•Coasts 2 Flashcards
What is weathering?
The break down of rocks in situ due to the atmospheric weather
What happens in freeze-thaw weathering?
Water renters areas of weakness and freezes
Ice occupies more space than water, exerting pressure on the rock
Fragments of rock break off, producing scree or talus
What happens in heating and cooling?
Rocks are heated to extreme temperatures during the day then cool at night
Temperature changes cause stresses in the rock to be set up and this causes it to disintegrate
This process is sometimes known as insolation weathering
What is wetting and drying?
Rocks expand when wet and contract when dry
Stresses induced by this cycle of wet and dry conditions cause the rock to crumble
This is also known as slaking and may occur in intertidal areas
What is exfoliation?
Rocks heat and cool at different rates due to poor conductivity
The outer layers of the rock split off (like the skin of an onion) as a result of heating and cooling)
This type of weathering is common where rainfall is low and temperatures are high
What is pressure release?
Bodies of rock may be exposed by erosion or the removal of ice, having been covered for millions of years, causing the rock to ‘relax’
The release of pressure causes the outer layer of the rock to split off (like the skin of an onion)
Domes are produced in this process which is also known as sheeting
What is crystal growth?
Crystals (magnesium sulphate and calcium carbonate are examples) grow in spaces within rock)
Growing crystals, often resulting from the evaporation of saline water, prise the rock apart
This process is also known as salt weathering and is common in semi-arid areas
What is organic action?
Roots exert a destructive force on rock as they grow
Tree roots prise rock apart
Burrowing animals may remove soil and expose rock to other forms of weathering
What is carbonation?
Carbon dioxide reacts with water to produce a weak carbonic acid
Carbonic acid reacts with calcium carbonate (limestone), producing calcium bicarbonate
Calcium bicarbonate is soluble in water
What is hydration?
Rock absorbs water
Anhydrite (a form of calcium sulphate) absorbs water and becomes gypsum
Rock swells and is easier to break down
What is oxidation?
Oxygen (often dissolved in water) combines with minerals in rock, forming oxides
When iron in a rock containing it and oxygen combine, rust forms and the molecular structure of the rock collapses
This process often happens in rock containing iron
What is hydrolysis?
Carbonic acid releases hydrogen in water, which reacts with the minerals in the rock
Water ions combine with ions from the rock, causing it to disintegrate
Rocks, such as granite, containing Feldspar, are commonly affected
What is chelation?
Lichens and mosses produce a weak acid
Weak acid dissolves rocks and minerals which are transported away by water
Rocks break down into smaller and smaller pieces and this process is significant in the formation of soils
What is solution weathering?
Certain minerals in rock, such as rock salt (halite), dissolve in water
No chemical reaction is required
This process is commonly associated with carbonation
What is rockfall?
Rapid movement on steep slopes that can be caused by extreme weathers
Broken materials fall to the cliff foot which is called talus
What is a landslide?
When rocks move downwards quickly due to gravity
Water in joints makes it more likely to happen
More likely if underlying bed is impermeable
What is a rotational slip?
The movement of material along a curved plane
Material takes on water which creates an increase in mass
Gravity pulls it down
What is a mudflow?
Clay particles with high water content rapidly move.
Likely to occur in mountainous and periglacial areas
What is solifluction?
The slow downhill moment of saturated soil that occurs in cold climates in gentle slopes
What is soil creep?
The extremely slow and continuous movement caused by lubrication by rain mainly on cliffs with no vegetation
What are the zones of a coast?
Onshore zone Backshore zone Swans zone Intertidal and nearshore zone Surf zone Breaker zone Offshore and subtidal zone
What are the main sources of energy at a coast?
Waves
Tides
Winds
Why are waves important in creating coastal landscapes?
They cause transportation, deposition and erosion
If have more energy they will cause erosion and transportation to form cliffs and shore platforms
If have less energy they will cause deposition to form beaches
Why are tides important in creating coastal landscapes?
Caused by the gravitational pull from the sun and the moon.
They are useful as they can deposit coarser material to form mudflats
How is wind important in the creating of coastal landscapes?
Used to transport finer materials to form landforms for example sand dunes.
Not as useful as tides and waves.
What causes waves?
Friction of the sea floor as water slows down or from the wind
What three factors determine the amount of energy a wave has?
The prevailing wind
The distance the wave has travelled (the fetch)
The depth of the water
Why do higher waves cause more erosion than lower ones?
Powerful waves are steep as they are high and have a short wavelength.
They have more energy as there is more water
What is fetch?
How does it influence erosion?
The larger the fetch, the bigger and more powerful a wave is
What is a dominant wave?
The fastest wave
What is prevailing wind?
What is the main prevailing wind in England?
The most common wind direction
South west
What is the trend between prevailing wind and dominant wave?
Often in the same direction
What is the difference between dominant wind and prevailing wind?
Dominant wind is the strongest wind but prevailing wind is the most common wind direction
What is the process of a wave breaking?
Prevailing wind blows over the sea and the friction transfers energy causing the water to move as waves
Movement of deep water is in a circular orbit
When the water becomes shallower, friction from the sea bed slows the base of the wave so that the water there, is travelling more slowly than at the crest
The waves become more and more elliptical in shape. Wave length reduces and height increases- when the two are roughly the same, the wave breaks
Smash runs up the beach and backwash is the return of water down it
What is a constructive wave?
