Weathering erosion and soil formation
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Weathering, Erosion and Soil Formation. What is weathering?. Weathering is the process by which rock materials are broken down. Mechanical Weathering. Chemical Weathering. The process by which rocks break down as a result of chemical reactions. Agents: Water Weak acids Air.

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Weathering, Erosion and Soil Formation

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Weathering, Erosion and Soil Formation

What is weathering?

Weathering is the process by which rock materials are broken down

Mechanical Weathering

Chemical Weathering

The process by which rocks break down as a result of chemical reactions.



Weak acids


  • The breakdown of rock into smaller pieces by using physical forces.

  • Agents:

  • Ice

  • Water

  • Wind

  • Gravity

  • Plants

  • Animals


  • Frost Action: the alternate freezing and thawing of soil and rock.

  • Ice wedging: when water seeps into cracks during warm weather, then freezes and expands during cold weather.

  • The ice pushes against the sides of the crack, causing the crack to widen.


  • Abrasion is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

  • There are three forms of abrasive weathering:

  • Water

  • Wind

  • Gravity


  • Water is the most powerful agent of mechanical weathering.

  • When rocks and pebbles roll along the bottom of a swiftly flowing bodies of water, they bump and scrape each other.

  • These rocks/pebbles eventually become smaller, rounder, smoother as a result of this friction


  • When wind blows sand and silt against exposed rock, the sand will wear away the rock’s surface.

  • These rocks have been shaped by blowing sand.

  • These rocks are called ventrifacts


  • Abrasion also happens when rocks fall on one another.

  • Rocks grind against each other as they tumble, creating smaller and smaller rocks.


  • Plants often send their roots into to an existing crack in a rock.

  • As the plant grows, the expanding root becomes so strong that the crack widens and the rock splits!


  • Animals can cause a lot of weathering!

    • Burrowing

      • worms

      • Ants

      • Mice

      • Coyotes

      • rabbits

    • Burrowing moves soil and exposes fresh surfaces to weathering

    • Some types of tropical worms can move an estimated 100 metric tons of soil per acre in a year.


  • Name three things that can cause abrasion

  • Wind

  • Water

  • Gravity

  • What is the most powerful agent of weathering?

  • Water

  • Describe the similarity of how ice and tree roots mechanically weather rock

  • Both ice and tree roots can force cracks in rocks to expand

Chemical Weathering

  • The process by which rocks break down as a result of chemicalreactions is called chemical weathering.

    • Common agents

      • Water

      • Weak acids

      • Air


  • Over thousands of years, water can dissolve even the hardest rocks

  • Usually it is by way of rain, sleet or snow with a high acid content


  • Acid can chemically weather rocks in different ways

  • Acid precipitation

  • Acids in groundwater

  • Acids in living things

Acid precipitation

  • Rain, sleet or snow that that contains a high concentration of acids is called acid precipitation.

  • All precipitation is naturally acidic, but acid precipitation has higher levels of acid.

  • This higher level of acidity can lead to very rapid weathering

  • Causes:

  • Volcanoes

  • Air pollution (burning fossil fuels)

Acids in groundwater

  • Some acids, such as carbonic and sulfuric acids occur naturally in groundwater.

  • If these acids come in contact with certain rocks, such as limestone, a chemical reaction occurs.

  • Over a long period of time, the limestone dissolves, forming caverns

  • Stalactites

  • Stalagmites

Acids in living things

  • Lichens, which consist of fungi and algae living together, produce acids that slowly break down rock.


  • Oxygen in the air reacts with elements, such as iron, to chemically weather objects

  • Called oxidation

  • Water is not necessary, but speeds up the process

  • RUST

Mechanical vs. Chemical Weathering

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