EROSION, HUMAN IMPACT

ON THELITHOSPHERE

EARTH SCIENCE UNIT 11

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Mechanical Weathering

Weathering

◆ Mechanical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.

◆ In nature three physical process are especially important causes of weathering: frost wedging, unloading, and biological activity.

Mechanical Weathering

Weathering

1. Frost wedging• The mechanical breakup of rock caused by the

expansion of freezing water in cracks and crevices

• Sections of rock that are wedged loose may tumble into large piles called talus, which typically form at the base of steep, rocky cliffs.

Frost Wedging

Mechanical Weathering

Weathering

2. Unloading

3. Biological activity

• Reduced pressure on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation.

• The activity of organisms, including plants, burrowing animals, and humans, can also cause mechanical weathering.

Unloading and Exfoliation of Igneous Rocks

Weathering and Biological Activity

Chemical Weathering

Weathering

◆ Chemical weathering is the transformation of rock into one or more new compounds.

◆ Chemical Weathering of Granite• Weathering of potassium feldspar produces clay

minerals, soluble salt (potassium bicarbonate), and silica in solution.

Chemical Weathering

Weathering

◆ Chemical weathering is the transformation of rock into one or more new compounds.

◆ Chemical Weathering of Granite and silicates• Weathering of potassium feldspar produces clay

minerals

Rate of Weathering

Weathering

◆ Two other factors affecting the rate of weathering are rock characteristics and climate.1. Rock characteristics

• Mineral composition and solubility• Physical features such as joints

Rate of Weathering

Weathering

2. Climate • Temperature and moisture are the most crucial

factors.• Chemical weathering is most effective in areas

with high temperatures and abundant moisture.

How do we get coal out of the ground?• Surface Mining:

– Typically occurs at depths above 180 ft. – Most common form in Wyoming

• Underground Mining– Typically occurs at depths below 300 ft.– Accounts for 60% of world coal production

Surface mining

• 4 Main Types of Surface Mining– Strip Mining

• Removal of large strips of overlying rock and soil to reveal coal.

– Open-Pit Mining• Removal of rock and soil creating a vast pit where coal can

be extracted.– Mountaintop Removal Mining

• Removal of mountain tops with explosives. Land made flat after reclamation.

– Highwall Mining• A continuous miner cuts holes horizontally into the coal

formation.

The paper aims to…

• Emphasize “deforestation” as a global environmental problem.

• Deforestation is the conversion of forested areas to non-forest land for use such as arable land, pasture, urban use, logged area, or wasteland. Generally, the removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity.

Deforestation…

• Results from removal of trees without sufficient reforestation, and results in declines in habitat and biodiversity, wood for fuel and industrial use, and quality of life.

Causes of Deforestation

• Population Growth– It is clear now that the role of population factors in

deforestation varies considerably from one setting to another depending on the local patterns of human occupancy and economic activity.

– Population (especially rapidly increasing or dense population) can increase demands for land and wood, eventually exceeding the carrying capacity of forests that are expected to supply wood fuels , food, and environmental protection for local people.

Causes of Deforestation

• Climate– Forest disappear naturally as a result of broad climate

changes or catastrophes such as fire and landslides.

• Agriculture– Growing populations need expanding food supplies,

so forests are cleared by shifting cultivators for annual or permanent crops. Rates of clearing are likely to be higher in countries where little or no progress has been made in agricultural productivity or where land productivity falls rapidly after the natural forest cover is removed.

Causes of Deforestation

• Logging– Commercial logging operations deplete forest stocks. Regulated timber

extraction should not permanently damage the forest, but when it is not controlled, mechanized logging or even selective timber harvesting may severely alter the character of the forest

• Fuel– Forests in developing countries provide wood fuels for local populations.

Fuelwood and charcoal are widely used for domestic cooking and heating.

• Burning and Grazing– Deforestation may occur in ways other than outright clearing or wood

removal. The practice of annual burning in many areas prevents forest regrowth , and grazing by sheep, goats and cattle has much the same effect.