Chapter: Weathering and Erosion061851f72b23d802adaa-d56582058559818728a814bdd94ad99a.r54… ·...
Transcript of Chapter: Weathering and Erosion061851f72b23d802adaa-d56582058559818728a814bdd94ad99a.r54… ·...
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Chapter: Weathering and Erosion
Section 1: Weathering and Soil
Formation
Minerals form rocks
Rocks form soil
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• Weathering is a mechanical or chemical surface process that breaks rocks into smaller pieces.
Weathering
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• Mechanical weathering breaks rocks into smaller pieces without changing them chemically.
• The small pieces are identical in composition to the original rock.
Mechanical Weathering
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• Chemical weathering occurs when the chemical composition of rock changes.
Chemical Weathering
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• Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plants.
• Organic matter includes decomposed leaves, twigs, roots, and other materials such as decaying animals.
Soil
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1.Ice Wedging – read page 317 – figure 2
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Freezing and thawing break up rocks
Ice crystals occupy more space than water
Exerting pressure on the rock .
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• Plant roots grow deep into cracks in rock
• Roots become thicker and longer, exerting pressure and breaking the rock apart.
2. Plants
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• Animals can break rocks apart when digging burrows
3. Animals
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• Some rocks react chemically with natural acids in the environment.
• EX: carbonic acid
• Carbonic acid is the result of the reaction between water and carbon dioxide
• Carbonic acid can dissolve rocks
1. Natural Acids
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• Many plants produce a substance called tannin.
• In solution, tannin forms tannic acid.
• This acid dissolves some minerals in rocks and the
rock can break
2. Plant Acids
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• Oxidation is the effect of chemical changes caused by oxygen, when in contact with iron
• Some minerals contain IRON, that can react with the oxygen in the air
• This weakens the rock and it can break
3. Effect of Oxygen
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• Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plants.
Soil
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• The type of soil will depend on the type of rock .
• For example, in areas where sandstone is weathered, sandy soil forms.
• Limestone will form a soil rich in clay
Parent Rock – is the rock that will be weathered, forming the soil
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• On steep hillsides, soil has little chance of developing.
• This is because rock fragments move downhill constantly.
The Slope of the Land
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• In areas where the land is flat, water and wind will help deposit sediments that will form rocks and soil
The Slope of the Land
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1) Affects the chemical weathering of Rocks –important for soil formation
Chemical weathering happens faster when the weather is wet and hot
Climate affects soil formation for two reasons
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2) Climate affects the amount of organic material in soil.
• In warm, humid climates, vegetation is lush
• There is a lot of decomposition of the dead plants and animals resulting in a lot of organic matter in the soil
• This organic matter is called Hummus
Climate
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• Humus helps soil hold water and provides nutrients that plants need to grow.
• Hummus makes the soil rich.
Climate
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• It can take thousands of years for some soil to form.
• As soils develop, they become less like the rock from which they formed.
Time
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• Organisms influence soil development.
Ex: Lichens
Organisms
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• Lichens can remove nutrients from rocks that are breaking down
• This action of the lichens will start forming a thin soil , allowing other plants to grow.
• The roots of these plants further break down the parent rock, creating more soil
Organisms
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Minerals are considered non-
renewable resources.
It takes millions of years to form
minerals
It is important to recycle all
materials obtained from
minerals…..
Minerals form rocks and
Rocks form soil
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• Unplanned use of soil, mining and
deforestation can increase erosion.
the consequences are:
1) loss of land that is good for agriculture
2) polluted streams and other waterways
3) increased flooding
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Importance of vegetation for soils
• Plant roots hold the soil in position
and prevent it from being washed away
by erosion agents such as wind and
water.
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Importance of vegetation for soils
• The presence of vegetation increases
the quality of the soil ( decomposition
of dead plants will contribute to the
formation of hummus, that fertilizes the
soil)