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OCR A Level Geography
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Coastal Landscapes2a. Coastal landforms develop due to a variety of interconnected climatic and geomorphic
processes
WEATHERING PROCESSES IN COASTAL LANDSCAPES:
MECHANICAL WEATHERING
Freeze-thaw Water enters cracks joints, expands, freezes. Exerts pressure on rock causing it
to split apart.
Pressure release Overlying rocks removed by weathering/erosion, underlying rock expands and
fractures parallel to surface.
Thermal expansion Rocks expand in heat, contract when cool. If subjected to frequent cycles of
temp change , outer layers may crack and fall off –insolation weathering.
Salt crystallisation Slightly saline water enters pore spaces. Evaporation = salt crystals = exert
stresses on rock – leads to disintegration of surface of rock.
CHEMICAL WEATHERING
Oxidation Rocks exposed to O2 = crumble – similar to rusting of metal e.g. iron. Rocks
change colour form blue grey to reddish brown.
Carbonation Rainwater combines with dissolved CO2 from atmosphere = weak carbonic
acid. Reacts (dissolves) with CaCo3 in rocks e.g. limestone = calcium
bicarbonate, which is soluble
Solution Any process by which mineral dissolves in water is known as solution,
although mineral specific processes, such as carbonation, can be identified.
Hydrolysis Chemical reaction b/n rock minerals and water. Silicates + water = secondary
minerals e.g. clays. Feldspar in granite reacts with hydrogen in water = kaolin
(China clay)
Hydration Water molecules added to rock minerals create new minerals of larger
volume. Happens when anhydrite takes up water to form gypsum. Hydration
causes surface flaking in many rocks,
BIOLOGICAL WEATHERING
Tree roots Plant/tree roots expand along joints and bedding planes. Blocks of rock
become detached. Burrowing animals may have a similar effect
Organic acids Organic acids produced during decomposition of plant and animal litter cause
soil water to become more acidic and react with some minerals in a process
called chelation. On shore platforms, molluscs may secrete acids which
produce small surface hollows in the rock.
MASS MOVMENT: Occurs when forces acting on slope material, mainly resultant force of gravity, exceed
forces trying to keep material on slope, predominantly friction.
- In coastal landscape systems, most sig mass movement processes are those acting on cliffs, =
addition of material to sediment budget by transferring rocks and regolith (loose layer of rock
material lying over bedrock) down onto shore below.
Landslides Cliffs made of softer rocks slip when loosened by rainfall.
Rockfalls Cliffs 40˚ >, rocks may become detached from slope by physical weathering
processes. Fall to foot of cliff under gravity. Wave processes remove
material/may accumulate as a relatively straight lower angled scree slope.
Mud flows Heavy rain causes fine material to move downhill.
Rotational slip/slumping Slides may be linear with movement along straight line slip plane, e.g. fault
, or bedding plane b/n layers of rock, or rotational - movement taking place
along curved slip plane. Slides occur due to undercutting by wave erosion at
base of cliff - removes support for materials above.
Rotational slides known as slumps. Common in weak rocks e.g. clay, which
also become heavier when wet, adding to downslope force.
Soil creep Very slow movement of soil particles down slope.
PROCESSES OF WAVE EROSION IN COASTAL ENVIRONMENTS:
Name of process Description
Hydraulic action Waves break against cliff face, air and water trapped in cracks and crevices
become compressed. Wave recedes, pressure released, air and water expand,
crack widened.
Wave pounding Occurs when mass of breaking wave exerts pressure on rock = weaken.
Abrasion Sand, shingle and boulders picked up by sea and hurled against cliff.
Attrition Wearing down of rocks and pebbles - rub against each other = smaller and
rounder, = sand.
Solution Fresh water mixes with salt water, acidity may increase and carbon-based
rocks will be broken down.
PROCESSES OF TRANSPORTATION BY WAVES IN COASTAL ENVIRONMENTS:
Name of process Description
Traction Large boulders rolled along sea bed
Saltation Small stones bounce along sea bed
Suspension Very small particles carried by currents – accounts for brown/muddy
appearance of some sea water. Larger particles also carried in this way – e.g.
storm events
Solution Minerals dissolved into mass of moving water – invisible and minerals remain
in solution until water is evaporated and they precipitate out of solution.
Longshore drift Waves approach shore at angle; swash moves material up beach in same
direction as wave; backwash moves material back down the steepest gradient
– usually perpendicular to where it is picked up by next incoming wave.
Deposition occurs when velocity and/or volume of water decreases , energy reduced. Takes place in
coastal environments when:
- Sediment accumulation exceeds removal
- Waves slow after breaking
- Backwash water percolates into beach material
- There is a sheltered area such as an estuary
Fluvial processes:
- Sig in estuarine environments. Fluvial erosion, weathering and mass movement processes supply
sediment to river channels. Transported downstream and deposited as rivers enter sea.
- Mud flats and salt marshes are landforms that form in sheltered low-energy coastlines.
Associated with large tidal ranges where powerful currents transport large quantities of fine
sediment.
Alluvial processes:
Formation of erosional
- Coastal landforms:
landscapes are sig influenced by winds.
- Wind
Headlands andpicks
bays:up sand particles and moves them = deflation.
- Attrition on land by windblown particles also effective over long distances. When wind speed falls,
- Form adjacent
material carriedtobyeach
the other –presence
wind will of bands of rock, have differing resistance to erosion.
be deposited.
- Rock outcrops lie perpendicular to coastline = weaker rocks eroded more easily + rapidly = bays.
More resistant rocks remain b/n bays as headlands. Results in formation of discordant coastline.
- E.g. Isle of Purbeck in Dorset - consists of alternating bands of limestone and chalk (more
resistant), and clay, (less resistant). Swanage Bay made up of clay, 2.5km wide; Durlston Head,
made up of limestone, 5+km wide
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