Weathering

What is Weathering?

Weathering is the breakdown and disintergration of rocks in situ where they stand.

There are 3 types of weathering: Phyiscal, chemical and biological 

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Physical Weathering

Physical weathering or also called mechanical weathering is the breakdown and disintergration of rocks by:- heat, pressure and impact. It is common where temperature range is greatest e.g the poles, deserts and mountains.

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Mechanical Weathering Processes

Pressure Release: When rocks are formed deep in the earth's crust, the pressure is high. As this pressure is released when they are at or near the surface, the rocks begin to expand. Cracks and fractures occur as "pressure is released". If a rock has no natural joints or bedding planes, these cracks and fracture may be more obvious.

Exfoliation: Different minerals in rocks will have varying rates of expansion and contraction so when temps have a great range the expansion/contraction will produce stresses. It creates "oinion skin" weathering or exfoliation.

Frost Shattering: Water expands by 9% when it freezes so pressure is exerted on rocks when temperatures fall and water is in the crevices/joints. Angular fragments of rocks are produced as the rock is "shattered" during this process.

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Chemical Weathering

Hydrolysis: Water and the minerals in rocks react, especially feldspars and the silicate minerals. If the watercontains carbonic acid then the hydogen ions in H20 and the carbonic acid react and produce minerals such as clay, carbonates and bicarbonatesin solution and they are washed away.

Carbonation: Limestone is the rock most affected by this. The equation is: CaCo3+H2CO3=Ca2++2HCO3

Calcite+Carbonic Acid= Calcium+ Hydrogen Carbonate ions in solution

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Biological Weathering

Burrowing: Lots of animals burrow for example mammals, worms and insects. When the burrow is created, rock debris come to the surface and is weathered more.

Root Action: Roots from plants and trees force their way through rocks for example bedding planes and into crevices. Water can then penetrate and chemical weathering occurs. Also continutes growth prises the crevice apart and makes it bigger

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