EARTH SCIENCE UNIT 11
EROSION,
HUMAN IMPACT
ON THE
LITHOSPHERE
◆
Weathering
Mechanical 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.
Weathering
Mechanical 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
Weathering
Mechanical Weathering
2. Unloading
• 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.
3. Biological activity
• 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
Weathering
Chemical 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.
Weathering
Chemical 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
Weathering
Rate of 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
Weathering
Rate of 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.