputs are in a state of balance the area is said to be in equilibrium.
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Dynamic equilibrium
This is when the system undergoes self-regulation and changes its form in order to restore the equilibrium.
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Negative feedback
The process of self-regulation which restores equilibrium to a system.
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Positive feedback
The process by which an initial change in a system is amplified and causes further change.
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Wavelength
The distance between two successive waves or troughs.
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Waveheight
The distance between the trough and the crest.
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Sediment cell
This is a stretch of coastline within which the movement of coarse sediment, sand and shingle is largely self-contained.
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The boundaries of sediment cells are determined by...
the topography (shape) of the land. Large physical features such as headlands act as natural barriers that prevent the transfer of sediment to adjacent cells.
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It is unlikely that sediment cells are completely closed because of:
1) Changes in wind direction. 2) Headland erosion/collapse. 3) Storm event. 4) Sand-mining/beach replenishment. 5) Tidal currents (wave direction) change.
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Tidal range
This is the vertical difference between the high tide and the succeeding low tide.
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Weathering
This is the in situ breakdown of rocks by mechanical, biological and chemical processes.
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Mechanical weathering
This is where changes in temperature and moisture cause rocks to break down into smaller particles.
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Insolation weathering
This is the in situ breakdown of rocks in tropical and sub-tropical deserts caused by extreme diurnal changes in surface temperature. Also called thermal expansion.
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Freeze-thaw weathering
This is a mechanical weathering process caused by water, confined in rock joints, expanding as it freezes, and as a result breaking rocks into smaller particles.
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Chemical weathering
This is the decay of rocks involving chemical reactions between moisture and some minerals within the rock.
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Hydration
The breakdown of rocks by cycles of wetting (expansion) and drying (contracting).
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Oxidation
A chemical process that weathers certain types of rock and involves the absorption of oxygen from either the atmosphere or water by rock materials.
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Solution (weathering)
The chemical weathering process by which rock minerals are dissolved.
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Biological weathering
This is the disintegration of rocks as a result of action by living organisms, such as the growth of plant roots.
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Chelation
A type of chemical weathering caused by acids derived from rainwater and dead organic material.
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Mass movement
This is when the forces acting on slope material (mainly the resultant force of gravity) exceed the forces trying to keep the material on the slope (predominantly friction).
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Rock fall
On cliffs of 40° or more, especially if the cliff face is bare, rocks may become detached from the slope by physical weathering processes. These then fall to the foot of the cliff under gravity. Wave processes usually remove this material (or scree).
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(Rock) Slides
This often occurs due to undercutting by wave erosion at the base of the cliff which removes support for the materials above. Slumps are common in weak rocks, such as clay, which also become heavier when wet, adding to the downslope force.
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Abrasion
This is when waves armed with rock particles scour the coastline – it is rock rubbing against rock.
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Attrition
This occurs when rock particles, transported by wave action, collide with each other and with coastal rocks and progressively become worn away. They become smaller, smoother and more rounded, eventually creating sand.
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Hydraulic action
This occurs when waves break against a cliff face, and air and water trapped in cracks and crevices become compressed. As the wave recedes the pressure is released, the air and water suddenly expands and the crack is widened.
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Pounding
This occurs when the mass of a breaking wave exerts pressure on the rock causing it to weaken.
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Solution (erosion)
This involves dissolving minerals like carbonates in coastal rock. However, as the pH of sea water is invariably around 7 or 8, this process is usually of limited significance unless the water is locally polluted & acidic; still needs lots of materia
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Solution (transportation)
Minerals that have been dissolved into the mass of moving water. This type of load is invisible and will remain in solution until water is evaporated and they precipitate out of solution.
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Suspension
Small particles of sand, silt and clay can be carried by currents. Larger particles can also be carried in this way during storm events.
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Saltation
This is a series of irregular movements of material which is too heavy to be carried continuously in suspension. Turbulent flow may enable sand-sized particles to be picked up (entrained) and carried for a short distance only to drop back down again.
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Traction
The largest particles in the load may be pushed along the sea floor by the force of the flow. Although this can be called rolling, again the movement is seldom continuous. Large boulders may undertake a partial rotation before coming to a rest again.
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Deposition
This is laying down of sediment transported by rivers, waves, glaciers and wind, as energy levels decline.
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Tree roots
Tree roots grow into cracks or joints in rocks and exert outward pressure. This operates in a similar way and with similar effects to freeze-thaw. When trees topple, their roots can also exert leverage on rock and soil, bringing them to the surface.
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Organic acids
Organic acids produced during decomposition of plant and animal litter cause soil water to become more acidic and react with some minerals in a process called chelation.
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Carbonation
Rainwater combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate, which is soluble.
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Hydrolysis
This is a chemical reaction between rock minerals and water. Silicates combine with water, producing secondary minerals such as clays.
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Pressure release
When overlying rocks are removed by weathering and erosion, the underlying rock expands and fractures parallel to the surface. The parallel fractures are sometimes called pseudo-bedding planes.
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Salt crystallisation
Solutions of salt can seep into the pore spaces in porous rocks. Here the salts precipitate, forming crystals. The growth of these crystals creates stress in the rock causing it to disintegrate.
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Longshore drift
The movement of sediment by waves and currents along a coastline.
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Lithology
The general physical and chemical characteristics of a rock or the rocks in a particular area.
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Igneous rock
This is formed through the cooling and solidification of magma or lava.
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Metamorphic rock
This is rock which has been changed from its original state (not melted) by extreme heat and pressure.
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Sedimentary rock
This is rock that has formed through the deposition of sediment, especially sediment transported by water, ice and wind. They are often deposited in layers, and frequently contain fossils.
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Weak lithology
Rock has little resistance to erosion, weathering and mass movements. This is because the bonds between the particles that make up the rock are quite weak.
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Strong lithology
The rock is highly resistant to erosion, weathering and mass movements as the particles have strong bonds between them
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Strata
A single bed of rock (often sedimentary), generally consisting of one kind of matter representing continuous deposition. In simple terms it is a layer of rock.
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Permeability
Rocks with pores/cracks in them are vulnerable to weathering and erosion.
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Primary permeability
In porous rocks such as chalk, tiny air spaces (pores) separate the mineral particles. The pores can absorb and store water.
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Secondary permeability
Carboniferous limestone is also permeable, but for a different reason. Water seeps into limestone because it has many joints/fractures. The joints are easily enlarged by solution.
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Concordant coast
This is a coastline with bands of different geologies lying parallel to the coast that tend to produce straight coastlines.
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Discordant coast
This is a coastline with bands of different geologies that lies perpendicular to the coast; the more resistant rocks form headlands; the weaker rocks form bays.
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Planform
The shape or outline of a coast.
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Bed (geology)
In geology, a bed of rock refers to small divisions of rock marked by well-defined divisional planes (bedding planes) separating it from layers above and below.
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Other cards in this set

Card 2

Front

This is the area lying between the high and low water marks, often submerged during high tides and exposed to lots of wave action.

Back

Foreshore

Card 3

Front

The area of deep waters where waves cease to impact the seabed and in which activity is largely limited to the deposition of sediments.

Back

Preview of the back of card 3

Card 4

Front

Area comprising only shallow waters close to shore. Waves have considerable impact upon the land at this point.

Back

Preview of the back of card 4

Card 5

Front

The time interval between wave crests in seconds.

Back

Preview of the back of card 5
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