Topic Physical and Chemical Weathering. Weathering vs. Erosion Weathering--Erosion--
Weathering, Erosion and Soil Formation
description
Transcript of Weathering, Erosion and Soil Formation
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Weathering, Erosion and Soil Formation
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What is weathering?
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Weathering is the process by which rock materials are broken down
Mechanical Weathering• The breakdown of rock
into smaller pieces by using physical forces.• Agents:
• Ice• Abrasion• Wind • Water • Gravity
• Plants• Animals
Chemical Weathering• The process by which
rocks break down as a result of chemical reactions.• Agents:
• Water• Weak acids• Air
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ICE
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ICE• 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.
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Abrasion• 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
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Water• 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
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Wind• 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
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Gravity• Abrasion also
happens when rocks fall on one another.• Rocks grind against
each other as they tumble, creating smaller and smaller rocks.
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Plants• 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!
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Animals• 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.
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Review• 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
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Chemical Weathering• The process by which
rocks break down as a result of chemical reactions is called chemical weathering.• Common agents• Water• Weak acids• Air
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Water• 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
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Acid• Acid can chemically
weather rocks in different ways
• Acid precipitation• Acids in groundwater• Acids in living things
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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
CausesVolcanoesAir pollution (burning fossil fuels)
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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
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Acids in living things• Lichens, which
consist of fungi and algae living together, produce acids that slowly break down rock.
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Air• 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