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Physical Geog = Coasts and Rivers > Coasts - KQ1 (coastal processes and landforms) > Flashcards

Coasts - KQ1 (coastal processes and landforms) Flashcards

1
Q

Fetch

A

The distance between coastlines (longer fetch = more energy)

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2
Q

Energy input

A

from waves, wind and solar sources

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3
Q

Energy output

A

noise, heat and constant movement of material

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4
Q

Material inputs

A

Sediment (silt, clay, cobbles, sand, pebbles) from oceans, rivers, cliffs and coastal areas further along the coast

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5
Q

Material outputs

A

Sediment is moved to other parts of the coast and offshore (through longshore drift and offshore currents)

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6
Q

Landform

A

A physical feature on the earth’s surface

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7
Q

Erosion

A
  • A moving agent

- The wearing away of material by the action of water, ice or wind

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8
Q

Weathering

A
  • Breaking down
  • The disintegration of rocks by the action of the weather, plants, animals and chemical action
  • Insitu breakdown
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9
Q

Marine processes

A

The action of the sea on coastal landforms

  • Abrasion
  • Hydraulic action
  • Attrition
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10
Q

Sub-aerial processes

A
  • Below the air

- Processes active on the face and top of cliffs

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11
Q

Salt crystallisation

A
  • Well jointed, fractured and porous rocks
  • Resulting from waves, spray and tides causing sea water to enter the rock
  • Evaporation of sea water resulting in salt crystallisation (crystal growth prises the rock apart)
  • Results in production of angular fragments
  • Common in coastal intertidal zones
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12
Q

Wetting and drying

A
  • Exposed rock surfaces
  • Rocks are periodically wetted and dried
  • Clay minerals expand and stresses are set up by repeated cycles causing the rock to break up (slaking)
  • Exposed rock surfaces heat up and expand more than cooler rocks below the surface
  • Causes the rocks to spall curved sheets often called onion skin weathering
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13
Q

Frost shattering (freeze-freeze thaw)

A
  • Well jointed, fractured and bedded rocks
  • Water enters cracks, joints and bedding planes
  • In climates where temperature fluctuate above and below 0*C water freezes and expands by 9%
  • This exerts pressure on the rocks, leading to progressive weakening and failure
  • Produces a residue of angular fragments (scree)
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14
Q

Heating and cooling (insolation weathering) and exfoliation

A
  • Exposed rock surfaces in areas with little rainfall and igneous rocks (eg granite)
  • Thermal expansion and contraction of the rock during rising and falling temperatures over a 30-50*C range
  • Stresses are set up in the rocks leading to explosive failure
  • Pressures caused by repeated expansion and contraction cause the rock to disintegrate
  • Honeycomb weathering is produced
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15
Q

Carbonation

A
  • Well jointed and bedded limestone
  • CO2 gas in the atmosphere reacts with rainwater and pore water in soil to form carbonic acid
  • The air in soil is rich in CO2 from plant decay making the rainwater even more acidic
  • Carbonate is removed in solution causing the rock to disintegrate and leaves a residue of insoluble clays
  • Dissolves cements leading to rock collapse
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16
Q

Oxidation

A
  • Rocks containing mineral with Fe
  • Some minerals in rocks react with O2 dissolved in water to form oxides and hydroxides
  • Fe2+ is changed into Fe3+ leading to the collapse of the molecular structure
  • Results in the formation of rust (limonite)
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17
Q

Hydrolysis

A
  • Rocks rich in feldspar (eg granites and sandstones)
  • Water enters the rock in cracks, joints, fractures and pores
  • The reaction between water and silicate minerals (especially feldspars) is sped up if the water contains carbonic acid
  • H+ ions react with mineral ions
  • The products are a residual clay mineral (kaolinite), silica and carbonate are lost in solution
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18
Q

Chelation

A
  • Lichens and decaying organic matter (humus) on any rock
  • Organic acids enter joints, cracks and pore spaces
  • Organic acids attack certain materials releasing Fe and Al
  • Al and Fe are lost in solution leading to rock disaggregation
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19
Q

