Weathering & Soil

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WeatheringWeatheringWeathering & its effectsWeathering & its effects

• Surface processes that break down Surface processes that break down rock.rock.

• Sediments: sand, silt, & claySediments: sand, silt, & clay• Weathering changes the Earth’s Weathering changes the Earth’s

surface.surface.

Mechanical WeatheringMechanical Weathering• Occurs when rocks are broken apart Occurs when rocks are broken apart

by physical processes.by physical processes.Caused by:Caused by:• Growing plantsGrowing plants• Burrowing animalsBurrowing animals• Expanding ice Expanding ice

• Ice wedging occurs where water enters Ice wedging occurs where water enters cracks in rocks, freezes, & expands.cracks in rocks, freezes, & expands.

• As surface area increases, more rock is As surface area increases, more rock is exposed to be weatheredexposed to be weathered..

Chemical WeatheringChemical Weathering• Chemicals dissolve the minerals in Chemicals dissolve the minerals in rocks or change them into different rocks or change them into different minerals.minerals.

• Naturally formed acids can weather Naturally formed acids can weather rocks chemicallyrocks chemically

•Carbonic acid forms when Carbon dioxide Carbonic acid forms when Carbon dioxide mixes with water. The acid reacts with calcite mixes with water. The acid reacts with calcite in limestone to form caves.in limestone to form caves.• Some roots & Some roots &

decaying plants give decaying plants give off acids that off acids that dissolve minerals in dissolve minerals in rock.rock.

• Oxidation occurs Oxidation occurs when some materials when some materials are exposed to are exposed to oxygen and water. oxygen and water. (Rust)(Rust)

Effects of ClimateEffects of Climate• Mechanical weathering occurs more in Mechanical weathering occurs more in

cold climates.cold climates.• Chemical weathering occurs more in Chemical weathering occurs more in

warm, wet climates.warm, wet climates.• Rock type can affect the rate of Rock type can affect the rate of

weathering in a particular climate.weathering in a particular climate.

SoilSoil A. Formation of SoilA. Formation of Soil•Weathering gradually breaks rocks into Weathering gradually breaks rocks into smaller and smaller fragments.smaller and smaller fragments.

•Plants and animals add organic matter to Plants and animals add organic matter to the rock fragments.the rock fragments.

• Soil is a mixture of Soil is a mixture of Weathered rock Weathered rock Decayed organic matterDecayed organic matterMineral fragmentsMineral fragmentsWaterWaterAirAir

• Causes for soil formation include: Causes for soil formation include: ClimateClimateSlopeSlopeTypes of rockTypes of rockTypes of vegetationTypes of vegetationLength of time that rock has been Length of time that rock has been

weatheringweathering

Composition of SoilComposition of Soil•Decayed organic matter turns into a dark-Decayed organic matter turns into a dark-colored material called humus.colored material called humus.

•Humus provides nutrients for plants.Humus provides nutrients for plants.•Burrowing creatures mix humus with the Burrowing creatures mix humus with the other rock fragments.other rock fragments.

C Horizon C Horizon • Made of partially weathered rock and is Made of partially weathered rock and is found at the bottom of a soil profile.found at the bottom of a soil profile.

Soil TypesSoil Types•Different types of soil vary in Different types of soil vary in color, color, depth, texture, & fertility.depth, texture, & fertility.•The type of soil depends on the region’s The type of soil depends on the region’s climate.climate.•Deserts are dry, prairies are semi-dry, & Deserts are dry, prairies are semi-dry, & temperate forests are mild & moist.temperate forests are mild & moist.

Soil ErosionSoil ErosionSoil – An Important ResourceSoil – An Important Resource

•Soil is eroded when it is moved to a Soil is eroded when it is moved to a new location by wind or water.new location by wind or water.•Soil erosion removes topsoil that is Soil erosion removes topsoil that is important for plant growth.important for plant growth.

Causes and Effects of Soil ErosionCauses and Effects of Soil Erosion•Human activities can increase the Human activities can increase the rate of soil erosion.rate of soil erosion.

•Soil erosion occurs rapidly on steep Soil erosion occurs rapidly on steep slopes and areas that are not covered by slopes and areas that are not covered by vegetation.vegetation.

•Forest harvesting & overgrazing Forest harvesting & overgrazing contribute to the rate at which erosion contribute to the rate at which erosion can occur.can occur.

Preventing Soil ErosionPreventing Soil Erosion• Farmers reduce erosion by planting Farmers reduce erosion by planting

shelter belts, using no-till farming, and shelter belts, using no-till farming, and planting cover crops after harvesting.planting cover crops after harvesting.

• Contour farming and terracing are used to Contour farming and terracing are used to control erosion on slopes.control erosion on slopes.

•Rows of trees (windbreaks) are Rows of trees (windbreaks) are planted on planted on the plains to reduce erosion caused by wind.the plains to reduce erosion caused by wind.