Chapter 9 Section 2
Differential Weathering
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Hard rocks, such as granite, weather more slowly than softer rocks, such as limestone.
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Differential weathering is the process by which softer, less weather-resistant rocks wear away and leave
harder, more weather-resistant rocks behind.
The Surface Area of Rocks
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The greater the proportion of a rock that is exposed to weathering, the faster the rock will wear down.
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A large rock has a large surface area that is exposed to weathering.
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But a large rock also has a large volume.
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Most of this volume is in the interior of the rock, protected from weathering agents.
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If the large rock is broken into smaller pieces, the rate of weathering increases.
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This is because the surface-to-volume ratio increases, and more surface area is exposed to weathering
agents.
Weathering and Climate
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Climate is the average weather conditions of an area over a long period of time.
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Temperature and moisture affect rates of chemical and mechanical weathering.
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More chemical reactions occur in climates that have higher temperatures.
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Climatic regions that experience many thaws and freezes have a greater rate of mechanical weathering.
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The rate of chemical reactions, such as oxidation, may increase in wet climates.
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Ice wedging and abrasion are also more common in wet climates.
Other Factors that Affect Weathering
Elevation
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Rocks at higher elevations are exposed to high winds and temperature extremes.
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They may also be exposed to large amounts of precipitation.
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These processes at high elevation can cause rapid weathering.
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However, rocks at sea level may also experience rapid weathering, through wave action.
Slope
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The steep sides of mountains and hills increase the speed of water running downhill.
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Water that flows more rapidly has more energy to break down rock.
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Thus, rocks on steeper slopes experience increased weathering.
Biological Factors
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Organisms in the soil, such as bacteria or fungi, can produce acids that can speed chemical weathering.
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The activities of burrowing animals and plant roots also speed mechanical weathering.