Coastal systems Flashcards
Dynamic equilibrium of places
Places are in dynamic equilibrium when there is a balance between inputs and outputs
Backshore
Backshore = the area between the high water mark and the landward limit of marine activity - changes normally take place here only during storm activity
Foreshore
Foreshore = the area lying between the high water mark and the low water mark - it is the most important zone for marine processes in times that are not influences by storm activity
Inshore
Inshore = the area between the low water mark and the point where waves cease to have any influence on the land beneath them
Offshore
Offshore = the area beyond the point where waves cease to impact upon the seabed and in which activity is limited to deposition of sediments
Nearshore
Nearshore = the area extending seaward from the high water mark to the area where waves begin to break
Zones included in the nearshore
Zones included in the the nearshore: swash zone, surf zone, breaker zone
Swash zone in the nearshore
Swash zone in the nearshore:
The area where a turbulent layer of water washes up the beach following the breaking of a wave
Surf zone in the nearshore
Surf zone in the nearshore:
The area between the point where waves break, forming a foamy, bubbly surface, and where the waves then move up the beach as swash in the swash zone
Breaker zone in the nearshore
Breaker zone in the nearshore:
The area where waves approaching the coastline begin to break, usually where the water depth is 5 to 10m
Inputs of coastal systems
Inputs of coastal systems:
-Energy from waves, tides and sea currents
-Sediment
-Geology of the coastline
-Sea level change
Components of coastal systems
Components of coastal systems:
-Characteristic erosional and depositional coastal landforms
Outputs of coastal systems
Outputs of coastal systems:
-Dissipation of wave energy
-Accumulation of sediment above the tidal limit
-Sediment removed beyond local sediment cells
Features of wind as an input into the coastal system
Features of wind as an input into the coastal system:
-Variations in the strength and duration of the wind (prevailing wind direction - controls the direction the waves approach the coast)
-Fetch - determines magnitude and energy of the waves
-Wind plays role in wave formation (created by the transfer of energy from wind blowing over sea surface
-Wind acts as an agent of erosion by picking up and removing sediment - eg abrasion
Fetch definition
Fetch - refers to the distance of open water over which a wind blows uninterrupted by major land obstacles - length of the fetch determines the magnitude and energy of the waves reaching the coast
Characteristics of waves
Characteristics of waves:
-Wave height or amplitude
-Wavelength
-Wave period
Wave height or amplitude
Wave height/amplitude: this is the height difference between a wave crest and the neighbouring trough
Wavelength
Wavelength: this is the distance between sucessive crests
Wave period
Wave period: the time for one complete wave to pass a particular point
What happens as the wave approaches shallow water?
As waves approach shallow water, friction with the seabed increases and the base of the wave begins to slow down - as a result it increases the height and steepness of the wave until the water breaks into the shore
Swash
Swash - rush of water up the beach
Backwash
Backwash - water running back down the beach and towards the sea
Constructive waves features
Constructive waves:
-Low wave height
-Long wavelength
-Low frequency
-Weak backwash
Why do constructive waves have a weak backwash?
Constructive waves have a weak backwash because the swash rapidly loses volume and energy as water percolates through the beach material
Result of a weak backwash (constructive waves)
Result of a weak backwash:
Insufficient force to pull sediment off the beach or to impede swash from the next wave
-Leads to the formation of ridges (berms)
Destructive waves features
Destructive waves features:
-High wave height
-Steep, high frequency
-Powerful backwash due to rapidly steepening and plunging down when approaching the coast
How are storm beaches formed?
Storm beaches are formed due to the force of each wave projecting towards the rear of the beach where it forms a large ridge called a storm beach.
How do constructive and destructive waves work together to form beaches?
Constructive waves build up the beach resulting in a steep beach profile - this encourages waves to become destructive as destructive waves are associated with steep beach profiles.
With time, the act of destructive waves moving material back towards the sea encourages constructive waves
-Therefore it is a cycle (negative feedback that maintains dynamic equilibrium)
Tides
Tides:
Regular rising and falling movements of the surface of the sea and caused by the effects of the gravitational pull of the moon and sun on the oceans.
Spring tides
Spring tides:
Sun, moon and earth all in one straight line –> highest high tides and lowest low tides = largest tidal range.
