3.2- Sources of energy at the coast- systems and processes Flashcards
(105 cards)
1
Q
The energy to drive the coastal system is provided by
A
Waves, wind, tides and currents
2
Q
Describe wind
A
Wind is the movement of air from one place to another. Air moves from areas of high atmospheric pressure to areas of low atmospheric pressure- this movement is known as wind. The greater the pressure gradient between 2 places, the stronger the wind
3
Q
Variations in atmospheric pressure primarily reflect differences in surface heating by the
A
Sun
4
Q
Wind is a vital input into the coastal system as it is a primary source of energy for other processes, but is also an important agent of
A
Erosion and transportation
5
Q
What are the features of wind as an input into the coastal system
A
- fetch
- wind is an agent of erosion
- wind is an important agent of moving sediment
6
Q
Explain how spatial variations in energy result from variations in the strength and duration of the wind
A
Where wind speeds are persistently high and uninterrupted, wave energy is likely to be higher. Although local weather patterns may influence short-term changes in wind speed and direction, most coastlines will have a prevailing wind direction. That is, the wind will generally reach the coast from one direction. This is important as it is one factor that controls the direction that waves approach the coastline and also the direction of the transport of material in the coastal zone.
7
Q
Explain fetch
A
Refers to the distance of open water over which a wind blows interrupted by major land obstacles. The length of the fetch helps to determine the magnitude and energy of the waves reaching the coast. The longer the fetch, the more powerful the waves
8
Q
In the U.K. The prevailing (most usual) direction is from the ____-____. Before reaching our coast, the winds have blown over the broad expanse of the Atlantic Ocean- this means that the wind has blown over 3000 miles of open water
A
South-West
9
Q
Explain how wind plays a vital role in wave formation
A
Waves are created by the transfer of energy from the wind blowing over the sea surface, referred to as the frictional drag of the wind.
10
Q
The energy acquired by waves depends upon the strength of
A
The wind, the length of time it is blowing and the fetch
11
Q
Wind is also an agent of erosion as
A
It can pick up and remove sediment e.g. sand from the coast and then use it to erode features- the most common type of wind erosion is abrasion
12
Q
Wind is an important agent of moving sediment along the coast or further inland and beyond the shoreline as
A
It can pick up and transport material
13
Q
How are waves formed?
A
As air moves across the water, frictional drag disturbs the surface and forms ripples or waves. In the open sea there is little horizontal movement of water. Instead, there is an orbital motion of the water particles
14
Q
What are key wave characteristics?
A
- wave height
- wavelength or amplitude
- wave frequency or wave period
15
Q
What is wave height?
A
Height difference between a wave crest and the neighbouring trough
16
Q
What is wavelength?
A
Difference between successive crests
17
Q
What is wave frequency?
A
The time between one crest and the following crest passing a fixed point
18
Q
Why do waves break?
A
- as waves approach shallow water, the circular orbit of the water particles changes to an elliptical shape
- the wavelength and the velocity both decrease and the wave height increases due to friction with the seabed also increasing causing water to break up from behind and rise to a point where it starts to topple over (break)
- the water rushes up the beach as swash and flows back as backwash
19
Q
Once waves have been created by the wind they are the main agent that shapes the
A
Coastline. Waves breaking at the coast can build up or remove materials depending on their characteristics
20
Q
What are constructive waves?
A
Waves with a low wave height, but with a long wavelength and low frequency of around 6-8/min. Their swash tends to be more powerful than their backwash and as a consequence, beach material is built up
21
Q
What are destructive waves?
A
Waves with a high wave height with a steep form and high frequency (10-14/min). Their swash is gradually stronger than their backwash, so more sediment is removed than is added.
22
Q
Explain the characteristics of constructive waves
A
- tend to have low wave height but with a long wavelength often up to 100m
- low frequency around 6-8/min
- add to beach deposition as their swash pushes more materials from offshore up the beach than backwash removes.
