- Created by: jositaylor
- Created on: 24-01-19 17:52
Components of System
The coast is an open system, meaning that energy and matter can cross the boundary of the system into the surrounding environment. It has:
- Inputs= which include kinetic energy from waves and wind, thermal energy from the heat of the sun, potential energy from material on slopes and material from processes of weathering, mass movement, erosion and deposition.
- Outputs= which include marine and wind erosion from beaches.
- Throughputs= stores including beach sediment and flows such as the movement along a beach by longshore drift.
When inputs and outputs of a system are equal it is in a state of equilibrium. However, coasts are dynamic (constantly changing) places and the equilibrium is often distributed, resulting in dynamic equilibrium.
Sediment movement occurs in distinct areas called cells- a stretch of coastline within which the movement of sediment,sand and shingle is largely self contained, If part of a larger cell they are called sub cells. For example, Flamborough Head- Humber Estuary sub-cell is part of the larger Flamborough Head-The Wash cell.
Influence of Physical Factors
- Wind - is the primary source of energy for a range of processes e.g. erosion and transportation. Many coastlines have a prevailing wind direction. Length of fetch determines the size and energy of waves. Wind creates waves due to frictional drag. Spatial variation in energy as the result of varying wind strength and direction. The energy of a wave is dependent upon the strength of the wind, its duration and the length of fetch.
- Waves- are undulations on the surface of the sea driven by wind.
WAVE FORMATION- Height (the difference between the crest of the wave and the trough of the wave), Length (the distance between crests), Frequency (swell waves have a wave period of up to 20 secs and storm waves have a wave period of up to 5 secs).
WAVE DEVELOPMENT AND BREAKING- a wave enters shallow water, friction with the sea bed increases, the wave slows as it drags along the bottom, the wavelength decreases and successive waves start to bunch up, wave increases in height and plunges or breaks onto the shoreline.
Breaking waves can be spilling (steep waves, gentle sloping beach), plunging (steep wave, steep beach), or surging (low angle wave, steep beach).
Constructive Waves - low, long length (up to 100m), low frequency (6-8 per minute), gentle spill onto the shore. Strong swash, weak backwash. Less sediment removed. Material slowly and gradually moved up the beach. Forming: berms.
Destructive Waves - high, steep, high frequency (10-14 per minute), rapid approach to shoreline. Strong backwash, weak swash. Sediment pulled away from beach. Little material moved up the beach. Forming: storm beaches.
Wave refracton is a process by which waves break onto an irregularly shaped coastline, e.g. a headland separated by two bays.
Waves drag in the shallow water approaching a headland, the wave becomes high (steep and short), the part of the wave in the deeper water moves forward faster, the wave bends, the low-energy wave spills into the bays as most of the wave energy is concentrated on the headland.
Tidal Cycles - the periodic rise and fall of the sea surface is produced by the gravitational pull of the moon and (to a lesser extent) the sun. The moon pulls water towards it, creating a high tide, there is a compensating 'bulge' on the opposite side of the earth, at locations between the two bulges there is a low tide, as the moon orbits the Earth the high tides follow it, the highest tides occur when the moon, Earth and sun are all aligned and so the gravitational pull is strongest= spring tides with a high tidal range. When the moon and sun are at angles to each other the gravitational pull is weak= neap tides with a low tidal range.
Tidal Range - is a significant factor in the development of coastlines as it influences where wave action occurs, the weathering processes and the impact of processes between tides, such as scouring.
Geology- Lithology and Structure
Lithology refers to the chemical and physical structure of rocks. This will impact on physical processes such as weathering, mass movement and erosion. Weak rocks such as clay will erode faster than resistant rocks such as basalt. Chalk and limestone are susceptible to chemical weathering because of their calcium carbonate content which is soluble in weak acids.
Structure refers to features of jointing, faulting and bedding planes in rocks and also to their permeability. Permeable rocks include chalk (water absorbed through tiny pores) and limestone (water absorbed through joints). Structure also affects the shape of the coastline: where rocks lie parallel to the coastline it tends to be straight or concordant; where rocks lie at right angles to the coast a series of headlands of bays are formed according to the bands of weak or resistant rock- this is a discordant coastline. Structure also affects the 'dip' of rocks towards the coastline: landward- dipping rock layers lead to steep cliffs and for seaward- dipping rock layers, cliffs follow the angle of the dip.
Currents are the permanent or seasonal movement of water in the seas and oceans. There are three types:
- Longshore Currents - most waves approach the shoreline at an angle. This creates a current of water running parallel to the shoreline. Effect: transports sediment parallel to the shoreline.
- Rip Currents - these are strong currents moving away from the shoreline as a result of a build-up of seawater and energy along the coastline. Effect: hazardous for swimmers.
- Upwelling - the global pattern of currents circulating in the oceans can cause deep, cold water to move towards the surface, displacing the warmer surface water. Effect: a cold current rich in nutrients.
Global Pattern of Ocean Currents
The global pattern of ocean currents is generated by the Earth's rotation and the currents are set in motion by the wind. Warm ocean currents transfer heat from low to high latitudes and cold ocean currents from high to low latitudes. The transfer of heat energy is significant to coastal development as it affects air temperature and, therefore, sub-aerial processes.
Coastal sediments form depositional features such as beaches and mudflats, and on coastlines there is a delicate balance between the input and removal of sediment, which is referred to as sediment budget. In its simplest form:
- more material added than removed = a positive budget (accretion of material), shoreline builds to the sea.
