Define hydraulic action
Hydraulic action occurs when waves break against a cliff face, and air and water trapped in cracks become compressed. As the wave recedes the pressure is released, the air and water suddenly expands and the crack is widened
Define pounding
Pounding occurs when the mass of a breaking wave exerts pressure on the rock causing it to weaken
Define solution
Solution involves dissolving minerals (e.g magnesium carbonate minerals) in coastal rock. Only effective if water is polluted and acidic and in rocks containing significant amounts of soluble minerals
Define saltation
Saltation: series of irregular movements of material which is too heavy to carry continuously in suspension. Turbulent flow may enable sand-sized particles to be picked up (entrained) for a short distance only to be dropped back down
What is mass movement?
The downhill movement of sediment that moves because of gravity
define regolith
a loose layer of rocky material overlying bedrock
Mass movement - slips - what is linear slips?
linear - movement along a straight line slip plane e.g fault or bedding plane between layers of rock
Mass movement - slips - what is rotational slips?
rotational - movement along a curved slip plane (aka slumping)
What often causes slides?
Slides occur due to undercutting by wave erosion at the base of the cliff = removes support for the materials above
Why are slumps common in weak rocks e.g clay?
Slumps are common in weak rocks such as clay because it can become heavier when it gets wet, adding to the downslope force
What is pressure release?
- overlying rocks removed
- underlying rocks expands and fractures parallel to surface
- parallel fractures called pseudo-bedding planes
What is thermal expansion?
- rocks expand when heated
- rocks contract when cooled
- frequent cycles of temperature change = outer layers crack and flake off
What is salt crystallisation?
- salts seep into pores of rocks
- salts precipitate, forming crystals
- crystals grow = creates stress on rock
- rock disintegrates
e.g sodium sulphate expands by 300%
What is oxidation?
- minerals react with oxygen (in air or water)
- becomes soluble under acidic conditions
- original structure destroyed
e.g attacks iron -rich cements that bind sand grains together in sandstone
What is hydration?(chemical weathering)
- water molecules added to rock minerals creates new minerals of larger volume
- e.g anhydrite absorbs water to form gypsum
- causes surface flaking in rocks
- because minerals expand by 0.5% as they absorb water
What is organic acids (bio weathering)?
- organic acids produced during decomposition of plant/animal litter
- causes soil water to become acidic and react with minerals (process called chelation)
