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GEOGRAPHY - coasts > 2.A - how do erosional coastal landforms develop? > Flashcards

2.A - how do erosional coastal landforms develop? Flashcards

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1
Q

what 3 flows of energy could be influencing a coastal landscape?

A
  1. solar energy
  2. GPE
  3. kinetic energy
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2
Q

how does a flow of solar energy influence a coastal system?

A
  • this partly drives tides which can determine where coastal processes occur
  • also drives winds
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3
Q

how does a flow of kinetic energy influence a coastal system?

A
  • wave energy is kinetic, which is caused by the winds (which are driven by solar energy)
  • this is probably the biggest input into a coastal system
  • this will also cause the movement of waves that drive longshore drift
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4
Q

how does a flow of GPE energy influence a coastal system?

A
  • water/sediment moving directly down under gravity
  • this causes the backwash to occur in waves (helps LSD and also helps destructive waves “drag” sediment away from a beach.)
  • also causes mass movement events on cliffs e.g. rock fall and slumping
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5
Q

what 4 flows of material could be influencing a coastal landscape?

A
  1. aeolian flows
  2. longshore drift
  3. ocean currents
  4. rivers
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6
Q

how does a flow of aeolian material influence a coastal system?

A
  • aeolian flows (wind) can move sediment from a beach to a sand dune
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7
Q

how does a flow of fluvial material influence a coastal system?

A
  • rivers
  • 70-80% of most sediment comes from these flows
  • therefore depositional features often dominate around river mouths (estuaries)
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8
Q

how does a flow of longshore drift material influence a coastal system?

A
  • LSD will move sediment along a beach/between beaches/ within a closed system/between open systems
  • usually west to east in SW UK
  • and from N to S in NE UK
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9
Q

how does a flow of ocean currents influence a coastal system?

A

ocean currents can input sediment from offshore

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10
Q

what is weathering?

A
  • weathering involves the disintegration and decomposition of rocks in situ by the combined actions of the weather, plants and animals
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11
Q

what is erosion?

A
  • erosion involves the removal of weathered material by the action of gravity, water, wind or ice.
  • the fragments of debris may then be used to wear down other material
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12
Q

what 5 conditions can deposition occur under?

A
  1. where the rate of sediment accumulation exceeds the rate of removal
  2. when waves slow down immediately after breaking
  3. at the top of the swash, where for a brief moment the water is no longer moving
  4. during backwash, when water percolates into the beach material
  5. in low energy environment, such as those sheltered from winds and waves, e.g. estuaries.
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13
Q

what is a mass movement event?

A

mass movement occurs when the forces acting on slope material, mainly the resultant force of gravity, exceed the forces trying to keep the material on the slope, predominantly friction.

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14
Q

what is flocculation?

A
  • a process by which salt causes the aggregation of minute clay particles into larger masses that are too heavy to remain suspended in water.
  • these fine, light materials clump together due to electrical charges between them in saline conditions.
  • as a result they become heavier and sink to the sea bed.
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15
Q

what is freeze-thaw weathering?

A
  • water enters cracks/joints and expands when it freezes.
  • over time the repeated process exerts pressure on the rock causing it to split and eventually break off.
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16
Q

what is pressure release (dilation)?

A

when overlying rocks are removed by erosion/weathering, the underlying rock expands and fractures, developing psuedo bedding planes

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17
Q

what is thermal expansion (exfoliation)?

A
  • rocks expand and contract as they heat up and cool down
  • eventually the outer layers crack and slowly peel away.
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18
Q

what is salt crystallisation?

A
  • salts such as sodium carbonate and sodium sulphate
  • salt crystals are deposited in cracks and over time the salt accumulates and applies pressure to the crack (similar to freeze-thaw weathering).
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19
Q

what is oxidation?

A

when minerals such as iron oxidise they can become more soluble and the structure will break down

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20
Q

what is carbonation?

A
  • rainwater often becomes acidic after dissolving CO2
  • this will then produce calcium bicarbonate when it comes into contact with calcium carbonate in limestone.
  • the bicarbonate is soluble and so the limestone gets broken down
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21
Q

what is solution?