Neap tides
Neap tides:
Sun and moon 90 degrees out of phase –> highest low tides and lowest low tides = smallest tidal range.
Wave energy
Wave energy:
- created by the frictional drag of the wind over the water.
- effect of wave depends on height. height is determined by wind speed and fetch of the wind.
- waves break as they approach the shore. Friction with the sea bed slows the bottom of the waves.
Factors that size of the wave depends on
Factors that size of the wave depends on :
- Distance wave has travelled
- Time wind has been blowing
- Strength of the wind
Wave refraction
Slowing and bending of progressive waves in shallow water.
Energy dissipates in deeper waters, waves are a lot smaller and don’t slow down as much at the deeper bays.
Energy of waves is concentrated at the headland, waves are bigger and erosion more likely in this shallow water.
Wind energy
- winds are created by air moving from areas of high pressure to areas of low pressure. During events such as storms, the jump from one to the other is large.
- strong winds produce powerful waves.
Most coastlines will have a prevailing wind direction. The wind will generally reach the coast from one direction.
This therefore controls:
1. the direction that waves approach.
2. the direction material is transported.
Prevailing wind
Prevailing wind: the dominant wind direction in a particular location.
Sea currents
Sea currents:
Current is the general flow of water in one direction - it can’t be caused by wind or by variations in water temperature and salinity.
They move material along the coast.
Termohaline circulation
currents driven by the difference in water’s density which is controlled by temperature and salinity.
High energy coasts
High energy coasts:
- typical landforms: headlands, cliffs, wave-cut platforms
- coastlines where strong, steady prevailing winds create high energy waves
- rate of erosion greater than rate of deposition
Low energy coasts
Low energy coasts:
- typical landforms: beaches, spits
- coastlines where wave energy is low
- rate of deposition often exceeds rate of erosion of sediment
- e.g. many estuaries, inlets and sheltered bays
Sediment budget
Sediment budget:
the difference between the amount of sediment that enters the system and the amount that leaves.
Positive sediment budget
Positive sediment budget: more sediment enters.
Negative sediment budget
Negative sediment budget: more sediment leaves.
Sediment cells
Sediment cells:
- the coast is divided into sediment cells, or littoral cells.
These cells are self-contained, sediment doesn’t move between the cells.
Processes in one cell don’t affect any other cell.
Each cell is a closed coastal system.
What is a spit?
Spit:
A spit is a stretch of sand or shingle extending from the mainland out to sea. They develop where there is a sudden change in the shape of the coastline such as at a headland. Normally, longshore drift transports beach sediment along a coastline.
Geology definition
Geology: the lithology and structure of rocks
Lithology definition
Lithology: the characteristics of rocks such as permeability and structure (how the rock is organised in layers)
Discordant coastlines
Discordant coastlines: when rocks run at right angles to the coast - allows the sea to penetrate weak clay and gravel to form bays
Concordant coastlines
Concordant coastlines: when rocks run parallel to the coast, which is where liestone and other resistant rock from headlands are
Importance of the dip of rocks
Dip of rocks are important, where rocks that dip steeply seawards are more quickly eroded due to the pull of gravity causing mudslides and sloping
Aeolian processes definition
Aeolian processes: refers to the entrainment, transport and deposition of sediment by the wind
How does the wind shape coastlines?
