What are sub-aerial processes? Use this Power Point to make notes about the different types of weathering & mass movement

What are sub-aerial processes? The coast is the narrow zone between the land and the sea. It is worth remembering that the landscape will be influenced by processes on the land as well as the sea. Sub-aerial processes include weathering and mass movement. These processes operate on the cliff face to weaken it and provide material for coastal erosion.

What is weathering?

Biological weathering What has caused the cracks to appear?

How do you think these rocks have become weathered? Chemical weathering How do you think these rocks have become weathered?

Can you explain… Colin forgot to chill the wine so he put it in the freezer to quickly make it cold – but then forgot it was there! Next time he went to the freezer he found it totally shattered. Explain what has happened. The water expanded as it froze, creating huge forces. These shattered the glass bottle.

What are the different types of weathering?

Mechanical weathering Freeze thaw Daily temperatures fluctuate around 0oC Ice occupies 9% more volume Freeze-thaw process widens joints

Mechanical weathering Thermal Expansion or Insolation Outer layers of rock warm faster and cool more rapidly Outer layers peel like an onion (onion skin weathering)

Mechanical weathering Pressure release Rocks developed under great pressure. Later exposure releases pressure and exposure to atmosphere. Cracks develop and sheeting occurs

Mechanical weathering Salt crystallisation Slightly saline water enters pore spaces Evaporation leaves salt crystals which exert stresses on the rock This leads to granular disintegration Sodium sulphate & sodium carbonate expand 300% in temperatures ranging 26-28oC

Biological Weathering Tree roots - Biological weathering Significant on cliff tops and cliff faces. Plant / tree roots expand along joints and bedding planes Blocks of rock become detached Burrowing animals have similar effect.

Biological Weathering Organic acids Decomposition of plant and animal litter = reaction with some minerals = chelation. E.g.s: Blue-green algae = shiny film of iron & manganese oxides on rock Molluscs secrete acids = hollows on rock surface.

Chemical weathering Oxidation Rocks exposed to oxygen causes rocks to crumble E.g. Iron in a ferrous state is changed by oxygen in to a ferric state. Rocks change colour from a blue grey to a reddish brown

Chemical weathering Hydration Rocks capable of absorbing water E.g. water added to anhydrite, gypsum results Active following periods of wet and dry weather Also classed as a physiochemical process – that is, they swell and exert pressure as well as change chemical structure

Chemical weathering Hydrolysis Hydrogen in water reacts with minerals = Silicates combine with water = clays E.g. Breakdown of feldspar (mineral in granite - igneous rock) to kaolin (china clay)

Chemical weathering Carbonation Rainwater contains carbon dioxide, which produces carbonic acid. Dissolves limestone in to solution (calcium bicarbonate (soluble)).

Chemical weathering Solution Minerals which are soluble dissolve, with increasing acidity in the water

Chemical weathering Rate of chemical weathering increases with temperature – 10oC increase in temperature = 2.5 times increase in chemical reaction rate. Climate change & Human activity increasing carbon dioxide, sulphur dioxide and nitrogen oxide = e.g. increased acidity in rainfall = e.g. increases rate of carbonation of limestone

What is mass movement?

What are the different types of mass movement? Click for clip