A
  • this is a general type of weathering when minerals dissolve in water
  • carbonation is a specific type of solution weathering
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22
Q

what is hydrolysis?

A
  • this involves a chemical reaction between water and rock minerals.
  • an example of this occurs in granite when feldspar reacts to form kaolin (china clay)
  • the kaoline is far weaker than the feldspar and eventually the granite will disintegrate.
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23
Q

what is hydration?

A
  • this occurs when water molecules chemically combine with rock mineral to expand them.
  • this then causes pressure in the rock and it eventually flakes
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24
Q

what is tree roots (weathering)?

A
  • this occurs when tree roots exert leverage on the rock by growing in joints and cracks
  • often, the roots will bring rock to the surface where it can be subjected to further weathering
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25
Q

what is organic acids?

A

when animals and plants decompose they release organic acids which are capable of dissolving minerals in rocks

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26
Q

describe the erosional process of ABRASION

A
  • when waves armed with rock particles scour the coastline
  • rock rubbing against rock
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27
Q

describe the erosional process of ATTRITION

A
  • occurs when rock particles, transported by wave action, collide with each other and with coastal rocks, and progressively become worn away
  • they become smoother and more rounded, as well as smaller, eventually producing sand.
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28
Q

describe the erosional process of HYDRAULIC ACTION

A
  • occurs when waves break against a cliff face, and air and water trapped in cracks and crevices become compressed.
  • as the wave receedes, the pressure is released, the air and water suddenly expands and the crack is widened
29
Q

describe the erosional process of POUNDING

A
  • occus when the 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
30
Q

describe the erosional process of corrosion

A
  • involves dissolving minerals like magnesium carbonate in coastal rock.
  • however as the pH of sea water is invariably around 7 or 8, this process is of limited significance, unless the water is locally polluted/acidic.
  • only coastal rocks containing significant amounts of soluble minerals are likely to be affected by this.
31
Q

describe the transportational process of suspension

A
  • small particles of sand, silt and clay can be carried by currents
  • this accounts for the brown/muddy appearance of some sea water
  • larger particles can also be carried in this way, perhaps during storm events
32
Q

describe the transportational process of traction

A
  • the largest particles in the load may be pushed along the sea floor by the force of the flow.
  • although this can be called rolling, the movement is rarely continuous.
  • large boulders may undertake a partial rotation before coming to rest again
33
Q

describe the transportational process of saltation

A
  • a series of irregular movements of material which is too heavy to be carried continously in suspension
  • turbulent flow may enable sand-sized particles to be picked up (entrained) and carried for a short distance only to drop back down again
  • similarly, other particles may be dislodged by the impact, allowing water to get beneath them and cause entrainment.
34
Q

describe the transportational process of solution

A
  • minerals that have been dissolved into the mass of moving water
  • this type of load is invisible
  • minerals will remain in solution until water is evaporated and they precipitate out of solution
35
Q

what is a rockfall?

A
  • a rockfall involves the sudden collapse or breaking away of individual rock fragments (or a block of rock) at a cliff face.
  • they are most commonly associated with steep or vertical cliffs in heavily jointed and often quite resistant rock
  • a rockfall is often triggered by mechanical weathering (particularly freezethaw) or an earthquake.
  • once broken away from the source, rocks fall or bounce down the slope to from scree at the foot.
  • scree often forms a temporary store within the coastal system, with material gradually being removed and transported elsewhere by the sea. when this occurs the scree forms an input into the sediment cell.
36
Q

what is a mudflow?

A
  • a mudflow involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock such as clay, often after heavy rainfall
  • water gets trapped within the rock, increasing pore water pressure, which forces rock particles apart and leads to slope failure.
  • pore water pressure is a form of energy within the slope system and it is an extremely important factor in determining slope instability.
  • mudflows are often sudden and fast-flowing so can represent a significant natural hazard.
37
Q

what is a landslide?

A
  • a landslide involves a block of rock moving very rapidly downhill along a planar surface, often a bedding plane that is roughly parallel to the ground.
  • unlike a mudflow, where the moving material becomes mixed, the moving block of material in a landslide remains largely intact
  • landslides are frequently triggered by earthquakes or very heavy rainfall, when the slip surface becomes lubricated and friction is reduced.
  • landslides tend to be very rapid and pose a considerable threat to people and property.
38
Q

what is a slump?

