COASTS 1 Flashcards
What are the inputs of open systems?
-Kinetic energy from wind and waves
-Thermal energy from the heat of the Sun
-Potential energy from the position of material on slopes
-Material from marine deposition
-Weathering and mass movement from cliffs
What are the outputs of open systems?
-Marine and wind erosion from beaches and rock surfaces
-Evaporation
What is equilibrium and when does it happen within a coastal system?
This happens when a systems inputs and outputs are equal and could happen at the rate at which the sediment being added to the beach is equal to the rate at which the sediment is being taken away from the beach. Therefore the beach will remain a similar size.
What is dynamic equilibrium and when does it happen within a coastal system?
This happens when equilibrium is disturbed and the system undergoes self regulation and changes its form in order to restore equilibrium.
What is a sediment cell?
A stretch of coastline and its associated nearshore area within the movement of coarse sediment, sand and shingle is largely self-contained. A sediment cell is a closed system, which suggests that no sediment is transferred from one cell to another. There are 11 large sediment cells around the coast of England and Wales. There are also many sub-cells of a smaller scale existing within the major cells
What is a closed system?
A system with no inputs or outputs
Is a sediment cell a completely closed system?
It is unlikely that sediment cells are completely closed. With variations in wind direction and the presence of tidal currents, it is inevitable that some sediment is transferred between neighbouring cells
What is wind and what impact does it have on the waves?
-It is the source of energy for coastal erosion and sediment transport by wave action which is generated by the frictional drag of winds moving across the ocean surface
-The higher the wind speed and the longer the fetch, the larger the waves and the more energy they possess
Onshore winds, blowing from the sea towards the land, are particularly effective at driving waves towards the coast
-If winds blow at an oblique angle towards the coast, the resultant waves will also approach obliquely and generate longshore drift.
-Wind is a moving force and as such is able to carry out erosion, transportation and deposition itself
-These aeolian processes contribute to the shaping of many coastal landforms.
What are the roles of waves within a coastal system?
-A wave possesses potential energy as a result of its position above the wave trough, and kinetic energy caused by the motion of the water within the wave
-It is important to realise that moving waves do not move the water forward, but rather the waves impart a circular motion to the individual water molecules
-A ball floating in the sea is an example of this phenomenon. As a moving wave passes beneath the ball, it rises and falls but does not move horizontally across the water surface
What is the formula for the amount of energy of a wave in deep water?
P=H^2 T
What are swell waves?
A wave with a long wavelength, low height and steepness. It has a wave period of up to 20 seconds
What are storm waves?
A wave generated locally by high wind energy. It has a short wavelength, greater height and a shorter wave period
What is a wave period?
The time interval between wave crests in seconds.
What are the 3 types of breaking waves?
Spilling, plunging and surging
What happens in a spilling wave?
Steep waves breaking onto gently sloping beaches; water spills gently forward as the wave breaks
What happens in a plunging wave?
Moderately steep waves breaking onto steep beaches; water plunges vertically downwards as the crust curls over
What happens in a surging wave?
Low-angle waves breaking onto steep beaches; the wave slides forward and may not actually break
What are the components of constructive waves?
-Deposits sediment
-Strong swash
-Weak backswash
-Low wave frequency
-Long wavelength
-Low in height
-Break by spilling forward
What are destructive waves?
-Erode material
-Weak swash
-Strong backswash
-High wave frequency
-Short wavelength
-High in height
-Break by plunging down
What are tides?
-The periodic rise and fall of the sea surface and are produced by the gravitational pull of the Moon and, to a lesser extent, the Sun
-The Moon pulls the water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the Earth
-The highest tides will occur when the Moon, Sun and Earth are all aligned and so the gravitational pull is at its strongest (spring tides)
-Also twice a month, the Moon and the Sun are at right angles to each other and the gravitational pull is therefore at its weakest, producing neap tides with a low range
What is Lithology?
-Lithology is the physical and chemical composition of the rock
-Some rock types, such as clay, have a weak lithology, with little resistance to erosion, weathering and mass movements
-This is because the bonds between the particles that make up the rock are quite weak
-Others such as basalt are made up of dense interlocking crystals which are more resistant and are more prominent to form coastal features such as cliffs and headlands
-Others such as chalk and limestone are soluble in weak acids and therefore vulnerable to chemical weathering
What is structure?
-The properties of individual rock types such as jointing, bedding and faulting. It also includes the permeability of rocks
-In porous rocks such as chalk with tiny air spaces, these pores can absorb and store water and these joints are easily enlarged by solutions
-Rock outcrops that run parallel to the coastline tend to produce straight coastlines (concordant coastlines)
-When rock runs at a right angle to the coast, they create a discordant platform which can lead to the formation of headland and bays
-Horizontally bedded strata, landward, seaward
What are rip currents?
-These are important in the transport of coastal sediment and are caused either by tidal motion or by waves breaking at right angles to the shore
-Once rip currents form, they modify the shore profile by creating cusps which help perpetuate the rip current, channeling flow through a narrow neck
What are ocean currents?