Types of chemical weathering

A

Carbonation, oxidation, hydrolysis and chelation

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20
Q

Types of mechanical weathering

A

Salt crystallisation, wetting and drying, frost shattering (freeze freeze thaw) and heating and cooling and exfoliation

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21
Q

Factors influencing the rate of marine weathering

A
  • Geology (rock type and structure)

- Climate

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22
Q

Rock cohesion

A
  • How well cemented the grains are

- Weakly cemented sandstones will have higher rates of weathering because it increases the surface area available

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23
Q

Lines of weakness

A
  • Sedimentary rocks are laid in horizontal beds (clay stone and chalk)
  • Bedding planes and joints are also increase surface area and are important for chemical weathering
24
Q

Composition

A

Containing iron = oxidation
Limestone = carbonation
Chalk = lots of calcium carbonate (oxidation)

25
Q

Mass movement

A

The large scale movement of the earths surface that is not accompanied by any agent of movement (eg water, glacier or wind)
- Driven by the force of gravity but other factors are important (eg coastal vegetation may bind slopes together but a lack of vegetation will make slopes more susceptible to mass movements)

26
Q

What are the types of mass movement?

A
  • Soil creep (slow)
  • Surface wash (flow)
  • Falls (fast)
  • Slumps (fast)
27
Q

What affects the strength of waves?

A
  • Prevailing wind (more = bigger)
  • Depth (deeper = bigger)
  • Fetch (more = bigger)
28
Q

Why do waves break?

A

Wave travels to shallow water

  • Frictional drag slows down base of wave
  • Forces wave to break
  • Less energy
29
Q

What are constructive waves?

A
  • Help build beaches
  • Long wavelengths and short (less than 1 metre)
  • Little energy
  • Swash greater than backwash
30
Q

What are destructive waves?

A
  • Remove sediment from beaches
  • The result of storm activity
  • Short wavelength and high (wave breaks from a height)
  • Lots of energy which is absorbed by the beach
  • Backwash greater than swash
31
Q

Abrasion

A

During storm conditions waves have enough energy to pick up sand particles and pebbles and throw them at the cliff face
- Most rapid marine erosion

32
Q

Hydraulic action

A
  • Breaking waves can exert a force of up to 40 tonnes per metre on a cliff base
  • Air is forced into cracks, is compressed and exerts pressure on surrounding rock
  • Will progressively splinter and remove pieces of rock
33
Q

What is wave quarrying?

A

When sea water retreats from the crack there may be explosive decompression of the trapped air (hydraulic action)

34
Q

What is cavitation?

A

The action of breaking bubbles exerting a force (hydraulic action)

35
Q

Corrosion

A

CO2 mixes with sea water to form a weak carbonic acid

  • CO2 comes from waves aerating the sea water and organisms releasing it in shallow water
  • Slightly acidic sea water can dissolve any calcium carbonate in rocks (eg limestone)
36
Q

What are the factors that influence the rate of marine erosion?

A
  • Geology (rock cohesion, lines of weakness and composition)

- Wave action

37
Q

Attrition

A

Blocks which have been eroded from the cliff base are transported away by the sea
- Collide with each other within the swash and backwash becoming smaller and more rounded pebbles

38
Q

Swash

A

Body of water pushing up a beach after a wave has broken

39
Q

Backwash

A

The movement of water back down a beach after a wave has reached its highest point

40
Q

How are marine deposits transferred?

A
  • Swash/backwash

- Longshore drift

41
Q

Longshore drift

A

The movement of material along a coast by waves which approach at an angle to the shore but recede directly away from it.

42
Q

What causes marine deposition?

A
  • Waves enter an area of shallow water
  • Waves enter a sheltered area, eg a cove or bay
  • There is little wind
  • There is a good supply of material
  • Flocculation
43
Q

Flocculation

A

The process by which suspended clay particles in fresh water mix with salt water

44
Q

What factors affect the amount of deposition?