Wind moves in response to pressure differences from high to low to pressure, which is set up by the cold sea and warm land -> sediment is picked up by the wind and deposited at low tide
Sub aerial processes definition
Sub aerial processes: processes that break down the coastline, weaken underlying rocks and allow sudden movement or erosion to happen more quickly
Chemical weathering
Chemical weathering: both rain and seawater contain chemicals that can react with chemical compounds in the rock, altering its structure
Biological weathering
Biological weathering: Living organisms can contribute to the weathering of coastal rocks through the activity of plants and animals
Physical weathering
Physical weathering: internal pressures are exerted on rock as a result of changes in the physical structure within its mass
Process of exfoliation (physical weathering)
Exfoliation:
Rock surface heats up and expands -> rock surface cools and contracts -> joints form in the outer layer of the rock and breaks off
Process of freeze thaw
Freeze thaw:
Water collects in rock crack -> water freezes and expands, causing the cracks to widen -> ice thaws, contracts and water gets deeper into rocks again -> repeated contraction and expansion causes further cracks until rock splits
Carbonation (chemical weathering)
Carbonation:
limestone + carbonic acid -> calcium carbonate
Oxidation (chemical weathering)
Oxidation:
Oxygen in water reacts with rock minerals, forming oxides and hydroxides
Mass movement definition
Mass movement: movement of solid rock and other material due to gravity
Types of mass movement
Types of mass movement: slumping, rockfall, soil creep, mudflows, landslides, runoff
Current definition
Current = refers to the permanent or seasonal movement of surface water in the seas and oceans
Three types of currents
Three types of currents:
-Longshore currents/Littoral drift
-Rip currents
-Upwelling
Longshore currents/Littoral drift
Longshore currents/Littoral drift:
-Where waves approach the shore at an angle and swash and backwash then transport material along the coast in the direction of the prevailing wind and waves
Rip currents
Rip currents:
-Strong currents moving away from the shoreline
-They develop when seawater is piled up along the coastline by incoming waves
-Initially the current may run parallel to the coast before flowing out through the breaker zone, possibly at a headland or where the coast changes direction - can be extremely hazardous
Upwelling
Upwelling:
-Movement of cold water from deep in the ocean towards the surface
-The more dense cold water replaces the warmer surface water and creates nutrient-rich cold ocean currents
-These currents can form part of the pattern of global ocean circulation currents
Wave refraction
Wave refraction: When waves approach a coastline that is not a regular shape, they are refracted and become increasingly parallel to the coastline.
The overall effect is that th wave energy becomes concentrated on the headland, causing greater erosion
The low-energy waves spill into the bay, resulting in beach deposition
Sediment cell definition
Sediment cell: A distinct area of coastline seperated from other areas by well-defined boundaries, such as headlands and stretches of deep water
Tidal/storm surges
Tidal/storm surges:
Occasions where meteroligical conditions give rise to strong winds which can produce much higher water levels than those at high tide
Hydraulic action/Wave pounding
Hydraulic action refers to the impact on rocks of the sheer force of the water itself this creates enormous pressure on the rock surface, therefore weakening it
Wave quarrying
Wave quarrying: breaking wave traps air as it hits a cliff face - force of water compresses this air into any gap in the rock face - creates lots of pressure within the joint - as water pulls back there is explosive effect of air under pressure being released
-Overwall effect - weakens rock
Cavitation
Cavitation = study of the effects of pressure changes in areas of rapid flow in rivers
Abrasion/corrasion
Abrasion/corrasion:
Material from the sea is picked up wears away rock as it is hurled against the rock
Attrition
Attrition: rocks in the sea crash against eachother and become smaller, rounder pieces
Solution/corrosion
Solution/Corrosion:
Form of weathering but also contributes to coastal erosion, involves the dissolving of calcium-based rocks (eg limestone)
-Also occurs when evaporation of salts from water in the rocks form crystals, which expand and place stress on the rocks
Factors affecting coastal erosion
Factors affecting coastal erosion:
-Wave steepness and breaking point
-Fetch
-Sea depth
-Coastal configuration
-Beach presence
-Human activity
How does wave steepness/breaking point affect coastal erosion?
Wave steepness and breaking point:
-Steeper wavves are high energy waves and have greater erosive power
-Wave breaking point: waves that break at the foot of the cliff release more energy than those that break some distance from the shore
How does fetch affect coastal erosion?
Fetch:
-How fare the wave has travelled determines how mcuh energy has been generated within it
How does sea depth affect coastal erosion?
Sea depth:
-A steeply-shelving seabed at the coast will create higher and steeper waves
How does coastal configuration affect coastal erosion?
