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