G3 Landforms resulting from erosion, weathering and depositional processes

Mind map of case studies, processes etc in coastal areas in the UK

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  • Coastal landforms
    • Created by deposition
      • Long shore drfit (LSD) is the method by which sediment is transported along the coastline. When waves approach the coastline at an angle, the sediment will be carried up the beach at the same angle then it moves back down at a 90 degree angle to the coast. (creates zig zag motion)
      • Land forms created by deposition processes:
        • Spits: are banks of sand and shingle which project from the land into the sea. They need a supply of sediment from LSD to build and maintain them
        • Hooked spit: Vary from normal spits because of a change in wind direction changing the direction of LSD
        • Double spit: Formed when LSD extends one spit in the direction of the prevailing wind and another from the opposite direction
        • Tombolos: are spits joining an island to the mainland formed when a spit continues to groe due to LSD
        • Barrier beaches: formed when spits grow across small bays
        • Cuspate Foreland: Triangular outgrowths of shingle ridges formed by LSD from opposite directions
      • Case study: Slapton sands barrier beach in Devon. 3 mile shingle beach. Formed over 10,000 years ago since the flandrian transgression (last ice age). As sea levels rose the flint sea floor rolled over This shingle was pushed landward as it was south where land was rebounding from glaciation. Tidal surges such as 4m tidal surge in 2001 can breach the bar
      • Case study: Dawlish Warren spit at the mouth of the Ex estuary, S England. Created about 7000 years ago by post glacial sea level rises. Over 200m of sand have been eroded since 1987 after a breakwater structure was built to the south west by Langstone rock. Defences built at Dawlish in 1992 costing £1.5 million for 17 groynes. 50 businesses are located there, it is a protected nature reserve (500 acres) with up to 600 plant species. up to 20,000 people use the spit at peak times
      • Case study: Chesil beach, Dorset, example of a Tombolo. It links the Isle of Portland to the Dorset mainland.  initially formed from  sandy deposits in Lyme Bay as water levels rose rapidly at the end of the last ice age 20,000-14,000 years ago. These deposits were eroded and the sand and gravel driven onshore as a barrier beach. As the barrier beach was driven further east by rising sea levels it overrode existing sediments. 18km long pebble beach. separated from mainland by fleet lagoon (saline water)
      • Case study: Double spit at poole harbour, Dorset. It is a drowned river valley. Formed about 7000 years ago at the end of the last ice age when rising sea broke through the chalk ridge which connected old harry rocks to the needles. It covers about 3,600 hectares. One of the largest natural harbours in the world.
      • Case study: Dungeness in kent, example of a cuspate foreland. Largest cuspate foreland in Britain covering about 2,158 hectares.  Formed mostly of flint shingle and is the result of coastal erosion, sea level rise and deposition of sediment.
      • Case study: Hooked spit. Spurn head on the Holderness coast. Formed due to erosion of the soft boulder cliffs. Erosion made worse due to long fetch over north sea (destructive wave types more likely) Average rate of erosion 2cm a year
    • Created by erosion/weathering
      • 4 processes of erosion:
        • 1. ABRASION: Material the sea has picked up wears away rock faces
        • 2. ATTRITION Material carried by the waves breaks up into smaller, smoother sediment
        • 3. HYDRAULIC ACTION waves enter faults in rock compressing the air inside, when the wave retreats, the air expands causing a minor explosion
        • 4. SOLUTION the acids in salt water slowly dissolve rocks on coast especially limestone and chalk
      • 4 processes of weathering:
        • 1) SALT WEATHERING sodium and magnesium compounds expand in joints weakening rock structures
        • 2) FREEZE-THAW water freezes, expands and degrades joints
        • 3) WATER LAYER water the wetting and drying of rocks
        • 4) BIOLOGICAL roots of seaweed, secretations by limpets barnacles and seagulls
      • Cave-arch-stack-stump sequence
        • 1) sea attacks line of weakness opening up a crack or joint
        • 2)  as the joint erodes further, a notch forms
        • 3) as the notch erodes further, a cave forms
        • 4) The cave is eroded through the headland to form an arch
        • 5) The arch eventually collapses leaving a stack
        • 6) After further erosion the stack collapses becoming a stump
      • Case study: Wave cut platform at southerndown in wales. Forms northern part of 5 mile SSSI by ogmore-on-sea
      • Case study: Headlands and bays along Isle of Purbeck (Jurassic coast)  more common along discordant coastline e.g Strudland bay, The foreland, Swanage bay, Peveril point
      • Case study:  Lulworth cove (Dorset) 140-70 million years old. UNESCO world heritage site. Back of cove is about 250 metres wide, made from chalk whereas opening of cove is formed of 30m band of portland limestone. Attracts 500,000 visitors a year.Stair hole is another cove forming next to it which will eventually join.
      • Case study: Durdle Door arch in Dorset
      • Case study: Old Harry Rocks. 40 feet tall. Made from chalk band of rock, discordant, surrounded by strudland bay and swanage bay . Chalk headland absorbs some of the energy of waves causing it to refract depositing sediment in the bays forming beaches which don't have LSD so sediment only taken away by destructive waves during storms. 10,000-20,000 years old. Old Harry's wife has now been submerged.

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