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How Do Rocks Weather?

written by: Mary Rajotte • edited by: Kellie Hayden • updated: 1/4/2012

Weathering is the name of the process which breaks down the Earth’s rocks. This article will explore the various factors which can impact the environment and lend themselves to rock weathering.

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    The process of rock weathering occurs when outside influences cause rocks to disintegrate.  Physical, chemical and biological processes play an integral part in the process of rock weathering, each affecting rocks in different ways.

    Weathering occurs differently based on the type of rock and the environmental conditions which the rocks are exposed to.

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    Physical Weathering

    freezethaw Physical weathering, also known as Mechanical Weathering, is a physical action which breaks up rocks.

    Some ways that mechanical weathering occurs is through:

    • Abrasion: when opposing rock surfaces come together and wearing or grinding breaks them down; also when particles moved by air, water and ice wear away rock
    • Crystallization: when ground water is drawn up into rocks, the water evaporates leaving salts behind, which creates stress and weakens the rock until it breaks
    • Frost Action/Freeze Thaw: when water gets into the cracks within rocks, freezes and expands. When this happens repeatedly, the crack in the rocks can grow, which can cause parts of the rock to break off along the cracks.

    Photo: Till Niermann

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    Chemical Weathering

    chemical weathering 

    Chemical weathering occurs when acids and other chemicals in the environment cause rocks to break down.

    The rate of weathering can differ greatly depending on how strong the chemicals are and the structure of the rocks themselves.

    A common display of the end result of chemical weathering is the formation of underground caves. When carbon dioxide reacts with water, it creates carbonic acid, which can attack rocks. When water containing this acid travels trough limestone, the stone is dissolved away, leaving empty pockets or caves behind.

    Photo: Mahlum

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    Biological Weathering

    bioweathering Biological weathering occurs when various bacteria, plants and animals beak down rocks. Various chemical or biological agents can break down rocks.

    Some examples of this type of weathering are:

    • Animals: when animals eat or burrowing in the soil
    • Trees & Plants: roots can find their way into cracks in rocks. As they grow, the roots create pressure on the rocks, causing pieces to split off and erode the rock. The shade and roots from trees can also create an increase of water in soil, which lends itself to physical and chemical weathering processes
    • Bacteria: algae and bacteria can break down the rocks, leeching them of their nutrients and causing them to weather

    Photo: Nigel Chadwick

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    Final Thoughts

    While rock weathering may seem like a destructive action, it is an important aspect to the geology of our world. Minerals from a wide variety of rocks can provide essential nutrients in soil, and a fertile soil is essential to sustaining our plants, trees and other flora that make an impact on our daily lives.

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    Sources

    • Chemical Weathering - Buzzle.com
    • Science Encyclopedia
    • The Encyclopedia of Earth

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