-Much larger phenomena, generated by the Earth’s rotation and by convection, and are set in motion by the movement of winds across the water surface, differences in temperature and the earths rotation
What are 3 terrestrial sources?
-Fluvial sediment from rivers
-LSD
-Wave erosion
How is fluvial sediment a coastal sediment source?
-80% or more of coastal sediment comes from rivers but this is not always a regular source and river flooding delivers a lot of sediment at once
-The sediment within the rivers comes from erosion by the river water Sometimes or wind and ice will erode material and this gets into the river system
-Sub-aerial processes also add sediment to rivers
How is wave erosion a coastal sediment source?
-This also makes a major addition of sediment
-This is especially true of cliffs with weak geology which experience storms or strong waves
How is LSD a coastal sediment source?
The transportation process of long shore drift will move sediment along the coast from one area to another
What are 3 offshore sediment sources?
-Aeolian deposition
-Marine erosion
-weathering
What is a human sediment source
-Beach nourishment
What is a discordant coastline?
-When the layers of rock are perpendicular to the direction of the coastline
-Bays and headlands begin to form
What is a concordant coastline?
-When the layers of rock are parallel to the direction of the coastline
-The outer hard rock provides a protective barrier to erosion of the softer rocks further inland
-Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind
-This creates a cove, a circular area of water with a relatively narrow entrance from the sea
What are the geomorphic processes?
-Weathering (Physical or mechanical, Chemical, Biological)
-Mass movement (Rock fall, Slides)
-Wave/Fluvial/Aeolian processes (Erosion, Transport and deposition)
What is weathering?
-Energy used to produce physically or chemically altered materials from the surface or near surface rock
-Can influence the formation of coastal landforms
What is physical/mechanical weathering?
-Is a process that breaks down rocks into smaller fragments without changing their chemical composition
-By increasing the exposed surface area of the rock, physical weathering allows further weathering to take place
-Examples of these are Freeze thaw, Salt crystallisation, Pressure release and Thermal expansion
What is freeze thaw?
Water enters cracks/joints and expands by nearly 10 per cent when it freezes. In confined spaces this exerts pressure on the rock causing it to split or pieces to break off, even in very resistant rocks
What is salt crystallisation?
-Solutions of salt (Sodium sulphate/Sodium carbonate) 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
-Can expand by 300% around temps of 26-28 degrees Celsius
What is pressure release?
When overlying rocks are removed by weathering and erosion, the underlying rock expands and fractures parallel to the surface. This is significant in the exposure of sub-surface rocks such as granite and is also known as dilatation. The parallel fractures are sometimes called pseudo-bedding planes.
What is thermal expansion?
Rocks expand when heated and contract when cooled. If they are subjected to frequent cycles of temperature change then the outer layers may crack and flake off. This is also known as insolation weathering, although experiments have cast doubts on its effectiveness unless water is present
What is oxidation?
Some minerals in rocks react with oxygen (O2), either in the air or in water. Iron is especially susceptible to this process. It becomes soluble under extremely acidic conditions and the original structure is destroyed. It often attacks the iron-rich cements that bind sand grains together in sandstone
What is chemical weathering?
-involves chemical reactions between moisture and some minerals within the rock. Chemical weathering may reduce the rock to its chemical constituents or alter its chemical and mineral composition. Chemical weathering processes produce weak residues of different material that may then be easily removed by erosion or transportation processes. Examples of this are Oxidation, Carbonation, Solution, Hydrolysis and hydration
What is 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. This process is reversible and precipitation of calcite happens during evaporation of calcium rich water in caves to form stalactites and stalagmites.
What is solution?
Some salts are soluble in water. Other minerals, such as iron, are only soluble in very acidic water, with a pH of about 3. Any process by which a mineral dissolves in water is known as solution, although mineral specific processes, such as carbonation, can be identified
What is hydrolosis?
This is a chemical reaction between rock minerals and water. Silicates combine with water, producing secondary minerals such as clays. Feldspar in granite reacts with hydrogen in water to produce kaolin (china clay)
What is hydration?
Water molecules added to rock minerals create new minerals of a larger volume. This happens when anhydrite takes up water to form gypsum. Hydration causes surface flaking in many rocks, partly because some minerals also expand by about 0.5 per cent during the chemical change because they absorb water
What is Van’t Hoffs Law?
States that a 10ºC increase in temperature leads to a 2.5 times increase in the rate of chemical reaction (up to 600ºC), so most chemical weathering processes occur at higher rates in tropical rather than temperate or polar regions
What is biological weathering?
Biological weathering may consist of physical actions such as the growth of plant roots or chemical processes such as chelation by organic acids. Although this, arguably, does not fit with the precise definition of weathering, biological processes are usually classed as a separate type of weathering. Examples are tree roots or organic acids.
What are 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 and exposing them to further weathering
What are organic acids?
Organic acids produced during decomposition of plant and animal litter causes soil water to become 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 manganese oxides on rocks. On shore platforms, molluscs may secrete acids which produce small surface hollows in the rock
What is mass movement?
