C -> 2.3 - 2.6 Flashcards
cliff erosion discordant cliff
- groundwater flows through the permeable sands but can’t flow through the impermeable clay, water flow along the sand/clay interface weakens the material leading to slumping
- surface runoff erosion where groundwater emerges on to the cliff face (impermeable clay)
- wave cut notch formed in weaker coal, siltstone overhangs the notch
- resistant rock at the cliff base creates a ‘bench’ feature
result is
scree slopes in most of the bays
black lower basalt caps underlying chalk which
protects it from weathering - this can be seen at white rocks further along coast
white rocks
- ulster limestone chalk
- protected from storm waves by the skerries
- basalt rock cap (on top) protects from sub aerial erosion
- series of cliffs, caves, arches, stacks, stumps - Gulls Point/ Sliddery cove
cave/arch/stack/ stumps process
- starts with headland/ land sticking out of sea
- headland makes the waves refract
- erosion processes are concentrated on weak points on the sides of the headland
- hydraulic action/abrasoion then form caves on the side
- caves meet, forming tunnel
- tunnel comes arch, which gets bigger til top of arch collapses and stack remains
- wave erode stack, stack unstable and collapses, leaving a base
cliffs and shore platforms
- starts at the base of a cliff
- cliffs are vertical slopes
- breaking waves (swash) erode away at cliff material
- curved-notch forms along the length of the cliff, weaker points might get caves
- rock above Is unsupported and collapses
- cliff line retreats (recession)
- leaving behind a flat/ slightly sloping area of rock - shore platform
- this platform is subject to weathering and erosion
- platforms could be left with so lots of rock pools or small ridges where rock is less/ more resistant
marine erosion
- often at headland sites
- wave cut notch and platform formation
- rate of erosion/debris varies over time
sub aerial weathering
- often at the back shore of bays
- refraction means lower marine energy
- cliff degradation increases from above
marine erosion dominated profile
steep face
active undercutting
limited cliff base debris
subaerial process dominated profile
curved slope profile
lower angle face
accumulated debris
Dunluce
- near horizontal/slightly dipping landward strata (17o)
- 100% basalt (agglomerate) near cliff
- 25% chalk near sea
- high tide
- constructive waves (0.7)
- variable subaerial weathering
positive feedback
process or mechanism that causes a change to be increased or exaggerated in the future, taking it further away from dynamic equilibrium, eg during the formation of a sport, the deposition shelters area behind it, encourage further deposition
negative feedback
process or mechanism that balances change by causing it to be reduced or dampened in the future eg a rockfall due to wave erosion, may protect the base of the cliff and reduce the amount if erosion
example of equilibrium part 1
- complex cliff profile = different rock types = permeability varies
eg, Causeway: UB (entablature + colonnade)/ laterite/ LB - water permeates through upper basalt (pervious) + laterite (porous), but not LB (impermeable)
- LB undercut by marine erosion, whilst laterite is saturated with rainwater from above = heavier
- heavy laterite stress> strength, with lubricated being plane = mass movement
example of equilibrium part 2
- material falls into the bays/ onto the wave cut platforms and absorbs wave energy
- materials break down = used fo abrasion on cliff, until disappears
- waves attack cliff again = wave cut notch/ platform with cliff retreat = equilibrium
- until tectonics/ isostatic rebound/ eustatic sea level changes whole situation
how does tectonics shape dunluce
tectonic events 56-62 million years ago formed the igneous bedrock at dunluce and the anticlines and synclines in rock
how does geology shape dunluce
type of rock type influences the coastal morphology as harder rock is harder to erode, vice versa
how does sea level shape dunluce
increased sea levels mean increased volume of water contacting the coast
how does wave energy shape dunluce
higher wave energy means erosion at a higher, which changes the coastal morphology at Dunluce
how does marine sub aerial process shape dunluce
rain increases the saturation of the superficial geology/rock, which can increase chances of landslides
how does marine processes shape dunluce
erosional processes form wave cut notches and platforms at usually headlands, but rate of erosion/ debris varies over time
biological weathering - tend to exacerbate rate of other weathering
- live on the rocks, scraping away to get food/ boring a hole in the rock - eg a piddock has a shake with serrated curing - edges
- holes bored into the rock, becoming weak points for weathering to act
- seaweed acid - eg, kelp - they have h2so4, so if cells break, the acid dissolves the rock away. rock minerals aren’t bonded together so rock crumble
- Tree root weathering = seeds fall into cracks, germinate and as plant grows, roots expand and thicker - tree roots exert tensional force and force rock apart.
frost shattering and freeze thaw
water seeps into cracks in rocks, when water freezes, expands in volume by 9%, exerting tensions force which widens rock, thawing allows more water to enter, and freeze, process repeats until cracks are forced open
salt crystallisation
saltwater penetrates small cracks or pores in rock at high tide, and evaporates at low tide, leaving precipitated salt crystals, repeated tidal cycles lead to growth of salt crystals until they begin to press against sdes of cracks - tensional processes, granular disintegration. Pans and loafs at eaglehawk neck Tasmania
chemical reactions
oxidation: addition of oxygen to minerals, especially iron compounds which produces iron oxides and increases volume. rock crumbles away, ie. erosion is much easier
carbonation - rainwater mixed with co2 to form weak carbonic acid ph 5.6, acidic rain mixed with calcium carbonate to form soluble calcium bicarbonate, minerals dissolve in solution
hydrolysis - mineral breakdown to form new clay minerals, plus material in solution, because of water/ dissolved CO2
tide comes in
salt water penetrates cracks and surface of rock
tide goes out
salt crystals form on and between the gaps of the rock as water evaporates
over time
salt crystals grow and push gaps in rock apart
pan
(Backshore) water pools on the top of the rocks furthest away from the ocean dries the fastest, so salt crystallisation is more intense on the rock surface here.
loaf
(Nearshore ) opposite to pan rocks are closer to water and experience less evaporation on the surface, so only joints are visibly depressed
tessellated pavement history
300-60 mil years ago, sediment accumulated and compacted to form base rock siltstone stresses in the rock causes cracks and joints, interaction of joints is what gives tessellated appearance of area.
water evaporates on rock, salt erosion occurs
factors that affect rock breakdown
sea level salt erosion temperature variation tectonic pressyre salt content human movement joints/ cracks
Complex cliff erosion at giants causeway
- Differential erosion occurs at varying rates, which is caused by different layers of strata
- Unconsolidated material such as fluvial alluvium is the weakest and easiest to erode, once saturated sediment can slump
- Giants causeway is made of entablature (more permeable rocks), easier to erode, which causes it to overhang over the colonnade (less permeable), but it is heavily jointed, so it becomes saturated and heavier, which can exacerbate mass movement
- Igneous rocks such as basalt and laterite are crystalline rocks which means they are made up of interlocking crystal minerals, more resistant rocks. However this depends on the age, permeability and jointing of the rock
Permeable rocks are
less resistant, so groundwater can enter the cracks in the rocks, which can exploit joints and reduce stability in the cliff
