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Coastal Landscapes - Coggle Diagram
Coastal Landscapes
How can coastal landscapes be viewed as systems?
Systems
Coastal landscapes transfer material (sediment from beaches, estuaries etc) using either kinetic, thermal, or potential energy
Coastal landscapes are open systems, meaning that energy and material can be transferred to and from neighbouring systems (as inputs and outputs). Eg; the input of fluvial sediment from a river
Features of Coastal Landscape System
Inputs- energy (kinetic form wind and waves, thermal from the sun), human activities (coastal management), atmospheric (climate and weather), geological (rock type), marine (waves, tides)
Processes- erosion (attrition, corrosion/abrasion, hydraulic action), weathering (freeze thaw, salt crystallisation, mass movement), deposition
Transfers- Long Shore Drift
Outputs- Erosional landforms (headlands, cliffs, arches, stacks), depositional landforms (beaches, spits, sand dunes, salt marshes), loss of wave energy
Equilibrium- inputs= outputs
Eg; In a coastal landscape system when, rate of which sediment being added to the beach= rate at which sediment is being removed from the beach; meaning the beach will remain the same size.
When this equilibrium is disturbed, the system undergoes self-regulation and changes in order to restore equilibrium. This is known as dynamic equilibrium and an example of negative feedback.
Negative feedback- when initial change within a system brings about further change in the same direction it is known as positive feedback, when a system returns to equilibrium following a change in the system this is known as negative feedback
Sediment Cells
Are a stretch of coastline and its nearshore area, where the movement of sediment, sand and shingle is largely self-contained
There are 11 large sediment cells, around England and Wales (Lands End- The River Severn)
Sediment cell boundaries are determined by the topography and shape of the coastline, eg; large physical features such as Lands’ End act as huge natural barriers that prevent the transfer of sediment to adjacent cells
They are regarded as closed systems, however in reality they are not entirely closed due to varying wind directions and tidal currents etc meaning sediment transferring to neighbouring cells is inevitable
Cells contain many sub-cells as well
A system is a set of interconnecting objects that store and transfer energy to form a working unit
Physical Factors that Influence Coastal Systems
Wind (Aeolian)
Provide the main source of energy (kinetic), which is transferred into the oceans due to the frictional drag of winds moving across the ocean surface
Onshore winds (sea to coast) generate waves that erode the coastline
Oblique winds (at an angle), result in waves hitting the coastline obliquely and longshore drift
The absence of wind leads to deposition
Waves
Form due to the frictional drag of wind over the surface creating small ripples which grow as the wind blows behind it
Wave Energy
Increase in energy when there is a higher wind speed and longer fetch
Possess potential energy (position above the wave trough) and kinetic energy (motion of water within the wave)
In the open sea there is no actual movement of water, just a movement of energy
The relationship between wave height and energy is non-linear, eg; Atlantic waves are eight times higher than English Channel waves, however have 70 times more energy (showing that wave height is a more important factor than wave period in determining wave energy)
Wave Anatomy
Wave Breaking
Start to break when the sea floor depth is half the size of the wave (as the deepest circling molecules come in contact with the sea floor)
Friction with the sea floor causes the wave to slow down, the deepest part more than the top, causing the crest to advance ahead of the base
When water depth is less than 1.3x wave height, the wave topples over and breaks against the shore
Water then moves up the beach as swash, slowing down the further it travels due to friction and the uphill gradient of the beach.
When swash has no more available energy to move up the beach it is drawn back down as backwash (comes down perpendicular to the beach under the force of gravity)
Constructive Waves
Low wave height
Long wave length
Low frequency (6-8/ minute)
Break as spilling waves
Strong swash
Weak backwash (due to the long wavelength, backwash returns to the sea before the next wave breaks, meaning the swash movement is un-interrupted and thus retains its energy)
Swash energy exceeds backwash energy (net gain of beach sediment)
Often form during summer months, far out at sea
Form steep beaches
Destructive Waves
High wave height
Short wave lengths
High frequency (12-14/ minute)
Break as plunging waves (meaning there is little forward energy to move water up the steeply sloping beach as swash so it doesn’t travel far before returning down the beach as backwash) (due to the short wavelength, the swash of the next wave is often slowed by the frictional effects of meeting the returning backwash of the previous wave)
Swash energy is less than backwash (net loss of beach sediment)
Often form during winter months, (in storms), close to shore
Form gently sloping beaches
Tides
They are the periodic rise and fall of the sea surface, produced by the gravitational pull of the moon (and to a lesser extent the sun)
The moon exerts a tidal force on the whole planet, however it has little effect on the earths land surfaces, because they are less flexible
Land surfaces can however move up to 55cm a day (these are called terrestrial tides), and can change an objects precise location. Volcanologists study terrestrial tides, because their movement of the earth’s crust can sometimes trigger a volcanic eruption
Marine Tides
The moon pulls water towards it creating high tides, and there is a compensatory bulge on the other side of the earth
Twice in a lunar month when the sun, moon, and earth are aligned, the tidal force is the strongest, producing spring tides (with the highest tidal range).