- material is slowly, but constantly moved up the beach leading to the formation of ridges (berms)
- as the backwash is reduced, the following swash is less impeded in its movement up the beach
23
Q
Explain the characteristics of destructive waves
A
- have high wave height with a steep form and high frequency around 10-14/min
- powerful backwash as when they approach the beach they rapidly steepen and when breaking they plunge down- also inhibits the swash from the next wave
- very little material is moved up the beach, leaving the backwash to pull material back down the beach
- net effect is removal of beach material along the shoreline
- commonly associated with steeper beach profile
- the force of each wave may project some shingle well towards the rear of the beach where it forms a large ridge known as the storm beach
24
Q
Give an example of negative feedback regarding beaches and waves
A
Where constructive waves operate to build up a beach, eventually the beach profile steepens which encourages destructive waves (plunging rather than surging) which then removes material from the beach and deposit it offshore. This in turn can result in the beach profile becoming less steep again, encouraging constructive rather than destructive waves to form. All things being equal, this will continue until a state of dynamic equilibrium is reached
25
Describe wave refraction
When waves approach a coastline that it indented they are refracted and become increasingly parallel to the coastline.
26
Describe effect of wave refraction on a headland
- Waves tend to 'bend' and have a higher frequency, wave height and steepness, which gives them greater energy to erode. This is because the waves approaching the headland meet shallower water first, while the part of the wave approaching the bay is still in deeper water. Friction with the sea floor slows the headland-approaching waves and causes their frequency to increase. In bays, the reverse occurs and the waves spread out and become less frequent which leads to a reduction in wave energy and produces a more constructive impact
- the overall effect of wave refraction is the wave energy becomes concentrated on the headland. It accounts for the presence of erosive features at headlands (cliffs and stacks) and deposition features in the bays (beaches). In theory, continued erosion of the headland and deposition in the bays would result in a state of equilibrium where the shape of the coastline would remain static due to balance between the potential erodibility of the rocks and the effect of wave refraction. (In reality, conditions rarely remain stable enough for long enough for this to happen)
27
The term currents refers to
The permanent or seasonal movement of surface water in the seas and oceans.
28
What are the 3 types of currents?
Longshore currents, rip currents and upwelling
29
Describe longshore currents
Occur as most waves do not hit the coastline 'head on' but approach at an angle to the shoreline. This generates a flow of water (current) running parallel to the shoreline which transports sediment parallel to the shoreline
30
Describe rip currents
Rip currents are strong localised underwater currents that occur on some beaches and move water away from the shoreline. They develop when a series of plunging waves cause a temporary build-up of water at the top of the beach, met with resistance from the breaking waves. The fast-flowing offshore surge of water can be hazardous to swimmers.
31
Describe upwelling
The 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
32
What are tides?
Periodic rise and fall in the level of the sea- they are caused by the gravitational pull of the sun and the moon,although the moon has the greatest influence as it it nearer.
33
How does the moon affect tides?
The moon pulls water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the Earth. In areas of the world between the two bulges, the tide is at its lowest
34
When are spring tides formed?
As the moon orbits the high tides follow it. Twice in a lunar month,when the moon sun and Earth are in a straight line the tide-raising force is the strongest. This produces the highest monthly tidal range or spring tide
35
When are neap tides formed?
Twice a month,the moon and the sun are perpendicular to each other in relation to the Earth. This alignment gives the lowest monthly tidal range or neap tides; at this time, the high and low tides are between 10 to 30% lower than average
36
The UK coastline experiences two high and low tides how often?
Each day
37
What is the tidal range?
The relative difference in height between high and low tides
38
Tidal range can be a significant factor in the development of a coastline as
Tidal ranges determine the upper and lower limits of erosion and deposition and the amount of time each day that the littoral zone is exposed and open to sub-aerial weathering
39
A tidal range generates relatively powerful tidal currents (important sources of energy), as tides rise and fall, which can be particularly strong in estuaries and narrow channels. Why are these currents important?
These currents are important in the transfer of sediment within the coastal system or beyond (as an output)
40
When do tidal/ storm surges occur?
When strong winds combine with high tides to produce much higher water levels than normal.
