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GEOGRAPHY COASTAL LANDSCAPES :earth_africa:, reaches of shoreline that…
GEOGRAPHY COASTAL LANDSCAPES :earth_africa:
Sediment Cells
Sediment cells are areas which are confined within boundaries of major headlands or large estuaries.
Sediment cells are linked systems of inputs, transfers and outputs of material along a section of coastline.
DYNAMIC EQUILIBRIUM
Dynamic Equilibrium happens when sediment is constantly generated in the source region, transported through the transfer and deposited as output, this happens when inputs and outputs are balanced.
It is known as a dynamic equilibrium as sediment is balanced but it still is in a constant state of movement.
Coastal Sediment Budget
: Identification of knowing how much sediment is available, where it comes from where it is stored and how it leaves a particular area.
Humans can upset the dynamic equilibrium by using methods to try and prevent coastal erosion. There are many examples of this:
Groynes cause management in the transfer region which may reduce or stop sediment supply to the output region. For example, when groynes trap the sediment to encourage beach outbuilding.
FEEDBACK
Positive Feedback: Amplify the initial change in the system. For example the ridge of a coastal sand dune breached by storm wave erosion may be undercut by wind erosion. Therefore the whole dune ridge may be driven further inland and a new state of equilibrium reached.
Negative Feedback: Diminish or lessen the effect of change. For example sand eroded during a storm from the front of the embryo and foredunes at the back of the may be redeposited offshore as sand bars which then help to protect the beach dune system from erosion.
System feedback occurs when there is a change of some sort in the system. The feedback can be either positive or negative. Switching the system to a new state of equilibrium or attempting to recover the system's original state of equilibrium.
Human intervention often cause undesirable feedback, often as a consequence to inappropriate coastal management.
In England and Wales, there are 11 primary sediment cells, with sub-cells within each primary cell.
Lithology, Mass Movement, Coastal Weathering
Coastal Weathering
Subaerial Weathering
Physical/mechanical weathering breakings off rock fragments of varying sizes, which fall to the foot of the cliff where they can protect the cliff from erosion.
Saltwater Crystal Growth
Crystals grow when saltwater that collects in cracks in the cliff face evaporates. As they grow, crystals exert pressure on the rock.
Freeze-Thaw
Repeated freezing and thawing of water causes a type of crystal growth that is most effective on high latitude coasts with significant precipitation.
Wetting and Drying
Expansion and contraction of minerals is most effective on clay and macro-tidal environments.
Chemical Weathering
Acts to decompose rock (certain types of rock are more susceptible) by altering the minerals in the rock.
Solution
Solubility of minerals depends on the temperature and acidity of the water. Limestones are affected by carbonation, although they may be less soluble in seawater. A spray charged with carbonic acid leads to honeycomb weathering.
Hydration
Minerals absorb water, weakening their crystal structure. Rock is then more susceptible to other weathering processes.
Hydrolysis
Reaction between mineral and water related to the hydrogen ion concentration in water, which particularly affects feldspar minerals in granite.
Oxidation/reduction
Adding or removing oxygen. Oxidation results from oxygen dissolved in water and particularly affects rocks with a high iron content. Reduction is common under waterlogged conditions.
Chelation
Organic acids, produced by plant roots and decaying organic matter, bind to metal ions, causing weathering.
Mass Movement
Rapid Movement
Rockfalls
Blocks of rock, dislodged by weathering fall to the cliff foot. E.g. in Svalbard rock blocks are loosened by freeze-thaw action.
Rockslides
Blocks of rock slide down the cliff face, especially where rocks are dipping steeply towards the sea.
Rock Toppling
Columns or rock weakened by weathering fall swawards.
Rotational Slides and Slumps
Sections of the cliff give way along a well-defined concave slip surface. The fallen material stays as an identifiable mass off the shore because it is often composed of cohesive clays so it may take a month for the sea to erode it.
Slow Movement
Creep
The slow downslope movement of regolith (the loose material above the bedrock)
Solifluction
The slow downslope movement of regolith, saturated by the melting of the active layer above the permafrost.
Lithology
The composition or type of rock
Chemical Composition
Mineral composition and solubility. Chemically inactive rocks like ones made from silica have more resistance and a low rate of chemical weathering. But others are altered by hydrolysis which causes an increase in vulnerability to both marine and subaerial processes.
Hardness
Heating and compression during the formation of some rocks
granite
cause them to be harder and more resistant to erosion. These rocks mainly comprise the cliffs of the north-western areas of Britain. But many of the rocks that form the south and eastern coastlines of Britain are 'soft rocks'
clay
, these tend to erode more easily.
Permeability
Pores or open textured fissures and cracks or joints. As water seeps through the cliff it increases the rock's resistance to sub-aerial processes, making it stronger.
Structure of the Coast
The way rocks are disposed or geologically arranged
Joints, bedding planes and faults in rocks has a significant impact on the rate of weathering.