Twice a lunar month, the sun and moon are at right angles to each other, meaning the gravitational pull is at its weakest, producing neap tides (with the lowest tidal range).
Effects of Tidal Ranges on Landforms
Spits- only really form in microtidal (small) environments, with tidal ranges of less than 3m
Salt marshes- The ebb and flow of tides are crucial to the formation of these features
Sand Dunes- form in areas that have large tidal ranges
Low tidal range = less opportunity for aeolian processes to occur
Beaches- effects the nature of the beach, eg; the presence of berms and ripples
Geology
Lithology= a part of geology describing the physical and chemical composition of rocks
Clay- weak lithology due to the weak bonds between particles (made up of layered alumina and silicate molecules), creating little resistance to erosion, weathering and mass movements. Eg; Holderness, Cumbria (UK)
Basalt- strong lithology due to dense interlocking crystals which are highly resistant, meaning they are likely to form prominent coastal features such as cliffs and headlands. Eg; South Wales, Isle of Sky
Chalk (and carboniferous limestone)- Due to being composed of calcium carbonate are soluble in weak acids, making them vulnerable to the chemical weathering process of carbonation Eg; Dover, Isle of Wight
Currents
Rip Currents
Strong flowing, narrow current of water that flows from the surf zone out to sea
Form when backwashes converge into a channel
They can remove vast quantities of sediment to offshore sinks
Ocean Currents
Are a much larger scale phenomenon
Generated by the earth’s rotation and convection currents in the air (wind)
Warm currents from the equator move north and south towards the poles, and vice versa for cold currents.
Sources of Coastal ediment
Terrestrial
Fluvial deposition, in some cases, up to 80% of coastal sediment comes from rivers (often in places where coasts have steep gradients, meaning their sediment is deposited directly at the coast)
Wave erosion of cliffs, is also a major contributor to coastal sediment budgets (in high energy wave environments it can contribute to up to 70% of sediment, however typically it contributes to much smaller amounts). This is contributor is increasing with rising sea levels and storm surges.
Longshore drift can supply coastal sediment from another area
Aeolian deposition of sand from nearby spits, bars or dunes
Offshore
Constructive waves bring sediment from offshore, adding to the sediment budget
Tides and currents do the same
Human
When there is a coastal sediment budget, humans often interact with beach nourishment (sediment is often brought in by lorry)
How are landforms developed?
Geomorphic Processes
Weathering
Physical/Mechanical
Pressure release- when overlying rocks are removed by weathering or erosion, the underlying rocks expand and fracture parallel to the surface (also known as dilation), the parallel fractures are also called pseudo-bedding planes
Thermal expansion- rocks expand when heated and contract when cooled, when they are subject to frequent temperature change the outer layer’s crack and flake off.
Salt crystallisation- salty sea water enters crack in rocks, when it evaporates it leaves salt crystals, the growth of these crystals causes stress on the rock and cause further cracking
Breaks down rocks, increasing the surface area allowing further weathering to take place Freeze thaw- water enters crack/ joints and freezes (when it freezes it expands by nearly 10%), exerting pressure on the rock further cracking
Chemical
The rate of chemical weathering, increases with temperature (Van’t- Hoffs law states that a 10 degrees’ Celsius rise in temperature leads to a 2.5% increase in the rate of chemical weathering). Therefore, more chemical weathering takes place in hot climates, other than carbonation, as co2 is more soluble in cold water.
Oxidation- undergoes a redox reaction with iron (haematite) and water to form hydrated iron oxides, which are weak
Carbonation- carbon dioxide dissolves in rainwater to form weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate, which is soluble. Ocean acidification due to climate change is increasing the rate of chemical weathering from carbonation. Algae in the sea also produces co2.
