2a- coastal landforms Flashcards
how are headlands and bays formed, explain NFL
soft rock is eroded hard rock is left as a headland which then receives lots of kinetic wave energy due to refraction so the destructive waves may erode it and constructive waves in the bays will deposit sand making beaches (NFL)
how are arches, stacks, and stumps formed
Kinetic energy from the waves is concentrated on the headland due to wave refraction and so it’s eroded by hydraulic action forming a crack which is further widened by hydraulic action and abrasion forming a cave, once this goes all the way through an arch is formed. The gravitational potential energy of the arch causes it to collapse leaving a stack which when eroded more by abrasion and hydraulic action will collapse leaving a stump
how are cliff platforms formed, explain NFL
high energy waves breaking at the cliffs’ foot allow undercutting to occur, creating a wave-cut notch. Continued erosion by the waves due to their kinetic energy weakens the support for the cliff and due to gravitational potential the cliff collapses. The process is repeated and the cliff moves backwards leaving a shore platform with scarring from abrasion, eventually, when it’s long enough it slows down the waves and stops cliff retreat can be 0.5km long and 0-3 degrees steep.
As the shore platform grows fewer waves reach it so less erosion occurs and so growth slows so as the platform grows the rate of growth decreases.
How are blowholes and geos formed
weak points in the geology are eroded rapidly compared to hard rock around it do to the kinetic energy in waves and biological weathering. Hydraulic action weakens the rock strata. This creates tunnel-like caves as it’s eroded more and more. If the roof collapses partially due to gravitational potential energy and creates a vertical shaft that reaches the cliff top a blowhole is formed. If the whole roof collapses then a geo is created.
how are on shore bars formed
sediment is moved along the beach by long shore drift. Where the land changes direction and waves loose energy the sediment is deposited forming a spit, as the spit grows over time if it connects to another headland across a bay and on shore bar is formed and the water behind it becomes a lagoon.
how are tombolos formed
long shore drift moves sediment along the coast and where the land changes direction sediment is deposited and over time this creates a spit. When this connects to an island it becomes a tombolo
how are spits and salt marshes formed
LSD carries sediment to the end of the beach (can be increased by storms as waves have more energy) over time sediment builds up creating a spit which will become curved due to wave refraction. As the area behind the spit is sheltered more deposition occurs there which starts the formation of a salt marsh.
Salt marshes are vegetated areas of deposited silts and clay and contains salt-tolerant plants that trap the sediment which increases the height of the marsh.
how are beaches formed, Sand vs shingle- percolation
beaches are an accumulation of deposited sediment between storm waves and the lowest tides. Beach material comes mainly from rivers, from cliff erosion and offshore sources.
Sand beaches have a gentle gradient and when the sand it wet it becomes compact so very little percolation occurs and as little energy is lost to percolation material is carried back down the beach creating ridges and runnels
Shingle beaches are steeper due to the strong swash (to carry larger sediment) and lots of percolation due to large gaps there is little back wash so material is left at the top of the beach.
how are storm ridges, berms and cusps formed
Storm ridges are formed when storm waves carry material to the top of the beach
berms- ridges that develop at the high tide mark
cusps- small semi-circular depressions formed by waves reaching the same point, swash going into the cusps creates a strong backwash and drags sediment down the beach