Mass movement occurs 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. Examples of this are rock fall and slides
What is rock fall?
On cliffs of 40º 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 it may accumulate as a relatively straight, lower angled scree slope
What are slides?
What are the wave processes?
-Erosion (Abrasion (or corrasion), Attrition, Hydraulic action, Pounding, Solution (or corrosion))
-Transportation (Solution, Suspension, Saltation, Traction)
-Deposition
What is abrasion?
When waves armed with rock particles scour the coastline; rock rubbing against rock
What is attrition?
Occurs when rock particles, transported by wave action, collide with each other and with coastal rocks and progressively become worn away. They become smoother and more rounded as well as well as smaller, eventually producing sand
What is hydraulic action
Occurs when waves break against a cliff face, and air and water trapped in cracks and crevices becomes compressed. As the wave recedes the pressure is released, the air and water suddenly expands and the crack is widened
What is pounding?
Occurs when the mass of a breaking wave exerts pressure on the rock causing it to weaken
What is corrosion?
Involves dissolving minerals like magnesium carbonate minerals 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 and acidic
What is solution?
Minerals that have been dissolved into the mass of moving water. This type of load is invisible and the minerals will remain in solution until water is evaporated and they precipitate out of solution
What is suspension?
Small particles of sand, silt and clay can be carried by currents; this accounts for the brown or muddy appearance of some sea water. Larger particles can also be carried in this way, perhaps during storm events
What is saltation?
This is a sense 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
-Bounce along the seabed
What is 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 rest again
What are fluvial processes?
In coastal environments such as river mouths, fluvial processes often play an important part in the development of landforms. Low-energy, estuarine environments have distinctive characteristic
What are Aeolian processes?
Due to their exposure to open sea surfaces, coastal landscapes can be significantly influenced by winds, especially those blowing onshore
What are erosional landofrms?
-Cliff and shore platforms
-Bays and headlands
-Geos and blowholes
-Caves, arches, stacks and stumps
What is horizontally bedded strata?
Undercutting by wave action leads to rockfall; the cliffs retreat inland, parallel to the coast
What is seaward dipping strata?
Undercutting by wave action remove basal support; rock layers loosened by weathering slide into the sea along the bedding planes
What is landward dipping strata?
Rocks loosened by weathering and wave action are difficult to dislodge; the slope profile is gradually lowered by weathering and mass movement.
What is wave refraction?
The bending of waves in shallow water so that they move nearly parallel to the shoreline
What are the depositional landforms?
-Beaches
-Spits
-Onshore bars
-Tombolos
-Salt marshes
-Deltas
What are beach cusps?
Semi-circular, scalloped depressions cut into the lower edge of the storm beach
How and why do sea levels change during a glacial?
-A decrease in temperature leads to more precipitation as snow. The snow turns to ice and so water is stored in solid form on the land.
-The volume of water in oceans reduces and sea levels fall worldwide
-A decrease in temperature means that water molecules contract, become more dense and reduce in volume
How and why do sea levels change during an interglacial?
-An increase in temperature leads to a higher rate of melting of stored ice. The ice turns into water and enters the ocean. The volume of water in oceans increases and sea levels rise worldwide.
-An increase in temperature means that water molecules expand, become less dense and increase in volume. A 1% rise in temperature results in about a 2m rise in sea level
What is eustatic?
worldwide change in sea level from decreases and increases in ocean temperatures, affecting the amount of water stored in the ocean
What is isostatic?
change in the level of land due to tectonic activity or removal of weight from land, i.e. glacial ice advancement or reduction
What are emergent landforms?
Landforms shaped by wave processes during times of high sea level are left exposed when sea level falls. These landforms may be found inland, some distance from modern coastlines. Examples of these can include raised beaches, marine terraces and abandoned cliffs.
How are emergent landforms modified overtime?
-Freeze-thaw weathering can loosen material which leads to rock fall
-Vegetation can cover much of the landforms making them difficult to recognise, this can increase biological weathering
-Chemical weathering can occur e.g. carbonation on limestone platforms
-If enhanced global warming continues, these landforms could find themselves closer to or at the coastline. Once again they may be influenced by wave processes
-Mass movement may also affect emergent landforms
What are submergent landforms?
Landforms created at the coast due to a rising sea level are called submergent landforms. It is as though they are submerging under the water. Examples are Rias, Fjords and Shingle Beaches
How are submergent landforms modified overtime?
-If enhanced global warming continues, water depth in Rias and Fjords will increase and wave erosion is likely to increase
-Shingle beaches are susceptible to continued erosion by long shore drift
-Increased storm events will easily move the unconsolidated material of the shingle beaches, these could be breached in the future
What are the 3 distinct components of a delta?
-The upper delta plain (furthest inland where river deposits)
-The lower delta plain (Inter tidal zone and composed of both river and marine deposits)
-The submerged delta plain (lies below mean low water mark and composed of mainly of marine sediment, represent seaward growth)
What is the foreshore plain
Below the low tide mark and high tide mark and is part of the shore that is alternately covered and uncovered by the regular ebb and flow of tides