Hydrolysis- Is a chemical reaction between rock minerals and water. Silicates combines with water, producing secondary minerals such as clays, and Feldspar in granite reacts with hydrogen in water to produce kaolin.
Hydration- rocks can absorb water, eg; anydrite takes up water to form gypsum. This hydration causes cracking, as rocks expand with water in them (up to 0.5% expansion can take place)
Biological
Tree roots- grow into cracks/ joints and exert pressure outwards
Burrowing animals
Organic acids- produced during the decomposition of plant and animal debris, cause soil water to become more acidic and react with some minerals in a process called chelation. Blue-green algae can have a weathering effect, excreting iron and manganese oxides on rocks (eroding them). Molluscs also secrete acids
Mass Movement
Occurs when gravity, exceeds the forces trying to keep the material on the slope (predominantly friction) and large amounts of material move. The movement of material down as slope as a result of gravity.
This can be a slow process (soil creep) or fast (rock falls). Water often acts as a lubricant during mass movement
The most significant mass movement process on coastal landscape systems are the processes on cliffs, which lead to the addition of material to the sediment budget by transferring rocks and regolith down onto the shore below.
Slides, material moves along a straight line slip plane such as a fault or bedding plane between layers of rock, or rotational, with movement taking place along a curved slip plane (also known as slumps)
Slides/ slumps often occur due to undercutting by wave erosion at the base of the cliff, as this removes support for the materials above
There is an increased likely hood of slides/ slumps in weak rocks (clay), as when they become wet they absorb it easily becoming heavy. Weathering and mass movement together are known as sub-aerial processes (land based processes which alter the shape of the coastline.
Soil creep
Slow but continuous process rarely exceeding speeds of 1cm a year
Typically occurring on slopes over 5 degrees
Occurs as a result of repeated expansion and contraction of material (freeze thaw cycles, as well as hydration and dehydration cycles)
Earth flows
Faster than soil creep but less sporadic
The slope material liquefies and runs out, forming a bowl of depression at the head ###Usually occurs in fine grained materials/ clay bearing rocks on moderate slopes or under saturated situations (however dry/ granular flows are also possible)
Usually occurs in fine grained materials/ clay bearing rocks on moderate slopes or under saturated situations (however dry/ granular flows are also possible)
Landslides
Are the downslope movement of a large block of material that moves as a coherent mass
Meaning it retains its internal structure until hitting the base of the slope and fracturing into smaller pieces
Rock fall
On cliffs of 40 degrees+, rock fall takes place
Erosion
Wave and Fluvial
Abrasion (corrasion)- waves armed with rock particles scour the coastline
Attrition- rock particles within the waves collide with each other, wearing each other away (becoming smoother, more rounded and eventually turn into sand)
Hydraulic action- occurs when waves break against a cliff face, air and water are forced into the cracks and compressed, when the pressure is release the air and water suddenly expand, causing cracks. The average pressure exerted by a breaking Atlantic wave is 11,000kg/ meter cubed.
Cavitation- the pure force of a breaking wave exerting pressure on the rock face.
Solution (corrosion)- certain rock types erode due to the presence of acid in the sea (not that effective unless local waters are polluted, as the average PH of the sea is 8.1)
Aeolian
Wind carries sand particles in a suspension, (only works with dry sand), this can erode cliffs/transport the sand material around
Transportation
Solution- dissolved material in the water
Suspension- Small particles of sand, silt and clay are suspended in the water
Saltation- Irregular movements of materials which are too heavy to be carried continuously in a suspension, bounce
Traction- Largest load particles are rolled along the sea floor (irregular movements)
Deposition
Deposition takes place when there is a loss in velocity, the velocity that particles are deposited is known as the settling velocity. (larger particles are deposited first as they need more energy to be transported)
Deposition takes place in wave environments;
When waves slow down immediately after breaking
At the top of the swash where for a brief moment the water is no longer moving
During the backwash when water percolates into the beach material
Deposition, as rivers enter the sea, there is a huge resistance causing velocity to fall hugely. The meeting of fresh and sea water also causes flocculation of clay particles, which clump together due to electrical charges between them in the saline conditions, as a result they become heavier and sink to the sea bed.
How do coastal landforms develop over time as climate changes?
How does human activity cause changes within coastal landscapes systems