41
The processes outlined combine to create low energy and high energy coasts. Define a low energy coast
A coastline where wave energy is low and the rate of deposition often exceeds the rate of erosion of sediment
42
Define a high energy coast
A coastline where strong, steady prevailing winds create high energy waves and the rate of erosion is greater than the rate of deposition
43
Give features of low energy coasts
- coastlines where wave energy is low
- the rate of deposition often exceeds the rate of erosion of sediment
- typical landforms include beaches and spits
- examples include: many estuaries, inlets and sheltered bays. The Baltic Sea is one of the best examples due to its sheltered waters and low tidal range
44
Give features of high energy coasts
- coastlines where strong, steady prevailing winds create high energy waves
- the rate of erosion is greater than the rate of deposition
- typical landforms include headlands, cliffs, and wave-cut platforms
- examples include: exposed Atlantic coasts of Northern Europe and North America, including the North Cornish coasts in south-west England
45
Alongside energy, sediment is an important input in coastal systems. Globally, most sediment comes from rivers, streams and coastal erosion, although there are local variations. What are the 5 main sources of sediment?
- rivers= sediment is transported in rivers and deposited in river mouth and estuaries where it is then reworked by waves, tides and currents. Most coastal sediment originates from rivers
- cliff erosion= particularly important along stretches of coastline where rocks are soft e.g. along Holderness coast, Yorkshire where glacial till forms unstable cliffs of boulder clay
- longshore drift= sediment is transported from one stretch of coastline (as an output) to another stretch of coastline (as an input)
- wind= in glacial or arid regions, wind-blown sand can be deposited in coastal regions. Sand dunes can act as both a sink and source of sediment (sand)
- offshore = sediment from offshore can be transferred into the coastal (littoral) zone by waves, tides and currents. In the UK, sea levels rose at the end of the last glacial period, resulting in a considerable amount of coarse sediment being bulldozed onto the south coast of England to form landforms such as Chesil Beach, Dorset. Storm surges can also result in inputs of sediment into the coastal system
46
What is a sediment cell?
A distinct area of coastline separated from other areas by well-defined boundaries, such as headlands and stretches of deep water- there are 11 along the coastline of England and Wales e.g. Cell 2 on the east coast of England which stretches from Flamborough Head to the Walsh
47
Research suggests that sediment movement occurs in
Distinct cells, within which inputs and outputs are balanced
48
In theory sediment cells are seen as closed systems from which nothing is gained or lost. However, in reality
It is easy for sediment to find its way around headlands and into adjacent cells (open system)
49
Cells vary in size and larger ones can be divided into smaller sub-cells for example
Cell 2 on the east coast of England which stretches from Flamborough Head to The Wash has a sub-cell within it that stretches from Flamborough Head to the mouth of the Humber Estuary
50
- each cell has:
- inputs ( sources) such as sediment from rivers, coastal erosion and offshore sources
- transfers (flows) such as LSD and onshore and offshore processes including rip currents
- stores (sinks) including beaches, sand dunes and offshore deposits such as bars
51
What is a coastal sediment budget?
The balance between sediment being added to and removed from a sediment cell coastal system
52
Contrast positive budget and negative budget
- if more material is added to the cell than is removed then there is a net accretion of material= positive budget or a surplus of sediment and, over time, the shoreline builds towards the sea
- if more material is removed from the cell than is added a negative budget or a deficit in sediment supply will result. This will cause the shoreline to retreat landwards.
53
In principle,what does the sediment budget seek?
Seeks to achieve a state of dynamic equilibrium where erosion and deposition are balanced. This balance however, can be upset by events, such as an increase in river sediment as a result of a flood; this in turn leads to exposition in the river estuary. A severe storm might also upset the balance by eroding a beach and transferring sediment outside the system
54
Calculating the sediment budget for a cell requires
The identification of all the sediment sources and sinks, and an estimation of the amount of sediment added and removed each year. Calculating budgets is extremely difficult and relies on the use of complex models and estimations
55
Coastlines are affected by two sets of geomorphological processes:
- marine processes = are those that operate upon a coastline that are connected with the sea, such as waves, tides and LSD
