What Determines the Type and Rate of Weathering that Occurs in an Area? 

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Just as new rocks are constantly being created by the different processes in the rock cycle, rocks at Earths surface are constantly being weathered away.  Every single rock you will ever see is in fact being worn away right before your eyes, both through chemical and mechanical weathering.  We can't see this happen because it takes a REALLY REALLY long time, but the exact rate of weathering depends on several factors. 

Factors Effecting the Rate of Weathering 

  Rock Type and Composition

All rocks are made from different minerals.  Different minerals also have different hardnesses.  ROCKS THAT ARE MADE FROM EXTREMELY HARD MINERALS ARE ABLE TO WITHSTAND WEATHERING FORCES LONGER THAN THOSE MADE FROM SOFT MINERALS.

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In the diagram above we see several layers of sedimentary rocks exposed to the atmosphere.  Each of them has been weathered to a certain extent, but if you look closely you will see that the Shale layer (B) has been weathered much more.  This is because shale is made from silt which is a very small and soft sediment, and a very brittle rock.

Amount of Surface Area Exposed  

All rocks weather because they are exposed to oxygen and water in the Earth's atmosphere.  Any part of the rock that is exposed is therefore weathering.  THE MORE SURFACE AREA A ROCK HAS EXPOSED TO THE AIR, THE FASTER IT WILL WEATHER.

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Because weathering makes rocks crack and break, as rocks weather their surface area increases.  So as a rock weathers and cracks, it starts to weather at a faster and faster rate. 

 

Which Will Occur, Mechanical or Chemical Weathering?

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All rock's on Earth's surface are constantly breaking apart because of both Chemical and Mechanical weathering.  However, different climates on Earth favor different types of weathering.

Cold and Wet Climates

COLD WET CLIMATES FAVOR MECHANICAL WEATHERING.

 This is because the cold temperature and presence of water create the perfect conditions for Ice Wedging to occur.

 

Warm and Wet Climates

HOT AND HUMID CLIMATES FAVOR CHEMICAL WEATHERING

.  This is because the hot temperature and the presence of water create the perfect conditions for Hydrolysis and Oxidation to occur. 

 

Dry Climates

Because there is very little water in dry climates, weathering of either type happens very slowly.