Weathering Processes:
Weathering = the breaking down of rocks caused by weather conditions , in situ
○ Caused by day to day changes in atmosphere
■ eg/ extremes of temperature or precipitation
Chemical weathering:
● Chemical weathering = caused by chemical reactions when rainwater hits rock and decomposes it
○ Carbonation → carbonic acid in rainwater reacts with calcium carbonate in limestone
■ Forms calcium bicarbonate
■ Calcium bicarbonate is soluble → limestone is carried away in solution
○ Hydrolysis → acidic rainwater breaks down rock and causes it to rot
○ Oxidation → rocks are broken down by oxygen and water
Mechanical/physical weathering:
● Mechanical weathering = disintegrates rocks rather than decomposing
● Is associated with extremes of temperature
○ Freeze-thaw weathering
1. Water enters cracks
2. Night temperatures fall below freezing → freezes water
○ Water volume increases by 9%
○ Puts pressure on area around rock
3. Daytime temperature rises above freezing → ice thaws and relieves pressure
4. Constant repetition causes angular rock fragments to break away and collect as scree at
base of cliff
○ Salt weathering
1. Salt spray from sea gets into cracks in rock
2. May evaporate and crystallise → puts pressure on surrounding rock / weakens structure
Transportation Processes:
● Load = transport of material by waves
○ Load varies from fine silt to large rocks
○ Larger and heavier load particles need greater velocity to transport it
● Marine erosion = removal of material by waves
○ Most marine load originates from river deposits, eroded headlands and sea bed
Transport processes:
● Solution → minerals are dissolved in water
○ Load transported in this way is called solute load
● Suspension → fine, light material is held up and carried with the river’s flow ; is called suspension load
● Saltation → small pebbles/stones are bounced along riverbed
○ Load is alternately lifted and dropped in line
○ There is a local rise and fall in velocity of the water
● Traction → large boulders/rocks are rolled over along the river bed , is called bedload
Longshore drift:
● Longshore drift = movement of load along the shore
○ Process:
1. Direction is determined by prevailing wind
○ Prevailing wind = a wind from the direction that is predominant
2. Causes swash to surge up at the beach at an oblique angle
○ Moves material towards the beach
3. In response to gravity → backwash goes down at 90° to the shore
○ Moves material back, away from the beach
4. Suspended load is transported along the coastline in a zigzag manner
Conditions needed for deposition
● Deposition = when waves drop and leave behind load they were transporting
○ Sediment = deposited load
● Deposition results in more sediment staying on the beach than is taken away by backwash
○ Deposition takes place in:
■ Low-energy, sheltered bays → constructive waves dominant
■ Areas with a large source of sediment updrift (eg/ an eroding headland)
■ Large expanses of flat beach → causes waves to lose energy and drop load
■ Areas where tidal material is trapped behind a spit
■ Where engineered structures trap sediment (eg/ groynes)