Mechanical Weathering:
• Freeze thaw = Water expands in rocks by 10% when frozen. Pressure causes splits.
• Pressure release = Underlying rock fractures parallel to surface as it expands when
overlying rock is removed.
• Thermal expansion = Rocks expand when heated and contract when cooled. Outer
surface cracks and flake off.
• Salt Crystallisation = Salt solutions seep into pores where it precipitates (sodium
carbonate increases by 300%). Stress in rocks leads to breaking.
Chemical Weathering:
• Oxidation = Some minerals react with oxygen.
• Carbonation = Rainwater and CO2 form a weak carbonic acid that reacts with
carbonate rocks.
• Solution = Any process where minerals dissolve with water.
• Hydrolysis = Chemical reaction of rock minerals with water.
• Hydration = Water molecules and rock minerals create a larger volume causing
surface flaking.
Biological Weathering:
• Tree roots = grow into cracks and exert outward pressure causing cracking. Trees can
also topple and exert leverage on rocks.
• Organic acids = Produced during decomposition of plant and animal litter which
increase soil acidity and react with minerals in chelation.
Mass Movement:
Movement of regolith (loose layer of rocky material overlying bedrock) down a slope.
• Landslides = Cliffs made of softer rocks slip when lubricated by rainfall
• Rockfalls = Rocks undercut by the sea/sloped affected by mechanical weathering.
• Mudflows = Heavy rain causes fine material to move.
• Rotational slip/slumping = Where soft material overlies resistant material and
excessive lubrication takes place.
• Soil creep = Very slow movement of soil particles down a slope.
Wave erosion:
• Hydraulic action = Waves push air in to cracks and as pressure releases it widens and
expands.
• Pounding = Breaking wave exerts pressure on rock.
• Abrasion = Waves carry rocks which scour the coast.
• Attrition = Rocks collide to become smooth and round.
• Solution = Where fresh water mixes with salt water acidity may increase and carbonbased rocks broken down.
Wave transportation:
• Traction = Large boulders roll along sea bed.
• Saltation = Small stones bounce along seabed.
• Suspension = Very small particles carried in moving water.
• Solution = Minerals dissolved in water.
Deposition occurs at settling velocity when energy reduces. Takes place when sediment
accumulation exceeds removal, waves slow after breaking, backwash percolates into beach
material and in sheltered areas (estuaries)
Once deposited, longshore drift moves sediment along shoreline.
Fluvial Processes:
Significant in estuarine environments. Erosion, weathering and mass movement supply
sediment to river channels which is transported downstream and sequentially deposited.
Flocculation of clay also occurs when fresh and salt water mix.
Aeolian Processes:
Winds pick up sand particles and move them in deflation. Land attrition by windblown
particles occurs over long distances. As wind speed falls (usually due to surface friction)
material is deposited.