Physical Geography - Coasts Flashcards
L8 Give the 4 types of erosion and define them
Abrasion - pebbles hurled at the cliff base by the waves causing erosion
Hydraulic action - waves cause air to be trapped in joints at high pressure which ‘explodes’ outwards as the waves retreat
Attrition - Wearing down of rocks by impact, gradually making stones rounder and smaller
Solution - Alkaline cliffs (chalk, limestone) are eroded by weakly acidic seawater
L8 What 2 things cause different rates of erosion?
Energy in waves, lithology - joints, bedding planes, faults, resistance - leading to differential erosion
L8 Describe how a wave cut platform is formed
Waves erode away the base of the cliff, cliff becomes unstable and collapses, rock is broken up and used in attrition to erode away the new cliff, cliff retreats
L9 Describe the 4 processes of marine transportation
Suspension - lighter sediment floats
Traction - large, heavy rocks roll along the seabed
Solution - dissolved sediment
Saltation - smaller rocks bounce along the seabed
L9 Describe the process of Longshore Drift
Swash hits the coast at an angle due to the prevailing wind, backwash is perpendicular to the coast due to gravity, sediment is transported up the beach
L9 Describe the formation of a spit and give an example
Longshore drift causes sediment to travel along a coast until the coast suddenly changes direction (e.g. an estuary), if this happens sediment is deposited, the end of a spit will begin to curve round due to wave refraction which carries material into the more sheltered water behind the spit, e.g. Spurn Point
L10 Describe the formation of a beach, give examples
Accumulation of sand/shingle, formed due to constructive waves, swash carries material up the shore but backwash has little energy so material is deposited, e.g. WSM, Blackpool, Southend
L10 Describe the formation of an offshore bar and give 2 examples
Sediment is eroded by destructive waves and deposited by backwash, located at offshore/nearshore boundary where the water particle orbit no longer reaches the seabed, used to construct wind farms or as a source of sand for beach nurishment, e.g. Loe Bar, Cornwall or Slapton Sands, Devon
L10 Describe what a bar is, give two ways they’re formed, and give an example
Linear ridges of sand that extend completely across a bay, e.g. Chesil Beach
Formed in 2 ways:
- LSD extends a spit across the width of a bay
- Rising sea levels cause constructive waves to drive a ridge of sediment onshore to coastlines with a gently sloping shallow sea bed (barrier beach)
L10 Describe what a tombolo is, 2 ways they can form, and give examples
Linear ridges of sand connecting an offshore island to the coastline, e.g. St Ninian’s tombolo, Shetland Islands or Portland Bill
Formed by:
- LSD which builds a spit which connects to the island
OR
- Wave refraction around both sides of the island, creates a collision of waves which cancel each other out, creates a still environment where deposition takes place
L10 Describe what a Cuspate Foreland is, how they’re formed, and give an example
Low lying triangular headlands extending out from the shoreline, e.g. Dungeness Kent (11km)
LSD currents from opposite directions converge at the boundary between two sediment cells, sediment is deposited out into the sea by both currents
L11 Describe the UK’s sediment cell system
Sediment is transported throughout the 11 UK sediment cells without crossing between them, ‘sediment budget’ within each cell, sediment is in a state of ‘dynamic equilibrium’ in each cell
L11 Give the 3 types of mechanical weathering
Freeze-thaw - water gets into the cracks of rocks and freezes in cold weather, expands by 10% volume, this expansion exerts pressure on the rock which forces the cracks to widen, after repeated cycles rocks break away and collect at the bottom of the cliff as talus
Salt-weathering - salt water evaporates leaving salt crystals behind, these exert stresses in the rock, causing it to break up after repeated cycles
Wetting and drying - frequent cycles of rain and dry means rocks rich in clay (e.g. shale) expand when they are wet and contract when dry, this causes them to crack & break up
L11 Describe some examples of biological weathering
- Thin plant roots get into cracks of rocks and expand as they grow
- Water running through decaying vegetation becomes acidic and leads to chemical weathering
- Birds/other animals burrow/dig into cliffs
- Marine organisms burrow into rocks (e.g. Piddocks) or secret acids (e.g. Limpets)
L11 Give and explain the 1 example of chemical weathering
Carbonation - rainwater absorbs CO2 from the air to form a weak carbonic acid, this reacts with calcium carbonate (in rocks like Limestone or Chalk) to form calcium bicarbonate, this is increased in winter as the cooler the rainwater, the more CO2 is absorbed
L12 Describe 3 types of flows (mass movement)
- Soil Creep - slowest form of mass movement, an almost continuous process, very slow downhill movement of soil particles
- Solifluction - 5cm-1m a year, tundra areas, top layer thaws in summer, layer below remains frozen, surface layer flows over the permafrost
- Earth flows and mudflows - increase in water reduces friction, causes earth and mud to flow over bedrock, in a flow the material becomes jumbled up
L12 Describe 2 types of slides (mass movement)
- Rockfalls - Strong, jointed, and steep rock faces exposed to mech. weathering, slopes over 40°, material bounces to form talus, block falls are similar - large blocks of rock fall due to jointing of the cliff
- Rock/Debris slide - Rocks that are jointed/bedding planes parallel to slope are susceptible, increase of water reduces friction, slabs of rock slide over underlying rocks
L12 Describe Slumps (mass movement)
Often saturated conditions, rotational movement (not sliding), moderate steep slopes, common where softer materials overlie resistant rock, can create a terraced cliff profile after repeated slumping
L12 Give an example of mass movement on the Jurassic Coast
Apr. 2021 - major landslide between Seatown and Eype, 300m of cliff (4000 tonnes) collapsed into the sea
- During wet 2021 winter, water infiltrated the permeable sandstone and reached the impermeable clay, water built up in the sandstone making it heavier, top of the clay became more slippery, sandstone dried up and lost strength, gave way due to gravity & slippery clay
L13 What are the 2 reasons why sea levels are currently rising?
Land ice melting, geothermal expansion of the ocean
L13 What is the difference between eustatic and isostatic sea level change?
Eustatic - sea level rises/falls itself
Isostatic - land itself rises/falls compared to the ocean
L13 Describe how isostatic change occurs in the UK
During glacial periods the weight of the ice on Northern areas pushed the land into the mantle (isostatic subsidence), as the ice melted the land readjusted and rose (isostatic recovery), due to the location of the glaciers the UK is tilting and London is sinking
