Weathering and Erosion Natures way of tearing down everything that has been built up over billions...
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![Page 1: Weathering and Erosion Natures way of tearing down everything that has been built up over billions of years.](https://reader035.fdocuments.in/reader035/viewer/2022062517/56649f395503460f94c55920/html5/thumbnails/1.jpg)
Weathering and Erosion
Natures way of tearing down everything that has been built up
over billions of years.
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What is mechanical weathering?
Objective- explain the ways that Earth’s surface is worn away by mechanical weathering.
Weathering- breaking down of rocks and other materials on Earth’s surface.
Mechanical weathering- weathering in which the chemical makeup of rocks does not change.
* Involves only physical changes, such as size and shape.
Mechanical weathering occurs as a result of;– temperature changes.– Ice wedging– Root action
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Mechanical Weathering
Temperature Changes• Rocks may be broken apart by temperature changes.
– Heat makes them expand. (daytime)– Cooling makes them contract. (night time)Exfoliation- the peeling of rock layers, created by temperature
extremes. (creates domed rocks)Ice wedging- mechanical weathering caused by the freezing and
melting of water.When water freezes it expands by 10%.Water enters cracks in the rock freezes, expands and
widens the crack. Repeated actions cause rocks to split apart.*Root wedging- Plant root in search of minerals and water can
grow in cracks of rocks.Roots force rocks apart, breaking them into smaller
pieces.*Burrowing animals- animals that dig next to rocks, exposing
them to the elements of weather.
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Mechanical Weathering
Exfoliation
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Mechanical Weathering
Ice wedging (frost wedging)
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Mechanical Weathering
Root Wedging
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Mechanical Weathering
Burrowing Animals
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What is chemical weathering?
Objective- Explain how Earth’s surface is worn away by chemical weathering.
Types of Chemical weathering;
In chemical weathering, substances in water cause substances in rock to dissolve.
*Chemical changes in rock occurs when minerals are broken down into new substances.
*Chemical weathering is usually caused by reactions with; oxygen, water, or acids.
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Chemical Weathering
Oxidation- chemical change that occurs when oxygen reacts with another substance.
New substances called oxides form.
*Rocks containing ferromagnetic minerals combine with oxygen forming rust. The rock is weakened and crumbles as a result of this process.
2Fe2SiO4 + 2H2O + O2 = 2Fe2O3.H2O + SiO2
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Chemical Weathering
Hydration- chemical reaction that occurs when minerals with little water content react with water.
*Most chemical weathering is caused by water. When feldspar reacts with water it turns to clay.
Na-feldspar and K-feldspar undergo hydrolysis to form kaolinite (clay) and Na+ and K+ ions.
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Chemical Weathering
Carbonation- chemical reaction that occurs when carbonic acid reacts with certain minerals.
*Carbon dioxide can dissolve in rain to form carbonic acid.
When the carbonic acid comes into contact with certain minerals a chemical reaction occurs called carbonation. The mineral calcite reacts with carbonic acid.
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Chemical Weathering
Carbonation
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Chemical Weathering
Acids and weathering
*Plants produce weak acids which can react with minerals weakening a rock and dissolve those minerals.
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Factors that affect the rate of weathering.
Objective- Identify three factors that affect the rate of weathering.
#1 Climate
* moisture speeds up chemical weathering.
* weathering occurs fastest in hot, wet climates.• In very cold, dry areas, there is little weathering.
#2 Surface area
* Weathering occurs on exposed surface areas of rocks and minerals.
* The more surface area a rock has, the faster it will weather.
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Factors that affect weathering
#3 Rock composition
* Slow weathering minerals; Quartz
* Fast weathering minerals; feldspar
* Weathering by carbonation; Calcium (limestone)
* Weathering by Oxidation; Iron
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Factors that affect rate of weathering
#4 Chemical reactions
* Carbonic acid weathers calcite (limestone/marble)
• Natural weathering through carbonation is slow.
• Anthropomorphic (human activity); factories produce carbon dioxide, sulfur and nitrogen. When combined with rainwater they produce acids or acid rain.
• Acid rain- rain containing acids produced by water chemically combining with certain gases.
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How does soil form?
Objective- explain how soil is a product of weathering and organic processes.
Formation of soil
Bedrock- solid rock that lies beneath the soil.• Bedrock is the parent material of soil. Weathering breaks
bedrock into soil.
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Soil formation
Living things and soil
Humus- decaying remains of plants and animals.
* Water helps speed up the breakdown of rock.
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Soil formation
Soil- mixture that includes silt, sand and clay.• Weathered pieces of rocks, minerals and humus are also
in soil.• Soil that is rich in humus is very dark.
Importance of soil
* Soil is important to plants. Potassium, phosphorous and nitrogen are important nutrinets.