Download WeatheringandErosion

Weathering and Erosion
Soil formation
Standards
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S6E5, S6CS2,
S6CS3, S6CS4,
S6CS5, S6CS6
S6E3, S6E5, S6CS2,
S6CS3, S6CS4,
S6CS6, S6CS10
Weathering
• 2 types
–Mechanical
–Chemical
Effects of rock type
• Hardness of rock determines weathering
rate
• Chemicals in air – air pollution
• Amount of water in air
• Temperature of area
Mechanical Weathering
• When rocks are
broken apart by
physical processes
• Chemical makeup of
rock stays the same
• Pressure release
–Under Earth’s surface
–Rock layers break apart
–Exfoliation
• Layers slowly break off
Plants and animals
• Water and nutrients collect in cracks and
soil
• Plants grow in cracks
• Animals burrow and leave tunnels and
holes in ground
Ice wedging
• Water enters cracks
in rock and freeze.
• Expanding water
causes rock to break
apart
• Ice melts and
processes repeat.
• Abrasion
–Wearing down by friction
–Moving water (river)
–Rocks hitting each other
–Ocean waves
Chemical weathering
• Chemical reactions
dissolve the minerals
in rocks or change
them into different
minerals
• Weakens rock
• Dissolving
–Water + carbon dioxide
–Dissolves rock into new
substance
• Rusting
–Iron in soil
–Oxygen rusts iron
–Soil is red in color
Natural Acids
• Water mixes with
carbon dioxide gas
and form carbonic
acid
• Roots and decaying
plants give off acids
• Dissolve minerals in
rock
Effects of Climate
• Pattern of weather that occur in a
particular area over a period of time
• Cold areas – mechanical weathering – ice
wedging
• Warm areas – chemical weathering – rain
Surface area
• Small pieces of rock
have more surface
area exposed than
large rock
• Allows more rock to
be exposed and
weathering to occur
4.2 Weathering and organic soil
formation
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Climate
Slope of land
Type of rock
Type of vegetation
Amount of time rock has been
weathering
Composition of Soil
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Rock sediment
Minerals
Organic plant matter
Decayed animals
Microorganisms – bacteria
Humus – decayed organisms
water
Soil horizons
• Horizon A – top layer of soil – litter of leaves
twigs and other organic material – litter prevents
erosion – topsoil – dark and fertile
• Horizon B – below A – lighter in color – no litter –
less fertile – leaching – removal of dissolved
minerals – move from A to B
• Horizon C - bottom layer – thickest layer- not
much organic matter-not fertile – many rocks
Soil types
• Type of soil determined
– Climate
– Region
– Rainfall
– Types of rock
Observable properties of soil
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Texture
Color
Pore space
Chemistry
Human activities
affect soil
Land-use
• Farming
– Overgrazing of animals=desertification
– Adding nutrients (organic or artificial)
– Top soil erosion
– Clear trees
– Wind
Construction and development
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Roads
Houses
Malls
Stores
What are some problems with this?
Mining
• How would this affect an area?
Protection of soil
• Crop-rotation
• Conservation tillage
• Terraces
• Contour plowing
• Windbreaks
Contour plowing
Crop-rotation
Windbreaks
Preventing Soil Erosion
• Managing crops
• Plant shelter belts – protect soil from wind
• Proper grazing management – arid areas
farmers do not plow under vegetation – allow
grazing of natural vegetation
• “No-till” farming –
– stalks are left as ground cover during the winter.
– Farmers seed area without plowing.
– Leftover stalks stop erosion, keep moisture in ground
and control weeds.
Reduce erosion at construction
sites
• Cover cleared areas with mulch, mats, or
plastic coverings
• Water sprayed onto cleared area
• New topsoil is added to exposed areas
• Area is seeded and reinforced with netting
or straws
• Retaining walls are built for steeper areas
– made of stone, concrete or wood