- more material removed than added = a negative budget, shoreline recedes landward.
Calculating sediment budgets is complex, as all possible inputs, stores and outputs of sediment needs to be identified.
Coastal Sub-Aerial (land-based processes) - RUNOFF, MASS MOVEMENT- landslide, rockfall, mudflow, rotational slip, soil creep. SUB-AERIAL WEATHERING - mechanical (freeze-thaw and pressure release), biological, chemical (carbonation, hydrolysis, hydration and oxidation).
Coastal Marine Processes - MARINE EROSION- wave quarrying, hydraulic action, abrasion, attrition, solution and cavitation. MARINE TRANSPORTATION- longshore drift, solution, saltation, suspension and traction. MARINE DEPOSITION- powerful swash, slow waves after breaking, accumulation of sediment faster than removal. AEOLIAN DEPOSITION- entrainment, transport and deposition of sediment by the wind.
Factors affecting erosion - shape of coastline, beach presence, human activity, geology, sea depth, fetch and wave characteristics.
Weathering is the break down of rocks in-situ.
Weathering is a significant process in the formation of coastal landscapes. There are three types of weathering: PHYSICAL (freeze-thaw, pressure release, salt crystallisation and thermal expansion), CHEMICAL (oxidation, carbonation, solution, hydrolysis and hydration) and BIOLOGICAL (tree roots, organic acids).
Mass Movement Processes
These processes refer to the movement of material (regolith) down a slope. They are sub-aerial (above ground) and are dependent on slope angle, particle size, temperature and saturation. The main forms are:
- Landslides - cliffs made of softer rocks slip when lubricated by rainfall.
- Rockfalls - rocks undercut by the sea or slopes affected by mechanical weathering.
- Mud Flows - heavy rain causes fine material to move downhill.
- Rotational Slip/ Slumping - when soft material overlies resistant material and excessive lubrication takes place.
- Soil Creep - very slow movement of soil particles down slope.
Breaking waves erode the coastline through a range of processes such as:
- Hydraulic Action - wave punding - the force of water on the rocks.
- Wave Pounding -
Processes of Transportation by Waves
- Traction- large boulders rolled along the sea bed.
- Saltation- small stones bounce along the sea bed.
- Suspension- very small particles carried in moving water.
- Solution- dissolved material.
- Longshore Drift- waves approach the shore at an angle; swash moves material up the beach in the same direction as the wave; backwash moves material back down the steepest gradient- usually perpendicular to where it is picked up by the next incoming wave.
Deposition occurs when velocity and/or volume of water decreases and energy is reduced. Deposition takes place in coastal environments when:
- sediment accumulation exceeds removal.
- waves slow down after breaking.
- backwash water percolates into beach material.
- there is a sheltered area such as an estuary.
These are significant in estuarine environments. Fluvial erosion, weathering and mass movement processes supply sediment to river channels. This is then transported downstream and deposited as rivers enter the sea.
Mud flats and salt marshes are landforms that form in sheltered low-energy coastlines. They are associated with large tidal ranges where powerful currents transport large quanitities of fine sediment.
Coastal landscape are significantly influenced by winds. Wind picks up sand particles and moves them, a process known as deflation. Attrition on land by windblown particles is also effective over long distances. When the wind speed falls, material carried by the wind will be deposited.
High and Low Energy Coastlines
High-Energy Coastlines - predominantly strong wave power, high waves, strong prevailing wind, long length of feth and erosion greater than deposition, Landforms= wave cut platforms e.t.c.
Low-Energy Coastlines - low wave energy, waves spread out, energy is dissipated, low waves, deposition greater than erosion and low tidal range. Landforms= inlets and sheltered bays e.t.c.
Sea Level Changes
Eustatic Change is a global change in the volume of seawater resulting from a rise or fall in the level of the sea itself, e.g. caused by the retreat of ice following a glacial period. Eustatic changes are influenced by variations in mean global temperature.
Isostatic Change is a local change in sea level resulting from land rising or falling relative to the sea, e.g. tectonic movements.
Cooling Climate and Emergent Landscapes
Climate change and sea level fall= fall in global temperature, more precipitation in the form of snow, snow turns to ice, more water stored on land as solid ice rather than liquid water which is returned to the oceans.
Influence of sea level fall= landforms shaped by wave processes when the sea level was higher are exposed when sea level falls. These may include: raised beaches, marine terraces and abandoned cliffs.
Modifications by sea level change= the emergent landforms are now affected by weathering and mass movement processes. In post-glacial periods, when the climate is wetter and warmer, vegetation develops. Warming is predicted in the future and could lead to chemical and biological weathering becoming more influential. If the rise in temperature is enough for sea level rise, these emergent features may then become closer to the coastline and wave processes will again be an influential factor.
Warming Climate and Submergent Landscapes
Climate change and sea level rise= rise in global temperature, melting of ice stores on land, increase in volume of water in the oceans, sea level rise. A 1 degree celsius rise in mean global temperature could lead to a rise of 2 metres at sea level.
Influence of sea level rise= main influence of a rise of sea level is the submergence of features such as river valleys, forming rias, and glacial valleys, forming fjords. Shingle beaches can also appear.
Modifications and sea level change= rias and fjords can me modified by wave processes; the height and intensity of waves will be increased as a result of future climate change. The valley sides will be modified by sub-aerial weathering processes. Shingle beaches will be modified by processes that transport sediment such as longshore drift.