Weathering is important in sediment production and rates of recession

examples of mechanical weathering

• freeze thaw

• Salt crystallisation

• Wetting and drying

What is freeze-thaw?

• water enters a joint/fault

• Water freezes and expands

• This exerts pressure on the rock and widens the crack until it breaks off

What is salt crystallisation?

• water enters a fault/joint at high tide

• Rock dries at low tide and water evaporates leaving salt crystals that grow over time

• This creates pressure as they grow overtime until chunks of rock break off

What is wetting and drying?

• clay in rock expands when wet and contracts when dry

• This repeating wetting and drying causes cracks and breaks down the rock

Biological weathering

• vegetation and coastal organisms

• Thin roots grow into cracks in the cliff face and break off rock when they grow

• Birds and animals burrow in the cliff

• Some marine organisms burrow and secrete acid that promotes solution e.g. limpets

What are examples of chemical weathering ?

• carbonation

• Oxidation

• Solution

What is carbonation?

• rainwater absorbs CO2 and forms a weak carbonic acid

• This reacts with carbonate rocks e.g. chalk and limestone and becomes easier to dissolve

• More effective in cooler temps

What is oxidation?

• minerals in rock react with oxygen in water

• This causes iron rich rocks to disintegrate

What is solution?

• rocks dissolving in saline water e.g. halite

How does temperate + precipitation influence weathering?

• mechanical dominates in cold

• Chemical dominates in wet + warm

• Lithology means some rocks are prone to certain types of weathering

E.g. basalt 1-2mm every 1000 years in cold