2B.4 marine erosion Flashcards
(20 cards)
what causes waves
friction between wind and water, with some energy being tranferred into the water. force of wind blowing over the surface generates ripples which grow into waves if wind is sustained
what factors determine the size of a wave
wind strength, duration of wind blowing, water depth, wave fetch
outline the process of a breaking wave
- waves start out at sea and have a circular orbit
- as waves approach the shore, friction slows down the base of the wave
- this causes an eliptical orbit
- eventually the top of the wave breaks over, as it is moving faster than the base of the wave.
- water swashes up the beach, and water from a previous wave returns to the sea as backwash.
where are waves the largset in the UK
cornwall as they are atlantic-facing, with a 4000km fetch from Florida
what are features of constructive waves
low height
wave spills
low frequency
flat beach gradient
low energy
main process is deposition
strong swash
what are features of a destructive wave
high height
wave plunges
high frequency
steep beach gradient
high energy
main process is erosion
strong backwash
how do you measure wave frequency
time the gap between the arrival of one wave crest and the next at some fixed point on the beach.
what is a summer beach profile like?
beaches are steeper, berms are built up. backwash is weaker so more sediment is deposited
what is a winter beach profile like?
high frequency waves, berms eroded quickly, strong backwash transports sediment offshore.
what is hydraulic action and its impact on lithology
the force of water crashing against the coastline causing material to be dislodged and carried away.
increase is pressure can weaken the rocks around the cracks so that small rock fragments are chipped off.
what is abrasion and what is the impact on lithology
when small rocks and fragments hit the rock platform, chipping and wearing it away.
leads to steeper beach profiles, smoother rocks
what is attrition and it’s impact on lithology
when rocks repeatedly knock into each other, which causes the rocks to erode or break. as the rocks continue to collide, they erode more and get smaller until they are sediment. leads to finer sediment, and silt/sand particles,
what is corrosion and its impact on lithology?
the acid in seawater and some seaweed erodes particular rock minerals, causing erosion and weakening the rock. certain minerals like iron are eroded from the rock, so it is weakened.
when is erosion fastest?
high waves
long fetch
high tide
heavy rainfall
in winter
permeable rocks
what are the 5 erosional landforms to know?
wave cut notch
wave cut platform
blowhole
caves/arches/stacks/stumps
cliffs
what is a wave cut notch?
when abrasion and hydraulic action cause the air in cracks to be compressed and then explode outwards breaking off bits of rock. The notch is the resulting landform in which the cliff looks undercut.
what is a wave cut platform
as the notch becomes larger, the cliff becomes unstable and collapses as a result of gravity. the overhand collapses and cliff retreats inland.
what is a blowhole
a sea cave grows landward and upward into vertical shafts and expose themselves towards the surface. can result in hydraulic compression of seawater that is released through a port from the top of the blowhole
outline a cave/arch/stack/stump sequence?
occurs on pinnacle headlands. erosion widens a fault at the base of a headland, widening over time to become a cave. the cave will widen due to erosion and sub aerial processes. it eventually eroded through the other side of the headland, creating an arch. the arch continues to widen until its unable to support itself, falling under its own weight, leaving a stack as one side of the arch becomes detached from the mainland. erosion attacks the base of the stack, it eventually collapses to a stump
what is a cliff
sea cliffs are steep faces of rock and soil that are formed by destructive waves. waves crashing against the coastline erode until a notch is formed. the erosion of this notch undercuts the ground above it until it becomes unstable and collapses. the process repeats itself and the sea cliff retreats inland.
