Weathering

Weathering - the decay and disintergration of rocks in situ.      (Does not transport material away)

Physical weathering - disintergration of rock (broken)

Chemical weathering - decomposition of rock (changed)

Biological weathering 

PROCESS Physical

• Water trickles into rock during day and freezes during night

• Expands and widens by 10%

• Repetition results in scree and felsenmeer

• Scree  = angular rock fragments, falling from a cliff and being deposited as a cone or fan shape

FACTORS

• Not active in winter where there's constant frost

• Shape and size dependant on nature of rock (direction and angle of cracks)

Critical feature : number of freeze-thaw cycles rather than intensity of frost.

PROCESS                                                                                                             Physical 

• Expansion (day)  and contraction (night) of rocks in deserts

• Granular : Mineral grains produced create a sand sea (ergs)

• Block : rock fragments result in stony desert (reg)

FACTORS

• Hot temperature, desert

• Different minerals

• Different axes of crystal

• Different sizes

• Colouring of rock - pale colours emit and absorb more heat than a darker colour

PROCESS                                                                                                                     Physical

• Salt solutions in pores or joints of rock crystalise

• Crystal expands, forcing rock apart

FACTORS

• Most effective : sodium sulfate, magnesium sulfate, calcium chloride,

• Temp around 27oC where fluctuations produce expansion rate up to 300%

PROCESS                                                                                                                physical

• Removes weight from previously buried rocks (very deep)

• Leads to expansion of upper parts of the rock, allowing cracks to occur parallel to ground surface  (pseudo-bedding planes)

• Horizontal pressure released by rock falling off cliffs allow cracks to grow vertically

FACTORS

• Horizontal pressure significant after glaciation caused by quarrying

• Areas where ground surface is lowered by erosion

PROCESS                                                                                                         Chemical

• Minerals broken down by a reaction including water

• Can include some carbonation

• Produces a clay residue and various other solutions, removed in groundwater

FACTORS

• Important in the silicate minerals that form most rocks

• Acid conditions

• Encouraged by decaying vegetation

• Carbonation encouraged by carbon dioxide from plants

PROCESS                                                                                                           Chemical 

• Wetting and drying

• Addition or removal of water causes expansion or contraction which assists disintegration

• Anhydrite and Gypsum affected

FACTORs

• If water is applied or removed from the rock

PROCESS                                                                                                              Chemical

• Weak carbonic acid which is in rainwater forms as the water absorbs carbon dioxide in the atmosphere

• Carbonic acid attacks carbonate minerals in limestone

• Calcium hydrogen removed and washed away down river, muddy insoluble impurities left as cley residue

• Process is responsible for limestone scenery characteristics (karst)

FACTORS

• Accelerated by pollutants such as sulfur dioxide and oxides of nitrogen

PROCESS                                                                                                                     biological

• Physical effect on rocks

• Seeds and roots in shallow soil find their way into cracks in bedrock

• As seeds germinate and roots grow, the cracks widen and deepen, eventually breaking bedrock

Biological weathering that assists chemical processes

• Humanic acids from decaying vegetation encourage hydrolysis

• Carbon dioxide from plants encourages carbonation

• Vegetation traps water, encouraging variety of chemical processes