- sub-aerial processes= operate on land but affect the shape of the coastline- such as weathering, mass movement and run-off
All processes interact to create a wide range of uniquely coastal landscapes
56
Marine erosion processes:
- hydraulic action
- wave pounding or quarrying
- abrasion
- solution
- attrition
Erosion:
Waves can break on the coastline with a large amount of energy- they may generate energy of 25-30 tonnes m (-2) as they break against the foot of a cliff
- in 2014, a particularly powerful storm hit Dawlish and destroyed part of the sea wall and a section of rail track cutting the rail connection between Devon and Cornwall for months. The storm of February 2014 altered the Devon coastline- large amounts of sediment were swept away from beaches and sand dunes at Dawlish Warren were seriously eroded
57
Describe hydraulic action
When waves break against a rock face with joints facing the wave, air inside the joints is highly compressed, creating enormous pressure within the fissure. As the water pulls back, there is an explosive effect of the air under pressure being released. The overall effect of this over time is to weaken the cliff face. Storms then may remove large chunks of it
58
Desribe wave pounding/quarrying
The impact on rocks of the sheer force of water itself (without debris). This can exert enormous pressure upon a rock surface, weakening and dislodging pieces
59
Describe abrasion
The material that the sea picks up also wears away rock faces. As waves advance, they pick up sand and pebbles from the seabed. When they break at the foot of the cliff, the transported material is hurled at the base of the cliff-chilling away at the rock
60
Describe solution
Some calcium-based rock such as chalk and limestone is really soluble and dissolved minerals can then be removed in the solution. This process is very similar to a type of weathering called carbonation
61
Describe attrition
Whilst attrition does not directly alter the shape of the coastline it does result in a wearing away of rock particles. Angular rock fragments are smoothed and reducing in size, form pebbles, shingle and sand. This occurs due to friction as particles are rolled over each other by the action of waves and currents
62
The rate of coastal erosion along any stretch of coastline is affected by a number of factors:
- waves: steeper high-energy waves have a greater erosive power than low energy waves. The point at which the wave breaks is important too- waves that break at the foot of a cliff release more energy than those that break off-shore
- fetch: a wave that has built up over a greater distance will have generated more energy
- sea depth: a steeply-shelving sea bed will create higher and steeper waves
- shape or the coastline: headlands attract wave energy through refraction
- beach presence: beaches absorb wave energy and provide some protection against erosion. Steep, narrow beaches are effective at dissipating energy from flatter waves. Flatter, wide beaches spread out incoming waves and are better at dissipating high wave- shingle beaches are absorb the impact of steep waves well, as energy is dissipated through friction
- human interaction: beach material (sand and shingle) is removed from some coastlines leading to an increase in erosion. In other areas, coastal protection, such as sea walls or groynes may reduce the rate of erosion
- geology
63
Why is geology perhaps the most important factor in determining the nature of erosional processes?
Geology includes the lithology (the physical strength and chemistry of rocks) and structure (the variation and arrangement of rocks along a coastline)
- lithology: some rocks like granite are very resistant to erosion, whilst others such as clay are very vulnerable to erosion- the glacial till (boulder clay) of the Holderness coast has been eroded by 120cm (12 cm a year!). Some rocks like limestone are porous and cracked which means the sea can penetrate along the lines of weakness, making the, more vulnerable to erosion
- structure: along some stretches of coastline, rocks lie parallel to the coast (concordant) whereas in other areas, rocks lie perpendicular to the coastline (discordant)
- dip: where cliffs have bedding planes they may dip or slope. When rocks dip inland, steeper cliffs may form. Where rocks dip towards the coasts, cliffs tend to produce more gently sloping features
64
Concordant and discordant coastline in more detail
Along a concordant coastline (e.g. Dorset) a resistant rock like limestone can protect the coastline from erosion, only allowing the sea to break through in a few places. Where the sea does break through it can more rapidly excavate the clay behind to form a cove e.g. Lulworth cove
Along a discordant coastline differential erosion occurs where there are band of hard and softer rock. This can result in a headlands and bays coastline
65
What are the 4 processes of marine transportation?