A
  • a slump differs from a landslide in that its slide surface is curved rather than flat.
  • slumps commonly occur in weak and unconsolidated clays and sands, often when permeable rock overlies impermeable rock, which causes a build up of pore water pressure.
  • slumps are characterised by a sharp break of slope and the formation of a scar.
  • multiple landslips can result in a terraced appearance on the cliff face.
39
Q

what is soil creep?

A
  • soil creep is an extremely slow form of movement of individual soil particles downhill.
  • this precise mechanism of movement often involves particles rising towards the ground surface due to wetting or freezing and then returning vertically to the surface in response to gravity as the soil dries out or thaws.
  • this zigzag movement is similar to that of longshore drift.
  • soil creep cannot be seen in operation but its action can be implied by the formation of shallow terratettes, the buildup of soil on the upslope side of walls and the bending of tree trunks.
40
Q

what is solifluction?

A
  • solifluction is similar to soil creep but specific to cold periglacial environments.
  • in the summer, the surface layer of soil thaws out and becomes extremely saturated because it lies on top of impermeable frozen ground (permafrost).
  • known as the active layer, this sodden soil with its blanket of vegetation slowly moves downhill by a combination of heave and flow
  • solifluction characteristically forms features called solifluction lobes.
41
Q

what is the significance of mass movement at the coast?

A
  • The material removed by mass movement is transported by the ocean and deposited along other parts of the coastline.
  • Therefore, mass movement plays a major role in the development of both coastal erosion landforms and coastal depositional landforms.
  • can be a key source of sediment to a coastline, and a key process that changes the shape (morphology) of a coastline.
42
Q

what are aeolian processes?

A
  • erosional, transportational and depositional processes by the wind.
43
Q

what is aeolian erosion?

A
  • wind moves sand particles by DEFLATION
  • saltation and surface rolling moves grains
  • grains are heavy so aeolian erosion has little effect on rock coastlines/cliffs
44
Q

what is aeolian transportation?

A
  • moving air transports material using the same mechanisms as water
  • only the smallest grains move by suspension
  • those too heavy to be saltated move by SURFACE CREEP
45
Q

what is aeolian deposition?

A
  • when wind speed falls - surface friction
  • inland - vegetation friction and surface irregularities increase from the sea
46
Q

what sort of sand is transported most easily by aeolian processes?

A

dry, small particles/silt sized

47
Q

when does sand get deposited by aeolian processes and what landforms does it help develop?

A
  • when wind speed falls
  • sand dunes/mounds
48
Q

describe the process of longshore drift

A
  1. waves approach the coast at an angle (due to wind direction)
  2. swash carries sediment up the beach at an angle
  3. material is transported within the nearshore zone by a steady current
  4. backwash carries sediment down the beach due to gravity
  5. there is a zig-zag movement of sediment along the beach
49
Q

what landform is created by LSD?

A

SPITS
- extended stretch of beach material that only joins the beach at one end
- they form when there is a change in the direction of coastline and deposition occurs

50
Q

what is wave refraction?

A
  • the reorientation of wave fronts as they enter shallower water
  • they approach almost parallel to the shoreline
51
Q

where does wave refraction primarily occur?

A

bays and headlands

52
Q

how does wave refraction occur with bays and headland?

A
  • waves are slowed by friction in shallower water of bay
  • wave crest in deeper water of headland moves faster as not slowed by friction
  • wave energy is focused on the headland => erosion is concentrated there (leads to arches, stacks and stumps)
  • longshore movement of eroded material to the bay => build up beach of sediment
53
Q

where do swash-aligned beaches form?

A
  • form in low energy environments such as bays that are affected by waves arriving roughly PARALLEL to the shore
  • swash-aligned sediment moves up and down the beach with little lateral transfer
54
Q

where do drift-aligned beaches form?

A
  • form where the waves approach the coast at an angle.
  • longshore drift moves sediment along the beach culminating in the formation of a spit
55
Q

which landforms are associated with swash-aligned beaches?

A

bay-head beaches/curved beaches

56
Q

which landforms are associated with drift-aligned beaches?