Joints and bedding planes at high densities weakens the rock and makes it more vulnerable to subaerial and marine erosion.
Faults or isolated joints can be exploited by the sea to form micro features such as narrow inlets or shatter zones, which are areas of weakness. Folds where rocks are stretched or compressed also form weak areas. Folding can affect the angle of the bedding plane wich influences cliff profile and erosion.
Tidal Patterns
Tides, Waves, Tidal Range
The tidal range is the different between the heigh during the high and low water during a monthly tidal cycle. This influences the zone where coastal processes occur.
Tides are created by the gravitational pull of the moon. It pulls water on Earth towards itself to make high tides. But this also makes a balance increase in sea level on the opposite side. Which makes two high tides and two low tides.
Waves are caused mostly by wind, they're created due to friction between the wind and the surface water. Waves have differing amounts of energy depending on the wind or the fetch.
High and Low Energy Coasts
High Energy Coasts
Powerful waves, more erosion over deposition, landform characteristics include; headlands, cliffs and wave-cut platform. High energy coasts are mainly on the Atlantic coast due to high rates of fetch that is seen because of the distance travelled.
Low Energy Coasts
Weaker waves, more deposition than erosion, landform characteristics include: beaches, spits. More sheltered areas whether by a reef, embayment, estuary or headland.
Marine Erosion
Hydraulic Action
Results from waves breaking on bedded, jointed or faulted rocks which creates hydraulic pressure in the holes. This leads to weakening and readying of the rocks for more wave action.
Quarrying
Occurs where powerful waves remove loose blocks.
Attrition
Occurs when detached rocks break down through rubbing and banging against each other, gradually rounding the blocks as well as reducing their size.
Corrasion
Occurs when the material provided by attrition and corrosion is used by waves to further erode the rock.
Corrosion
Occurs when rocks such as limestone are chemically attacked by waves.
Cliff and shore platforms
Geology
Hardness and structure of the rocks are very important in the formation of cliffs. With igneous and metamorphic rocks, and some sedimentary rocks such as limestone and sandstone, forming steep cliffs.
Unconsolidated rocks such as clays and sands usually result in low-angled cliffs. Marine erosion at the base of the cliff can lead to slope failure, this can leave a steep slope ready to be undercut once more.
Steep cliffs are associated with either horizontal or vertical geological structure. The angle of inclination of the bedding planes is important with seaward dipping cliffs having low angles and landward dipping cliffs having near vertical faces.
Cliff retreat and the formation of shore platforms
Wave-cut notch is formed by wave quarrying and corrosion at the base of the cliff, which effectively undermines the cliff, causing slope failure either via slumping or vertical cliff collapse.
Where cliffs are fronted by a narrow shore, a cycle of notch formation, cliff failure, debris removal and cliff retreat takes place.
A wide shore platform develops. Cliffs no longer within reach of marine action other than storm waves in Spring. Cliff profile becomes degraded.
Shore Platforms
Wave cut platforms are created by wave quarrying and abrasion. Bio-erosion and salt weathering also affect. Shore platforms are flat expanses of gently sloping rock, at the foot of a cliff extending out to sea. Shore platforms also show the influence of rock structure.
Headlands and Bays
Headland and bay formation results from the differential erosion of juxtaposed rocks of varying resistance, especially where the coast is discordant (varying between hard and soft rock). But concordant coasts, where cove formation is a key feature.
Coastal Transport and Deposition
Bedload
Grains are supported by continuous traction or intermittent contact with the sea floor. The grains slide along the seabed, traction is slow mode of transport. Only strong currents can move pebbles by saltation, where grains are bounced along the seabed. Saltation is an important mechanism for sand transport by the wind.
Suspended Load
Where grains are supported by turbulence, when moderate currents are transporting silt or clay in suspension.
Solution
Corded particles from limestone being dissolved by salt water and carried by the sea.
Longshore Drift
Prevailing winds blow at an oblique angle to the shoreline and therefore cause incoming waves to approach the shore at an oblique angle, where the swash pushes pebbles and sand up the beach diagonally.
Because of gravity, the backwash from the same wave moves back towards the sea at right angles, carrying some of the deposited beach materials with it.
Long-term, this moves sand, pebbles and gravel along the shore from one end of the beach to the other.
It's irregular everyday, its direction depends on both the prevailing winds and the orientation of the shoreline. In longer term over months or years, it operates in a preferred direction.
Deposition
Material is deposited in open water when the energy of the transporting water is too low to transport the sediment, with the sediment deposited being directly proportional to the size of the sediment.
Where clay particles come together to form flocs, flocculation increases the fall velocity, therefore speeds up deposition.
In shallow waters, differing energy causes differing deposition. With the largest cobbles and boulders throw above the high water mark by the storm waves to form a storm beach.
Aeolian Processes
Sand Dunes
Saltation
Fluvial Processes
Eustatic and Isostatic Change
reaches of shoreline that encompasses the intertidal and nearshore movement of sediment.
