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  • Created by: Qiao-Chu
  • Created on: 16-04-13 20:17

What is Weathering?

Disintegration or decay of rocks in their original place at or close to ground surface. Largely caused by elements of weather such as rainfall or changes in temperature. Affects natural outcrops of rock as well as manmade structures causing small pits, flaking and discolouration.

Mechanical - aka physical, disintegration of rocks without change in chemicals, results in angular rock fragments called scree found at foot of bare rocky outcrops.

Chemical - chemical change occurs, slightly acidic rainwater dissolves certain rocks and minerals, those unaffected left behind to form clay deposit.

Biological - actions of flora and fauna, plant roots effective at growing and expanding in cracks in rocks, rabbits effective in burrowing into weak rocks like sand.

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Freeze-thaw/Frost Shattering

Action of water freezing and thawing in crack or hole in rock. Coomon process, occurs wherever plenty of water and fluctutating temperatures above and below freezing.

Liquid water collects in pores, at night water freezes and expands approximately 9%. Water is in confined space so expansion creates stress on rock, widening existing gaps. When temperature rises, water thaws and water seeps deeper into rock through new cracks. Repeated cycles of freezing and thawing, fragments of rock detach and fall to foot of slope as scree.

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Exfoliation/Onion Skin

Most commonly associated with fluctuations in temperature, hot deserts. Rock poor conductor of heat so only outer part of rock warms up and cools in response to temperature change. As it warms during day, it expands, and contracts at night because cooler. 

Repeated cycles lead to outer skin peeling from rock, presence of water makes exfoliation faster as weakens rock, more vulnerable to flaking.

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Minerals and rocks dissolving in rainwater. Rock salt is sedimentary rock formed under desert conditions from accumulation of salt crystals on dried lake bed. Rock salt deposits found in Cheshire, extracted and used as de-icer in winter on roads and pavements. Just like table salt, rock salt dissolves in water so more vulnerable to weathering process of solution.

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Similar to solution as dissolving involved. Affects rocks made up of calcium carbonate CaCO3 such as limestone and chalk. 

Responsible for forming some landforms associated with limestone.

Rainwater picks up CO2 from air, becomes weak carbonic acid, reacts with calcium carbonate to form calcium bicarbonate, dissolves.

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