Coastal configuration:
-Headlands attract wave energy through refraction
How does beach presence affect coastal erosion
Beach presence:
-Beaches absorb wave energy and can therefore provide protection against marine erosion
-Steep, narrow beaches easily disspate the energy from flatter waves whilst flatter, wider beaches spread out the incoming wave energy and are best at dissipating high and rapid energy inputs
Human activity as a factor affecting coastal erosion
Human activity:
-People may remove protective materials from beaches which may lead to more erosion, or they may reduce erosion by the construction of sea defences
-Sea defences however may lead to more erosion elsewhere on the coastline
Processes of marine transporation
Processes of marine transportation:
-Traction (boulders rolling along the seabed)
-Saltation (small stones bouncing along the seabed)
-Suspension (small particles carried along by moving water)
-Solution (materials dissolved and then carried along in the seawater)
Types of mass movement
Types of mass movement:
-Landslides
-Rock falls
-Mudflows
-Rotation slip/slumping
-Soil creep
Landslides
Landslides = occurs on cliffs made from softer rock, which slip as a result of failure within it when lubricated
Rockfalls
Rockfalls = occur when cliffs are undercut by the sea, or on slopes affected by mechanical weathering
Mudflows
Mudflows = heavy rain causing large quantities of fine material to flow downhill -> soil becomes saturated here and so water cannot percolate deeper and the surface layers become fluid and flow downhill
Rotational slip/Slumping
Rotational slip/Slumping = where softer material overlies much more resistant materials, cliffs are subject to slumping -> whole sections of cliff may move downwards with excessive lubrication
Soil creep
Soil creep = occurs when there is a very slow continuous movement of individual soil particles downlope - reason unknown but it could be due to soil moisture along with weathering processes
Run-off
Run-off = process that operates on coastlines - it is the flow of water that occurs when excess water flows over the earth’s surface.
What does the characteristics of coastal landscapes depend on?
-High or low energy coast
-Dominated by processes of erosion or deposition
-More or less intensely managed by people
Inputs that lead to the formation of headlands and bays
Inputs that lead to the formation of headlands and bays:
-The geology and lithology of the coast
-The angle of the dip of the coastline in front of the headland
-The nature of the waves approaching the coast
-The direction and strength of the prevailing wind
The components/processes of the system involved in the formation of headlands and bays
The components/processes of the system involved in the formation of headlands and bays:
-Wave refraction
-The differential rates of erosion of the different rocks
-Erosion of the headland
-Deposition in the bay
Outputs involved in the system to form headlands and bays
Outputs involved in the system to form headlands and bays:
-The characteristic features of the resulting landscape (headlands, bays, erosional features of the headland, the depositional features of the bays)
How are wave-cut platforms formed?
Wave-cut platform formation:
1). High steep waves break at the foot of the cliff, energy and erosive action concentrated there
2). So cliff becomes undercut which forms a wave-cut notch
3). Further erosion increases the stress on the cliff above and will collapse eventually
4). Cliff line begins to retreat and, after successive collapses, a gently sloping smooth wave-cut platform is formed at the base of the cliff
Formation of a geo
Geo:
Joints on cliffs -> attacked by the sea -> water will cut inland, widening the crack to form a narrow steep-sided inlet known as a geo
Formation of a cave
Cave:
Caves are formed when cliffs are undercut, usually from a combination of marine processes
Formation of a blowhole
Blowhole:
Erosion headed vertically upwards from a cave -> cave extends upwards and a blowhole is formed
Where do landforms of coastal deposition occur?
Landforms of deposition occur on coastlines where sand and shingle accumulate faster than they are removed - often takes place where the waves are low energy or where rapid coastal erosion provides an abundant supply of material
3 main components of beaches
3 main components of beaches:
-the nearshore (where the land begins to affect the sea),
-the foreshore (surf zone)
-the backshore (usually above the high tide mark). The backshore typically features the material deposited by storm waves.
Why does the backwash up a beach become weak?
The backwash up a beach becomes weaker than the swash because a greater proportion of the water drains away by percolation, rather than running down the beach
Ridges and runnels on beaches
-Ridges and runnels form parallel to the shoreline in the foreshore zone
-Ridges are areas of the foreshore that are raised above the adjacent shore which dips into a runnel
-The runnels are disrupted by channels that help to drain the water down the beach
Storm ridges on beaches
Storm ridges on beach consists of the largest material thrown up by the strong swash of the larger waves
Berms
Berms are smaller ridges formed beneath the storm ridge
Cusps on beaches
Cusps are semi-circular shaped depressions which form when waves break directly on to the beach and swash and backwash are strong
-They usually occur at the junction of the shingle and sandy beaches
-Sides of the cusp channel incoming swash into the centre of the embayment and this produces a stronger backwash in the central area which drags material down the beach, deepening the cusp
Ripples on a beach
Ripples: ripples develop on the sand by wave action or tidal currents
