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alevel geography- coasts > Chapter 2 > Flashcards

Chapter 2 Flashcards

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1
Q

What is physical/ mechanical weathering

A

Breaks the rock down into smaller fragments of the same rock

Increasing the exposed SA of the rock exposes more to physical weathering

In many coastal landscapes the sea prevents temps dropping below O degrees which reduces extent and effectiveness of some physical weathering processes

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2
Q

Types of physical weathering

A

Freeze thaw
Thermal expansion
Pressed release
Salt crystallisation

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3
Q

Freeze thaw

A

Wages enters cracks/ joints and expands by 10% when freezes

In confined space this exerts pressure on the rock causing it to spilt or have sections break off

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4
Q

Thermal expansion

A

Rocks expand when heated and contract when cooled

Frequent cycles of this cause outer layers to crack and break and flake

Doubts unless water is present

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5
Q

Pressure release

A

When overlying rocks are removed by weathering the underlying rock expands and fractures

Exposes subsurface rocks like granite(✅✅)

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6
Q

Salt crystallisation

A

Salt solutions can seep deep into pores in rock and from crystals

Growth creates stress in the rock and can result in disintegration

NaS and NaCO3- can expand by 300%

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7
Q

What is weathering

A

Uses energy to alter the physical or chemical materials on surface rock

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8
Q

Weathering definition

A

Process of weakening and breaking up rocks m

Physical and chemical breakdown of rocks and minredals near the earths surface

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9
Q

Biological weathering

A

Together of plant roots/ chemical actions like organic acids

Categorised separately

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10
Q

Chemical weathering

A

Chemical reactions between moisture and minerals

Chemical weathering creates WEAK residues that are then easily washed away

Higher temp=higher rate

Change in climate= co2 to rainfall and ocean= more acidic

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11
Q

Types of chemical weathering

A 
Carbonation 
Hydrolysis 
Solution 
Oxidation 
Hydration
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12
Q

Carbonation

A

Chemical

Rainwater and dissolved co2, weak carbonic acid, reacts with caco3 in rocks in limestone= calcium bicarbonate

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13
Q

Hydrolysis

A

Chemical

Chemical reactions between rock minerals and water

Silicates combined with h20 to produce secondsry minerals eg clays

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14
Q

Solution

A

Chemical

Minerals dissolved BUT iron- only in acidic water

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15
Q

Oxidation

A

Minerals in rocks react with o2 especially iron

Extremely acidic - original structure is destroyed

Sandstone - bindings destroyed

CHEMICAL

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16
Q

Hydration

A

Chemical

H20 added to rock minerals - new minerals of larger volume

Surface flaking - some minerals expand 0,5% during chemical change

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17
Q

Mass movement

A

When gravity exceeds the force holding material to the cliff eg friction

Once mass movement has occurred, large amounts of sediment added to sediment budget

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18
Q

Regolith

A

Sediment from mass movement

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19
Q

Types of mass movement

A

Rock fall

Slides

Slumps

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20
Q

Rock fall

A

Slopes of 40 degrees or more

Bare cliff face- no vegetation to bind

Gravity, weathering- rocks become detached

Waves may wash it away or it forms a SCREE SLOPE ( gently sloping slope away from the cliff)

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21
Q

Slides

A

Linear movement

Slip, fault or bedding plane present

Or rotational - along a curved bedding plan

Undercutting at base of cliff

Wave cut platform because of MANY slides

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22
Q

slumps

A

Weak rocks

Heavier when wet = greater downward force

Sand above clay - rainwater penetrates sand but not clay

Greater pore pressure in sand

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23
Q

What are the geomorphic processes

A 
Wave processes 
Weathering 
Mass movement 
Flyvial processes 
Aeolian processes
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24
Q

Fluvial processes - erosion

A

Fluvial erosion in the upper catchment is MAIN source of a rivers sediment load

Rivers use similar erosional processes to waves

Sediment also derived from weathering and mass movement

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25
Q

Deposition - fluvial processes

A

Low energy at river mouth
As rivers enter sea, reduction in their velocity as waters enters static sea
Energy reduced, rivers sediment deposited

Largest particles first

Fresh water and salt water = flocculation of clay particles( clump together= HEAVIER) due to electifcal charges between them in saline conditions

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26
Q

Aeolian processes- erosion and transportation

A

Wind is able o pick ups and particles and move them by deflation

Surface creep- when sand is moved across surface due to wind

Attrition on land very effective, particles carried for greater distances and NOT protected from collisions by film of water around them

Except from solution - transported material using same mechanic as a as water

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27
Q

Deposition - aeolian processes

A

Wind speed falls

Vegetation traps more sand from air and builds dunes

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28
Q

Wave processes - erosion ( what are the 5 processes)

A 
Abrasion 
Attrition 
Hydraulic action
Pounding 
Solution
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29
Q

