What is weathering?

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

What has caused the cracks to appear?Biological weathering

How do you think these rocks have become weathered?Chemical weatheringCan 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 weatheringFrost shatteringDaily temperatures fluctuate around 0oCIce occupies 9% more volumeFreeze-thaw process widens joints

Mechanical weatheringExfoliationOuter layers of rock warm faster and cool more rapidlyOuter layers peel like an onion (onion skin weathering)

Mechanical weatheringPressure releaseRocks developed under great pressure.Later exposure releases pressure and exposure to atmosphere.Cracks develop and sheeting occursMechanical weatheringSalt crystallisationSlightly saline water enters pore spacesEvaporation leaves salt crystals which exert stresses on the rockThis leads to granular disintegration

Biological WeatheringBiological weatheringPlant / tree roots expand along joints and bedding planesBlocks of rock become detached

Chemical weatheringOxidationRocks exposed to oxygen causes rocks to crumbleE.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 weatheringHydrationRocks capable of absorbing waterE.g. water added to anhydrite, gypsum resultsActive following periods of wet and dry weatherAlso classed as a physiochemical process that is, they swell and exert pressure as well as change chemical structure

Chemical weatheringHydrolysisHydrogen in water reacts with mineralsE.g. Breakdown of feldspar (mineral in igneous rock) to graniteChemical weatheringCarbonationRainwater contains carbon dioxide, which produces carbonic acid.Dissolves limestone in to solution (calcium bicarbonate (soluble)).

Chemical weatheringSolutionMinerals which are soluble dissolve, with increasing acidity in the water

Chemical weatheringAcid rainHuman activity increasing carbon dioxide, sulphur dioxide and nitrogen oxideIncreases rate of carbonation of limestoneWhat is mass movement?What are the different types of mass movement?

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