5 - processes of coastal mass movement, weathering, erosion

Question 1

what are the main types of weathering

Answer 1

• physical
• chemical
• biological

presence of corrosive seawater can intensify destructive influences

Question 2

what is salt water crystal growth as a form of physical weathering

Answer 2

• salt crystals grow in seawater that collects in cracks in cliff face evaporate
• they grow and exert pressure on rock breaking pieces through mechanical forces

Question 3

what is freeze thaw as a form of physical weathering

Answer 3

• repeated freezing and thawing of water causing type of crystal growth
• most effective on high latitude coasts with significant precipitation

Question 4

what is wetting and drying as a form of physical weathering

Answer 4

• expansion/contraction of minerals

- most effective on clay and macro-tidal environments

Question 5

what are the processes involved with chemical weathering (5)

Answer 5

1. SOLUTION (solubility depending on temp, acidity of water. limestones affected)
2. HYDRATION (minerals absorb water, weakening crystal structure and rock more susceptible to other weathering processes)
3. HYDROLYSIS (reaction between mineral and water related to hydrogen ion concentration in water)
4. OXIDATION/REDUCTION (adding/removing oxygen, oxidation = oxygen dissolved in water, reduction = common under waterlogged conditions)
5. CHELATION (organic acids, produced by plant roots and decaying organic matter, bind to metal ions causing weathering)

Question 6

what can be seen as biological weathering

Answer 6

• BIOTIC weathering = plant roots active on vegetated upper slopes of cliffs opening up cliff face to other destructive processes
• burrowing animals weather softer rocks and seagull guano extremely acidic and weathers limestone and chalk rocks

Question 7

what is mass movement

Answer 7

defined as ‘downslope movement of material under gravity influence’

closely related to geologic structure and lithology of coastline

Question 8

what are the rapid mass movement types

Answer 8

• ROCK FALL
• ROCK SLIDES
• ROCK TOPPING
• ROTATIONAL SLIDES/SLUMPS

Question 9

what is a rock fall

Answer 9

blocks of rock dislodged by weathering fall to cliff foot

Question 10

what is a rock slide

Answer 10

blocks of rock slide down cliff face especially where there is a steep dip

Question 11

what is rock topping

Answer 11

blocks/columns of rock weakened by weathering fall seawards

Question 12

what are rotational slides/slumps

Answer 12

sections of cliff giving way along well defined concave slip surface

material remaining visible for months as could be clay so takes a while to be eroded by sea

Question 13

what are the processes of slow mass movement

Answer 13

• CREEP

- SOLIFLUCTION

Question 14

what is a creep

Answer 14

extremely slow (imperceptible) downslope movement of regolith (loose material including soil above bedrock)

Question 15

what is solifluction

Answer 15

slow downslope movement of regolith, saturated by melting of active layer above permafrost (summer of periglacial regions)

Question 16

describe the process of a sea cliff formation

Answer 16

1. destructive waves attack coast with subaerial weathering, erosion and mass movement at work
2. notch carved and enlarged
3. upper slope unsupported/undermining occurs
4. slope collapses = steep face, erosion/weathering/gravity
5. cliff retreats and increases in height
6. rock left at base is wave cut platform, bigger platform, less rate of erosion

Question 17

what is impact of geological resistance on cliffs

Answer 17

when cliffs contain more resistant geology, well jointed material and few lines of weakness so taller vertical cliffs formed

less resistant geology = less vertical cliffs as many lines of weakness

Question 18

which erosional features are found on discordant coastlines

Answer 18

• headlands/bays
• coves
• cliffs, wave cut platforms/notches
• CASS

Question 19

how are headlands and bays formed

Answer 19

1. headlands are more resistant rock, bays softer rock
2. discordant coastline geology influences sequence
3. less resistant rocks erode faster
4. wave refraction = more powerful waves concentrated on headland, low energy waves in bay = build of material = beach
5. headlands and bays form along concordant too, bands of rock parallel
6. here, sea may erode through harder rock on coastline and rate of erosion accelerated as soft rock exposed and eroded to create cove

Question 20

how can a bay also be formed

Answer 20

plate tectonics can create a bay;
- continents drift together and rift apart, large bays can form where land once was

ocean overflowing coastline

Question 21

what is a geo and how are they formed

Answer 21

GEO - inlet, gully or deep cleft in cliff face

created by erosion of fault lines or bedding planes in cliff face and can be created by sea cave collapse, extending geo inland

they are linked to blow holes - hydraulic action creating blow hole which then collapses leaving a geo

Question 22

what is a blowhole

Answer 22

usually found in roof of coastal cave

impact of air and water forced up into caves by wave action leading to development of vertical shafts and tunnels upwards to ground surface to form blow hole

Question 23

what occurs within a blowhole

Answer 23

air/water forced through hole by breaking waves, at certain tides and wind directions, with explosive force

large pressure changes in cave and further erosion

collapse of roof of cave may lead to geo being formed