Abrasion

A

Waves armed with rock particles scour the coastline, rock rubbing against rock

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30
Q

Attrition

A

Rock particles, transported by wave action collide with each other and with coastal rocks, progressively become worn away

Become smoother, rounded and smaller ( eventually sand )

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31
Q

Hydraulic action

A

Waves break against the cliff face
Air and water trapped in cracks and crevices becomes compressed
As the wave recedes, the pressure is released and the air and water suddenly expand

The crack is widened

the aw pressure of Atlantic breaking wave is 11,000 kg2

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32
Q

Pounding

A

Mass of a breaking wave exerts pressure on the rock causing it to weaken

Forces of as much as 30 tonnes per m2 can be exerted by high energy waves

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33
Q

Solution

A

Dissolving minerals like MgCO minerals in coastal rock

PH of sea water= 7-8

Process is limited of significant unless h20 is polluted or acidic

But even then onlycoastal rocks containing significant amount of soluble minerals are likely to be affected

34
Q

Wave processes - transportation

A 
Solution 
Suspension 
Saltation 
Traction 
Longshore drift
35
Q

Solution

A

Minerals that have been dissolved into mass of moving water
This type of load is invisible and the minerals will remain in solution until the water is evaporated and they precipitate out of solution

36
Q

Suspension

A

Small particles of sand , silts, clays can be carried by currents

This accounts for the brown muddy appearance

37
Q

Saltation

A

Series of irregular movements of material which is too heavy to be carried continuously in solution
Hopping motion
Turbulent low may enable sand sized particles to be pinched up and carried for a short distance
Other particles may be dislodged by impact, allowing h20 to get beneath them and cause entrainment

38
Q

What is entrainment

A

When sand sized particles get picked up by water

39
Q

Traction

A

Largest particles in the load may be pushed along the sea floor by the once of the flow
Movement is rarely have continuous
Large boulders may undertake a partial rotation before coming to rest again

40
Q

Longshore drift

A

Deposited onshore
May move by lsd
Waves approach coast at an angle due to direction of dominant wind
When waves break, smash carries particles diagonally up the beach - gravity moves them perpendicularly down

41
Q

Deposition - wave processes

A

When a loss of energy caused by velocity decrease and or water VoLTE
Rate of sediment accumulation exceeds removal rate
When waves slow down immediately after breaking
At the top of swash where water doesn’t move
During backwash- when water percolates into the beach material
In low energy environments- eg sheltered from waves and wind

42
Q

What is settling velocity

A

Velocity in which sediment particles are deposited

43
Q

How are cliffs and shore platforms formed

A

Destructive waves break repeatedly on relatively steeply sloping coastlines
Undercutting can occur between high and low tide levels ( wave cut notch)
Weakens support for the rock strata above- collapses = steep profile and a cliff

44
Q

What happens with cliffs and shore platforms when rock debris is Boulder sized

A

Accumulates on platform
Gets so wide it produces shallow water and Smallwood aves- friction slows approaching waves so undercutting slows and eventually stops

45
Q

How do wave cut platforms occur

A

When backwash carries away eroded material. Leavin a wave cut platform

46
Q

At what angles do shore platforms slope seawards

A

Between 0-3 degrees

47
Q

When are water levels constant for longest

A

High and low tide

Erosio is greater at these points

48
Q

Cliffs and shore platforms - High tide

A

Ramp

49
Q

Cliffs and shore platforms - low tide

A

Small cliff

50
Q

Best tidal range for shore platforms developing (tidal range)

A

<4
If its higher - erosion is spread over a wider area of the platform , water is at its high and low tide positions for a shorter time and so platform is more uniform and steeply sloping

Lower - cliff

51
Q

Factors forming shore platforms

A

Erosion
Solution
Freeze thaw
Salt crystallisation

ALGAE
- at night they release c02- mixes with sea water=more acidic nd more chemical weathering
-

52
Q

Horizontally bedded strata- cliff erosion

A

Undercutting by wave a to leads to rock fall, the clouds retreat inland - parallel to coast

53
Q

Seaward dipping strata- cliff profiles

A

Undercutting by wave action removes basal support
Rock layers loosened by weathering
Slide into sea along bedding planes

54
Q

Landward dipping strata- cliff profiles

A

Rocks loosened by weathering and wave action
Is difficult to dislodge
Slope profile lowered by weathering and mass movement

55
Q

Caves arches stacks and stumps

A

Wave refraction - energy has concentrated on sides of headlands
Points of weakness( faults and joints) exploited by erosion all processes , particularly abrasion and hydraulic action
CAVE
Concentrated wave attack between high and low tide
Arch- 2 caves
Widen arch ad weakened support- stack- stump

56
Q

Headlands and bays formation

A

Weaker rocks erode more rapidly
More resistant rocks Reve more slowly= headlands (shelter bays)
DISCONCORDANT
Width of bays = width f band of weaker rock
Bay depth - depend on differential rates of erosion between the more resistant and weaker rocks

