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: