Coasts Flashcards
What is endogenetic energy?
Driven by geothermal energy from the earths interior
What is exogenetic energy
Driven by solar energy which heats the surface creates wind waves and drives the hydrological cycle
Examples of inputs
Waves Sunshine Tides Currents Offshore sediment River sediment Estuary and land sediment
Examples of processes
Erosion Deposition Sedimentation Weathering Mass movements Transportation
Examples of outputs
Silt and clay Sand Organic matter Tides Dredged sediment Noise and heat
Examples of stores
Saltmarshes Mudflats Sand banks Sand, shingle and gravel beaches Spits
What physical factors influence the coastal landscape
Winds Waves Tides Geology Ocean current circulation
What is a landform
A physical feature on the earths surface
What is erosion
The wearing away of material by the action of the weather, ice or wind
What is weathering
The disintegration of rocks by the action of the weather, plants, animals and chemical action
What are marine processes
The action of the sea on coastal landforms
What are sub aerial processes
Processes active on the face and top of cliffs
What is mass movement
Movement of material downslope as a result of gravity
What features may develop as a result of erosion
Caves Arches Stacks Stumps Wave cut platforms
What landforms develop from depositional processes
Spits
Bars
Tombolos
What factors combine to generate powerful waves
Strength of wind
Length of time it blows
Fetch
What is fetch
The distance over which the wind has been blowing
What is wavelength
Distance between crests
What is frequency
Time between wave
What is swash
Wave moves up the beach
What is backwash
Wave moves back into the ocean
what factors affect waves in the ocean
low pressure systems, fetch, size of swell window, sea floor gradient
what is wave period
time for 1 wave to travel 1 wavelength
what is the dominant wind
perpendicular to the coast - usually storm winds
what is the prevailing wind
the most common direction
beach store outputs
dredging and mining, wind and storm overwash, longshore drift, offshore transport
beach store inputs
onshore transport, longshore drift, river sediment, cliff and sand dune erosion
Constructive waves
Low in height
Long wavelength
Strong swash
Weak backwash
Destructive waves
Greater height
Short wavelengths
Weak swash
Strong backwash
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
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 as granite and is also known as dilatation. The parallel fractures are sometimes called pseudo-bedding planes.
Thermal expansion
Rocks expand when heated and contract when cooled. If they are subjected it 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
Salt crystallisation
Solution of salt can seep into the pore spaces in porous rocks. Here the salts precipitate, forming crystals. The growth of these crystals create stress in the rock causing it to disintegrate.
Oxidation
Some minerals in rocks react with oxygen, either in the air on 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 the sand grains together
Carbonation
Rainwater combines with dissolved co2 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.
How does wind affect the coastline?
Wave energy is generators by the frictional drag of winds moving across the surface.
The higher the wind speed and the longer the fetch, the larger the waves and the more energy they possess.
What is a sediment cell?
Stretch of coastline and it’s associated nearshore area within which the movement of coarse sediment, sand and shingle is largely contained
Tree roots
Grow into cracks and joints and exert pressure. When trees topple their roots can also exert leverage in rock and soil, bringing them to the surface subject to more weathering
Abrasion
Waves armed with rock particles scour the coastline, rock rubbing against rock
Attrition
Rock particles collide with each other and progressively become worn away eventually producing sand
Hydraulic action
Waves break against the cliff face and air and water trapped in cracks becomes compressed. As the wave recedes the pressure is released, the air and water expands and the crack is widened
Solution
Dissolving of minerals e.g. Magnesium carbonate
Suspension
Small particles of sand,silt and clay can be carried by currents
Saltation
Series of irregular movements of material which is too heavy to be carried in suspension
Traction
The largest particles in the load may be pushed along sea floor
Horizontally bedded strata
Undercutting by wave action leads to rockfall
The cliff retreats inland
Seaward dipping strata
Undercutting by wave action removes basal support
Rock layers loosened by weathering slide into sea along bedding planes
Landward dipping strata
Rocks loosened by wave action are difficult to dislodge
Wave refraction
When waves approach an irregularly shaped coastline, wave refraction takes place. As each wave nears the coastline it is slowed by friction in the shallower water. At the same time the part of the wave crest in the deeper water approaching the bay moves faster as it is not being slowed by friction. Therefore the waves bend and refract around the headland
Sand beaches
Gentle gradient because small particle size means it becomes compact when wet allowing little percolation so material is carried down the beach
Shingle beaches
Steep.
Little backwash occurs due to rapid percolation because if larger air spaces
Spits
Formed by longshore drift occurring in one dominant direction. The end of the spit often becomes received as a result of wave refraction
Onshore bars
When a spit continues to grow until it joins on to the land on the other side
Tombolos
Beaches that connect mainland to an offshore island
Salt marshes
Vegetated areas of deposited silt and clay.
Salt tolerant species such a sell grass help trap sediment gradually increasing height of marsh.
Climate change decrease
Decrease in global temperatures leads to more precipitation being in the form of snow.
Eventually the snow turns into ice and so water is stored on land in solid form rather than in the sea as liquid
