formation of wave
- winds move across surface of water, frictional drag (resistance to wind by water)
- creates small ripples and waves
- leads to circular orbital motion of water particles in ocean
- as seabed shallower, orbit of water particles becomes more elliptical, leading to more horizontal movement
- increased friction as waves approach the rough seabed, base of wave slowed down
- as base slows, top fo wave continues, and breaks
size/energy of a wave
- strength of wind
- duration of wind (energy builds up)
- size of the fetch (longer it is, more powerful wave, time to build up)
constructive waves
- formed by weather systems that operate in open ocean
- long wavelength
- 6-9 per min
- low waves, surge up beach
- strong swash, weak backwash
- gently sloped beaches
destructive waves
- localised storm events with stronger winds operating closer to coast
- short wavelength
- 11-16 per min
- high waves, plunge onto beach
high energy coastline
- more powerful waves, occur in areas where large fetch
- rocky headlands and landforms, frequent destructive waves
- often eroding as rate of erosion exceeds rate of deposition
low energy coastline
- less powerful waves, occur in sheltered area
- constructive waves prevail, leads to sandy areas
- depositional landforms, as deposition > erosion
wave refraction
- @ headland and uneven coastlines
- wave energy focused on headlands, creates erosive features in these areas
- energy dissipated in bays, so forms depositional features (associated w low energy) such as beaches
Marine Action
hydraulic action
- air forced into cracks, joints and faults in rock when wave crashes onto rockface
- pressure from air causes cracks to force apart and widen when wave retreats and air expands
- over time causes rocks to fracture and weaken, and then break apart
corrasion/abrasion
- when rocks/other materials carried by sea picked up by strong waves and thrown at coastline = more material broken off, carried away by the sea
- size/shape/weight of sediment picked up, asw as wave speed, affects erosive power
solution
- water dissolving in rocks and materials into solutions. acidic seawater cases alkaline rock e.g limestone to be eroded
attrition
- wave action = rocks and pebbles hit each other, wearing down, = rounder and smaller.
sub aerial process
- land-based process, occurs above the waterline
- mass movement, weathering
traction
large, heavy sediment rolls along sea bed, pushed by currents
saltation
smaller sediment bounces along sea bed, pushed by currents, sediment too heavy to be fully picked up by flow of water
suspension
- small sediment carried within flow of water
- greater velocity water able to suspend larger, heavier pieces
solution
dissolved material carried within water in chemical form potentially
flocculation
clay particles clump together due to chemical attraction and then sink due to high density
sediment sources
rivers
- majority sediment in coastal zones from input from rivers, esp high rainfall environments where lots of erosion
- e.g gulf Mexico, sediment flowing from river delta
- deposited in estuaries, brackish areas where rivers flow into sea. important wildlife habitat.
- sediment transported throughout coastal system by waves, tides, currents
cliff erosion
- unconsolidated cliffs eroded easily.
- some areas cliffs can retreat up to 10m yearly, providing lot of sediment
- most erosion in winter due to storm ssn
wind
- coastal energy source, causes sand to be blown along/up beach
- sediment transport by wind maybe where sand dunes or in glacial/desert env
glaciers
- in some systems (Antarctica, Alaska etc) glaciers flow directly into ocean depositing sediment that was stored in ice
- occurs when glaciers calve, a process where3 ice breaks off glacier
offshore
- sediment transferred to coastal zone when waves, tides, currents erode offshore sediment sinks (offshore bars)
- sediment transported up beach, helping build it up
- storm surges/tsumani waves also transfer sediment
LSD
- waves hit beach @ angle (prevailing wind)
- sediment up beach as swash, down beach as backwash
- moves along beach over time
human action
- hard/soft engineering starts (beach nourishment)
sediment cells
- bordered by prominent headlands
- movement of sediment contained within headlands, flows of sediment act in dynamic equilibrium
steep cliffs
most common where rock is strong and resistant to erosion
- sedimentary rocks that have vertical strata v. resistant to erosion
- absence of beach, long fetch + high energy waves promote steep cliff development
gentle cliffs
- areas with weaker rocks, less resistant to erosion, prone to slumping
- large beach also reduces wave energy, prevents steep cliffs by reducing erosion
rate of retreat
- depends on relative importance of marine factors (fetch, beach, wave energy), and terrestrial factors (subaerial processes, geology, rock strength)
- most likely unconsolidated rock and sands will retreat
spits
- formed when LSD causes beach to extend to sea, from change in direction of coastline
- makes slt harsh behind it due to sheltered saline environment, slower water speed
- change in wind/wave direction can cause end of spit to curve (recurved)
- received may be abandoned, new spit will form on recurved end, forming many spits (compound spit)
offshore bar
- offshore area where send deposited as waves don’t have enough energy to carry sediment to shore
- formed when wave breaks early
- or destructive waves backwash removing sediment from beach
tombolo
spit that connects mainland to offshore island
barrier beach
- when beach or spit extends across bay to join 2 headlands
- traps water behind leading to formation of brackish lagoon
barrier beach (bar)
when beach/spit extends across bay to join 2 headlands
- traps water behind to form lagoon
