5 - processes of coastal mass movement, weathering, erosion Flashcards
what are the main types of weathering
- physical
- chemical
- biological
presence of corrosive seawater can intensify destructive influences
what is salt water crystal growth as a form of physical weathering
- 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
what is freeze thaw as a form of physical weathering
- repeated freezing and thawing of water causing type of crystal growth
- most effective on high latitude coasts with significant precipitation
what is wetting and drying as a form of physical weathering
- expansion/contraction of minerals
- most effective on clay and macro-tidal environments
what are the processes involved with chemical weathering (5)
- SOLUTION (solubility depending on temp, acidity of water. limestones affected)
- HYDRATION (minerals absorb water, weakening crystal structure and rock more susceptible to other weathering processes)
- HYDROLYSIS (reaction between mineral and water related to hydrogen ion concentration in water)
- OXIDATION/REDUCTION (adding/removing oxygen, oxidation = oxygen dissolved in water, reduction = common under waterlogged conditions)
- CHELATION (organic acids, produced by plant roots and decaying organic matter, bind to metal ions causing weathering)
what can be seen as biological weathering
- 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
what is mass movement
defined as ‘downslope movement of material under gravity influence’
closely related to geologic structure and lithology of coastline
what are the rapid mass movement types
- ROCK FALL
- ROCK SLIDES
- ROCK TOPPING
- ROTATIONAL SLIDES/SLUMPS
what is a rock fall
blocks of rock dislodged by weathering fall to cliff foot
what is a rock slide
blocks of rock slide down cliff face especially where there is a steep dip
what is rock topping
blocks/columns of rock weakened by weathering fall seawards
what are rotational slides/slumps
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
what are the processes of slow mass movement
- CREEP
- SOLIFLUCTION
what is a creep
extremely slow (imperceptible) downslope movement of regolith (loose material including soil above bedrock)
what is solifluction
slow downslope movement of regolith, saturated by melting of active layer above permafrost (summer of periglacial regions)
describe the process of a sea cliff formation
- destructive waves attack coast with subaerial weathering, erosion and mass movement at work
- notch carved and enlarged
- upper slope unsupported/undermining occurs
- slope collapses = steep face, erosion/weathering/gravity
- cliff retreats and increases in height
- rock left at base is wave cut platform, bigger platform, less rate of erosion
what is impact of geological resistance on cliffs
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
which erosional features are found on discordant coastlines
- headlands/bays
- coves
- cliffs, wave cut platforms/notches
- CASS
how are headlands and bays formed
- headlands are more resistant rock, bays softer rock
- discordant coastline geology influences sequence
- less resistant rocks erode faster
- wave refraction = more powerful waves concentrated on headland, low energy waves in bay = build of material = beach
- headlands and bays form along concordant too, bands of rock parallel
- here, sea may erode through harder rock on coastline and rate of erosion accelerated as soft rock exposed and eroded to create cove
how can a bay also be formed
plate tectonics can create a bay;
- continents drift together and rift apart, large bays can form where land once was
ocean overflowing coastline
what is a geo and how are they formed
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
what is a blowhole
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
what occurs within a blowhole
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
