logo(1).gif (11000 bytes)A More Revealing Facts of the Earth
Home Up Type of Rocks Physical Weathering Chemical Weathering Factors

 

 

Weathering is the process by which rocks are gradually broken down in situ.

Erosion is the breaking down of  rocks  and being removed by weathering agents e.g. water and winds.

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PHYSICAL WEATHERING

Physical weathering is more effective in areas which have :

~     a little vegetation

~    a large diurnal range of temperature or

~    temperatures fluctuating around 0 degrees Celsius

  Pressure Release             

It takes place when the overlying rocks are removed by erosion. With the release of pressure, the rock expands. causing stress within the rock. Cracks are formed parallel to the rock surface. Over a period of time, the outer layers of the rock break away in sheets.

Exfoliation  

It occurs in places like hot deserts where the day temperature often soars to 40 degrees Celsius and night temperature falls to below 10 degrees Celsius. The repeated heating by day and cooling by night cause the outer layers of the rock to expand and contract alternately. Stress is created in the rock, producing cracks and gradually, the outer layers of rock will peel off.

Frost Shattering                                                                                                      

It occurs in cold temperate regions and mountain tops where temperatures fluctuate above and below freezing point. Water fills the cracks or joints in the rock and freezes at night or during winter. Repeated freeze- thaw will eventually shatter the rock along the cracks or joints into angular pieces. The broken materials collect at the foot of the slope to form a scree.

  Crystallization                                

or weathering by growth of salt crystals takes place in deserts where evaporation draws ground water containing dissolved salts upwards into the pores of the rock. When the water evaporates , the salts are left behind as crystals. The build-up of the salt crystals creates stress in the rock, weakens it and breaks it down into grains.

Biological Weathering                                            

roots growing into the cracks and joints in rocks                                                                
earthworms and termites making tunnels in the ground                                                        
man building roads and cultivating the land , exposing the rocks to other agents of weathering.

 

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