- traction
- saltation
- suspension
- solution
66
Wave or tidal energy not used for erosion or not lost through friction with the seabed can be used to
transport material at the coast
67
The transportation of sediment by the sea is not only an important agent of change in terms of processes of erosion and deposition, but represents
A significant flow/transfer of material
68
Describe traction
Large stones and boulders are rolled and slid along the seabed and beach by moving seawater- this happens in high energy environments
69
Describe saltation
Small stones bounce or leapfrog along the seabed or beach- this process is associated with relatively high energy conditions and as the particles land they may dislodge others
70
Describe suspension
Minute particles of sand and silt are carried along by the moving water, within the flow- suspension most likely where flow is turbulent. Large amounts of suspended load, especially near estuaries can cause a murky appearance of the sea
71
Describe solution
Dissolved materials are transported within the mass of the moving water- this form of transportation plays an important role in the carbon cycle, transferring and depositing carbon in the oceans
72
The direction of coastal transportation is important in terms of sediment movement along a coastline. While waves move material up and down beaches, waves rarely approach the the coastline head-on so
The processes of transport described above combine to move material along the coast
73
Longshore drift occurs when
Waves approach the shore at the same direction as the prevailing wind at an angle and material is 'pushed' up the beach by the swash in the same direction as the wave approached. As the water runs back down the beach the backwash drags material down the steepest gradient, which is usually perpendicular back down the beach (due to the force of gravity), where it is then picked up by the following incoming wave- the net effect of this zig-zag movement is known as longshore (littoral) drift
74
Longshore drift is responsible for
Transferring vast amounts of sediment along the coastline and eventually back to sea- it is very important in a sediment cell and if interrupted by coastal management strategies, such as groynes, natural patterns and processes can be distorted
75
Note: offshore currents, including rip currents move material out to sea at right angles to the shore- the material they deposit is usually deposited
Some distance from the shore to form sand banks
76
Deposition takes place when
The velocity of the water or the wind falls below a critical value for a particular size of particle and can no longer be transported and so occurs once the energy flow that is moving the material declines
77
Regarding deposition, what are some factors which reduce the energy flow that moves the material?
- currents may weaken e.g. neap ride or prevailing winds may lighten in strength altering the energy source
- where opposing currents meet, turbulence may occur resulting in deposition below the surface- this can often happen at the end of a spit
- as waves move over the seabed or shore land features, friction occurs which results in deposition of larger particles
- where rivers add additional sediment to the sea, deposition may occur as energy is insufficient to transport the additional load
78
Sediment deposition is an important part of a sediment cell- areas of deposition including
Beaches, spits, mudflats, sand dunes and offshore bars are all sediment sinks/stores; they can be both outputs and inputs
79
What is aeolian deposition?
Aeolian processes relate to wind and wind plays an important role in shaping the coastline. During the day, wind tends to on-shore as the the sea is colder than the land. When there is a large tidal range, large amounts of sand may be exposed at low tide; this provides a supply of sediment that can be picked up and transported by the wind. Sand is most likely to be carried by the wind and is usually transported close to the ground and over relatively short distances
- -sand is transported by wind in 2 ways (which are dependent on wind speed and how dry or moist the source of sand is)
1) surface creep: a process similar to traction, where wind rolls or slides sand grains along the surface
2) saltation: where the wind is strong enough to temporarily lift the grains into the airflow to heights of up to one metre for distances up to 20-30cm
- wind action can shape and form a range of landforms along the coast, including beaches and sand dunes
80
As well as marine processes there are also sub-aerial (land-based) processes which shape the coastline; these come under the general headings of
Weathering and mass movement
81
Sub-aerial weathering includes processes that slowly (usually)
Break down the coastline, weaken the underlying rocks and allow sudden movements of erosion to occur more easily- material is broken down in situ, remaining near or near its original position
82
Why are weathering processes common at the coast?
Due to the presence of air and water and cycles of wetting and drying and can be categorised as:
- mechanical/ physical weathering
- biological weathering
- chemical weathering
83
Mechanical weathering processes that occur at the coast depend on the nature of
The climate- in latitudes where temperatures fluctuate above and below freezing, freeze-thaw action is common, especially as there is a ready supply of water
84
What is mechanical weathering?
Involves the break-up of rocks without any chemical changes taking place
85
Describe freeze-thaw
Water enters that enters cracks in rocks (often highly porous rocks) freezes as temperatures remain below 0 degrees; as it freezes, the water expands by 10% meaning the ice occupies more space and so exerts pressure on the surrounding rock. As the processes repeats, the crack widens and eventually pieces of rock break away and collect at the base of a cliff as scree. These fragments are then used by the sea to aid erosional processes such as abrasion
86
Describe wetting and drying cycles (mechanical erosion)
Wetting and drying cycles are common on the coast and can affect rocks that are rich in clay- the clay expands when wet and contracts and cracks when dry; over time, this can cause the rocks to break up. Also, the cracks can allow water to seep into the cliff and make them more susceptible to other processes including mass movement
87
What does biological weathering involve?
