chapter: weathering and erosion061851f72b23d802adaa-d56582058559818728a814bdd94ad99a.r54… ·...
TRANSCRIPT
Chapter: Weathering and Erosion
Section 1: Weathering and Soil
Formation
Minerals form rocks
Rocks form soil
• Weathering is a mechanical or chemical surface process that breaks rocks into smaller pieces.
Weathering
Weathering and Soil Formation
1
• Mechanical weathering breaks rocks into smaller pieces without changing them chemically.
• The small pieces are identical in composition to the original rock.
Mechanical Weathering
Weathering and Soil Formation
1
• Chemical weathering occurs when the chemical composition of rock changes.
Chemical Weathering
Weathering and Soil Formation
1
• 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
Weathering and Soil Formation
1
1.Ice Wedging – read page 317 – figure 2
1
Freezing and thawing break up rocks
Ice crystals occupy more space than water
Exerting pressure on the rock .
• Plant roots grow deep into cracks in rock
• Roots become thicker and longer, exerting pressure and breaking the rock apart.
2. Plants
1
• Animals can break rocks apart when digging burrows
3. Animals
Weathering and Soil Formation
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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
Weathering and Soil Formation
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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
Weathering and Soil Formation
1
• 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
Weathering and Soil Formation
1
• Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plants.
Soil
Weathering and Soil Formation
1
• 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
Weathering and Soil Formation
1
• On steep hillsides, soil has little chance of developing.
• This is because rock fragments move downhill constantly.
The Slope of the Land
Weathering and Soil Formation
1
• 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
Weathering and Soil Formation
1
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
Weathering and Soil Formation
1
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
Weathering and Soil Formation
1
• Humus helps soil hold water and provides nutrients that plants need to grow.
• Hummus makes the soil rich.
Climate
Weathering and Soil Formation
1
• 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
Weathering and Soil Formation
1
• Organisms influence soil development.
Ex: Lichens
Organisms
Weathering and Soil Formation
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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
Weathering and Soil Formation
1
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
• 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
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.
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)