57
Q

Wave refraction

A

When waves approach an irregularly shaped coastline become more parallel
Waves slow down by friction in shallower water of the headland and the part if the Eva crest n deter water moves faster as there’s no fraction waves bend round the headland and the orthography converge

58
Q

Bays - refraction

A

Orthogal converge and energy is dissipated
Deposition
As waves break on sides of headland at an angle there’s LSD of eroded material in bays

59
Q

Blowholes

A

Part of a roof of a tunnel like cave collapses along a major joint- may form a vertical shaft that reaches cliff top ( blowhole)

In storm conditions- large waves may force white aerate water out

Eg trevone, Cornwall

60
Q

Geos

A

Narrow, steep sided inlets
Even on coastlines with resistant geology , may be lines 0[of weakness like joints and faults
These are eroded more rapidly by wave action than the rocks around
Hydraulic action - force air and water and weaken strate

Eg huntsman leap in penbookshire

61
Q

What are deltas

A

Large areas of sediment formed at mouths of rivers

Deltaic sediments are deposited by rivers and tidal currents, form when rivers and tidal currents deposit sediment at a faster rate than the wave and tides can remove it

Deltas are crossed crossed by branched network of distributaries

62
Q

What happens when deltas get overloaded with sediment

A

Deposition in the channel forms bars which cause the channel to split in. 2
This produces 2 channels with reduced energy levels and so more deposition and further dividing occurs
Although these channels may be lined with levees i their banks, in times of floor these natural embankments are breached and deposition of lobes of sediment will take place in low lying areas between them

63
Q

Where do deltas form

A

Low energy environments
Tidal ranges low
Rivers entering sea are carrying large sediment loads
A broad continental shelf margin exists at the river mouth to provide a platform for sediment accumulation

64
Q

Types of delta

A

Cusp ate
Birds food
Arcuate

65
Q

Cuspate delta

A

Pointed extension to the coastline occurs when sediment accumulates , but this is shaped by regular gentle currents from opposite directions

66
Q

BIRDSFOOT delta

A

Distributaries build out form the coast ina. Branching pattern

River sediment supply exceeding some rates of removal by waves oand current

67
Q

Arcuate delta

A

Sufficient sediment supply is availed for the delta to grow seawards, wave action strong enough but ti smooth leading edge

68
Q

Structure of delta ( 3)

A

Upper delta plain
Submerged delta plain
Lower delta plain

69
Q

Upper delta plain

A

Furthest inland, beyond the reach of tides and composed entirely of river deposits

70
Q

Submerged delta plain

A

Lies below mean low water mark and is composed mainly of marine deposits
Seawards growth of delta

71
Q

Lower delta plain

A

In the inter-tidal zone regularly submerged and composed of BOTH river and marine depots

72
Q

Tombolos

A

Beaches that connect mainland to an offshore island

Often formed form spits that have continued growing seawards until the hey reach and join an island

Eg 30km shingle beach at chesil near Weymouth

73
Q

Beaches

A

Most common landform. Of depostion

Accumulation of material deposited between lowest tides ad. Higher storm waves

74
Q

Sources of beach material

A

Cliff erosion - 5%

Offshore - Combed From sea bed often during periods of rising sea levels, 5%

Rivers- 90% carried onto coastal syste as suspended and bed load though river mouths

75
Q

Sandy beaches

A

Gentle gradient
<5 degrees
Small particle size means it becomes compact when wet , allowing LITTLE percolation
Material is carried back down the beach rather than being left at top- gentle gradient adn ridges/ tunnels parallel to top of beach

76
Q

Shingle beaches

A

Steeper gradient
Smash stronger than backwash so net movement of shingle on beach
Shingle may make up upper part of the beach, where rapid percolation due to larger air spaces mean that little backwash and so material is left at top of beach

77
Q

Spits

A

Long narrow beaches of sand or shingle attatched to land
Extend across bay , estuary or indentation
Longshore dritt
Strong winds/ tided currents can cause spit to develop curved end ( recurred end)
Wave refraction

78
Q

Onshore bars

A

If a spit. From across an indentation such as a cove or bay in the coastline until it joins land
Form a lagoon fo brackish water on the landward
Waves approaching a gently sloping coast deposit sediment due to friction with the sea bed
The build up of sediment offshore causes waves to break at some distance from coast

79
Q

What happens behind spit

A

Sheltered area
Depostion
Silt and mud build up
Salt marsh

80
Q

Berms

A

Smaller ridges tat develop at the position of the mean high tide mark
Depostion at top of smash

81
Q

Cusps

A

Smaller , semi circular depressions
Temporary features formed by a collection of waves reaching the same poitn and when the smash adn backwash have similar strengt

Sides of cusp channel incoming swash into the centre of the depression - this produces STRONG backwash , which drags material Down the beach from centre of cusp enlarging the depression

alevel geography- coasts (4 decks)

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