A
  • Wave height (bigger = more)
  • Direction of wind (towards beach = more)
  • Fetch (bigger = more)
45
Q

What factors affect the rate of weathering?

A
  • Temperature range (more fluctuation = more)
  • Amount of precipitation (more = more)
  • Rock type (weaker = more)
  • Amount of vegetation (more = more)
46
Q

What factors affect the rate of mass movements?

A
  • Slope angle (steeper = more)
  • Amount of vegetation (less = more)
  • Amount of water (more = more)
  • Amount of regolith = loose material created by weatering (more = more)
47
Q

What is eustatic sea level change?

A

When the sea level changes due to an alteration in the volume of water in the oceans or, alternatively, a change in the shape of an ocean basin and hence a change in the amount of water the sea can hold
- Eustatic change is always a global effect

48
Q

What is isostatic sea level change?

A

The result of an increase or decrease in the height of the land

  • When the height of the land increases, the sea level falls and when the height of the land decreases the sea level rises
  • Isostatic change is a local sea level change whereas eustatic change is a global sea level change
49
Q

What causes eustatic sea level change?

A

During and after an ice age, eustatic change takes place

  • At the beginning of an ice age, the temperature falls and water is frozen and stored in glaciers inland, suspending the hydrological cycle
  • Results in water being taken out of the sea but not being put back in leading to an overall fall in sea level
  • As an ice age ends, the temperature begins to rise and so the water stored in the glaciers will reenter the hydrological cycle and the sea will be replenished, increasing the sea levels
  • Increases in temperature outside of an ice age will also effect the sea level since an increasing temperature will cause the ice sheets to melt, putting more water in the sea
50
Q

What causes isostatic sea level change?

A
  • During an ice age
  • Caused by the build up of ice on the land
  • As water is stored on the land in glaciers, the weight of the land increases and the land sinks slightly, causing the sea level to rise slightly = compression
  • When the ice melts at the end of an ice age, the land begins to rise up again and the sea level falls = decompression or isostatic rebound
  • Isostatic rebound takes place incredibly slowly and to this day, isostatic rebounding is still taking place from the last ice age
  • Can also be caused by tectonic uplift or depression
  • As this only takes place along plate boundaries, this sort of isostatic change only takes place in certain areas of the world
51
Q

What are the landforms created by emergence?

A

Raised beaches = wave-cut platforms & beaches that are above the current sea level

  • Normally found on old cliffs (relic cliffs)
  • Behind these raised beaches with wave-cut notches, arches, stacks etc. along them
52
Q

What are emergent landforms?

A
  • Begin to appear towards the end of an ice age and they occur when isostatic rebound takes place faster than a eustatic rise in sea level (the land’s height rises faster than the sea’s)
  • Emergent features are features of coastal erosion that appear to have developed well above the current sea level (developed when the sea was at that level and then the sea level changed during and ice age and now they’re above sea level)
53
Q

What are submergent landforms?

A
  • Form when the eustatic rise in sea level takes place faster than the isostatic rebound after an ice age (the water starts to flood the land and fills up landforms on the land)
54
Q

What are landforms created by submergence?

A

RIA = river valley that’s been flooded by the eustatic rise in sea level

  • a typical river valley but they have even more water in them
  • The cross section of a ria is really similar to the one found in the lower course of the river
  • The floodplain of the river also gets flooded, altering the cross profile of a ria ever so slightly so that it includes the floodplain

FJORD = steeper and deeper variants of rias that are relatively narrow

  • U-shaped cross profile and are often found in particularly icy sections of the world
  • Flooded glacial valleys
  • Very deep however they have a shallow mouth (known as a threshold) as this is where the glacier deposited its load.
  • Example = Sogne Fjord in Norway which is really big.
55
Q

What are the main landforms of marine erosion?

A
  • Wave cut platform
  • Wave cut notches
  • Cliffs
  • Headlands
  • Bays

Physical Geog = Coasts and Rivers (8 decks)

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