Involves the break down of rocks by organic activity, including vegetation and coastal organisms
88
Describe some biological weathering processes
- the roots of surface plants on cliff tops can create and expand tiny fissures; these cracks widen as roots grow, which can break up the rock
- sub-surface seaweed, which attaches itself to rock, can weaken and detach them as it sways in the currents of stormy conditions
89
Why is chemical weathering common on coasts?
It occurs where rocks are exposed to air and moisture so chemical processes can break down the rock- as mineral compounds undergo chemical reaction, they can alter the rock structure- solution is the most common chemical process
90
What are the 4 main chemical weathering processes we need to know on top of solution?
- oxidation
- hydration
- hydrolysis
- carbonation
91
Describe the process of oxidation
Oxidation causes rocks to disintegrate when the oxygen dissolved in water reacts with some rock minerals, forming oxides and hydroxides- it especially affects ferrous, iron-rich rocks evident by a brownish staining of the rock surface
92
Describe the process of hydration
Makes rocks more susceptible to further chemical weathering, although it involves the physical addition of water to minerals in the rock, causing the rock to expand creating stress which can itself cause the rock to disintegrate. Overall, the process weakens the rock and creates cracks allowing further chemical weathering to occur
93
Describe the process of hydrolysis
Where mildly acidic water reacts or combines with minerals in the rock to create clays and dissolvable salts; this itself degrades the rock, which makes it more prone to further degradation
94
Describe the process of carbonation
Occurs where carbon dioxide dissolved in rainwater makes a weak carbonic acid; this reacts with calcium carbonate in rocks like limestone and chalk to create calcium bicarbonate which then dissolves easily in water- carbonation more effective in locations with cooler temperatures as this increases the the amount of carbon dioxide that is dissolved in water
95
As well as naturally occurring carbon dioxide there are increasing levels of other gases associated with industry and the combustion of fossil fuels in the atmosphere that also react with rainwater making it
Mildly acidic- this acid rain then reacts with various minerals in different rocks weakening or even dissolving them
96
What is mass movement?
The downhill movement of material under the influence of gravity, that can be rapid or slow- mass movement processes are a common feature of coastlines with higher relief. Mass movement processes are important in transferring both energy (in response of gravity) and sediment- the sediment provides an important input to shoreline processes, forming the 'tools' for erosion and providing material to be transported and deposited elsewhere along the coastline
97
The nature of mass movement is experienced on a particular coastline is dependent on a number of factors:
- the level of cohesion within the sediment
- the height of the slope and the slope angle
- grain size within sediment
- temperature and level of saturation
98
What are the types of mass movement we need to know?
- landslides
- rock falls
- mudflows
- rotational slip or slumping
- soil creep
99
Describe landslides
Occur on cliffs made from softer rock or deposited rock, which slips as a result of failure within it when lubricated, usually following heavy rainfall
100
Describe rockfall
Arch roofs, stacks and cliff faces collapse as a weakness becomes unsupportable- rockfalls are usually sudden and are often associated with steep or vertical cliffs in well-jointed and often quite resistant rock and mechanical weathering can trigger rock falls. As a result, scree forms at the base of the cliff until material is removed by waves
101
Describe mudflows
Heavy rain can cause large quantities of fine material to flow downhill. Here the soil becomes saturated and if excess water cannot percolate deeper into the ground, surface layers become very fluid and flow downhill. The nature of the flow is dependent on the level of saturation, type of sediment and slope angle; on relatively gentle slopes, the flows are often referred to as 'solifluction'
102
Describe rotational slip/slumping
Where softer material overlies much more resistant materials, cliffs are subject to slumping. With excessive lubrication, whole sections of the cliff face may move downwards with a side plane that is concave, producing a rotation movement
103
Slumps are a common feature of
The British coast, particularly where glacial deposits form the coastal areas
104
Describe soil creep
The gradual movement downhill of individual soil particles; so the presence of soil increases the likelihood of soil creep- there is some uncertainty about about the exact causes of creep, but most geographers agree that the presence of soil moisture is important, together with a range of weathering processes
105
Note: run-off is another important process that operates on coastlines. It may take the form of
A stream emerging in a bay, taking with it large quantities of of load during flood. It can also simply be water that flows over the surface to reach the coastline, the presence of which will assist many of the mass movement processes