A
  • ridges of sand/shingle beaches
57
Q

erosional landforms - CLIFFS AND SHORE PLATFORMS

A
  • cliffs are usually at a steep angle of more than 40° but may be vertical/overhanging
  • they are often found at the coast with a shore platform
58
Q

what is a wave cut notch?

A
  • may be found at the base of cliffs due to long-term wave-attack and is the point at which cliffs are undercut
  • the overhanging cliff face will eventually fall under the force of gravity, driven by subaerial weathering and mass movement processes.
  • may be rapidly created and pronounced on coastlines with a microtidal range (less than 2m tidal range) as the sea’s erosive energy is concentrated over a smaller area.
59
Q

when and how is a shore platform created?

A
  • as a cliff retreats over time
  • it is usually covered at high tide.
    1. the sea attacks a weakness in the base of the cliff (e.g. a joint in chalk)
    2. a wave cut notch is created by erosional processes such as hydraulic action and abrasion
    3. the cliff retreats inland
    4. the material from the collapsed cliff is eroded and transported away, this leaves a wave cut platform
    5. the process repeats over time
60
Q

how is cliff morphology influenced by the geology of a coastline?

A
  • most particularly by the STRUCTURE and LITHOLOGY of the rock type as this will affect how cliffs respond to erosion and sub-aerial processes.
  • cliffs receede mainly during storms when they are subject to attack from wave erosion, and hydraulic pressure and abrasion dominate.
61
Q

when do cliffs mainly receede?

A

cliffs receede mainly during storms when they are subject to attack from wave erosion, and hydraulic pressure and abrasion dominate.

62
Q

how are cliffs formed?

A
  1. erosional processes:
    - abrasion
    - hydraulic action
    - pounding
    - corrosion
  2. weathering processes:
    - freeze-thaw
    - salt crystallisation
    - carbonation
63
Q

erosional landforms - CAVES

A
  • caves are natural cavities in rock faces which form when weaknesses in local geology are attacked by marine erosion.
  • they are common in areas in which the rock has many joints, faults or weaknesses.
  • caves are less likely to form in weaker rocks as the cave will likely collapse soon after it is created and undercuts the rock above.
  • they occur when waves force their way into cracks in the cliff face. the water contains sand and other materials that grind away at the rock until the cracks become a cave. hydraulic action is the predominant process.
64
Q

erosional landforms - ARCHES

A
  • a sea arch is an opening through a mass of rock, commonly seen at the coast where waves have eroded through a cave.
  • arches form when caves extend through headlands due to powerful wave action.
  • the arch will gradually become bigger until it can no longer support the top of the arch. when the arch collapses, it leaves the headland on one-side and a stacks on the other.
65
Q

erosional landforms - STACKS

A
  • coastal promontories may be dissected over time
  • a natural arch roof may collapse as it grows thinner through prolongued attack by weathering and erosion processes to leave a stack, an isolated pillar of rock which rises steeply from the sea, which stands separately from the cliffed coast that it was previously connected to.
  • the stack will be attacked at the base in the same way that a wave-cut notch is formed
66
Q

erosional landforms - STUMPS

A
  • further erosion at the base of a stack may cause further collapse, leaving a small, flat portion of the original stack as a stump.
  • this may only be visible at low tide.
67
Q

erosional landforms - GEOS

A
  • a geo, or a coastal gorge, is created when a faultline is eroded to form a narrow inlet, or gulley.
  • they are created by the wave driven erosion of cliffs along faults and bedding planes in the rock
  • geos can have caves at their heads
  • those caves may collapse, extending the geo, or leaving depressions inland from the geo
68
Q

erosional landforms - BLOWHOLES

A
  • blowholes are vertical clefts in cliffs which link sea-caves with the cliff top
  • likely to occur in areas where there are crevices.
  • formation of a blowhole system begins as a littoral cave is formed (hydraulic action)
  • incoming waves trap and compress air within a cave and repeated force can puncture the roof of a cave and water and spray can be driven through the roof of the cave, being especially powerful in storm conditions.
  • blowholes have the capacity to change the topography near their locations, eroding the area surrounding the cave which can eventually collapse.

GEOGRAPHY - coasts (9 decks)

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