They have a low wave height
Low frequency
Long wavelength
Strong swash
Weak backwash
Build up beach
What is a destructive wave?
They have a high wave height
High frequency
Steep shape
Weak swash
Strong backwash
Remove sediment
What is wave refraction?
The wave direction changes due to a change in the depth of the water.
In shallow water, waves get slower and in deep water they are quicker so the wave bends for example near a headland where it will drag and bend
How to wave refraction affect wave energy?
The energy around headlands becomes more concentrated whereas the energy around bays is more spread out so headlands are more vulnerable to erosion and a bay is more vulnerable to deposition
What is a swash-aligned beach?
When waves approach the shore with their crests parallel to the land
What is a drift-aligned beach?
When waves approach the coast at an oblique angle of around 30 degrees
What is a rip current?
When backwash is particularly powerful
They can erode and scour the beach of material
Also known as undertow
What causes tides?
The gravitational pull of the moon and the sun
What is a spring tide?
When the sun and the moon are aligned so forces work together
What is a neap tide?
When the sun and moon are at right angles so forces work in different directions
What is the difference between high and low tide called?
The tidal range
What are the three types of tidal range?
Macrotidal - more than 4m
Mesotidal - 2m to 4m
Microtidal - up to 2m
What does a small tidal range mean?
Energy becomes concentrated so erosion becomes focused on one area
Depositional beaches will be narrow
What are the two main hazards that occur in spring tides?
Flooding and erosion
What is the role of tides in shaping coastal landscapes?
High tides create caves, arches and stacks.
Neap and low tide causes deposition to form spits, mudflats and salt marshes
What are tidal currents?
They operate on a local scale with flood currents occurring as water moves onshore at high tide and ebb currents happening as water moves offshore at low tide
Also known as surface current
What are global surface ocean currents?
They are driven by winds created by the global circulation model
Also known as long shore current
What is thermohaline circulation?
They occur on the surface and at depths throughout the ocean
Linked to heat and salinity of water
Cold and salty water sinks then is returned to the surface
Also known as upwelling
How is limestone vulnerable?
It is vulnerable to sub aerial weathering in particular carbonation
What is permeability?
A description of a substance that allows water to pass through it
What is porosity?
The amount of areas between particles of a rock called pores. They determine how much water can pass through
What is perviousness?
Rocks that have joints or fissures where water can flow
What is impermeable?
A rock that doesn’t absorb water or allow water to pass through e.g granite
It causes surface run-off
What is aspect?
The direction in which a coast faces
How will a change in temperature affect the climate?
Higher= More chemical weathering e.g hydrolysis
Less= more physical
How will a change in precipitation levels affect the climate?
High = strong chemical and physical e.g freeze- thaw
Low = slight physical
How will a change in wind affect climate?
High = more mass movement
Low = more deposition
How will processes change inland ?
Less erosion inland.
Mainly sub aerial weathering
Only erosion will be aoelian erosion
What is clastic sediment?
Comes from weathering and erosion
What is biogenic sediment?
Comes from the shells and skeletons of marine organisms
What is fluvial sediment?
Sediment that has been transported to the coastal environment by rivers
What is solution transportation?
Removal of dissolved minerals and weathered products by rainfall and percolating groundwater carried in water (dissolved)
What is suspension transportation?
Small material carried in the flow of water
What is saltation transportation?
Particles are lifted upwards and forwards before going back to their original surface (bouncing)
What is traction transportation?
Pebbles and larger sediment are rolled along the sea bed
What is the dynamic equilibrium?
When even though erosion, transportation and deposition occur, these differences balance each other out
How many sediment cells are there on the coast of England and Wales?
11
What is a sediment cell?
A length of coastline and its associated nearshore area within which the movement of coarse sediment (sand and shingle) is largely self-contained
What happens at the boundary of a sediment cell?
The coastline changes direction
What is a sediment budget?
The total amount of sediment circulating within each cell
What is wave quarrying ?
The transportation and removal of loosened chunks of rock by waves as they retreat. Air forced into cracks by breaking waves has an explosive effect and loosens the material in the first place
What is wave pounding?
The repeated force of waves breaking against cliffs weakens rock. This release of energy ultimately leads to the breakdown of the rock. This is sometimes said to be the same as hydraulic action
What is hydraulic action?
Breaking waves can force air into the gaps in rocks/cliffs, exerting pressure on the rocks, particularly on gaps in them. This causes rock particles to become dislodged and removed. It is sometimes said to be the same as wave pounding
What is corrosion?
The dissolving of rock and sediment by chemicals, mainly weak acids, in the sea water. This process is more effective in warmer waters. There is some overlap with chemical weathering processes here
What is cavitation?
The collapse of bubbles that have formed within moving water, releasing energy that exerts a force against rock rather like hammer blows.
Linked to wave quarrying as it can leave to removing rock particles
What is attrition?
The erosion of material being transported by the sea, making it smaller and more rounded, as a result of the collision with, or the pounding of particles against, other material
What is transport?
The carrying of eroded particles from one location to another
What is detachment?
The separation of particles from the parent material
What is entrainment?
The picking up of eroded particles to enable transportation to take place
What are marine processes?
Caused by the waves from the sea wearing down the cliff foot
What are sub-aerial processes?
Caused by the action of the weather on the cliff face. Can change the shape of the coast without moving material
