WeatheringWeathering
What Will We Learn In This Chapter?What Will We Learn In This Chapter? Distinigiush between weathering and erosion Identify variables that affect the rate of weathering Analyze the impact of living and nonliving things on the
processes of weathering and erosion. Describe the realtionship of gravity to all agents of erosion Describe how soil forms Explain the relationship between the organic and inorganic
components of soil Identify Soil Characteristics Recognize soil horizons in a soil profile
Development of SoilDevelopment of Soil
Almost found every where on earth Soil
loose covering of broken rock particlesPlus Decaying Organic MaterialResults from – Chemical Weathering– Mechanical Weathering– Biological Activity
Development of SoilDevelopment of Soil
Soil CompositionSoil Composition Soil is developed from the breakdown of the
exposed bedrock As pieces weather they rest on top of bedrock Over time soil becomes more inhabitable Living and Dead material plus weathered rock
remain Residual Soil
Soil located above the parent material
Soil CompositionSoil Composition
Soil that is exposed to the elements can be transported. This type of soil is called Transported Soil
Check for UnderstandingCheck for Understanding
Soil is composed of which of the following?a) Weathered rockb) Living organismsc) Dead organismsd) Moisturee) Atmospheric gasesf) All of the above
Check for UnderstandingCheck for Understanding
Soil is composed of which of the following?a) Weathered rock b) Living organismsc) Dead organismsd) Moisturee) Atmospheric gasesf) All of the above
Soil ProfilesSoil Profiles
Soil ProfileIs a vertical sequence of soil layers
Soil Layers are called… Soil Horizons
A distinct layer or zone4 Types– O, A, B, C
Classification of an Soil ProfileClassification of an Soil Profile
O HorizonLiving, Organic matterGrey to Black
A HorizonRich in Humus
B HorizonEnriched with clay
C HorizonWeathered Parent Material
Soil Profile of WisconsinSoil Profile of Wisconsin
Soil Profiles are Due to TopographySoil Profiles are Due to Topography
The topography of a region affects the thickness of soil
Sloped Areas: thinner layers of soil because of erosionLowlands/Valleys: thicker layers of soil because of increased depositionSouth-Facing Areas: areas facing the south receive more sunlight more vegetation more soil than areas facing other directions
Soil TypesSoil Types Classified mainly based of climatic conditions of the area 4 major types
Polar Soils: very thin layers of soil covering the frozen, permafrost, groundTemperate Soils: vary greatly; support vast array of organisms
– Type of soil most of WI has
Desert Soil: receives little precipitation little vegetation thin A soil horizonTropical Soil: high temps & precipitation intense weathering with a high degree of bacteria in soil very little humus & few nutrients found in soil poor growing soil
Soil TextureSoil Texture Soil Triangle
Tells us the texture of soil based on it feelThree main types of sediments thatmake up soil
– Sand– Silt– Clay
The proportion of these sediments give soil its texture
Weathering is the process that produces change in the surface of rocks exposed to the atmosphere
and/or hydrosphere.
Two Types OF Weathering:Two Types OF Weathering: Mechanical
weathering is breaking rock by force.
ex: hitting, scratching, cracking
Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.
Frost WedgingFrost Wedging Frost action (ice wedging)-
1.Water seeps into small cracks in rocks.
2.When the water freezes it expands creating great pressure.
3.The crack widens and allows water to seep deeper into the rock.
Root WedgingRoot Wedging Plant action-
1.Tiny root hairs seek out small cracks and pits in rock.
2.Once the root hairs find a place they grow and expand.
3.The expansion causes great pressure and cracks the rock.
ExfoliationExfoliation
1. Rocks formed deep in the Earth are made under high pressure.
2. When the pressure is released the rocks expand & crack.
3. May also be caused by alternate heating and cooling of rocks by weather conditions.
Types of Chemical WeatheringTypes of Chemical Weathering Oxidation-
Oxygen in the atmosphere chemically reacts with minerals. ex.: rusting of a nail Iron SilicatesIron Sulfides
Types of Chemical WeatheringTypes of Chemical Weathering Hydrolysis
Minerals are dissolved in water. ex.: Halite, calcite
Feldspars react with water to form clay plus other minerals
Rates of weathering will be influenced by:Rates of weathering will be influenced by:
Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur.
A full, solid block has the least surface area.
The interior is safe from exposure.
A smashed piece has greatest surface area exposed. The interior can now be attacked.
Mineral composition- some minerals are more resistant than
others. – ex.:Quartz is resistant to chemical and
physical weathering.
Rates of Weathering will depend on:Rates of Weathering will depend on:
Where is the rock more resistant to weathering?Where is the rock more resistant to weathering?
Where is the rock least resistant to weathering?Where is the rock least resistant to weathering?
You might also see it like this…You might also see it like this…
Climatic Conditions:Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly.
Rates of Weathering will depend on:Rates of Weathering will depend on:
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