Mechanical Weathering

• Breaks down rocks into smaller pieces
• Nothing created or destroyed
• Mineral Composition is the same

Mechanical Weathering

• Called Physical Weathering
• Occurs faster in cold climates

Types

• Ice Wedging
• Exfoliation
• Thermal Expansion

Ice Wedging

• Water is trapped in cracks
• Cold weather causes it to freeze

Ice Wedging

• when frozen, it expands and pushes the cracks farther apart until the rock breaks

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Exfoliation

• Rocks pieces peel off in thin layers on individual boulders, or in thick slabs

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Thermal Expansion

• heating and cooling due to climate changes causes minerals to expand and contract, which can cause fractures in the rock

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Biological Weathering

• caused by biotic factors
• animals burrowing
• plant roots
• bacteria, lichens, animal feces that secreting acid

Biological Mechanical Weathering

• Plant Growth – plants send out root systems, roots find way into cracks . As the roots increase in size, they force rock sections apart.

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Animal Mechanical Weathering

• Animals can cause wedging between cracks
• Burrowing, foraging and den-making activities can also cause rocks to become exposed

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Chemical Weathering

• the process that breaks down rock through chemical changes and produces rock particles that have a different mineral makeup from the rock they came from.

Chemical Weathering

• occurs faster in warm, moist climates
• water is a major agent/factor
• Not all minerals can be chemical weathered!

Types of Chemical Weathering

• dissolving (dissolution)
• oxidation
• hydrolysis

Dissolving (Dissolution)

• Water, containing acid from dissolved carbon dioxide, dissolves minerals from a rock body leaving cavities in the rock.
• Create sinkholes or cave features such as stalactites and stalagmites.

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Acid Rain

Oxidation (Rust)

• Minerals combine with oxygen to form new minerals that are not as hard.
• For example, the iron-containing mineral pyrite forms a rusty-colored mineral called limonite

Hydrolysis

• Minerals may chemically combine with water to form new minerals.
• new minerals are softer

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